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

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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  degree freely  at the  this  thesis  in  University of  available for reference  copying  of  department  this thesis for or  by  his  or  partial  fulfilment  of  the  British Columbia, I agree and study. I further  representatives.  that the  It  is  granted  Department  of  C l i n i c a l Dental  The University of British Columbia Vancouver, Canada Date O c t .  DE-6 (2/88)  13,  1989  Sciences  an  advanced  Library shall make  by the  understood  publication of this thesis for financial gain shall not be allowed permission.  for  agree that permission for  scholarly purposes may be her  requirements  that  it  extensive  head of copying  my or  without my written  r  ABSTRACT  Airway  obstruction  in  p a t i e n t s i s b e l i e v e d t o occur  Obstructive i n the  Sleep  supine  Apnea  (OSA)  p o s i t i o n during  s l e e p . I n o r d e r t o i n v e s t i g a t e t h e r e l a t i o n s h i p between upper airway  s i z e and g e n i o g l o s s u s ( G G ) 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 p o s t u r e )  and s u p i n e cephalograms were o b t a i n e d f o r  twenty OSA and t e n asymptomatic c o n t r o l s u b j e c t s . Tongue EMG pressure  r e c o r d i n g s were o b t a i n e d w i t h t h e s u r f a c e  and p r e s s u r e t r a n s d u c e r s  and  electrodes  i n t e n asymptomatic c o n t r o l s u b j e c t s .  The S t u d e n t ' s t t e s t and W i l c o x o n s i g n e d rank t e s t were used t o test  f o r d i f f e r e n c e s between t h e two  groups and  between body  positions. The OSA soft  palate  vertically  group r e v e a l e d  a l o n g e r tongue (p< 5%), a l a r g e r  (p<  anteroposteriorly  1%),  lengthened  an upper  airway  (p<  1%) ,  narrower a  inferiorly  p o s i t i o n e d h y o i d bone (p< 1%), a more extended head p o s t u r e 5%)  and a s m a l l e r hypopharynx (p< 1%)  position.  After  changing  from  the  i n the u p - r i g h t up-right  to  the  p o s i t i o n , t h e tongue 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 4.3% and 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 3 6.5%  (p< 1%)  and  i n t h e OSA  (p<  standing supine (p<  5%)  group.  When comparing t h e s u p i n e t o t h e u p - r i g h t c o n t r o l cephalograms, changes i n tongue area were not o b s e r v e d , but t h e t h i c k n e s s of t h e s o f t p a l a t e i n c r e a s e d (p< 1%) . D i f f e r e n c e s i n tongue c r o s s -  ii  s e c t i o n a l a r e a between two groups become s i g n i f i c a n t w i t h body positional  changes  from t h e u p - r i g h t t o t h e s u p i n e (p< 1%) .  W i t h body p o s i t i o n a l changes, t h e h y o i d bone moves s u p e r i o r l y toward t h e m a n d i b u l a r p l a n e i n t h e c o n t r o l group  (p< 1%), b u t  a n t e r i o r l y toward t h e m a n d i b u l a r symphysis i n t h e OSA group (p< 5%) . The r e s t EMG a c t i v i t y o f t h e GG muscle i n c r e a s e d 33.8% (p< 5%) and t h e p o s t e r i o r tongue p r e s s u r e  i n c r e a s e d 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 s u p i n e . O v e r a l l , t h e o r o p h a y n g e a l c r o s s - s e c t i o n a l a r e a c o l l a p s e d 28.8% (p< 1%) d e s p i t e a 34% i n c r e a s e asymptomatic  control  (p< 5%) i n GG muscle a c t i v i t y  group  as a r e s u l t  o f body  i n the  positional  changes. F u r t h e r m o r e , a 17% i n c r e a s e o f tongue p r e s s u r e on t h e p o s t e r i o r l o a d c e l l i n d i c a t e s p o s i t i o n a l change o f t h e tongue. I n c o n c l u s i o n , i t may n o t be t h e s i z e o f t h e s o f t p a l a t e a l o n e b u t a l s o t h e 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 o f t h e tongue w h i c h c o u l d a c t i v e l y OSA.  Quantification  c o n t r i b u t e t o t h e development o f  of subtle  o r o p h a r y n g e a l s i z e and p o s i t i o n ,  differences geometry  i n tongue  of the hyoid  and bone,  upper a i r w a y muscle a c t i v i t y and tongue p r e s s u r e accompanied by body  positional  changes  p a t h o g e n e s i s o f OSA.  aids  i n our understanding o f the  TABLE OF CONTENTS PAGE L i s t of Tables  v i i  L i s t of Figures  viii  Acknowledgements I.  ix  Introduction A. What i s s l e e p apnea?  1  B. P a t h o g e n e s i s o f O b s t r u c t i v e S l e e p Apnea  4  1] Overview o f pathogeneses  5  2] P r e d i s p o s i n g f a c t o r s  6  a. S l e e p  6  b. A n a t o m i c a l 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. B i o m e c h a n i c a l r e l a t i o n s h i p between p o s t u r e and a i r w a y adequacy  20  1] Head p o s t u r e  20  2] Body p o s t u r e  22  II.  Statement o f Problem  24  III.  Methods A. E x p e r i m e n t a l s u b j e c t s  iv  26  PAGE B.  Experimental 1]  procedures  Cephalometric  study  a.  Lateral  b.  D e f i n i t i o n s and r a t i o n a l e planes,  cephalograms  angulations,  measurements  c. 2]  28  of  a r e a s and  their  "  36  Hard-tissue  landmarks  36  2.  Soft-tissue  landmarks  40  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  T r a c i n g and d i g i t i z a t i o n  50  study  Data a q u i s i t i o n system  and  recording  technique  C.  landmarks,  1.  EMG and p r e s s u r e a.  28  51  b.  E q u i p m e n t and d a t a p r o c e s s i n g  57  c.  Experimental  59  Statistical  method  procedure  62  v  IV.  V.  Results A. R e l i a b i l i t y t e s t s f o r t h e methods  65  B. C e p h a l o m e t r i c s t u d y  73  C. EMG  81  and p r e s s u r e s t u d y  Discussion A. C e p h a l o m e t r i c s t u d y B. EMG  88  and p r e s s u r e s t u d y  100  C. Overview  112  D. P i t f a l l s and f u t u r e s t u d y  113  VI.  Summary  115  VII.  Bibliography  117  vi  LIST OF TABLES  TABLE  PAGE  I  Demographic V a r i a b l e s f o r t h e E x p e r i m e n t a l S u b j e c t s  II  R e l i a b i l i t y o f t h e S o f t - t i s s u e M e a s u r i n g Techniques  27  and an Example o f t h e C a l c u l a t i o n o f t h e Houston's Reliability III  Index  68  R e p r o d u c i b i l i t y S t u d i e s o f N a t u r a l Head P o s i t i o n and Measurement  IV  70  Comparison o f OSA and Asymptomatic C o n t r o l s i n U p - r i g h t and Supine C e p h a l o m e t r i c P o s i t i o n s  V  74  Comparison o f U p - r i g h t and Supine Cephalograms i n OSA and Asymptomatic C o n t r o l s  76  VI  ANCOVA t e s t o f t h e Age E f f e c t on t h e H y o i d V a r i a b l e s 79  VII  Comparison o f t h e EMG and P r e s s u r e o f t h e Tongue between U p - r i g h t and Supine P o s i t i o n s i n Asymptomatic C o n t r o l s  VIII  L i n e a r and A r e a V a r i a b l e Comparisons Between R e p o r t and Other S t u d i e s  vii  82 Current 90  LIST OF FIGURES  1  Measurement o f Head P o s t u r e w i t h t h e M o d i f i e d F l u i d L e v e l Device  2  29  Schematic Diagrams t o I l l u s t r a t e Assembly o f t h e M o d i f i e d F l u i d L e v e l Device  33  3  Photograph o f t h e Supine C e p h a l o m e t r i c P r o c e d u r e  35  4  C e p h a l o m e t r i c Hard T i s s u e Landmarks  39  5  C e p h a l o m e t r i c S o f t T i s s u e Landmarks  43  6  C e p h a l o m e t r i c L i n e a r Measurements  46  7  C e p h a l o m e t r i c A n g u l a r and Area Measurements  49  8  Schematic I l l u s t a t i o n s o f t h e S u r f a c e E l l e c t r o d e s f o r t h e M a s s e t e r , S u p r a - h y o i d and O r b i c u l a r i s O r i s M u s c l e s , and t h e I n t r a o r a l A p p l i a n c e  52  9  P r e s s u r e T r a n s d u c e r 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  F l o w - c h a r t f o r Data A q u i s i t i o n  58  12  Tray Used t o Measure t h e B a s e - l i n e P r e s s u r e o f t h e Tongue  13  61  R e l a t i o n s h i p between L e v e l Device A n g l e and t h e FH/True H o r i z o n t a l C e p h a l o m e t r i c A n g l e  14  RE:  72  Tongue EMG and P r e s s u r e Changes a t R e s t i n U p - r i g h t and Supine P o s i t i o n s  84  P a t i e n t I n s t r u c t i o n Used f o r C u r r e n t Study  31  viii  ACKNOWLEDGEMENT  The a u t h o r i s a p p r e c i a t i v e o f t h e s u g g e s t i o n s p r o v i d e d by Dr. C. P r i c e a t t h e commencement o f t h i s s t u d y .  Also, this  s t u d y was d e s i g n e d  and Dr. J .  w i t h Dr. K. S a s a k i ' s guidance  Fleetham's d i r e c t i o n . Scott  I w i s h t o e x p r e s s my g r a t i t u d e t o Ms. J .  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. T s u c h i y a ' s s u g g e s t i o n s and comments improved the  text.  Dr. B. M o r r i s o n  s t a t i s t i c a l anaysis.  provided  suggestions  about t h e  Above a l l , I am g r e a t l y i n d e b t e d t o Dr.  A. Lowe f o r h i s guidance, s u p p o r t , and t h e o r g a n i z a t i o n o f t h i s study i n a l l aspects.  F i n a l l y , I thank my w i f e and c h i l d r e n ,  Joseph and C a n d i c e , f o r t h e i r p a t i e n c e and p r a y e r . T h i s r e s e a r c h was f i n a n c i a l l y s u p p o r t e d by MRC g r a n t MA3849 t o Dr. A. Lowe and by a UBC Graduate F e l l o w s h i p .  ix  INTRODUCTION  It become  i s only  concerned  recently that with  the  the f i e l d  obstructive  o f d e n t i s t r y has  sleep  apnea  (OSA)  syndrome. However, OSA i s no l o n g e r an unknown i n t h e f i e l d o f dental research.  F a m i l i a r i t y w i t h t h i s syndrome has  increased  not o n l y because o f i t s h i g h r a t e o f i n c i d e n c e b u t a l s o because o r t h o d o n t i s t s and o r a l  surgeons a r e b e g i n n i n g  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 t h e use o f i n t r a o r a l d e v i c e s and/or o r t h o g n a t h i c s u r g e r y . I t has been suggested t h a t OSA may be one o f t h e most p r e v a l e n t d i s e a s e s 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 s u g g e s t s  in  a prevalence rate  of 0.89% as a l o w e r l i m i t i n t h e a d u l t male p o p u l a t i o n 1983).  modern  (Lavie,  I n s p i t e o f t h e remarkable amount o f r e s e a r c h t h a t has  been done i n t h i s f i e l d i n t h e l a s t decade, t h e 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 s l e e p apnea ? An apnea i s d e f i n e d as a c e s s a t i o n o f a i r f l o w a t t h e  nose and mouth f o r more t h a n 10 seconds ( G u i l l e m i n a u l t e t a l . , 1975).  According  to Tassinari et al.(1972),  apnea have been d e f i n e d . as  three  types of  The f i r s t , c e n t r a l apnea i s d e f i n e d  t h e complete a r r e s t o f r e s p i r a t i o n 1  f o r 5-10  seconds. The  second, o b s t r u c t i v e apnea i s d e f i n e d as an i n t e r r u p t i o n of airflow  f o r 10  to  60  seconds w h i l e  the  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. t h i r d type,  complex apnea i s d e f i n e d  apnea f o r 5-10 apnea.  seconds f o l l o w e d  According  order  never  hypopnea as  as an e p i s o d e of c e n t r a l an e p i s o d e o f  obstructive  t o G u i l l e m i n a u l t et a l . ( 1 9 7 5 ) , the  seems an  by  to  occur.  Guilleminault  i n c o m p l e t e form of  The  reverse  (1985)  defined  apnea w h i c h i s i n d u c e d  d e c r e a s e d d i a p h r a g m a t i c e f f o r t and  partial  o b s t r u c t i o n of  by the  airway. There a r e sleep  apnea.  several The  ways of  Apnea Index  number o f apnea i n c i d e n t s per 60. as  describing  the  (Al) i s d e f i n e d  total  sleep  severity as  the  of  total  time m u l t i p l i e d  by  G u i l l e m i n a u l t e t a l . ( 1 9 8 7 ) suggested an Apnea Index of 5 the  upper  limit  of  normality.  The  RDI  (Respiratory  D i s t u r b a n c e Index) i s a n o t h e r i n d e x measuring t h e s l e e p apnea and In  named Joe  i s d e f i n e d as t h e Apnea p l u s Hypopnea Index.  his  Club"(1837),  book  Charles  who  "Posthumous  Papers  Dickens described  an  of  the  Pickwick  extremely  s u f f e r e d from p e r s i s t e n t somnolence.  S i r William Osier obese and  s e v e r i t y of  coined  the  term " P i c k w i c k i a n " ,  hypersomnolent p a t i e n t s  (Burwell,  fat In  boy 1918,  to r e f e r to  1956).  Several  s t u d i e s r e v i e w e d t h e symptoms of the P i c k w i c k i a n syndrome.  In  1964,  of  Gastaut  and  his  associates  reported  the  r e p e t i t i v e o b s t r u c t i v e apnea d u r i n g s l e e p i n t h e patient.  In  1966,  the  same 2  group  evaluated  presence  "Pickwickian" the  sleep,  r e s p i r a t i o n and b l o o d gas c h e m i s t r y o f t h e p a t i e n t by means o f polygraphic of  r e g i s t r a t i o n . They measured EEG, s p i r o g r a m and EMG  d i a p h r a g m a t i c and m y l o h y o i d muscle a c t i v i t y ,  hypothesized  t h e p a t h o g e n e s i s o f o b s t r u c t i v e s l e e p 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 was  first  used  apnea. The term  i n 1971 by Kumashiro  'sleep  et a l . .  apnea'  I n 1972,  G u i l l e m i n a u l t e t 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 s l e e p apnea b o t h from  the Pickwickian  syndrome  and from  f o l l o w i n g year(1973), they reported as a new syndrome and f i n a l l y  narcolepsy.  In the  i n s o m n i a w i t h S l e e p Apnea  named i t s l e e p apnea syndrome.  OSA i s p r e d o m i n a n t l y a d i s e a s e o f obese m i d d l e aged men, y e t i s l e s s known i n obese women o r c h i l d r e n . R e g a r d l e s s o f t h e age o r sex o f t h e s u f f e r e r , s n o r i n g i s c o n s i d e r e d sign  of sleep  patterns and  apnea.  Patients  may  present  the cardinal  restless  sleep  such as t u r n i n g , t o s s i n g , f l a i l i n g o f t h e e x t r e m i t i e s  even  sleep  walking.  Some  s e n s a t i o n o f c h o k i n g o r gagging.  patients  may  complain  of a  G u i l l e m i n a l t (1987) o b s e r v e d  esophageal r e f l u x i n a number o f 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 early or  m i d d l e s t a g e s o f t h e development o f t h e d i s e a s e ,  i n s o m n i a may  be observed;however, e x c e s s i v e daytime s l e e p i n e s s and/or f a t i g u e is  another  patient  hallmark  falls  asleep  symptom while  o f OSA. I n extreme  talking,  eating  cases, the  and even d r i v i n g .  D e t e r i o r a t i o n o f t h e memory, d i s o r i e n t a t i o n , morning and hypnogogic h a l l u c i n a t i o n s were r e p o r t e d hypersomnolence.  Occasionally, 3  a  confusion  as s i d e - e f f e c t s o f  hyponasal  voice,  noisy  breathing  and mouth b r e a t h i n g  In  1960,  are  noticed.  hemodynamic a b n o r m a l i t i e s  i n extremely  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 .  obese  Burwell  et  a l . ( 1 9 5 6 ) p r e s e n t e d a c o m p a r a t i v e hemodynamic s t u d y between t h e reduced w e i g h t s t a t e t o 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 i s w e l l documented by s e v e r a l r e s e a r c h e r s and  Phillipson  develop vagal  1985).  polycythemia,  bradycardia  and  system  (Scharf,1984).  during  the  obstructive  ( B r a d l e y 1988,  H y p o x i a , hypercapnea and systemic  hypertension,  nocturnal  cardiac  hemodynamic e f f e c t o c c u r s m e c h a n i c a l l y Decreased apneic period  function Bradley  acidosis  cor  pulmonale,  arrhythmia. i n the  may  Another  cardiovascular  intra-thoracic  pressure  creates  negative  large  l o a d s i n t h e p l e u r a l c a v i t y , which i n c r e a s e s t h e venous r e t u r n t o t h e r i g h t v e n t r i c l e , and may  B.  P a t h o g e n e s i s of As  result i n cardiac  OSA  mentioned p r e v i o u s l y , OSA  complex phenomenon. A t  l e a s t three  i n v o l v e d i n t h e p a t h o g e n e s i s of OSA: and  upper  airway  malfunction.  muscle  function.  is still  an  f a c t o r s are  unclarified, thought t o  be  s l e e p , upper a i r w a y anatomy S u l l i v a n et  r e v i e w e d a number of l e a d i n g t h e o r i e s and has  al.(1984)  suggested t h a t a  b a l a n c e d f o r c e between t i s s u e w e i g h t , muscle t o n e , and  airway  lumen s u c t i o n p r e s s u r e l i k e l y governs t h e p a t h o p h y s i o l o g y of  OSA  syndrome. No one t h e o r y has been a c c e p t e d , a l t h o u g h a l l of them may  c o n t r i b u t e i n p a r t t o t h e p a t h o g e n e s i s of OSA 4  .  1]  Overview I n 1978, Remmers e t a l . undertook an e l a b o r a t e l y d e s i g n e d  s t u d y on humans i n an attempt OSA.  They  between  hypothesized  t h a t an u n c o o r d i n a t e d  genioglossus(GG)  transmural  pressure  t o e x p l a i n the pathogenesis of force  balance  muscle f o r c e and t h e o r o p h a r y n g e a l  causes  pharyngeal  occlusion.  When t h e  p h a r y n g e a l t r a n s m u r a l p r e s s u r e i n c r e a s e s more t h a n t h e GG muscle f o r c e , o c c l u s i o n o f t h e upper a i r w a y may o c c u r .  Sullivan et  a l . ( 1 9 8 4 ) summarized t h a t t h e narrower a i r w a y 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 a i r w a y p a t e n c y . concluded  that  provoking  airway  muscle  airway  suction  o c c l u s i o n ; i . e.  pressure  was  t h e key  of a i r f l o w  area, the  and t h e g r e a t e r t h e  t r a n s m u r a l p r e s s u r e g r a d i e n t f a v o r i n g upper a i r w a y Guilleminault  (1987) e x p l a i n e d t h a t once a i r w a y  o c c u r s due t o t h e 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 anatomic muscle  compliance should  collapse. obstruction  (for instance,  a b n o r m a l i t i e s o f t h e upper a i r w a y , d e c r e a s e d activity,  small  pharyngeal  and i n c r e a s e d upstream  rise.  Increased  Pco  2  force  the greater the inspiratory  f o r c e and t h e s m a l l e r t h e c r o s s - s e c t i o n a l  higher the l i n e a r v e l o c i t i e s  They  cavity,  high  resistance),  t e n s i o n causes  an  pharyngeal  Pco  2  tension  increase i n  d i a p h r a g m a t i c e f f o r t which may r e s u l t i n more n e g a t i v e t h o r a c i c and o r o p h a r y n g e a l p r e s s u r e s .  airway  intra-  As a c o u n t e r f a c t o r t o  the negative f o r c e s 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 forces  o f t h e upper  airway  dilators 5  are c r u c i a l .  Whether  d e t e r m i n e d by a s l e e p r e l a t e d f a i l u r e of t h e upper a i r w a y 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 , t h e characteristics underlying studies  of  the  dilator  muscles  suggest  that  upper  airway  most  higher  than  normal  (Suratt  hemodynamic r e p o r t s of o v e r n i g h t level.  2  I n 1987,  resistance,  i n sleep  Moreover, t h e a i r w a y r e s i s t a n c e i n OSA  a high Pco  the  dominant f a c t o r i n t h e mechanism of OSA.  expiratory resistance, i s increased  be  are  et  Pco  2  threshold  p a t i e n t s i s assumed t o a l . , 1985)  s t u d i e s , i n OSA  and  of  Eye-Movement) s l e e p  2  a t any  p a t i e n t s show  the  GG,  in  They found  comparison  to  the  NREM(Non-Rapid-Eye-  t e n s i o n and d u r i n g p h a s i c REM(RapidC0  tension.  2  They p o s t u l a t e d  t h i s imbalance between t h e GG and t h e diaphragm may t h e upper a i r w a y t o i n s p i r a t o r y o c c l u s i o n d u r i n g  2] P r e d i s p o s i n g  many  P a r i s i and a s s o c i a t e s compared t h e  diaphragm, i s d i s p r o p o r t i o n a l b o t h d u r i n g Movement) s l e e p a t low C0  Several  (Orem, 1986).  2  the  likely  especially  Pco t h r e s h o l d of t h e GG and t h e diaphragm i n g o a t s . that  specific  that  predispose  sleep.  Factors  a. S l e e p Most of t h e p s y c h i a t r i c phenomena t h a t o c c u r i n OSA be e x p l a i n e d  on t h e b a s i s of s l e e p derangement (Singh,  can  1984) .  By d e f i n i t i o n , s l e e p may be c o n s i d e r e d as r e c u r r e n t spontaneous e p i s o d e s of motor q u i e s c e n c e accompanied by of s e n s o r y response (McGrinty  and  raised  Beahm,1984).  On  thresholds the  basis  of e l e c t r o p h y s i o l o g i c a l measurements, mammalian s l e e p i s d i v i d e d 6  i n t o two d i s t i n c t t y p e s : NREM and REM s l e e p . alternate  throughout  the night.  REM and NREM s l e e p  NREM s l e e p ,  c a l l e d slow-wave s l e e p o r s y n c h r o n i z e d  which  i s also  sleep, c o n s i s t s of four  s t a g e s . I n i n f a n t s , REM s l e e p i s a l s o c a l l e d p a r a d o x i c a l s l e e p o r 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 , a b r u p t motor  events,  eye movements o r t w i t c h e s  o f t h e f a c i a l and  e x t r e m i t y muscles (McGrinty and Beahm, 1984). shows a low a m p l i t u d e ,  high freqency(13  Stage 1 NREM s l e e p n o r m a l l y  phasic  The waking stage  t o 3 5 Hz) b e t a wave.  c o n s i s t s o f 5-10% o f t o t a l  sleep  t i m e , and i s a t r a n s i t i o n a l phase between w a k e f u l n e s s and s l e e p . I t i s c h a r a c t e r i z e d by m i x e d - f r e q e n c y a c t i v i t y i n t h e b e t a and t h e t a ( 4 - 7 H z ) waves.  Stage 2 i s marked by t h e appearance o f EEG  s l e e p s p i n d l e s ( i . e . , b u r s t o f 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 - c o m p l e x e s ( w e l l - d e l i n e a t e d , negative  slow,  EEG d e f l e c t i o n s ) . D e l t a s l e e p , t h e deepest s t a g e , i s  d i s t i n g u i s h e d by slow d e l t a waves g r e a t e r t h a n 75juV, peak t o peak. I n REM s l e e p , t h e EEG c o n s i s t s o f mixed f r e q u e n c y , l o w voltage  activity  resembling  stage  1 NREM  sleep.  REM  sleep  p e r i o d s t e n d t o become l o n g e r as s l e e p p r o g r e s s e s and c o n s t i t u t e about 2 0% o f t o t a l s l e e p t i m e i n t h e h e a l t h y a d u l t . REM s l e e p is  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 m a i n t a i n s i t s l o w e s t l e v e l d u r i n g REM s l e e p , t h e e x t r a ocular  muscles  show  rapid,  movements. I n about 8 0%  intermittant,  conjugated  o f wakenings from REM s l e e p ,  eye people  r e c a l l dreams ( H a u r i and O r r , 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) . 