Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A comparative study of the relationship between airway size, tongue activity and body position 1989

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1989_A6_7 P33.pdf
UBC_1989_A6_7 P33.pdf [ 6.58MB ]
UBC_1989_A6_7 P33.pdf
Metadata
JSON: 1.0097550.json
JSON-LD: 1.0097550+ld.json
RDF/XML (Pretty): 1.0097550.xml
RDF/JSON: 1.0097550+rdf.json
Turtle: 1.0097550+rdf-turtle.txt
N-Triples: 1.0097550+rdf-ntriples.txt
Citation
1.0097550.ris

Full Text

A COMPARATIVE STUDY OF THE RELATIONSHIP BETWEEN AIRWAY SIZE, TONGUE ACTIVITY AND BODY POSITION By EUNG-KWON PAE D.D.S., The Yonsei University, Korea, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CLINICAL DENTAL SCIENCES We accept this thesis conforming to the required standard UNIVERSITY OF BRITISH COLUMBIA October, 1989 ©Eung-Kwon Pae, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C l i n i c a l Dental Sciences The University of British Columbia Vancouver, Canada Date O c t . 13, 1989 DE-6 (2/88) r ABSTRACT Airway o b s t r u c t i o n i n O b s t r u c t i v e Sleep Apnea (OSA) p a t i e n t s i s b e l i e v e d t o occur i n the supine p o s i t i o n during sleep. In order t o i n v e s t i g a t e the r e l a t i o n s h i p between upper airway s i z e and genioglossus(GG) muscle a c t i v i t y , u p - r i g h t ( i n n a t u r a l head posture) and supine cephalograms were obtained f o r twenty OSA and ten asymptomatic c o n t r o l s u b j e c t s . Tongue EMG and pressure recordings were obtained w i t h the s u r f a c e e l e c t r o d e s and pressure transducers i n ten asymptomatic c o n t r o l s u b j e c t s . The Student's t t e s t and Wilcoxon signed rank t e s t were used to t e s t f o r d i f f e r e n c e s between the two groups and between body p o s i t i o n s . The OSA group revealed a longer tongue (p< 5%), a l a r g e r s o f t p a l a t e (p< 1%), an a n t e r o p o s t e r i o r l y narrower and v e r t i c a l l y lengthened upper airway (p< 1%) , a i n f e r i o r l y p o s i t i o n e d hyoid bone (p< 1%), a more extended head posture (p< 5%) and a s m a l l e r hypopharynx (p< 1%) i n the u p - r i g h t standing p o s i t i o n . A f t e r changing from the u p - r i g h t t o the supine p o s i t i o n , the tongue c r o s s - s e c t i o n a l area increased 4.3% (p< 5%) and oropharyngeal area decreased 3 6.5% (p< 1%) i n the OSA group. When comparing the supine t o the u p - r i g h t c o n t r o l cephalograms, changes i n tongue area were not observed, but the t h i c k n e s s of the s o f t p a l a t e increased (p< 1%) . D i f f e r e n c e s i n tongue c r o s s - i i s e c t i o n a l area between two groups become s i g n i f i c a n t w i t h body p o s i t i o n a l changes from the u p - r i g h t t o the supine (p< 1%) . With body p o s i t i o n a l changes, the hyoid bone moves s u p e r i o r l y toward the mandibular plane i n the c o n t r o l group (p< 1%), but a n t e r i o r l y toward the mandibular symphysis i n the OSA group (p< 5%) . The r e s t EMG a c t i v i t y of the GG muscle increased 33.8% (p< 5%) and the p o s t e r i o r tongue pressure increased 17% (p< 5%) w i t h body p o s i t i o n a l changes from u p - r i g h t t o supine. O v e r a l l , the orophayngeal c r o s s - s e c t i o n a l area c o l l a p s e d 28.8% (p< 1%) de s p i t e a 34% increase (p< 5%) i n GG muscle a c t i v i t y i n the asymptomatic c o n t r o l group as a r e s u l t of body p o s i t i o n a l changes. Furthermore, a 17% increase of tongue pressure on the p o s t e r i o r load c e l l i n d i c a t e s p o s i t i o n a l change of the tongue. In c o n c l u s i o n , i t may not be the s i z e of the s o f t p a l a t e alone but a l s o the v e r t i c a l and a n t e r o p o s t e r i o r p o s i t i o n of the tongue which could a c t i v e l y c o n t r i b u t e t o the development of OSA. Q u a n t i f i c a t i o n of s u b t l e d i f f e r e n c e s i n tongue and oropharyngeal s i z e and p o s i t i o n , geometry of the hyoid bone, upper airway muscle a c t i v i t y and tongue pressure accompanied by body p o s i t i o n a l changes a i d s i n our understanding of the pathogenesis of OSA. TABLE OF CONTENTS PAGE L i s t of Tables v i i L i s t of Figures v i i i Acknowledgements i x I. I n t r o d u c t i o n A. What i s sleep apnea? 1 B. Pathogenesis of O b s t r u c t i v e Sleep Apnea 4 1] Overview of pathogeneses 5 2] Predisposing f a c t o r s 6 a. Sleep 6 b. Anatomical f a c t o r s 8 c. F u n c t i o n a l f a c t o r s 12 C. Biomechanical r e l a t i o n s h i p between posture and airway adequacy 2 0 1] Head posture 2 0 2] Body posture 2 2 I I . Statement of Problem 24 I I I . Methods A. Experimental subjects 2 6 i v PAGE B. E x p e r i m e n t a l p r o c e d u r e s 1] C e p h a l o m e t r i c s t u d y 2 8 a . L a t e r a l cephalograms 2 8 b . D e f i n i t i o n s and r a t i o n a l e o f l a n d m a r k s , p l a n e s , a n g u l a t i o n s , a r e a s and t h e i r measurements " 3 6 1. H a r d - t i s s u e landmarks 3 6 2. S o f t - t i s s u e landmarks 4 0 3. L i n e a r measurements 44 4. A n g u l a r measurements 47 5. A r e a measurements 47 c . T r a c i n g and d i g i t i z a t i o n 50 2] EMG and p r e s s u r e s tudy a . Data a q u i s i t i o n system and r e c o r d i n g t e c h n i q u e 51 b . Equipment and d a t a p r o c e s s i n g 57 c . E x p e r i m e n t a l p r o c e d u r e 59 C . S t a t i s t i c a l method 62 v IV. R e s u l t s A. R e l i a b i l i t y t e s t s f o r the methods 65 B. Cephalometric study 7 3 C. EMG and pressure study 81 V. D i s c u s s i o n A. Cephalometric study 88 B. EMG and pressure study 100 C. Overview 112 D. P i t f a l l s and f u t u r e study 113 VI. Summary 115 V I I . B i b l i o g r a p h y 117 v i LIST OF TABLES T A B L E P A G E I Demographic V a r i a b l e s f o r the Experimental Subjects 27 I I R e l i a b i l i t y of the S o f t - t i s s u e Measuring Techniques and an Example of the C a l c u l a t i o n of the Houston's R e l i a b i l i t y Index 68 I I I R e p r o d u c i b i l i t y Studies of N a t u r a l Head P o s i t i o n and Measurement 7 0 IV Comparison of OSA and Asymptomatic C o n t r o l s i n Up-right and Supine Cephalometric P o s i t i o n s 74 V Comparison of Up-right and Supine Cephalograms i n OSA and Asymptomatic Cont r o l s 76 VI ANCOVA t e s t of the Age E f f e c t on the Hyoid V a r i a b l e s 79 VII Comparison of the EMG and Pressure of the Tongue between Up-right and Supine P o s i t i o n s i n Asymptomatic Controls 82 V I I I L i n e a r and Area V a r i a b l e Comparisons Between Current Report and Other Studies 9 0 v i i LIST OF FIGURES 1 Measurement of Head Posture w i t h the M o d i f i e d F l u i d Level Device 2 9 2 Schematic Diagrams t o I l l u s t r a t e Assembly of the Mo d i f i e d F l u i d Level Device 33 3 Photograph of the Supine Cephalometric Procedure 3 5 4 Cephalometric Hard Tissue Landmarks 39 5 Cephalometric S o f t Tissue Landmarks 43 6 Cephalometric L i n e a r Measurements 4 6 7 Cephalometric Angular and Area Measurements 49 8 Schematic I l l u s t a t i o n s of the Surface E l l e c t r o d e s f o r the Masseter, Supra-hyoid and O r b i c u l a r i s O r i s Muscles, and the I n t r a o r a l Appliance 52 9 Pressure Transducer and I t s S p e c i f i c a t i o n s 54 10 C a l i b r a t i o n System and C a l i b r a t i o n R e s u l t s 56 11 Flow-chart f o r Data A q u i s i t i o n 58 12 Tray Used t o Measure the B a s e - l i n e Pressure of the Tongue 61 13 R e l a t i o n s h i p between Level Device Angle and the FH/True H o r i z o n t a l Cephalometric Angle 72 14 Tongue EMG and Pressure Changes at Rest i n Up-right and Supine P o s i t i o n s 84 RE: P a t i e n t I n s t r u c t i o n Used f o r Current Study 31 v i i i ACKNOWLEDGEMENT The author i s a p p r e c i a t i v e of the suggestions provided by Dr. C. P r i c e at the commencement of t h i s study. A l s o , t h i s study was designed w i t h Dr. K. Sasaki's guidance and Dr. J . Fleetham's d i r e c t i o n . I wish t o express my g r a t i t u d e t o Ms. J . Scott and Ms. M. Wang f o r t h e i r computer e x p e r t i s e . Dr. Diewert and Dr. M. Tsuchiya's suggestions and comments improved the t e x t . Dr. B. Morrison provided suggestions about the s t a t i s t i c a l anaysis. Above a l l , I am g r e a t l y indebted t o Dr. A. Lowe f o r h i s guidance, support, and the o r g a n i z a t i o n of t h i s study i n a l l aspects. F i n a l l y , I thank my wi f e and c h i l d r e n , Joseph and Candice, f o r t h e i r patience and prayer. This research was f i n a n c i a l l y supported by MRC grant MA- 3849 t o Dr. A. Lowe and by a UBC Graduate F e l l o w s h i p . i x INTRODUCTION I t i s only r e c e n t l y t h a t the f i e l d of d e n t i s t r y has become concerned w i t h the o b s t r u c t i v e sleep apnea (OSA) syndrome. However, OSA i s no longer an unknown i n the f i e l d of d e n t a l research. F a m i l i a r i t y w i t h t h i s syndrome has increased not only because of i t s high r a t e of incidence but a l s o because o r t h o d o n t i s t s and o r a l surgeons are beginning t o p l a y a more s i g n i f i c a n t r o l e i n t r e a t i n g OSA syndrome w i t h the use of i n t r a - o r a l devices and/or orthognathic surgery. I t has been suggested t h a t OSA may be one of the most prevalent diseases i n modern s o c i e t y . One e p i d e m i o l o g i c a l r e p o r t suggests a prevalence r a t e of 0.89% as a lower l i m i t i n the a d u l t male p o p u l a t i o n (Lavie, 1983). In s p i t e of the remarkable amount of research t h a t has been done i n t h i s f i e l d i n the l a s t decade, the OSA syndrome i s masked by v a r i o u s symptoms and by the i n t r i c a c y of i t s pathogenesis. A . What i s sleep apnea ? An apnea i s defined as a c e s s a t i o n of a i r flow at the nose and mouth f o r more than 10 seconds ( G u i l l e m i n a u l t et a l . , 1975). According t o T a s s i n a r i et al . ( 1 9 7 2 ) , three types of apnea have been defined. The f i r s t , c e n t r a l apnea i s defined as the complete a r r e s t of r e s p i r a t i o n f o r 5-10 seconds. The 1 second, o b s t r u c t i v e apnea i s defined as an i n t e r r u p t i o n of the a i r f l o w f o r 10 t o 60 seconds whi l e the abdominal pneumogram i n d i c a t e s p e r s i s t e n c e of i n e f f e c t i v e r e s p i r a t o r y movement. The t h i r d type, complex apnea i s defined as an episode of c e n t r a l apnea f o r 5-10 seconds followed by an episode of o b s t r u c t i v e apnea. According t o G u i l l e m i n a u l t et a l . ( 1 9 7 5 ) , the reverse order never seems to occur. G u i l l e m i n a u l t (1985) defined hypopnea as an incomplete form of apnea which i s induced by decreased diaphragmatic e f f o r t and p a r t i a l o b s t r u c t i o n of the airway. There are s e v e r a l ways of d e s c r i b i n g the s e v e r i t y of sleep apnea. The Apnea Index (Al) i s d e f i n e d as the t o t a l number of apnea i n c i d e n t s per t o t a l sleep time m u l t i p l i e d by 60. G u i l l e m i n a u l t et al.(1987) suggested an Apnea Index of 5 as the upper l i m i t of normality. The RDI (Respiratory Disturbance Index) i s another index measuring the s e v e r i t y of sleep apnea and i s defined as the Apnea plus Hypopnea Index. In h i s book "Posthumous Papers of the Pickwick Club"(1837), Charles Dickens described an extremely f a t boy named Joe who s u f f e r e d from p e r s i s t e n t somnolence. In 1918, S i r W i l l i a m Osier coined the term " P i c k w i c k i a n " , t o r e f e r t o obese and hypersomnolent p a t i e n t s (Burwell, 1956). Several s t u d i e s reviewed the symptoms of the P i c k w i c k i a n syndrome. In 1964, Gastaut and h i s a s s o c i a t e s reported the presence of r e p e t i t i v e o b s t r u c t i v e apnea during sleep i n the " P i c k w i c k i a n " p a t i e n t . In 1966, the same group evaluated the sleep, 2 r e s p i r a t i o n and blood gas chemistry of the p a t i e n t by means of polygr a p h i c r e g i s t r a t i o n . They measured EEG, spirogram and EMG of diaphragmatic and mylohyoid muscle a c t i v i t y , hypothesized the pathogenesis of o b s t r u c t i v e sleep apnea and d i s t i n g u i s h e d c e n t r a l apnea from o b s t r u c t i v e apnea. The term 'sleep apnea' was f i r s t used i n 1971 by Kumashiro et a l . . In 1972, G u i l l e m i n a u l t et a l . d i f f e r e n t i a t e d o b s t r u c t i v e sleep apnea both from the P i c k w i c k i a n syndrome and from narcolepsy. In the f o l l o w i n g year(1973), they reported insomnia w i t h Sleep Apnea as a new syndrome and f i n a l l y named i t sleep apnea syndrome. OSA i s predominantly a disease of obese middle aged men, yet i s l e s s known i n obese women or c h i l d r e n . Regardless of the age or sex of the s u f f e r e r , snoring i s considered the c a r d i n a l s i g n of sleep apnea. P a t i e n t s may present r e s t l e s s sleep p a t t e r n s such as t u r n i n g , t o s s i n g , f l a i l i n g of the e x t r e m i t i e s and even sleep walking. Some p a t i e n t s may complain of a sensation of choking or gagging. G u i l l e m i n a l t (1987) observed esophageal r e f l u x i n a number of p a t i e n t s and n o c t u r i a was a l s o reported as a more common symptom i n c h i l d r e n . In the e a r l y or middle stages of the development of the disease, insomnia may be observed;however, excessive daytime s l e e p i n e s s and/or f a t i g u e i s another hallmark symptom of OSA. In extreme cases, the p a t i e n t f a l l s asleep w h i l e t a l k i n g , e a t i n g and even d r i v i n g . D e t e r i o r a t i o n of the memory, d i s o r i e n t a t i o n , morning confusion and hypnogogic h a l l u c i n a t i o n s were reported as s i d e - e f f e c t s of hypersomnolence. O c c a s i o n a l l y , a hyponasal v o i c e , noisy 3 b r e a t h i n g and mouth breathing are n o t i c e d . In 1960, hemodynamic ab n o r m a l i t i e s i n extremely obese p a t i e n t s were s t u d i e d by S i e k e r and h i s c o l l e a g u e s . Burwell et al.(1956) presented a comparative hemodynamic study between the reduced weight s t a t e to i n i t i a l s t a t e i n a P i c k w i c k i a n p a t i e n t . Abnormal a l t e r a t i o n of gas exchange and c a r d i o v a s c u l a r f u n c t i o n i s w e l l documented by s e v e r a l researchers (Bradley 1988, Bradley and P h i l l i p s o n 1985). Hypoxia, hypercapnea and a c i d o s i s may develop polycythemia, systemic hypertension, cor pulmonale, vagal bradycardia and nocturnal c a r d i a c arrhythmia. Another hemodynamic e f f e c t occurs mechanically i n the c a r d i o v a s c u l a r system (Scharf,1984). Decreased i n t r a - t h o r a c i c pressure during the o b s t r u c t i v e apneic p e r i o d creates l a r g e negative loads i n the p l e u r a l c a v i t y , which increases the venous r e t u r n t o the r i g h t v e n t r i c l e , and may r e s u l t i n c a r d i a c malfunction. B. Pathogenesis of OSA As mentioned p r e v i o u s l y , OSA i s s t i l l an u n c l a r i f i e d , complex phenomenon. At l e a s t three f a c t o r s are thought t o be i n v o l v e d i n the pathogenesis of OSA: sleep, upper airway anatomy and upper airway muscle f u n c t i o n . S u l l i v a n et al.(1984) reviewed a number of l e a d i n g t h e o r i e s and has suggested t h a t a balanced f o r c e between t i s s u e weight, muscle tone, and airway lumen s u c t i o n pressure l i k e l y governs the pathophysiology of OSA syndrome. No one theory has been accepted, although a l l of them may c o n t r i b u t e i n p a r t t o the pathogenesis of OSA . 4 1] Overview In 1978, Remmers et a l . undertook an e l a b o r a t e l y designed study on humans i n an attempt t o e x p l a i n the pathogenesis of OSA. They hypothesized t h a t an uncoordinated f o r c e balance between genioglossus(GG) muscle fo r c e and the oropharyngeal transmural pressure causes pharyngeal o c c l u s i o n . When the pharyngeal transmural pressure increases more than the GG muscle f o r c e , o c c l u s i o n of the upper airway may occur. S u l l i v a n et al.(1984) summarized t h a t the narrower airway i s more v u l n e r a b l e and dependent on d i l a t o r muscle tone f o r airway patency. They concluded t h a t airway s u c t i o n pressure was the key for c e provoking airway o c c l u s i o n ; i . e. the gr e a t e r the i n s p i r a t o r y muscle f o r c e and the smaller the c r o s s - s e c t i o n a l area, the higher the l i n e a r v e l o c i t i e s of a i r f l o w and the g r e a t e r the transmural pressure gradient f a v o r i n g upper airway c o l l a p s e . G u i l l e m i n a u l t (1987) explained t h a t once airway o b s t r u c t i o n occurs due t o the v a r i o u s p r e d i s p o s i n g f a c t o r s ( f o r i n s t a n c e , anatomic a b n o r m a l i t i e s of the upper airway, decreased airway muscle a c t i v i t y , small pharyngeal c a v i t y , high pharyngeal compliance and increased upstream r e s i s t a n c e ) , Pco 2 t e n s i o n should r i s e . Increased Pco 2 t e n s i o n causes an increase i n diaphragmatic e f f o r t which may r e s u l t i n more negative i n t r a - t h o r a c i c and oropharyngeal pressures. As a counter f a c t o r t o the negative forces t r i g g e r i n g airway c o l l a p s e , the s t a b i l i z i n g f o r c e s of the upper airway d i l a t o r s are c r u c i a l . Whether 5 determined by a sleep r e l a t e d f a i l u r e of the upper airway muscle a c t i v i t y and/or d e f e c t i v e chemorecepter f u n c t i o n , the s p e c i f i c c h a r a c t e r i s t i c s of the d i l a t o r muscles are the most l i k e l y u n d e r l y i n g dominant f a c t o r i n the mechanism of OSA. Several s t u d i e s suggest t h a t upper airway r e s i s t a n c e , e s p e c i a l l y e x p i r a t o r y r e s i s t a n c e , i s increased i n sleep (Orem, 1986). Moreover, the airway r e s i s t a n c e i n OSA p a t i e n t s i s assumed to be higher than normal (Suratt et a l . , 1985) and many hemodynamic r e p o r t s of overnight s t u d i e s , i n OSA p a t i e n t s show a high Pco 2 l e v e l . In 1987, P a r i s i and a s s o c i a t e s compared the Pco 2 t h r e s h o l d of the GG and the diaphragm i n goats. They found t h a t the Pco 2 t h r e s h o l d of the GG, i n comparison to the diaphragm, i s d i s p r o p o r t i o n a l both during NREM(Non-Rapid-Eye- Movement) sleep at low C0 2 t e n s i o n and during phasic REM(Rapid- Eye-Movement) sleep at any C0 2 t e n s i o n . They p o s t u l a t e d t h a t t h i s imbalance between the GG and the diaphragm may predispose the upper airway to i n s p i r a t o r y o c c l u s i o n during sleep. 2] P r e d i s p o s i n g Factors a. Sleep Most of the p s y c h i a t r i c phenomena t h a t occur i n OSA can be explained on the b a s i s of sleep derangement (Singh, 1984) . By d e f i n i t i o n , sleep may be considered as r e c u r r e n t spontaneous episodes of motor quiescence accompanied by r a i s e d t h r e s h o l d s of sensory response (McGrinty and Beahm,1984). On the b a s i s of e l e c t r o p h y s i o l o g i c a l measurements, mammalian sleep i s d i v i d e d 6 i n t o two d i s t i n c t types: NREM and REM sleep. REM and NREM sleep a l t e r n a t e throughout the ni g h t . NREM sleep, which i s a l s o c a l l e d slow-wave sleep or synchronized sleep, c o n s i s t s of four stages. In i n f a n t s , REM sleep i s a l s o c a l l e d p a r a d o x i c a l sleep or a c t i v e s l e e p , and i s c h a r a c t e r i z e d by b r i e f , abrupt phasic motor events, eye movements or twitch e s of the f a c i a l and extremity muscles (McGrinty and Beahm, 1984). The waking stage shows a low amplitude, high freqency(13 t o 3 5 Hz) beta wave. Stage 1 NREM sleep normally c o n s i s t s of 5-10% of t o t a l sleep time, and i s a t r a n s i t i o n a l phase between wakefulness and sleep. I t i s c h a r a c t e r i z e d by mixed-freqency a c t i v i t y i n the beta and theta(4-7Hz) waves. Stage 2 i s marked by the appearance of EEG sleep s p i n d l e s ( i . e . , b u r s t of a c t i v i t y from 12 t o 14 Hz l a s t i n g one h a l f t o two seconds) and K-complexes(well-delineated, slow, negative EEG d e f l e c t i o n s ) . Delta sleep, the deepest stage, i s d i s t i n g u i s h e d by slow d e l t a waves gr e a t e r than 75juV, peak to peak. In REM sleep, the EEG c o n s i s t s of mixed frequency, low- vo l t a g e a c t i v i t y resembling stage 1 NREM sleep. REM sleep periods tend t o become longer as sleep progresses and c o n s t i t u t e about 2 0% of t o t a l sleep time i n the healthy a d u l t . REM sleep i s c h a r a c t e r i z e d by broad p h y s i o l o g i c a l changes. While EMG a c t i v i t y maintains i t s lowest l e v e l during REM sleep, the e x t r a - o c u l a r muscles show r a p i d , i n t e r m i t t a n t , conjugated eye movements. In about 8 0% of wakenings from REM sle e p , people r e c a l l dreams (Hauri and Orr, 1982) which are v i v i d , a c t i v e and f i l l e d w i t h c o l o r f u l and complex i d e a t i o n (Baker, 1985) . Phasic 7 components w i t h i n REM sleep are c h a r a c t e r i z e d by a high autonomic v a r i a b i l i t y such as i r r e g u l a r heart r a t e and blood pressure which may t r a n s i e n t l y increase as much as 4 0 mmHg (Coccagna et a l , 1972). C o n t r a r i l y , during t o n i c REM s l e e p , the heart r a t e and blood pressure are more constant and there i s g r e a t e r r e l a x a t i o n i n most muscles. Cerebral blood flow i s g r e a t e r during REM than e i t h e r NREM or wakefulness. R e s p i r a t i o n a l s o seems a l t e r e d during REM sleep. Many upper airway muscles and i n t e r c o s t a l muscles become hypotonic whereas the diaphragm maintains a c t i v i t y and C0 2 s e n s i t i v i t y i s l o s t w i t h frequent phasic events ( S u l l i v a n et a l , 1979b). Loss of i n t e r c o s t a l EMG a c t i v i t y may l ead t o p a r a d o x i c a l c o l l a p s e of the chest during i n s p i r a t i o n (Henderson-Smart, 1984). Rib cage 'paradox' i s exacerbated by increased upper airway r e s i s t a n c e (McGrinty, 1984). The tone of the GG and geniohyoid muscles may s i g n i f i c a n t l y decrease during REM stage. In other words, REM sleep i s a s s o c i a t e d w i t h a decreased upper airway patency and increased transpharyngeal r e s i s t a n c e ( G u i l l e m i n a u l t , 1988). b. Anatomical Factors I t i s not d i f f i c u l t t o assume a r e s p i r a t o r y m alfunction i n p a t i e n t s who have apparent anatomical anomalies, pathoses or neuromuscular d e f e c t s . Moran (1987) enumerated many of the abnormal p h y s i c a l c h a r a c t e r i s t i c s which could be found i n OSA p a t i e n t s . However, a great number of p a t i e n t s s u f f e r i n g from moderate or l e s s severe OSA symptoms are not l i k e l y t o have 8 obvious p h y s i c a l d e f i c i e n c i e s , except o b e s i t y . OSA i s o f t e n c o i n c i d e n t w i t h o b e s i t y and snoring. W i t t e l s (1985) defined o b e s i t y as a body weight at l e a s t 2 0% above the i d e a l . Obesity induces numerous changes i n pulmonary and c a r d i o v a s c u l a r f u n c t i o n . According t o W i t t e l s , i n the case of o b e s i t y , the t o t a l lung volume, f u n c t i o n a l r e s i d u a l c a p a c i t y and t i d a l volume are diminished. In a d d i t i o n , the accumulation of f a t around the chest w a l l decreases chest compliance. Due t o the low lung volume, r e s p i r a t o r y r e s i s t a n c e i s increased. Because the r e s p i r a t o r y work of breathing i s somewhat g r e a t e r than normal, the oxygen cost i s increased. An increased c a r d i a c output i s demanded i n the obese p a t i e n t , hence l e f t v e n t r i c u l a r stroke work i s increased, which f i n a l l y leads t o an increased l e f t v e n t r i c u l a r e n d - d i a s t o l i c pressure. An i n t e r e s t i n g survey was undertaken by Grunstein et al.(1989) i n Western Samoa. The ANCOVA(Analysis of Covariance) study revealed a s i g n i f i c a n t c o r r e l a t i o n between snoring and c o l l a r s i z e , BMI(Body Mass Index), blood pressure and smoking, and yet no r e l a t i o n was found w i t h aging. S u r a t t and co-workers (1987) found i n a p r o s p e c t i v e study t h a t moderate weight l o s s i n obese p a t i e n t s w i t h OSA improves disordered breathing during both sleep and wakefulness. They hypothesized t h a t a narrow c o l l a p s i b l e pharyngeal airway i n awake subjects i s an important f a c t o r i n the pathophysiology of OSA. A p r e c i s e l y weight-matched i n v e s t i g a t i o n by Horner et al.(1988) concluded t h a t there are no systemic d i f f e r e n c e s i n f a t deposit d i s t r i b u t i o n between OSA 9 p a t i e n t s and normal p a t i e n t s , and t h a t there are no s i g n i f i c a n t f a t d e p o s i t s immediately p o s t e r i o r t o the airway i n any of the s u b j e c t s . Furthermore, R u b i n s t e i n and colleagues (1988) p o s t u l a t e d t h a t improvement of OSA symptoms a f t e r weight l o s s may be r e l a t e d t o improvement i n pharyngeal g l o t t i c f u n c t i o n , i n other words, weight l o s s r e s u l t s i n b e n e f i c i a l changes i n pharyngeal mechanics. Furthermore, Lugaresi (1988) supposed t h a t the narrower and longer oropharyngeal isthmus i n snorers and OSA p a t i e n t s r e s u l t s from the repeated heavy i n s p i r a t o r y e f f o r t s a s s o c i a t e d w i t h a downward s t r e t c h of the laryngo- t r a c h e o - b r o n c h i a l t r e e . They hypothesized t h a t a l o s s of even a few kgs of body weight can reverse a t y p i c a l OSA i n t o simple snoring. Weight i s i n t i m a t e l y r e l a t e d t o the airway s i z e . Numerous researchers have attempted t o measure upper airway s i z e (Jackson et a l . , 1980; Lowe et a l . , 1986; M a r t i n et a l . , 1987). Several v i s u a l i z a t i o n techniques are a v a i l a b l e i n c l u d i n g cephalometry, CT (Computerized Tomogram) scans, MRI (Magnetic Resonance Imaging) , cineradiography, nasopharyngoscopy, a c o u s t i c r e f l e c t a n c e and flow volume curves. Among them, CT and MRI could be used f o r three-dimensional(3D) r e c o n s t r u c t i o n s (Lowe et a l . , 1986,1989). Lowe et a l . emphasized the obvious l i m i t a t i o n of two- dimensional (2D) methods si n c e they may not a c c u r a t e l y q u a n t i f y 3D s p a t i a l r e l a t i o n s h i p s . In t h i s respect, 3D CT or MRI r e c o n s t r u c t i o n i s recommended as a more r e l i a b l e method. However, such a 3D r e c o n s t r u c t i o n technique i s time-consuming 10 and expensive f o r r o u t i n e c l i n i c a l use. As a non-invasive technique, Fredberg and co-workers(1980) a c t i v e l y adapted the a c o u s t i c r e f l e c t i o n technique f o r measuring airway geometry. D'urzo et al.