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Cardiovascular responses to sustained isometric work in a hot environment 1977

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CARDIOVASCULAR RESPONSES TO SUSTAINED ISOMETRIC WORK IN A HOT ENVIRONMENT by JOSEPH IACOBELLLS B.P.E., University of B r i t i s h Columbia, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION i n the School of We accept this thesis as conforming to the Physical Education and Recreation required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1977 Joseph I a c o b e l l i s , 1977 In p resent ing t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree t h a t permiss ion for e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of Physical Education and Recreation The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date A p r i l 27, 1977 i ABSTRACT The purpose of t h i s study was to investigate the changes i n cardio- vascular dynamics as depicted by s y s t o l i c time i n t e r v a l s , blood pressure and heart rate during a 50% MVC and 100% MVC isometric contraction of the forearm i n a control and heated environment. Fourteen normal male volunteers aged 20 to 31 were used as subjects. Simultaneous recordings of the phonocardiogram, electrocardiogram, c a r o t i d pulse wave and blood pressure were conducted f o r each subject at rest and during exercise i n a seated p o s i t i o n . Subjects were tested, i n room temperature and i n a sauna where the skin temperature was raised to 40°C - 41°C. Testing took place on two separate days with one day of re s t i n between. Half of the subjects experienced the heated conditions f i r s t , while the other h a l f was tested i n room conditions f i r s t . The r e s u l t s from two of the subjects were discarded because of poor q u a l i t y reproduction of the time i n t e r v a l recordings. For each recording only the three c l e a r e s t cycles c l o s e s t to the termination of the contraction period were used f or s t a t i s t i c a l a n a l y s i s . The data were treated with a two-way ANOVA for each dependent v a r i a b l e . In some cases a post-hoc analysis (Newman-Keuls method) was used to determine s p e c i f i c differences between workload or environment e f f e c t s . The fourteen dependent variables studied were divided into the following groups: a) Systole r e l a t e d variables l e f t v e n t r i c u l a r e j e c t i o n time (LVET) mechanical systole (MS) t o t a l systole (TS) ejection time index (ETI) Diastole related variables cycle time (CT) diastole (DIAS) Sympathoadrenergic A c t i v i t y ( C o n t r a c t i l i t y ) pre-ejection period (PEP) isovolumetric contraction period (ICP) PEP/LVET (ratio) Afterload s y s t o l i c blood pressure (BPs) d i a s t o l i c blood pressure (BPd) Electromechanical Lag (EML) Heart Rate (HR) Myocardial Oxygen Consumption (Index) t r i p l e product (TRIP) -CONCLUSIONS The oxygen consumption of the myocardium as depicted by the t r i p l e product s i g n i f i c a n t l y increased during submaximal and maximal isometric handgrip contraction. This increase was evident at room temperature and during body heating. There was no s i g n i f i c a n t change i n the myocardial oxygen consumption as depicted by TRIP at rest or during isometric forearm contraction i i i between the control and heated environments. This suggests that the heat stress did not s i g n i f i c a n t l y increase the myocardial oxygen requirements. 3. In a state of rest, increasing the skin temperature to between 40°C - 41°C did not s i g n i f i c a n t l y a l t e r either BPs or BPd when compared to a resting state at room temperature. However, BPs and BPd were substantially lower during isometric work i n the heat than during isometric work at room temperature. 4. BPs and BPd s i g n i f i c a n t l y increased during 50% MVC and 100% MVC s t a t i c contractions of the forearm. This increase was demonstrated i n both environmental conditions. 5. A l l variables depicting changes i n l e f t ventricular systole (LVET; MS; TS) and ventricular diastole (diastole and CT) were found to become s i g n i f i c a n t l y reduced with submaximal and maximal s t a t i c contractions of the forearm. These changes were evident i n both environments. 6. A strong inverse correlation was found between HR and LVET, CT and diastole. HR s i g n i f i c a n t l y increased from rest to 100% MVC i n both environmental conditions. Consequently, i t i s suggested that alterations i n LVET, CT and diastole are largely determined by the rate of myocardial contraction. 7. The ejection time index s i g n i f i c a n t l y increased i n both environmental conditions with a 50% MVC and 100% MVC s t a t i c contraction of the forearm. i v The electromechanical lag showed a general tendency to decrease during an isometric handgrip contraction. However, subsequent post-hoc analysis (Newman-Keuls) demonstrated that EML did not s i g n i f i c a n t l y decrease during a submaximal or maximal isometric contraction of the forearm. I t i s suggested that care be taken to choose a proper s t a t i s t i c a l procedure for analysis of EML. The c o n t r a c t i l i t y of the heart as depicted by changes i n LCP, PEP and PEP/LVET increases i n response to a pressure load produced by s t a t i c exertion but i s not s i g n i f i c a n t l y altered by an augmented volume load associated with heat stress. HR, LVET, MS, TS, PEP, ICP, PEP/LVET and EML changed i n an additive fashion from rest to 100% MVC during subjection to a volume load and pressure load simultaneously. In contrast alterations i n BPs, BPd, ETI, CT, diastole, and TRIP displayed interactive characteristics during the same test conditions . V TABLE OF CONTENTS Chapter Page 1. STATEMENT OF THE PROBLEM 1 I. Introduction 1 I I . Purpose 4 I I I . Subproblems 5 IV. Assumptions and Limitations . . . . 