7  Phasic  components  within  REM  autonomic v a r i a b i l i t y pressure  w h i c h may  sleep such  greater  as  c h a r a c t e r i z e d by  i n c r e a s e as  much as  high blood  4 0 mmHg  C o n t r a r i l y , d u r i n g t o n i c REM s l e e p , t h e  b l o o d p r e s s u r e a r e more c o n s t a n t and  relaxation  a  i r r e g u l a r h e a r t r a t e and  transiently  (Coccagna e t a l , 1972). h e a r t r a t e and  are  i n most muscles.  Cerebral  there i s  blood  flow  is  g r e a t e r d u r i n g REM t h a n e i t h e r NREM o r w a k e f u l n e s s . R e s p i r a t i o n a l s o seems a l t e r e d d u r i n g REM and  s l e e p . Many upper a i r w a y muscles  i n t e r c o s t a l muscles become h y p o t o n i c whereas t h e diaphragm  maintains  activity  p h a s i c events  and  C0  2  sensitivity  ( S u l l i v a n e t a l , 1979b).  i s lost with  frequent  Loss o f i n t e r c o s t a l  EMG  a c t i v i t y may  l e a d t o p a r a d o x i c a l c o l l a p s e of the chest d u r i n g  inspiration  (Henderson-Smart,  exacerbated  by  1984).  The  i n c r e a s e d upper  tone  significantly  1984).  of  decrease  the  GG  Rib  airway and  d u r i n g REM  'paradox'  resistance  geniohyoid  stage.  s l e e p i s a s s o c i a t e d w i t h a decreased  cage  is  (McGrinty,  muscles  may  I n o t h e r words,  REM  upper a i r w a y patency  and  i n c r e a s e d t r a n s p h a r y n g e a l 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. A n a t o m i c a l  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 a l f u n c t i o n i n p a t i e n t s who have apparent a n a t o m i c a l a n o m a l i e s , pathoses neuromuscular d e f e c t s .  Moran (1987) enumerated  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 c o u l d be patients.  many o f t h e found  in  However, a g r e a t number o f p a t i e n t s s u f f e r i n g  moderate o r l e s s  severe  OSA  symptoms a r e not 8  or  likely  OSA from  t o have  obvious p h y s i c a l d e f i c i e n c i e s , c o i n c i d e n t w i t h o b e s i t y and  except o b e s i t y .  i s often  W i t t e l s (1985)  defined  o b e s i t y as a body w e i g h t a t l e a s t 2 0% above t h e i d e a l .  Obesity  induces  numerous  function.  changes  According  snoring.  OSA  in  pulmonary  and  cardiovascular  t o W i t t e l s , i n t h e case of o b e s i t y , t h e  t o t a l l u n g 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. chest  In a d d i t i o n , the accumulation  w a l l decreases  volume,  chest  compliance.  respiratory resistance  is  of f a t around the  Due  to  the  increased.  low  lung  Because  the  r e s p i r a t o r y work of b r e a t h i n g i s somewhat g r e a t e r t h a n normal, t h e oxygen c o s t i s i n c r e a s e d .  An i n c r e a s e d  c a r d i a c output i s  demanded i n t h e obese p a t i e n t , hence l e f t v e n t r i c u l a r s t r o k e work i s i n c r e a s e d ,  which f i n a l l y  leads  v e n t r i c u l a r e n d - d i a s t o l i c pressure. u n d e r t a k e n by  Grunstein  ANCOVA(Analysis correlation Index),  of  Covariance)  between  blood  snoring  pressure  found w i t h a g i n g .  increased  left  An i n t e r e s t i n g s u r v e y  was  e t al.(1989)  and  and  t o an  i n Western Samoa.  study  revealed  collar  size,  smoking, and  S u r a t t and  a  yet  co-workers  The  significant  BMI(Body  no  Mass  relation  (1987) found  was in a  p r o s p e c t i v e study t h a t moderate w e i g h t l o s s i n obese p a t i e n t s w i t h OSA  improves d i s o r d e r e d b r e a t h i n g d u r i n g b o t h s l e e p  wakefulness.  They  pharyngeal airway the  hypothesized  that  a  narrow  i n awake s u b j e c t s i s an i m p o r t a n t  pathophysiology  of  OSA.  A  i n v e s t i g a t i o n by Horner e t a l . ( 1 9 8 8 )  precisely  collapsible factor in  weight-matched that there  are  no s y s t e m i c d i f f e r e n c e s i n f a t d e p o s i t d i s t r i b u t i o n between  OSA  9  concluded  and  patients  and normal p a t i e n t s , and t h a t t h e r e a r e no s i g n i f i c a n t  f a t d e p o s i t s i m m e d i a t e l y p o s t e r i o r t o t h e a i r w a y i n any o f t h e subjects.  Furthermore,  Rubinstein  p o s t u l a t e d t h a t improvement o f OSA may  and  colleagues  (1988)  symptoms a f t e r w e i g h t  be r e l a t e d t o improvement i n p h a r y n g e a l g l o t t i c  loss  function,  i n o t h e r words, weight  loss results  i n b e n e f i c i a l changes i n  pharyngeal  Furthermore,  L u g a r e s i (1988)  mechanics.  t h a t t h e narrower  and l o n g e r o r o p h a r y n g e a l  and OSA  patients results  efforts  associated with  isthmus  from t h e r e p e a t e d heavy a  downward  stretch  of  supposed  i n snorers inspiratory  the  laryngo-  t r a c h e o - b r o n c h i a l t r e e . They h y p o t h e s i z e d t h a t a l o s s o f even a few kgs o f body weight can r e v e r s e 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 t h e a i r w a y s i z e . Numerous r e s e a r c h e r s have attempted t o measure upper a i r w a y s i z e (Jackson e t a l . , 1980; Lowe e t a l . , 1986; M a r t i n e t a l . , 1987). 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  Several  cephalometry,  CT (Computerized Tomogram) scans, MRI (Magnetic Resonance Imaging) , cineradiography,  nasopharyngoscopy,  f l o w volume c u r v e s .  acoustic reflectance  Among them, CT and MRI  and  c o u l d be used f o r  t h r e e - d i m e n s i o n a l ( 3 D ) r e c o n s t r u c t i o n s (Lowe e t a l . , 1986,1989). Lowe  et  al.  emphasized  the  obvious  d i m e n s i o n a l (2D) methods s i n c e t h e y may 3D  spatial  relationships.  reconstruction  is  In  recommended  this as  limitation  more  3D  CT  reliable  However, such a 3D r e c o n s t r u c t i o n t e c h n i q u e i s 10  two-  not a c c u r a t e l y q u a n t i f y respect,  a  of  or  MRI  method.  time-consuming  and  expensive  f o r routine  clinical  use.  As a  non-invasive  t e c h n i q u e , F r e d b e r g and co-workers(1980) a c t i v e l y adapted t h e acoustic  r e f l e c t i o n t e c h n i q u e f o r measuring a i r w a y  geometry.  D'urzo e t a l . ( 1 9 8 7 ) performed a v a l i d i t y t e s t f o r t h e a c o u s t i c reponse measurement w i t h compatibility.  respect  t o CT, and p r o v e d  The c e p h a l o m e t r i c t e c h n i q u e i s a n o t h e r p r e v 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 . but  also  area  al.(1989)  i t s high  measurement  attempted  have  t o prove  Not o n l y l i n e a r measurement become  feasible.  Pae e t  a c o m p a t i b i l i t y o f 2D  lateral  c e p h a l o m e t r i c t e c h n i q u e t o 3D CT r e c o n s t r u c t i o n , y e t f a i l e d t o demonstrate a h i g h c o r r e l a t i o n between 2D and 3D o f t h e tongue, s o f t p a l a t e and pharynx. Several identify  visualization  the occlusion  identification found  site  are  available  to  CT has been used as a t o o l f o r  of the occlusion  the obstruction  oropharynx.  site.  techniques  site.  mainly  Using fluoroscopy,  Haponik e t a l . ( l 9 8 3 )  a t t h e nasopharynx  Suratt  and a s s o c i a t e s  and  (1983)  o b s e r v e d t h a t t h e o b s t r u c t i o n always b e g i n s d u r i n g i n s p i r a t i o n when t h e s o f t p a l a t e t o u c h e s t h e tongue and p o s t e r i o r p h a r y n g e a l wall.  Chaban e t a l . ( 1 9 8 8 ) developed a t e c h n i q u e based on t h e  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. catheter  They used a movable  p r e s s u r e t r a n s d u c e r l o c a l i z e d by c e p h a l o m e t r i c s and  identified  two  different  obstruction  sites:  the  posterior  p o r t i o n o f t h e s o f t p l a t e and t h e base o f t h e tongue.  By means  of cine-CT s c a n s , Crumley and a s s o c i a t e s o b s t r u c t i o n s i t e and found a d i m i n u t i o n 11  (1987) examined t h e  i n the anteroposterior  d i a m e t e r a f t e r assuming the s u p i n e p o s i t i o n . They presumed t h a t t h e tongue m u s c u l a t u r e appears t o s e t t l e p o s t e r i o r l y under the p u l l o f g r a v i t y i n the c o n f i r m e d Crumley and  supine p o s i t i o n .  S t e i n et  associates' observations  and  al.(1987) 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 a t the u v u l a and  oropharynx m a i n l y .  Hoover e t a l . ( 1 9 8 7 ) r e v i e w e d  the  magnetic resonance imaging t e c h n i q u e o f the l a r y n x and the base of t h e tongue and demonstrated the s u p e r i o r i t y o f t h e MR o f t h e s o f t t i s s u e s t r u c t u r e and of the  s t r e s s e d the  image  non-invasiveness  MRI.  c. F u n c t i o n a l  Factors  As mentioned e a r l i e r , upper a i r w a y muscle f u n c t i o n a l s o p l a y a p r i m a r y r o l e i n the p a t h o g e n e s i s of OSA. OSA  may  As f a r as  i s concerned, the GG has been the most c l o s e l y s t u d i e d upper  a i r w a y muscle i n the l a s t decade. The a s s o c i a t e d w i t h the h y p o g l o s s a l ( X I I )  GG i s a v i r t u a l nucleus.  protrudor  I n a d u l t humans,  t h e GG c o n s i s t s of t h r e e p a r t s : an a n t e r i o r p o r t i o n a t t a c h e d  to  t h e s u p e r i o r t u b e r c l e , a m i d d l e fan-shaped o b l i q u e p o r t i o n which i s attached  by a s e p a r a t e tendon l a t e r a l t o t h a t t u b e r c l e ,  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 a t t a c h e d between the s u p e r i o r and  of  the  hyoid  t o t h e mandible  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  i n f e r i o r p o r t i o n are a t t a c h e d  bone. A h o r i z o n t a l component i n s e r t e d  Bagget,1972).  the  t o the upper a s p e c t of t h e body into  p o s t e r i o r o n e - t h i r d of the tongue i s the main p r o t r u d o r and  and  None of the 12  GG  muscle f i b r e s a r e  the  (Doran inserted  through  apex  Hellstrand,  of  the  1980) .  tongue  tip  Histologically,  (Doran  and  Bagget,  both type  I and  1972;  type I I  f i b r e s a r e i d e n t i f i e d i n t h e 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 I*  and  nomenclature o f t h e human s k e l e t a l muscle,  'type I I ' f i b r e s , a r e based  upon f i b r e  'type  identification  w i t h t h e m y o f i b r i l l a r adenosine t r i p h o s p h a t a s e (ATPase)  reaction  a t PH 9.4. A c c o r d i n g t o E n g e l ( 1 9 7 4 ) , t h e muscle f i b r e s  markedly  p r e d o m i n a t i n g i n t h e r e d muscles a r e t y p e I , whereas t h e f i b r e s occuring exclusively  i n w h i t e muscles  with  tissue,  white  muscle  are type I I .  biochemical  assays  Compared of  tissue  homogenates show t h a t r e d muscle has more m y o g l o b i n , s u c c i n a t e dehydrogenase, ATPase,  and  lactate  cytochrome o x i d a s e , and  dehydrogenase,  has  less  myosine  diphosphopyridine nucleotide-  1 i n k e d a l p h a g l y c e r o p h o s p h a t e dehydrogenase, p h o s p h o r y l a s e  and  m i t o c h o n d r i a l a l p h a g l y c e r o p h o s p h a t e dehydrogenase. A l l t y p e I I fibres  are  fast-twitch  units,  but  some  of  these  are  fast  f a t i g u i n g and o t h e r s a r e f a t i g u e r e s i s t a n t , whereas t y p e I u n i t s a r e a l l s l o w - t w i t c h and f a t i g u e  resistant.  Hellstrand  found t h a t 75-81% o f t h e tongue e x t r i n s i c muscles t y p e I I f i b r e s , whereas t h e d i g a s t r i c type I I f i b r e s  ( M i l l e r and F a r i a s ,  consist  muscle c o n s i s t s  1988).  (1980)  of  I n humans, t h e  of 60% 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 o t h e r mammals such as cats,  r a t s and dogs (Doran, Sauerland  and  1975).  Mitchell  (1970), demonstrated  phasic  muscle a c t i v i t y d u r i n g i n s p i r a t i o n by means o f b i p o l a r e l e c t r o d e s . I n 1975,  t h e y observed a markedly  GG  needle  increased tonic  a c t i v i t y o f t h e GG i n t h e s u p i n e p o s i t i o n . They i n t e r p r e t e d t h a t t h e base l i n e a c t i v i t y of t h e GG tongue r e l a p s e due  to counteract  t o the g r a v i t a t i o n a l p u l l .  Harper (1976) r e c o r d e d t h e GG EMG various  increased  sleep stages.  the  Sauerland  and  a c t i v i t y i n humans d u r i n g  the  Remmers e t a l . ( 1 9 7 6 ) d e s c r i b e d  the  role  of t h e GG muscle i n upper a i r w a y o b s t r u c t i o n d u r i n g s l e e p . They s u g g e s t e d t h a t a t o n i a of  t h e GG c o n t r i b u t e d t o t h e i n s p i r a t o r y  upper a i r w a y o b s t r u c t i o n . G u i l l e m i n a u l t e t a l . ( 1 9 7 8 ) a l s o found significantly  decreased  GG  apnea. However, w i t h t h e  EMG  activity  during  t h e y negated  the  s i n g u l a r i n v o l v e m e n t of t h e GG muscle i n t h e g e n e s i s of t h e  OSA  syndrome, groups,  but  "tent hypothesis",  obstructive  suggested  primarily  the  the  involvement  superior  comparison s t u d i e s of t h e GG  and  of  several  constrictors. A  number  t h e diaphragm soon  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 t h e GG chemoreceptor i n p u t and n o n - s p e c i f i c s t i m u l i i s  muscle of  followed.  response t o  qualitatively  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 r e s p o n s e s . Onal and c o l l e a g u e s ( 1 9 8 1 ) observed  synchronous a c t i v i t y of  the  GG and t h e diaphragm i n normal human s u b j e c t s and emphasized t h e importance  of  the  inspiratory function  muscles i n m a i n t a i n i n g  of  the  upper  upper a i r w a y p a t e n c y . They  airway  postulated  t h a t t h e GG and g e n i o h y o i d muscles m a i n t a i n upper a i r w a y p a t e n c y by  pulling  the  inspiration.  tongue  and  hyoid  bone  forward  Haxhiu e t a l . ( 1 9 8 7 ) d e s i g n e d an  during  experiment  to  compare t h e response of t h e diaphragm and upper a i r w a y 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 t h e GG d i f f e r e n t l y t h a n  t h e diaphragm, and  suggested  t h i s might be due t o t h e 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 o f h y p o g l o s s a l and p h r e n i c neurons. From t h e p o i n t o f view o f t h e mechanics o f r e s p i r a t i o n , the  s u p r a - h y o i d muscles have o n l y r e c e n t l y been r e c o g n i z e d as  important.  Doran and Baggett  (1972) d i s c u s s t h e r e l a t i o n s h i p  between t h e GG muscle and h y o i d a p p a r a t u s .  They observed  that  some f i b r e s o f t h e i n f e r i o r p o r t i o n o f t h e GG a r e a t t a c h e d t o t h e upper p o r t i o n o f t h e body o f t h e h y o i d bone. T h i s  finding  agreed w i t h t h a t o f Abd-El-Malek (1938), b u t n o t w i t h H e l l s t r a n d (1980).  Doran  phylogenetic  and  stage,  Baggett  postulated  that  i n the early  t h e GG muscle and t h e g e n i o h y o i d  might be t h e one s u p r a - h y o i d  muscle  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 o f tongue m o b i l i t y , which s u g g e s t t h a t movement o f t h e tongue depends l a r g e l y on t h e movement o f t h e h y o i d bone. By  definition,the  s t y l o h y o i d , mylohyoid Among ^  them,  dilatation directly  supra-hyoid  group  includes  and g e n i o h y o i d muscles  the geniohyoid function;i.e.,  muscle  i t pulls  alone  digastric,  (Kaneko, 1975). has  the elevated  the hyoid  f o r w a r d which i n c r e a s e s t h e a n t e r o p o s t e r i o r  o f t h e pharynx  (Romanes, 1979).  bone  diameter  In contrast, the stylohyoid  muscle p u l l s t h e h y o i d bone p o s t e r i o r l y ; t h e m y l o h y o i d s t a b i l i z e s e i t h e r t h e mandible o r h y o i d bone. hyoid  airway  muscle  Of t h e i n f r a -  m u s c l e s , t h e s t e r n o h y o i d and t h y r o h y o i d muscles p u l l t h e  h y o i d muscle down (Kaneko, 1975).  I n 1984, van de G r a a f f e t  a l . e x p l a i n e d t h a t t h e r e s p i r a t o r y f u n c t i o n o f t h e h y o i d muscle 15  and h y o i d a r c h a f f e c t upper a i r w a y r e s i s t a n c e . They t h a t t h e s t r a t e g i c l o c a t i o n o f t h e h y o i d a r c h may the  patency  of  upper  airway  and  the  suggested  contribute to  decreased  or  poorly  c o o r d i n a t e d f u n c t i o n o f t h e h y o i d muscle may i n d u c e upper a i r w a y o c c l u s i o n . T h i s h y p o t h e s i s was  suggested  by Mathew (1984),  as  w e l l as by R o b e r t s e t a l . ( 1 9 8 4 ) . Blood  gas  changes,  pressure  changes,  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 Hudgel,1986).  As  l u n g volume  increases during  and  tissue  (Cherniac  respiration,  s t i m u l a t i o n o f pulmonary s t r e t c h r e c e p t o r s feeds back t o respiratory  c e n t e r v i a the vagus nerve.  Hering-Breuer et  This  i s the  r e f l e x ( P a r i s i and Neubauer,1986).  al.(1984)  i n v e s t i g a t e d the  volume-related  feedback  on  the  and  the  classic  Van  Lunteren  vagally  mediated  effects  of  activity  of the  upper  airway  muscles and  found t h a t the amount o f d e p r e s s i o n a t t h e end  inspiratory  a i r f l o w was  g r e a t e r f o r a l l of the  upper  of  airway  muscles t h a n f o r the diaphragm. They e x p l a i n e d 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 o f t h e upper a i r w a y muscles f o r i n s p i r a t o r y  depression  or to a vagal  depression  e f f o r t on t h e upper a i r w a y muscle o r p o s s i b l y t o b o t h .  Agostoni  e t a l . ( 1 9 8 6) undertook an e x a m i n a t i o n on t h e t i m e - c o u r s e d  effect  o f t h e s t r e t c h r e c e p t o r o f t h e b r o n c h i o r t r a c h e a on GG muscle activity  in  facilitates  rabbits GG  and  activity  reported at  the  that  bronchial  end-expiratory  volume  i n h i b i t s i t a t l a r g e r volumes. A h y p e r c a p n i c response 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;  input and  has been  Douglas e t  a l , 1 9 8 2 ; Berton-Jones and S u l l i v a n ; Weiner e t a l , 1982). St.  John e t a l . ( 1 9 8 4 )  reported i n cat that a c t i v i t y  hypoglossal  nerves  phrenic  and  parallel  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  increases  o f Onal  or  i n the  decreases  et al.(1981).  in  However, a  number o f r e c e n t 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 t h e GG and t h e diaphragm i n c o n d i t i o n s o f p e r s i s t i n g h y p e r c a p n i a ( P a r i s i e t a l . , 1987;  H i x h i u e t a l . , 1987).  Nevertheless, i t  i s o b v i o u s t h a t a r o u s a l i n c r e a s e s t h e GG a c t i v i t y more t h a n t h a t of t h e diaphragm. A number o f r e s e a r c h s t u d i e s s u p p o r t t h e i d e a that  i t i s not  hypoxia  but  hypercapnia  or  provokes t h e a r o u s a l (Fleetham e t a l , 1982;  asphyxia  I s s a and  which  Sullivan,  1986; M a t h i o t e t a l , 1986). Kuna (1987) c a r r i e d out an experiment concerned w i t h t h e i n t e r a c t i o n o f h y p e r c a p n i a and p h a s i c volume feedback motor c o n t r o l o f t h e upper a i r w a y and  intubated cats.  He  found  on  the  i n decerebrate, paralyzed,  t h a t the  hypoglossus  i s more  s e n s i t i v e t h a n t h e r e c u r r e n t l a r y n g e a l nerve t o s u p p r e s s i o n by phasic  volume  feedback.  Kuna  (1987)  p o t e n t i a t e the e f f e c t  also  concluded  hypercapnia  may  suppression  o f t h e upper a i r w a y motor neuron a c t i v i t y .  o f l u n g volume on  phenomenon i m p l i e s t h a t t h e r e s p i r a t o r y designed muscles i.e.,  t o decrease  energy  that the This  c o n t r o l mechanism i s  e x p e n d i t u r e o f t h e upper  airway  t o suppress t h e i r a c t i v a t i o n when t h e y a r e not needed,  i n t h e presence o f p h a s i c volume feedback, which  i n augmented upper a i r w a y motorneuron a c t i v i t y . 17  results  The mechanism  of  the c y c l i c  changes  i n ventilation  fundamental f a c t o r i n r e s p i r a t o r y  has been  function.  considered  Several  a  studies  (Van L u n t e r e n and S t r o h l , 1986; A d a c h i e t a l . , 1989; Hudgel and Harasick,  1989) s u g g e s t t h a t t h e i n s p i r a t o r y  upper a i r w a y muscles s l i g h t l y p r e c e d e s in  normal s i t u a t i o n s .  factor  feedback  control  (Longobardo e t a l . , assume t h a t  this  The  instability  of r e s p i r a t i o n  1982).  could  critical i n the  provoke  C h e r n i a c and Longobardo  disturbance  of the  t h a t o f t h e diaphragm  T h i s r h y t h m i c o r d e r may be a  o f t h e p a t h o g e n e s i s o f OSA.  rhythmic  activity  i n feedback rhythm may  OSA  (1986) trigger  r e c u r r e n t apneas. Sullivan  e t a l . ( 1 9 8 1 ) have  developed  CPAP(Continuous  P o s i t i v e A i r w a y P r e s s u r e ) t o a s s i s t i n t h e maintenance o f upper a i r w a y p a t e n c y . The mechanism h y p o t h e s i z e d was t h a t t h e CPAP would  a c t as a  pneumatic  splint  and p r e v e n t upper  airway  o c c l u s i o n , p u s h i n g t h e s o f t t i s s u e and tongue f o r w a r d and away from t h e p o s t e r i o r  pharyngeal w a l l .  However, t h e r e has been  c o n s i d e r a b l e c o n t r o v e r s y about t h e r a t i o n a l e o f CPAP use and its  immediate r e l a p s e tendency a f t e r withdraw.  On t h e o t h e r  hand, a number o f n e g a t i v e p r e s s u r e s t u d i e s have been r e p o r t e d . The i n f l u e n c e o f upper a i r w a y n e g a t i v e p r e s s u r e change on t h e respiratory activity r a b b i t s by Mathew  o f upper a i r w a y muscles was examined i n  (1982a, 1982b,  presence  of a reflex  response  t o t h e upper  Lunteren e t a l .  pathway  that  1984). He h y p o t h e s i z e d t h e regulates  airway pressure  loads.  