(1987) performed a v a l i d i t y t e s t f o r the a c o u s t i c reponse measurement wit h respect t o CT, and proved i t s high c o m p a t i b i l i t y . The cephalometric technique i s another prev a l e n t method, d e s p i t e i t s 2D l i m i t a t i o n s . Not only l i n e a r measurement but a l s o area measurement have become f e a s i b l e . Pae et al.(1989) attempted to prove a c o m p a t i b i l i t y of 2D l a t e r a l cephalometric technique t o 3D CT r e c o n s t r u c t i o n , yet f a i l e d t o demonstrate a high c o r r e l a t i o n between 2D and 3D of the tongue, s o f t p a l a t e and pharynx. Several v i s u a l i z a t i o n techniques are a v a i l a b l e to i d e n t i f y the o c c l u s i o n s i t e . CT has been used as a t o o l f o r i d e n t i f i c a t i o n of the o c c l u s i o n s i t e . Haponik et a l . ( l 9 8 3 ) found the o b s t r u c t i o n s i t e mainly at the nasopharynx and oropharynx. Using fluoroscopy, S u r a t t and a s s o c i a t e s (1983) observed t h a t the o b s t r u c t i o n always begins during i n s p i r a t i o n when the s o f t p a l a t e touches the tongue and p o s t e r i o r pharyngeal w a l l . Chaban et al.(1988) developed a technique based on the a n a l y s i s of i n s p i r a t o r y a i r f l o w pressures. They used a movable ca t h e t e r pressure transducer l o c a l i z e d by cephalometrics and i d e n t i f i e d two d i f f e r e n t o b s t r u c t i o n s i t e s : the p o s t e r i o r p o r t i o n of the s o f t p l a t e and the base of the tongue. By means of cine-CT scans, Crumley and a s s o c i a t e s (1987) examined the o b s t r u c t i o n s i t e and found a diminution i n the a n t e r o p o s t e r i o r 11 diameter a f t e r assuming the supine p o s i t i o n . They presumed t h a t the tongue musculature appears to s e t t l e p o s t e r i o r l y under the p u l l of g r a v i t y i n the supine p o s i t i o n . S t e i n et al.(1987) confirmed Crumley and a s s o c i a t e s ' observations and conclusions and i l l u s t r a t e d the o b s t r u c t i o n s i t e s by means of cine-CT at the uvula and oropharynx mainly. Hoover et al.(1987) reviewed the magnetic resonance imaging technique of the l a r y n x and the base of the tongue and demonstrated the s u p e r i o r i t y of the MR image of the s o f t t i s s u e s t r u c t u r e and s t r e s s e d the non-invasiveness of the MRI. c. F u n c t i o n a l Factors As mentioned e a r l i e r , upper airway muscle f u n c t i o n may a l s o p l a y a primary r o l e i n the pathogenesis of OSA. As f a r as OSA i s concerned, the GG has been the most c l o s e l y s t u d i e d upper airway muscle i n the l a s t decade. The GG i s a v i r t u a l protrudor a s s o c i a t e d w i t h the hypoglossal(XII) nucleus. In a d u l t humans, the GG c o n s i s t s of three p a r t s : an a n t e r i o r p o r t i o n attached t o the s u p e r i o r t u b e r c l e , a middle fan-shaped oblique p o r t i o n which i s attached by a separate tendon l a t e r a l to t h a t t u b e r c l e , and an i n f e r i o r , almost h o r i z o n t a l p o r t i o n attached t o the mandible between the s u p e r i o r and i n f e r i o r t u b e r c l e s . Some f i b r e s of the i n f e r i o r p o r t i o n are attached t o the upper aspect of the body of the hyoid bone. A h o r i z o n t a l component i n s e r t e d i n t o the p o s t e r i o r o n e - t h i r d of the tongue i s the main protrudor (Doran and Bagget,1972). None of the GG muscle f i b r e s are i n s e r t e d 12 through apex of the tongue t i p (Doran and Bagget, 1972; H e l l s t r a n d , 1980) . H i s t o l o g i c a l l y , both type I and type I I f i b r e s are i d e n t i f i e d i n the e x t r i n s i c tongue muscle i n c a t s . The f i b r e - t y p e nomenclature of the human s k e l e t a l muscle, 'type I* and 'type I I ' f i b r e s , are based upon f i b r e i d e n t i f i c a t i o n w i t h the m y o f i b r i l l a r adenosine triphosphatase (ATPase) r e a c t i o n at PH 9.4. According t o Engel(1974), the muscle f i b r e s markedly predominating i n the red muscles are type I, whereas the f i b r e s o c c u ring e x c l u s i v e l y i n white muscles are type I I . Compared w i t h white muscle t i s s u e , biochemical assays of t i s s u e homogenates show t h a t red muscle has more myoglobin, succinate dehydrogenase, and cytochrome oxidase, and has l e s s myosine ATPase, l a c t a t e dehydrogenase, diphosphopyridine n u c l e o t i d e - 1inked alpha glycerophosphate dehydrogenase, phosphorylase and m i t o c h o n d r i a l alpha glycerophosphate dehydrogenase. A l l type I I f i b r e s are f a s t - t w i t c h u n i t s , but some of these are f a s t f a t i g u i n g and others are f a t i g u e r e s i s t a n t , whereas type I u n i t s are a l l slow-twitch and f a t i g u e r e s i s t a n t . H e l l s t r a n d (1980) found t h a t 75-81% of the tongue e x t r i n s i c muscles c o n s i s t of type I I f i b r e s , whereas the d i g a s t r i c muscle c o n s i s t s of 60% type I I f i b r e s ( M i l l e r and F a r i a s , 1988). In humans, the GG muscle i s p r o p o r t i o n a t e l y l a r g e r than i n other mammals such as c a t s , r a t s and dogs (Doran, 1975). Sauerland and M i t c h e l l (1970), demonstrated phasic GG muscle a c t i v i t y during i n s p i r a t i o n by means of b i p o l a r needle e l e c t r o d e s . In 1975, they observed a markedly increased t o n i c a c t i v i t y of the GG i n the supine p o s i t i o n . They i n t e r p r e t e d t h a t the base l i n e a c t i v i t y of the GG increased t o counteract the tongue r e l a p s e due t o the g r a v i t a t i o n a l p u l l . Sauerland and Harper (1976) recorded the GG EMG a c t i v i t y i n humans during the v a r i o u s sleep stages. Remmers et al.(1976) described the r o l e of the GG muscle i n upper airway o b s t r u c t i o n during sleep. They suggested t h a t a t o n i a of the GG c o n t r i b u t e d t o the i n s p i r a t o r y upper airway o b s t r u c t i o n . G u i l l e m i n a u l t et al.(1978) a l s o found s i g n i f i c a n t l y decreased GG EMG a c t i v i t y during o b s t r u c t i v e apnea. However, w i t h the "tent hypothesis", they negated the s i n g u l a r involvement of the GG muscle i n the genesis of the OSA syndrome, but suggested the involvement of s e v e r a l muscle groups, p r i m a r i l y the s u p e r i o r c o n s t r i c t o r s . A number of comparison s t u d i e s of the GG and the diaphragm soon followed. B r o u i l l e t t e and Thach(1980) p o s t u l a t e d t h a t the GG response to chemoreceptor input and n o n - s p e c i f i c s t i m u l i i s q u a l i t a t i v e l y s i m i l a r but q u a n t i t a t i v e l y d i f f e r e n t from diaphragm responses. Onal and colleagues(1981) observed synchronous a c t i v i t y of the GG and the diaphragm i n normal human subjects and emphasized the importance of the i n s p i r a t o r y f u n c t i o n of the upper airway muscles i n maintaining upper airway patency. They p o s t u l a t e d t h a t the GG and geniohyoid muscles maintain upper airway patency by p u l l i n g the tongue and hyoid bone forward during i n s p i r a t i o n . Haxhiu et al.(1987) designed an experiment to compare the response of the diaphragm and upper airway d i l a t i n g muscle a c t i v i t y i n s l e e p i n g c a t s . They found t h a t hypercapnea 14 a f f e c t s the GG d i f f e r e n t l y than the diaphragm, and suggested t h i s might be due t o the d i f f e r e n t t h r e s h o l d c h a r a c t e r i s t i c s of hypoglossal and phrenic neurons. From the p o i n t of view of the mechanics of r e s p i r a t i o n , the supra-hyoid muscles have only r e c e n t l y been recognized as important. Doran and Baggett (1972) d i s c u s s the r e l a t i o n s h i p between the GG muscle and hyoid apparatus. They observed t h a t some f i b r e s of the i n f e r i o r p o r t i o n of the GG are attached t o the upper p o r t i o n of the body of the hyoid bone. This f i n d i n g agreed w i t h t h a t of Abd-El-Malek (1938), but not w i t h H e l l s t r a n d (1980). Doran and Baggett p o s t u l a t e d t h a t i n the e a r l y phylogenetic stage, the GG muscle and the geniohyoid muscle might be the one supra-hyoid group. They r e l y on L i v i n g s t o n ' s (1965) c r i t e r i a of tongue m o b i l i t y , which suggest t h a t movement of the tongue depends l a r g e l y on the movement of the hyoid bone. By d e f i n i t i o n , t h e supra-hyoid group i n c l u d e s d i g a s t r i c , s t y l o h y o i d , mylohyoid and geniohyoid muscles (Kaneko, 1975). Among them, the geniohyoid muscle alone has the airway ^ d i l a t a t i o n f u n c t i o n ; i . e . , i t p u l l s the ele v a t e d hyoid bone d i r e c t l y forward which increases the a n t e r o p o s t e r i o r diameter of the pharynx (Romanes, 1979). In c o n t r a s t , the s t y l o h y o i d muscle p u l l s the hyoid bone p o s t e r i o r l y ; the mylohyoid muscle s t a b i l i z e s e i t h e r the mandible or hyoid bone. Of the i n f r a - hyoid muscles, the sternohyoid and thyrohyoid muscles p u l l the hyoid muscle down (Kaneko, 1975). In 1984, van de Graaff et a l . explained t h a t the r e s p i r a t o r y f u n c t i o n of the hyoid muscle 15 and hyoid arch a f f e c t upper airway r e s i s t a n c e . They suggested t h a t the s t r a t e g i c l o c a t i o n of the hyoid arch may c o n t r i b u t e t o the patency of upper airway and the decreased or p o o r l y coordinated f u n c t i o n of the hyoid muscle may induce upper airway o c c l u s i o n . This hypothesis was suggested by Mathew (1984), as w e l l as by Roberts et al.(1984). Blood gas changes, pressure changes, and t i s s u e d i s t o r t i o n can e l i c i t r e s p i r a t o r y r e f l e x e f f e c t s (Cherniac and Hudgel,1986). As lung volume increases during r e s p i r a t i o n , s t i m u l a t i o n of pulmonary s t r e t c h receptors feeds back to the r e s p i r a t o r y center v i a the vagus nerve. This i s the c l a s s i c Hering-Breuer r e f l e x ( P a r i s i and Neubauer,1986). Van Lunteren et al.(1984) i n v e s t i g a t e d the e f f e c t s of v a g a l l y mediated volume-related feedback on the a c t i v i t y of the upper airway muscles and found t h a t the amount of depression at the end of i n s p i r a t o r y a i r f l o w was greater f o r a l l of the upper airway muscles than f o r the diaphragm. They explained t h i s phenomenon as p o s s i b l y due e i t h e r t o a lower t h r e s h o l d of the upper airway muscles f o r i n s p i r a t o r y depression or t o a vagal depression e f f o r t on the upper airway muscle or p o s s i b l y t o both. Agostoni et al.(198 6) undertook an examination on the time-coursed e f f e c t of the s t r e t c h receptor of the bronchi or trachea on GG muscle a c t i v i t y i n r a b b i t s and reported t h a t b r o n c h i a l input f a c i l i t a t e s GG a c t i v i t y at the end-expiratory volume and i n h i b i t s i t at l a r g e r volumes. A hypercapnic response has been e x t e n s i v e l y s t u d i e d by s e v e r a l groups (Bulow, 1963; Douglas et al,1982; Berton-Jones and S u l l i v a n ; Weiner et a l , 1982). St. John et al.(1984) reported i n cat t h a t a c t i v i t y i n the phrenic and hypoglossal nerves increases or decreases i n p a r a l l e l f a s h i o n w i t h the hypercapneic c o n d i t i o n . This f i n d i n g concurrs w i t h the r e s u l t s of Onal et al.(1981). However, a number of recent s t u d i e s show a c u r v i l i n e a r r e l a t i o n s h i p between the GG and the diaphragm i n c o n d i t i o n s of p e r s i s t i n g hypercapnia ( P a r i s i et a l . , 1987; H i x h i u et a l . , 1987). Nevertheless, i t i s obvious t h a t arousal increases the GG a c t i v i t y more than t h a t of the diaphragm. A number of research s t u d i e s support the idea t h a t i t i s not hypoxia but hypercapnia or asphyxia which provokes the arousal (Fleetham et a l , 1982; I s s a and S u l l i v a n , 1986; Mathiot et a l , 1986). Kuna (1987) c a r r i e d out an experiment concerned w i t h the i n t e r a c t i o n of hypercapnia and phasic volume feedback on the motor c o n t r o l of the upper airway i n decerebrate, p a r a l y z e d , and intubated c a t s . He found t h a t the hypoglossus i s more s e n s i t i v e than the r e c u r r e n t l a r y n g e a l nerve t o suppression by phasic volume feedback. Kuna (1987) a l s o concluded t h a t hypercapnia may p o t e n t i a t e the e f f e c t of lung volume on the suppression of the upper airway motor neuron a c t i v i t y . This phenomenon i m p l i e s t h a t the r e s p i r a t o r y c o n t r o l mechanism i s designed t o decrease energy expenditure of the upper airway muscles t o suppress t h e i r a c t i v a t i o n when they are not needed, i . e . , i n the presence of phasic volume feedback, which r e s u l t s i n augmented upper airway motorneuron a c t i v i t y . The mechanism 17 of the c y c l i c changes i n v e n t i l a t i o n has been considered a fundamental f a c t o r i n r e s p i r a t o r y f u n c t i o n . Several s t u d i e s (Van Lunteren and S t r o h l , 1986; Adachi et a l . , 1989; Hudgel and Harasick, 1989) suggest t h a t the i n s p i r a t o r y a c t i v i t y of the upper airway muscles s l i g h t l y precedes t h a t of the diaphragm i n normal s i t u a t i o n s . This rhythmic order may be a c r i t i c a l f a c t o r of the pathogenesis of OSA. The i n s t a b i l i t y i n the rhythmic feedback c o n t r o l of r e s p i r a t i o n could provoke OSA (Longobardo et a l . , 1982). Cherniac and Longobardo (1986) assume t h a t t h i s disturbance i n feedback rhythm may t r i g g e r r e c u r r e n t apneas. S u l l i v a n et al.(1981) have developed CPAP(Continuous P o s i t i v e Airway Pressure ) t o a s s i s t i n the maintenance of upper airway patency. The mechanism hypothesized was t h a t the CPAP would act as a pneumatic s p l i n t and prevent upper airway o c c l u s i o n , pushing the s o f t t i s s u e and tongue forward and away from the p o s t e r i o r pharyngeal w a l l . However, there has been con s i d e r a b l e controversy about the r a t i o n a l e of CPAP use and i t s immediate r e l a p s e tendency a f t e r withdraw. On the other hand, a number of negative pressure s t u d i e s have been reported. The i n f l u e n c e of upper airway negative pressure change on the r e s p i r a t o r y a c t i v i t y of upper airway muscles was examined i n r a b b i t s by Mathew (1982a, 1982b, 1984). He hypothesized the presence of a r e f l e x pathway t h a t r e g u l a t e s GG a c t i v i t y i n response t o the upper airway pressure loads. In 1984, van Lunteren et a l . found i n dogs t h a t the d u r a t i o n of i n s p i r a t i o n 18 and the length of i n s p i r a t o r y a c t i v i t y of a l l upper airway muscles increased i n p r o p o r t i o n t o the amount of negative pressure a p p l i e d . They concluded t h a t negative pressure i n the upper airway i n h i b i t s the a c t i v i t y of the diaphragm and p r e a c t i v a t e s the upper airway d i l a t i n g muscles. Recently, Kuna (1988a, 1988b) and h i s a s s o c i a t e s c a r r i e d out two d i f f e r e n t experiments i n normal human su b j e c t s . From the i n v e s t i g a t i o n to determine the e f f e c t of nasal o c c l u s i o n on GG a c t i v i t y , they concluded t h a t subatmospheric pressure i n the upper airway and withdrawal of phasic volume feedback may not p l a y an important r o l e i n the r e g u l a t i o n of upper airway muscle a c t i v i t y i n normal s l e e p i n g a d u l t s . However, Kuna et a l . d i d not exclude completely the p o s s i b i l i t y of the c r i t i c a l r o l e of the GG even though t h i s r o l e may be very s m a l l . Secondly, by means of CT, they compared s i z e of the upper airway area, w h i l e a p p l y i n g the CPAP, to i t s s i z e without the CPAP. Furthermore, Kuna and h i s co-workers compared EMG a c t i v i t y of the GG between w i t h and without CPAP during wakefulness. They observed no change i n phasic and t o n i c EMG a c t i v i t y between the two p r o t o c o l s . However, they found a l i n e a r increase i n airway area p r o p o r t i o n a l t o the increment i n p o s i t i v e pressure. I s s a et al.(1988) examined how sensory i n f o r m a t i o n from the upper airway i n f l u e n c e s the v e n t i l a t o r y and GG muscle response t o airway o c c l u s i o n during d i f f e r e n t sleep stages. I n t e r e s t i n g l y , they conducted a nasal o c c l u s i o n experiment i n dogs i n the same manner as Kuna et a l . . Nasal o c c l u s i o n caused 19 a markedly increased GG EMG a c t i v i t y , w h i l e t r a c h e a l o c c l u s i o n created a sm a l l e r increase i n GG a c t i v i t y . I s s a and h i s a s s o c i a t e s p o s t u l a t e d an upper airway p r o t e c t i v e load-compensation r e f l e x i n NREM sleep. Furthermore, they suggested t h a t damage t o a f f e r e n t receptors i n the upper airway, caused by the mechanical trauma of snoring might l e a d t o the reduced e f f e c t i v e n e s s of such a r e f l e x and thus t o OSA. Aronson and colleagues (1989) conducted an experiment t o examine the e f f e c t i v e n e s s of nasal CNAP(Continuous Negative Airway Pressure) i n normal human s u b j e c t s . They found t h a t during wakefulness, both diaphragmatic and GG a c t i v i t i e s increased immediately i n response t o CNAP. However, during NREM sle e p , d e s p i t e p r o g r e s s i v e diaphragmatic and GG responses, airway patency was not r e e s t a b l i s h e d u n t i l a r o u s a l . They are d o u b t f u l of r a t i o n a l e of the CNAP hypothesis and presume t h a t the gradual increment of GG a c t i v i t y probably r e f l e c t s a response t o changing blood gas composition and i s not due.to the mechanical r e c e p t o r . C . Biomechanical r e l a t i o n s h i p between postures and airway adequacy 1] Head posture C o n t r o l of head p o s i t i o n i s a complex process t h a t i n t e g r a t e s i n f o r m a t i o n from a v a r i e t y of sources t o generate f u n c t i o n a l l y appropriate motor a c t i v i t y (Schor et a l . , 1988). B a s i c a l l y , three feedback subsystems r e l a y i n f o r m a t i o n about head p o s i t i o n by means of d i f f e r e n t sensory m o d a l i t i e s . The 2 0 c e r v i c o c o l l i c reflex(CCR) subsystem r e l a y s somatosensory in f o r m a t i o n t o monitor the p o s i t i o n of the head w i t h respect t o the body;the v e s t i b u l o c o l l i c reflex(VCR) and o p t o c o l l i c reflex(OCR) subsystems s i g n a l movements of the head i n space using v e s t i b u l a r and v i s u a l s i g n a l s . These feedback systems undoubtly connect c e n t r a l l y as w e l l as p e r i p h e r a l l y , and thus c o n t r i b u t e t o the c e n t r a l v o l u n t a r y commands as w e l l as t o r e f l e x responses. Since the head c o n t r o l system contains a number of feedback loops, i t i s d i f f i c u l t t o d i s t i n g u i s h r e f l e x from v o l u n t a r y responses. The r e l a t i o n s h i p between head posture and c r a n i o f a c i a l morphology has long been a research t a r g e t f o r a n t h r o p o l o g i s t s (Moss and Young, 1960; R i e s e n f e l d , 1967) and o r t h o d o n t i s t s (Moorrees and Kean, 1958; Bench, 1963; Carlsoo and L e i j o n , 1960). Solow et al.(1971, 1979, 1984) hypothesized an in t i m a t e r e l a t i o n s h i p between head p o s i t i o n , airway adequacy and c r a n i o f a c i a l morphology. Their f i n d i n g s are a l s o concurrent w i t h Woodside and Linder-Aronson (1976) and V i g et al. ( 1 9 8 0 ) . Solow et al.(1979, 1984) po s t u l a t e d t h a t inadquate patency of the nasopharynx induces an extended neck posture. Recently, L i i s t r o et al.(1988) i l l u s t r a t e d t h a t head posture i n f l u e n c e s upper airway r e s i s t a n c e and provided evidence t h a t r e s i s t a n c e i s decreased when the head i s extended. 21 2] Body posture I s s a and S u l l i v a n (1986) observed t h a t some p a t i e n t s e x h i b i t e d c e n t r a l apnea wh i l e asleep i n a supine p o s i t i o n , but e x h i b i t e d obstructed apnea or simple snoring when i n the l a t e r a l recumbent p o s i t i o n . According t o P a r i s i and Neubauer (198 6), changes i n pulmonary mechanics during sleep would occur p r i m a r i l y when changing body p o s i t i o n . In the u p - r i g h t p o s i t i o n , i n s p i r a t o r y muscle a c t i v a t i o n r e s u l t s i n increased lung volume v i a outward movement of the chest w a l l . However, i n the supine p o s i t i o n , due t o the g r a v i t a t i o n a l e f f e c t , the same p a t t e r n of muscle a c t i v i t y produces greater abdominal output than chest w a l l displacement. In a d d i t i o n , the supine p o s i t i o n decreases f u n c t i o n a l r e s i d u a l c a p a c i t y (Behrakis et a l . , 1983). A number of experiments support the hypothesis t h a t changes i n lung volume d i r e c t l y i n f l u e n c e the upper airway flow patency (van de Graaff,1989; Navajas et al,1988). S t r o h l (1986) explained the increase i n upper airway r e s i s t a n c e i n the supine p o s i t i o n by two mechanisms: f i r s t , g r a v i t y moves the mandible and hypoglossal s t r u c t u r e s p o s t e r i o r l y , compromising the s i z e of the airway. Secondly, s u p r a g l o t t i c r e s i s t a n c e increases due i n l a r g e measure t o increased blood i n the nasal mucosa (Anch et al.1982). Several groups(Brown et al,1987;Navajas et a l , 1988; Fouke and S t r o h l , 1987) found a decreased pharyngeal c r o s s - s e c t i o n a l area i n the supine p o s i t i o n . Notably, Fouke and S t r o h l (1987) have shown t h a t the decreased pharyngeal c r o s s - 22 s e c t i o n a l area i s a r e s u l t of the change from the u p - r i g h t to the supine p o s i t i o n , independent from the change i n the FRC (F u n c t i o n a l Residual C a p a c i t y ) . While the presence of a small airway does not appear to determine OSA (Rodenstein et a l . , 1989), a high R e s p i r a t o r y Disturbance Index i n d i c a t e s i t s presence. George et al.(1989) f u r t h e r confirm t h a t the RDI(Respiratory Disturbace Index = AHI) i s s i g n i f i c a n t l y higher i n a supine p o s i t i o n , i n NREM sleep. 23 STATEMENT OF PROBLEM Airway o b s t r u c t i o n i n OSA p a t i e n t s occurs i n the supine p o s i t i o n . Previous i n v e s t i g a t o r s have shown a s m a l l e r airway s i z e , an extended head posture and a reduced GG muscle a c t i v i t y i n OSA p a t i e n t s . Fouke et al.(1987) compared pharyngeal s i z e i n h ealthy subjects w i t h a c o u s t i c r e f l e c t i o n techniques and reported t h a t the s i z e of the pharynx was 23% s m a l l e r i n the supine p o s i t i o n when compared t o the u p - r i g h t p o s i t i o n . C o n t r a c t i o n of the GG muscle advances the tongue base, d i l a t e s the upper airway, and decreases a i r f l o w r e s i s t a n c e . Increased GG muscle a c t i v i t y i n the supine p o s i t i o n has been reported by s e v e r a l i n v e s t i g a t o r s . However, such a c t i v i t y does not always i n d i c a t e a c t u a l muscle shortening, s i n c e the muscle shortens only when the neural output produces enough c o n t r a c t i l e f orces to overcome an e x t e r n a l load. Airway s i z e measurements from up- r i g h t l a t e r a l cephalograms can ha r d l y be matched w i t h supine EMG data which approximates the s l e e p i n g body p o s i t i o n . Few a r t i c l e s have reported s i z e changes of the upper airway and f u n c t i o n a l changes of the upper airway muscles i n the supine p o s i t i o n at the same time. To i n v e s t i g a t e the r e l a t i o n s h i p between upper airway s i z e and GG muscle a c t i v i t y , the f o l l o w i n g questions were presented. 24 1. How are airway s i z e and p o s i t i o n a l r e l a t i o n s h i p s of the hyoid bone a f f e c t e d by body p o s i t i o n a l changes i n OSA and c o n t r o l groups ? 2. What do changes i n body p o s i t i o n a f f e c t GG muscle EMG and tongue pressure ? 