5 V. Hypotheses 6 VI. Definitions 8 VII. Significance of the Study 10 2. REVIEW OF THE LITERATURE 11 I. H i s t o r i c a l Introduction 11 I I . Cardiac Intervals 12 A. Left Ventricular Systole 12 Ejection Time Index 14 B. Ventricular Diastole 15 C. Sympathoadrenergic A c t i v i t y 16 D. E l e c t r i c a l A c t i v i t y Within the Left Ventricle 21 I I I . Myocardial Oxygen Consumption 22 IV. Circulatory Changes with Stat i c Work 23 V. CV Changes i n a Hot Environment 26 v i TABLE OF CONTENTS Chapter Page 3. METHODS AND PROCEDURES 28 I. Subjects 28 I I . Experimental Period 28 I I I . Pre-Experimental Instructions • • • 29 IV. Procedures 30 V. S t a t i s t i c a l Concerns 35 4. RESULTS AND DISCUSSION . 39 I. Results 39 S t a t i s t i c a l Results 40 Blood Pressure 41 Heart Rate 47 Ventricular Systole (LVET; MS; TS) 50 Ejection Time Index 56 Diastole and CT 59 ' Sympathoadrenergic A c t i v i t y 65 Electromechanical Lag 72 TRIP . . 76 I I . Discussion 78 Blood Pressure ? • • 78 Heart. Rate 80 Ventricular Systole 80 Ejection Time Index 81 Diastole 84 v i i TABLE OF CONTENTS Chapter Page Sympathoadrenergic A c t i v i t y 85 Electromechanical Lag 86 Myocardial Oxygen Consumption 88 The Interaction (EC) Effect 88 Summary 89 5. SUMMARY AND CONCLUSIONS 92 Conclusions • 94 REFERENCES 97 APPENDICES 106 APPENDIX A 107 Raw Scores - Subjects Tested i n Neutral Environment F i r s t 108 Raw Scores - Subjects Tested i n Heated Environment F i r s t 109 APPENDIX B 110 Correlation Coefficients - At Rest i n a Neutral Environment I l l Correlation Coefficients - At 50% MVC i n a Neutral Environment • • 112 Correlation Coefficients - At 100% MVC i n a Neutral Environment 113 Correlation Coefficients - At Rest i n a Heated Environment 114 Correlation Coefficients - At 50% MVC i n a Heated Environment 115 Correlation Coefficients - At 100% MVC i n a Heated Environment 116 v i i i 1 LIST OF TABLES Table Page 1. Means and Standard Deviations . 39 2. Summary of ANOVA - Blood Pressure (Systolic) 44 3. Summary of ANOVA - Blood Pressure (Diastolic) 44 4. Newman-Keuls Analysis (Workload Effect) 45 5. Newman-Keuls Analysis (Environment Effect) 46 6. Correlation Coefficients - BPs 47 7. Summary of ANOVA - Heart Rate 49 8. Correlation Coefficients - Heart Rate 49 9. Summary of ANOVA - Left Ventricular Ejection Time . . . 54 10. Summary of ANOVA - Mechanical Systole 54 11. Summary of ANOVA - Total Systole 55 12. Summary of ANOVA - Ejection Time Index 55 13. Newman-Keuls Analysis - ETI 56 14. Summary of ANOVA - Diastole 62 15. Summary of ANOVA - Cycle Time 62 16. Newman-Keuls Analysis - Diastole and CT (Workload Effect) 59 17. Newman-Keuls Analysis - Diastole and CT (Environmental Effect) 63 18. Correlation Coefficients - CT 64 19. Summary of ANOVA - Isovolumetric Contraction Period . . 69 20. Summary of ANOVA - Pre-ejection Period 69 21. Summary of ANOVA - PEP/LVET 70 22. Newman-Keuls Analysis - ICP (Heat vs. Neutral) 71 i x LIST OF TABLES Table Page 23. Summary of ANOVA - Electromechanical Lag . 72 24. Newman-Keuls Analysis - EML 74 25. Correlation Coefficients T EML 75 26. Summary of ANOVA - Triple Product v 75 27. Newman-Keuls Analysis - TRIP (Workload Effect) 76 28. Newman-Keuls Analysis - TRIP (Heat vs. Neutral) . . . . 78 X LIST OF FIGURES Figure Page 1. BPd: ICP: dp/dt 18 2. Testing Scheme 30 3. Sy s t o l i c Time Intervals 34 4. Test Design 37 5. 2 x 3 F a c t o r i a l Design 38 6. S y s t o l i c Blood Pressure 42 7. D i a s t o l i c Blood Pressure 43 8. Heart Rate 48 9. Left Ventricular Ejection Time 51 10. Total Systole 52 11. Mechanical Systole 53 12. Ejection Time Index 57 13. Diastole 60 14. Cycle Time 61 15. Isovolumetric Contraction Period 66 16. Pre-ejection Period 67 17. Pre-ejection Period: Left Ventricular Ejection Time (Ratio) 68 18. Electromechanical Lag 73 19. Triple Product 77 x i ACKNOWLEDGEMENTS Special gratitude i s expressed to Dr. Kenneth Coutts of the University of B r i t i s h Columbia, for his technical assistance and to Dr. Robert Schutz of the University of B r i t i s h Columbia, for his advice concerning s t a t i s t i c a l matters. Appreciation i s also extended to P a t r i c i a Schulze and Mike Zarzycki for thei r laboratory assistance. CHAPTER I STATEMENT OF THE PROBLEM I. INTRODUCTION Recently, substantial e f f o r t has been incorporated into the investigation of the diseased heart, and as an offshoot of th i s work there has been much concern about the use of isometrics as a useful stressor to the heart for purposes of dynamic analysis. In contrast, there has been substantially less work performed on the changes i n cardiac dynamics of a normal heart with bouts of isometric exercise. Since isometrics i s reported