GG  activity in I n 1984, van  found i n dogs t h a t t h e d u r a t i o n o f i n s p i r a t i o n 18  and  the  l e n g t h of  muscles  inspiratory  activity  of  increased i n p r o p o r t i o n t o the  a l l upper  amount o f  airway  negative  p r e s s u r e a p p l i e d . They c o n c l u d e d t h a t n e g a t i v e p r e s s u r e i n t h e upper  airway  inhibits  the  activity  of  the  diaphragm  and  p r e a c t i v a t e s t h e upper a i r w a y d i l a t i n g muscles. R e c e n t l y , Kuna (1988a,  1988b) and  experiments  his associates carried  i n normal  human s u b j e c t s .  out  two  From t h e  different  investigation  t o determine t h e e f f e c t o f n a s a l o c c l u s i o n on GG a c t i v i t y , t h e y c o n c l u d e d t h a t subatmospheric  p r e s s u r e i n t h e upper a i r w a y  w i t h d r a w a l o f p h a s i c volume feedback may  and  not p l a y an i m p o r t a n t  r o l e i n t h e r e g u l a t i o n o f upper a i r w a y muscle a c t i v i t y i n normal sleeping  adults.  However,  Kuna  et  a l . did  not  exclude  c o m p l e t e l y t h e p o s s i b i l i t y o f t h e c r i t i c a l r o l e o f t h e GG even though t h i s r o l e may  be v e r y s m a l l .  S e c o n d l y , by means o f  t h e y compared s i z e o f t h e upper a i r w a y a r e a ,  w h i l e a p p l y i n g the  CPAP, t o i t s s i z e w i t h o u t t h e CPAP. Furthermore, co-workers without  compared EMG  activity  CPAP d u r i n g w a k e f u l n e s s .  phasic  and  However,  tonic  they  EMG  found  activity a  linear  o f t h e GG  the  increase  Kuna and h i s  between w i t h  They observed between  CT,  no  two in  and  change i n protocols.  airway  area  p r o p o r t i o n a l t o t h e increment i n p o s i t i v e p r e s s u r e . I s s a e t a l . ( 1 9 8 8 ) examined how the  upper  response  airway t o airway  influences occlusion  I n t e r e s t i n g l y , t h e y conducted  the  s e n s o r y i n f o r m a t i o n from  ventilatory  during d i f f e r e n t  and  GG  muscle  sleep stages.  a n a s a l o c c l u s i o n experiment  dogs i n t h e same manner as Kuna e t a l . . 19  in  N a s a l o c c l u s i o n caused  a markedly created  i n c r e a s e d GG EMG a c t i v i t y , w h i l e t r a c h e a l  a s m a l l e r i n c r e a s e i n GG  activity.  Issa  occlusion 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 a i r w a y p r o t e c t i v e l oad-compen s a t i o n  reflex  i n NREM s l e e p .  Furthermore,  they  suggested t h a t damage t o a f f e r e n t r e c e p t o r s i n t h e upper a i r w a y , caused  by t h e m e c h a n i c a l  trauma o f s n o r i n g might l e a d t o t h e  reduced e f f e c t i v e n e s s o f such a r e f l e x and t h u s t o OSA. Aronson and  c o l l e a g u e s (1989) conducted  an experiment  t o examine t h e  e f f e c t i v e n e s s o f n a s a l CNAP(Continuous N e g a t i v e A i r w a y P r e s s u r e ) i n normal  human s u b j e c t s . They found t h a t d u r i n g w a k e f u l n e s s ,  b o t h d i a p h r a g m a t i c and GG a c t i v i t i e s response  to  CNAP.  However,  increased immediately i n  during  NREM  sleep,  despite  p r o g r e s s i v e d i a p h r a g m a t i c and GG r e s p o n s e s , a i r w a y 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 a r e d o u b t f u l o f r a t i o n a l e  of  t h e CNAP h y p o t h e s i s and presume t h a t t h e g r a d u a l  of  GG a c t i v i t y  increment  p r o b a b l y r e f l e c t s a response t o c h a n g i n g  blood  gas c o m p o s i t i o n and i s n o t due.to t h e m e c h a n i c a l r e c e p t o r .  C.  Biomechanical  relationship  between  postures  and  airway  adequacy 1] Head p o s t u r e Control  o f head  position  i n t e g r a t e s i n f o r m a t i o n from  is a  t h r e e feedback  head p o s i t i o n  process  that  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 a p p r o p r i a t e motor a c t i v i t y Basically,  complex  (Schor e t a l . ,  subsystems r e l a y  by means o f d i f f e r e n t 20  1988).  i n f o r m a t i o n about  sensory  modalities.  The  cervicocollic  reflex(CCR)  subsystem  relays  somatosensory  i n f o r m a t i o n t o m o n i t o r t h e p o s i t i o n o f t h e head w i t h r e s p e c t t o the  body;the  vestibulocollic  reflex(VCR)  and  optocollic  r e f l e x ( O C R ) subsystems s i g n a l movements o f t h e head i n space using  vestibular  and v i s u a l  signals.  These  feedback systems  u n d o u b t l y c o n n e c t 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 t h u s contribute reflex  t o the central  responses.  Since  voluntary  t h e head  commands as w e l l  control  as t o  system c o n t a i n s  a  number o f feedback l o o p s , 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 r e s p o n s e s . The r e l a t i o n s h i p between head p o s t u r e and c r a n i o f a c i a l morphology has l o n g been a r e s e a r c h t a r g e t f o r anthropologists  (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; C a r l s o o and L e i j o n , 1960).  Solow e t a l . ( 1 9 7 1 , 1979, 1984) h y p o t h e s i z e d an  i n 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 , a i r w a y adequacy and c r a n i o f a c i a l morphology. T h e i r f i n d i n g s a r e a l s o c o n c u r r e n t w i t h Woodside and L i n d e r - A r o n s o n (1976) and V i g e t a l . ( 1 9 8 0 ) . et al.(1979, nasopharynx  1984) p o s t u l a t e d induces  an  that  Solow  inadquate patency of the  extended neck  posture.  Recently,  L i i s t r o e t a l . ( 1 9 8 8 ) i l l u s t r a t e d t h a t head p o s t u r e  influences  upper a i r w a y r e s i s t a n c e and p r o v i d e d e v i d e n c e t h a t  resistance  i s d e c r e a s e d when t h e head i s extended.  21  2] Body p o s t u r e Issa  and S u l l i v a n  (1986) observed  t h a t some  patients  e x h i b i t e d c e n t r a l apnea w h i l e a s l e e p i n a s u p i n e p o s i t i o n , b u t e x h i b i t e d o b s t r u c t e d apnea o r s i m p l e s n o r i n g when i n t h e l a t e r a l recumbent p o s i t i o n . changes  According t o P a r i s i  i n pulmonary  mechanics  and Neubauer (198 6 ) ,  during  sleep  would  occur  p r i m a r i l y when changing body p o s i t i o n . I n t h e 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 i n c r e a s e d l u n g volume v i a outward movement o f t h e c h e s t w a l l . However, i n t h e s u p i n e p o s i t i o n , due t o t h e g r a v i t a t i o n a l e f f e c t , t h e same p a t t e r n o f muscle a c t i v i t y  produces  g r e a t e r abdominal  w a l l displacement. In a d d i t i o n ,  output than  chest  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 ( B e h r a k i s e t a l . , 1983).  A number  of  experiments  volume d i r e c t l y  support  t h e h y p o t h e s i s t h a t changes  i n lung  i n f l u e n c e t h e upper a i r w a y f l o w p a t e n c y  G r a a f f , 1 9 8 9 ; Navajas e t a l , 1 9 8 8 ) .  Strohl  (van de  (1986) e x p l a i n e d t h e  i n c r e a s e i n upper a i r w a y r e s i s t a n c e i n t h e s u p i n e p o s i t i o n by two  mechanisms:  first,  gravity  moves  the  mandible  and  h y p o g l o s s a l s t r u c t u r e s p o s t e r i o r l y , compromising t h e s i z e o f t h e a i r w a y . S e c o n d l y , s u p r a g l o t t i c r e s i s t a n c e i n c r e a s e s due i n l a r g e measure  t o increased  al.1982).  Strohl  i n the nasal  mucosa  (Anch  et  S e v e r a l groups(Brown e t a l , 1 9 8 7 ; N a v a j a s e t a l , 1988;  Fouke and S t r o h l , sectional  blood  area  1987) found  a decreased  i n the supine p o s i t i o n .  pharyngeal Notably,  cross-  Fouke and  (1987) have shown t h a t t h e d e c r e a s e d p h a r y n g e a l c r o s s 22  s e c t i o n a l a r e a i s a r e s u l t o f t h e change from t h e u p - r i g h t t o the supine p o s i t i o n ,  independent  (Functional Residual Capacity).  from t h e change i n t h e  While the presence of a small  a i r w a y does not appear t o d e t e r m i n e OSA 1989),  a  presence.  high  Respiratory  George  et  FRC  (Rodenstein et a l . ,  D i s t u r b a n c e Index  al.(1989)  further  indicates i t s  confirm  that  the  R D I ( R e s p i r a t o r y D i s t u r b a c e Index = AHI) i s s i g n i f i c a n t l y h i g h e r i n a s u p i n e p o s i t i o n , i n NREM s l e e p .  23  STATEMENT OF PROBLEM  A i r w a y o b s t r u c t i o n i n OSA p a t i e n t s o c c u r s i n t h e s u p i n e position.  P r e v i o u s i n v e s t i g a t o r s have shown a s m a l l e r a i r w a y  s i z e , an extended head p o s t u r e and a reduced GG muscle a c t i v i t y i n OSA p a t i e n t s . in  Fouke e t a l . ( 1 9 8 7 ) compared  healthy subjects with acoustic r e f l e c t i o n  r e p o r t e d t h a t t h e s i z e o f t h e pharynx supine  position  when  compared  to  pharyngeal  size  t e c h n i q u e s and  was 23% s m a l l e r i n t h e the up-right  position.  C o n t r a c t i o n o f t h e GG muscle advances t h e tongue base, t h e upper a i r w a y , and d e c r e a s e s a i r f l o w r e s i s t a n c e .  dilates  Increased  GG muscle a c t i v i t y i n t h e s u p i n e p o s i t i o n has been r e p o r t e d 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 n o t always i n d i c a t e a c t u a l muscle s h o r t e n i n g , s i n c e t h e muscle o n l y when t h e n e u r a l output produces  shortens  enough c o n t r a c t i l e f o r c e s  t o overcome an e x t e r n a l l o a d . A i r w a y s i z e measurements from upr i g h t l a t e r a l cephalograms can h a r d l y be matched w i t h s u p i n e EMG d a t a which approximates t h e 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 r e p o r t e d s i z e changes o f t h e upper a i r w a y and f u n c t i o n a l changes o f t h e upper a i r w a y muscles  i n the supine p o s i t i o n a t  t h e same t i m e . To i n v e s t i g a t e t h e r e l a t i o n s h i p between upper a i r w a y s i z e and  GG  muscle  activity,  the following  presented.  24  questions  were  1.  How a r e a i r w a y 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 o f t h e h y o i d 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 p r e s s u r e ?  25  METHODS  The c u r r e n t experiment was  composed o f two major p a r t s ;  a c e p h a l o m e t r i c s t u d y , and tongue EMG  and p r e s s u r e r e c o r d i n g s .  The c e p h a l o m e t r i c s t u d y was undertaken OSA  and  i n ten  asymptomatic  i n twenty p a t i e n t s w i t h  controls.  The  tongue  EMG  and  p r e s s u r e s t u d y was c a r r i e d out i n t h e t e n asymptomatic c o n t r o l s .  A.  Experimental subjects A t o t a l o f t h i r t y s u b j e c t s were e v a l u a t e d and s e l e c t e d  as s t u d y m a t e r i a l from a p o p u l a t i o n r e c r u i t e d o v e r a t e n month period  (1988-1989) a t t h e U n i v e r s i t y  H o s p i t a l (UBC  Vancouver. Twenty s u b j e c t s w i t h diagnosed OSA  site)  in  as d e t e r m i n e d  by  o v e r n i g h t s l e e p s t u d i e s were used as t h e p a t i e n t group. asymptomatic s u b j e c t s found overnight  monitoring  controls.  The  Respiratory  and/or  not t o have OSA medical  Sleep  Disorder  Clinic  on t h e b a s i s o f  histories  overnight sleep study  was  and  Ten  were  carried  used  out  at  as the  a l l anthropometric,  pulmonary f u n c t i o n and s l e e p s t u d y d a t a used i n t h i s s t u d y were p r o v i d e d by t h e c l i n i c . E d e n t u l o u s an  ongoing  respiratory  infection  s u b j e c t s , s u b j e c t s who o r any  medication  had  known t o  a f f e c t muscle a c t i v i t y , s u b j e c t s who needed o r t h o g n a t h i c s u r g e r y and t h o s e u n a b l e t o g i v e f u l l y  i n f o r m e d consent were e x c l u d e d  from t h e s t u d y . A l l i n d i v i d u a l s i n c l u d e d i n t h e s t u d y were a d u l t males (see T a b l e I ) . 26  Table I  Demographic Variables for the Experimental Subjects  DEMOGRAPHIC VARIABLES OSA (N = 20)  CONTROL (N = 10)  MEAN  S.D.  MEAN  S.D.  48.4 97.78 31.55 29.91  13.03 22.64 7.88 29.88  33.5 78.20 26.30  5.95 11.72 3.19  AGE WEIGHT BMI RDI  Legend T a b l e I  Age = y e a r s , Weight = kg, BMI(Body Mass Index) = kg/m R D I ( R e s p i r a t o r y D i s t u r b a n c e Index) = Apnea Index + Hypopnea Index 2  27  The average age o f t h e twenty s u b j e c t s composing t h e OSA group was 4 8.4 y e a r s and ranged from 2 0 t o 71 y e a r s (see T a b l e I) . T h e i r w e i g h t s ranged from 69Kg t o 150Kg;the mean was 97.8Kg. Average BMI [Body Mass Index = W e i g h t ( K g ) / H e i g h t (m )] was 31.5 2  (ranging  2  from 24.76 t o 47.48). A l l o f t h e OSA s u b j e c t s were  s n o r e r s . The mean A l was 9.99, and t h e mean RDI was 29.91. The ages o f t h e c o n t r o l s u b j e c t s ranged from 2 3 t o 4 6 y e a r s ; t h e mean age was 3 3.5. The average weight o f t h e 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, r a n g i n g from 21.45 t o 32.18.  B.  Experimental Procedures  1] C e p h a l o m e t r i c s t u d y A pair  of i n d i v i d u a l  i d e n t i c a l equipment  cephalograms  were o b t a i n e d w i t h  ( C o u n t e r b a l a n c e d Cephalometer Model W-105,  Wehmer Co.) and by an i d e n t i c a l method  (165 cm s o u r c e 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 s e c ; Kodak 8x10" f i l m s , Kodak Lanex R e g u l a r Screens) f o r each s u b j e c t 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 and s u p i n e p o s i t i o n . A l l o f t h e cephalograms were t a k e n a t t h e end o f t h e e x p i r a t i o n phase.  a. U p - r i g h t v e r s u s s u p i n e l a t e r a l To posture  obtain up-right  was d e t e r m i n e d  lateral  by v i s u a l  cephalograms cephalograms, feedback  natural  head  i n a m i r r o r and  r e c o r d e d by a m o d i f i e d l e v e l d e v i c e (see F i g . 1) a t t a c h e d t o t h e s o f t - t i s s u e FH p l a n e ( i n f r a o r b i t a l n o t c h 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  A n g l e between t h e u p p e r m a r g i n o f t h e t a p e and t h e t r u e h o r i z o n t a l ( l e v e l of the l i q u i d ) represents the natural head p o s t u r e .  29  Natural  head  considered  posture  highly  Siersbaek-Nielson  and  feedback  in  method  in  standing  reproducible  standing The  position  (Moorrees  Solow, 1982;  c u r r e n t experiment. away from and  the  and  s u b j e c t was  been  Kean,  1958;  A  visual  Sandham, 1988).  p o s i t i o n was  i n f r o n t of t h e  has  employed  for  the  r e q u i r e d t o s t a n d 1.5  mirror  (150  cm  long) .  r e l a x e d and n a t u r a l body p o s t u r e , t h e s u b j e c t was  In  m a  instructed to  swing h i s head back and f o r t h and g r a d u a l l y reduce t h e magnitude of t h e swing. head p o s t u r e sight.  This  F i n a l l y , t h e s u b j e c t stopped a t h i s own d e t e r m i n e d by h i s own p r o c e d u r e was  natural  sense o f head b a l a n c e  carried  out  with  the  eyes  and  closed  f i r s t , t h e n t h e second time w i t h t h e eyes open and g a z i n g i n t h e 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 s h e e t , p30). head p o s t u r e  was  i n d i c a t e d by t h e  This process  was  repeated  2-3  fluid  The degree of t h e  level  i n the  t i m e s , averaged and  device.  recorded.  l a t e r a l cephalogram was t a k e n of t h e s u b j e c t i n h i s own  A  natural  p o s t u r e as p r e v i o u s l y determined w i t h t h e m o d i f i e d l e v e l d e v i c e . In  order  to  take  the  supine  i n s t r u c t e d t o l i e down on  cephalogram,  a s t r e t c h e r and  the  t o mimick h i s  u s u a l s l e e p i n g p o s i t i o n and p i l l o w h e i g h t . The recorded  after  comfortable, lateral  the  natural  patient  was  cephalogram was  taken  with  relaxed position.  30  head a n g l e  established  sleeping position. the  subject  in  Finally, jaw  in a  his  the  was own was own  supine  completely  CEPHALOMETRIC INSTRUCTIONS FOR PATIEHTS You are  going to  have two head x - r a y s  taken.  The f i r s t  obtained i n a s t a n d i n g p o s i t i o n w i t h a n e u t r a l head p o s t u r e ,  is 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 t h e b l a c k l i n e i n f r o n t of the m i r r o r . 2.  Stand i n a c o m f o r t a b l e p o s i t i o n and l o o k d i r e c t l y at your own eyes i n the m i r r o r as i f you were g a z i n g o f f i n t o the d i s t a n c e .  3.  C l o s e your eyes and nod y o u r head back and f o r t h and g r a d u a l l y reduce the magnitude o f t h e s w i n g . P l e a s e stop when you f e e l you have a n a t u r a l head p o s t u r e .  4. Repeat the above t a s k t w i c e w i t h your eyes open. B. STANDING POSITION 1. Stand on the f o o t p r i n t and reproduce your n e u t r a l head posture as  instructed.  2. Relax your jaw and b i t e s l i g h t l y on your back 3. A f t e r t h r e e r e g u l a r b r e a t h s , breathe o u t ,  teeth.  and h o l d your breath  u n t i l the x - r a y 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 c a n . 2.  Please mimick your u s u a l s l e e p i n g p o s i t i o n . Let your jaw r e l a x as you would when you are  asleep.  Do not b i t e on your back  teeth. 3. A f t e r t h r e e r e g u l a r b r e a t h s , u n t i l the x - r a y i s completed.  31  breathe o u t ,  and h o l d your breath  The  level  experiment  device  which  was  employed  i n the  current  (see F i g . 2 ) was an improved t y p e m o d e l l e d on s e v e r a l  former l e v e l d e v i c e s (Showfety e t a l , 1983; Huggare,  1985).  T h i s m o d i f i e d l e v e l d e v i c e , 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 o f t h e D i v i s o n o f R a d i o l o g y i n F a c u l t y o f D e n t i s t r y a t UBC,  was  composed o f t h r e e p i e c e s o f a c r y l i c p l a t e and  acrylic  tube.  degrees was  A  microfied  polyvinyl  protractor  measuring  360  a t t a c h e d t o t h e s m a l l m i d d l e a c r y l i c p l a t e so t h a t  an a n g l e c o u l d be Prescribed  circular  an  r e a d up  to half  s a t u r a t e d radiopaque tube  a degree i n any  liquid  was  held  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  position. inside  plane  on  the the  f i l m . The l i q u i d was composed a p p r o x i m a t e l y o f 30% l e a d n i t r a t e (PbN03),  r e d dye, s u r f a c t a n t and  In  order  to  determine  i n f r a - o r b i t a l n o t c h was Two  water.  the  soft-tissue  p a l p a t e d and  FH  t r a g i o n was  plane,  the  determined.  l e a d markers were a t t a c h e d t o t h e i n f r a o r b i t a l n o t c h  and  t r a g i o n w i t h an a p p r o p r i a t e l e n g t h of c o l o u r e d s c o t c h t a p e .  The  m o d i f i e d l e v e l d e v i c e was p l a c e d on t h e t a p e which i n d i c a t e s t h e s o f t - t i s s u e FH p l a n e and was s i d e d tape  (see F i g . 1) .  adhered  t o the l i n e w i t h  A f t e r t h e n a t u r a l head p o s t u r e  d e c i d e d i n t h e manner d e s c r i b e d above, one Microtrast  Esophageal  double  cream  (Esobar,  d e l i v e r e d . The dorsum o f t h e tongue  was  tablespoon of the  Therapex  Inc.)  was  and upper p h a r y n g e a l a i r w a y  were c o a t e d w i t h t h e radiopaque cream t o 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 F i g . 2  T h e p l a s t i c t u b e ( d i a m e t e r = 3.3 mm) r e d d y e , s u r f a c t a n t and w a t e r .  c o n t a i n s PbN0 , 3  Subsequently, placed  on  a l e a d marker w i t h  the midpoint  of  the  a diameter tongue  o f 5.0 mm  t i p by  means  was of  b i o c o m p a t i b l e a d h e s i v e s ( I s o Dent, E l l m a n D e n t a l Inc.) i n o r d e r t o r e g i s t e r t h e e x a c t p o s i t i o n o f t h e tongue t i p . The tongue t i p r e p r e s e n t s t h e m i d s a g i t t a l j u n c t i o n o f t h e tongue dorsum and t h e i n f e r i o r mucous membrane.  The s u b j e c t was i n s t r u c t e d t o s t a n d  on t h e f o o t p r i n t i n t h e c e p h a l o s t a t and t o reproduce  h i s own  n a t u r a l head p o s t u r e w i t h t h e a i d o f t h e a n g u l a t i o n r e c o r d e d by t h e m o d i f i e d l e v e l d e v i c e . A m e t a l c h a i n was suspended from t h e s u r f a c e o f t h e c a s s e t t e t o c o n f i r m and r e g i s t e r a t r u e v e r t i c a l p l a n e on t h e f i l m .  Finally,  cephalograms were t a k e n  i n the  i n s t r u c t e d p o s i t i o n i n b o t h t h e u p - r i g h t and s u p i n e p o s i t i o n a t 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, p l a n e s ,  lines,  a n g u l a t i o n s , a r e a s 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  variables,  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 t o evaluate  the  Specific  s i z e and  landmarks,  identified.  All  l o c a t i o n of lines  and  lateral  upper  angles  airway were  cephalometric  structures. designed  landmarks  and were  c o o r d i n a t e d w i t h X and Y axes, and t h e s e 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  1 . H a r d - t i s s u e landmarks (see S  Sella  N  Nasion  - The  estimated  lines.  Fig.4)  c e n t r e of t h e s e l l a  - The most a n t e r i o r p o i n t of t h e  turcica.  naso-frontal  suture. Or  Orbitale  - The most i n f e r i o r p o i n t of t h e  infra-orbital  margin. ANS  A n t e r i o r nasal spine  - The  apex of t h e a n t e r i o r n a s a l  spine. PNS  P o s t e r i o r nasal spine posterior  R  - The p o s t e r i o r t i p of  the  n a s a l s p i n e of t h e p a l a t i n e bone.  Roof of t h e pharynx  - The  p o i n t on t h e p o s t e r i o r  p h a r y n g e a l w a l l c o n s t r u c t e d by a l i n e PNS  t o the  s e c t i o n a l p o i n t of t h e c r a n i a l base and t h e pterygoid plate.  36  cross-  lateral  A point  Subspinale  - The deepest p o i n t on t h e a n t e r i o r  s u r f a c e o f t h e m a x i l l a r y a l v e o l a r bone. B point  Submentale  - The deepest p o i n t on t h e a n t e r i o r  surface of the mandibular Pog  Pogonion  symphysis.  - The most prominent p o i n t on t h e a n t e r i o r  s u r f a c e o f t h e m a n d i b u l a r symphysis i n r e s p e c t t o t h e mandibular plane. Me  Menton  - The most i n f e r i o r p o i n t on t h e m a n d i b u l a r  symphysis. Gn  Gnathion  - The m i d p o i n t between Pog and Me on t h e  b i s e c t i n g l i n e o f t h e a n g l e formed by m a n d i b u l a r p l a n e and f a c i a l p l a n e . RGN  Retrognathion  - The most p o s t e r i o r p o i n t o f t h e  m a n d i b u l a r symphysis a l o n g a l i n e p e r p e n d i c u l a r t o the Go  FH  Gonion  (Frnkfort Horizontal) plane. - The most i n f e r i o r , p o s t e r i o r and o u t e r most  p o i n t o f t h e m a n d i b u l a r a n g l e , d e t e r m i n e d by a b i s e c t o r < the  a n g l e formed by t h e t a n g e n t t o t h e p o s t e r i o r and  i n f e r i o r b o r d e r l i n e o f t h e mandible. Po  Porion  CV2tg  - The uppermost p o i n t o f t h e e a r r o d .  Second  V e r t e b r a 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 t h e p o s t e r i o r s u r f a c e o f t h e second v e r t e b r a l corpus. CV2ip  Second V e r t e b r a 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 o f t h e 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 point of the f o u r t h v e r t e b r a l corpus. C3  Third Vertebra  - The most a n t e r i o r i n f e r i o r p o i n t o f t h e  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 o f t h e  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 ) , A N S ( A n t e r i o r Nasal S p i n e ) , P N S ( P o s t e r i o r Nasal S p i n e ) , R(Roof of the pharynx), A ( S u b s p i n a l e ) , B(Submentale), Pog(Pogonion), Me(Menton) , Gn(Gnathion) , RGN(Retrognathion) , Go(Gonion) , P o ( P o r i o n ) , CV2tg(Second V e r t e b r a 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 ) , C 3 ( T h i r d V e r t e b r a ) , C4(Fourth Vertebra)  39  2 . S o f t - t i s s u e landmarks (see F i g . 5 ) a) Tongue TT  Tongue T i p -  The c e n t e r o f t h e l e a d d i s c  attached  t o t h e b o r d e r between t h e v e n t r a l and d o r s a l  surfaces  of t h e tongue t i p . TH  Tongue H e i g h t - The h i g h e s t p o i n t o f t h e tongue curvature r e l a t i v e  t o a l i n e from base o f t h e e p i g l o t t i s  t o TT. Eb  Base o f E p i g l o t t i s  - The deepest p o i n t o f t h e  epiglottis. Et  Tip of Epiglottis  - The most s u p e r i o r p o i n t o f t h e  epiglottis. 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 o f t h e  h y o i d bone. b) S o f t p a l a t e P  Palate Point -  The most i n f e r i o r t i p o f t h e s o f t  palate. AP  Anterior Palate  - The a n t e r i o r p o i n t o f 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  to a  l i n e from PNS t o P. PP  Posterior Palate  - The p o s t e r i o r p o i n t o f maximum  p a l a t a l t h i c k n e s s determined along a l i n e to  PNS-P.  40  perpendicular  AST  A n t e r i o r S u p e r i o r Tongue - The c r o s s - s e c t i o n a l p o i n t on t h e tongue c u r v a t u r e d e t e r m i n e d by a l i n e t h r o u g h t h e m i d - p o i n t o f PNS-P and p a r a l l e l t o Go-B.  ASP  A n t e r i o r S u p e r i o r P a l a t e - The a n t e r i o r  cross-sectional  p o i n t o f t h e 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. PSP  P o s t e r i o r S u p e r i o r P a l a t e - The p o s t e r i o r  cross-  s e c t i o n a l p o i n t o f t h e s o f t p a l a t e d e t e r m i n e d 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 S u p e r i o r Pharynx - The c r o s s - s e c t i o n a l  point  o f t h e p o s t e r i o r p h a r y n g e a l 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) P h a r y n g e a l a i r w a y 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 t h e  tongue on a l i n e t h r o u g h p o i n t P p a r a l l e l t o Go-B. MPA  M i d d l e P o s t e r i o r Airway - The p o i n t on t h e p o s t e r i o r p h a r y n g e a l w a l l on a l i n e t h r o u g h  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 A i r w a y - The a n t e r i o r p o i n t on t h e p o s t e r i o r s u r f a c e  cross-sectional  o f t h e tongue o r s o f t  p a l a t e determined by a extended l i n e o f 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 A i r w a y - The p o s t e r i o r point  on t h e p o s t e r i o r p h a r y n g e a l w a l l  line  Go-B.  42  cross-sectional  d e t e r m i n e d by  the  Legend F i g . 5  TT(Tongue T i p ) , TH(Tongue H e i g h t ) , 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 ( H y o i d a l e ) , P(Palate Point), AP(Anterior Palate), PP(Posterior P a l a t e ) , A S T ( A n t e r i o r S u p e r i o r Tongue), A S P ( A n t e r i o r Superior Palate), PSP(Posterior Superior Palate), P S P h ( P o s t e r i o r S u p e r i o r Pharynx), MMA(Middle A n t e r i o r A i r w a y ) , MPA(Middle P o s t e r i o r A i r w a y ) , I A A ( I n f e r i o r A n t e r i o r A i r w a y ) , I P A ( I n f e r i o r P o s t e r i o r Airway) 43  Several  linear,  angular  and  area  variables  were  determined. 3.  L i n e a r measurements  (see F i 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 H e i g h t - The l i n e a r d i s t a n c e between a p o i n t on  t h e most s u p e r i o r c u r v a t u r e o f t h e tongue dorsum  and  t h e base o f a l i n e drawn p e r p e n d i c u l a r  TT-Eb  to the  line.  b) S o f t P a l a t e PNS-P  S o f 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  MPT  P.  Maximum P a l a t e T h i c k n e s s - The maximum t h i c k n e s s of t h e  s o f t p a l a t e measured on a l i n e  perpendicular  t o t h e PNS-P. c) Upper A i r w a y SPAS  S u p e r i o r P o s t e r i o r A i r w a y Space - The t h i c k n e s s o f 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 t o t h e Go-B p o i n t  MAS  plane.  M i d d l e A i r w a y Space - The t h i c k n e s s o f t h e a i r w a y a l o n g a l i n e p a r a l l e l t o t h e Go-B p o i n t P l a n e t h r o u g h P.  IAS  Inferior  A i r w a y Space - The t h i c k n e s s o f t h e a i r w a y  a l o n g a l i n e extended t h r o u g h t h e Go-B p o i n t 44  plane.  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) H y o i d Bone MPH  M a n d i b u l a r P l a n e t o H y o i d - The l i n e a r d i s t a n c e a l o n g a p e r p e n d i c u l a r from H t o t h e m a n d i b u l a r p l a n e .  HH1  V e r t i c a l H y o i d - The l i n e a r d i s t a n c e between H and a p e r p e n d i c u l a r t o t h e C3-RGN p l a n e .  HRGN  H o r i z o n t a l H y o i d - 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 H y o i d - The l i n e a r d i s t a n c e between C3 and H.  45  I  4. A n g u l a r measurements (see F i g . 7 ) E-TT  Tongue Angle - The a n g l e c o n s t r u c t e d by an e x t e n s i o n of t h e Eb-TT p l a n e and t h e t r u e h o r i z o n t a l .  CVTPP  V e r t e b r a e t o P a l a t a l p l a n e - The a n g l e c o n s t r u c t e d by an e x t e n s i o n l i n e o f CV2tg-CV4ip p l a n e and p a l a t a l plane .  CVTSN  V e r t e b r a e t o SN p l a n e - The a n g l e c o n s t r u c t e d by an e x t e n s i o n l i n e o f CV2tg-CV4ip p l a n e and SN p l a n e .  OPTPP  Odontoid t o P a l a t a l p l a n e - The a n g l e c o n s t r u c t e d by an e x t e n s i o n l i n e o f CV2tg-CV2ip p l a n e and P a l a t a l plane.  OPTSN  Odontoid t o SN p l a n e - The a n g l e c o n s t r u c t e d by an e x t e n s i o n l i n e o f CV2tg-CV2ip p l a n e and SN p l a n e .  5. Area measurements (see F i g . 7 ) a) Tongue  The a r e a o u t l i n e d configuration  by t h e d o r s a l  o f t h e tongue s u r f a c e 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 a r e a c o n f i n e d by t h e o u t l i n e o f t h e s o f t p a l a t e which s t a r t s and ends a t PNS t h r o u g h P. c) Nasopharynx The a r e a o u t l i n e d PNS,  by a l i n e between R and  an e x t e n s i o n o f t h e P a l a t a l p l a n e t o t h e  posterior  p h a r y n g e a l w a l l , and t h e  posterior  pharyngeal  47  wall.  Oropharynx  The a r e a o u t l i n e d by t h e i n f e r i o r b o r d e r of t h e nasopharynx,  p o s t e r i o r s u r f a c e of the  s o f t p a l a t e , a l i n e from P t o t h e d o r s a l s u r f a c e o f t h e tongue p a r a l l e l t o t h e 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 u r f a c e of the tongue, a l i n e p a r a l l e l t o t h e p a l a t a l p l a n e t h r o u g h t h e p o i n t E t , and t h e p o s t e r i o r pharyngeal w a l l , e) Hypopharynx The a r e a o u t l i n e d by t h e i n f e r i o r b o r d e r o f t h e oropharynx, t h e p o s t e r i o r s u r f a c e o f t h e epiglottis,  a l i n e p a r a l l e l t o the p a l a t a l  p l a n e t h r o u g h t h e p o i n t C4, and t h e 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 A n g l e ) , C V T P P ( V e r t e b r a e t o P a l a t a l p l a n e ) , C V T S N ( V e r t e b r a e t o SN p l a n e ) , OPTPP(Odontoid t o P a l a t a l p l a n e ) , 0PTSN(Odontoid t o SN p l a n e ) , Tongue, jjjggjSSoft P a l a t e i l l l Nasopharynx', Oropharynx, Hypopharynx  49  C. T r a c i n g  and d i g i t i z a t i o n  T r a c i n g s were made on a c e t a t e paper w i t h  a .5mm  pencil  f o r each o f t h e p o i n t s , p l a n e s and o u t l i n e s f o r t h e tongue, s o f t palate  and  upper  airway  B o u n d a r i e s were o u t l i n e d zones t o t a k e i n t o account  structures i n the  by  one  investigator.  middle of t i s s u e t r a n s i t i o n  a v e r a g i n g . A d a t a e n t r y program was  w r i t t e n t o permit d i g i t i z a t i o n  o f cephalograms by means o f a  d i g i t i z e r (HP Model 9874) . A c r o s s - h a i r c u r s o r was used t o e n t e r t h e p o i n t s and c o n t o u r s o f each s t r u c t u r e i n t o t h e 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 d e t e r m i n e t h e length,  angulation  and  cross-sectional  area  of  s t r u c t u r e s . A l l o f t h e d i g i t i z a t i o n p r o c e d u r e s were  specific fulfilled  by one i n v e s t i g a t o r .  2] EMG and p r e s s u r e s t u d y EMG and p r e s s u r e d i f f e r e n c e s o f t h e tongue and p e r i o r a l m u s c u l a t u r e 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 t h r e e t a s k s was  ( i . e . r e s t , maximum p r o t r u s i o n , maximum opening)  performed on 10 asymptomatic c o n t r o l s i n u p - r i g h t and s u p i n e  body p o s i t i o n s . The computer s t o r e d during  s i g n a l s every  millisecond  t h e two seconds o f t h e a c t u a l s a m p l i n g t i m e , a f t e r a l l  2000 s i g n a l s  were d e t e c t e d .  The s i g n a l s  averaged by e x i s t i n g computer s o f t w a r e .  50  were i n t e g r a t e d  and  a. Data a q u i s i t i o n system and r e c o r d i n g  technique  A t o t a l o f s i x c h a n n e l s were used i n o r d e r t o o b t a i n and  pressure  s i g n a l s : four  channels  o r b i c u l a r i s o r i s and s u p r a - h y o i d  f o r t h e GG,  EMG  masseter,  muscle group and two c h a n n e l s  f o r t h e a n t e r i o r and p o s t e r i o r p r e s s u r e r e c o r d i n g s o f t h e tongue (see F i g . 8 ) . c h a n n e l 0 :EMG a c t i v i t y o f t h e GG was t a k e n with a b a l l - t y p e b i p o l a r surface  intra-orally electrode.  c h a n n e l 1 :EMG a c t i v i t y from t h e r i g h t - s i d e m a s s e t e r was taken with conventional  surface  electrodes.  c h a n n e l 2 :EMG s i g n a l s from t h e 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 by c o n v e n t i o n a l  surface  detected  electrodes.  c h a n n e l 3 :EMG a c t i v i t y from t h e r i g h t - s i d e  supra-hyoid  muscle group was t a k e n w i t h c o n v e n t i o n a l  surface  electrodes. c h a n n e l 1 0 : P r e s s u r e s i g n a l s from t h e a n t e r i o r p o r t i o n o f t h e tongue were t a k e n w i t h a s t r a i n gauge t y p e load c e l l positioned i n a c r y l i c appliance midpoint  at the  of the c e n t r a l i n c i s o r s .  c h a n n e l 1 1 : P r e s s u r e s i g n a l s from t h e p o s t e r i o r p o r t i o n o f t h e r i g h t s i d e o f t h e tongue were t a k e n w i t h t h e load c e l l positioned i n a c r y l i c opposite  the  appliance  r i g h t m a n d i b u l a r 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 a p p l i a n c e was  constructed  as a c a r r i e r on t h e i n d i v i d u a l m a n d i b u l a r c a s t and a d j u s t e d i n t h e mouth  (see F i g . 8 ) . A f t e r a d e t e r m i n e d t h i c k n e s s ( 2 mm)  r e s i n p l a t e i n t h e dough s t a g e was  of  a p p l i e d on t h e l i n g u a l s i d e  of t h e m a n d i b u l a r t e e t h and g i n g i v a on t h e c a s t , a s m a l l amount of r u b b e r base m a t e r i a l ( R e p r o s i l p u t t y 1500, to  the r e s i n ,  adjusted  and  molded. Two  Densply) was  added  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 f l a n g e of the a p p l i a n c e t o r e c o r d d i r e c t l y from t h e GG muscle (Doble e t a l . , 1985;  M i l i d o n i s e t a l . , 1988). The  pressure  transducers  were  mounted a t t h e m i d p o i n t  of the m a n d i b u l a r c e n t r a l i n c i s o r s  lingual  mandibular  to  the  right  m a n d i b u l a r molar r e g i o n was differences positional  in  tongue  change.  The  first  thickened  pressure  in  thickness  of  molar.  i n order  The to  accordance the  and  right  exaggerate with  appliance  body  and  the  l o c a t i o n of t h e t r a n s d u c e r s were c a r e f u l l y s t a n d a r d i z e d and  the  s e n s i t i v i t y o f each t r a n s d u c e r was d e t e r m i n e d and c a l i b r a t e d a t proper gain. Kyowa  A diaphragm t y p e  electronic  instruments  of l o a d c e l l , Co.,  which  manufactured contains  by  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 b r i d g e ) was  used t o r e c o r d tongue p r e s s u r e .  t r a n s d u c e r was in  d i a m e t e r and  a PS-A 0.6  provided i n Figure  The  t y p e , w i t h a 10Kgf/cm mm  thickness.  9.  53  miniature 2  pressure  of c a p a c i t y , 6  Specification details  mm are  Fig. 9  Pressure Transducer and Its Specifications  >  Glossy surface  t  i t  - Pressure Da  0.6 ±0 1 (mm)  Specifications Type  PS-A  Safe excitation input/output resistance Compensated temperature range Safe temperature range Temperature effect on output Safe overload rating  3V I20n 0-+50.C -20-+70.C ± 0.2%/. C 150%  (Type PS-A)  54  A s t a t i c c a l i b r a t i o n was undertaken  with a calibration  system f o r each o f t h e t r a n s d u c e r s i n v i t r o b e f o r e and a f t e r t h e e x p e r i m e n t a l s e s s i o n (see F i g . 1 0 ) .  The c a l i b r a t i o n system  was s e t up w i t h a d e n t a l p l a s t e r h o u s i n g  and a r u b b e r b a l l o n  c o n t a i n i n g water w i t h no bubbles a t a temperature  approximately  36°C. Weights were s e t a t 100 g i n t e r v a l s on t h e c a l i b r a t i o n system.  The n o i s e  adjusted 1.5g/cm  2  levels  sensitivity  were  o f both  less  than  5mV  p e r min. The  transducers  was  approximately  i n b o t h 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.10). represented  The by  linearity a  of s e n s i t i v i t y  correlation  coefficient  r=0.9878; p o s t e r i o r s i d e r=0.9954 ). were c a l c u l a t e d  i n load  cells  ( anterior  was side  Both o f t h e l i n e a r i t i e s  from 0 t o 400g i n f o r c e changes on t h e g i v e n  s u r f a c e a r e a . Based upon t h e r e g r e s s i o n l i n e o f t h e s c a t t e r g r a m (see F i g . 10) , out  lmV o f e l e c t r i c a l change i n t h e l o a d c e l l t u r n e d  t o be e q u i v a l e n t t o a p p r o x i m a t e l y  1.5g/cm  change as an average f o r both t r a n s d u c e r s .  55  2  of pressure  Fig. 10  Calibration System and Calibration Results  Pressure Transducer  * Anterior Transducer  0 100 Legend F i g . i o  • Posterior Transducer  200 300 400 500 {g ) The o b t a i n e d p r e s s u r e s i g n a l s from the p r e s s u r e t r a n s d u c e r are d e l i v e r e d t o D i g i t a l M u l t i m e t e r ( H e w l e t t Packard) and d i s p l a y e d as numbers ( ntV ).  56  b. Equipment and d a t a p r o c e s s i n g (see Fig.11) EMG d a t a from t h e 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  differential  a m p l i f i e r ( A l 2010 Axon) . Each' o f s i g n a l s was a m p l i f i e d by d u a l a m p l i f i c a t i o n ( m a i n l y 20K  o r 40K was  high(lKHz)  filterings  noise  movement a r t i f a c t s  from  coming  from  other  used) and low(30 Hz)  and  i n o r d e r t o reduce  the  were conducted and  equipment.  electrical  The  amplified  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 (  into  an  A/D  converter(3852A  frequency  signals  were  4701 T e k t r o n i x i n c . )  and a c o n t r o l r a c k . Through a t r i g g e r system, passed  high  t h e s i g n a l s were  DATA ACQUISITION/CONTROL  UNIT) . A f t e r c o n v e r s i o n o f t h e s i g n a l s , t h e y were i n t e g r a t e d  and  averaged  and  stored  by means o f t h e pre-programed computer s o f t w a r e in  the  computer. first  The  passed  signals  transducers  were  into  preamplifier  t h r o u g h a b r i d g e box.  The  a  from  the  custom-made  s i g n a l s were  pressure carrier amplified  by p r e - a d j u s t e d and c a l i b r a t e d g a i n and were s e n t t o t h e s t o r a g e monitor  (2221  Tektronik)  to v e r i f y the  s i g n a l s were s e n t t o t h e A/D  tongue  forces.  c o n v e r t e r t h r o u g h t h e same t r i g g e r  and t h e r a c k . The d a t a t r a n s f o r m e d t o d i g i t a l form was and s t o r e d  The  i n t h e same manner as t h e EMG  57  signals.  averaged  Fig. 11  Flow-chart tor Data Aquisition  Pressure Transducer  Carrier pre-amplifier  EMG Electrodes  Storage Oscilloscope  Differential Amplifier 8-channel Multiplexor 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 and t h e s t o r a g e oscilloscope.  58  8-channel  multiplexor  c. E x p e r i m e n t a l  procedure  . To sample t h e EMG and p r e s s u r e d a t a f o r t h e r e s t t a s k , the  p a t i e n t was r e q u i r e d  t o maintain  a relaxed  and r e s t i n g  m a n d i b u l a r p o s i t i o n t o m o n i t o r r e s t i n g p o t e n t i a l s i n t h e GG, m a s s e t e r , i n f e r i o r o r b i c u l a r i s o r i s and s u p r a - h y o i d muscles. To record  the protrusion task,  t h e s u b j e c t s were i n s t r u c t e d t o  p e r f o r m a maximum p r o t r u s i o n o f t h e tongue a g a i n s t t h e p r e s s u r e t r a n s d u c e r on t h e a n t e r i o r l i n g u a l s i d e o f t h e a p p l i a n c e . r e c o r d maximum opening,  t h e s u b j e c t s were r e q u e s t e d  t h e i r mouth as much as p o s s i b l e . pressure,  in  (see F i g . 1 2 ) .  t o open  To sample t h e tongue b a s e l i n e  a s p e c i a l l y constructed  intra-orally  To  a c r y l i c t r a y was i n t r o d u c e d  The s u b j e c t s were i n s t r u c t e d t o s i t  a d e n t a l c h a i r i n an u p - 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  p o s t u r e which c o u l d be reproduced by t h e m o d i f i e d l e v e l d e v i c e . 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 o r d e r t o t a k e t h e base  l i n e r e c o r d i n g o f t h e tongue p r e s s u r e w i t h o u t any c o n t a c t o f t h e tongue on t h e t r a n s d u c e r  surface.  A f t e r t h e t r a y was removed  from t h e mouth, EMG and p r e s s u r e were r e c o r d e d  a t the absolute  r e s t p o s i t i o n o f t h e mandible. Maximum p r o t r u s i o n and opening t a s k s were r e c o r d e d  immediately  i n a c o n s e c u t i v e manner.  Each  of t h e t a s k s was performed i n n o t l e s s t h a n t h r e e seconds. Four r e c o r d i n g s e s s i o n s o f base l i n e , maximum opening were r e p e a t e d  r e s t , maximum p r o t r u s i o n and  f i v e times.  Body movement, head  movement and s w a l l o w i n g were m o n i t o r e d t h r o u g h o u t t h e s e s s i o n . A f t e r t h e u p - r i g h t p o s i t i o n s e s s i o n , t h e s u b j e c t s were r e q u e s t e d  t o r e c l i n e on a s t r e t c h e r  i n a p o s i t i o n i d e n t i c a l to that  used  f o r the supine cephalograms. A l l t a s k s were repeated i n the same manner as i n the u p - r i g h t  position.  60  Fig. 12  Tray Used to Measure the Base-line Pressure of the Tongue  Legend P i g . 1 2  Arrows i n the upper p i c t u r e i n d i c a t e the pressure transducers, the arrow i n the lower p i c t u r e indicates the a c r y l i c 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 thes t a t i s t i c a l computer s t a t i s t i c a l and  5%  significant  t e s t s were conducted by means o f t h e  package c a l l e d SYSTAT. level  positives(Type I error).  was  used  A two-tail  f o r detecting  test false  The S t u d e n t ' s t t e s t and W i l c o x o n  s i g n e d rank t e s t were employed f o r t h e comparison between t h e OSA group  and t h e asymptomatic  comparison Pearson's  between simple  the up-right  correlation  controls,  and a l s o  and s u p i n e  coefficient,  body  for  the  position.  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  calculate  reproducibility  and  experimental  error.  A d d i t i o n a l l y , ANCOVA was conducted i n o r d e r t o t e s t t h e e f f e c t s o f age on t h e v a r i a b l e s . The  i n d e x o f r e l i a b i l i t y , used t o t e s t t h e r e l i a b i l i t y  of t h e cephalometric v a r i a b l e s , 1979.  was i n t r o d u c e d by Houston i n  He c l a s s i f i e d t y p e s o f e r r o r i n t o s y s t e m i c  (or b i a s ) and random e r r o r . systemic  errors  error  The s i m p l e s t approach t o  i s t h e one sample t t e s t  detect  f o r each p a i r o f  r e p l i c a t e s . I n g e n e r a l , a t l e a s t 25 c a s e s s h o u l d be r e p l i c a t e d for detection cephalograms  of systemic errors (Houston, 1979).  