25 METHODS The c u r r e n t experiment was composed of two major p a r t s ; a cephalometric study, and tongue EMG and pressure recordings. The cephalometric study was undertaken i n twenty p a t i e n t s w i t h OSA and i n ten asymptomatic c o n t r o l s . The tongue EMG and pressure study was c a r r i e d out i n the ten asymptomatic c o n t r o l s . A . Experimental subjects A t o t a l of t h i r t y subjects were evaluated and s e l e c t e d as study m a t e r i a l from a population r e c r u i t e d over a ten month pe r i o d (1988-1989) at the U n i v e r s i t y H o s p i t a l (UBC s i t e ) i n Vancouver. Twenty subjects w i t h diagnosed OSA as determined by overnight sleep s t u d i e s were used as the p a t i e n t group. Ten asymptomatic subjects found not to have OSA on the b a s i s of overnight monitoring and/or medical h i s t o r i e s were used as c o n t r o l s . The overnight sleep study was c a r r i e d out at the R e s p i r a t o r y Sleep Disorder C l i n i c and a l l anthropometric, pulmonary f u n c t i o n and sleep study data used i n t h i s study were provided by the c l i n i c . Edentulous s u b j e c t s , s u b j e c t s who had an ongoing r e s p i r a t o r y i n f e c t i o n or any medication known to a f f e c t muscle a c t i v i t y , subjects who needed orthognathic surgery and those unable to give f u l l y informed consent were excluded from the study. A l l i n d i v i d u a l s i n cluded i n the study were a d u l t males (see Table I ) . 26 Table I Demographic Variables for the Experimental Subjects DEMOGRAPHIC VARIABLES OSA (N = 20) CONTROL (N = 10) MEAN S.D. MEAN S.D. AGE 48.4 13.03 33.5 5.95 WEIGHT 97.78 22.64 78.20 11.72 BMI 31.55 7.88 26.30 3.19 RDI 29.91 29.88 Legend Table I Age = years, Weight = kg, BMI(Body Mass Index) = kg/m2 RDI(Respiratory Disturbance Index) = Apnea Index + Hypopnea Index 27 The average age of the twenty s u b j e c t s composing the OSA group was 4 8.4 years and ranged from 2 0 to 71 years (see Table I) . Th e i r weights ranged from 69Kg t o 150Kg;the mean was 97.8Kg. Average BMI [Body Mass Index = Weight(Kg)/Height 2 (m 2)] was 31.5 (ranging from 24.76 t o 47.48). A l l of the OSA sub j e c t s were snorers. The mean A l was 9.99, and the mean RDI was 29.91. The ages of the c o n t r o l subjects ranged from 2 3 to 4 6 years;the mean age was 3 3.5. The average weight of the c o n t r o l group was 78.2Kg and ranged from 62Kg t o 9 5Kg. The average BMI was 2 6.3, ranging from 21.45 t o 32.18. B. Experimental Procedures 1] Cephalometric study A p a i r of i n d i v i d u a l cephalograms were obtained w i t h i d e n t i c a l equipment (Counterbalanced Cephalometer Model W-105, Wehmer Co.) and by an i d e n t i c a l method (165 cm source t a r g e t d i s t a n c e , 14 cm f i l m t a r g e t d i s t a n c e ; 90 kVp, 15mA, 1.25 sec; Kodak 8x10" f i l m s , Kodak Lanex Regular Screens) f o r each subject i n the u p - r i g h t standing p o s i t i o n and supine p o s i t i o n . A l l of the cephalograms were taken at the end of the e x p i r a t i o n phase. a. Up-right versus supine l a t e r a l cephalograms To o b t a i n u p - r i g h t l a t e r a l cephalograms, n a t u r a l head posture was determined by v i s u a l feedback i n a m i r r o r and recorded by a modified l e v e l device (see F i g . 1) attached to the s o f t - t i s s u e FH plane( i n f r a o r b i t a l notch t o t r a g i o n ) . 28 Fig. 1 Measurement of Head Posture with the Modified Fluid Level Device Legend F i g . l Angle between the upper margin of the tape and the true h o r i z o n t a l ( l e v e l of the l i q u i d ) r epresents the n a t u r a l head posture. 29 N a t u r a l head posture i n the standing p o s i t i o n has been considered h i g h l y r e p r o d u c i b l e (Moorrees and Kean, 1958; Siersbaek-Nielson and Solow, 1982; Sandham, 1988). A v i s u a l feedback method i n standing p o s i t i o n was employed f o r the c u r r e n t experiment. The subject was r e q u i r e d t o stand 1.5 m away from and i n f r o n t of the m i r r o r (150 cm long) . In a r e l a x e d and n a t u r a l body posture, the subject was i n s t r u c t e d t o swing h i s head back and f o r t h and g r a d u a l l y reduce the magnitude of the swing. F i n a l l y , the subject stopped at h i s own n a t u r a l head posture determined by h i s own sense of head balance and s i g h t . This procedure was c a r r i e d out w i t h the eyes c l o s e d f i r s t , then the second time w i t h the eyes open and gazing i n the m i r r o r (see p a t i e n t i n s t r u c t i o n sheet, p30). The degree of the head posture was i n d i c a t e d by the f l u i d l e v e l i n the device. This process was repeated 2-3 times, averaged and recorded. A l a t e r a l cephalogram was taken of the subject i n h i s own n a t u r a l posture as p r e v i o u s l y determined w i t h the modified l e v e l device. In order t o take the supine cephalogram, the subject was i n s t r u c t e d t o l i e down on a s t r e t c h e r and t o mimick h i s own usual s l e e p i n g p o s i t i o n and p i l l o w height. The head angle was recorded a f t e r the p a t i e n t was e s t a b l i s h e d i n h i s own comfortable, n a t u r a l s l e e p i n g p o s i t i o n . F i n a l l y , the supine l a t e r a l cephalogram was taken w i t h the jaw i n a completely r e l a x e d p o s i t i o n . 30 CEPHALOMETRIC INSTRUCTIONS FOR PATIEHTS You are going to have two head x-rays taken. The f i r s t i s obtained i n a standing p o s i t i o n with a neutral head posture, the other i s taken i n a r e c l i n e d p o s i t i o n . A. NATURAL HEAD POSTURE 1. Stand on the black l i n e i n f r o n t of the m i r r o r . 2 . Stand i n a comfortable p o s i t i o n and look d i r e c t l y at your own eyes i n the mirror as i f you were gazing o f f into the dis tance . 3 . Close your eyes and nod your head back and f o r t h and gradually reduce the magnitude of the swing. Please stop when you f e e l you have a na tura l head posture . 4. Repeat the above task twice with your eyes open. B. STANDING POSITION 1. Stand on the foot p r i n t and reproduce your neutra l head posture as i n s t r u c t e d . 2. Relax your jaw and b i t e s l i g h t l y on your back t e e t h . 3. A f t e r three regular breaths, breathe out, and hold your breath u n t i l the x-ray i s completed. C. SUPINE POSITION 1. L i e down on the s t r e t c h e r and make y o u r s e l f as comfortable as you can. 2 . Please mimick your usual s l e e p i n g p o s i t i o n . Let your jaw relax as you would when you are as leep . Do not b i t e on your back teeth . 3. A f t e r three regular breaths , breathe out, and hold your breath u n t i l the x-ray i s completed. 31 The l e v e l device which was employed i n the c u r r e n t experiment (see Fig.2) was an improved type modelled on s e v e r a l former l e v e l devices (Showfety et a l , 1983; Huggare, 1985). This modified l e v e l device, developed i n c o n s u l t a t i o n w i t h Dr. C. P r i c e of the D i v i s o n of Radiology i n F a c u l t y of D e n t i s t r y at UBC, was composed of three pieces of a c r y l i c p l a t e and an a c r y l i c tube. A m i c r o f i e d c i r c u l a r p r o t r a c t o r measuring 360 degrees was attached t o the small middle a c r y l i c p l a t e so t h a t an angle could be read up to h a l f a degree i n any p o s i t i o n . P r e s c r i b e d s aturated radiopaque l i q u i d was h e l d i n s i d e the p o l y v i n y l tube t o r e g i s t e r the t r u e h o r i z o n t a l plane on the f i l m . The l i q u i d was composed approximately of 30% l e a d n i t r a t e (PbN03), red dye, s u r f a c t a n t and water. In order to determine the s o f t - t i s s u e FH plane, the i n f r a - o r b i t a l notch was palpated and t r a g i o n was determined. Two l e a d markers were attached t o the i n f r a o r b i t a l notch and t r a g i o n w i t h an appropriate length of coloured scotch tape. The modified l e v e l device was placed on the tape which i n d i c a t e s the s o f t - t i s s u e FH plane and was adhered t o the l i n e w i t h double sid e d tape (see F i g . 1) . A f t e r the n a t u r a l head posture was decided i n the manner described above, one tablespoon of the M i c r o t r a s t Esophageal cream (Esobar, Therapex Inc.) was d e l i v e r e d . The dorsum of the tongue and upper pharyngeal airway were coated w i t h the radiopaque cream to enhance r a d i o p a c i t y of the o u t l i n e . 32 Rg. 2 Schematic Diagrams to Illustrate Assembly of the Modified Fluid Level Device Legend Fig.2 The p l a s t i c tube(diameter= 3.3 mm) c o n t a i n s PbN03, r e d dye, s u r f a c t a n t and water. Subsequently, a lead marker w i t h a diameter of 5.0 mm was placed on the midpoint of the tongue t i p by means of biocompatible adhesives (Iso Dent, Ellman Dental Inc.) i n order to r e g i s t e r the exact p o s i t i o n of the tongue t i p . The tongue t i p represents the m i d s a g i t t a l j u n c t i o n of the tongue dorsum and the i n f e r i o r mucous membrane. The subject was i n s t r u c t e d t o stand on the f o o t p r i n t i n the cephalostat and t o reproduce h i s own n a t u r a l head posture w i t h the a i d of the an g u l a t i o n recorded by the modified l e v e l device. A metal chain was suspended from the surface of the c a s s e t t e to confirm and r e g i s t e r a t r u e v e r t i c a l plane on the f i l m . F i n a l l y , cephalograms were taken i n the i n s t r u c t e d p o s i t i o n i n both the u p - r i g h t and supine p o s i t i o n at end- e x p i r a t i o n . Figure 3 i l l u s t r a t e s the posture maintained f o r t a k i n g the supine cephalogram. 34 Fig. 3 Photograph of the Supine Cephalometric Procedure b. D e f i n i t i o n s and r a t i o n a l e of landmarks, planes, l i n e s , a n g u l a t i o n s , areas and' t h e i r measurements In a d d i t i o n t o the t r a d i t i o n a l cephalometric v a r i a b l e s , s e v e r a l s o f t - t i s s u e and v e r t e b r a l p o i n t s and l i n e s were used to evaluate the s i z e and l o c a t i o n of upper airway s t r u c t u r e s . S p e c i f i c landmarks, l i n e s and angles were designed and i d e n t i f i e d . A l l l a t e r a l cephalometric landmarks were coordinated w i t h X and Y axes, and these two axes were o r i e n t e d t o t r u e h o r i z o n t a l and v e r t i c a l l i n e s . 1.Hard-tissue landmarks (see Fig.4) S S e l l a - The estimated centre of the s e l l a t u r c i c a . N Nasion - The most a n t e r i o r p o i n t of the n a s o - f r o n t a l suture. Or O r b i t a l e - The most i n f e r i o r p o i n t of the i n f r a - o r b i t a l margin. ANS A n t e r i o r nasal spine - The apex of the a n t e r i o r nasal spine. PNS P o s t e r i o r nasal spine - The p o s t e r i o r t i p of the p o s t e r i o r nasal spine of the p a l a t i n e bone. R Roof of the pharynx - The p o i n t on the p o s t e r i o r pharyngeal w a l l constructed by a l i n e PNS to the c r o s s - s e c t i o n a l p o i n t of the c r a n i a l base and the l a t e r a l p t e r y g o i d p l a t e . 3 6 A p o i n t Subspinale - The deepest p o i n t on the a n t e r i o r surface of the m a x i l l a r y a l v e o l a r bone. B p o i n t Submentale - The deepest p o i n t on the a n t e r i o r surface of the mandibular symphysis. Pog Pogonion - The most prominent p o i n t on the a n t e r i o r surface of the mandibular symphysis i n respect t o the mandibular plane. Me Menton - The most i n f e r i o r p o i n t on the mandibular symphysis. Gn Gnathion - The midpoint between Pog and Me on the b i s e c t i n g l i n e of the angle formed by mandibular plane and f a c i a l plane. RGN Retrognathion - The most p o s t e r i o r p o i n t of the mandibular symphysis along a l i n e p e r p e n d i c u l a r t o the FH ( F r n k f o r t H o r i z o n t a l ) plane. Go Gonion - The most i n f e r i o r , p o s t e r i o r and outer most p o i n t of the mandibular angle, determined by a b i s e c t o r < the angle formed by the tangent t o the p o s t e r i o r and i n f e r i o r border l i n e of the mandible. Po Porion - The uppermost p o i n t of the ear rod. CV2tg Second Vertebra Tangent - The most p o s t e r i o r and s u p e r i o r p o i n t on the p o s t e r i o r surface of the second v e r t e b r a l corpus. CV2ip Second Vertebra I n f e r i o r P o s t e r i o r - The most p o s t e r i o r and i n f e r i o r p o i n t of the second v e r t e b r a l corpus. CV4ip Fourth Vertebra I n f e r i o r P o s t e r i o r - The most p o s t e r i e r p o i n t of the f o u r t h v e r t e b r a l corpus. C3 T h i r d Vertebra - The most a n t e r i o r i n f e r i o r p o i n t of the t h i r d v e r t e b r a l corpus. C4 Fourth Vertebra - The most a n t e r i o r i n f e r i o r p o i n t of the f o u r t h v e r t e b r a l corpus. 38 Legend Fig.4 S ( s e l l a ) , N(Nasion), O r ( O r b i t a l e ) , ANS(Anterior Nasal Spine) , PNS(Posterior Nasal Spine) , R(Roof of the pharynx), A(Subspinale) , B(Submentale), Pog(Pogonion), Me(Menton) , Gn(Gnathion) , RGN(Retrognathion) , Go(Gonion) , Po(Porion), CV2tg(Second Vertebra Tangent) , CV2ip(Second Vertebra I n f e r i o r P o s t e r i o r ) , CV4ip(Fourth Vertebra I n f e r i o r P o s t e r i o r ) , C3(Third Ver tebra) , C4(Fourth Vertebra) 39 2 . S o f t - t i s s u e landmarks (see Fig.5) a) Tongue TT Tongue Tip - The center of the lead d i s c attached t o the border between the v e n t r a l and d o r s a l surfaces of the tongue t i p . TH Tongue Height - The highest p o i n t of the tongue curvature r e l a t i v e t o a l i n e from base of the e p i g l o t t i s t o TT. Eb Base of E p i g l o t t i s - The deepest p o i n t of the e p i g l o t t i s . Et T ip of E p i g l o t t i s - The most s u p e r i o r p o i n t of the e p i g l o t t i s . H Hyoidale - The most a n t e r i o r and s u p e r i o r p o i n t of the hyoid bone. b) S o f t p a l a t e P P a l a t e P o i n t - The most i n f e r i o r t i p of the s o f t p a l a t e . AP A n t e r i o r P a l a t e - The a n t e r i o r p o i n t of maximum p a l a t a l t h i c k n e s s determined along a l i n e p e r p e n d i c u l a r t o a l i n e from PNS t o P. PP P o s t e r i o r P a l a t e - The p o s t e r i o r p o i n t of maximum p a l a t a l t h i c k n e s s determined along a l i n e p erpendicular t o PNS-P. 40 AST A n t e r i o r Superior Tongue - The c r o s s - s e c t i o n a l p o i n t on the tongue curvature determined by a l i n e through the mid-point of PNS-P and p a r a l l e l t o Go-B. ASP A n t e r i o r Superior P a l a t e - The a n t e r i o r c r o s s - s e c t i o n a l p o i n t of the s o f t p a l a t e determined by a l i n e b i s e c t i n g PNS-P and p a r a l l e l to Go-B. PSP P o s t e r i o r Superior P a l a t e - The p o s t e r i o r c r o s s - s e c t i o n a l p o i n t of the s o f t p a l a t e determined by a l i n e b i s e c t i n g PNS-P and p a r a l l e l t o Go-B. PSPh P o s t e r i o r Superior Pharynx - The c r o s s - s e c t i o n a l p o i n t of the p o s t e r i o r pharyngeal w a l l by a l i n e b i s e c t i n g PNS-P and p a l a l l e l t o Go-B. c) Pharyngeal airway MAA Middle A n t e r i o r Airway - The a n t e r i o r p o i n t on the tongue on a l i n e through p o i n t P p a r a l l e l t o Go-B. MPA Middle P o s t e r i o r Airway - The p o i n t on the p o s t e r i o r pharyngeal w a l l on a l i n e through p o i n t P and p a r a l l e l t o Go-B. IAA I n f e r i o r A n t e r i o r Airway - The a n t e r i o r c r o s s - s e c t i o n a l p o i n t on the p o s t e r i o r surface of the tongue or s o f t p a l a t e determined by a extended l i n e of Go-B p o i n t plane. 41 IPA I n f e r i o r P o s t e r i o r Airway - The p o s t e r i o r c r o s s - s e c t i o n a l p o i n t on the p o s t e r i o r pharyngeal w a l l determined by the l i n e Go-B. 42 Legend Fig. 5 TT(Tongue T i p ) , TH(Tongue Height ) , Eb(Base of E p i g l o t t i s ) , E t ( T i p of E p i g l o t t i s ) , H(Hyoidale) , P(Palate P o i n t ) , AP(Anterior Pa la te ) , PP(Posterior Pala te ) , AST(Anterior Superior Tongue), ASP(Anterior Superior Pala te ) , PSP(Posterior Superior Pa la te ) , PSPh(Posterior Superior Pharynx), MMA(Middle A n t e r i o r Airway) , MPA(Middle Pos ter ior Airway) , I A A ( I n f e r i o r A n t e r i o r Airway) , I P A ( I n f e r i o r P o s t e r i o r Airway) 43 Several l i n e a r , angular and area v a r i a b l e s were determined. 3 . L i n e a r measurements (see Fi g . 6 ) a) Tongue TGL Tongue Length - The l i n e a r d i s t a n c e between TT and Eb. TGH Tongue Height - The l i n e a r d i s t a n c e between a p o i n t on the most s u p e r i o r curvature of the tongue dorsum and the base of a l i n e drawn perpe n d i c u l a r to the TT-Eb l i n e . b) S o f t P a l a t e PNS-P Sof t P a l a t e Length - The l i n e a r d i s t a n c e between PNS and P. MPT Maximum Pa l a t e Thickness - The maximum t h i c k n e s s of the s o f t p a l a t e measured on a l i n e p e r p e n d i c u l a r t o the PNS-P. c) Upper Airway SPAS Superior P o s t e r i o r Airway Space - The t h i c k n e s s of the airway behind the s o f t p a l a t e along a l i n e p a r a l l e l to the Go-B p o i n t plane. MAS Middle Airway Space - The t h i c k n e s s of the airway along a l i n e p a r a l l e l t o the Go-B p o i n t Plane through P. IAS I n f e r i o r Airway Space - The t h i c k n e s s of the airway along a l i n e extended through the Go-B p o i n t plane. 4 4 VAL V e r t i c a l Airway Length - The l i n e a r d i s t a n c e between PNS and Eb. d) Hyoid Bone MPH Mandibular Plane t o Hyoid - The l i n e a r d i s t a n c e along a perpendicular from H t o the mandibular plane. HH1 V e r t i c a l Hyoid - The l i n e a r d i s t a n c e between H and a perpendicular to the C3-RGN plane. HRGN H o r i z o n t a l Hyoid - The l i n e a r d i s t a n c e between H and RGN. C3H V e r t e b r a l Hyoid - The l i n e a r d i s t a n c e between C3 and H. 45 I 4. Angular measurements (see Fig.7) E-TT Tongue Angle - The angle constructed by an extension of the Eb-TT plane and the t r u e h o r i z o n t a l . CVTPP Vertebrae t o P a l a t a l plane - The angle constructed by an extension l i n e of CV2tg-CV4ip plane and p a l a t a l plane . CVTSN Vertebrae t o SN plane - The angle constructed by an extension l i n e of CV2tg-CV4ip plane and SN plane. OPTPP Odontoid t o P a l a t a l plane - The angle constructed by an extension l i n e of CV2tg-CV2ip plane and P a l a t a l plane. OPTSN Odontoid to SN plane - The angle constructed by an extension l i n e of CV2tg-CV2ip plane and SN plane. 5. Area measurements (see Fig.7) a) Tongue The area o u t l i n e d by the d o r s a l c o n f i g u r a t i o n of the tongue surface and l i n e s which connect TT, RGN, H and Eb. b) S o f t P a l a t e The area confined by the o u t l i n e of the s o f t p a l a t e which s t a r t s and ends at PNS through P. c) Nasopharynx The area o u t l i n e d by a l i n e between R and PNS, an extension of the P a l a t a l plane to the p o s t e r i o r pharyngeal w a l l , and the p o s t e r i o r pharyngeal w a l l . 47 Oropharynx The area o u t l i n e d by the i n f e r i o r border of the nasopharynx, p o s t e r i o r surface of the s o f t p a l a t e , a l i n e from P t o the d o r s a l surface of the tongue p a r a l l e l t o the p a l a t a l plane, the p o s t e r i o r i n f e r i o r s urface of the tongue, a l i n e p a r a l l e l t o the p a l a t a l plane through the p o i n t Et, and the p o s t e r i o r pharyngeal w a l l , e) Hypopharynx The area o u t l i n e d by the i n f e r i o r border of the oropharynx, the p o s t e r i o r surface of the e p i g l o t t i s , a l i n e p a r a l l e l t o the p a l a t a l plane through the p o i n t C4, and the p o s t e r i o r pharyngeal w a l l . 48 Rg. 7 Cephalometric Angular and Area Measurements Legend F i g .7 E-TT(Tongue Angle), CVTPP(Vertebrae to P a l a t a l plane), CVTSN(Vertebrae to SN plane), OPTPP(Odontoid t o P a l a t a l plane), 0PTSN(Odontoid to SN plane), Tongue, jjjggjSSoft Palate i l l l Nasopharynx', Oropharynx, Hypopharynx 49 C. Tracing and d i g i t i z a t i o n Tracings were made on acetate paper w i t h a .5mm p e n c i l f o r each of the p o i n t s , planes and o u t l i n e s f o r the tongue, s o f t p a l a t e and upper airway s t r u c t u r e s by one i n v e s t i g a t o r . Boundaries were o u t l i n e d i n the middle of t i s s u e t r a n s i t i o n zones t o take i n t o account averaging. A data entry program was w r i t t e n t o permit d i g i t i z a t i o n of cephalograms by means of a d i g i t i z e r (HP Model 9874) . A c r o s s - h a i r cursor was used t o enter the p o i n t s and contours of each s t r u c t u r e i n t o the computer (HP 1000E s e r i e s ) . A n a l y s i s programs were w r i t t e n t o determine the leng t h , a n g u l a t i o n and c r o s s - s e c t i o n a l area of s p e c i f i c s t r u c t u r e s . A l l of the d i g i t i z a t i o n procedures were f u l f i l l e d by one i n v e s t i g a t o r . 2] EMG and pressure study EMG and pressure d i f f e r e n c e s of the tongue and p e r i o r a l musculature i n d i f f e r e n t body p o s i t i o n s were i n v e s t i g a t e d . Each of three tasks ( i . e . r e s t , maximum p r o t r u s i o n , maximum opening) was performed on 10 asymptomatic c o n t r o l s i n u p - r i g h t and supine body p o s i t i o n s . The computer st o r e d s i g n a l s every m i l l i s e c o n d during the two seconds of the a c t u a l sampling time, a f t e r a l l 2000 s i g n a l s were detected. The s i g n a l s were i n t e g r a t e d and averaged by e x i s t i n g computer software. 50 a. Data a q u i s i t i o n system and rec o r d i n g technique A t o t a l of s i x channels were used i n order t o o b t a i n EMG and pressure s i g n a l s : four channels f o r the GG, masseter, o r b i c u l a r i s o r i s and supra-hyoid muscle group and two channels f o r the a n t e r i o r and p o s t e r i o r pressure recordings of the tongue (see F i g . 8 ) . channel 0 :EMG a c t i v i t y of the GG was taken i n t r a - o r a l l y w i t h a b a l l - t y p e b i p o l a r surface e l e c t r o d e . channel 1 :EMG a c t i v i t y from the r i g h t - s i d e masseter was taken w i t h conventional surface e l e c t r o d e s . channel 2 :EMG s i g n a l s from the r i g h t - s i d e i n f e r i o r o r b i c u l a r i s o r i s muscle were detected by conventional surface e l e c t r o d e s . channel 3 :EMG a c t i v i t y from the r i g h t - s i d e supra-hyoid muscle group was taken w i t h conventional surface e l e c t r o d e s . channel 10:Pressure s i g n a l s from the a n t e r i o r p o r t i o n of the tongue were taken w i t h a s t r a i n gauge type load c e l l p o s i t i o n e d i n a c r y l i c appliance at the midpoint of the c e n t r a l i n c i s o r s . channel 11:Pressure s i g n a l s from the p o s t e r i o r p o r t i o n of the r i g h t s i d e of the tongue were taken w i t h the load c e l l p o s i t i o n e d i n a c r y l i c appliance opposite the r i g h t mandibular f i r s t molar. 51 Fig. 8 Schematic lllustations of the Surface Ellectrodes for the Masseter, Supra-hyoid and Orbicularis Oris Muscles, and the Intraoral Appliance pressure transducers EMG A customized a c r y l i c and rubber base appliance was constructed as a c a r r i e r on the i n d i v i d u a l mandibular c a s t and adjusted i n the mouth (see F i g . 8 ) . A f t e r a determined t h i c k n e s s ( 2 mm) of r e s i n p l a t e i n the dough stage was a p p l i e d on the l i n g u a l s i d e of the mandibular t e e t h and g i n g i v a on the c a s t , a small amount of rubber base m a t e r i a l ( R e p r o s i l putty 1500, Densply) was added to the r e s i n , adjusted and molded. Two custom made b a l l - t y p e e l e c t r o d e s were embedded on each s i d e of l i n g u a l flange of the appliance t o record d i r e c t l y from the GG muscle (Doble et a l . , 1985; M i l i d o n i s et a l . , 1988). The pressure transducers were mounted at the midpoint of the mandibular c e n t r a l i n c i s o r s and l i n g u a l t o the r i g h t mandibular f i r s t molar. The r i g h t mandibular molar region was thickened i n order t o exaggerate d i f f e r e n c e s i n tongue pressure i n accordance w i t h body p o s i t i o n a l change. The t h i c k n e s s of the appliance and the l o c a t i o n of the transducers were c a r e f u l l y standardized and the s e n s i t i v i t y of each transducer was determined and c a l i b r a t e d at proper gain. A diaphragm type of load c e l l , manufactured by Kyowa e l e c t r o n i c instruments Co., which contains four e l e c t r i c a l l y connected s t r a i n gauges ( i . e . a wheatstone bridge) was used to record tongue pressure. The m i n i a t u r e pressure transducer was a PS-A type, w i t h a 10Kgf/cm 2 of c a p a c i t y , 6 mm i n diameter and 0.6 mm t h i c k n e s s . S p e c i f i c a t i o n d e t a i l s are provided i n Figure 9. 53 Fig. 9 Pressure Transducer and Its Specifications > Glossy t- surface i Pressure Da t 0.6 ±0 1 (mm) (Type PS-A) Specifications Type PS-A Safe excitation 3 V input/output resistance I 2 0 n Compensated temperature range 0 - + 5 0 . C Safe temperature range - 2 0 - + 7 0 . C Temperature effect on output ± 0 . 2 % / . C Safe overload rating 1 5 0 % 54 A s t a t i c c a l i b r a t i o n was undertaken w i t h a c a l i b r a t i o n system f o r each of the transducers i n v i t r o before and a f t e r the experimental s e s s i o n (see Fig.10). The c a l i b r a t i o n system was set up w i t h a dental p l a s t e r housing and a rubber b a l l o n c o n t a i n i n g water w i t h no bubbles at a temperature approximately 36°C. Weights were set at 100 g i n t e r v a l s on the c a l i b r a t i o n system. The noise l e v e l s were l e s s than 5mV per min. The adjusted s e n s i t i v i t y of both transducers was approximately 1.5g/cm2 i n both channels and a l i n e a r i t y was e s t a b l i s h e d (see Fig.1 0 ) . The l i n e a r i t y of s e n s i t i v i t y i n load c e l l s was represented by a c o r r e l a t i o n c o e f f i c i e n t ( a n t e r i o r s i d e r=0.9878; p o s t e r i o r s i d e r=0.9954 ). Both of the l i n e a r i t i e s were c a l c u l a t e d from 0 t o 400g i n for c e changes on the given surface area. Based upon the r e g r e s s i o n l i n e of the scattergram (see F i g . 10) , lmV of e l e c t r i c a l change i n the load c e l l turned out to be equi v a l e n t t o approximately 1.5g/cm2 of pressure change as an average f o r both transducers. 