by some to be a b e n e f i c i a l method of exercising the body and improving muscular strength, the popularity of pract i s i n g isometric work has increased markedly. Such interest i n isometric or s t a t i c exercising has stimulated the c u r i o s i t y of researchers the majority of which seem to be hesitant to prescribe the use of s t a t i c exercises for purposes of keeping f i t . I t would therefore be of interest to investigate the dynamic alterations i n the cardiac cycle of a normal heart during sustained isometric contraction. The heart may be stressed i n a variety of ways, one of which has already been mentioned and another being the exposure of the body to higher than normal temperatures. Excessive heat and humidity are espe- c i a l l y a burden to cardiac function and may induce f a t a l consequences for the diseased heart. The r e s p o n s i b i l i t y for transporting large quantities of heat from the central areas of the body to i t s surface, where i t i s mainly l o s t , l i e s primarily with the cardiovascular system. The cardiac 2 pump works with increasing power and speed of contraction i n an e f f o r t to bring adequate quantities of blood to the skin surface. As a result the heart rate (HR), cardiac output (CO) and Cardiac work done per unit time increase markedly. Imposing such a volume load stress on the heart undoubtedly causes the humoral and neural mechanisms of the body to react i n favor of improving the cardiac dynamics i n order to adequately meet the physiological demands of temperature regulation. In addition to heat stress, the CV system i s also responsive to" changes i n a r t e r i a l pressure, whereupon a pressure load on the myocardial fibers during systole a l t e r s the c o n t r a c t i l e state of the f i b e r s . Both s y s t o l i c and d i a s t o l i c pressure can be augmented temporarily during bouts of isometric contraction. In fact, during maximal voluntary contractions (MVC), the mean blood pressure has been shown to exceed resting values of hypertensive diseased individuals (33, 40). Since i t i s known that hyper- tensive states w i l l cause alterations i n cardiac dynamics (19, 23, 33) i t would seem appropriate to suggest that an acute hypertensive state within a normal i n d i v i d u a l may also produce changes i n cardiac dynamics. Investigations into the effects of isometric exercise on the cardio- vascular system can be divided into those which concern themselves with changes i n l e f t ventricular s y s t o l i c time intervals and others which deal mainly with changes i n hemodynamics. Lind and McNicol (38, 39) have conducted numerous studies concerning the effects of isometric exercise on the central circulatory responses. However the majority of these investigations were conducted i n a neutral environment and l i t t l e i s known about cardiovascular adaptations to simultaneous stresses of heat and s t a t i c work i n man. Rowell (69) reviews some c l a s s i c a l experiments i n cardiovascular adjustments to both dynamic exercise and thermal stress, but again studies concerning themselves with simultaneous induction of thermal and isometric stresses are rare. A substantial amount of informa- tion i s known about hemodynamic adjustments of the cardiovascular system with isometric exercise and thermal stress separately, but no one has yet shown how these two quite different conditions w i l l interact with each other i n producing a coupled adjustment of cardiovascular function. S p e c i f i c a l l y i t i s of interest to t h i s investigator to examine alterations i n cardiac dynamics as depicted by the s y s t o l i c time intervals during a variety of conditions involving combinations of thermal and isometric work stress. This approach i s an attempt not only to study functional changes i n cardiac function under conditions which have never been u t i l i z e d before, but also to substantiate the findings of cardiovascular adjustments to separate stress conditions of excessive heat and s t a t i c work. Sys t o l i c intervals have been shown to be good indicators of v e n t r i - cular function and have also been found to correlate s i g n i f i c a n t l y with invasive methods for the study of cardiac dynamics (48). The majority of studies which have employed s y s t o l i c time intervals for functional analyses of the l e f t v e n t r i c l e during bouts of isometric work have used heart disease or hypertensive patients as their subjects. The intent of course was to i d e n t i f y ventricular functional abnormalities resulting from excessive production of a r t e r i a l pressure during isometric exercise. This non-invasive method of cardiac investigation has proven to be a useful 4 c l i n i c a l t o o l and has become popular i n view of the fact that the body i s not subject to in t e r n a l testing. A consideration of the above stated findings supports the idea that i f both a pressure load induced by sustained isometric handgrip and volume load induced by heat stress were to burden the heart simultaneously, s i g n i f i c a n t interactions i n cardiac responses would r e s u l t . I t i s there- fore possible to investigate the extent of these cardiovascular (CV) interactions imposed by heat and sustained work by