a r i s i n g i n obtaining  On t h e c o n t r a r y , random  can a r i s e as a r e s u l t o f v a r i a t i o n i n p o s i t i o n i n g o f t h e  lateral errors patient  i n t h e c e p h 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 o f t h e landmarks and inaccuracy of d i g i t i z a t i o n . f o r m u l a ( s=J  Houston emphasizes t h a t Dahlberg's  Ed / 2 (n-1) ) which has been t r a d i t i o n a l l y used f o r 2  62  the  calculation  o f t h e method e r r o r ,  could  not d i s c r i m i n a t e  s y s t e m i c e r r o r s from random e r r o r s . T h e r e f o r e , he s u g g e s t s a new coefficient  of r e l i a b i l i t y  of r e l i a b i l i t y ( T )  and index  r e p r e s e n t pure random e r r o r . The f o r m u l a i s ; where  T  i s index  of r e l i a b i l i t y ,  Sd  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  2  which  r = J l - Sd /Sg , 2  2  i s the variance  of  i s the greater variance  between two o f t h e r e p l i c a t e v a r i a n c e s . The a and  Student's  t t e s t has t r a d i t i o n a l l y been a c c e p t e d as  r o b u s t p a r a m e t r i c method. The t t e s t examines v a r i a n c e f i r s t determines  t h e f o r m u l a t o be used l a t e r on (Armitage and  B e r r y , 1987).  I n cases o f e q u a l v a r i a n c e , t h e f o r m u l a o f t h e  t t e s t i s t=X -X /SE (X -X ) , f o l l o w i n g t - d i s t r i b u t i o n 1  2  1  2  2 degree o f freedom. I n cases original  on n +n 1  2  o f unequal v a r i a n c e and i f t h e  means o f t h e two samples a r e n o t t o o d i f f e r e n t , i t  would be d i f f i c u l t substantially  t o f i n d a p r o p e r t r a n s f o r m a t i o n form which  reduces  this  parity  between  the variances.  T h e r e f o r e , a p o o l e d e s t i m a t e o f v a r i a n c e s was u t i l i z e d . d= X^-X /J(S^ /n^  + S / n ) c o u l d be used, w h i c h i s a p p r o x i m a t e l y  2  2  z  2  2  a s t a n d a r d i z e d normal d e v i a t e i f n l and n2 a r e r e s o n a b l y l a r g e . The  Wilcoxon  comparison s t u d y rather small. f r e e method  signed  rank  test  was  employed  f o rthe  (EMG and p r e s s u r e ) , s i n c e t h e sample s i z e was  The W i l c o x o n  (Armitage  s i g n e d rank t e s t i s a d i s t r i b u t i o n  and B e r r y ,  1987). The o b s e r v a t i o n s a r e  put i n a s c e n d i n g o r d e r o f magnitude, i g n o r i n g t h e s i g n , and g i v e the  ranks  positive  1 t o n' . values  L e t T+ be t h e sum o f t h e ranks  and T-  that  of the negative. 63  On  of the  the n u l l  h y p o t h e s i s T+ and T- would n o t be expected  to differ greatly;  t h e i r sum T+ and T- i s l / 2 n ' (n'+l) , so an a p p r o p r i a t e t e s t would c o n s i s t i n e v a l u a t i n g t h e p r o b a b i l i t y o f a v a l u e o f T+ e q u a l t o o r more extreme t h a n t h a t observed.  F o r l a r g e v a l u e s o f n , T+  and  distributed  T- a r e a p p r o x i m a t e l y  n'(n'+l)(2n'+l)/24  1  normally  with  variance  w i t h c o n t i n u i t y c o r r e c t i o n w h i c h i s g i v e n by  [T+ - l / 4 n ' ( n ' + l ) ] - l / 2 /  J{n (n'+1)(2n +1)/24}. 1  1  I f there are numerically t i e d variables,  they  are given  tied  r a n k s and reduced v a r i a n c e o f T+ by t ( t + l ) / 4 8 , where t= number 2  of t i e s .  However, A r m i t a g e and B e r r y (1987) commented t h a t t h e  s i 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 t h e n u m e r i c a l magnitudes o f t h e o b s e r v a t i o n s o t h e r t h a n t h e i r s i g n s . I f a h i g h p r o p o r t i o n o f l a r g e o b s e r v a t i o n s were p o s i t i v e  this  would  was  strengthen  t h e evidence  that  the d i s t r i b u t i o n  a s y m m e t r i c a l l y above z e r o . Two-way a n a l y s i s o f variance(Two-way ANOVA) was employed to  investigate the repeatability  measurement w i t h t h e f l u i d (1987)  stated  that  covariance(ANCOVA) variation. that  a  the  l e v e l device. purpose  i s to correct bias  I n the present  comparison  of natural  study,  a t t h e same  desirable.  64  of  head  posture  A r m i t a g e and B e r r y the  analysis  and t o reduce  t h e ANCOVA was used, age would  have  been  of  random given more  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 o u t on t h e r e s u l t s o f the  comparative  t h e OSA and from  study o f t h e u p - r i g h t and s u p i n e p o s i t i o n s i n  asymptomatic c o n t r o l groups. R e s u l t s were o b t a i n e d  cephalometric,  EMG  and  pressure  measurements.  P a r t i c u l a r l y , t h e c e p h a l o m e t r i c comparison s t u d y o f t h e up-right pieces  and s u p i n e  p o s i t i o n s provided  several  of information regarding the anatomical  o c c u r i n c o n j u n c t i o n w i t h body p o s i t i o n a l changes. pressure r e s u l t s also y i e l d e d  significant changes  that  The EMG and  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 t h o s e o f t h e c e p h a l o m e t r i c s t u d y . The r e s u l t s a r e r e p o r t e d as non-transformed  d a t a ( n e i t h e r l o g n o r square r o o t ) and a r e  summarized as measurements which a r e s t a t i s t i c a l l y at  p<  .05 l e v e l  asterisks.  denoted  by one a s t e r i s k  significant  o r p<.001 by two  A l l o f t h e l i n e a r c e p h a l o m e t r i c measurements were  e n l a r g e d by 8.5% and no c o r r e c t i o n o f t h e enlargement e f f e c t was attempted.  A. R e l i a b i l i t y  tests  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 t h e 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 o f  t h e n a t u r a l head p o s t u r e , and v a l i d i t y t e s t f o r t h e f l u i d d e v i c e were performed.  65  level  The evaluated. twice  with  fatigue. Pearson's  random Two  error  of  the  digitizing  procedure  p o i n t s on t h e same cephalogram were  enough  o f a time  i n t e r v a l to avoid  For representation of the d i g i t i z i n g simple  correlation  coefficient  r e l i a b i l t y i n d e x were employed.  was  digitized digitizing  random  ( r ) and  error,  Houston's  An example o f t h e c a l c u l a t i o n  f o r t h e i n t r a - e x a m i n e r random e r r o r i s as f o l l o w s :  1st time MP-H H-RGN PNS-P TGL MEAN SD Variance  2nd t i m e  14.4 41.0 56.5 86.6  14.5 41.0 56.5 86.4  49.62 30.16 909.63  49.60 30.04 902.40  r  Difference 0.1 0.0 0.0 0.2 0.08 0.10 0.09  1.000 Index o f r e l i a b i l i t y  r= 0.9985  As a r e s u l t o f t h e i n t r a - e x a m i n e r e r r o r , r=1.000 were o b t a i n e d ; as a r e s u l t o f t h e e x t r a - e x a m i n e r and T=0.9614 were observed.  and T=0.9985  e r r o r , r=0.9670  From t h e s e r e s u l t s , t h e d i g i t i z i n g  method, as used i n t h e c u r r e n t s t u d y , was found t o be r e l i a b l e and t h e i n t r a - e x a m i n e r 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 o f t h e hard t i s s u e measurement has been r e v i e w e d by numerous i n v e s t i g a t i o n s (Baumrind e t a l . , 1971,1976; Houston,  1979,1983;  reproducibility  test  Discussion f o r the  section).  soft-tissue  However,  measurements  a was  u n d e r t a k e n on f o u r  selected variables  (H-RGN, PNS-P,  IAS and  S o f t P a l a t e a r e a ) . 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 t h e f i r s t  tracings. Differences of  each  simple  series  o f measurements were  correlation  linearity  between each o f t h e p a i r s and v a r i a n c e s  coefficient  calculated.  (r) which  o f t h e randomness, t o g e t h e r w i t h  e r r o r and Houston's r e l i a b i l i t y (Table I I ) .  index  Pearson's  represents  the  D a h l b e r g s method 1  (T) were a l s o  provided  Minimum mean d i f f e r e n c e was d e t e r m i n e d from t h e  measurements o f t h e TGL(mean d i f f e r e n c e between t h e f i r s t and second measurement=0.5  mm; min=0.01mm; max=1.43mm). Pearson's  s i m p l e c o r r e l a t i o n c o e f f i c i e n t ( r ) between t h e two s e t s o f measurements was reliability  .9991; Dahlberg's  S.E. was  i n d e x was .9995. The v a r i a b l e  .49; Houston's  showing t h e l a r g e s t  mean d i f f e r e n c e among t h e 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 PNSP  (mean=.67mm;  min=.14mm;  max=1.61mm).  The  correlation  c o e f f i c i e n t o f t h e P-PNS measurement was .9966; D a h l b e r g ' s S.E. was .60; t h e r e l i a b i l i t y  i n d e x was .9986.  The r e p r o d u c i b i l i t y o f t h e s o f t p a l a t e showed a mean d i f f e r e n c e o f 27.47 mm  2  a r e l i a b i l i t y i n d e x o f .9959. I I showed h i g h r e l i a b i l i t i e s (  cross-sectional  area  , an r - v a l u e o f .9875 and  A l l o f t h e measurements i n T a b l e r > 0.9900) and n e g l i g i b l e method  e r r o r s i . e . n o t g r e a t e r t h a n 1mm i n l e n g t h and 3 0mm  2  67  i n area.  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 Soft Palate  Dahlberg's Houston's SE Index  Mean  Min. (mm) (mm) (mm) (mm) (mm*)  Legend Table I I  0.60 0.60 0.52 0.49 24.22  .9980 .9986 .9906 .9995 .9959  Mean v a l u e i n d i c a t e s average d i f f e r e n c e s between 1st and 2nd measurement on the same v a r i a b l e s , s r e v e a l s v a r i a n c e between 10 p a i r s o f measurements, r r e p r e s e n t s 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 e q u a t i o n of D a h l b e r g ' s SE i s J(X1-X2) /2(n-1) An example o f the c a l c u l a t i o n o f Houston's r e l i a b i l i t y i s as f o l l o w : 2  2  Subj e c t s  TGL ( Tongue Length) 1st 2nd  1 2 3 4 5 6 7 8 9 10 MEAN s SD 2  r 2d  Difference  83.82 94.16 98.99 78.99 69.91 82.98 97.01 96.50 76.77 90.58  83.00 93.94 98.98 78.77 69.45 81.55 96.98 95.66 76.08 90.29  0.82 0.22 0.01 0.22 0.46 1.43 0.03 0.84 0.69 0.29  86.47 101.66 10.08  86.97 98.38 9.92  0.50 0.20 0.45  0.9991 2  ; reliability  index (r) =  4.29  J 1 - S d / Sg 2  S d : v a r i a n c e of the d i f f e r e n c e s 2  S g 2  68  :the greater variance  2  Reproducibility  o f t h e n a t u r a l head p o s i t i o n has  s t u d i e d by s e v e r a l r e s e a r c h e r s and T a l l g r e n , 1976;  Solow  S i e r s b a e k - N i e l s e n and Solow, 1982 ; Showfety  e t a l . ; Sandham, 1988). The and  (Moorrees and Kean, 1958;  been  measurement o f  reproducibility  n a t u r a l head p o s t u r e  of r e p o s i t i o n i n g  was  i n v e s t i g a t e d by  r e p e a t e d measurements a t t h r e e d i f f e r e n t t i m e s on f o u r s u b j e c t s (see T a b l e body and  I I I ) . The  s u b j e c t s were p o s i t i o n e d i n t h e n a t u r a l  head p o s t u r e  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 d e v i c e on t h e head.  The degree on t h e l e v e l d e v i c e  was  time.  recorded  twice  per  each  The  second  and  third  measurements were c a r r i e d out a t a minimum i n t e r v a l o f a week i n t h e same manner as f o r 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 . two-way ANOVA was  used f o r t h e t e s t o f r e p e a t a b i l i t y and  A the  r e s u l t s a r e r e p r e s e n t e d 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 t h e a n g u l a t i o n o f the head p o s t u r e was from  subject  to  subject(p=0.000),  d i f f e r e n t times(0.192) f o r t h e probability(p=.009)  i n the  yet  significantly was  not  same s u b j e c t s .  Subject*Measurement  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 t h e same c e l l .  69  different  different A  at  significant (interaction)  Table III  Reproducibility Studies of Natural Head Position and Measurement  Measurements 1st  2nd  3rd  15/15 7/5 -2/-2 2/3  15/15 6/7 -2/-3 1/0  13/12 6/7 -1/-1 0/2  Subjects 1 2 3 4  unit = degree  T W O - W A Y ANALYSIS OF VARIANCE SOURCE  SUM-OF SQUARES  SUBJECTS MEASUREMENT SUBJECT * MEASUREMENT ERROR  Legend T a b l e I I I  DF  MEAN-SQUARE  F-RATIO  890.833 1.583  3 2  296.944 0.792  712.667 1.900  0.000 0 192  12.471 5.000  6 12  2.069 0.417  4.967  0.009  A p a i r o f numbers i n e a c h c e l l i n t o p t a b l e r e v e a l s t h e d e g r e e o f head p o s t u r e from t h e f l u i d l e v e l d e v i c e . The p r o b a b i l i t y ( 0 . 0 0 9 ) o f t h e i n t e r a c t i o n term(SUBJECT*MEASUREMENT column) i n t h e lower t a b l e s u g g e s t s 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 t h e same c e l l .  70  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 d e v i c e , t h e o v e r a l l c o r r e l a t i o n between t h e head p o s t u r e a n g l e from t h e m o d i f i e d l e v e l d e v i c e and t h e a n g l e from t h e FH p l a n e 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 upright  cephalograms and  represented  graphically  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 intercept confidence 1.5°  -0.1089  at  interval  P  less  suggests  than  i n Figure  13.  0.9505; s l o p e 0.9388;  0.001  level.  The  95%  a d e v i a t i o n o f not g r e a t e r  than  o f t h e head p o s t u r e a n g l e i n between t h e l e v e l d e v i c e  and  t h e measured a n g l e on the cephalograms (1.097 as a upper l i m i t , 0.7869 as a lower l i m i t ) . T h e r e f o r e , 95% o f t h e v a l u e s measured by  the  modified  level  device  are  measured on t h e cephalograms w i t h 1.5°  71  identical  to  the  of d e v i a t i o n .  values  Fig. 13  Relationship between Level Device Angle and the FH/True Horizontal Cephalometric Angle  Legend F i g . 1 3  The g r a p h i c a l d i s t r i b u t i o n o f t h e p o i n t s s u g g e s t s a s t r o n g l i n e a r tendancy (Pearson's r=0.9505).  B. C e p h a l o m e t r i c s t u d y The r e s u l t s o f t h e l a t e r a l c e p h a l o m e t r i c comparison s t u d y o f OSA  and asymptomatic c o n t r o l s i n d i f f e r e n t body  positions  (see T a b l e IV) show t h a t , e x c e p t f o r t h e TGH(p=.331), most of t h e 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 t h e upr i g h t cephalograms.  I n u p - r i g h t cephalograms, t h e OSA  group  showed a l o n g e r tongue, a l o n g e r and t h i c k e r s o f t p a l a t e , anteroposteriorly  narrower  and  superoinferiorly  an  lengthened  a i r w a y , and a more 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 bone t h a n t h e asymptomatic c o n t r o l s . For t h e a n g u l a t i o n measurements,  t h e 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 t h e asymptomatic c o n t r o l group; t h e former r e g i s t e r e d an E-TT v a l u e o f 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) a n g u l a t i o n s , w h i c h 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 up-right  cephalograms. On t h e o t h e r hand, t h e s u p i n e cephalograms c o u l d not p r o v i d e a p p r o p r i a t e a n g u l a r comparisons o f t h e head p o s t u r e o f t h e OSA and t h e asymptomatic c o n t r o l group due t o s i g n i f i c a n t variations  i n p i l l o w h e i g h t . I n t h e comparison o f t h e c r o s s -  sectional  area  differences  measurements,  between  the  two  there groups  were i n the  no  significant  tongue(p=.060),  nasopharynx(p=.239) and oropharynx(p=.214) a r e a s i n t h e u p - r i g h t cephalograms.  Y e t , t h e OSA  group  did reveal  a  larger  soft  palate(p=.005) and a s m a l l e r hypopharyngeal area(p=.004) i n t h e u p - r i g h t cephalograms.  Table IV  Comparison of OSA and Asymptomatic Controls In Up-right and Supine Cephalometric Positions  Up Riglit Conlrol  OSA Mean  Supine OSA  SD  Mean  SD  P less than  Conlrol  Mean  SD  Mean  SD  P less than  Tongue TGL  90.76  8 .09  83 .25  5 .21  .013  87.4 1  6.22  79.74  6.84  .005 * *  TGH  40.79  4 .49  39 .19  3 .34  .331  42.90  3.10  38.54  2.89  .001 * *  PNS-P  49.01  10.54  40.37  3 .90  .019 *  50.36  9.98  41.55  2.97  .011  MPT  14.99  4 .61  1 1. 5 4  1.64  .030  14.44  3.9 I  12.70  1.15  .100  SPAS  5.33  2 99  9 .24  2.68  .002 + +  2.97  2.53  10.37  II.30  MAS  9.96  3 14  13.57  3 34  .007  9.63  8.54  12.49  3.50  IAS  7.52  3.99  1 1. 2 7  3 28  .016  5.37  3.89  9.90  2.45  .002 * *  87.30  7 14  7 3 01  3 57  .000 + *  84.45  5.88  68.17  6.07  .000 • *  28.30  8 64  17 0 9  3 87  24.93  7.52  12.06  4.96  .000  18.90  7 37  12 21  4 54  .001 ** .014 *  16.44  7.29  6.72  4.57  .001 *+  40.76  7.96  36.29  5.74  .126  Soft  I'alatc •  Airway  VAL Hyoid  .008 • * .323  bone  MP-H H-Hl H-RGN  •  44.65  7 10  38 8 8  2 88  .021  38.05  6 82  28 9 5  7 92  .003  CVTPP  104.20  6 97  96 73  6 04  CVTSN  113.12  7 87  105 7 6  .008 * + .012 +  OPTPP  98.83  7 75  89 82  10 22  OPTSN  107.78  8 24  9 8 84  9 96  3826.68  573 45  3 4 3 7 05  3 5 6 73  3992.80  475.74  3436.5 1  519.12  154 34  364 99  5 3 . 25  .005 * *  554.74  132.86  431.90  48.70  .009 * *  Nasopharynx  205.29  8 7 . 88  242. 96  6 3 . 31  .239  2 0 3 84  88.11  230.35  63.60  .406  Oropharynx  497.70  1 8 5 . 76  5 7 9 86  1 17 1 2  .214  315 95  127.13  412.42  123.09  .058  171.02  98.99  330.81  102.50  .000 * *  Tongue BIT Vertebrae  Tongue Soft  Palate  Hypopharynx  Legend T a b l e IV  161 .08  87. 63  29 2. 5 7  5. 1 1  14 1. 1 2  .013 .014 * .060  .004  **  The comparison i s performed by the Student t t e s 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 .  510.99  .006 • *  In  contrast,  area(p=.006)  TGH(p=.001)  showed  significant  and  tongue  differences  cross-sectional between  OSA  and  c o n t r o l s u b j e c t s i n t h e s u p i n e p o s i t i o n , but not i n t h e 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 t h e OSA and t h e asymptomatic c o n t r o l groups i n t h e s u p i n e cephalograms but were significantly sectional  different  area  of  difference(p=.058)  i n the u p - r i g h t p o s i t i o n .  the  oropharynx  between  the  two  failed groups  The  to in  crossshow  the  a  supine  cephalograms. The  results  of  the  lateral  cephalometric  comparisons  between t h e u p - r i g h t and s u p i n e p o s i t i o n s f o r each o f t h e different  groups  variables,  TGH,  are  provided  PNS-P,  MAS  i n Table did  not  V.  Of  yield  the  two  linear  differences  c o r r e s p o n d i n g t o p o s i t i o n a l changes i n b o t h groups. The  tongue  length(TGL) was reduced s i g n i f i c a n t l y by a p p r o x i m a t e l y t h e same amount  i n the  height(TGH) control  supine  position  i n c r e a s e d i n t h e OSA  i n both group,  groups.  The  tongue  but d e c r e a s e d  i n the  group i n t h e s u p i n e p o s i t i o n ; h o w e v e r ,  statistically,  t h e r e 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) the  r e v e a l e d no s i g n i f i c a n t change i n t h e OSA control  group(p=.002)  corresponding t o the  showed  group,  significant  p o s i t i o n a l changes. The  but i n  thickening  cross-sectional  s i z e of t h e upper a i r w a y was reduced i n t h e s u p i n e 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 t h e OSA group (p=. 018) , but not i n t h e 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 OSA Up Mean  right  Control Supine  SD  Mean  SD  P  less than  Up Mean  right  Supine  SD  Mean  SD  P  less than  Tongue 1CL  90 .76  8 .09  87.4 1  6 .22  .021  TGH  40 .79  4 .49  42.90  3 .10  .062  4 9 .01 14 . 9 9  10 . 5 4 4 .61  50.36 14.44  9 .98  .074  3 .91  .323  5 .33  2 .99  2.97  2 .53  .000 * •  Soft  *  Palate PNS-P MPT  MAS  9 96  3 .14  9.63  8 54  .870  IAS  7 52  3 .99  5.37  3 89  .018  14  84.45  5 88  .078  VAL Hyoid  87  30  7  1  8 3.25 39 .19  5 .21  79 .74  6.84  .021  3 .34  38 .54  2.89  .544  1  4 0. 3 7 II .54  3 .90 1 .64  41 .55 1 2.70  2.97  .225  1.15  .002 * *  9 .24  2 .68  10 . 3 7  1 1.30  1  Airway SPAS  1  *  *  .772  1 3 47  3 34  12 4 9  3.50  .161  1 1 27  3 28  9 90  .195  7 3 01  3 57  68  17  2.45 6.07  .007  * • ,0  bone  1  MP-H  28 30  8 64  24.93  7 52  .074  11 I I I  18 9 0 44 65  7 37  16.44  7  10  40.76  7 29 7 96  .115 .04 1 • 1  3 8 2 6 . 68  573. 45  3992.80  4 7 5 . 74  5 1 9 . 12  1 5 4 . 34  554.74  132. 86  2 0 5 . 29 497. 70 161 . 0 8  8 7 . 88 185. 76 87. 63  303.84  ll-RGN Tongue Soft Palate Nasopharynx Oropharynx llypopharynx  315.95 1 7 1 .02  88. 1 1 1 2 7 . 13 98. 99  j  09  3 87  12 0 6  4.96  .000 * •  1 2 21  4 54  6 72  3 8 88  2 88  36. 29  4.57 5.74  .109  .014 •  3 4 3 7 . 05  3 5 6 . 73  3 4 3 6 . 51  510.99  .996  .043 •  3 6 4 . 99  5 3 . 25  4 3 1 . 90  48.70  .000 * *  .918  242. 96  .354  5 7 9 . 86 292'. 5 7  2 3 0 . 35 4 12.42  63.60  .000 + *  6 3 . 31 1 17. 1 2 14 1. 1 2  .660  17  3 3 0 . 81  1 23.09 102.50  .003 * *  .000 * • .142  Again,  IAS  was  shown t o be  shorter(p=.018) i n t h e s u p i n e  p o s i t i o n i n t h e OSA group, b u t not i n t h e asymptomatic group(p=.195). The v e r t i c a l l e n g t h o f t h e a i r w a y a s i g n i f i c a n t change OSA  d i d not show  (VAL) f o l l o w i n g p o s i t i o n a l change  group, b u t d i d i n t h e asymptomatic c o n t r o l  l e v e l . MP-H  control  i n the  a t t h e p=.007  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  t h e u p - r i g h t and supine(p=.074) p o s i t i o n s i n t h e OSA group, but differed  i n the control  group a t t h e 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 t h e OSA group.  The d i s t a n c e between t h e h y o i d  bone and t h e r e 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 s h o r t e n e d i n t h e OSA group(p=.041) however,  no  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;  significant  change  was  seen  group(p=.109). The tongue c r o s s - s e c t i o n a l  in  the  control  a r e a was shown t o 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 t h e u p - r i g h t p o s i t i o n i n t h e OSA  group(p=.014);however,  d i f f e r e n c e was o b s e r v e d i n t h e c o n t r o l group(p=.996).  no  Although  the s o f t p a l a t e became l a r g e r i n b o t h 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, t h e i n c r e a s e i n s i z e was more s i g n i f i c a n t in  t h e asymptomatic  degree o f c o l l a p s e the  body  In both groups, a  large  was shown i n t h e o r o p h a r y n g e a l a r e a ,  after  positional  nasopharynx  and  control  change,  group.  