55 Fig. 10 Calibration System and Calibration Results Pressure Transducer * Anterior Transducer • Posterior Transducer 0 100 200 300 400 500 {g ) Legend F i g . i o The obtained pressure s ignals from the pressure transducer are del ivered to D i g i t a l Multimeter(Hewlett Packard) and displayed as numbers ( ntV ). 56 b. Equipment and data processing (see Fig.11) EMG data from the GG, masseter, i n f e r i o r o r b i c u l a r i s o r i s and supra-hyoid muscles were passed through a d i f f e r e n t i a l a m p l i f i e r (Al 2010 Axon) . Each' of s i g n a l s was a m p l i f i e d by dual a m p l i f i c a t i o n ( mainly 20K or 40K was used) and low(30 Hz) and high(lKHz) f i l t e r i n g s were conducted i n order t o reduce the noise from movement a r t i f a c t s and e l e c t r i c a l high frequency coming from other equipment. The a m p l i f i e d s i g n a l s were d e l i v e r e d t o an e i g h t channel m u l t i p l e x o r ( 4701 T e k t r o n i x inc.) and a c o n t r o l rack. Through a t r i g g e r system, the s i g n a l s were passed i n t o an A/D converter(3852A DATA ACQUISITION/CONTROL UNIT) . A f t e r conversion of the s i g n a l s , they were i n t e g r a t e d and averaged by means of the pre-programed computer software and s t o r e d i n the computer. The s i g n a l s from the pressure transducers were f i r s t passed i n t o a custom-made c a r r i e r p r e a m p l i f i e r through a bridge box. The s i g n a l s were a m p l i f i e d by pre-adjusted and c a l i b r a t e d gain and were sent t o the storage monitor (2221 Tektronik) t o v e r i f y the tongue f o r c e s . The s i g n a l s were sent t o the A/D converter through the same t r i g g e r and the rack. The data transformed t o d i g i t a l form was averaged and s t o r e d i n the same manner as the EMG s i g n a l s . 57 Fig. 11 Flow-chart tor Data Aquisition EMG Electrodes Differential Amplifier 8-channel Multiplexor Pressure Transducer Carrier pre-amplifier Storage Oscilloscope Trigger ^ / A/D Converter Computer Legend F i g . 1 1 A l l s i g n a l s a r e d i s p l a y e d on t h e 8 - c h a n n e l m u l t i p l e x o r and t h e s t o r a g e o s c i l l o s c o p e . 58 c. Experimental procedure . To sample the EMG and pressure data f o r the r e s t task, the p a t i e n t was re q u i r e d t o maintain a r e l a x e d and r e s t i n g mandibular p o s i t i o n t o monitor r e s t i n g p o t e n t i a l s i n the GG, masseter, i n f e r i o r o r b i c u l a r i s o r i s and supra-hyoid muscles. To record the p r o t r u s i o n task, the subjects were i n s t r u c t e d t o perform a maximum p r o t r u s i o n of the tongue agai n s t the pressure transducer on the a n t e r i o r l i n g u a l s i d e of the appliance. To record maximum opening, the subjects were requested t o open t h e i r mouth as much as p o s s i b l e . To sample the tongue b a s e l i n e pressure, a s p e c i a l l y constructed a c r y l i c t r a y was introduced i n t r a - o r a l l y (see F i g . 1 2 ) . The subjects were i n s t r u c t e d t o s i t i n a d e n t a l c h a i r i n an up - r i g h t p o s i t i o n w i t h n a t u r a l head posture which could be reproduced by the modified l e v e l device. The t r a y was d e l i v e r e d i n t r a - o r a l l y i n order t o take the base l i n e r e c o r d i n g of the tongue pressure without any contact of the tongue on the transducer surface. A f t e r the t r a y was removed from the mouth, EMG and pressure were recorded at the absolute r e s t p o s i t i o n of the mandible. Maximum p r o t r u s i o n and opening tasks were recorded immediately i n a consecutive manner. Each of the tasks was performed i n not l e s s than three seconds. Four r e c o r d i n g sessions of base l i n e , r e s t , maximum p r o t r u s i o n and maximum opening were repeated f i v e times. Body movement, head movement and swallowing were monitored throughout the s e s s i o n . A f t e r the u p - r i g h t p o s i t i o n s e s s i o n , the sub j e c t s were requested to r e c l i n e on a stretcher i n a pos i t i o n i d e n t i c a l to that used for the supine cephalograms. A l l tasks were repeated i n the same manner as i n the up-right p o s i t i o n . 6 0 Fig. 12 Tray Used to Measure the Base-line Pressure of the Tongue Legend P i g . 1 2 Arrows in the upper picture indicate the pressure transducers, the arrow in the lower picture indicates the acrylic tray. Notice the free space between the tray and the appliance. 61 C . S t a t i s t i c a l method A l l the s t a t i s t i c a l t e s t s were conducted by means of the computer s t a t i s t i c a l package c a l l e d SYSTAT. A t w o - t a i l t e s t and 5% s i g n i f i c a n t l e v e l was used f o r d e t e c t i n g f a l s e p o s i t i v e s ( T y p e I e r r o r ) . The Student's t t e s t and Wilcoxon signed rank t e s t were employed f o r the comparison between the OSA group and the asymptomatic c o n t r o l s , and a l s o f o r the comparison between the up - r i g h t and supine body p o s i t i o n . Pearson's simple c o r r e l a t i o n c o e f f i c i e n t , Dahlberg's method e r r o r , Houston's r e l i a b i l i t y t e s t and two-way ANOVA were used to c a l c u l a t e r e p r o d u c i b i l i t y and experimental e r r o r . A d d i t i o n a l l y , ANCOVA was conducted i n order t o t e s t the e f f e c t s of age on the v a r i a b l e s . The index of r e l i a b i l i t y , used t o t e s t the r e l i a b i l i t y of the cephalometric v a r i a b l e s , was introduced by Houston i n 1979. He c l a s s i f i e d types of e r r o r i n t o systemic e r r o r (or bias) and random e r r o r . The simples t approach t o detect systemic e r r o r s i s the one sample t t e s t f o r each p a i r of r e p l i c a t e s . In general, at l e a s t 25 cases should be r e p l i c a t e d f o r d e t e c t i o n of systemic e r r o r s a r i s i n g i n o b t a i n i n g l a t e r a l cephalograms (Houston, 1979). On the cont r a r y , random e r r o r s can a r i s e as a r e s u l t of v a r i a t i o n i n p o s i t i o n i n g of the p a t i e n t i n the ceph a l o s t a t , f a u l t y i d e n t i f i c a t i o n of the landmarks and inaccuracy of d i g i t i z a t i o n . Houston emphasizes t h a t Dahlberg's formula ( s=J Ed 2 / 2 (n-1) ) which has been t r a d i t i o n a l l y used f o r 62 the c a l c u l a t i o n of the method e r r o r , could not d i s c r i m i n a t e systemic e r r o r s from random e r r o r s . Therefore, he suggests a new c o e f f i c i e n t of r e l i a b i l i t y and index of r e l i a b i l i t y ( T ) which represent pure random e r r o r . The formula i s ; r = J l - Sd 2/Sg 2 , where T i s index of r e l i a b i l i t y , Sd 2 i s the va r i a n c e of d i f f e r e n c e s between r e p l i c a t e s , and Sg 2 i s the g r e a t e r variance between two of the r e p l i c a t e v a r i a n c e s . The Student's t t e s t has t r a d i t i o n a l l y been accepted as a robust parametric method. The t t e s t examines va r i a n c e f i r s t and determines the formula t o be used l a t e r on (Armitage and Berry, 1987). In cases of equal v a r i a n c e , the formula of the t t e s t i s t=X 1-X 2/SE (X 1-X 2) , f o l l o w i n g t - d i s t r i b u t i o n on n1+n2- 2 degree of freedom. In cases of unequal v a r i a n c e and i f the o r i g i n a l means of the two samples are not too d i f f e r e n t , i t would be d i f f i c u l t t o f i n d a proper t r a n s f o r m a t i o n form which s u b s t a n t i a l l y reduces t h i s p a r i t y between the v a r i a n c e s . Therefore, a pooled estimate of var i a n c e s was u t i l i z e d . d= X^-Xz/J(S^2/n^ + S 2 2/n 2) could be used, which i s approximately a standardized normal deviate i f n l and n2 are resonably l a r g e . The Wilcoxon signed rank t e s t was employed f o r the comparison study (EMG and pressure), s i n c e the sample s i z e was ra t h e r s m a l l . The Wilcoxon signed rank t e s t i s a d i s t r i b u t i o n f r e e method (Armitage and Berry, 1987). The observations are put i n ascending order of magnitude, i g n o r i n g the s i g n , and give the ranks 1 t o n' . Let T+ be the sum of the ranks of the p o s i t i v e values and T- tha t of the negative. On the n u l l 63 hypothesis T+ and T- would not be expected t o d i f f e r g r e a t l y ; t h e i r sum T+ and T- i s l/2n' (n'+l) , so an appropriate t e s t would c o n s i s t i n e v a l u a t i n g the p r o b a b i l i t y of a value of T+ equal to or more extreme than t h a t observed. For l a r g e values of n 1 , T+ and T- are approximately normally d i s t r i b u t e d w i t h v a r i a n c e n'(n'+l)(2n'+l)/24 w i t h c o n t i n u i t y c o r r e c t i o n which i s given by [T+ - l / 4 n ' ( n ' + l ) ] - l / 2 / J{n1(n'+1)(2n1+1)/24}. I f there are nu m e r i c a l l y t i e d v a r i a b l e s , they are given t i e d ranks and reduced variance of T+ by t ( t 2 + l ) / 4 8 , where t= number of t i e s . However, Armitage and Berry (1987) commented t h a t the si g n t e s t l o s e s something by i g n o r i n g a l l i n f o r m a t i o n about the numerical magnitudes of the observations other than t h e i r s i g n s . I f a high p r o p o r t i o n of la r g e observations were p o s i t i v e t h i s would strengthen the evidence t h a t the d i s t r i b u t i o n was asymmetrically above zero. Two-way a n a l y s i s of variance(Two-way ANOVA) was employed t o i n v e s t i g a t e the r e p e a t a b i l i t y of n a t u r a l head posture measurement wi t h the f l u i d l e v e l device. Armitage and Berry (1987) s t a t e d t h a t the purpose of the a n a l y s i s of covariance(ANCOVA) i s to c o r r e c t b i a s and t o reduce random v a r i a t i o n . In the present study, the ANCOVA was used, given t h a t a comparison at the same age would have been more d e s i r a b l e . 64 RESULTS A s t a t i s t i c a l a n a l y s i s was c a r r i e d out on the r e s u l t s of the comparative study of the u p - r i g h t and supine p o s i t i o n s i n the OSA and asymptomatic c o n t r o l groups. R e s u l t s were obtained from cephalometric, EMG and pressure measurements. P a r t i c u l a r l y , the cephalometric comparison study of the u p - r i g h t and supine p o s i t i o n s provided s e v e r a l s i g n i f i c a n t p i e c es of informa t i o n regarding the anatomical changes t h a t occur i n con j u n c t i o n w i t h body p o s i t i o n a l changes. The EMG and pressure r e s u l t s a l s o y i e l d e d i n t e r e s t i n g r e s u l t s i n agreement w i t h those of the cephalometric study. The r e s u l t s are reported as non-transformed d a t a ( n e i t h e r l o g nor square root) and are summarized as measurements which are s t a t i s t i c a l l y s i g n i f i c a n t at p< .05 l e v e l denoted by one a s t e r i s k or p<.001 by two a s t e r i s k s . A l l of the l i n e a r cephalometric measurements were enlarged by 8.5% and no c o r r e c t i o n of the enlargement e f f e c t was attempted. A. R e l i a b i l i t y t e s t s R e l i a b i l i t y and r e p r o d u c i b i l i t y t e s t s f o r the d i g i t i z i n g procedure, s o f t - t i s s u e t r a c i n g and d i g i t i z i n g , measurement of the n a t u r a l head posture, and v a l i d i t y t e s t f o r the f l u i d l e v e l device were performed. 65 The random e r r o r of the d i g i t i z i n g procedure was evaluated. Two p o i n t s on the same cephalogram were d i g i t i z e d twice w i t h enough of a time i n t e r v a l t o avoid d i g i t i z i n g f a t i g u e . For r e p r e s e n t a t i o n of the d i g i t i z i n g random e r r o r , Pearson's simple c o r r e l a t i o n c o e f f i c i e n t (r) and Houston's r e l i a b i l t y index were employed. An example of the c a l c u l a t i o n f o r the intra-examiner random e r r o r i s as f o l l o w s : 1st time 2nd time D i f f e r e n c e MP-H 14.4 14.5 0.1 H-RGN 41.0 41.0 0.0 PNS-P 56.5 56.5 0.0 TGL 86.6 86.4 0.2 MEAN 49.62 49.60 0.08 SD 30.16 30.04 0.10 Variance 909.63 902.40 0.09 r 1.000 Index of r e l i a b i l i t y r= 0.9985 As a r e s u l t of the intra-examiner e r r o r , r=1.000 and T=0.9985 were obtained; as a r e s u l t of the extra-examiner e r r o r , r=0.9670 and T=0.9614 were observed. From these r e s u l t s , the d i g i t i z i n g method, as used i n the current study, was found t o be r e l i a b l e and the intra-examiner e r r o r was a l s o acceptable. R e p r o d u c i b i l i t y of the hard t i s s u e measurement has been reviewed by numerous i n v e s t i g a t i o n s (Baumrind et a l . , 1971,1976; Houston, 1979,1983; Dis c u s s i o n s e c t i o n ) . However, a r e p r o d u c i b i l i t y t e s t f o r the s o f t - t i s s u e measurements was undertaken on four s e l e c t e d v a r i a b l e s (H-RGN, PNS-P, IAS and Soft P a l a t e area). Ten cephalograms were randomly s e l e c t e d and the second t r a c i n g s were completed two weeks a f t e r the f i r s t t r a c i n g s . D i f f e r e n c e s between each of the p a i r s and variances of each s e r i e s of measurements were c a l c u l a t e d . Pearson's simple c o r r e l a t i o n c o e f f i c i e n t (r) which represents the l i n e a r i t y of the randomness, together w i t h Dahlberg 1s method e r r o r and Houston's r e l i a b i l i t y index (T) were a l s o provided (Table I I ) . Minimum mean d i f f e r e n c e was determined from the measurements of the TGL(mean d i f f e r e n c e between the f i r s t and second measurement=0.5 mm; min=0.01mm; max=1.43mm). Pearson's simple c o r r e l a t i o n c o e f f i c i e n t ( r ) between the two sets of measurements was .9991; Dahlberg's S.E. was .49; Houston's r e l i a b i l i t y index was .9995. The v a r i a b l e showing the l a r g e s t mean d i f f e r e n c e among the l i n e a r s o f t - t i s s u e v a r i a b l e s was PNS- P (mean=.67mm; min=.14mm; max=1.61mm). The c o r r e l a t i o n c o e f f i c i e n t of the P-PNS measurement was .9966; Dahlberg's S.E. was .60; the r e l i a b i l i t y index was .9986. The r e p r o d u c i b i l i t y of the s o f t p a l a t e c r o s s - s e c t i o n a l area showed a mean d i f f e r e n c e of 27.47 mm2 , an r-value of .9875 and a r e l i a b i l i t y index of .9959. A l l of the measurements i n Table I I showed high r e l i a b i l i t i e s ( r > 0.9900) and n e g l i g i b l e method e r r o r s i . e . not greater than 1mm i n length and 3 0mm2 i n area. 67 Table ll Reliability of the Soft-tissue Measuring Techniques and an Example of the Calculation of the Houston's Reliability Index Difference between 1st measurement and 2nd measurement H-RGN PNS-P IAS TGL (mm) (mm) (mm) (mm) Soft Palate (mm*) Min. Mean Dahlberg's Houston's SE Index 0.60 0.60 0.52 0.49 24.22 .9980 .9986 .9906 .9995 .9959 Legend Table II Mean value indica tes average di f ferences between 1st and 2nd measurement on the same v a r i a b l e s , s 2 r e v e a l s variance between 10 p a i r s o f measurements, r represents the c o r r e l a t i o n c o e f f i c i e n t between 1st and 2nd measurements. The equation of Dahlberg's SE i s J(X1-X2)2/2(n-1) An example of the c a l c u l a t i o n of Houston's r e l i a b i l i t y i s as f o l l o w : Subj TGL ( Tongue Length) ects 1st 2nd Difference 1 83.82 83.00 0.82 2 94.16 93.94 0.22 3 98.99 98.98 0.01 4 78.99 78.77 0.22 5 69.91 69.45 0.46 6 82.98 81.55 1.43 7 97.01 96.98 0.03 8 96.50 95.66 0.84 9 76.77 76.08 0.69 10 90.58 90.29 0.29 MEAN 86.47 86.97 0.50 s 2 101.66 98.38 0.20 SD 10.08 9.92 0.45 r 0.9991 2d2 4.29 ; r e l i a b i l i t y index (r) = J 1 - S2 d / S2 g S2 d :variance of the differences S 2 g : the greater variance 6 8 R e p r o d u c i b i l i t y of the n a t u r a l head p o s i t i o n has been s t u d i e d by s e v e r a l researchers (Moorrees and Kean, 1958; Solow and T a l l g r e n , 1976; Siersbaek-Nielsen and Solow, 1982 ; Showfety et a l . ; Sandham, 1988). The r e p r o d u c i b i l i t y of r e p o s i t i o n i n g and measurement of n a t u r a l head posture was i n v e s t i g a t e d by repeated measurements at three d i f f e r e n t times on four subjects (see Table I I I ) . The subjects were p o s i t i o n e d i n the n a t u r a l body and head posture i n standing p o s i t i o n w i t h the modified f l u i d l e v e l device on the head. The degree on the l e v e l device was recorded twice per each time. The second and t h i r d measurements were c a r r i e d out at a minimum i n t e r v a l of a week i n the same manner as f o r the u p - r i g h t standing p o s i t i o n . A two-way ANOVA was used f o r the t e s t of r e p e a t a b i l i t y and the r e s u l t s are represented i n Table I I I . The r e s u l t s i n d i c a t e t h a t the a n g u l a t i o n of the head posture was s i g n i f i c a n t l y d i f f e r e n t from subject t o subject(p=0.000), yet was not d i f f e r e n t at d i f f e r e n t times(0.192) f o r the same su b j e c t s . A s i g n i f i c a n t probability(p=.009) i n the Subject*Measurement ( i n t e r a c t i o n ) term i n d i c a t e s a v a r i a t i o n w i t h i n the same c e l l . 69 Table III Reproducibility Studies of Natural Head Position and Measurement Measurements Subjects 1st 2nd 3rd 1 15/15 15/15 13/12 2 7/5 6/7 6/7 3 -2/-2 -2/-3 -1/-1 4 2/3 1/0 0/2 unit = degree TWO-WAY ANALYSIS OF VARIANCE SOURCE SUM-OF SQUARES DF MEAN-SQUARE F-RATIO SUBJECTS 890.833 3 296.944 712.667 0.000 MEASUREMENT 1.583 2 0.792 1.900 0 192 SUBJECT * MEASUREMENT 12.471 6 2.069 4.967 0.009 ERROR 5.000 12 0.417 Legend Table I I I A p a i r of numbers i n each c e l l i n top t a b l e reveals the degree of head posture from the f l u i d l e v e l device. The probability(0.009) of the i n t e r a c t i o n term(SUBJECT*MEASUREMENT column) i n the lower t a b l e suggests a s i g n i f i c a n t v a r i a t i o n w i t h i n the same c e l l . 7 0 For the v a l i d i t y t e s t of the f l u i d l e v e l device, the o v e r a l l c o r r e l a t i o n between the head posture angle from the modified l e v e l device and the angle from the FH plane and t r u e h o r i z o n t a l l i n e was i n v e s t i g a t e d by twenty randomly s e l e c t e d up- r i g h t cephalograms and represented g r a p h i c a l l y i n Figure 13. Pearson's c o r r e l a t i o n c o e f f i c i e n t ( r ) was 0.9505; slope 0.9388; i n t e r c e p t -0.1089 at P l e s s than 0.001 l e v e l . The 95% confidence i n t e r v a l suggests a d e v i a t i o n of not g r e a t e r than 1.5° of the head posture angle i n between the l e v e l device and the measured angle on the cephalograms (1.097 as a upper l i m i t , 0.7869 as a lower l i m i t ) . Therefore, 95% of the values measured by the modified l e v e l device are i d e n t i c a l t o the values measured on the cephalograms w i t h 1.5° of d e v i a t i o n . 71 Fig. 13 Relationship between Level Device Angle and the FH/True Horizontal Cephalometric Angle Legend Fig.13 The g r a p h i c a l d i s t r i b u t i o n of the p o i n t s suggests a s t r o n g l i n e a r tendancy (Pearson's r=0.9505). B. Cephalometric study The r e s u l t s of the l a t e r a l cephalometric comparison study of OSA and asymptomatic c o n t r o l s i n d i f f e r e n t body p o s i t i o n s (see Table IV) show t h a t , except f o r the TGH(p=.331), most of the l i n e a r measurements were s i g n i f i c a n t l y d i f f e r e n t i n the up- r i g h t cephalograms. In u p - r i g h t cephalograms, the OSA group showed a longer tongue, a longer and t h i c k e r s o f t p a l a t e , an a n t e r o p o s t e r i o r l y narrower and s u p e r o i n f e r i o r l y lengthened airway, and a more i n f e r i o r l y p o s i t i o n e d hyoid bone than the asymptomatic c o n t r o l s . For the an g u l a t i o n measurements, the OSA group was s i g n i f i c a n t l y d i f f e r e n t from the asymptomatic c o n t r o l group; the former r e g i s t e r e d an E-TT value of p=.003 l e v e l and a l s o shown s i g n i f i c a n t l y l a r g e r CVTPP(p=.008), CVTSN(p=.012), 0PTPP(p=.013) and OPTSN(p=.014) angulations, which i n d i c a t e s a s t r o n g l y extended head and neck r e l a t i o n s h i p i n the u p - r i g h t cephalograms. On the other hand, the supine cephalograms could not provide appropriate angular comparisons of the head posture of the OSA and the asymptomatic c o n t r o l group due t o s i g n i f i c a n t v a r i a t i o n s i n p i l l o w height. In the comparison of the c r o s s - s e c t i o n a l area measurements, there were no s i g n i f i c a n t d i f f e r e n c e s between the two groups i n the tongue(p=.060), nasopharynx(p=.239) and oropharynx(p=.214) areas i n the u p - r i g h t cephalograms. Yet, the OSA group d i d r e v e a l a l a r g e r s o f t palate(p=.005) and a smaller hypopharyngeal area(p=.004) i n the u p - r i g h t cephalograms. Table IV Comparison of OSA and Asymptomatic Controls In Up-right and Supine Cephalometric Positions Up O S A Mean S D Riglit C o n l r o l Mean S D S u p i n e O S A C o n l r o l P less than Mean T o n g u e T G L 9 0 . 7 6 8 .09 83 .25 5 .21 .013 T G H 4 0 . 7 9 4 .49 39 .19 3 .34 .331 Soft I'alatc P N S - P 49 .01 10 .54 4 0 . 3 7 3 .90 .019 * M P T 14 .99 4 .61 1 1 .54 1 .64 .030 A i r w a y S P A S 5 . 3 3 2 99 9 .24 2 .68 .002 + + M A S 9 . 9 6 3 14 13 .57 3 34 .007 I A S 7 . 5 2 3 . 9 9 1 1 .27 3 28 .016 V A L 8 7 . 3 0 7 14 73 01 3 57 .000 + * H y o i d bone M P - H 2 8 . 3 0 8 64 17 09 3 87 .001 ** H - H l 18 .90 7 37 12 21 4 54 .014 * H - R G N 4 4 . 6 5 7 10 38 88 2 88 .021 • T o n g u e B I T 3 8 . 0 5 6 82 28 95 7 92 .003 V e r t e b r a e C V T P P 104 .20 6 97 96 73 6 04 .008 * + C V T S N 113 .12 7 87 105 76 5. 1 1 .012 + O P T P P 9 8 . 8 3 7 75 89 82 10 22 .013 O P T S N 107 .78 8 24 98 84 9 96 .014 * T o n g u e 3 8 2 6 . 6 8 573 45 3 4 3 7 05 356 73 .060 Soft Palate 5 1 9 . 1 2 154 34 364 99 5 3 . 25 .005 * * N a s o p h a r y n x 2 0 5 . 2 9 8 7 . 88 2 4 2 . 96 6 3 . 31 .239 O r o p h a r y n x 4 9 7 . 7 0 185. 76 579 86 1 17 1 2 .214 H y p o p h a r y n x 161 .08 87. 63 29 2. 5 7 14 1. 1 2 .004 * * SD 87.4 1 42 .90 5 0 . 3 6 14.44 2 .97 9 .63 5 .37 84 .45 24 .93 16.44 4 0 . 7 6 6 .22 3 .10 9 .98 3.9 I 2 .53 8.54 3 .89 5.88 7 .52 7 .29 7 .96 Mean 79 .74 38 .54 4 1 . 5 5 12.70 10.37 12.49 9 .90 6 8 . 1 7 12.06 6 .72 3 6 . 2 9 Legend Table IV The comparison i s performed by the Student t tes t . S i g n i f i c a n t l e v e l s of p< .05 are denoted by one a s t e r i s k and p< .01 by two a s t e r i s k s . SD 6 .84 2 . 8 9 2 .97 1.15 I I . 3 0 3 . 5 0 2 .45 6 .07 4 . 9 6 4 . 5 7 5 .74 3 9 9 2 . 8 0 4 7 5 . 7 4 3 4 3 6 . 5 1 5 1 0 . 9 9 5 5 4 . 7 4 132 .86 4 3 1 . 9 0 4 8 . 7 0 203 84 88.11 230 .35 6 3 . 6 0 315 95 127 .13 4 1 2 . 4 2 123 .09 171.02 98.99 330.81 102 .50 P less than .005 * * .001 * * .011 • .100 .008 • * . 323 .002 * * .000 • * .000 .001 .126 *+ .006 • * .009 * * .406 .058 .000 * * In c o n t r a s t , TGH(p=.001) and tongue c r o s s - s e c t i o n a l area(p=.006) showed s i g n i f i c a n t d i f f e r e n c e s between OSA and c o n t r o l s u bjects i n the supine p o s i t i o n , but not i n the u p - r i g h t cephalograms. MPT(p=.100), MAS(p=.323) and H-RGN(p=.126) d i d not prove t o be s i g n i f i c a n t l y d i f f e r e n t between the OSA and the asymptomatic c o n t r o l groups i n the supine cephalograms but were s i g n i f i c a n t l y d i f f e r e n t i n the u p - r i g h t p o s i t i o n . The c r o s s - s e c t i o n a l area of the oropharynx f a i l e d t o show a difference(p=.058) between the two groups i n the supine cephalograms. The r e s u l t s of the l a t e r a l cephalometric comparisons between the u p - r i g h t and supine p o s i t i o n s f o r each of the two d i f f e r e n t groups are provided i n Table V. Of the l i n e a r v a r i a b l e s , TGH, PNS-P, MAS d i d not y i e l d d i f f e r e n c e s corresponding t o p o s i t i o n a l changes i n both groups. The tongue length(TGL) was reduced s i g n i f i c a n t l y by approximately the same amount i n the supine p o s i t i o n i n both groups. The tongue height(TGH) increased i n the OSA group, but decreased i n the c o n t r o l group i n the supine position;however, s t a t i s t i c a l l y , there were no s i g n i f i c a n t d i f f e r e n c e s . The s o f t p a l a t e t h i c k n e s s (MPT) revealed no s i g n i f i c a n t change i n the OSA group, but i n the c o n t r o l group(p=.002) showed s i g n i f i c a n t t h i c k e n i n g corresponding t o the p o s i t i o n a l changes. The c r o s s - s e c t i o n a l s i z e of the upper airway was reduced i n the supine p o s i t i o n . The SPAS was s i g n i f i c a n t l y reduced i n the OSA group (p=. 018) , but not i n the c o n t r o l group(p=.195). 75 Table V Comparison of Up-right and Supine Cephalograms in OSA and Asymptomatic Controls O S A C o n t r o l U p r ight S u p i n e U p r i g h t S u p i n e M e a n S D M e a n S D P less than M e a n SD M e a n S D P less than T o n g u e 1 C L 9 0 . 7 6 8 . 0 9 8 7 . 4 1 6 . 2 2 .021 * 1 8 3 . 2 5 5 .21 7 9 .74 6 . 8 4 .021 * T G H 4 0 . 7 9 4 . 4 9 4 2 . 9 0 3 . 1 0 . 0 6 2 1 3 9 . 1 9 3 .34 38 . 5 4 2 . 8 9 . 5 4 4 Soft Palate P N S - P 4 9 .01 10 . 5 4 5 0 . 3 6 9 . 9 8 . 0 7 4 1 4 0 . 3 7 3 . 9 0 41 . 5 5 2 . 9 7 . 2 2 5 M P T 14 . 9 9 4 .61 1 4 . 4 4 3 .91 . 3 2 3 1 I I . 5 4 1 . 64 1 2 . 7 0 1 . 1 5 .002 * * A i r w a y S P A S 5 . 3 3 2 . 9 9 2 . 9 7 2 . 5 3 .000 *• 9 . 2 4 2 . 68 10 . 3 7 1 1 . 3 0 . 7 7 2 M A S 9 9 6 3 . 1 4 9 . 6 3 8 54 . 8 7 0 1 3 4 7 3 34 12 4 9 3 . 5 0 . 1 6 1 I A S 7 5 2 3 . 9 9 5 . 3 7 3 8 9 .018 * 1 1 27 3 28 9 9 0 2 . 4 5 . 1 9 5 V A L 8 7 3 0 7 14 8 4 . 4 5 5 88 . 0 7 8 7 3 01 3 5 7 6 8 17 6 . 0 7 .007 * • ,0 H y o i d bone M P - H 2 8 3 0 8 6 4 2 4 . 9 3 7 5 2 . 0 7 4 j 1 1 7 0 9 3 87 12 0 6 4 . 9 6 .000 * • 11 I I I 18 9 0 7 37 1 6 . 4 4 7 2 9 . 1 1 5 12 21 4 54 6 7 2 4 . 5 7 .003 * * l l - R G N 4 4 65 7 10 4 0 . 7 6 7 96 .04 1 • 1 38 88 2 88 3 6 . 29 5 . 7 4 . 1 0 9 T o n g u e 3 8 2 6 . 6 8 5 7 3 . 4 5 3 9 9 2 . 8 0 4 7 5 . 74 .014 • 3 4 3 7 . 0 5 3 5 6 . 73 3 4 3 6 . 51 5 1 0 . 9 9 . 9 9 6 Sof t Palate 5 1 9 . 12 1 5 4 . 