observing the changes i n s y s t o l i c time i n t e r v a l s , heart rate, and blood pressure. The intent of t h i s study i s to show l e f t ventricular cardiac adjustments to thermal stress, isometric exercise, which produces an a r t e r i a l pressure load, and simultaneous exposure of thermal and isometric stress. I t i s hoped that a conclusion may be arrived at concerning the differences between myocardial dynamics and oxygen consumption during isometric stress i n a neutral environment and isometric stress accompanied by greater than normal skin temperature. Such conclusions would answer the query of whether the heart i s supporting a s i g n i f i c a n t l y greater functional stress during a simultaneous volume and pressure load as opposed to only a pressure load. I I . PURPOSE The purpose of th i s study i s to investigate the changes i n CV dynamics as depicted by s y s t o l i c time i n t e r v a l s , BP, and HR during sustained submaximal and maximal isometric work i n a hot and neutral environment. I I I . SUBPROBLEMS 1. To compare changes i n STI at rest between a neutral environment and a hot environment. 2. To compare changes i n STI between r e s t , 50% MVC, and 100% MVC i n two separate environments (heat and neutral). 3. To investigate how BP and HR change during the above stated i n t e r - ventions i n an attempt to support previous studies. 4. To show any s i g n i f i c a n t differences i n cardiac dynamics as depicted by changes i n STI, HR, and BP during the above stated environmental conditions between a submaximal s t a t i c contraction and a maximal s t a t i c contraction. 5. To show whether the CV changes induced by s t a t i c contractions are additive or merely interactive with those e l i c i t e d by thermal stress upon the body. IV. ASSUMPTIONS AND LIMITATIONS 1. Invasive measurements concerned with changes i n LVEDP were not taken. This l i m i t s the extent to which conclusions can be made from alterations i n s y s t o l i c time intervals during a s t a t i c contraction. However the l i t e r a t u r e c l e a r l y states that the LVEDP i n a normal intact heart does not s i g n i f i c a n t l y change during an increased pressure load. 2. I t was assumed that a l l subjects produced a maximum effo r t when asked to grip the hand dynamometer for an i n i t i a l MVC reading. 6 3. When using s y s t o l i c time intervals the electromechanical lag (EML) i s measured as the i n t e r v a l Q-S;_. This i n t e r v a l very closely approximates the period from the onset of e l e c t r i c a l stimulation of the l e f t v e n t r i c l e to the beginning of ventricular contraction. However the Q-S_ i n t e r v a l i s s l i g h t l y longer than the true EML since the i n i t i a t i o n of the f i r s t heart sound (Sj) i s associated with the closing of the at r i o v e n t r i c u l a r (AV) valves rather than the actual commencement of myocardial contraction. In order to investigate the true changes i n EML an apexcardiogram should have been used. However i t was not available for th i s study. 4. The most appropriate method of s t a t i s t i c a l l y analyzing the data would have been to use a multivariate analysis of variance (MANOVA). However the number of subjects required i n order to use this method were far too great. The s t a t i s t i c a l analysis was therefore confined to u t i l i z i n g the standard analysis of variance (ANOVA). V. HYPOTHESES 1. Oxygen consumption of the myocardium as reflected by the index (HR x BPs x LVET) s i g n i f i c a n t l y increases from rest to 100% MVC i n both a heated and neutral environment. 2. Oxygen consumption of the myocardium as reflected by TRIP during a resting state i s s i g n i f i c a n t l y greater i n the hot environment than i n the neutral. 3. Oxygen consumption of the myocardium as reflected by TRIP i s s i g n i f i c a n t l y greater when the body i s subjected simultaneously to heat and s t a t i c muscular work than when the body i s subjected to s t a t i c muscular contraction alone. 4. The l e v e l of BPs and BPd i s not s i g n i f i c a n t l y altered during rest, 50% MVC, and 100% MVC from a neutral to a heated environment. 5. BPs and BPd s i g n i f i c a n t l y increase from resting values during a 50% MVC and 100% MVC isometric contraction. 6. Changes i n BPs, BPd, HR, variables representing ventricular systole (LVET, MS, TS and ETI), variables representing diastole (diastole and CT), variables representing the contr a c t i l e state of the myocardium (ICP, PEP, and PEP/LVET), and EML change i n an in t e r a c t i v e fashion from rest to 100% MVC during simultaneous stress of heat and s t a t i c work. S p e c i f i c a l l y the slopes between each workload condition are s i g n i f i c a n t l y different i n the two environments resulting i n a s i g n i f i c a n t interaction for a l l variables. 7. A l l variables depicting changes i n l e f t ventricular systole (LVET; MS; TS) decrease from resting values during a 50% MVC and 100% MVC isometric contraction. 8. ETI s i g n i f i c a n t l y increases from a resting value during a 50% MVC and 100% MVC isometric contraction. 9. Diastole and CT s i g n i f i c a n t l y decrease while HR increases from resting values during a 50% MVC and a 100% MVC isometric contraction. 