but  hypopharynx.  this  While  was the  not  seen  i n the  oropharyngeal area  d e c r e a s e d by 3 6.5% i n t h e OSA group, i t d e c r e a s e d by 29% i n t h e asymptomatic c o n t r o l s . However, t h e d i f f e r e n c e between t h e two 77  groups  was h a r d l y  noticeable  i n both p o s i t i o n s  cephalograms(p=.214 i n t h e u p - r i g h t  cephalograms;  used  f o r the  .058 i n t h e  s u p i n e cephalograms). An ANCOVA t e s t was used t o i n v e s t i g a t e t h e age e f f e c t on the  hyoid  variables  variables,  yet the r e s u l t s  indicate  that  none o f  (MP-H p=.353, H-Hl p=.135, H-RGN .228) were a f f e c t e d  by an age (see T a b l e V I ) .  78  Table VI  ANCOVA test of the Age Effect on the Hyoid Variables  DEP VAR: M P - H  29  N:  MULTIPLE R:  .621  SQUARED MULTIPLE R:386  ANALYSIS OF VARIANCE SOURCE  DF  MEAN-SQUARE  F-RATIO  432.326 50.414  1 1  432.326 50.414  7.667 0.894  1466.130  26  56.390  N:  29  MULTIPLE R:  SUM-OF-SQUARES  SUBJECTS AGE ERROR  DEP VAR: H"H1  512  0.010 0.353  SQUARED MULTIPLE R:262  ANALYSIS OF VARIANCE SOURCE  SUM-OF-SQUARES  SUBJECTS AGE ERROR  DF  MEAN-SQUARE  F-RATIO  77.515 102.117  1 1  77.515 102.117  1.806 2.379  1116.176  26  42.930  29  MULTIPLE R:  DEP VAR: H-RGN  .492  0.191 0.135  SQUARED MULTIPLE R:242  ANALYSIS OF VARIANCE SOURCE  SUM-OF-SQUARES  SUBJECTS AGE ERROR  Legend Table VI  DF  MEAN-SQUARE  F-RATIO  293.305 54.859  1 1  293.305 54.859  3.151 1.524  935.621  26  35.985  0.008 0.228  The p r o b a b i l i t y of the age r e v e a l s t h e comparisons of the h y o i d 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 The  of  the  OSA g r o u p  palate,  an  cephalometric showed  a  longer  anteroposteriorly  superoinferiorly  lengthened  positioned  bone,  extended  The  hyoid head  up-right  posture  standing  OSA g r o u p  tongue  study:  and  a  a  tongue,  a  narrower upper  more  and a  larger  and  airway,  up-right smaller  soft  a  inferiorly  tongue,  a  more  hypopharynx  in  the  position.  showed  greater  smaller  tongue  hypopharyngeal  height, area  a  in  larger  the  supine  position. With the in  the  positional  thickness the  airway With the  control was  the  in  by  tongue 4.3%  bone  the  symphysis The  more  the  by  palate  of  supine,  more the  upper  OSA g r o u p .  moved up t o w a r d  i n the  the  to  supine,  mandibular  and toward  the  plane  mandibular  OSA g r o u p . area  supine p o s i t i o n  3 6.5%  size  from u p - r i g h t  subjects,  to  increased  the  i n the  changes  cross-sectional  i n the  decreased  was  from u p - r i g h t  whereas  decreased  control  more  soft  group,  positional  hyoid  more  of  changes  i n the  80  increased and  significantly  oropharyngeal  OSA g r o u p .  area  C. EMG and p r e s s u r e s t u d y A comparison  o f EMG and P r e s s u r e v a r i a b l e s o b t a i n e d i n  t h e u p - r i g h t and t h e s u p i n e p o s i t i o n s Table V I I .  A l l o f t h e comparisons  are provided i n  were performed  by means o f  W i l c o x o n Signed Rank t e s t . The r e s t i n g a c t i v i t y o f t h e GG muscle i n c r e a s e d a p p r o x i m a t e l y 34 % (from 2.58 t o 3.33 g/cm ) a t t h e 2  p=.037 l e v e l w i t h t h e body p o s i t i o n a l change from u p - r i g h t t o 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 t h e s u p i n e p o s i t i o n a t t h e p=.008 l e v e l .  For  t h e p r o t r u s i o n t a s k , t h e s u p r a - h y o i d muscle group r e v e a l e d a significantly  increased  activity  (p=.014).  The  GG  muscle  r e v e a l e d s i g n i f i c a n t l y l a r g e r v a l u e s on maximum opening t a s k i n t h e u p - r i g h t and t h e s u p i n e p o s i t i o n s a t t h e 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 Rest  Protrusion  Max. Opening  Up- Right  Geniogiossus Masseter Orbicularis Oris Supra-hyoid Geniogiossus Masseter Orbicularis Oris Supra-hyoid Geniogiossus Masseter Orbicularis Oris Supra-hyoid  Mean 2.58 2.22 3.69 1.87 93.41 12.78 11.13 27.11 16.87 12.03 49.93 49.64  SD 1.03 1.78 3.50 0.67 48.89 12.04 8.22 50.36 9.89 14.70 46.17 28.60  Supine  Mean 3.33 2.47 2.49 2.02 93.10 12.30 12.07 35.45 21.79 12.69 62.76 57.58  SD P less than 1.58 .037 * 1.91 .260 1.56 .008 " 0.77 .066 56.93 .959 11.27 .575 11.60 .767 69.97 .014 * 10.42 .028 * 14.32 .878 63.75 .086 37.08 .285  unit:= uV  Pressure Rest Protrusion Max. Opening  Anterior Posterior Anterior Posterior Anterior Posterior  10.33 12.01 799.79 136.49 11.29 28.25  9.10 5.76 293.80 93.47 10.81 16.98  7.83 14.01 808.08 116.54 11.85 32.02  6.88 5.46 300.77 73.26 13.65 18.74  unit= g/cm  Legend T a b l e V I I  2  E a c h EMG a n d p r e s s u r e v a l u e was c o n v e r t e d and c a l i b r a t e d t o (iV a n d g/cm . 1  82  .333 .017 * .878 .314 .859 .241  F o r t h e p r e s s u r e d a t a , t h e p o s t e r i o r tongue p r e s s u r e a t r e s t r e v e a l e d an i n c r e a s e d v a l u e o f 17% (2g/cin ) a t t h e .017 2  level  (where, two e x t r e m e l y i n c r e a s e d o r d e c r e a s e d v a l u e s were  precluded).  The r e s t i n g EMG a c t i v i t y o f t h e s u p r a - h y o i d muscle  group showed an almost s i g n i f i c a n t v a l u e  (p=.066); i . e . , o n l y  two s u b j e c t s o u t o f t e n r e v e a l e d decreased supine  position,  and i n t u r n ,  showed  EMG v a l u e s i n t h e  a s t r o n g tendency  to  i n c r e a s e t h e s u p r a - h y o i d muscle a c t i v i t y i n t h e s u p i n e p o s i t i o n (see F i g . 1 4 ) . maximum  The EMG a c t i v i t y  o f t h e s u p r a - h y o i d muscle a t  p r o t r u s i o n was s i g n i f i c a n t l y  greater  i n t h e supine  p o s i t i o n t h a n i n t h e u p - r i g h t p o s i t i o n , and t h e GG EMG a c t i v i t y a t maximum opening a l s o showed a s i g n i f i c a n t l y h i g h v a l u e i n t h e s u p i n e p o s i t i o n . The EMG a c t i v i t y o f t h e masseter muscle d i d n o t 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 o f t h e t a s k s .  83  Fig 14  Tongue E M G and Pressure Changes at Rest in Up-right and Supine Positions  EMG  EMG  mV  Pressure  mV  UP-RIGHT  SUPINE  G G muscle Legend F i g . 1 4  UP-RIGHT  SUPINE  S u p r a h y o i d muscle  UP-RIGHT Post,  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 increasing c h a n g e o f EMG and p r e s s u r e due t o t h e c h a n g e i n body position, whereas t h e broken lines show a decrease change.  SUPINE  transducer  As a summary o f t h e r e s t EMG  and p r e s s u r e s t u d y ,  with  t h e p o s i t i o n a l changes from u p - r i g h t t o s u p i n e , t h e asymptomatic c o n t r o l group showed: 1. The EMG  a c t i v i t y o f t h e GG muscle i n c r e a s e d by 3 3.8%.  2. The p r e s s u r e o f t h e p o s t e r i o r p o r t i o n o f t h e tongue i n c r e a s e d 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 o f t h e i n f e r i o r  orbicularis  o r i s d e c r e a s e d by 32.5%. 4. The EMG  a c t i v i t y o f t h e s u p r a - h y o i d group i n c r e a s e d  y e t t h e change was not s t a t i s t i c a l l y  In  conclusion,  8%,  significant.  the oropharyngeal c r o s s - s e c t i o n a l  c o l l a p s e d by a p p r o x i m a t e l y muscle a c t i v i t y  by  30% d e s p i t e a 34%  increase  area i n GG  i n t h e 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 t h e tongue o b s e r v e d i n t h e s u p i n e p o s i t i o n i n t h e non-apneic group.  was In  a d d i t i o n , 17% o f t h e tongue p r e s s u r e i n c r e m e n t was r e c o r d e d on the p o s t e r i o r load c e l l .  W i t h t h e p o s i t i o n a l changes, t h e s i z e  o f t h e s o f t p a l a t e i n c r e a s e d by 18.3% i n t h e c o n t r o l group. A l l t h e hypopharynx changes a r e 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 a r e a o f t h e hypopharynx i n c r e a s e d by 13% which was  accompanied by an 8%  increase  i n the supra-hyoid  a c t i v i t y and a 6% d e c r e a s e i n t h e H-RGN v a l u e .  85  muscle  DISCUSSION  The  current  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 , a i r w a y s i z e and body posture.  For  comparisons  of  airway  size,  measurements were employed; f o r comparisons  cephalometric  o f tongue and o t h e r  muscle a c t i v i t y , EMG and p r e s s u r e s t u d i e s were u n d e r t a k e n . The s u p i n e c e p h a l o m e t r i c t e c h n i q u e was u t i l i z e d i n t h e c u r r e n t s t u d y and a comparison  between t h e u p - r i g h t and s u p i n e cephalograms  was made. I t appeared t h a t t h e OSA p a t i e n t s have l a r g e r and s m a l l e r o r o p h a r y n g e a l a i r w a y s i n t h e s u p i n e  tongues  cephalograms.  I n a d d i t i o n , t h e l o c a t i o n a l change o f t h e tongue i n t h e s u p i n e position  was  quantified  by  a  change  i n posterior  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 s m a l l a i r w a y  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 . Lowe e t al.(1986,1989)  the c o n s t r i c t i o n  a r e a and  measured t h e s i z e o f t h e upper a i r w a y by means o f  computer  aided  visualized  Recently,  t h r e e - d i m e n s i o n a l CT r e c o n s t r u c t i o n .  In spite  of the  j u d i c i o u s combined study o f t h e CT and t h e p r e s s u r e t r a n s d u c e r , Stauffer  et  differences  al.(1987), i n airway  asymptomatic c o n t r o l s . seems more l i k e l y  could  size  not  between  They c o n c l u d e d  t o be r e l a t e d  find  any  patients  with  t h a t airway  t o t h e AHI  significant OSA and  resistance  (Apnea Hypopnea  Index) t h a n t o t h e c r o s s - s e c t i o n a l s i z e o f t h e a i r w a y . Adequate 86  GG muscle  a c t i v i t y may  t h e g e n e s i s o f OSA.  be one o f t h e most d e c i s i v e f a c t o r s i n  Remmers e t a l . ( 1 9 7 8 ) m o n i t o r e d t h e EMG  of  t h e GG muscle u s i n g f i n e w i r e 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 t h e a s s o c i a t i o n of t h e muscle w i t h OSA  symptoms. S u b s e q u e n t l y ,  several  the  publications  have  addressed  inter-relationship  between d i a p h r a g m a t i c and GG EMG a c t i v i t y . A n o t h e r group w o r k i n g w i t h the h y o i d apparatus  suggested  t h a t the p o s i t i o n  of  the  h y o i d a r c h p l a y s an i m p o r t a n t r o l e i n t h e m a i n t a i n e n c e o f upper a i r w a y p a t e n c y (Van de G r a a f f e t a l . , 1984; Van L u n t e r e n e t a l . , 1987) .  They p o s t u l a t e d t h a t d e c r e a s e d  hyoid  muscle  hypopharyngeal  activity  could  be  or p o o r l y coordinated  a  crucial  factor  in  o b s t r u c t i o n . However, most i n f o r m a t i o n a c q u i r e d  t o d a t e from t h i s s o r t o f b i o m e c h a n i c a l s t u d y has been r e t r i e v e d from a n i m a l e x p e r i m e n t s . The  c o u p l i n g a c t i o n o f t h e h y o i d and  GG muscles i n dogs and c a t s may be d i f f e r e n t i n humans; y e t few s t u d i e s have been done on human s u b j e c t s . R e c e n t l y , Lowe and coworkers  ( p e r s o n a l communication)  presented a f a c i a l p r o f i l o g r a m  o f 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 ,  h y o i d bone  was  reported  i n t h e OSA  a  inferiorly  p a t i e n t group  positioned as one  of the  significant  r e s u l t s o f t h e c u r r e n t s t u d y i n agreement w i t h p r e v i o u s d a t a from s e v e r a l e a r l i e r s t u d i e s . T o n i c a c t i v i t y o f t h e GG o r h y o i d muscle group may be more i m p o r t a n t t h a n p h a s i c a c t i v i t y , f o r t h e tonic  activity  o f t h e upper  a i r w a y muscles  d i r e c t l y r e l a t e d t o the s i z e of the  to  be  a i r w a y . I n an age-matched  s t u d y by Brown and a s s o c i a t e s (1987), 87  is likely  i t was  emphasized  that  t h e OSA  group i s d i s t i n g u i s h e d not by t h e c r o s s - s e c t i o n a l a r e a  but by t h e d i s t e n s i b i l i t y  o f t h e pharynx.  Similarily,  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 did  not  differentiate  patients  w i t h OSA  symptoms  from  non-  p a t i e n t s . However, t h e c u r r e n t s t u d y d i d show t h a t o r o p h a r y n g e a l a r e a was more c o l l a p s e d i n t h e OSA group i n t h e s u p i n e p o s i t i o n even though i t was Table I V ) .  Consequently,  c o n s i d e r OSA s m a l l . We  not s t a t i s t i c a l l y i t may  s i g n i f i c a n t ( P = . 0 5 8 ) (see  be an o v e r s i m p l i f i c a t i o n t o  as a d i s e a s e which may  o c c u r when t h e a i r w a y i s  s h o u l d t h e r e f o r e c o n s i d e r not o n l y m o r p h o l o g i c a l and  functional  factors  but  also  the  inter-relationship  of  both  factors. A. C e p h a l o m e t r i c s t u d y Numerous  investigators  have  measured  the  anatomical  s t r u c t u r e s o f t h e upper a i r w a y (Jackson and O l s o n , 1980; Hoponik e t a l . , 1983 ; Lowe e t a l . , 1986;  and  M a r t i n e t a l . , 1987).  C e p h a l o m e t r i c a n a l y s e s have l o n g been used f o r t h e i n v e s t i g a t i o n o f f a c i a l growth and development i n t h e f i e l d o f o r t h o d o n t i c s . Cephalometric  t e c h n i q u e s 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 e v a l u a t e t h e s i z e o f t h e tongue and (Riley et a l . , Strelzow  1983; Lowe e t a l . ,  e t a l . , 1988;  Lyberg et a l . , two-dimensional considered  1989).  1986; Jamieson  deBerry-Borowiecki  et a l . ,  e t a l . , 1988;  1986; and  I n s p i t e o f o b v i o u s l i m i t a t i o n s as a  method o f a n a l y s i s ,  a convenient,  airway  less  cephalometrics i s  invasive,  t e c h n i q u e t o e v a l u a t e upper a i r w a y s i z e . 88  and  less  still  expensive  I n 1983, R i l e y and co-  workers  a c t i v e l y i n t r o d u c e d c e p h a l o m e t r i c a n a l y s i s t o t h e OSA  r e s e a r c h 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 t h e f l o w volume c u r v e . Lowe and a s s o c i a t e s (1986) r e v i e w e d t h e s o f t and h a r d t i s s u e c h a r a c t e r i s t i c s o f OSA p a t i e n t s by means o f c e p h a l o m e t r i c 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 u s i n g 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 o f t h e c u r r e n t s t u d y agree w i t h most o f t h e s o f t - t i s s u e measurements t h a t t h e y a n a l y z e d .  As a  r e s u l t o f t h e development o f computer equipment and s o f t w a r e , several  measurement s t u d i e s on s o f t - t i s s u e  areas  and a i r w a y  space have been produced. S t r e l z o w e t a l . ( 1 9 8 8 ) r e p o r t e d r e s u l t s from a c e p h a l o m e t r i c s t u d y which c o n c e n t r a t e d more on t h e s i z e and p o s i t i o n a l changes o f t h e tongue, s o f t p a l a t e , p h a r y n g e a l space and t h e l o c a t i o n o f t h e h y o i d bone. Not s u r p r i s i n g l y , n o t o n l y t h e l i n e a r measurements b u t a l s o t h e measurements o f t h e c r o s s - s e c t i o n a l a r e a o f t h e tongue and s o f t p a l a t e the r e s u l t s  o f t h e c u r r e n t study  approximate  (see T a b l e V I I I ) .  Another  s t u d y ( d e B e r r y - B o r o w i e c k i e t a l . , 1988) which adopted  virtually  t h e same d e f i n i t i o n s o f l i n e a r measurements and tongue and s o f t palate  cross-sectional  areas  as t h e former  study,  provided  s i m i l a r r e s u l t s b u t a s h o r t e r s o f t p a l a t e and s m a l l e r tongue a r e a (see T a b l e V I I I ) . undertook  R e c e n t l y , Lyberg and a s s o c i a t e s (1989)  a cephalometric study t h a t i s h i g h l y compatible w i t h  t h e p r e s e n t p r o j e c t i n terms o f t h e d e f i n i t i o n s o f t h e l i n e a r , angular  and  area  measurement  variables.  They  obtained  cephalograms i n n a t u r a l head p o s t u r e , a l t h o u g h i t i s n o t c l e a r whether t h e s u b j e c t s were s t a n d i n g o r s i t t i n g . 89  TABLE Vlll A.  Linear and Area Variable Comparisons Between Current Report and Other Studies  Linear Comparisons  unit=mm  Current study  PNS-P MPT MAS IAS  OSA(20) Mean SD 49.01 3.9 14.99 4.6 9.96 3.1 7.52 3.9  Lyberg et al.  CONTROL (10) Mean SD 40.47 3.9 11.54 1.6 13.57 3.3 3.3 11.27  OSA(25) SD Mean 4.3 48.0 2.0 14.0 8.4 3.5 4.0 10.3  deBerry-Borowiecki et al.  PNS-P MPT  OSA (30) SD Mean 6.0 41.6 6.0 14.0  CONTROL(12) Mean SD 34.7 7.0 10.0 2.0  CONTROL (10) Mean SD 35.3 4.6 11.2 1.5 13.7 3.8 13.8 3.8  Strelzow et al. OSA (90) SD Mean 46.0 7.0 2.0 13.0  CONTROL (12) SD Mean 36.0 8.0 11.0 2.0  Jamieson et al.  PNS-P MPT IAS B.  0SA(138) Mean SD 46.7 3.0 5.3  3.0  CONTROL (7) SD Mean 36.4 4.4 12.4  3.5  Area Comparisons unit=mm Current study  3  OSA(20) Mean SD Tongue 3826 Soft Palate 519  573 154  Lyberg et al.  CONTROL (10) Mean SD 3437 364  356 53  OSA (25) Mean SD  CONTROL (10) Mean SD  3597 485  3486 288  deBerry-Borowiecki et al. OSA (30) Mean SD Tongue 3790 Soft Palate 459 Legend T a b l e V I I I  CONTROL (12) Mean SD  375 3215 134 251  471 63  459 80  Strelzow et al. OSA(90) Mean SD 3884 457  CONTROL (12) Mean SD  404 3374 105 289  Numbers i n a p a r e n t h e s i s i n d i c a t e sample  90  344 62  293 88 size.  Lyberg e t a l . p r o v i d e d  v a l u e s f o r t h e PNS-P, MPT,  MAS, IAS,  tongue and s o f t p a l a t e a r e a t h a t a r e r e m a r k a b l y  s i m i l a r t o the  r e s u l t s o f t h e c u r r e n t s t u d y (see T a b l e V I I I ) .  The s t u d i e s by  Jamieson  and a s s o c i a t e s ( 1 9 8 6 )  and d e B e r r y - B o r o w i e c k i  et a l .  (1988) p r o v i d e d age-matched r e s u l t s which i n c l u d e d f e m a l e s . The controls  used  i n the study  by Lyberg  e t a l . were g e n e r a l l y  younger i n d i v i d u a l s ( m e a n age =2 3.6). The tongue  a r e a and s o f t  p a l a t e o f t h e c o n t r o l group i n t h e s t u d y by d e B e r r y - B o r o w i e c k i et  a l . were v e r y  compared  t o those  s m a l l even though t h e s u b j e c t s were o l d e r i n the other  studies.  The  present  study  r e v e a l e d t h e l o n g e s t and l a r g e s t s o f t p a l a t e o f a l l t h e s e v e r a l research  p r o j e c t s i n Table  VIII;  but i n these  s t u d i e s the  maximum t h i c k n e s s o f t h e s o f t p a l a t e was v e r y s i m i l a r . T h i s i s p o s s i b l y due t o t h e f a c t t h a t most o f t h e asymptomatic c o n t r o l s u b j e c t s employed i n t h e c u r r e n t s t u d y were s n o r e r s , 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). Interestingly,  Lyberg  et a l . f a i l e d  d i f f e r e n c e between t h e OSA  to find  and t h e c o n t r o l  a  significant  group f o r tongue  a r e a , as t h e c u r r e n t s t u d y d i d . However, t h e c r o s s - s e c t i o n a l a r e a o f t h e 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 t h e two studies.  A supine  cephalogram may  p r o v i d e 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 t h a n t h e u p - r i g h t cephalogram. The tongue a r e a 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 t h e two groups at  a  probability  level  of  less  than  1%  in  the  supine  cephalograms (see T a b l e V ) . I n t h e OSA group, t h e tongue c r o s s -  sectional  a r e a became s i g n i f i c a n t l y  position  (see T a b l e  V).  broadened  However,  the  i n the supine  tongue  area  of  asymptomatic c o n t r o l s d i d n o t show s i g n i f i c a n t change (see T a b l e V) .  T h e r e f o r e , d i f f e r e n c e s became more a p p a r e n t i n t h e s u p i n e  cephalograms. I n a d d i t i o n , t h e a i r w a y b e h i n d t h e s o f t p a l a t e and tongue(SPAS and IAS) was reduced i n t h e s u p i n e p o s i t i o n i n t h e OSA  group  (Table  V) , b u t n o t i n t h e group  symptoms (Table V) . These  without apneic  findings explain that not only the  c r o s s - s e c t i o n a l a r e a o f t h e tongue i s changed b u t a l s o t h a t t h e tongue mass s e t t l e s i n f e r i o r l y position,  p r o b a b l y due  i n OSA p a t i e n t s  to gravitational  i n the supine  pull  (Crumley  et  al,1987) . On t h e o t h e r hand, i n t h e non-apneic group, t h e tongue fell  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 actual  tongue a r e a was reduced and t h e SPAS was l e n g t h e n e d t o keep t h e a i r w a y open. T h i s d i s p a r i t y may be s u r m i s e d from t h e s i g n i f i c a n t d i f f e r e n c e i n t h e p o s t e r i o r tongue p r e s s u r e v a l u e s between t h e u p - r i g h t and s u p i n e p o s i t i o n i n t h e 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 r e s e a r c h e r s . On t h i s b a s i s , t h e tongue sank down more i n t h e symptomatic group due t o l a c k o f GG muscle c o n t r a c t i o n . Among the  h y o i d v a r i a b l e s , v e r t i c a l measurements o f t h e h y o i d bone  such as MP-H o r H-Hl d i d n o t change w i t h t h e p o s i t i o n a l change i n t h e symptomatic p a t i e n t  group  (see T a b l e V) ;however,  they  changed s i g n i f i c a n t l y i n t h e 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 t h e GG muscle e f f i c i e n c y between t h e two groups. I n c o n t r a s t , 92  the h o r i z o n t a l variables  among t h e h y o i d measurements (H-RGN) d i d not show s i g n i f i c a n t change i n t h e non-apneic group (Table V ) . On t h e o t h e r hand, t h e l e n g t h was  s i g n i f i c a n t l y s h o r t e n e d i n t h e OSA  group (Table V ) .  