34 5 5 4 . 7 4 1 3 2 . 86 .043 • 3 6 4 . 9 9 5 3 . 25 4 3 1 . 9 0 4 8 . 7 0 .000 * * N a s o p h a r y n x 2 0 5 . 2 9 8 7 . 88 3 0 3 . 8 4 8 8 . 1 1 . 9 1 8 2 4 2 . 96 6 3 . 31 2 3 0 . 35 6 3 . 6 0 . 3 5 4 O r o p h a r y n x 4 9 7 . 7 0 1 8 5 . 7 6 3 1 5 . 9 5 1 2 7 . 13 .000 + * 5 7 9 . 86 1 17 . 1 2 4 12 . 4 2 1 2 3 . 0 9 .000 * • l l y p o p h a r y n x 161 . 0 8 8 7 . 6 3 1 7 1 . 0 2 9 8 . 9 9 . 6 6 0 292' . 5 7 14 1. 1 2 3 3 0 . 81 1 0 2 . 5 0 . 1 4 2 Again, IAS was shown to be shorter(p=.018) i n the supine p o s i t i o n i n the OSA group, but not i n the asymptomatic c o n t r o l group(p=.195). The v e r t i c a l length of the airway d i d not show a s i g n i f i c a n t change (VAL) f o l l o w i n g p o s i t i o n a l change i n the OSA group, but d i d i n the asymptomatic c o n t r o l at the p=.007 l e v e l . MP-H was not s i g n i f i c a n t l y d i f f e r e n t i n a comparison of the u p - r i g h t and supine(p=.074) p o s i t i o n s i n the OSA group, but d i f f e r e d i n the c o n t r o l group at the p=.000 l e v e l . H-Hl was shortened s i g n i f i c a n t l y i n the supine p o s i t i o n i n the c o n t r o l group, but not i n the OSA group. The d i s t a n c e between the hyoid bone and the re t r o g n a t h i o n (H-RGN) was s i g n i f i c a n t l y shortened i n the OSA group(p=.041) a f t e r a r e c l i n i n g p o s i t i o n was assumed; however, no s i g n i f i c a n t change was seen i n the c o n t r o l group(p=.109). The tongue c r o s s - s e c t i o n a l area was shown to be s i g n i f i c a n t l y l a r g e r ( 4 . 7 % increased) i n the supine p o s i t i o n than i n the u p - r i g h t p o s i t i o n i n the OSA group(p=.014);however, no d i f f e r e n c e was observed i n the c o n t r o l group(p=.996). Although the s o f t p a l a t e became l a r g e r i n both groups a f t e r a r e c l i n i n g p o s i t i o n was assumed, the increase i n s i z e was more s i g n i f i c a n t i n the asymptomatic c o n t r o l group. In both groups, a l a r g e degree of c o l l a p s e was shown i n the oropharyngeal area, a f t e r the body p o s i t i o n a l change, but t h i s was not seen i n the nasopharynx and hypopharynx. While the oropharyngeal area decreased by 3 6.5% i n the OSA group, i t decreased by 29% i n the asymptomatic c o n t r o l s . However, the d i f f e r e n c e between the two 77 groups was h a r d l y n o t i c e a b l e i n both p o s i t i o n s used f o r the cephalograms(p=.214 i n the up - r i g h t cephalograms; .058 i n the supine cephalograms). An ANCOVA t e s t was used t o i n v e s t i g a t e the age e f f e c t on the hyoid v a r i a b l e s , yet the r e s u l t s i n d i c a t e t h a t none of v a r i a b l e s (MP-H p=.353, H-Hl p=.135, H-RGN .228) were a f f e c t e d by an age (see Table V I ) . 78 Table VI ANCOVA test of the Age Effect on the Hyoid Variables DEP VAR: M P - H N: 29 MULTIPLE R: .621 SQUARED MULTIPLE R:386 SOURCE SUM-OF-SQUARES SUBJECTS AGE ERROR 432.326 50.414 1466.130 ANALYSIS OF VARIANCE DF MEAN-SQUARE 1 1 26 432.326 50.414 56.390 F-RATIO 7.667 0.894 0.010 0.353 DEP VAR: H"H1 N: 29 MULTIPLE R: 512 SQUARED MULTIPLE R:262 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES SUBJECTS AGE ERROR 77.515 102.117 1116.176 DF MEAN-SQUARE 1 1 26 77.515 102.117 42.930 F-RATIO 1.806 2.379 0.191 0.135 DEP VAR: H-RGN 29 MULTIPLE R: .492 SQUARED MULTIPLE R:242 SOURCE SUM-OF-SQUARES SUBJECTS AGE ERROR 293.305 54.859 935.621 ANALYSIS OF VARIANCE DF MEAN-SQUARE F-RATIO 1 1 26 293.305 54.859 35.985 3.151 1.524 0.008 0.228 Legend Table VI The p r o b a b i l i t y of the age reveals the comparisons of the hyoid v a r i a b l e s are not s i g n i f i c a n t l y a f f e c t e d by age. 79 Summary o f t h e c e p h a l o m e t r i c s t u d y : T h e OSA g r o u p s h o w e d a l o n g e r t o n g u e , a l a r g e r s o f t p a l a t e , a n a n t e r o p o s t e r i o r l y n a r r o w e r a n d s u p e r o i n f e r i o r l y l e n g t h e n e d u p p e r a i r w a y , a i n f e r i o r l y p o s i t i o n e d h y o i d b o n e , a more u p - r i g h t t o n g u e , a m o r e e x t e n d e d h e a d p o s t u r e a n d a s m a l l e r h y p o p h a r y n x i n t h e u p - r i g h t s t a n d i n g p o s i t i o n . T h e OSA g r o u p s h o w e d g r e a t e r t o n g u e h e i g h t , a l a r g e r t o n g u e a n d a s m a l l e r h y p o p h a r y n g e a l a r e a i n t h e s u p i n e p o s i t i o n . W i t h t h e p o s i t i o n a l c h a n g e s f r o m u p - r i g h t t o s u p i n e , t h e t h i c k n e s s o f t h e s o f t p a l a t e i n c r e a s e d m o r e i n t h e c o n t r o l g r o u p , w h e r e a s t h e s i z e o f t h e u p p e r a i r w a y was m o r e d e c r e a s e d i n t h e OSA g r o u p . W i t h t h e p o s i t i o n a l c h a n g e s f r o m u p - r i g h t t o s u p i n e , t h e h y o i d b o n e was moved up t o w a r d t h e m a n d i b u l a r p l a n e m o r e i n t h e c o n t r o l s u b j e c t s , a n d t o w a r d t h e m a n d i b u l a r s y m p h y s i s m o r e i n t h e OSA g r o u p . T h e t o n g u e c r o s s - s e c t i o n a l a r e a i n c r e a s e d s i g n i f i c a n t l y b y 4.3% i n t h e s u p i n e p o s i t i o n a n d o r o p h a r y n g e a l a r e a d e c r e a s e d b y 3 6.5% i n t h e OSA g r o u p . 8 0 C. EMG and pressure study A comparison of EMG and Pressure v a r i a b l e s obtained i n the u p - r i g h t and the supine p o s i t i o n s are provided i n Table V I I . A l l of the comparisons were performed by means of Wilcoxon Signed Rank t e s t . The r e s t i n g a c t i v i t y of the GG muscle increased approximately 34 % (from 2.58 t o 3.33 g/cm2) at the p=.037 l e v e l w i t h the body p o s i t i o n a l change from u p - r i g h t to supine. A c t i v i t y of the i n f e r i o r o r b i c u l a r i s o r i s decreased s i g n i f i c a n t l y i n the supine p o s i t i o n at the p=.008 l e v e l . For the p r o t r u s i o n task, the supra-hyoid muscle group revealed a s i g n i f i c a n t l y increased a c t i v i t y (p=.014). The GG muscle revealed s i g n i f i c a n t l y l a r g e r values on maximum opening task i n the u p - r i g h t and the supine p o s i t i o n s at the p=.028 l e v e l . 81 Table VII Comparison of the EMG and Pressure of the Tongue between Up-right and Supine Positions in Asymptomatic Controls EMG Up- Right Supine Mean SD Mean SD P less than Rest Geniogiossus 2.58 1.03 3.33 1.58 .037 * Masseter 2.22 1.78 2.47 1.91 .260 Orbicularis Oris 3.69 3.50 2.49 1.56 .008 " Supra-hyoid 1.87 0.67 2.02 0.77 .066 Protrusion Geniogiossus 93.41 48.89 93.10 56.93 .959 Masseter 12.78 12.04 12.30 11.27 .575 Orbicularis Oris 11.13 8.22 12.07 11.60 .767 Supra-hyoid 27.11 50.36 35.45 69.97 .014 * Max. Geniogiossus 16.87 9.89 21.79 10.42 .028 * Opening Masseter 12.03 14.70 12.69 14.32 .878 Orbicularis Oris 49.93 46.17 62.76 63.75 .086 Supra-hyoid 49.64 28.60 57.58 37.08 .285 unit: = uV Pressure Rest Anterior 10.33 9.10 7.83 6.88 .333 Posterior 12.01 5.76 14.01 5.46 .017 * Protrusion Anterior 799.79 293.80 808.08 300.77 .878 Posterior 136.49 93.47 116.54 73.26 .314 Max. Anterior 11.29 10.81 11.85 13.65 .859 Opening Posterior 28.25 16.98 32.02 18.74 .241 unit= g/cm2 Legend Table VII Each EMG and p r e s s u r e v a l u e was co n v e r t e d and c a l i b r a t e d t o (iV and g/cm1 . 8 2 For the pressure data, the p o s t e r i o r tongue pressure at r e s t revealed an increased value of 17% (2g/cin 2 ) at the .017 l e v e l (where, two extremely increased or decreased values were precluded). The r e s t i n g EMG a c t i v i t y of the supra-hyoid muscle group showed an almost s i g n i f i c a n t value (p=.066); i . e . , only two su b j e c t s out of ten revealed decreased EMG values i n the supine p o s i t i o n , and i n t u r n , showed a strong tendency t o increase the supra-hyoid muscle a c t i v i t y i n the supine p o s i t i o n (see Fig.14). The EMG a c t i v i t y of the supra-hyoid muscle at maximum p r o t r u s i o n was s i g n i f i c a n t l y g r e a t e r i n the supine p o s i t i o n than i n the u p - r i g h t p o s i t i o n , and the GG EMG a c t i v i t y at maximum opening a l s o showed a s i g n i f i c a n t l y high value i n the supine p o s i t i o n . The EMG a c t i v i t y of the masseter muscle d i d not r e v e a l any s i g n i f i c a n t d i f f e r e n c e s i n any of the t a s k s . 8 3 Fig 14 Tongue EMG and Pressure Changes at Rest in Up-right and Supine Positions E M G E M G mV Pressure mV UP-RIGHT SUPINE UP-RIGHT SUPINE UP-RIGHT SUPINE G G muscle S u p r a h y o i d muscle Post, transducer Legend F i g . 1 4 The s o l i d l i n e s o f each graph r e p r e s e n t t h e i n c r e a s i n g change o f EMG and p r e s s u r e due t o t h e change i n body p o s i t i o n , whereas t h e broken l i n e s show a d e c r e a s e c h a n g e . As a summary of the r e s t EMG and pressure study, w i t h the p o s i t i o n a l changes from u p - r i g h t t o supine, the asymptomatic c o n t r o l group showed: 1. The EMG a c t i v i t y of the GG muscle increased by 3 3.8%. 2. The pressure of the p o s t e r i o r p o r t i o n of the tongue increased by 17%. 3. The r e s t i n g p o t e n t i a l a c t i v i t y of the i n f e r i o r o r b i c u l a r i s o r i s decreased by 32.5%. 4. The EMG a c t i v i t y of the supra-hyoid group increased by 8%, yet the change was not s t a t i s t i c a l l y s i g n i f i c a n t . In c o n c l u s i o n , the oropharyngeal c r o s s - s e c t i o n a l area c o l l a p s e d by approximately 30% d e s p i t e a 34% increase i n GG muscle a c t i v i t y i n the asymptomatic c o n t r o l group as a r e s u l t of body p o s i t i o n a l changes. No s i z e change i n the tongue was observed i n the supine p o s i t i o n i n the non-apneic group. In a d d i t i o n , 17% of the tongue pressure increment was recorded on the p o s t e r i o r load c e l l . With the p o s i t i o n a l changes, the s i z e of the s o f t p a l a t e increased by 18.3% i n the c o n t r o l group. A l l the hypopharynx changes are not s t a t i s t i c a l l y s i g n i f i c a n t . The c r o s s - s e c t i o n a l area of the hypopharynx increased by 13% which was accompanied by an 8% increase i n the supra-hyoid muscle a c t i v i t y and a 6% decrease i n the H-RGN value. 85 DISCUSSION The c u r r e n t study was proposed to evaluate the r e l a t i o n s h i p between GG muscle a c t i v i t y , airway s i z e and body posture. For comparisons of airway s i z e , cephalometric measurements were employed; f o r comparisons of tongue and other muscle a c t i v i t y , EMG and pressure s t u d i e s were undertaken. The supine cephalometric technique was u t i l i z e d i n the curren t study and a comparison between the u p - r i g h t and supine cephalograms was made. I t appeared t h a t the OSA p a t i e n t s have l a r g e r tongues and s m a l l e r oropharyngeal airways i n the supine cephalograms. In a d d i t i o n , the l o c a t i o n a l change of the tongue i n the supine p o s i t i o n was q u a n t i f i e d by a change i n p o s t e r i o r tongue pressure. Previous i n v e s t i g a t o r s have p o s t u l a t e d a small airway s i z e and reduced GG muscle a c t i v i t y i n OSA p a t i e n t s . Recently, Lowe et al.(1986,1989) v i s u a l i z e d the c o n s t r i c t i o n area and measured the s i z e of the upper airway by means of computer aided three-dimensional CT r e c o n s t r u c t i o n . In s p i t e of the j u d i c i o u s combined study of the CT and the pressure transducer, S t a u f f e r et al.(1987), could not f i n d any s i g n i f i c a n t d i f f e r e n c e s i n airway s i z e between p a t i e n t s w i t h OSA and asymptomatic c o n t r o l s . They concluded t h a t airway r e s i s t a n c e seems more l i k e l y t o be r e l a t e d to the AHI (Apnea Hypopnea Index) than t o the c r o s s - s e c t i o n a l s i z e of the airway. Adequate 86 GG muscle a c t i v i t y may be one of the most d e c i s i v e f a c t o r s i n the genesis of OSA. Remmers et al.(1978) monitored the EMG of the GG muscle using f i n e wire b i p o l a r e l e c t r o d e s and e l u c i d a t e d the a s s o c i a t i o n of the muscle w i t h OSA symptoms. Subsequently, s e v e r a l p u b l i c a t i o n s have addressed the i n t e r - r e l a t i o n s h i p between diaphragmatic and GG EMG a c t i v i t y . Another group working w i t h the hyoid apparatus suggested t h a t the p o s i t i o n of the hyoid arch plays an important r o l e i n the maintainence of upper airway patency (Van de Graaff et a l . , 1984; Van Lunteren et a l . , 1987) . They p o s t u l a t e d t h a t decreased or p o o r l y coordinated hyoid muscle a c t i v i t y could be a c r u c i a l f a c t o r i n hypopharyngeal o b s t r u c t i o n . However, most i n f o r m a t i o n acquired to date from t h i s s o r t of biomechanical study has been r e t r i e v e d from animal experiments. The c o u p l i n g a c t i o n of the hyoid and GG muscles i n dogs and cats may be d i f f e r e n t i n humans; yet few s t u d i e s have been done on human su b j e c t s . Recently, Lowe and co- workers (personal communication) presented a f a c i a l p r o f i l o g r a m of OSA p a t i e n t s i n which a t y p i c a l appearance of the c h i n was shown. In a d d i t i o n , a i n f e r i o r l y p o s i t i o n e d hyoid bone was reported i n the OSA p a t i e n t group as one of the s i g n i f i c a n t r e s u l t s of the c u r r e n t study i n agreement w i t h previous data from s e v e r a l e a r l i e r s t u d i e s . Tonic a c t i v i t y of the GG or hyoid muscle group may be more important than phasic a c t i v i t y , f o r the t o n i c a c t i v i t y of the upper airway muscles i s l i k e l y t o be d i r e c t l y r e l a t e d t o the s i z e of the airway. In an age-matched study by Brown and a s s o c i a t e s (1987), i t was emphasized t h a t 87 the OSA group i s d i s t i n g u i s h e d not by the c r o s s - s e c t i o n a l area but by the d i s t e n s i b i l i t y of the pharynx. S i m i l a r i l y , i n the c u r r e n t study, the s i z e of the pharyngeal c r o s s - s e c t i o n a l area d i d not d i f f e r e n t i a t e p a t i e n t s w i t h OSA symptoms from non- p a t i e n t s . However, the current study d i d show t h a t oropharyngeal area was more c o l l a p s e d i n the OSA group i n the supine p o s i t i o n even though i t was not s t a t i s t i c a l l y s i g n i f i c a n t ( P = . 0 5 8 ) (see Table I V ) . Consequently, i t may be an over s i m p l i f i c a t i o n to consider OSA as a disease which may occur when the airway i s s m a l l . We should t h e r e f o r e consider not only morphological and f u n c t i o n a l f a c t o r s but a l s o the i n t e r - r e l a t i o n s h i p of both f a c t o r s . A. Cephalometric study Numerous i n v e s t i g a t o r s have measured the anatomical s t r u c t u r e s of the upper airway (Jackson and Olson, 1980; Hoponik et a l . , 1983 ; Lowe et a l . , 1986; and M a r t i n et a l . , 1987). Cephalometric analyses have long been used f o r the i n v e s t i g a t i o n of f a c i a l growth and development i n the f i e l d of o r t h o d o n t i c s . Cephalometric techniques have more r e c e n t l y become a r o u t i n e d i a g n o s t i c t o o l t o evaluate the s i z e of the tongue and airway ( R i l e y et a l . , 1983; Lowe et a l . , 1986; Jamieson et a l . , 1986; Strelzow et a l . , 1988; deBerry-Borowiecki et a l . , 1988; and Lyberg et a l . , 1989). In s p i t e of obvious l i m i t a t i o n s as a two-dimensional method of a n a l y s i s , cephalometrics i s s t i l l c onsidered a convenient, l e s s i n v a s i v e , and l e s s expensive technique t o evaluate upper airway s i z e . In 1983, R i l e y and co- 88 workers a c t i v e l y introduced cephalometric a n a l y s i s t o the OSA research f i e l d and showed i t s c o m p a t i b i l i t y t o the flow volume curve. Lowe and a s s o c i a t e s (1986) reviewed the s o f t and hard- t i s s u e c h a r a c t e r i s t i c s of OSA p a t i e n t s by means of cephalometric a n a l y s i s and e x t r a c t e d s i g n i f i c a n t v a r i a b l e s using a p r i n c i p a l component a n a l y s i s . The r e s u l t s of the current study agree w i t h most of the s o f t - t i s s u e measurements t h a t they analyzed. As a r e s u l t of the development of computer equipment and software, s e v e r a l measurement s t u d i e s on s o f t - t i s s u e areas and airway space have been produced. Strelzow et al.(1988) reported r e s u l t s from a cephalometric study which concentrated more on the s i z e and p o s i t i o n a l changes of the tongue, s o f t p a l a t e , pharyngeal space and the l o c a t i o n of the hyoid bone. Not s u r p r i s i n g l y , not only the l i n e a r measurements but a l s o the measurements of the c r o s s - s e c t i o n a l area of the tongue and s o f t p a l a t e approximate the r e s u l t s of the current study (see Table V I I I ) . Another study (deBerry-Borowiecki et a l . , 1988) which adopted v i r t u a l l y the same d e f i n i t i o n s of l i n e a r measurements and tongue and s o f t p a l a t e c r o s s - s e c t i o n a l areas as the former study, provided s i m i l a r r e s u l t s but a s h o r t e r s o f t p a l a t e and sma l l e r tongue area (see Table V I I I ) . Recently, Lyberg and a s s o c i a t e s (1989) undertook a cephalometric study t h a t i s h i g h l y compatible with the present p r o j e c t i n terms of the d e f i n i t i o n s of the l i n e a r , angular and area measurement v a r i a b l e s . They obtained cephalograms i n n a t u r a l head posture, although i t i s not c l e a r whether the subjects were standing or s i t t i n g . 89 TABLE Vlll Linear and Area Variable Comparisons Between Current Report and Other Studies A . Linear Comparisons unit=mm Current study Lyberg et al. OSA(20) CONTROL (10) OSA(25) CONTROL (10) Mean SD Mean SD Mean SD Mean SD PNS-P 49.01 3.9 40.47 3.9 48.0 4.3 35.3 4.6 MPT 14.99 4.6 11.54 1.6 14.0 2.0 11.2 1.5 MAS 9.96 3.1 13.57 3.3 8.4 3.5 13.7 3.8 IAS 7.52 3.9 11.27 3.3 10.3 4.0 13.8 3.8 deBerry-Borowiecki et al. Strelzow et al. OSA (30) CONTROL(12) OSA (90) CONTROL (12) Mean SD Mean SD Mean SD Mean SD PNS-P 41.6 6.0 34.7 7.0 46.0 7.0 36.0 8.0 MPT 14.0 6.0 10.0 2.0 13.0 2.0 11.0 2.0 Jamieson et al. 0SA(138) CONTROL (7) Mean SD Mean SD PNS-P 46.7 3.0 36.4 4.4 MPT IAS 5.3 3.0 12.4 3.5 B. Area Comparisons unit=mm3 Current study OSA(20) Mean SD CONTROL (10) Mean SD Tongue 3826 Soft Palate 519 573 3437 154 364 356 53 Lyberg et al. OSA (25) Mean SD CONTROL (10) Mean SD 3597 485 459 80 3486 288 344 62 deBerry-Borowiecki et al. Strelzow et al. OSA (30) CONTROL (12) OSA(90) CONTROL (12) Mean SD Mean SD Mean SD Mean SD Tongue 3790 375 3215 471 3884 404 3374 293 Soft Palate 459 134 251 63 457 105 289 88 Legend Table VIII Numbers i n a parenthesis i n d i c a t e sample s i z e . 90 Lyberg et a l . provided values f o r the PNS-P, MPT, MAS, IAS, tongue and s o f t p a l a t e area t h a t are remarkably s i m i l a r t o the r e s u l t s of the curren t study (see Table V I I I ) . The s t u d i e s by Jamieson and associates(1986) and deBerry-Borowiecki et a l . (1988) provided age-matched r e s u l t s which i n c l u d e d females. The c o n t r o l s used i n the study by Lyberg et a l . were g e n e r a l l y younger individuals(mean age =2 3.6). The tongue area and s o f t p a l a t e of the c o n t r o l group i n the study by deBerry-Borowiecki et a l . were very small even though the su b j e c t s were o l d e r compared t o those i n the other s t u d i e s . The present study revealed the longest and l a r g e s t s o f t p a l a t e of a l l the s e v e r a l research p r o j e c t s i n Table V I I I ; but i n these s t u d i e s the maximum t h i c k n e s s of the s o f t p a l a t e was very s i m i l a r . This i s p o s s i b l y due t o the f a c t t h a t most of the asymptomatic c o n t r o l s u b j e c t s employed i n the current study were snorers, r e l a t i v e l y obese (mean BMI=26.3) and were a d u l t males (mean age = 33.5). I n t e r e s t i n g l y , Lyberg et a l . f a i l e d t o f i n d a s i g n i f i c a n t d i f f e r e n c e between the OSA and the c o n t r o l group f o r tongue area, as the curren t study d i d . However, the c r o s s - s e c t i o n a l area of the s o f t p a l a t e was s i g n i f i c a n t l y d i f f e r e n t i n the two s t u d i e s . A supine cephalogram may provide more p h y s i o l o g i c a l i n f o r m a t i o n than the u p - r i g h t cephalogram. The tongue area was s i g n i f i c a n t l y d i f f e r e n t i n the two groups at a p r o b a b i l i t y l e v e l of l e s s than 1% i n the supine cephalograms (see Table V). In the OSA group, the tongue c r o s s - s e c t i o n a l area became s i g n i f i c a n t l y broadened i n the supine p o s i t i o n (see Table V). However, the tongue area of asymptomatic c o n t r o l s d i d not show s i g n i f i c a n t change (see Table V) . Therefore, d i f f e r e n c e s became more apparent i n the supine cephalograms. In a d d i t i o n , the airway behind the s o f t p a l a t e and tongue(SPAS and IAS) was reduced i n the supine p o s i t i o n i n the OSA group (Table V) , but not i n the group without apneic symptoms (Table V) . These f i n d i n g s e x p l a i n t h a t not only the c r o s s - s e c t i o n a l area of the tongue i s changed but a l s o t h a t the tongue mass s e t t l e s i n f e r i o r l y i n OSA p a t i e n t s i n the supine p o s i t i o n , probably due t o g r a v i t a t i o n a l p u l l (Crumley et al,1987) . On the other hand, i n the non-apneic group, the tongue f e l l back i n t o a 'bunched up' p o s i t i o n , t h e r e f o r e the a c t u a l tongue area was reduced and the SPAS was lengthened t o keep the airway open. This d i s p a r i t y may be surmised from the s i g n i f i c a n t d i f f e r e n c e i n the p o s t e r i o r tongue pressure values between the up - r i g h t and supine p o s i t i o n i n the asymptomatic c o n t r o l s . Weak GG muscle a c t i v i t y i n OSA p a t i e n t s has been presumed by s e v e r a l researchers. On t h i s b a s i s , the tongue sank down more i n the symptomatic group due t o l a c k of GG muscle c o n t r a c t i o n . Among the hyoid v a r i a b l e s , v e r t i c a l measurements of the hyoid bone such as MP-H or H-Hl d i d not change w i t h the p o s i t i o n a l change i n the symptomatic p a t i e n t group (see Table V) ;however, they changed s i g n i f i c a n t l y i n the asymptomatic group (Table V) . This phenomenon a l s o i m p l i e s a d i s p a r i t y i n the GG muscle e f f i c i e n c y between the two groups. In c o n t r a s t , the h o r i z o n t a l v a r i a b l e s 92 among the hyoid measurements (H-RGN) d i d not show s i g n i f i c a n t change i n the non-apneic group (Table V). On the other hand, the le n g t h was s i g n i f i c a n t l y shortened i n the OSA group (Table V). This f i n d i n g suggests t h a t the s i z e of the hypopharnygeal airway i s l a r g e enough to permit breathing i n asymptomatic c o n t r o l s where the supra-hyoid muscle group does not need to c o n t r a c t . In c o n t r a s t , according to the r e s u l t s of the c u r r e n t study, the hypopharyngeal airway i n the OSA group i s approximately h a l f the s i z e of t h a t of the c o n t r o l s i n terms of c r o s s - s e c t i o n a l area i n the supine p o s i t i o n ; thus, the supra-hyoid muscle group must co n t r a c t a c t i v e l y t o keep the airway open. Moreover, the maximum p a l a t a l t h i c k n e s s of the s o f t p a l a t e was ' a c t i v e l y ' increased i n s u b j e c t s without symptoms i n the supine p o s i t i o n ; no change was shown i n the OSA group. I t may t h e r e f o r e be the tongue and i t s r e l a t e d muscles, not the s o f t p a l a t e , which a c t i v e l y generates an apneic c o n d i t i o n . One of the important f a c t o r s t o consider i n the measurement of airway s i z e i s head posture. For comparison of head posture between OSA and c o n t r o l s , some head posture angulations t h a t are b e l i e v e d t o be most s e n s i t i v e were employed. Of the v a r i a b l e s r e p r e s e n t i n g head posture, the CVTPP may be the v a r i a b l e which most s t r o n g l y supports the hypothesis t h a t the p a t i e n t group has a more extended head posture than the c o n t r o l s . The a n g u l a t i o n v a r i a b l e s between the vertebrae and p a l a t a l plane (CVTPP and OPTPP, suggested by Dr. Diewert), while newly designed and employed f o r the f i r s t time, were 93 nonetheless, very s i g n i f i c a n t v a r i a b l e s . The r e l a t i o n s h i p between head posture and airway adequacy has been s t u d i e d by numerous researchers. Span and Hyatt(1971) measured upper airway r e s i s t a n c e i n conscious men and found t h a t r e s i s t a n c e of the upper airway may be a f f e c t e d by the head posture. Solow and T a l l g r e n (1971) hypothesized t h a t each i n d i v i d u a l has h i s / h e r own head posture which i s p r e c i s e l y r e p r o d u c i b l e only i n the standing p o s i t i o n . Following s t u d i e s of Solow et al.(1984), Woodside and Linder-Aronson(1979) and V i g et al.