10. EML s i g n i f i c a n t l y decreases while HR increases from resting values during a 50% MVC and a 100% MVC isometric contraction. 11. The co n t r a c t i l e state of the myocardium as depicted by changes i n ICP, PEP, and PEP/LVET increases with isometric exercise. 8 VI. DEFINITIONS 1. Inotropic State of Myocardium Inotropes are agents which change the c o n t r a c t i l i t y of the heart. Negative inotropes weaken the strength of contraction while positive inotropes augment the power of contraction. An increase i n the inotropic state of the heart means that the myocardium i s affected by positive inotropes such as d i g i t a l i s and catecholamines which strengthen the contraction of the heart. 2. Pressure Load A. pressure load upon the CV system and the heart pump i n par t i c u l a r i s due to an increase i n a r t e r i a l pressure. 3. Volume Load A volume load i s associated with an increased CO and HR. I t simply means that the heart has to pump more blood per unit time than normal. 4. Contractile State of Myocardium The cont r a c t i l e state of the myocardium may be associated with i t s inotropic state since positive inotropes augment myocardial c o n t r a c t i l i t y . By d e f i n i t i o n c o n t r a c t i l i t y i s the power of contraction where "Power" i s equal to load x ve l o c i t y of fi b e r shortening: P = L x V Therefore an increase i n c o n t r a c t i l i t y may be due to either an increased load or strength of contraction and/or an increased speed of contraction. 5. MVC A maximal voluntary contraction i s a 100% isometric squeeze on the hand dynamometer. 9 6. S y s t o l i c Time Intervals The STI are time components of a single cardiac cycle. I t i s customary to divide the cardiac cycle into the following phases: a) Cycle Time (CT) - time for one complete beat of the heart; measured as the i n t e r v a l S2~"^2" b) Diastole (D) - relaxation phase of the cycle time; time from end of ejection to onset of excitation measured as S2~Q. c) Electromechanical Lag (EML) - time from onset of e l e c t r i c a l a c t i v i t y to the onset of mechanical a c t i v i t y ; measured as Q-S^. d) Isovolumetric Contraction Period (ICP) - time from onset of contraction to onset of ej e c t i o n ; measured as S^-S2 minus ^^-C^. e) Left Ventricular Ejection Period (LVET) - time from the onset to the end of ejection; measured by C-j. -^* f) Mechanicai Systole (MS) - time from the onset of contraction to end of ejection; measured by S^-S^. g) Total Systole (TS) - from onset of excitation to end of ejection; measured as Q-Ŝ . h) Pre-ejection Period (PEP) - from onset of excitation to onset of ejection; measured by EML + ICP. i ) PEP/LVET - r a t i o of the amount of time spent i n preparation for ejection to the amount of time actually spent i n ejecting blood from the l e f t v e n t r i c l e . 7. Triple Product (TRIP) An index of myocardial oxygen consumption derived from the product of BP ( s y s t o l i c ) , heart rate, and LVET. TRIP = BPs x HR x LVET 10 8. Ejection Time Index (ETI) The ETI i s LVET corrected for the effects of HR. ETI = LVET + 1.7 HR 9. Vmax Maximum veloc i t y of myo f i b r i l contraction at zero load. 10. dp/dt The f i r s t derivative of ventricular pressure denoting the change i n pressure with time. 11. Contractile Element Velocity (VCE) Speed of contraction of the my o f i b r i l being derived at specified pressure loads. 12. Pressure Rate Product (PRP) A second index of myocardial oxygen consumption derived as: PRP = BPs x HR VII. SIGNIFICANCE OF THE STUDY This study w i l l lead to a better understanding of the changes i n cardiac dynamics involved i n a hot environment during both rest and sustained s t a t i c work. In addition i t w i l l demonstrate how the heart reacts to loads of volume and pressure simultaneously. This may shed some l i g h t upon the understanding of cardiac f i b e r functional l i m i t a t i o n s . CHAPTER I I REVIEW OF THE LITERATURE I. HISTORICAL INTRODUCTION The f i r s t comprehensive major study of the consecutive phases of the cardiac cycle was done by Wiggers (86, 87) i n 1921. He u t i l i z e d pressure curves from the cardiac chambers and arteries of dogs to record the changes i n the ventricular cycles. In 1923 Katz and F e i l (31) modified the pro- cedures used by Wiggers. They recorded the s y s t o l i c time intervals from simultaneous tracings of heart sounds, the subclavian a r t e r i a l pulse and the electrocardiogram (Lead I I ) . This contemporary procedure allowed for the investigation of cardiac function i n the intact heart of humans without entering the body. I t therefore became advantageous to use such non- invasive methods of investigation which allowed researchers such as Lombarde and Cope (43) i n 1927 to show d i s t i n c t differences i n the s y s t o l i c intervals between the sexes. Further work i n this area was limited i n the years to come due to the renaissance of investigation into the quantitative measures of the isolated heart preparation. However, with advancement of technology the interest i n s y s t o l i c time intervals has been revived. Within the l a s t two decades a multitude of studies have been completed most of which focus t h e i r e f f o r t s on the dynamic changes of the diseased heart. With the recent concern about heart disease the information available from investigations of cardiac intervals has been found to be useful i n the diagnosis of myocardial malfunction. 