T h i s f i n d i n g s u g g e s t s t h a t t h e s i z e o f t h e hypopharnygeal is  airway  l a r g e enough t o p e r m i t b r e a t h i n g i n asymptomatic c o n t r o l s  where t h e s u p r a - h y o i d muscle group does not need t o c o n t r a c t . I n c o n t r a s t , a c c o r d i n g t o t h e r e s u l t s o f t h e c u r r e n t s t u d y , the hypopharyngeal  a i r w a y i n t h e OSA group i s a p p r o x i m a t e l y h a l f t h e  s i z e o f t h a t o f t h e c o n t r o l s i n terms o f c r o s s - s e c t i o n a l  area  i n t h e s u p i n e p o s i t i o n ; t h u s , t h e s u p r a - h y o i d muscle group must c o n t r a c t a c t i v e l y t o keep t h e a i r w a y open. Moreover, t h e maximum p a l a t a l t h i c k n e s s of t h e s o f t p a l a t e was  'actively' increased  i n s u b j e c t s w i t h o u t symptoms i n t h e s u p i n e p o s i t i o n ; no change was its  shown i n t h e OSA related  group. I t may  muscles,  not  the  t h e r e f o r e be t h e tongue and  soft  p a l a t e , which  actively  g e n e r a t e s an a p n e i c c o n d i t i o n . One  of  the  important  factors  to  measurement o f a i r w a y s i z e i s head p o s t u r e . head  posture  angulations  between that  are  OSA  and  believed  controls, to  be  consider  in  the  For comparison some  most  head  of  posture  sensitive  were  employed. Of t h e v a r i a b l e s r e p r e s e n t i n g head p o s t u r e , t h e CVTPP may be t h e v a r i a b l e which most s t r o n g l y s u p p o r t s t h e h y p o t h e s i s t h a t t h e p a t i e n t group has a more extended head p o s t u r e t h a n t h e controls.  The  a n g u l a t i o n v a r i a b l e s between t h e v e r t e b r a e  and  p a l a t a l p l a n e (CVTPP and OPTPP, suggested by Dr. D i e w e r t ) , w h i l e newly  designed  and  employed 93  for  the  first  time,  were  nonetheless,  very  significant  between head p o s t u r e  variables.  and a i r w a y  The r e l a t i o n s h i p  adequacy has been s t u d i e d by  numerous r e s e a r c h e r s . Span and Hyatt(1971) measured upper a i r w a y r e s i s t a n c e i n conscious upper a i r w a y Tallgren  may be a f f e c t e d by t h e head p o s t u r e .  (1971) h y p o t h e s i z e d  own head p o s t u r e standing  men and found t h a t r e s i s t a n c e o f t h e  t h a t each i n d i v i d u a l has h i s / h e r  which i s p r e c i s e l y r e p r o d u c i b l e  p o s i t i o n . Following  Woodside  and  Solow and  studies  Linder-Aronson(1979)  o f Solow and  only  i n the  et al.(1984),  Vig  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 p o s t u r e s i n accordance with  airway  adequacy.  They  concluded  that  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 angulation.  When t h e r e s u l t s a r e compared, a s m a l l d i f f e r e n c e  can be noted i n t h e measurement  o f t h e CVTSN between Solow and  T a l l g r e n ' s r e s u l t (97.72°) and t h e v a l u e t h e c u r r e n t study composition older  (105.76°) . T h i s d i f f e r e n c e may d e r i v e from t h e  of the subject  subjects  from t h e c o n t r o l s i n  were  group,  i.e. relatively  recruited f o r the current  study.  d i s p a r i t y was a l s o seen when comparisons t o o t h e r K y l a m a r k u l a and Huggare  heavy and Such a  s t u d i e s by  (1985) and Sandham (1988) were made.  Measurements o f head a n g u l a t i o n i n OSA p a t i e n t s were completed by  Kalbfleisch  measurement  in  1988,  variable  study;however,  the  and  that  extended  regrettably,  coincides head  with  posture  there  i s no  the  current  as  a  typical  c h a r a c t e r e s t i c o f t h e OSA p a t i e n t i s demonstrated i n h i s r e p o r t . The importance o f c e r v i c o c r a n i a l a n g u l a t i o n i s a l s o due t o t h e  specific  relationship  t o airway  size.  As t h e a i r w a y  changes, t h e head p o s t u r e changes and v i c e v e r s a . (1988) demonstrated  Kalbfleisch  a decrease i n a i r w a y s i z e w i t h neck f l e x i o n  by means o f l a t e r a l  cephalometry.  c i n e f l u o r o g r a p h y , demonstrated upon  size  hyperextension  of  Greene e t a l . ( 1 9 6 1 ) , u s i n g  an i n c r e a s e i n upper a i r w a y s i z e  t h e neck  i n the supine  position.  T h e r e f o r e , i t i s e x t r e m e l y i m p o r t a n t t o measure t h e upper a i r w a y s i z e i n a s t a n d a r d i z e d head p o s t u r e . Another  v a r i a b l e t o be accounted  upper a i r w a y s i z e ,  f o r before  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 n o t  o n l y muscular a c t i v i t y b u t a l s o a i r w a y s i z e . worker  (1982)  measuring  found  that supra-glottic  Anch and h i s c o -  airway  resistance i s  s i g n i f i c a n t l y l a r g e r i n t h e s u p i n e than i n t h e s i t t i n g p o s i t i o n i n b o t h normal  and OSA groups.  They h y p o t h e s i z e s u p r a - g l o t t i c  a i r w a y n a r r o w i n g i n OSA p a t i e n t s . explained  through  phenomenon  i s due  their  However, Navajas e t a l . (1988)  pressure transducer study  that  this  to the reduction 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 .  N e v e r t h e l e s s , Fouke  and S t r o h l (1987) n u l l i f i e d t h e e f f e c t i v e n e s s o f t h e reduced FRC i n t h e s u p i n e p o s i t i o n by means o f an Emerson c u i r a s s * and  * Cuirass  A s h e l l l i k e c a s i n g which i s c l o s e l y f i t t e d around t h e t h o r a x i n t r e a t m e n t o f weakness o f t h e r e s p i r a t o r y muscles, so t h a t e v a c u a t i o n o f a i r from w i t h i n t h e c u i r a s s causes o f t h e t h o r a x and hence i n h a l a t i o n 95  expansion  (Wiley e t a l . , 1 9 8 6 ) .  i d e n t i f i e d t h e degree  o f c o l l a p s e due  t o t h e body  positional  change. They found t h a t t h e 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 was  23% s m a l l e r i n t h e s u p i n e t h a n i n t h e u p - r i g h t p o s i t i o n . This  information i s pertinent  to the  interpretation  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  current  results  show  a  12.7%  r e d u c t i o n i n t h e e n t i r e p h a r y n g e a l a i r w a y (and a 28.9% r e d u c t i o n in  t h e oropharynx)  2 0.1%  reduction  oropharynx)  i n t h e asymptomatic in  the  i n t h e OSA  pharyngeal  control airway  group; (3 6.6%  and in  i n the supine p o s i t i o n  15%  FRC  i n t h e case o f t h e c u r r e n t s t u d y ; t h e  r e s u l t from Brown e t a l . ( 1 9 8 7 ) was n e a r l y i d e n t i c a l group,  the  p a t i e n t group. The d i s c r e p a n c y between  23% and 13% c o u l d be e x p l a i n e d by t h e e f f e c t o f a reduced  OSA  a  i n the  normal  group) t o t h e  (21% i n t h e  results  of  the  c u r r e n t study. Ultimately,  one  s h o u l d t a k e i n t o account head p o s t u r e ,  body p o s i t i o n , g l o t t i c c l o s u r e and s w a l l o w i n g f o r a c o m p a r a t i v e study of the airway s i z e . conditions  mentioned  standardized;however,  I n t h e p r e s e n t s t u d y , most o f t h e here  controlled  and  c e r t a i n l i m i t a t i o n s of the cephalometric  t e c h n i q u e c o u l d not be overcome. midsagittal  were  cross-sectional  g e t f u l l i n f o r m a t i o n about  The  cephalogram  provides a  a r e a , so t h a t i t i s i m p o s s i b l e t o t h e volume. I n o t h e r words, we  may  not even be a b l e t o r e a d t h e i m m e d i a t e l y a d j a c e n t p a r a - s a g i t t a l a r e a c o r r e c t l y . Furthermore, even CT scans may  not be a b l e 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 t w o - d i m e n s i o n a l technique.  For instance,  S t a u f f e r and a s s o c i a t e s (1987) were  u n a b l e t o demonstrate t h a t mean p h a r y n g e a l 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, o n l y the minimal  area  showed a s i g n i f i c a n t  AHI(r=0.53, P<.01). I n t h e same sense  correlation  with the  as mentioned  earlier,  d i s c r i m i n a t i o n o f t h e tongue s i z e d i f f e r e n c e by means o f t h e upright  cephalogram  was  impossible i n the present  supine cephalometric technique provides is  possibly  hidden  study.  The  new i n f o r m a t i o n which  by t h e t w o - d i m e n s i o n a l  limitation  of the  technique.  Review o f r e p r o d u c i b i l i t y t e s t s  The  reproducibility  f o r hard t i s s u e  test  structures  i n c e p h a l o m e t r i c s has a l o n g  h i s t o r y and has been w i d e l y i n v e s t i g a t e d by s e v e r a l  statistical  methods.  Solow (1970) i n t r o d u c e d a computer-aided c e p h a l o m e t r i c  analysis  based  on d i g i t i z i n g  principles.  I n 1979, Houston  r e v i e w e d t h e r o b u s t n e s s , a c c u r a c y , and convenience o f d i g i t i z i n g methods. I n a d d i t i o n , he  enumerates t h e s o u r c e o f e r r o r s t h a t  can a r i s e i n t h e d i g i t i z i n g method. e r r o r s can a r i s e  According t o h i s review,  from:  - i n c o r r e c t i d e n t i f i c a t i o n o f a landmark, -an i n c o r r e c t sequence o f d i g i t i z a t i o n , -movement o f t h e r e c o r d i n g d u r i n g 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  digitizer,  - 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) r e v i e w e d 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 o f t h e 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 o f u s i n g c o r n e r f i d u c i a l s w h i c h p r o v i d e s c o n s i d e r a b l e p r o t e c t i o n a g a i n s t t h e impact o f r o t a t i o n a l e r r o r s and i n c r e a s e d r e l i a b i l i t y .  R e c e n t l y , Sandham(1988) e x t e n s i v e l y  r e v i e w e d r e p r o d u c i b i l i t y t e s t s o f c e p h a l o m e t r i c measurements f o r h a r d t i s s u e s . He proposes a s t a n d a r d d e v i a t i o n r a n g i n g from 0.4 3 t o 2.11 mm f o r d i f f e r e n c e s between r e p e a t e d l i n e a r measurements. I n h i s s t u d y , a l l o f t h e k u r t o s i s v a l u e s were a c c e p t a b l e a t a l e v e l l e s s t h a n 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 h i g h v a l u e s compared t o p r e v i o u s work. T h i s might be e x p l a i n e d by t h e  memorization  effect  with a  time  Houston (1976) c l a r i f i e d  that  even though t h e  r e t r a c i n g was  l a p s e o f a t l e a s t one month. immediate r e d i g i t i z a t i o n  was  undertaken  significantly  more r e p r o d u c i b l e  due t o a memory e f f e c t .  R e p e a t a b i l i t y to reproduce n a t u r a l head p o s t u r e  Moorrees and Kean (1958) i n v e s t i g a t e d t h e h y p o t h e s i s of n a t u r a l head p o s t u r e and t e s t e d the a c c u r a c y o f r e p r o d u c i n g t h e natural reported  head p o s i t i o n 2.05  by  ° Standard  means of  lateral  head  films.  Deviation i n repositioning  of  n a t u r a l head p o s t u r e and c l a r i f i e d t h a t t h e t r u e v e r t i c a l  They the line  f o r r e f e r e n c e purposes i s more r e l i a b l e t h a n t h e r o u t i n e l y used FH l i n e .  S i e r s b a e k - N i e l s e n 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 p o s t u r e  i n a young age group. They a p p l i e d M ^ l h a v e s 1  most r e p r o d u c i b l e n a t u r a l s t a n d i n g p o s i t i o n as a s t a n d a r d i z e d 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  p o s t u r e . They u l t i m a t e l y r e p o r t e d 2.3 - 3.4 ° o f method e r r o r f o r p o s i t i o n i n g o f t h e head, which was s t a t i s t i c a l l y a c c e p t a b l e . A n o t h e r r e c e n t work by Sandham (1988) c o n f i r m e d t h e h y p o t h e s i s of r e p r o d u c i b l e n a t u r a l head p o s t u r e . He d i s p l a y e d 5.44 ° o f SD as a maximumly d e v i a t e d v a l u e f o r t h e OPT/HOR a n g l e ( a n g u l a t i o n between o d o n t o i d p r o c e s s and t r u e h o r i z o n t a l  V a l i d i t y of the modified l e v e l For validity  future of  associates  study,  line).  device  i t i s worthwhile  the modified  level  t o discuss the  device.  G r e e n f i e l d and  (1989) e v a l u a t e d t h e i n f l u e n c e o f t h e e a r r o d on  cephalometric  analysis.  They  concluded  that  taking  a  cephalogram w i t h o u t t h e e a r r o d p r o v i d e s b e t t e r r e p r o d u c i b i l i t y in  head  positioning.  They used  a photogragh  as a  reference  method f o r t h e c e p h a l o m e t r i c t e c h n i q u e and suggested  that the  photogragh method i s a 'quick and d i r t y ' method t o measure head p o s t u r e . However, t h e m o d i f i e d l e v e l d e v i c e t e c h n i q u e superior t o other techniques  may be  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 a n a l y s e s .  P r i o r t o the v a l i d i t y  test  a  f o r the modified  level  device,  r e p r o d u c i b i l i t y t e s t was undertaken. examined t h e r e p r o d u c i b i l i t y  carefully  designed  I n 1985, T s u c h i y a e t a l .  of i d e n t i f i c a t i o n  of the soft-  t i s s u e i n f r a - o r b i t a l n o t c h by means o f p a l p a t i o n . They c o n c l u d e d 99  that  on  average  the  soft-tissue  orbitale  was  palpated  c o n s i s t a n t l y a t 1mm s u p e r i o r t o t h e bony o r b i t a l e on a f i l m . Another the  s o f t - t i s s u e landmark employed i n t h e c u r r e n t s t u d y was  tragion  which  i s t h e notch  on t h e upper margin  of the  t r a g u s . The m o d i f i e d l e v e l d e v i c e was a t t a c h e d on t h e l i n e which was  assumed t o be t h e s o f t - t i s s u e FH p l a n e 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 T a b l e I I I encompasses r e p r o d u c i b i l i t y o f t h e e n t i r e  measuring  procedure.  B.  EMG and p r e s s u r e s t u d y Contraction  conducted motor  of  skeletal  muscle  i s triggered  by  a  a c t i o n p o t e n t i a l . When t h e t h r e s h o l d i s reached a t a  end p l a t e ,  a conducted  action  potential  i s elicited.  Myoplasms a r e f a i r l y good e l e c t r i c a l c o n d u c t o r s , t h e r e f o r e i t i s possible t o record the e l e c t r i c a l  changes  ( t h e sum o f t h e  number o f d e p o l a r i z a t i o n s ) i n t h e muscle by means o f e l e c t r o d e s . S u r f a c e e l e c t r o d e s used i n t h e c u r r e n t s t u d y cannot be used f o r a s i n g l e motor u n i t s t u d y easy  t o apply.  ;however, they a r e n o n - i n v a s i v e and  The i n t r a - o r a l  s u r f a c e e l e c t r o d e f o r t h e GG  muscle was f i r s t developed and e v a l u a t e d by Doble and co-workers (1985). I n 1988, M i l i d o n i s e t a l . compared t h e r e c o r d i n g s made w i t h t h e s e custom f i t t e d i n t r a - o r a l s u r f a c e e l e c t r o d e s t o t h e b i - p o l a r f i n e w i r e r e c o r d i n g s o f t h e GG muscle and proved t h a t t h e two methods a r e s u f f i c i e n t l y  100  compatible.  Due  to calibration  problems,  pressure i s not a simple task.  r e c o r d i n g o f t h e tongue  P r o f f i t e t al.(1969)  employed  a p r e s s u r e chamber f o r c a l i b r a t i o n o f t h e mercury s t r a i n gauge and p r e s e n t e d h i g h r e p r o d u c i b i l i t y f o r tongue p r e s s u r e . However, as w i t h EMG, i t i s d i f f i c u l t t o produce h i g h r e p e a t a b i l i t y i n p r e s s u r e r e c o r d i n g s . R e c e n t l y , H e l l s i n g and L ' E s t r a n g e  (1987)  i n v e s t i g a t e d p r e s s u r e change on t h e l i p f o l l o w i n g head p o s t u r e change and change i n mode o f b r e a t h i n g . They used a s t r a i n gauge t y p e t r a n s d u c e r developed by P r o f f i t which has a t r a n s d u c e r head w i t h a a r e a o f 0.04 3 cm . The t r a n s d u c e r was c a l i b r a t e d d i r e c t l y 2  i n t h e s u b j e c t ' s mouth by means o f a pen w i t h a s p r i n g l o a d system. However, i t i s so hard t o reproduce tongue c o n t a c t t h a t t h e r e a r e s t i l l o f a b s o l u t e tongue p r e s s u r e s t u d y employed a rubber  t h e e x a c t mode o f  l a r g e v a r i a t i o n s i n terms  from s t u d y t o s t u d y .  The c u r r e n t  s a c i m i t a t i n g t h e 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 t h e c u r r e n t p r o j e c t was c a r r i e d o u t merely Even  as a comparison s t u d y .  though  this  asymptomatic  controls,  significant  pieces  study  was  the current  of  carried results  information  and  out only provide suggest  with  several several  i m p l i c a t i o n s f o r t h e r e l a t i o n s h i p between s i z e o f t h e a i r w a y , body p o s i t i o n a l change and upper a i r w a y muscle a c t i v i t y . The GG a c t i v i t y i n c r e a s e d by a p p r o x i m a t e l y  3 4 % i n the supine  position  i n comparison t o t h e u p - r i g h t p o s i t o n i n t h e s u b j e c t s w i t h o u t symptoms. The EMG a c t i v i t y  of the supra-hyoid  i n c r e a s e d by 8%, b u t i t was n o t s t a t i s t i c a l l y 101  muscle  group  significant.  A more c u r i o u s phenomenon was an i n c r e m e n t i n p o s t e r i o r tongue p r e s s u r e d e s p i t e augmentation o f t h e GG and s u p r a - h y o i d muscle activity  as a r e s u l t  of p o s i t i o n a l  changes  o f t h e body.  EMG  a c t i v i t y changes i n t h e s u p i n e p o s i t i o n a r e w e l l documented and it  i s r e a s o n a b l e t o assume an increment i n s u p r a - h y o i d muscle  activity  a f t e r c h a n g i n g t h e body p o s i t i o n .  Airway patency i s  r e l a t e d t o t h e changes i n muscle t o n e o f t h e e n t i r e upper a i r w a y i n t h e s u p i n e p o s i t i o n . However, t h e muscle can s h o r t e n o n l y when  the  neural  activity  overcomes  example,  t h e w e i g h t o f t h e tongue  revealed  an  e n l a r g e d tongue  s u p i n e p o s i t i o n i n t h e OSA  i t s external itself.  The  cross-sectional  load,  for  c u r r e n t study  area(4%) i n the  group, y e t t h e same tongue a r e a i n  the non-apneic group. The c r o s s - s e c t i o n a l a r e a o f t h e oropharynx was  reduced by  s l i g h t l y (7%)  nearly  more  difference(4%+7%)  the  in in  the the  same amount OSA  group.  waking  state  i n b o t h groups, This in  subtle  controls  c o n s i d e r a b l y i n d u c e s e r i o u s problems d u r i n g s l e e p group. a  34%  but size  could  i n the  OSA  The oropharynx c o l l a p s e d a p p r o x i m a t e l y 3 0% i n s p i t e of increment  i n the  GG  muscle  activity  in  asymptomatic  c o n t r o l s . I n a d d i t i o n , t h e p o s t e r i o r tongue p r e s s u r e i m p l i e d t h e actual  tongue  location,  which was  l o w e r down. C h e r n i a c k 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 i n d e x o f t h e m e c h a n i c a l a c t i o n of a muscle. For i n s t a n c e , the  s t e r n o h y o i d muscle can l e n g t h e n 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 et al.,1987).  (Luntern  Brown e t a l . ( 1 9 8 7 ) c o n c l u d e d from t h e i r 102  age  and weight-matched s t u d y t h a t changes i n p o s t u r e a l o n e a r e not sufficient  t o convert a snorer i n t o  a p a t i e n t w i t h OSA.  The  c u r r e n t s t u d y h y p o t h e s i z e s t h a t l e s s t o n i c muscle a c t i v i t y o r a h e a v i e r tongue i n r e s p e c t t o t h e GG a c t i v i t y accompanied a narrowed a i r w a y may of  by  play a primary r o l e i n the pathogenesis  OSA. From a f u n c t i o n a l s t a n d p o i n t t h e muscle s p i n d l e a c t s as  a l e n g t h m o n i t o r i n g system. I t c o n s t a n t l y f e e d s back i n f o r m a t i o n t o t h e CNS r e g a r d i n g t h e s t a t e o f e l o n g a t i o n o r c o n t r a c t i o n o f 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 , t h e muscle s p i n d l e i n f o r m s t h e CNS o f 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 m o n i t o r e d by b o t h t h e G o l g i tendon organ and t h e muscle s p i n d l e .  The m a n d i b u l a r r e s t p o s i t i o n i s an example of  t h e neuromuscular mechanism pull  (Okeson, 1989). The  gravitational  o f t h e mandible body prompts t h e p a s s i v e s t r e t c h o f t h e  e l e v a t o r muscles. This p a s s i v e 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 t h e a f f e r e n t f i b r e s ( l a o r I I ) f i r i n g i n t h e muscle s p i n d l e s a c , t h i s i n f o r m a t i o n ascends t o t h e  higher  c e n t e r . The CNS s t i m u l a t e s a motor e f f e r e n t neurons. T h i s 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 . Automatically, the length of t h e muscle s p i n d l e i s s h o r t e n e d . T h i s s h o r t e n i n g b r i n g s about a d e c r e s e i n a f f e r e n t o u t p u t o f t h e muscle s p i n d l e . The  same  p r i n c i p l e c o u l d be a p p l i e d f o r t h e GG muscle i n s u p i n e p o s i t i o n . Normal  muscle  tonus does not c r e a t e  fatigue.  The  overload  s t i m u l a t e s t h e GG muscle t o overwork and t h i s c r e a t e s a c h r o n i c f a t i g u e . S c a r d e l l a e t a l ( 1 9 8 9 ) r e c e n t l y r e p o r t e d t h a t due t o t h e 103  high  percentage  of type  I I f i b r e s (white)  i n t h e GG  muscle,  r e l a t i v e l y s m a l l i n c r e a s e s i n i t s a c t i v i t y would p r e d i s p o s e t o f a t i g u e . They conducted  a f a t i g u e s t u d y by means o f a l i n g u a l  f o r c e t r a n s d u c e r and an i n t r a - o r a l e l e c t r o d e and c o n c l u d e d t h a t t h e GG i s a r e a d i l y f a t i g a b l e 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 structure  h y o i d a p p a r a t u s . The h y o i d bone i s a suspended  l o c a t e d between  Brodie(1963)  muscle.  the chin  and c e r v i c a l  vertebrae.  a n a l y z e d t h e h y o i d bone as t h e p o s t u r e  apparatus  o f t h e head and jaws which b a l a n c e s t h e s u p r a - and i n f r a - h y o i d m u s c u l a t u r e s . From t h e e a r l y developmental  s t a g e , t h e h y o i d bone  i s c l o s e l y a l l i e d w i t h t h e tongue. The p o s t e r i o r p o r t i o n o f t h e tongue i s d e r i v e d from t h e second so  the floor  mylohyoid  o f t h e mouth  muscles.  