(1980) demonstrated s i g n i f i c a n t l y d i f f e r e n t head postures i n accordance w i t h airway adequacy. They concluded t h a t a reduced nasopharyngeal airway i s a s s o c i a t e d w i t h a l a r g e r c r a n i o c e r v i c a l a n g u l a t i o n . When the r e s u l t s are compared, a small d i f f e r e n c e can be noted i n the measurement of the CVTSN between Solow and T a l l g r e n ' s r e s u l t (97.72°) and the value from the c o n t r o l s i n the c u r r e n t study (105.76°) . This d i f f e r e n c e may d e r i v e from the composition of the subject group, i . e . r e l a t i v e l y heavy and o l d e r s u b j e c t s were r e c r u i t e d f o r the current study. Such a d i s p a r i t y was a l s o seen when comparisons t o other s t u d i e s by Kylamarkula and Huggare (1985) and Sandham (1988) were made. Measurements of head angulation i n OSA p a t i e n t s were completed by K a l b f l e i s c h i n 1988, and r e g r e t t a b l y , there i s no measurement v a r i a b l e t h a t c o i n c i d e s w i t h the current study;however, the extended head posture as a t y p i c a l c h a r a c t e r e s t i c of the OSA p a t i e n t i s demonstrated i n h i s r e p o r t . The importance of c e r v i c o c r a n i a l angulation i s a l s o due to the s p e c i f i c r e l a t i o n s h i p t o airway s i z e . As the airway s i z e changes, the head posture changes and v i c e v e rsa. K a l b f l e i s c h (1988) demonstrated a decrease i n airway s i z e w i t h neck f l e x i o n by means of l a t e r a l cephalometry. Greene et al. ( 1 9 6 1 ) , using ci n e f l u o r o g r a p h y , demonstrated an increase i n upper airway s i z e upon hyperextension of the neck i n the supine p o s i t i o n . Therefore, i t i s extremely important to measure the upper airway s i z e i n a standardized head posture. Another v a r i a b l e t o be accounted f o r before measuring upper airway s i z e , i s body p o s i t i o n . Body p o s i t i o n a l t e r s not only muscular a c t i v i t y but a l s o airway s i z e . Anch and h i s co- worker (1982) found t h a t s u p r a - g l o t t i c airway r e s i s t a n c e i s s i g n i f i c a n t l y l a r g e r i n the supine than i n the s i t t i n g p o s i t i o n i n both normal and OSA groups. They hypothesize s u p r a - g l o t t i c airway narrowing i n OSA p a t i e n t s . However, Navajas et a l . (1988) explained through t h e i r pressure transducer study t h a t t h i s phenomenon i s due to the re d u c t i o n of the FRC(Functional R e s i d u a l Capacity) i n the supine p o s i t i o n . Nevertheless, Fouke and S t r o h l (1987) n u l l i f i e d the e f f e c t i v e n e s s of the reduced FRC i n the supine p o s i t i o n by means of an Emerson c u i r a s s * and * Cuirass A s h e l l l i k e c a sing which i s c l o s e l y f i t t e d around the thorax i n treatment of weakness of the r e s p i r a t o r y muscles, so t h a t evacuation of a i r from w i t h i n the c u i r a s s causes expansion of the thorax and hence i n h a l a t i o n (Wiley et al.,1986). 95 i d e n t i f i e d the degree of c o l l a p s e due t o the body p o s i t i o n a l change. They found t h a t the pharyngeal c r o s s - s e c t i o n a l area was 23% s m a l l e r i n the supine than i n the u p - r i g h t p o s i t i o n . This i n f o r m a t i o n i s p e r t i n e n t t o the i n t e r p r e t a t i o n of the c u r r e n t r e s u l t s even though Fouke and S t r o h l used a d i f f e r e n t method of measurement. The cu r r e n t r e s u l t s show a 12.7% r e d u c t i o n i n the e n t i r e pharyngeal airway (and a 28.9% r e d u c t i o n i n the oropharynx) i n the asymptomatic c o n t r o l group; and a 2 0.1% r e d u c t i o n i n the pharyngeal airway (3 6.6% i n the oropharynx) i n the OSA p a t i e n t group. The discrepancy between 23% and 13% could be explained by the e f f e c t of a reduced FRC i n the supine p o s i t i o n i n the case of the c u r r e n t study; the r e s u l t from Brown et al.(1987) was n e a r l y i d e n t i c a l (21% i n the OSA group, 15% i n the normal group) to the r e s u l t s of the c u r r e n t study. U l t i m a t e l y , one should take i n t o account head posture, body p o s i t i o n , g l o t t i c c l o s u r e and swallowing f o r a comparative study of the airway s i z e . In the present study, most of the c o n d i t i o n s mentioned here were c o n t r o l l e d and standardized;however, c e r t a i n l i m i t a t i o n s of the cephalometric technique could not be overcome. The cephalogram provides a m i d s a g i t t a l c r o s s - s e c t i o n a l area, so t h a t i t i s impossible t o get f u l l i n f o r m a t i o n about the volume. In other words, we may not even be able t o read the immediately adjacent p a r a - s a g i t t a l area c o r r e c t l y . Furthermore, even CT scans may not be able t o g i v e c o r r e c t i n f o r m a t i o n when i t i s used as a two-dimensional technique. For instance, S t a u f f e r and a s s o c i a t e s (1987) were unable t o demonstrate t h a t mean pharyngeal s i z e i s s i g n i f i c a n t l y d i f f e r e n t between p a t i e n t s and c o n t r o l s u b j e c t s . However, only the minimal area showed a s i g n i f i c a n t c o r r e l a t i o n w i t h the AHI(r=0.53, P<.01). In the same sense as mentioned e a r l i e r , d i s c r i m i n a t i o n of the tongue s i z e d i f f e r e n c e by means of the up- r i g h t cephalogram was impossible i n the present study. The supine cephalometric technique provides new i n f o r m a t i o n which i s p o s s i b l y hidden by the two-dimensional l i m i t a t i o n of the technique. Review of r e p r o d u c i b i l i t y tests for hard tissue structures The r e p r o d u c i b i l i t y t e s t i n cephalometrics has a long h i s t o r y and has been widely i n v e s t i g a t e d by s e v e r a l s t a t i s t i c a l methods. Solow (1970) introduced a computer-aided cephalometric a n a l y s i s based on d i g i t i z i n g p r i n c i p l e s . In 1979, Houston reviewed the robustness, accuracy, and convenience of d i g i t i z i n g methods. In a d d i t i o n , he enumerates the source of e r r o r s t h a t can a r i s e i n the d i g i t i z i n g method. According to h i s review, e r r o r s can a r i s e from: - i n c o r r e c t i d e n t i f i c a t i o n of a landmark, -an i n c o r r e c t sequence of d i g i t i z a t i o n , -movement of the rec o r d i n g during d i g i t i z a t i o n , -environmental v a r i a t i o n a f f e c t i n g a s e n s i t i v e d i g i t i z e r , - i n t e r m i t t e n t mechanical f a u l t s i n the apparatus. 97 Baumrind and M i l l e r (1980) reviewed a computer-aided head f i l m a n a l y s i s and i l l u s t r a t e d a t y p i c a l f e a t u r e of d i s t r i b u t i o n of the e r r o r s from s e v e r a l r e p r e s e n t a t i v e anatomic landmarks. They suggest a method of using corner f i d u c i a l s which provides c o n s i d e r a b l e p r o t e c t i o n against the impact of r o t a t i o n a l e r r o r s and increased r e l i a b i l i t y . Recently, Sandham(1988) e x t e n s i v e l y reviewed r e p r o d u c i b i l i t y t e s t s of cephalometric measurements f o r hard t i s s u e s . He proposes a standard d e v i a t i o n ranging from 0.4 3 to 2.11 mm f o r d i f f e r e n c e s between repeated l i n e a r measurements. In h i s study, a l l of the k u r t o s i s values were acceptable at a l e v e l l e s s than 0.1%. The r e l i a b i l i t y of the c u r r e n t study i n s o f t t i s s u e measurement showed r e l a t i v e l y high values compared to previous work. This might be explained by the memorization e f f e c t even though the r e t r a c i n g was undertaken w i t h a time lapse of at l e a s t one month. Houston (1976) c l a r i f i e d t h a t immediate r e d i g i t i z a t i o n was s i g n i f i c a n t l y more r e p r o d u c i b l e due t o a memory e f f e c t . Repeatability to reproduce natural head posture Moorrees and Kean (1958) i n v e s t i g a t e d the hypothesis of n a t u r a l head posture and t e s t e d the accuracy of reproducing the n a t u r a l head p o s i t i o n by means of l a t e r a l head f i l m s . They reported 2.05 ° Standard D e v i a t i o n i n r e p o s i t i o n i n g of the n a t u r a l head posture and c l a r i f i e d t h a t the t r u e v e r t i c a l l i n e f o r reference purposes i s more r e l i a b l e than the r o u t i n e l y used FH l i n e . Siersbaek-Nielsen and Solow (1982) s t u d i e d v a r i a b i l i t y 98 i n head posture i n a young age group. They a p p l i e d M^lhave 1s most r e p r o d u c i b l e n a t u r a l standing p o s i t i o n as a standardized body p o s i t i o n , and s e l f - b a l a n c e d p o s i t i o n as a n a t u r a l head posture. They u l t i m a t e l y reported 2.3 - 3.4 ° of method e r r o r f o r p o s i t i o n i n g of the head, which was s t a t i s t i c a l l y acceptable. Another recent work by Sandham (1988) confirmed the hypothesis of r e p r o d u c i b l e n a t u r a l head posture. He d i s p l a y e d 5.44 ° of SD as a maximumly deviated value f o r the OPT/HOR angle (angulation between odontoid process and t r u e h o r i z o n t a l l i n e ) . V a l i d i t y of the modified l e v e l device For f u t u r e study, i t i s worthwhile t o d i s c u s s the v a l i d i t y of the modified l e v e l device. G r e e n f i e l d and as s o c i a t e s (1989) evaluated the i n f l u e n c e of the ear rod on cephalometric a n a l y s i s . They concluded t h a t t a k i n g a cephalogram without the ear rod provides b e t t e r r e p r o d u c i b i l i t y i n head p o s i t i o n i n g . They used a photogragh as a reference method f o r the cephalometric technique and suggested t h a t the photogragh method i s a 'quick and d i r t y ' method t o measure head posture. However, the modified l e v e l device technique may be s u p e r i o r t o other techniques p a r t i c u l a r l y when comparing two body p o s i t i o n s w i t h d i f f e r e n t analyses. P r i o r to the v a l i d i t y t e s t f o r the modified l e v e l device, a c a r e f u l l y designed r e p r o d u c i b i l i t y t e s t was undertaken. In 1985, Tsuchiya et a l . examined the r e p r o d u c i b i l i t y of i d e n t i f i c a t i o n of the s o f t - t i s s u e i n f r a - o r b i t a l notch by means of p a l p a t i o n . They concluded 99 t h a t on average the s o f t - t i s s u e o r b i t a l e was palpated c o n s i s t a n t l y at 1mm s u p e r i o r to the bony o r b i t a l e on a f i l m . Another s o f t - t i s s u e landmark employed i n the cu r r e n t study was the t r a g i o n which i s the notch on the upper margin of the tragus. The modified l e v e l device was attached on the l i n e which was assumed t o be the s o f t - t i s s u e FH plane between s o f t - t i s s u e o r b i t a l e and t r a g i o n . The s i g n i f i c a n c e l e v e l which i s shown i n Table I I I encompasses r e p r o d u c i b i l i t y of the e n t i r e measuring procedure. B. EMG and pressure study C o n t r a c t i o n of s k e l e t a l muscle i s t r i g g e r e d by a conducted a c t i o n p o t e n t i a l . When the t h r e s h o l d i s reached at a motor end p l a t e , a conducted a c t i o n p o t e n t i a l i s e l i c i t e d . Myoplasms are f a i r l y good e l e c t r i c a l conductors, t h e r e f o r e i t i s p o s s i b l e t o record the e l e c t r i c a l changes (the sum of the number of d e p o l a r i z a t i o n s ) i n the muscle by means of e l e c t r o d e s . Surface e l e c t r o d e s used i n the current study cannot be used f o r a s i n g l e motor u n i t study ;however, they are non-invasive and easy t o apply. The i n t r a - o r a l surface e l e c t r o d e f o r the GG muscle was f i r s t developed and evaluated by Doble and co-workers (1985). In 1988, M i l i d o n i s et a l . compared the recordings made wi t h these custom f i t t e d i n t r a - o r a l surface e l e c t r o d e s t o the b i - p o l a r f i n e wire recordings of the GG muscle and proved t h a t the two methods are s u f f i c i e n t l y compatible. 100 Due t o c a l i b r a t i o n problems, r e c o r d i n g of the tongue pressure i s not a simple task. P r o f f i t et al.(1969) employed a pressure chamber f o r c a l i b r a t i o n of the mercury s t r a i n gauge and presented high r e p r o d u c i b i l i t y f o r tongue pressure. However, as w i t h EMG, i t i s d i f f i c u l t t o produce high r e p e a t a b i l i t y i n pressure recordings. Recently, H e l l s i n g and L'Estrange (1987) i n v e s t i g a t e d pressure change on the l i p f o l l o w i n g head posture change and change i n mode of breathing. They used a s t r a i n gauge type transducer developed by P r o f f i t which has a transducer head w i t h a area of 0.04 3 cm2 . The transducer was c a l i b r a t e d d i r e c t l y i n the subject's mouth by means of a pen wit h a s p r i n g load system. However, i t i s so hard to reproduce the exact mode of tongue contact t h a t there are s t i l l l a r g e v a r i a t i o n s i n terms of absolute tongue pressure from study t o study. The current study employed a rubber sac i m i t a t i n g the tongue musculature. No c a l i b r a t i o n system i s p e r f e c t and the c u r r e n t p r o j e c t was c a r r i e d out merely as a comparison study. Even though t h i s study was c a r r i e d out only w i t h asymptomatic c o n t r o l s , the current r e s u l t s provide s e v e r a l s i g n i f i c a n t pieces of informat i o n and suggest s e v e r a l i m p l i c a t i o n s f o r the r e l a t i o n s h i p between s i z e of the airway, body p o s i t i o n a l change and upper airway muscle a c t i v i t y . The GG a c t i v i t y increased by approximately 3 4 % i n the supine p o s i t i o n i n comparison t o the up - r i g h t p o s i t o n i n the sub j e c t s without symptoms. The EMG a c t i v i t y of the supra-hyoid muscle group increased by 8%, but i t was not s t a t i s t i c a l l y s i g n i f i c a n t . 101 A more curious phenomenon was an increment i n p o s t e r i o r tongue pressure d e s p i t e augmentation of the GG and supra-hyoid muscle a c t i v i t y as a r e s u l t of p o s i t i o n a l changes of the body. EMG a c t i v i t y changes i n the supine p o s i t i o n are w e l l documented and i t i s reasonable t o assume an increment i n supra-hyoid muscle a c t i v i t y a f t e r changing the body p o s i t i o n . Airway patency i s r e l a t e d t o the changes i n muscle tone of the e n t i r e upper airway i n the supine p o s i t i o n . However, the muscle can shorten only when the neural a c t i v i t y overcomes i t s e x t e r n a l load, f o r example, the weight of the tongue i t s e l f . The c u r r e n t study revealed an enlarged tongue c r o s s - s e c t i o n a l area(4%) i n the supine p o s i t i o n i n the OSA group, yet the same tongue area i n the non-apneic group. The c r o s s - s e c t i o n a l area of the oropharynx was reduced by n e a r l y the same amount i n both groups, but s l i g h t l y (7%) more i n the OSA group. This s u b t l e s i z e difference(4%+7%) i n the waking s t a t e i n c o n t r o l s could c o n s i d e r a b l y induce s e r i o u s problems during sleep i n the OSA group. The oropharynx c o l l a p s e d approximately 3 0% i n s p i t e of a 34% increment i n the GG muscle a c t i v i t y i n asymptomatic c o n t r o l s . In a d d i t i o n , the p o s t e r i o r tongue pressure i m p l i e d the a c t u a l tongue l o c a t i o n , which was lower down. Cherniack and Hudgel (1985) agreed t h a t e l e c t r i c a l a c t i v i t y i s not n e c e s s a r i l y a good index of the mechanical a c t i o n of a muscle. For instance, the sternohyoid muscle can lengthen i n i n s p i r a t i o n even though there i s a considerable increase i n e l e c t r i c a l a c t i v i t y (Luntern et al.,1987). Brown et al.(1987) concluded from t h e i r age 102 and weight-matched study t h a t changes i n posture alone are not s u f f i c i e n t t o convert a snorer i n t o a p a t i e n t w i t h OSA. The cu r r e n t study hypothesizes t h a t l e s s t o n i c muscle a c t i v i t y or a heavier tongue i n respect t o the GG a c t i v i t y accompanied by a narrowed airway may play a primary r o l e i n the pathogenesis of OSA. From a f u n c t i o n a l standpoint the muscle s p i n d l e a c t s as a len g t h monitoring system. I t c o n s t a n t l y feeds back in f o r m a t i o n to the CNS regarding the s t a t e of e l o n g a t i o n or c o n t r a c t i o n of muscle s t r e t c h . When a muscle i s p a s s i v e l y s t r e t c h e d , the muscle s p i n d l e informs the CNS of a feed-back a c t i v i t y . A c t i v e muscle c o n t r a c t i o n i s monitored by both the G o l g i tendon organ and the muscle s p i n d l e . The mandibular r e s t p o s i t i o n i s an example of the neuromuscular mechanism (Okeson, 1989). The g r a v i t a t i o n a l p u l l of the mandible body prompts the passive s t r e t c h of the e l e v a t o r muscles. This passive s t r e t c h i n g a l s o s e n s i t i z e s the muscle s p i n d l e . Through the a f f e r e n t f i b r e s ( l a or I I ) f i r i n g i n the muscle s p i n d l e sac, t h i s i nformation ascends t o the higher center. The CNS s t i m u l a t e s a motor e f f e r e n t neurons. This evokes c o n t r a c t i o n of the e x t r a f u s a l f i b r e s . A u t o m a t i c a l l y , the length of the muscle s p i n d l e i s shortened. This shortening b r i n g s about a decrese i n a f f e r e n t output of the muscle s p i n d l e . The same p r i n c i p l e could be a p p l i e d f o r the GG muscle i n supine p o s i t i o n . Normal muscle tonus does not create f a t i g u e . The overload s t i m u l a t e s the GG muscle t o overwork and t h i s c reates a chronic f a t i g u e . S c a r d e l l a et al(1989) r e c e n t l y reported t h a t due t o the 103 high percentage of type I I f i b r e s (white) i n the GG muscle, r e l a t i v e l y small increases i n i t s a c t i v i t y would predispose t o f a t i g u e . They conducted a f a t i g u e study by means of a l i n g u a l f o r c e transducer and an i n t r a - o r a l e l e c t r o d e and concluded t h a t the GG i s a r e a d i l y f a t i g a b l e muscle. Another p l a u s i b l e f a c t o r inducing the apneic c o n d i t i o n i s a malarranged hyoid apparatus. The hyoid bone i s a suspended s t r u c t u r e l o c a t e d between the c h i n and c e r v i c a l vertebrae. Brodie(1963) analyzed the hyoid bone as the posture apparatus of the head and jaws which balances the supra- and i n f r a - h y o i d musculatures. From the e a r l y developmental stage, the hyoid bone i s c l o s e l y a l l i e d w i t h the tongue. The p o s t e r i o r p o r t i o n of the tongue i s de r i v e d from the second and t h i r d b r a n c h i a l arches, so the f l o o r of the mouth i s formed by the geniohyoid and mylohyoid muscles. According t o Bench(1963), i n an average person at the age of three, the hyoid bone i s maintained at a l e v e l between the t h i r d and f o u r t h c e r v i c a l vertebrae and g r a d u a l l y descends t o a l e v e l of the f o u r t h v e r t e b r a by f u l l adulthood. The hyoid bone i s a unique s t r u c t u r e f l o a t i n g among the muscles without any bony a r t i c u l a t i o n . The hyoid apparatus i n c l u d e s at l e a s t eleven p a i r s of muscles and three p a i r s of ligaments, i n t o t a l twenty-eight r e l a t e d s o f t - t i s s u e s t r u c t u r e s . Bibby (1981) conducted a study on the hyoid t r i a n g l e and emphasized t h a t the hyoid bone r e f l e c t s the r e l a t i v e t ensions of the muscles, ligaments and f a s c i a attached t o i t . 104 The hyoid bone serves two b a s i c f u n c t i o n s ; d e g l u t i t i o n and r e s p i r a t i o n . Pruzansky (1960) demonstrated a low hyoid p o s i t i o n caused by excessive i n f r a - h y o i d a c t i v i t y i n a p a t i e n t w i t h a n k y l o s i s of the TMJ. In 1963, Bosma observed a r e f l e c t i v e r e a c t i o n of the hyoid bone t o keep the airway open i n i n f a n t s and explained t h a t a n t e f l e x i o n of the head and neck i n order t o s t a b i l i z e the hyoid and l a r y n x i s a p a r t of the r e a c t i o n of the maintenance of pharyngeal airway. Recently, M i k i et al.(1988) t e s t e d a new treatment f o r OSA p a t i e n t s , a p p l i n g e l e c t r i c a l s t i m u l a t i o n t o the submental reg i o n . The overnight polysomnography study supported t h e i r p o s t u l a t i o n t h a t submental s t i m u l a t i o n might ameliorate the symptoms of OSA p a t i e n t s . Why do the OSA p a t i e n t s have a lower p o s i t i o n e d hyoid apparatus? F i r s t , age may a c c e l e r a t e the i n f e r i o r m i g r a t i o n of the hyoid bone. Again, i n Bench 1s(1963) growth study, he found t h a t the tongue i s higher i n the younger samples. He p o s t u l a t e d t h a t hyoid bone lowering tends to continue a f t e r f a c i a l growth. Recently, T a l l g r e n and Solow (1987) i n v e s t i g a t e d the r e l a t i o n s h i p between hyoid bone p o s i t i o n , f a c i a l morphology and head posture i n r e l a t i o n to age. They demonstrated a more i n f e r i o r (2.55mm against mandibular plane) and a n t e r i o r (1.64mm agains t vertebrae) p o s i t i o n e d hyoid bone i n an o l d e r group. H p f f s t e i n et al.(1989) found t h a t there was a negative c o r r e l a t i o n of pharyngeal area w i t h age only i n males. The decrement i n the airway s i z e w i t h age i s seemed to be r e l a t e d 105 t o the decrement i n the e x p i r a t o r y reserve volume (Leblanc et al,1970). A second p o s t u l a t e f o r an i n f e r i o r l y p o s i t i o n e d hyoid bone i s t h a t i t i s r e l a t e d t o a s m a l l e r upper airway i n the p a t i e n t s w i t h OSA. A s m a l l e r airway than the optimal s i z e induces a extended head posture f o r b e t t e r airway adequacy. An extended head posture e l i c i t e s a passive s t r e t c h of the supra- hyoid muscle. A recent extensive study by Winnberg and associates(1988) reported a s e r i e s of p r e c i s e l y conducted s t u d i e s on hyoid biomechanics. The researchers synchronized EMG and videofluorography and i n v e s t i g a t e d the dynamic and s t a t i c r e l a t i o n s h i p s between the hyoid bone l o c a t i o n and head posture. They i l l u s t r a t e d a more inferior(22mm) and anterior(14mm) p o s i t i o n e d hyoid bone wi t h a 15-25 degree extended head posture. A more extended head posture drops the hyoid apparatus i n f e r i o r l y and a n t e r i o r l y and s t r e t c h e s the supra-hyoid muscles. This passive s t r e t c h may s e n s i t i z e the muscle s p i n d l e s . This i n f o r m a t i o n feeds back to the CNS and r e a c t s t o the c o n t r a c t i o n . However, as long as b e t t e r airway adequacy i s r e q u i r e d , the extended head p o s i t i o n i n g may be a c t i v e l y continued because c o n t r a c t i o n at low muscle t e n s i o n has no e f f e c t on muscle s t i f f n e s s (Bressler,1974). Consequently, the supra-hyoid muscles, not only the GG and geniohyoid, but a l s o the omohyoid and a n t e r i o r d i g a s t r i c muscles, f a t i g u e and are l e s s e f f e c t i v e . As was mentioned e a r l i e r , due t o the r e l a t i v e l y excessive i n f r a - hyoid behavior, s i m i l a r to the case of a TMJ ankylosed p a t i e n t , 106 the hyoid bone migrates i n f e r i o r l y . Mixed type s k e l e t a l muscles f a i l when the force c o n t i n u o u s l y imposed on them exerts 15% t o 2 0% of t h e i r maximal f o r c e ( G r a s s i n o et a l . , 1988). An important determining f a c t o r i n muscle f a i l u r e ( i . e . f a tigue) i s the a v a i l a b i l i t y of blood c i r c u l a t i o n t o the muscle. Blood washes out c a t a b o l i t e s generated during c o n t r a c t i o n and i t provides n u t r i e n t s and oxygen t o the muscle. Fatigue i s a r e v e r s i b l e p h y s i o l o g i c a l s i t u a t i o n , and i t shows a p a r t i c u l a r time constant of recovery. Recovery of maximal for c e i s p r o g r e s s i v e and i s completed i n 10- 15 minutes. However, the c a p a c i t y t o reproduce the i n i t i a l endurance time i s recovered s l o w l y , perhaps over i n 18-24 hours (Grassino et a l . , 1988). P a r t i c u l a r l y , the f a t i g u e generated by low frequency s t i m u l a t i o n may take s e v e r a l hours t o recover. The development of f a t i g u e reduces the maximal f o r c e a muscle can generate and impairs i t s c o n t r a c t i l i t y and the muscle c o n t r a c t i l i t y i s d i r e c t l y r e l a t e d t o muscle compliance. A muscle forced t o c o n t r a c t c h r o n i c a l l y against heavy loads may develop c h r o n i c f a t i g u e or weakness. Recently, Couser and Berman(1989) reported t h a t r e s p i r a t o r y muscle f a t i g u e might generate a f u n c t i o n a l upper airway o b s t r u c t i o n . Not only because of f a t i g u e but a l s o because of muscle o r i e n t a t i o n , the GG and supra-hyoid muscle may not be able t o work e f f i c i e n t l y . Robert et al.(1984) discussed the pharyngeal airway s t a b i l i z i n g f u n c t i o n of the hyoid muscle group i n r a b b i t s . In agreement w i t h Brodie 1s(1950) understanding they found the s t a b i l i z i n g f u n c t i o n of the 107 sternohyoid and s t e r n o t h y r o i d muscles t o r e s i s t pharyngeal airway c o l l a p s e due t o negative i n t r a - l u m i n a l pressure. Through a s e r i e s of i n v e s t i g a t i o n s Van Lunteren and h i s a s s o c i a t e s (1987 a,b) r e i n f o r c e d t h i s hypothesis of hyoid muscle a c t i v i t y i n bre a t h i n g . The coordinated a c t i v a t i o n of both of the supra- and i n f r a - h y o i d muscles may produce a v e c t o r of f o r c e s , which d i s p l a c e s the hyoid arch i n a outward d i r e c t i o n , r e s u l t i n g i n a d i l a t e d upper airway. Furthermore, s e v e r a l i n v e s t i g a t o r s reported t h a t the head posture a l t e r s not only the r e s t i n g l ength of the hyoid muscles but a l s o the geometrical arrangements of these muscles, and i n t u r n , airway s i z e . Van Lunteren and co-workers (1987b) confirmed t h i s hypothesis by means of sonomicrometry i n c a t s . They found t h a t an increment i n upper airway volume lengthens the r e s t i n g lengths of the geniohyoids i n c a t s , but causes v a r i a b l e changes i n sternohyoid l e n g t h . Extension of the neck increases the leng t h of both the geniohyoid and sternohyoid muscles. With f l e x i o n of the head, they observed opposite r e s u l t s . Therefore, they concluded t h a t w i t h a given upper airway geometry there i s an i n v e r s e r e a c t i o n between upper airway volume and hyoid muscle l e n g t h , which i s e s p e c i a l l y strong f o r the geniohyoid muscle. They d i d not perform the experiment on the upper airway volume change induced J by extension and f l e x i o n of the head and neck. However, much research done by d i f f e r e n t groups has supported the idea t h a t patency of the upper airway i s enhanced w i t h an extension of the head posture. In a d d i t i o n , Van Lunteren et al.