11 12 I I . CARDIAC INTERVALS The changes i n s y s t o l i c intervals are dependent on a variety of physiological parameters some of which have been i d e n t i f i e d and others which are unknown. Franks et al.(18) combined data from several studies to determine the orthogonal (independent) factors of the l e f t ventricular time components. Four factors accounted for v i r t u a l l y a l l of the variance of the eight intervals studied. Factor I represents primarily l e f t ventricular systole, with high loadings for LVET, MS, and TS. Factor I I represents ventricular diastole with high loadings for diastole and CT. Factor I I I represents the l e v e l of ventricular sympathoadrenergic a c t i v i t y which i s closely associated with the contractile state of the myocardial tissue. This factor has high loadings for ICP and PEP. Factor IV i s s p e c i f i c a l l y associated with the e l e c t r i c a l a c t i v i t y of the l e f t v e n t r i c l e represented by the time from the onset of excitation to the onset of contraction as measured by EML. A. LEFT VENTRICULAR SYSTOLE The most studied f r a c t i o n of ventricuiar systole i s LVET which has been reported by a number of authors to vary inversely with HR and d i r e c t l y with CT and SV (15, 36). Braunwald et a l . (5) studied the independent factors influencing the duration of LVET i n isolated heart preparations. They showed that an increase i n SV alone lengthens LVET and an increase i n HR alone at any given stroke volume shortens the duration of ejection per beat but prolongs the duration of ejection per minute. When mean a o r t i c pressure was elevated at any given stroke volume and heart rate, no 13 s i g n i f i c a n t change i n LVET was evident u n t i l the mean ao r t i c pressure reached 175-200 mm Hg. at which time a lengthening of LVET occurred. Administration of sympathomimetic amines, at any given SV, caused LVET to shorten. Similar results were obtained by Wallace et a l . (80) when studying the effects of a l t e r i n g separately, SV, mean BP (BPm) and HR on the duration of LVET and ICP i n denervated dog heart preparations. Augmenting stroke volume was found to prolong LVET and shorten ICP and had an i n s i g n i f i c a n t effect on TS. Elevating BPm to 140-160 mm Hg. shortened LVET, prolonged ICP and had l i t t l e effect on TS. These results are i n opposition to Braunwald's findings which suggest that increasing BPm below 175 mm Hg. causes l i t t l e change i n LVET. Wallace also showed that increasing heart rate alone or administering d i g i t a l i s and norepinephrine shortened a l l phases of systole including LVET and TS. These findings cl e a r l y demonstrate that the influence of hemodynamic variables on the duration of certain phases of ventricular systole interact with each other such that i t i s not possible to change one variable without a l t e r i n g others. However a systematic analysis of the effects of changing selected hemodynamic variables on the duration of each phase of systole may help to decipher the changes i n s y s t o l i c time intervals of the intact heart. We should always keep i n mind that by means of i n t r i n s i c mechanisms the myocardial tissue exhibits a remarkable capability to adjust the duration of each phase of systole to cope with the changing hemodynamic conditions. Lindquist et a l . (42) studied the effect of a 50% MVC isometric contraction of the forearm for one and one half minutes i n 21 normal subjects and showed that LVET decreased s i g n i f i c a n t l y with the contraction. 14 However when LVET was corrected for HR using a regression equation there was a smaller i n s i g n i f i c a n t decrease i n LVET. Frank and Haberen (15) also showed that during a s t a t i c contraction of the forearm l a s t i n g four minutes at 30% MVC the LVET shortened s i g n i f i c a n t l y . When LVET was corrected for HR using Weissler's (82) regression equation there was no s i g n i f i c a n t change i n ALVET. Quarry and Spodick (65) produced similar results i n normal males during an IHG contraction i n a s i t t i n g position. I t was found that at 50% MVC LVET was reduced s i g n i f i c a n t l y during the f i r s t t h i r t y seconds of contraction but i n s i g n i f i c a n t l y during the l a s t t h i r t y seconds of a one minute contraction. The greatest decrease i n LVET was shown to be during a t h i r t y second contraction at 100% MVC. It seems as i f the changes i n LVET associated with a s t a t i c contraction are probably more closely related to changes i n HR rather than changes i n BPm both of which are elevated during s t a t i c work. This suggests that the proper inducing factor i n the reduction of LVET during s t a t i c muscular contraction i s the development of tachycardia caused by neural and humoral stimulation of the cardiac tissue. EJECTION TIME INDEX (ETI) It i s wel l known that i n normal individuals the LVET varies inverseiy with heart rate. For th i s reason some researchers attempted to assess other determinants of the