and t h i r d b r a n c h i a l a r c h e s ,  i s formed by t h e g e n i o h y o i d and  According  t o Bench(1963),  i n an  average  p e r s o n a t t h e age o f t h r e e , t h e h y o i d bone i s m a i n t a i n e d a t a level  between  the t h i r d  and f o u r t h  cervical  v e r t e b r a e and  g r a d u a l l y descends t o a l e v e l o f t h e f o u r t h v e r t e b r a by  full  a d u l t h o o d . The h y o i d bone i s a unique s t r u c t u r e f l o a t i n g among t h e muscles w i t h o u t any bony a r t i c u l a t i o n . The h y o i d  apparatus  i n c l u d e s a t l e a s t e l e v e n p a i r s o f muscles and t h r e e p a i r s o f 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 structures. Bibby  (1981)  conducted  a  study  on t h e h y o i d  triangle  and  emphasized t h a t t h e h y o i d bone r e f l e c t s t h e r e l a t i v e t e n s i o n s o f t h e muscles,  l i g a m e n t s and f a s c i a a t t a c h e d t o i t .  104  The and  h y o i d bone s e r v e s two  respiration.  Pruzansky  basic functions; deglutition  (1960)  demonstrated  a  low  hyoid  p o s i t i o n caused by e x c e s s i v e 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 with  ankylosis  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 o f t h e h y o i d bone t o keep t h e a i r w a y  open  i n i n f a n t s and e x p l a i n e d t h a t a n t e f l e x i o n o f t h e head and  neck  i n o r d e r t o s t a b i l i z e t h e h y o i d and  l a r y n x i s a p a r t of  the  r e a c t i o n o f t h e maintenance o f p h a r y n g e a l a i r w a y . R e c e n t l y , M i k i et al.(1988) electrical  t e s t e d a new  treatment  f o r OSA  patients, appling  s t i m u l a t i o n t o t h e submental r e g 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 stimulation  might  ameliorate  the  symptoms  of  OSA  t h e OSA  p a t i e n t s have a lower p o s i t i o n e d h y o i d  patients. Why apparatus?  do  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  t h e h y o i d bone. A g a i n , i n Bench s(1963) growth s t u d y , he  found  1  that  t h e tongue i s h i g h e r i n t h e younger samples. He p o s t u l a t e d  t h a t h y o i d bone l o w e r i n g t e n d s t o c o n t i n u e a f t e r f a c i a l growth. Recently,  Tallgren  and  Solow  (1987)  investigated  the  r e l a t i o n s h i p between h y o i d bone p o s i t i o n , f a c i a l morphology and head p o s t u r e  in relation  to  age.  They demonstrated  a more  i n f e r i o r (2.55mm a g a i n s t m a n d i b u l a r plane) and a n t e r i o r (1.64mm against vertebrae) Hpffstein correlation  et of  p o s i t i o n e d h y o i d bone i n an o l d e r group.  al.(1989) pharyngeal  found  that  area  with  decrement i n t h e airway s i z e w i t h age 105  there age  was  only  a  negative  i n males.  i s seemed t o be  The  related  t o t h e decrement i n t h e e x p i r a t o r y r e s e r v e volume ( L e b l a n c  et  al,1970). A  second p o s t u l a t e f o r an  inferiorly  positioned 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 a i r w a y patients  with  OSA.  A  smaller  airway  than  the  i n the  optimal  size  i n d u c e s a extended head p o s t u r e f o r b e t t e r a i r w a y adequacy. extended head p o s t u r e e l i c i t e s a p a s s i v e s t r e t c h o f t h e hyoid  muscle.  A  associates(1988)  recent  reported  extensive  study  a  of  s t u d i e s on h y o i d biomechanics. and v i d e o f l u o r o g r a p h y  and  series  by  supra-  Winnberg  precisely  An  and  conducted  The r e s e a r c h e r s s y n c h r o n i z e d  i n v e s t i g a t e d t h e dynamic and  EMG  static  r e l a t i o n s h i p s between the h y o i d bone l o c a t i o n and head p o s t u r e . They  illustrated  a  more  inferior(22mm)  and  anterior(14mm)  p o s i t i o n e d h y o i d bone w i t h a 15-25  degree extended head p o s t u r e .  A  drops  more  extended  head  posture  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 t h e s u p r a - h y o i d m u s c l e s . T h i s p a s s i v e s t r e t c h may  s e n s i t i z e t h e muscle s p i n d l e s . T h i s  i n f o r m a t i o n feeds back t o t h e CNS and r e a c t s t o t h e c o n t r a c t i o n . However, as l o n g as extended  head p o s i t i o n i n g may  contraction stiffness  b e t t e r airway  at  low  muscle  (Bressler,1974).  be  tension  adequacy i s r e q u i r e d , actively has  no  Consequently,  continued effect the  on  the  because muscle  supra-hyoid  m u s c l e s , not o n l y t h e GG and g e n i o h y o i d , but a l s o t h e omohyoid and a n t e r i o r d i g a s t r i c m u s c l e s , f a t i g u e and a r e 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 e x c e s s i v e i n f r a h y o i d b e h a v i o r , s i m i l a r t o t h e case o f a TMJ a n k y l o s e d p a t i e n t , 106  t h e h y o i d bone m i g r a t e s i n f e r i o r l y . Mixed  type  skeletal  muscles  fail  when  the  force  c o n t i n u o u s l y imposed on them e x e r t s 15% t o 2 0% o f t h e i r maximal f o r c e ( G r a s s i n o e t a l . , 1988). in  muscle  failure(i.e.  circulation generated  to  the  An i m p o r t a n t d e t e r m i n i n g f a c t o r  fatigue) muscle.  Blood  during contraction  oxygen t o t h e muscle.  i s the a v a i l a b i l i t y  and  washes  out  of blood  catabolites  i t provides nutrients  Fatigue i s a r e v e r s i b l e  and  physiological  s i t u a t i o n , and i t shows a p a r t i c u l a r t i m e c o n s t a n t o f r e c o v e r y . Recovery o f maximal f o r c e i s p r o g r e s s i v e and i s completed i n 1015  minutes.  However, t h e  capacity  to  reproduce  the  initial  endurance t i m e i s r e c o v e r e d s l o w l y , perhaps o v e r i n 18-24  hours  ( G r a s s i n o e t a l . , 1988). P a r t i c u l a r l y , t h e f a t i g u e g e n e r a t e d by low f r e q u e n c y s t i m u l a t i o n may t a k e s e v e r a l hours t o r e c o v e r . The development o f f a t i g u e reduces t h e maximal f o r c e a muscle generate  and  impairs  its  contractility  and  the  can  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 c o m p l i a n c e . A muscle f o r c e d t o c o n t r a c t c h r o n i c a l l y a g a i n s t heavy l o a d s may c h r o n i c f a t i g u e o r weakness. reported  that  respiratory  develop  R e c e n t l y , Couser and Berman(1989) muscle  fatigue  might  generate  a  f u n c t i o n a l upper a i r w a y o b s t r u c t i o n . Not o n l y because o f f a t i g u e b u t a l s o because o f muscle o r i e n t a t i o n , t h e GG and s u p r a - h y o i d muscle may not be a b l e t o work e f f i c i e n t l y . R o b e r t e t a l . ( 1 9 8 4 ) discussed  the pharyngeal  airway  stabilizing  function  of  the  h y o i d muscle group i n r a b b i t s . I n agreement w i t h B r o d i e s ( 1 9 5 0 ) 1  understanding  they  found  the 107  stabilizing  function  of  the  sternohyoid  and s t e r n o t h y r o i d muscles  to resist  pharyngeal  a i r w a y c o l l a p s e due t o n e g a t i v e i n t r a - l u m i n a l p r e s s u r e . Through a s e r i e s o f i n v e s t i g a t i o n s Van L u n t e r e n 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  o f h y o i d muscle a c t i v i t y i n  b r e a t h i n g . The c o o r d i n a t e d a c t i v a t i o n o f b o t h o f t h e s u p r a - and infra-hyoid  muscles  may  produce  a vector  of forces,  which  d i s p l a c e s t h e h y o i d a r c h 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  dilated  reported length  upper  airway.  Furthermore,  t h a t t h e head p o s t u r e of  the  hyoid  Lunteren  and co-workers  means o f sonomicrometry in  upper a i r w a y  alters  muscles  arrangements o f t h e s e muscles,  several  but  investigators  not only also  the resting  the  geometrical  and i n t u r n , a i r w a y  (1987b) c o n f i r m e d  t h i s h y p o t h e s i s by  i n c a t s . They found t h a t an  volume l e n g t h e n s  s i z e . Van  the resting  increment  lengths of the  g e n i o h y o i d s i n c a t s , b u t causes v a r i a b l e changes i n s t e r n o h y o i d l e n g t h . E x t e n s i o n o f t h e neck i n c r e a s e s t h e l e n g t h o f b o t h t h e g e n i o h y o i d and s t e r n o h y o i d muscles. t h e y observed  With  f l e x i o n o f t h e head,  opposite r e s u l t s . Therefore, they concluded  that  w i t h a g i v e n upper a i r w a y geometry t h e r e i s an i n v e r s e r e a c t i o n between upper a i r w a y volume and h y o i d muscle l e n g t h , which i s especially  strong  f o r the geniohyoid  p e r f o r m t h e experiment  muscle.  They  d i d not  on t h e upper a i r w a y volume change induced  by e x t e n s i o n and f l e x i o n o f t h e head and neck. However, much r e s e a r c h done by d i f f e r e n t groups has s u p p o r t e d  the idea that  patency o f t h e upper a i r w a y i s enhanced w i t h an e x t e n s i o n o f t h e head p o s t u r e . I n a d d i t i o n , Van L u n t e r e n e t a l . ( 1 9 8 7 ) p o s t u l a t e d 108  J  that i t i s the geniohyoid p l a y s an i m p o r t a n t  muscle, n o t t h e s t e r n o h y o i d ,  r o l e as a hypopharyngeal d i l a t o r  They added t h a t t h e s t e r n o h y o i d muscle a c t s f a s h i o n t o prevent  i n an  which  i n cats. accessory  e x c e s s i v e movement t o t h e c r a n i a l s i d e due  t o g e n i o h y o i d 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 t h e h y o i d  bone i n a f o r w a r d  direction.  d e s c r i b e d i n t h e a n k y l o s e d TMJ case o f Pruzansky's  However, as observation,  t h e 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 t h e h y o i d bone l o c a t i o n . From t h e b i o m e c h a n i c a l  p o i n t o f view, an 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 bone may n o t y i e l d  a sufficient  forward  movement.  This  might be due t o m u s c u l a r m a l f u n c t i o n and/or t o t h e 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 vector  sum.  In other  words,  the  a n g u l a t i o n c o n s t r u c t e d by t h e g e n i o h y o i d muscle and s t e r n o h y o i d 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 n o t be  a b l e t o produce a v e 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  size. H e l l i n g ( 1 9 8 6 ) d e s c r i b e d t h e s u p r a - h y o i d muscle as a group  o f muscles i n c l u d i n g t h e a n t e r i o r d i g a s t r i c , t h e g e n i o h y o i d and t h e GG.  Van de G r a a f f and a s s o c i a t e s ( 1 9 8 4 )  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 t h e h y o i d bone and may be  another  important  Winnberg(1987)  determinant  of  hyoid  included the a n t e r i o r b e l l y  muscle, t h e mylohyoid  bone  position.  of the d i g a s t r i c  muscle and t h e g e n i o h y o i d muscle i n h i s  d e f i n i t i o n o f t h e s u p r a - h y o i d muscle group.  W h i l e t h e mandible  i s i n t h e r e s t p o s i t i o n w i t h 2-4mm o f 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 t h e s u p r a - h y o i d muscles o n l y 109  t h e g e n i o h y o i d 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 t h e r e s u l t s of t h e p r e s e n t supra-hyoid  study,  an  8%  increase i n  muscle a c t i v i t y i s presumed i n t h e s u p i n e  compared t o t h e  up-right position.  This  amount of  muscle a c t i v i t y i n t h e s u p i n e p o s i t i o n may  position increased  r e p r e s e n t augmented  EMG  a c t i v i t y of t h e s u p r a - h y o i d muscle t o keep t h e a i r w a y open.  In  contrast,  s i g n i f i c a n t decrease  i n f e r i o r o r b i c u l a r o r i s muscle, may reclining  of  the  body.  posterior  movement of  the  i n EMG  activity in  the  represent a r e l a x a t i o n a f t e r  Harper(1988)  postulated  mandible may  occur  that  i n the  the  supine  p o s i t i o n d u r i n g s l e e p due t o r e l a x a t i o n of t h e l a t e r a l p t e r y g o i d and  masseter muscles.  In  addition,  Hollowell 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 patients  during  sleep  and  the  same  group(1989)  s i g n i f i c a n t i n c r e a s e of masseter muscle a c t i v i t y with  the  masseter  level  of  hypercapnea.  a c t i v i t y was  observed  d u r i n g t h e p r e s e n t study.  However, with  the  no  OSA  showed  a  i n accordance change  positional  in  the  changes  B r o d i e ( 1 9 5 0 ) o b s e r v e d t h a t t h e mouth  opening accompanies t h e backward movement of t h e h y o i d bone. He assumed a s h o r t e n i n g airway  open  opening,  EMG  during  of t h e opening  activities  supra-hyoid of  from  the the  muscles t o keep  mouth.  During  maximum  digastric  muscle  obscure  g e n i o h y o i d a c t i v i t y r e g a r d l e s s o f body p o s i t i o n . GG  activity is s t i l l  the  However,  r e q u i r e d i n the supine than the  more  up-right  p o s i t i o n due t o t h e g r a v i t a t i o n a l p u l l . T h i s e x p l a n a t i o n agrees w i t h t h e r e s u l t of t h e c u r r e n t study 110  t h a t GG  a c t i v i t y during  maximum opening  i s increased i n the supine  position.  As was d i s c u s s e d e a r l i e r , measuring o f a b s o l u t e v a l u e o f t h e tongue p r e s s u r e  i s extremely  difficult.  L e a r and  h i s co-  w o r k e r s (1965) d i s c u s s e d t h i s m a t t e r 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 e x p r e s s e d i n f o r c e p e r square c e n t i m e t e r . T h i s term  i m p l i e s t h a t m u s c u l a r a c t i v i t y and  must d i s t r i b u t e of  the  surface configuration  f o r c e e v e n l y over t h e e n t i r e  transducer.  tissues invariably  However, t h e r e  i s no  sensing platform  evidence  that  oral  a c t i n a manner analogous t o an a i r f i l l e d  b a l l o n ( P r o f f i t e t a l 1964), a mass o f sponge r u b b e r , o r a water f i l l e d b a l l o n ( p r e s e n t s t u d y ) . Furthermore,  where t h i s  contact  o c c u r e d on t h e t r a n s d u c e r s u r f a c e i s unknown. Even when p r e s s u r e transducers are c a l i b r a t e d pay  i n an i n - v i t r o s i t u a t i o n ,  one  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  to a given load according to the d i s t r i b u t i o n this  point,  Lear  et  al.(1965)  recommended  objections.  problem,  a  small  detected  signals  computer s o f t w a r e .  In  the  current  transducer(0.28 were The  cm ) 2  i n t e g r a t e d and  that  was  to  the  (see F i g . 10).  Ill  use  employed  averaged  by  On of  overcome  minimize  l i n e a r i t y i n - v i t r o of the  employed f o r t h e p r e s e n t study was a comparison study  study,  response  of the l o a d .  p r e s s u r e t r a n s d u c e r s w i t h s m a l l e r s e n s i n g s u r f a c e s may these  must  this  and  the  means  of  transducers  shown t o be a c c e p t a b l e f o r  C.  Overview Recently,  Suratt  and co-workers  (1988)  presented  a  p a 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 t h e upper a i r w a y muscle a c t i v i t y may be more augmented i n OSA p a t i e n t s t h a n 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 p h a s i c GG group activity  during  NREM s l e e p ,  which  could  be e x p l a i n e d  as a  p r e c a r i o u s compensatory mechanism. S t r o h l (1986) emphasized t h e importance o f t h e t o n i c a c t i v i t y  o f t h e m u s c l e s . He e x p l a i n e d  t h a t changes i n t o n i c a c t i v i t y c o u l d a f f e c t a i r w a y s i z e as w e l l as  muscle  length;  thus  tonic  activity  o f t h e GG and h y o i d  muscles overcomes s u r f a c e t e n s i o n o f t h e b l o c k e d f i n a l l y promotes t h e airway The  occlusion.  r o l e o f age i n OSA i s n o t c l e a r .  e t a l . ( 1 9 8 8 ) r e c e n t l y observed t h a t a i r w a y level  a i r w a y , and  o f t h e tongue base m a i n l y  jiowever,  Chaban  obstructions at the  happen i n o l d e r age groups,  whereas o b s t r u c t i o n s a t t h e l e v e l o f t h e s o f t p a l a t e o c c u r i n younger groups. of s n o r e r s study  L u g a r e s i e t a l . ( 1 9 8 0 ) found t h a t t h e f r e q u e n c y  i n the population  i n c r e a s e d w i t h age. The c u r r e n t  f a i l e d t o match age and BMI.  However, t h e r e s u l t s from  t h e ANCOVA t e s t i n t h e c u r r e n t 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 t h e comparisons o f t h e h y o i d v a r i a b l e s between t h e OSA  and  asymptomatic  Nevertheless,  control  as d e s c r i b e d  earlier,  groups  (see T a b l e  the resistance of a i r f l o w  i n c r e a s e s w i t h age, and i n a d d i t i o n t h e h y o i d bone i n f e r i o r l y and a n t e r i o r l y .  VI) .  migrates  These f i n d i n g s i m p l y t h a t age may  be  another  factor  e x a c e r b a t i n g OSA  symptoms.  Anatomically,  upper a i r w a y s a r e l i n e d by mucous membranes w i t h t h e m u s c u l a t u r e underneath,  and a r e l o n g and c o n v o l u t e d as w e l l . However, t h e  s m a l l s i z e o f t h e upper a i r w a y t h e apnea. Furthermore,  may  t h e s t a b i l i t y o f t h e upper a i r w a y does  not seem t o be t o t a l l y determined or  by  pulmonary  not a l o n e be a b l e t o induce  function  alone.  e i t h e r by m u s c u l a r The  activity  functional  feedback c o n t r o l o f r e s p i r a t i o n o r chemico- o r  roles  of  mechanoreceptors  a r e s i g n i f i c a n t . Moreover, from a b i o m e c h a n i c a l p o i n t o f view, t h e c o o r d i n a t e d l i n k a g e of t h e a i r w a y s i z e ,  tongue  activity,  h y o i d bone l o c a t i o n , as w e l l as t h e s u p i n e p o s i t i o n o f t h e body, may  c o n t r i b u t e t o t h e p a t h o g e n e s i s o f t h e OSA  symptoms.  D. P i t f a l l s and F u t u r e S t u d i e s The p r e s e n t s t u d y was d e s i g n e d t o compare a n a t o m i c a l and physiological  relationships  between  airway  structures  in  accordance w i t h body p o s i t i o n a l changes i n OSA and asymptomatic controls.  Therefore,  r e p r o d u c i b l e and data  cephalometric  study  required  However,  the  experiment  failed  to  exclude  i n e v i t a b l e problems i n h e r e n t t o t h i s p r o c e d u r e .  i n s t a n c e , t h e p a t i e n t s were t o l d t o h o l d t h e mandible closed  i n an  up-right standing position,  mandible  i n the  affected  by  supine  this  d i s c r e p a n c y was  a  standardized recording p o s i t i o n f o r accurate  collection.  several  the  major  position. change  but  Obviously,  i n mandibular  to  For  slightly relax  airway  the  size  position.  is  This  o b v i o u s from t h e onset but t o compare our d a t a 113  base w i t h a l l p r e v i o u s OSA r e p o r t s , t h e 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 t h e u p - r i g h t p o s i t i o n was used. the supine plane.  p o s i t i o n was c a r r i e d o u t w i t h o u t  Subjects  were i n s t r u c t e d o n l y  Head p o s i t i o n i n a fixed  reference  t o mimick t h e i r  normal  s l e e p p o s i t i o n . There was no s t a n d a r d i z e d p r o t o c o l t o c o n f i r m whether t h e r e l a t i o n s h i p between t h e head p o s i t i o n on a p i l l o w and  t h e body  posture  on a s t r e t c h e r a c t u a l l y  represents  a  natural sleep p o s i t i o n . The p r e s e n t p i l o t s t u d y d i d n o t i n c l u d e EMG o r p r e s s u r e e x p e r i m e n t s i n t h e OSA symptomatic group. An EMG and p r e s s u r e study  on t h e OSA group may w e l l be t h e n e x t l o g i c a l  future  i n v e s t i g a t i o n s . Overnight  synchronized  with  EMG,  could  tongue  be a f i n a l  pressure  step f o r recording,  objective f o r this  c o m p a r a t i v e s t u d y . I f , by means o f t h e c u r r e n t method, we c o u l d segregate  t h e ' a c t i v e ' GG EMG from t h e ' p a s s i v e ' GG EMG  (that  EMG a c t i v i t y w i t h no change i n t h e muscle l e n g t h d u r i n g s l e e p ) , we  may  be  pathogenesis  able  t o develop  a better  o f OSA.  114  understanding  of the  SUMMARY  The c e p h a l o m e t r i c s t u d y 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 r e v e a l e d a l o n g e r tongue, a l a r g e r  soft  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 l e n g t h e n e d upper 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 bone, a more u p - r i g h t tongue, a more extended  head p o s t u r e and a s m a l l e r hypopharynx  i n the  up-right standing p o s i t i o n . 2.  The OSA group showed  g r e a t e r tongue h e i g h t , a l a r g e r  tongue and a s m a l l e r hypopharyngeal a r e a i n t h e s u p i n e position. 3.  W i t h t h e p o s i t i o n a l changes from 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 more i n t h e c o n t r o l group, whereas t h e s i z e o f t h e upper a i r w a y was d e c r e a s e d more i n t h e OSA group.  4.  W i t h t h e p o s i t i o n a l changes from u p - r i g h t t o s u p i n e , t h e h y o i d bone was moved up toward t h e m a n d i b u l a r p l a n e more i n t h e c o n t r o l s u b j e c t s , b u t more toward t h e m a n d i b u l a r symphysis i n t h e OSA group.  5.  The tongue 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  significantly  by 4.3% i n t h e s u p i n e p o s i t i o n and 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 by 3 6.5% i n t h e OSA group.  115  As a summary o f t h e r e s t EMG  and p r e s s u r e s t u d y , w i t h  t h e p o s i t i o n a l changes from u p - r i g h t t o s u p i n e , t h e asymptomatic c o n t r o l group showed:  1.  The EMG  a c t i v i t y of t h e g e n i o g i o s s u s muscle  was  i n c r e a s e d by 3 3.8%. 2.  The p r e s s u r e o f t h e p o s t e r i o r p o r t i o n o f t h e tongue i n c r e a s e d by 17%.  3.  The  resting  potential  activity  of  the  inferior  o r b i c u l a r i s o r i s d e c r e a s e d by 32.5%. 4.  The EMG  a c t i v i t y o f t h e s u p r a - h y o i d group i n c r e a s e d  8%, y e t t h e change was not s t a t i s t i c a l l y  116  significant.  by  BIBLIOGRAPHY 1. Abd-El-Malek S. 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