(1987) p o s t u l a t e d 108 t h a t i t i s the geniohyoid muscle, not the sternohyoid, which pl a y s an important r o l e as a hypopharyngeal d i l a t o r i n c a t s . They added t h a t the sternohyoid muscle acts i n an accessory f a s h i o n t o prevent excessive movement to the c r a n i a l s i d e due to geniohyoid c o n t r a c t i o n , and t h a t i t f u n c t i o n s s y n e r g i s t i c a l l y t o move the hyoid bone i n a forward d i r e c t i o n . However, as described i n the ankylosed TMJ case of Pruzansky's observation, the i n f r a - h y o i d muscle g r e a t l y a f f e c t s the hyoid bone l o c a t i o n . From the biomechanical p o i n t of view, an i n f e r i o r l y p o s i t i o n e d hyoid bone may not y i e l d a s u f f i c i e n t forward movement. This might be due t o muscular malfunction and/or t o the i n e f f i c i e n c y of the d i r e c t i o n of the v e c t o r sum. In other words, the ang u l a t i o n constructed by the geniohyoid muscle and sternohyoid muscle i s a l t e r e d t o become obtuse, and t h e r e f o r e , may not be able t o produce a ve c t o r sum s u f f i c i e n t t o a l l o w an adequate airway s i z e . Helling(1986) described the supra-hyoid muscle as a group of muscles i n c l u d i n g the a n t e r i o r d i g a s t r i c , the geniohyoid and the GG. Van de Graaff and associates(1984) commented t h a t i n humans, GG has some f i b r e s i n s e r t i n g i n t o the hyoid bone and may be another important determinant of hyoid bone p o s i t i o n . Winnberg(1987) included the a n t e r i o r b e l l y of the d i g a s t r i c muscle, the mylohyoid muscle and the geniohyoid muscle i n h i s d e f i n i t i o n of the supra-hyoid muscle group. While the mandible i s i n the r e s t p o s i t i o n with 2-4mm of i n t e r - o c c l u s a l space i n an u p - r i g h t s i t t i n g p o s i t i o n , among the supra-hyoid muscles only 109 the geniohyoid muscle may be f i r i n g i n phase w i t h r e s p i r a t i o n . Based on the r e s u l t s of the present study, an 8% increase i n supra-hyoid muscle a c t i v i t y i s presumed i n the supine p o s i t i o n compared to the u p - r i g h t p o s i t i o n . This amount of increased muscle a c t i v i t y i n the supine p o s i t i o n may represent augmented EMG a c t i v i t y of the supra-hyoid muscle t o keep the airway open. In c o n t r a s t , s i g n i f i c a n t decrease i n EMG a c t i v i t y i n the i n f e r i o r o r b i c u l a r o r i s muscle, may represent a r e l a x a t i o n a f t e r r e c l i n i n g of the body. Harper(1988) p o s t u l a t e d t h a t the p o s t e r i o r movement of the mandible may occur i n the supine p o s i t i o n during sleep due t o r e l a x a t i o n of the l a t e r a l p t e r y g o i d and masseter muscles. In a d d i t i o n , H o l l o w e l l et al.(1989) observed a s i g n i f i c a n t d e c l i n e i n masseter a c t i v a t i o n i n the OSA p a t i e n t s during sleep and the same group(1989) showed a s i g n i f i c a n t increase of masseter muscle a c t i v i t y i n accordance w i t h the l e v e l of hypercapnea. However, no change i n the masseter a c t i v i t y was observed w i t h the p o s i t i o n a l changes during the present study. Brodie(1950) observed t h a t the mouth opening accompanies the backward movement of the hyoid bone. He assumed a shortening of the supra-hyoid muscles to keep the airway open during opening of the mouth. During maximum opening, EMG a c t i v i t i e s from the d i g a s t r i c muscle obscure geniohyoid a c t i v i t y r e g a r d l e s s of body p o s i t i o n . However, more GG a c t i v i t y i s s t i l l r e q u i r e d i n the supine than the u p - r i g h t p o s i t i o n due t o the g r a v i t a t i o n a l p u l l . This e x p l a n a t i o n agrees w i t h the r e s u l t of the c u r r e n t study t h a t GG a c t i v i t y during 110 maximum opening i s increased i n the supine p o s i t i o n . As was discussed e a r l i e r , measuring of absolute value of the tongue pressure i s extremely d i f f i c u l t . Lear and h i s co- workers (1965) discussed t h i s matter q u i t e s k e p t i c a l l y . Pressure i s t r a d i t i o n a l l y expressed i n f o r c e per square centimeter. This term i m p l i e s t h a t muscular a c t i v i t y and surface c o n f i g u r a t i o n must d i s t r i b u t e f o r c e evenly over the e n t i r e sensing p l a t f o r m of the transducer. However, there i s no evidence t h a t o r a l t i s s u e s i n v a r i a b l y act i n a manner analogous to an a i r f i l l e d b a l l o n ( P r o f f i t et a l 1964), a mass of sponge rubber, or a water f i l l e d b a l l o n ( p r e s e n t study). Furthermore, where t h i s contact occured on the transducer surface i s unknown. Even when pressure transducers are c a l i b r a t e d i n an i n - v i t r o s i t u a t i o n , one must pay a t t e n t i o n t o the i n c o n s i s t e n c y of the transducer response to a given load according to the d i s t r i b u t i o n of the load. On t h i s p o i n t , Lear et al.(1965) recommended t h a t the use of pressure transducers w i t h smaller sensing surfaces may overcome these o b j e c t i o n s . In the c u r r e n t study, t o minimize t h i s problem, a small transducer(0.28 cm2) was employed and the detected s i g n a l s were i n t e g r a t e d and averaged by means of computer software. The l i n e a r i t y i n - v i t r o of the transducers employed f o r the present study was shown to be acceptable f o r a comparison study (see F i g . 10). I l l C . Overview Recently, S u r a t t and co-workers (1988) presented a pa r a d o x i c a l r e p o r t . They p o s t u l a t e d t h a t the upper airway muscle a c t i v i t y may be more augmented i n OSA p a t i e n t s than i n normal c o n t r o l s . They found t h a t OSA p a t i e n t s have more phasic GG group a c t i v i t y during NREM sleep, which could be expl a i n e d as a prec a r i o u s compensatory mechanism. S t r o h l (1986) emphasized the importance of the t o n i c a c t i v i t y of the muscles. He explained t h a t changes i n t o n i c a c t i v i t y could a f f e c t airway s i z e as w e l l as muscle l e n g t h ; thus t o n i c a c t i v i t y of the GG and hyoid muscles overcomes surface t e n s i o n of the blocked airway, and f i n a l l y promotes the airway o c c l u s i o n . The r o l e of age i n OSA i s not c l e a r . jiowever, Chaban et al.(1988) r e c e n t l y observed t h a t airway o b s t r u c t i o n s at the l e v e l of the tongue base mainly happen i n o l d e r age groups, whereas o b s t r u c t i o n s at the l e v e l of the s o f t p a l a t e occur i n younger groups. Lugaresi et al.(1980) found t h a t the frequency of snorers i n the popu l a t i o n increased w i t h age. The current study f a i l e d t o match age and BMI. However, the r e s u l t s from the ANCOVA t e s t i n the current study i l l u s t r a t e d t h a t age does not a f f e c t the comparisons of the hyoid v a r i a b l e s between the OSA and asymptomatic c o n t r o l groups (see Table VI) . Nevertheless, as described e a r l i e r , the r e s i s t a n c e of a i r f l o w increases w i t h age, and i n a d d i t i o n the hyoid bone migrates i n f e r i o r l y and a n t e r i o r l y . These f i n d i n g s imply t h a t age may be another f a c t o r exacerbating OSA symptoms. Anatomically, upper airways are l i n e d by mucous membranes w i t h the musculature underneath, and are long and convoluted as w e l l . However, the small s i z e of the upper airway may not alone be able t o induce the apnea. Furthermore, the s t a b i l i t y of the upper airway does not seem to be t o t a l l y determined e i t h e r by muscular a c t i v i t y or by pulmonary f u n c t i o n alone. The f u n c t i o n a l r o l e s of feedback c o n t r o l of r e s p i r a t i o n or chemico- or mechanoreceptors are s i g n i f i c a n t . Moreover, from a biomechanical p o i n t of view, the coordinated l i n k a g e of the airway s i z e , tongue a c t i v i t y , hyoid bone l o c a t i o n , as w e l l as the supine p o s i t i o n of the body, may c o n t r i b u t e to the pathogenesis of the OSA symptoms. D. P i t f a l l s and Future Studies The present study was designed t o compare anatomical and p h y s i o l o g i c a l r e l a t i o n s h i p s between airway s t r u c t u r e s i n accordance w i t h body p o s i t i o n a l changes i n OSA and asymptomatic c o n t r o l s . Therefore, the cephalometric study r e q u i r e d a r e p r o d u c i b l e and standardized r e c o r d i n g p o s i t i o n f o r accurate data c o l l e c t i o n . However, the experiment f a i l e d t o exclude s e v e r a l i n e v i t a b l e problems inherent t o t h i s procedure. For i n s t a n c e , the p a t i e n t s were t o l d t o hold the mandible s l i g h t l y c l o s e d i n an u p - r i g h t standing p o s i t i o n , but t o r e l a x the mandible i n the supine p o s i t i o n . Obviously, airway s i z e i s a f f e c t e d by t h i s major change i n mandibular p o s i t i o n . This discrepancy was obvious from the onset but t o compare our data 113 base w i t h a l l previous OSA r e p o r t s , the maximum i n t e r c u s p a t i o n p o s i t i o n i n the u p - r i g h t p o s i t i o n was used. Head p o s i t i o n i n the supine p o s i t i o n was c a r r i e d out without a f i x e d reference plane. Subjects were i n s t r u c t e d only t o mimick t h e i r normal sleep p o s i t i o n . There was no standardized p r o t o c o l t o confirm whether the r e l a t i o n s h i p between the head p o s i t i o n on a p i l l o w and the body posture on a s t r e t c h e r a c t u a l l y represents a n a t u r a l sleep p o s i t i o n . The present p i l o t study d i d not i n c l u d e EMG or pressure experiments i n the OSA symptomatic group. An EMG and pressure study on the OSA group may w e l l be the next l o g i c a l step f o r fut u r e i n v e s t i g a t i o n s . Overnight tongue pressure r e c o r d i n g , synchronized w i t h EMG, could be a f i n a l o b j e c t i v e f o r t h i s comparative study. I f , by means of the current method, we could segregate the ' a c t i v e ' GG EMG from the 'passive' GG EMG (that EMG a c t i v i t y w i t h no change i n the muscle len g t h d u r i n g s l e e p ) , we may be able t o develop a b e t t e r understanding of the pathogenesis of OSA. 114 SUMMARY The cephalometric study d i f f e r e n t i a t e d OSA p a t i e n t s from asymptomatic c o n t r o l s as f o l l o w s : 1. The OSA group revealed a longer tongue, a l a r g e r s o f t p a l a t e , an a n t e r o p o s t e r i o r l y narrower and s u p e r o i n f e r i o r l y lengthened upper airway, a i n f e r i o r l y p o s i t i o n e d hyoid bone, a more u p - r i g h t tongue, a more extended head posture and a s m a l l e r hypopharynx i n the up - r i g h t standing p o s i t i o n . 2. The OSA group showed gr e a t e r tongue he i g h t , a l a r g e r tongue and a sma l l e r hypopharyngeal area i n the supine p o s i t i o n . 3. With the p o s i t i o n a l changes from u p - r i g h t t o supine, the t h i c k n e s s of the s o f t p a l a t e increased more i n the c o n t r o l group, whereas the s i z e of the upper airway was decreased more i n the OSA group. 4. With the p o s i t i o n a l changes from u p - r i g h t to supine, the hyoid bone was moved up toward the mandibular plane more i n the c o n t r o l s u b j e c t s , but more toward the mandibular symphysis i n the OSA group. 5. The tongue c r o s s - s e c t i o n a l area increased s i g n i f i c a n t l y by 4.3% i n the supine p o s i t i o n and oropharyngeal area decreased by 3 6.5% i n the OSA group. 115 As a summary of the r e s t EMG and pressure study, w i t h the p o s i t i o n a l changes from u p - r i g h t t o supine, the asymptomatic c o n t r o l group showed: 1. The EMG a c t i v i t y of the geniogiossus muscle was increased by 3 3.8%. 2. The pressure of the p o s t e r i o r p o r t i o n of the tongue increased by 17%. 3. The r e s t i n g p o t e n t i a l a c t i v i t y of the i n f e r i o r o r b i c u l a r i s o r i s decreased by 32.5%. 4. The EMG a c t i v i t y of the supra-hyoid group increased by 8%, yet the change was not s t a t i s t i c a l l y s i g n i f i c a n t . 116 BIBLIOGRAPHY 1. Abd-El-Malek S. A c o n t r i b u t i o n t o the study of the movement of the tongue i n animals, w i t h s p e c i a l reference t o the cat. J . Anat. 73:15, 1938. 2. Agostoni, E.,Mugnai Cavagna, A. and C i t t e r i o , G. E f f e c t s of s t r e t c h recepters of bronchi or trachea on geniogiossus muscle a c t i v i t y . Resp. P h y s i o l . 67:335, 1987. 3. Anch, A.M., Remmers, J.E. and B u n c e l l l , H. S u p r a g l o t t i c airway r e s i s t a n c e i n normal subjects and p a t i e n t s w i t h o c c l u s i v e sleep apnea. J . Appl. P h y s i o l . : R e s p i r a t . Environ. E x e r c i s e P h y s i o l . 53(5):1158, 1982. 4. Archer, S.Y. and V i g , P.S. E f f e c t s of head p o s i t i o n on i n t r a o r a l pressures i n Class I and^ClassII a d u l t s . Am. J . Orthod. 87(4):311, 1985. 5. Armitage, P. and Berry, G. Further a n a l y s i s of variance:214, D i s t r i b u t i o n f r e e methods:408, In S t a t i s t i c a l Methods i n Medical Research 2nd e d d i t i o n , B l a c k w e l l S c i e n t i f i c P u b l i c a t i o n s , 1987. 6. Aronson, R.M., Onal, E., Carley, D.W. and Lopata, M. Upper airway and r e s p i r a t o r y muscle responses t o continuous negative airway pressure. J . Appl. P h y s i o l . 66(3):1373, 1989. 7. Baker, T.L. I n t r o d u c t i o n t o sleep and sleep d i s o r d e r s Med. C l i n . N. Am. 69(6):1123, 1985. 8. Bhandary, P.R., H o l l o w e l l , D.E., and S u r a t t , P.M. A c t i v a t i o n of masseter muscles i n normal s u b j e c t s . Abs. Am. Rev. Res p i r . Dis. 139(4):A448, 1989. 9. Baumrind, S. and Frantz, R.C. The r e l i a b i l i t y of head f i l m measurements. 1. Landmark i d e n t i f i c a t i o n . Am. J . Orhtod. 60(4):111, 1971. 10. Baumrind, S. and Frantz, R.C. The r e l i a b i l i t y of head f i l m measurements. 2. Conventional angular and l i n e a r measures. Am. J . Orhtod. 60(5) :505, 1971. 11. Baumrind, S., M i l l e r , D., and Molthen, R. The r e l i a b i l i t y of head f i l m measurements. 3. Tracing s u p e r i m p o s i t i o n . Am. J . Orthod. 70(6):617, 1976. 12. Baumrind, S. and M i l l e r , D.M. Computer-aided head f i l m a n a l y s i s : The UCSF method. Am. J . Orthod. 78(1):41, 1980. 117 1 3 . B e h r a k i s , P . K . , B a y d u r , A . , J a e g e r , M . J . a n d M i l i c - E m i l i , J . L u n g m e c h a n i c s i n s i t t i n g a n d h o r i z o n t a l b o d y p o s i t i o n s . C h e s t 8 3 ( 4 ) : 6 4 3 , 1 9 8 3 . 14 . B e n c h , R . W . G r o w t h o f t h e c e r v i c a l v e r t e b r a e a s r e l a t e d t o t o n g u e , f a c e , a n d d e n t u r e b e h a v i o r . Am. J . O r t h o d o n t i c s 4 9 ( 3 ) : 1 8 3 , 1 9 6 3 . 1 5 . B e r t h o n - J o n e s , M . a n d S u l l i v a n , C . E . V e n t i l a t o r y a n d a r o u s a l r e s p o n s e s t o h y p o x i a i n s l e e p i n g h u m a n s . Am. R e v . R e s p i r . D i s . 1 2 5 : 6 3 2 , 1982 . 1 6 . B i b b y , R . E . a n d P r e s t o n , C B . T h e h y o i d t r i a n g l e . Am. J . O r t h o d o n t i c s 8 0 ( 1 ) : 9 2 , 1 9 8 1 . 1 7 . B o n o r a , M . , B a r t l e t t , D . a n d K n u t h , S . C h a n g e s i n u p p e r a i r w a y m u s c l e a c t i v i t y r e l a t e d t o h e a d p o s i t i o n i n awake c a t s . R e s p . P h y s i o l . 6 0 : 1 8 1 , 1 9 8 5 . 18 . B r a d l e y , T . D . a n d P h i l l i p s o n , E . A . P a t h o g e n e s i s a n d p a t h o p h y s i o l o g y o f t h e OSA s y n d r o m e . M e d . C l i n . N . Am. 6 9 ( 6 ) : 1 1 6 9 , 1 9 8 5 . 1 9 . B r a d l e y , T . D . , B r o w n , I . G . , G r o s s m a n , R . F . , Z a m e l , N . , M a r t i n e z , D . , P h i l l i p s o n , E . A . , a n d H o f f s t e i n , V . P h a r y n g e a l s i z e i n s n o r e r s , n o n s n o r e r s , a n d p a t i e n t s w i t h o b s t r u c t i v e s l e e p a p n e a . N . E n g l . J . M e d . 3 1 5 : 1 3 2 7 , 1986 . 2 0 . B r a d l e y , T . D . D i a g n o s i n g a n d a s s e s s i n g o b s t r u c t i v e s l e e p a p n e a . J . R e s p i r . D i s . M a r c h : 3 2 , 1 9 8 8 . 2 1 . B r e s s l e r , B . H . a n d C l i n c h , N . F . T h e c o m p l i a n c e o f c o n t r a c t i n g s k e l e t a l m u s c l e . J . P h y s i o l . 2 3 7 : 4 7 7 , 1 9 7 4 . 2 2 . B r o d i e , A . G . A n a t o m y a n d p h y s i o l o g y o f h e a d a n d n e c k m u s c u l a t u r e . Am. J . O r t h o d o n t i c s 3 6 : 8 3 1 , 1 9 5 0 . 2 3 . B r o o k e , M . H . a n d K a i s e r , K . K . M u s c l e f i b e r t y p e s : How many a n d w h a t k i n d ? A r c h . N e u r o l . 2 3 : 3 6 9 , 197 0 . 2 4 . B r o w n , I . B . , M c C l e a n , P . A . , B o u c h e r , R . , Z a m e l , N . , a n d H o f f s t e i n V . C h a n g e s i n p h a r y n g e a l c r o s s - s e c t i o n a l a r e a w i t h p o s t u r e a n d a p p l i c a t i o n o f c o n t i n u o u s p o s i t i v e a i r w a y p r e s s u r e i n p a t i e n t s w i t h o b s t r u c t i v e s l e e p a p n e a . Am. R e v . R e s p i r . D i s . 1 3 6 : 6 2 8 , 1 9 8 7 . 2 5 . B r o u i l l e t t e , R . T . a n d T h a c h , B . T . C o n t r o l o f g e n i o g l o s s u s m u s c l e i n s p i r a t o r y a c t i v i t y . J . A p p l . P h y s i o l . : R e s p i r a t . E n v i r o n . E x e r c i s e P h y s i o l . 4 9 ( 5 ) : 8 0 1 , 1 9 8 0 . 118 26. Billow, K. and Ingva, D.H. R e s p i r a t i o n and s t a t e of wakefulness i n normals, s t u d i e d by spirography, capnography and EEG. Acta. P h y s i o l . Scand. 51:230, 1961. 27. Biilow, K. and Ingvar, D.H. R e s p i r a t i o n and electrocephalography i n narcolepsy. Neurology 13:321, 1963. 28. Biilow, K. R e s p i r a t i o n and wakefulness i n man. Acta. P h y s i o l . Scand. 59:1, 1963. 29. B u r w e l l , C.S., Robin, E.D., Whaley, R.D., and Bickelmann, A.G. Extreme o b e s i t y a s s o c i a t e d w i t h a l v e o l a r h y p o v e n t i l a t i o n - A P i c k w i k i a n syndrome. Am. J . Med. 21:811, 1956. 30. Carlsoo, S. and L e i j o n , G. A r a d i o g r a p h i c study of the p o s i t i o n of the hyo-laryngeal complex i n r e l a t i o n t o the s k u l l and the c e r v i c a l column i n man. Trans. R. Sch. Dent. 5:13, 1960. 31. Chaban, R., Cole, P. and H o f f s t e i n , V. S i t e of upper airway o b s t r u c t i o n i n p a t i e n t s w i t h i d i o p a t h i c o b s t r u c t i v e sleep apnea. Laryngoscope 98:641, 1988. 32. Cherniack, N.S. and Longobardo, G.S. A b n o r m a l i t i e s i n r e s p i r a t o r y rhythm:728, In Handbook of Physiology, R e s p i r a t o r y system vol.11, C o n t r o l of Breathing, American P h y s i o l o g i c a l S c i e t y , Bethesda, 1986. 33. Cherniack, N.S. and Hudgel, D.W. The upper airway muscles: T h e i r r o l e i n s l e e p - r e l a t e d r e s p i r a t o r y dysrhythmias.:29 In C o n t r o l of Breathing During Sleep and Anesthesia, e d i t e d by Karczewski, W.A., Grieb, P., Kulesza, J . and Bonsignore, G., 1987 . 34. Close, R.I. Dynamic p r o p e r t i e s of mammalian s k e l e t a l muscles. P h y s i o l o g i c a l reviews 52(1):129, 1972. 35. Coccogna, G., Mantovani, M., B r i g n a n i , F., P a r c h i , C. and L u g a r e s i , E. Continuous re c o r d i n g of the pulmonary and systemic a r t e r i a l pressure during sleep i n syndromes of hypersomnia w i t h p e r i o d i c breathing. B u l l . P h y sio-pathol. R e s p i r . 8:1217, 1972 36. C o l l i e r , CR. and A f f e l d t , J.E. V e n t i l a t o r y e f f i c i e n c y of the c u i r a s s r e s p i r a t o r i n t o t a l l y p aralyzed c h r o n i c p o l i o m y e l i t i s p a t i e n t s . J . Appl. P h y s i o l . 6:531, 1954. 37. Couser, J . I . and Berman, J.S. R e s p i r a t o r y muscle f a t i g u e from f u c t i o n a l upper airway o b s t r u c t i o n . Chest 96(3):689, 1989 . 119 38. Crumley, R.L., S t e i n , M., Golden, J . , Gamsu, G., and Dermon, S. Determination of o b s t r u c t i v e s i t e i n o b s t r u c t i v e sleep apnea. Laryngoscope 97:301, 1987. 39. DeBerry-Borowiecki, B., Kukwa, A., and Blanks, R.H. Cephalometric a n a y l y s i s f o r d i a g n o s i s and treatment of o b s t r u c t i v e sleep apnea. Laryngoscope 98:226, 1988. 40. Doble, E.A., L e i t e r , J . C , Knuth, S.L., daubenspeck, J.A., and B a r t l e t t , D. J r . A noninvasive i n t r a o r a l electromyographic e l e c t r o d e f o r genioglossus muscle. J . Appl. P h y s i o l . 58(4):1378, 1985. 41. Doran, G.A. and Baggett, H. The genioglossus muscle: a reassessment of i t s anatomy i n some mammals, i n c l u d i n g man. Acta. anat. 83:403, 1972. 42. Doran, G.A. Review of the e v o l u t i o n and phylogeny of the mammalian tongue. Acta. anat. 91:118, 1975. 43. Douglas, N.J., White, D.P., W e i l , J.V., P i c k e t t , C.K., and Z w i l l i c h , C.W. Hypercapnic v e n t i l a t o r y response i n s l e e p i n g a d u l t s . Am. Rev. Respir. Dis. 126:758, 1982. 44. D'urzo, A.D., Lawson, V.G., V a s s a l , K.P., Rebuck, A.S., S l u t s k y , A.S., and H o f f s t e i n , V. Airway area by a c o u s t i c response measurements and computerized tomography. Am. Rev. R e s p i r . Dis. 135:392, 1987. 45. Engel, W.K. Fiber-type nomenclature of human s k e l e t a l muscle f o r h i s t o c h e m i c a l purposes. Neurology A p r i l : 3 4 4 , 1974 . 46. Farkas, L.G. E x a m i n a t i o n s , In Anthropometry of the head and face i n medicine. Chapter 2, E l s e v i e r , N.Y., 1981. 47. Fouke, J.M. and S t r o h l , K.P. E f f e c t of p o s i t i o n and lung volume on upper airway geometry. J . Appl. P h y s i o l . 63(1):375, 1987. 48. Fleetham, J . , West, P., Mezon, B., Conway, W., Roth, T., and Kryger, M. Sleep, arousals and oxigen d e s a t u r a t i o n i n COPD. The e f f e c t of oxygen therapy. Am. Rev. R e s p i r . Dis. 126:429, 1982. 49. Fredberg, J . J . , Wohl, M. E. B., Glass, G.M. and Dorkin, H.L. Airway area by a c o u s t i c r e f l e c t i o n s measured at the mouth. J . Appl. 48(5):749, 1980. 120 50. Forsberg, C., H e l l s i n g , E., Linder-Aronson, S. and Sheikholeslam, A. EMG a c t i v i t y i n neck and masticatory muscles i n r e l a t i o n t o extension and f l e c t i o n of the head. European J . Orthodontics 7:177, 1985. 51. Gastaut, H., T a s s i n a r i , CA., and Duron, B. Polygraphic study of the e p i s o d i c d i u r n a l and n o c t u r n a l (hypnic and r e s p i r a t o r y ) m a n i f e s t a t i o n s of the Pickwick syndrome. B r a i n Research, 2:167, 1966. 52. George, C.F., M i l l a r , T.W. and Kryger, M.H. Sleep apnea and body p o s i t i o n during sleep. Sleep 11(1):90, 1988. 53. Goldstone, J . , Mulvey, D., K o u l o u r i s , N., C a r r o l l , M. and Green, M. The e f f e c t of posture of maximum s t a t i c mouth pressures. Abs. Europ. Respir. J . Suppl. 1:82S, 1988. 54. Grassino, A. Pathways l e a d i n g t o s k e l e t a l muscle f a t i g u e . In R e s p i r a t o r y Muscles i n Chronic O b s t r u c t i v e Pulmonary Disease: 77-87, e d i t e d by A. Grassino, C. F r a c c h i a , C. Rampulla, L. Zocchi, p u b l i s h e r s S p r i n g e r - V e r l a g , 1988. 55. Green, D.G., Elam, J.O., Dobkin, A.B., and Studley, C.L. C i n e f l u o r o g r a p h i c study of hypertension of the neck and upper airway patency. J.A.M.A. 20:57 0, 19 61. 56. G r e e n f i e l d , B., Kraus, S., Lawrence, E., and Wolf, S.L. The i n f l u e n c e of c e p h a l o s t a t i c ear rods on the p o s i t i o n s of the head and neck during p o s t u r a l recordings. Am. J . Orthod. Dentofac. Orthop. 95(4):312, 1989. 57. Grunstein, R.R., Lawrence, S., Spies, J.M., Faaloupo, P., Vermeulen, W., P h i l l i p s , K., Handelsman, D.J. and S u l l i v a n , C.E. "Snoring i n Paradice" The Western Samoa sleep study. Europ. Abs. Resp. J . suppl. 2(5):401S, 1989. 58. G u i l l e m i n a u l t , C , E l d r i d g e , F. and Dement, W.C Insomnia, narcolepsy, and sleep apnea. B u l l . P h y s i o - p a t h o l . R e s p i r . 8:1127, 1972. 59. G u i l l e m i n a u l t , C , E l d r i d g e , F.L., and Dement, W.C. Insomnia w i t h sleep apnea: A new syndrome. Science 181:856, 1973 . 60. G u i l l e m i n a u l t , C , E l d r i d g e , F.L., Simmon, F.B., and Dement, W.C Sleep apnea syndrome West J . Med. 123:7, 197 5. 61. G u i l l e m i n a u l t , C , T i l k i a n , A. and Dement, W.C. The sleep apnea syndromes. Ann. Rev. Med. 27:465, 1976. 121 62. G u i l l e m i n a u l t , C., H i l l , M.W., Simmons, F.B., and Dement, W.C. Ob s t r u c t i v e sleep apnea: Electromyographic and f i b r o p t i c s t u d i e s . Experimental Neurology 62:48, 1978. 63. G u i l l e m i n a u l t , C. Sleep apnea syndrome:Impact of sleep and sleep s t a t e s . Sleep 3(3/4):227, 1980. 64. G u i l l e m i n a u l t C. Ob s t r u c t i v e sleep apnea syndrome. A review. P s y c h i a t r i c C l i n i c s of North America 10(4):607, 1987. 65. G u i l l e m i n a u l t , C. The r o l e of sleep and sleep s t a t e s on brea t h i n g d i s o r d e r s . Schweiz. med.Wschr. 118:1331, 1988. 66. Haponik, E.F., Smith, P.L., Bohlman, M.E., A l l e n , R.P., Goldman, S.M., and Bleecker, E.R. Computerized tomography i n o b s t r u c t i v e sleep apnea. Am. Rev. Resp i r . Dis. 127:221, 1983. 