duration of LVET by d i l u t i n g the effect of HR upon the LVET. An index of the reiationship between HR and LVET was sub- sequently derived and was termed the ejection time index (ETI). Weissler et a l . (81) showed that the ETI was s i g n i f i c a n t l y correlated with cardiac 15 output i n normal subjects and i n patients with congestive heart f a i l u r e . I t was found that a f a l l i n cardiac output was reflected i n a decrease i n the ETI and concluded that the ETI offers a useful semiquantitative measure of the l e v e l of the cardiac output i n normal individuals and i n patients with congestive heart f a i l u r e . Quarry and Spodick (65) found that the ETI s i g n i f i c a n t l y increased (p < 0.01) at 30% MVC from control through four minutes of an isometric hand grip. The ETI was found to increase most during a 50% MVC of the forearm for one minute. However only a small i n s i g n i f i c a n t increase i n ETI was found during a 100% MVC of the forearm for t h i r t y seconds. The authors state that although efforts were made to avoid Valsalva maneuvers throughout IHG, some subjects may have performed this maneuver during 100% MVC contraction. Since the Valsalva maneuver has been shown to increase HR but decrease LVET and ETI (16) they suggest that the combined effects of this s t r a i n pattern could account for the lower ETI at 100% MVC. B. VENTRICULAR DIASTOLE Changes i n diastole per se have not been paid much attention i n the l i t e r a t u r e for the simple reason that alterations i n diastole or CT are very closely related to changes i n HR. Therefore results pertaining to diastole are used i n support of other findings within the cardiac cycle and do not provide additional or novel information about cardiac dynamics. In one of the few studies which has actually presented data for CT and diastole Coutts (8) showed that both variables shortened s i g n i f i c a n t l y with an isometric hand grip of 75% MVC. The importance of diastole seems 16 obvious since i t includes time for ventricular rest, f i l l i n g , and coronary c i r c u l a t i o n . The shorter the period of time i n which the myocardium has to accomplish these tasks, as occurs during tachycardia, the shorter diastole and CT w i l l be. C. SYMPATHOADRENERGIC ACTIVITY There i s common agreement within the recent l i t e r a t u r e which acknowledges the fact that PEP, ICP and possibly PEP/LVET are good indicators of myocardial c o n t r a c t i l i t y and the sympathoadrenergic tone of the myocardium (1, 17, 54, 83). However there i s no conclusive evidence to suggest that any one of these variables i s a better indicator of the contra c t i l e state of the heart than another. In most cases a l l three variables are used simultane- ously for purposes of investigation. Lindquist et a l . (42) found that PEP and ICP decreased s i g n i f i c a n t l y by the end of a bout of dynamic exercise but did not change during a 50% MVC for one and one half minutes. PEP/LVET did not change with a s t a t i c work bout but decreased s i g n i f i c a n t l y during ergometry work. In addition attempts were undertaken to determine whether there were any s i g n i f i c a n t relationships between the STI and HR, BPs and BPd. No s i g n i f i c a n t regressions were found between ICT and HR or any of the STI and blood pressure during isometric exercise. Ahmed et a l . (3) showed that an increase i n the inotropic stimulus to the heart either i n response to dynamic exercise or isoproterenol infusions would cause an increase i n the contra c t i l e element v e l o c i t y (VCE) of the myocardium but reduce the PEP/LVET r a t i o . 17 Garrard et a l . (19) found a high inverse correlation between PEP/LVET and Ejection Fraction (EF) r = -.90 (EF = SV/LVEDV). These authors suggest that a decrease i n EF measures diminished contractile power of the heart. Therefore an increase i n PEP/LVET may be due to poor myocardial contract- i l i t y . Grossman et a l . (21) showed that i n normals a 50% MVC for three minutes caused a decrease i n PEP/LVET. However i n heart disease patients with poor cardiac reserves the r a t i o did not s i g n i f i c a n t l y decrease. In normals the decrease i n PEP/LVET was paralleled by an increase i n stroke work without change i n LVEDP, while i n the patients LVEDP rose s i g n i f i c a n t l y and stroke work did not, r e f l e c t i n g a wide va r i a t i o n i n ind i v i d u a l responses. In addition, both Vmax and l e f t ventricular dp/dt showed s i g n i f i c a n t increases during IHG i n normals. In patients increases i n Vmax and dp/dt were also evident, although the resting and peak values were of smaller magnitude than i n the normal group. These results indicate that the heart reacts to an afterload by contracting with more power without changes i n LVEDP (preload). This change i s associated with no increase i n the PEP/ LVET r a t i o . However i n the diseased heart an increase i n afterload i f severe enough may cause changes i n preload as depicted by increases i n LVEDP. In such cases where the diseased myocardial tissue i s not able to cope with the afterload the PEP/LVET w i l l r i s e . Martin et al. (48) studied s i x patients with normal coronary angiograms using both STI and