67. Harper, R.M. OSA mechanisms. CDA J o u r n a l Oct.:35, 1988. 68. Haxhiu, M.A., van Lunteren, E., M i t r a , J . , and Cherniac, N.S. Comparison of the response of diaphragm and upper airway d i l a t i n g muscle a c t i v i t y i n s l e e p i n g c a t s . R e s p i r a t i o n Physiology 70:183, 1987. 69. Ha u r i , P. and Orr, W.C. The sleep d i s o r d e r s . In Current Concept, 2nd e d i t i o n , The upjohn. 1982. 70. H e l l s i n g , E., Frosberg, C., Linder-Aronson, S., and Sheiholeslam, A. Changes i n p o s t u r a l EMG a c t i v i t y i n the neck and masticatory muscles f o l l o w i n g o b s t r u c t i o n of the nasal airways. European J o u r n a l of Orthodontics 8:247, 1986. 71. H e l l s i n g , E. and L 1Estrange, P. Changes i n l i p pressure f o l l o w i n g extension and f l e x i o n of the head and at changed mode of breat h i n g . Am. J . Orthod. Dentofac. Orthop. 91:286, 1987 . 72. H e l l s t r a n d , E. Morphological and h i s t o c h e m i c a l p r o p e r t i e s of tongue muscles i n cat. Acta. P h y s i o l . Scand. 110:187, 1980. 73. Henderson-Smart, D.J. Regulation of bre a t h i n g i n the p e r i n a t a l period:403, Chapter 12, In Sleep and Breathing e d i t e d by Sauders, N.A. and S u l l i v a n , C.E., 1984. 74. H o f f s t e i n , V., Brown, I.G., and Zamel, N. Pharyngeal c r o s s - s e c t i o n a l area i n normal man and woman. Abs. Am. Rev. Respi r . Dis. 139(4):A306, 1989. 122 75. H o l l o w e l l , D.E., Jensen, P., Funsten, A.W., and S u r a t t , P.M. A c t i v a t i o n of masseter muscles during sleep i n O b s t r u c t i v e Sleep Apnea. Abs. Am. Rev. Respir. Dis. Abs. 139(4):A448, 1989 . 76. Hoover, L.A., Wortham, D.G., L u f k i n , R.B., and Hanafee, W.N. Magnetic resonance imaging of the la r y n x and tongue base: C l i n i c a l a p p l i c a t i o n s . Otolaryngology-Head and Neck Surgery 97(3):245, 1987. 77. Horner, R.L., Low e l l , D.G., Mohaiddin, R., Shea, S.A., Burman, E., Longmore, D.B., and Guz, A. I s abnormal f a t d e p o s i t i o n around the pharynx a feature of o b s t r u c t i v e sleep apnea? Abs. Europ. Respir. J . , Suppl.l:95S, 1988. 78. Hudgel, D.W., Mulholland, M., and Hendricks, C. Neuromuscular and mechanical responses t o i n s p i r a t o r y r e s i s t i v e l o a d i n g during sleep. J . Appl. P h y s i o l . 63(2):603, 1987. 79. Hudgel, D.W. and Harasik, T.M. R e s p i r a t o r y t i m i n g imbalance i n OSA. Abs. Am. Rev. Resp i r . Dis. 139(4):A450, 1989. 80. Huggare, J . The " f l u i d - l e v e l method" f o r r e c o r d i n g n a t u r a l head posture. Proc. Finn. Dent. Soc. 81:199, 1985. 81. Huggare, J . Head posture and c r a n i o f a c i a l morphology i n a d u l t s from northern F i n l a n d . Proc. Finn. Dent. Soc. 82:199, 1986. 82. Houston, W.J.B. The a p p l i c a t i o n of computer aided d i g i t a l a n a l y s i s t o orthodontic records. Eur. J . Orthod. 1:71, 1979. 83. Houston, W.J.B. The a n a l y s i s of e r r o r s i n or t h o d o n t i c measurements. Am. J . Orthod. 83(5):382, 1983. 84. I s s a , F.G. and S u l l i v a n , C.E. Reversal of c e n t r a l sleep apnea us i n g Nasal CPAP. Chest 92(2):165, 1986. 85. I s s a , F.G., Edwards, P., Szeto, E., Lauff, D., and S u l l i v a n , C. Geniogiossus and breathing responses to airway o c c l u s i o n : e f f e c t of sleep and route of o c c l u s i o n . J . Appl. P h y s i o l . 64(2):543, 1988. 86. Jackson, A.C. and Olson, D.E. Comparison of d i r e c t and a c o u s t i c a l measurements i n p h y s i c a l models of human c e n t r a l airways. J . App. P h y s i o l . 48:896, 1980. 123 87. Jamieson, A., G u i l l e m i n a u l t , C., P a r t i n e n , M., and Quera- Salv a , M.A. O b s t r u c t i v e sleep apneic p a t i e n t s have craniomandibular a b n o r m a l i t i e s . Sleep 9(4):469, 1986. 88. K a l b f l e i s c h , J . A cephalometric study of the s k e l e t a l r a d i o g r a p h i c determinants of oropharyngeal dimension i n i d i o p a t h i c OSA p a t i e n t s . Master's Thesis, Univ. Toronto, 1988. 89. Kuhlo, W. Sleep a t t a c k s w i t h apnoea:205, In Ab n o r m a l i t i e s of Sleep i n Man, e d i t e d by Gastaut, H., Lu g a r e s i , E., B e r t i - C eroni, G., Coccagna, G. Bologna, I t a l y , 1968. 90. Kumashiro, H., Sato, M., H i r a t o , J . , Baba, O. and O t s u k i , S. Sleep apnoea and sleep r e g u l a t i n g mechanism. F o l i a P s y c h i a t . Neurol. Jap. 25:41, 1971. 91. Kuna, S.T. I n t e r a c t i o n of hypercapnea and phasic volume feedback on motor c o n t r o l of the upper airway. J . Appl. P h y s i o l . 63(5):1744, 1987. 92. Kuna, S.T., Bedi, D.G., and Ryckman, C. E f f e c t of nasal airway p o s i t i v e pressure on upper airway s i z e and c o n f i g u r a t i o n . Am. Rev. Res p i r . Dis. 138:969, 1988. 93. Kuna, S.T. and Smickley, J . Response of genioglossus muscle a c t i v i t y t o nasal airway o c c l u s i o n i n normal s l e e p i n g a d u l t s . J . Appl. P h y s i o l . 64(1):347, 1988. 94. L a v i e , P. Incidence of sleep apnea i n a presumably healthy working p o p u l a t i o n : A s i g n i f i c a n t r e l a t i o n s h i p w i t h excessive daytime s l e e p i n e s s . Sleep, 64(4):312, 1983. 95. Leblanc, P., Ruff, F., and M i l i c - E m i l i , J . E f f e c t s of age and body p o s i t i o n on "airway c l o s u r e " i n man. J . of Appl. P h y s i o l . 28(4):448, 1970. 96. Lear, C.S.C, Catz, J . , Grossman, R.C, Flanagan, J.B., and Moorrees, C.F.A. Measurement of l a t e r a l muscle f o r c e s on the d e n t a l arches. Arch, o r a l B i o l . 10:669, 1965. 97. L i i s t r o , G., Stanescu, D., Dooms, G., Rodenstein, D., and V e r i t e r , C. Head p o s i t i o n modifies upper airway r e s i s t a n c e i n men. J . Appl. P h y s i o l . 64(3):1285, 1988. 98. Longobardo, G.S., Gothe, B., Goldman, M.D. and Cherniack, N.S. Sleep apnea considered as a c o n t r o l system i n s t a b i l i t y . R e s p i r a t i o n Physiology 50:311, 1982. 124 99. Lowe, A.A. and Johnston, W.D. Tongue and jaw muscle a c t i v i t y i n response to mandibular r o t a t i o n s i n a sample of normal and a n t e r i o r open-bite s u b j e c t s . Am. J . Orthod. 76(5):565, 1979. 100. Lowe, A.A. C o r r e l a t i o n s between o r o f a c i a l muscle a c t i v i t y and c r a n i o f a c i a l morphology i n a sample of c o n t r o l and a n t e r i o r open-bite s u b j e c t s . Am. J . Orthod. 78(1):89, 1980. 101. Lowe, A.A. The neural r e g u l a t i o n of tongue movements. Prog. Neurobiol. 15:295, 1981. 102. Lowe, A.A. Tongue movement- Brainstem mechanism and c l i n i c a l p o s t u l a t e s . B r a i n Behav. E v o l . 25:128, 1984. 103. Lowe, A.A., Santamaria, J . , Fleetham, J . , and P r i c e , C. F a c i a l morphology and o b s t r u c t i v e sleep apnea. Am. J . Orthodfac. Orthop. 90:484, 1986. 104. Lowe, A.A., Gionhaku, N., Takeuchi, K., and Fleetham, J . A. Three-dimensional CT r e c o n s t r u c t i o n s of tongue and airway i n a d u l t subjects w i t h o b s t r u c t i v e sleep apnea. Am. J . Orthod. Dentofac. Orthop. 90:364, 1986. 105. Lowe, A.A., Fleetham, J.A., S a t o s h i , A., and Ryan, F. Cephalometric and CT p r e d i c t o r s of apnea index s e v e r i t y . Sleep, In press, 1989. 106. Lowe, A.A., Pae, E., Adachi, S., and Fleetham, J.A. Two and three dimensional analyses of tongue, airway and s o f t p a l a t e s i z e . In A t l a s of the D i f f i c u l t Airway, e d i t e d by M.L. Norton, 1989. In press. 107. Luce, J.M. and Culver, B.H. R e s p i r a t o r y muscle f u n c t i o n i n h e a l t h and disease. Chest, 81(1):82, 1982. 108. L u g a r e s i , E., C i r i g n o t t a , F., Coccagna, G., and Piana, C. Some e p i d e m i o l o g i c a l data on snoring and c a r d i o c i r c u l a t o r y disturbances. Sleep, 3(3/4):221, 1980. 109. L u g a r e s i , E., C i r i g n o t t a , F., and Montagna, P. P a t h o l o g i c aspects of snoring and o b s t r u c t i v e apnea syndrome. Schweiz. med. Wschr. 118:1333, 1988. 110. Lyberg, T. , Krogstad, 0., and Djupesland, G. Cephalometric a n a l y s i s i n p a t i e n t s w i t h o b s t r u c t i v e sleep apnoea syndrome: I I . s o f t t i s s u e morphology. J . Laryngo. and O t o l . 103:293, 1989. 125 111. McGrinty, D.J. and Beahm, E.K. Neurobiology of sleep:1, Chapter 1, In Sleep and Breathing, e d i t e d by Saunders, N.A. and S u l l i v a n , C.E., 1984. 112. M a r t i n , T.R., C a s t i l e , R.G., Fredberg, J . J . , Wohl. M.E.B. and Mead, J . Airway s i z e i s r e l a t e d sex not lung s i z e i n normal a d u l t s . J . Appl. P h y s i o l . 63(5):2042, 1987. 113. Mathew, O.P., Abu-Osba, Y.K., and Thach, B. Influence of upper airway pressure changes on genioglossus muscle r e s p i r a t o r y a c t i v i t y . J . Appl. P h y s i o l . 52(2):438, 1982. 114. Mathew, O.P., Abu-Osba, Y.K., and Thach, B. Genioglossus muscle responses t o upper airway pressure changes: A f f e r e n t pathways. J . Appl. P h y s i o l . 52(2): 445, 1982. 115. Mathew, O.P. and Remmers, J.E. R e s p i r a t o r y f u n c t i o n of the upper airway. Chapter 4.:163, In Sleep and Breathing, e d i t e d by sauders, N.A. and S u l l i v a n , C.E., 1984. 116. Mathew, O.P. Upper airway negative-pressure e f f e c t s on r e s p i r a t o r y a c t i v i t y of upper airway muscles. J . Appl. P h y s i o l . 56(2):500, 1984. 117. Mathiot, M.J., Bonnel, A.M., and Grimaud, C. E f f e c t s of a i r f l o w r e s i s t a n c e v a r i a t i o n s on r e s i s t i v e load d e t e c t i o n i n normal s u b j e c t s . B u l l . Eur. P h y s i o p a t h o l . R e s p i r . 22:99, 1986. 118. M i k i , H., Hida, W., Inoue, H. and Takishima, T. A new treatment f o r o b s t r u c t i v e sleep apnea syndrome by e l e c t r i c a l s t i m u l a t i o n of submental reg i o n . Tohoku J . exp. Med. 154:91, 1988. 119. M i l l e r , A.J., and F a r i a s , M. Histochemical and e l e c t r o g r a p h i c a n a l y s i s of craniomandibular muscles i n the Rhesus monkey, Macaca mulatta. J . Oral M a x i l l o f a c . Surg. 46:767, 1988. 120. M i l i d o n i s , M.K., Widmer, C.G., Segal, R.L. and Kraus, S.L. Surface i n t r a o r a l genioglossus EMG re c o r d i n g technique f o r k i n e s i o l o g i c s t u d i e s . Am. J . Orthod. Dentofac. Orthop. 94:240, 1988. 121. Moorrees, C.F.A. and Kean, M.R. Na t u r a l head p o s i t i o n , a b a s i c c o n s i d e r a t i o n i n the i n t e r p r e t a t i o n of cephalometric radiographs. Am. J . Phys. Anthropol. 16:213, 1958. 122. Moran, W.B. J r . O b s t r u c t i v e sleep apnea: Diagnosis by h i s t o r y , p h y s i c a l examination, and s p e c i a l studies:19, In Snoring and O b s t r u c t i v e Sleep Apnea, e d i t e d by Fairbanks, D.N.F., F u j i t a , S., Ikematsu, T., and simmon, F.B., 1987. 126 12 3. Moss, M.L. and Young, R.W. A f u n c t i o n a l approach to c r a n i o l o g y . Am. J . Phys. Anthrop. 18:281, 1960. 124. M u e l l e r , W.H. and Wohlleb, J.C. Anatomical d i s t r i b u t i o n of subcutaneous f a t and i t s d e s c r i p t i o n by m u l t i v a r i a t e methods: How v a l i d are p r i n c i p a l components? Am. J . Phys. Anthrop. 54:25, 1981. 125. Navajas, D., Farre, R., Rotger, M.M., M i l i c - E m i l i , J . , and Sanchis, J . E f f e c t of body posture on r e s p i r a t o r y impedance. J . Appl. P h y s i o l . 64(1):194, 1988. 12 6. Okeson, J.P. F u n c t i o n a l neurotomy and physiology of the masticatory system:27, Chapter 2, In Management of temporomandibular d i s o r d e r s and o c c l u s i o n , 2nd e d i t i o n , Mosby, 1989. 127. Onal, E., Lopata, M., and O'connor, T.D. Diaphragmatic and g e n i o g l o s s a l electrogram responses t o C02 r e b r e a t h i n g i n humans. J . Appl. P h y s i o l . 50(5):1052, 1981. 128. Orem, J.M. R e s p i r a t o r y neuronal a c t i v i t y i n sleep:19, Chapter 2, In Breathing Disorders of Sleep, e d i t e d by Edelman, N.H. and Santiago, T.V., 1986. 129. Pae, E., Lowe, A.A., S a t o s h i , A., and Fleetham, J.A. Radiographic comparisons of tongue, airway and s o f t p a l a t e s i z e . Abs. J . Dental Res.68:185, 1989. 13 0. P a r i s i , R.A. and Neubauer, J.A. C o n t r o l of b r e a t h i n g d u r i n g sleep:45, Chapter 3, In Breathing Disorders of sleep, e d i t e d by Elderman, N.H. and Santiago, T.V., 1986. 131. P a r i s i , R.A., Neubauer, J.A., Frank, M.M., Edelman, N.H., and Santiago, T.V. C o r r e l a t i o n between g e n i o g l o s s a l and diaphragmatic responses t o hypercapnia during sleep. Am. Rev. R e s p i r . Dis. 135:378, 1987. 132. P a r i s i , R.A., Santiago, T.V., and Edelman, N.H. G e n i o g l o s s a l and diaphragmatic EMG responses t o hypoxia during sleep. Am. Rev. Respir. Dis. 138:610, 1988. 133. P r o f f i t , W.R., Kydd, W.L., W i l s k i e , G.H. and T a y l o r , D.T. I n t r a - o r a l pressures i n a young a d u l t samples. J . Dental Res. 43:555, 1964. 134. P r o f f i t , W.R., Fogle, J.L., H e i t l i n g e r , L.W., C h r i s t i a n s e n , R.L., and McGlone, R.E. Dynamic c a l i b r a t i o n of l i n g u a l pressure transducers. J . Appl. P h y s i o l . 21(4):1417, 1966. 127 135. Pruzansky, S. The c o n t r i b u t i o n of roentgenographic cephalometry to the study of c o n g e n i t a l and aquired malformations of the face. D. C l i n , of North America, 395,1960. 136. Remington, R.D. and Schork, M.A. The a n a l y s i s of v a r i a n c e : 275, Chapter 10, In S t a t i s t i c s w i t h A p p l i c a t i o n s t o the B i o l o g i c a l and Health Sciences. 2nd e d d i t i o n , 1985. 137. Remmers, J.E., deGroot, W.J., and Sauerland, E.K. Upper airway o b s t r u c t i o n during sleep: Role of the genioglossus. Abs. C l i n i c a l Research 24:33A, 1976. 13 8. Remmers, J.E., deGroot, W.J., Sauerland, E.K., and Anch, A.M. Pathogenesis of upper airway o c c l u s i o n during sleep. J . Appl. P h y s i o l . 44(6):931, 1978. 139f. R i c k e t t s , R.M. R e s p i r a t o r y o b s t r u c t i o n s and t h e i r r e l a t i o n t o tongue posture. C l e f t P a l a t e B u l l . 8 : 4 , 1958. 140. R i c k e t t s , R.M. The f u n c t i o n a l d i a g n o s i s of malocclusion. Eur. Orhtod. S o c i . Report of the 34th congress, 42, 1958. 141. R i l e y , R., G u i l l e m i n a u l t , C., Herran, J , and Powell, N. Cephalometric analyses and flow-volume loops i n o b s t r u c t i v e sleep apnea p a t i e n t s . Sleep, 6(4):303, 1983. 142. R i v l i n , J . , H o f f s t e i n , V., K a l b f l e i s c h , J . , McNicholas, W., Zamel, J . , and Bryan, A.C. Upper airway morphology i n p a t i e n t s w i t h i d i o p a h t i c o b s t r u c t i v e sleep apnea. Am. Rev. R e s p i r . Dis. 129:355, 1984. 14 3. Roberts, J.L., Reed, W.R., and Thach, B.T. Pharyngeal a i r w a y - s t a b i l i z i n g f u n c t i o n of sternohyoid and s t e r n o t h r o i d muscles i n the r a b b i t . J . Appl. P h y s i o l . 57(6):1790, 1984. 144. Rodenstein, D.O., Thomas, Y., L i i s t r o , G., Dooms, G., Aubert-Tulkens, G. and Stanescu, D.C. Pharyngeal shape and s i z e i n snoring and sleep apnea. Abs. Am. Rev. R e s p i r . Dis. 139(4) :A373, 1989 . 145. Romanes, G.J. Head and neck and b r a i n v o l . 3:108, In Cunningham's Manual of P r a c t i c a l Anatomy, 14 e d i t i o n , Oxford press, 1979. 146. R u b i n s t e i n , I . , c o l a p i n t o , N., R o t s t e i n , L.E., Brown, I.G., and H o f f s t e i n , V. Improvement i n upper airway f u n c t i o n a f t e r weight l o s s i n p a t i e n t s w i t h o b s t r u c t i v e sleep apnea. Am. Rev. Respir. Dis. 138:1192, 1988. 128 147. Sandham, A., R e p e a t a b i l i t y of head posture recordings from l a t e r a l cephalometric radiographs. B r i t i s h J . Orthod. 15:157, 1988. 148. Sandler, P.J. R e p r o d u c i b i l i t y of cephalometric measurements. B r i t i s h J . Orthod. 15:105, 1988. 149. Sauerland, E.K. and M i t c h e l l , S.P. Electromyographic a c t i v i t y of i n t r i n s i c and e x t r i n s i c muscles of the human tongue. Texas R. on B i o l , and Med. 33(3):445, 1975. 150. Sauerland, E.K. and Harper, R.M. The human tongue during sleep: Electromyographic a c t i v i t y of the geniogiossus muscle. Experimental Neurology 51:160, 1976. 151. Sauerland, E.K., Sauerland, B.A.T., Orr, W.C, and H a i r s t o n , L.E. Non-invasive electromyography of human g e n i o g l o s s a l (tongue) a c t i v i t y . Electromyogr. c l i n . Neurophysiol. 21:279, 1981. 152. Savage, A.W., Showfety, K.J., and Yancey, J . Repeated measures a n a l y s i s of g e o m e t r i c a l l y constructed and d i r e c t l y determined cephalometric p o i n t s . Am. J . Orthod. Orthop. 91(4):295, 1987. 153. S c a r d e l l a , A.T., Co, M.A., P e t r o z z i n o , J . J . , Krawciw, N., Elderman, N.H., and Santiago, T.V. Strength and endurance c h a r a c t e r e s t i c s of the normal human geniogiossus. Abs. Am. Rev. R e s p i r . Dis. 139(4):A449, 1989. 154. Scharf, S.M. Influence of sleep s t a t e and br e a t h i n g on c a r d i o v a s c u l a r f u n c t i o n . Chapter 6:22, In Sleep and Breathing Eddited by Saunders N.A. and S u l l i v a n , C.E., 1984. 155. Schor, R.H., Kearney, R.E., and D i e r i n g e r , N. R e f l e x s t a b i l i z a t i o n of the head:141, Chpter 12, In Co n t r o l of Head Movement Oxford univ. press, 1988. 156. Schwartz, A.R., Smith, P.L., Wise, R.A., Gold, A.R., and Permutt, S. Induction of upper airway o c c l u s i o n i n s l e e p i n g i n d i v i d u a l s w i t h subatmospheric nasal pressure. J.Appl. P h y s i o l . 64(2):535, 1988. 157. Showfety, K.J., V i g . P.S., and Matteson, S. A simple method f o r t a k i n g n a t u r a l - h e a d - p o s i t i o n cephalograms. Am. J . Orthod. 83:459, 1983. 158. Siersbaek-Nielsen, S. and Solow, B. I n t r a - and interexaminer v a r i a b i l i t y i n head posture recorded by den t a l a u x i l i a r i e s . Am. J . Orthod. 82(1):50, 1982. 129 159. S i e k e r , H.O., Heyman, A., and B i r c h f i e l d , R.I. The e f f e c t s of n a t u r a l sleep and hypersomnolent s t a t e s on r e s p i r a t o r y f u n c t i o n . Ann. of I n t . Med. 52:1, 1960. 160. Singh, B. Sleep apnea: A p s y c h i a t r i c perspective:403, C h a p t e r l l , In Sleep anf Breathing, e d i t e d by Saunders N.A. and S u l l i v a n , C.E., 1984. 161. Smith, P.L., Wise, R.L., Gold, A.R., Schwartz, A.R., and Permutt, S. Upper airway pressure-flow r e l a t i o n s h i p s i n o b s t r u c t i v e sleep apnea. J . Appl. P h y s i o l . 64(2):789, 1988. 162. Solow, B. Computers i n cephalometric research. Comput. B i o l . Med. 1:41, 1970. 163. Solow, B. and T a l l g r e n , A. Head posture nad c r a n i o f a c i a l morphology. Am. J . Phys. Anthrop. 44:417, 1976. 164. Solow, B. and Greve, E. C r a n i o c e r v i c a l a n g u l a t i o n and nasal r e s p i r a t o r y r e s i s t a n c e : 8 7 , In McNamara JA J r . ( e d i t o r ) : N a s o - r e s p i r a t o r y f u n c t i o n and c r a n i o f a c i a l growth. Ann Arbor, Univ. of Michigan, 1979. 165. Solow, B., Siersbaek-Nieisen, S., and Greve, E. Airway adequacy, head posture, and c r a n i o f a c i a l morphology. Am. J . Orthod. 86(3):214, 1984. 166. Spann, R.W. and Hyatt, R.E. Factors a f f e c t i n g upper airway r e s i s t a n c e i n conscious man. J . Appl. P h y s i o l . 31(5):708, 1971. 167. St.John, W.M., Knuth, K.V., and R i s t , K.E. Dynamic changes of hypoglossal and phrenic a c t i v i t i e s by hypoxia and hypercapnia. R e s p i r a t i o n Physiology 56:237, 1984. 168. S t a u f f e r , J.L., Z w i l l i c h , C.W., Cadieux, R.J., B i x l e r , E.O., Kales, A., Varano, L.A., and White, D.P. Pharyngeal s i z e and r e s i s t a n c e i n o b s t r u c t i v e sleep apnea. Am. Rev. R e s p i r . Dis. 136:623, 1987. 169. S t e i n , M.G., Gamsu, G., deGeer, G. , Golden, J.A., Crumley, R.L., and Webb, W.R. Cine CT i n o b s t r u c t i v e sleep apnea. A.J.R. 148:1069, 1987. 170. Stepovich, M.L. A cephalometric p o s i t i o n a l study of the hyoid bone. Am. J . Orthod. 51(12):882, 1965. 171. Strelzow, V.V., Blanks, R.H.I., B a s i l e , A., and Strelzow, A.E. Cephalometric airway a n a l y s i s i n o b s t r u c t i v e sleep apnea syndrome. Laryngoscope 98:1149, 1988. 130 172. S t r o h l , K.P. C o n t r o l of the upper airway during sleep:115, Chapter 6, In Breathing Disorders of sleep, e d i t e d by Elderman, N.H. and Santiago, T.V., 1986. 173. S t r o h l , K.P., Cherniack,N.S., and Gothe, B. P h y s i o l o g i c b a s i s of therapy f o r sleep apnea. Am. Rev. R e s p i r . Dis. 134:791, 1986. 174. S t r o h l , K.P. and Olson, L.G. Concerning the importance of pharyngeal muscles i n the maintenance of upper airway patency during sleep. Chest 92(5):918, 1987. 175. S u l l i v a n , C.E., I s s a , F.G., Berthon-Johnes, M., and Eves, L. Reversal of o b s t r u c t i v e sleep apnoea by continuous p o s i t i v e airway pressure a p p l i e d through the nares. The Lancet 18:862, 1981. 176. S u l l i v a n , C.E., Saunders, N.A., I s s a , F.G., and Berthon- Johnes, M. Pathophysiology of sleep apnea:299, Chapter 9, In Sleep and Breathing, e d i t e d by Saunders, N.A. and S u l l i v a n , C.E., 1984. 177. S u r a t t , P.M., Dee, P., Atkinson, R.L., Armstrong, P., and W i l h o i t , S.C. F l u o r o s c o p i c and computed tomographic fea t u r e s of the pharyngeal airway i n o b s t r u c t i v e sleep apnea. Am. Rev. R e s p i r . Dis. 127:487, 1983. 178. S u r a t t , P.M., McTier, R.F., and W i l h o i t , S.C. C o l l a p s i b i l i t y of the Nasopharyngeal airway i n o b s t r u c t i v e sleep apnea. Am. Rev. R e s p i r . Dis. 132:967, 1985. 179. S u r a t t , P.M., McTier, R.F., F i n d l e y , L . J . , Pohl, S.L., and W i l h o i t , S.C. Changes i n br e a t h i n g and the pharynx a f t e r weight l o s s i n o b s t r u c t i v e sleep apnea. Chest 92(4):631, 1987 180. S u r a t t , P.M., McTier, R.F., and W i l h o i t , S.C. Upper airway muscle a c t i v a t i o n i s augmented i n p a t i e n t s w i t h o b s t r u c t i v e sleep apnea compared wi t h t h a t i n normal s u b j e c t s . Am. Rev. R e s p i r . Dis. 137:889, 1988. 181. T a l l g r e n , A. and Solow, B. Hyoid bone p o s i t i o n , f a c i a l morphology and head posture i n a d u l t s . Eur. J . of Orthod.9:1, 1987. 182. T a s s i n a r i , CA., Dalla-Bernardina, B, C i r i g n o t t a , F. and Ambrosetto, G. Apneic p e r i o d and r e s p i r a t o r y r e l a t e d a r o u s a l p a t t e r n s during sleep i n P i c k w i k i a n syndrome: A p o l y g r a p h i c study. B u l l . P h ysio-pathol. R e s p i r . 8:1087, 1972 . 131 183. Teeter, J.P., S t r o h l , K.P., and Fouke, J.M. Comparison of volume changes i n the upper airway and thorax. J . Appl. P h y s i o l . 62(1):284, 1987. 184. Tsuchiya, M., Takada, K., and Sakuda, M. The r e l i a b i l i t y of moire topography f o r f a c i a l measurement. J . Japan Orthod. Soc. 44 (3) :493, 1985. 185. Van de Graaff, W.B., G o t t f r i e d , S.B., M i t r a , J . , Van Lunteren, E., Cherniack, N.S., and S t r o h l , K.P. R e s p i r a t o r y f u n c t i o n of hyoid muscles and hyoid arch. J . Appl. P h y s i o l . 57(1):197, 1984. 186. Van de Graaff, W.B. Influence of passive changes i n t h o r a c i c volume on upper airway patency. Abs. Am. Rev." R e s p i r . Dis. Suppl. 137(4):125, 1988. 187. Van Ludteren, E. , S t r o h l , K.P., Parker, D.M., Bruce, E.N., Van de Graaff, W.B., and Cherniack, N.S. Phasic volume- r e l a t e d feedback on upper airway muscle a c t i v i t y . J . Appl. P h y s i o l . 56(3):730, 1984. 188. Van Lunteren, Van de Graaff, W.B., Parker,D.M., M i t r a , J . , Haxhiu, M.A., S t r o h l , K.P., and Cherniack, N.S. Nasal and l a r y n g e a l r e f l e x responses t o negative upper airway pressure. J . Appl. P h y s i o l . 56(3):746, 1984. 189. Van Lunteren, E. and S t r o h l , K.P. The muscles of the upper airways. C l i n i c s i n Chest Medicine 7(2):171, 1986. 190. Van Lunteren, E., Haxhiu, M.A., and Cherniack, N.S. Mechanical f u n c t i o n of hyoid muscles during spontaneous breat h i n g i n c a t s . J . Appl. P h y s i o l . 62(2):582, 1987. 191. Van Lunteren, E., Haxhiu, M.A., and Cherniack, N.S. R e l a t i o n between upper airway volume and hyoid lenghth. J . Appl. P h y s i o l . 63(4):1443, 1987. 192. V i g , P.S., Showfety, K.J., and P h i l l i p s , C. Experimental manipulation of head posture. Am. J . Orthod., 77:258, 1980 . 193. Vincent, N.J., Knudson, R., L e i t h , D.E., Macklem, P.T., and Mead, J . Factors i n f l u e n c i n g pulmonary r e s i s t a n c e . J . Appl. P h y s i o l . 29(2) :236, 1970. 194. Vincken, W., G u i l l e m i n a u l t , C., S i l v e s t r i , L., Cosio, M., and Grassino, A. I n s p i r a t o r y muscle a c t i v i t y as a t r i g g e r causing the airways to open i n o b s t r u c t i v e sleep apnea. Am. Rev. Respir. Dis. 135:372, 1987. 132 195. Weiner, D., M i t r a , J . , Salamone, J . , and Cherniack E f f e c t of chemical s t i m u l i on nerves supplying upper airway muscles. J . Appl. P h y s i o l . 52(2):530, 1982. 196. Wiley, J . and sons In I n t e r n a t i o n a l D i c t i o n a r y of Medicine and Biology i n Three Volumes. A Wiley Med. P u b l i c , 1986. 197. Wilson, D.O., Rogers, R.M., Wright, E.C., and Anthonisen, N.R. Body weight i n c h r o n i c o b s t r u c t i v e pulmonary disease. Am. Rev. Respir. Dis. 139:1435, 1989. 198. Winnberg, A. Suprahyoid biomechanics and head posture. Swed. Dent. J . Suppl. 46:36-38, 117, 1987. 199. Winnberg, A., Pancherz, H. , and Westesson, P. Head posture and hyo-mandibular f u n c t i o n i n man. Am. J . Orthod. Dentofac. Orthop. 94(5):393, 1988. 200. W i t t e l s , E.H. Obesity and hormonal f a c t o r s i n sleep and sleep apnea. Med. c l i n . of North Am. 69(6):1265, 1985. 2 01. Woodside, D. and Linder-Aronson, The c h a n n e l i z a t i o n of upper and lower a n t e r i o face heights compared t o p o p u l a t i o n standards i n males between ages 6 to 2 0 years. Eur. J . Orthod. 1:25, 1979. 133

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
United States 7 2
China 2 0
Canada 1 1
Turkey 1 0
Brazil 1 0
City Views Downloads
Mountain View 6 2
Beijing 2 0
Unknown 2 1
Brampton 1 1
Ashburn 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items