catheter invasive measurements during a variety of interventions one of which was a 100% MVC isometric contraction of the forearm. They showed that STI correlated well with invasive measurements 18 but most importantly the data demonstrated an inverse relationship between PEP and ICP to dp/dt. Metzger et a l . (54) found exactly the same r e l a t i o n - ship with anesthetized dogs. In this study an attempt was made to f i n d the r e l a t i o n of true isovolumetric contraction time, as measured by invasive techniques, with two external indexes of ventricular performance, namely ICP and PEP. Excellent lin e a r correlations were found between absolute values of true isovolumetric contraction time and both ICP and PEP. As was mentioned above the inverse relationship between true isovolumetric contraction time and dp/dt was also accurately reflected by the PEP and ICP. The authors suggest that ICP and PEP r e f l e c t r e l i a b l e changes i n true isovolumetric contraction time. In view of the fact that ICP and dp/dt are associated with a l t e r a t i o n i n afterload (BPd) and preload (LVEDP) Metzger i l l u s t r a t e s the relationship between these variables by the use of a right t r i a n g l e . He states that at constant LVEDP and constant dp/dt, ICP i s determined by changes i n afterload. Conversely, at a constant LVEDP and BPd, LCP i s inversely related to the maximal dp/dt. This concept i s i l l u s t r a t e d i n Figure 1. Figure 1. ICP BPd: ICP: dp/dt 19 In summary i t i s concluded that when changes i n BPd are considered, with only small alterations i n LVEDP, PEP and ICP give useful information about changes i n ventricular performance including an estimation of changes i n l e f t v e ntricular dp/dt and c o n t r a c t i l i t y . The right triangle relationship i s supported by the findings of Matsura and Goodyer (51) who studied the effects of a pressure load on l e f t ventricular s y s t o l i c time intervals i n 22 open-chested anesthetized dogs. Under normal control conditions and with infusions of isoproterenol an increase i n aor t i c pressure reduced ICP but increased LVEDP. However propranolol infusions, which act to decrease the contr a c t i l e power of the my o f i b r i l s , caused ICP to be prolonged and LVET to decrease as the a f t e r - load was increased. These results suggest that an afterload on a healthy heart w i l l induce an increase i n the power of contraction of the heart which i s associated with increased dp/dt with l i t t l e change or a s l i g h t reduction i n ICP. Quarry and Spodick (65) conducted an investigation comparing STI during a variety of s t a t i c work loads. They showed that ICP and PEP would s i g n i f i c a n t l y decrease during the f i r s t t h i r t y seconds succeeded by a rapid reascent to s l i g h t l y below control levels during the l a s t t h i r t y seconds of a one minute 50% MVC contraction. However both ICP and PEP decreased s i g n i f i c a n t l y at 100% MVC. The PEP/LVET showed no change during the 50% MVC and a s l i g h t i n s i g n i f i c a n t decrease during a t h i r t y second 100% MVC. Stefadouros et al. (75) used STI to show changes i n ventricular performance i n normal males during a 50% MVC for three minutes. These authors found that during the s t a t i c contraction l e f t ventricular dimensions, EF, PEP/LVET and shortening v e l o c i t y did not s i g n i f i c a n t l y change. These 20 results were explained by an increase i n the inotropic state of the heart which was elevated to increase the c o n t r a c t i l e state of the heart i n response to the augmented afterload caused by the IHG. In addition these authors also found a strong negative correlation between the PEP/LVET rat i o and EF at rest (r = -.879) and during s t a t i c work (r = -.775) which i s i n agreement with the findings of Garrard. Talley et al. (78) evaluated the PEP as an estimate of myocardial c o n t r a c t i l i t y by both invasive and non-invasive measurements of STI i n dogs under a variety of experimental conditions. No effect of HR on the PEP was noted when LVEDP, BPd, and contractile indexes were held constant. Increases i n a o r t i c d i a s t o l i c pressure alone caused s i g n i f i c a n t but small increases i n PEP. Increases i n LVEDP were shown to s i g n i f i c a n t l y a l t e r the PEP i n an inverse fashion. There was, however, a s i g n i f i c a n t correlation between the PEP and the i n t e r n a l indexes of c o n t r a c t i l i t y (dp/dt and maximal dp/dt) over a wide range of inotropic s t i m u l i i n experiments i n which LVEDP was shown to vary i n a random manner. According to the authors these studies indicate that PEP may be used as an index of myocardial state i n situations i n which LVEDP does not vary systematically under the conditions being studied. In summary i t seems as i f these sympathoadrenergic associated intervals are affected by not only the inotropic state of the myocardium but also by changes i n LVEDP (preload) and BPd (afterload). In a normal heart, catheterization studies have shown that despite considerable increase i n LV stroke work during IHG exercise, no change i n LVEDP i s evident (21, 25, 58, 75). Therefore i t requires l i t t l e thought to conceive that when the 21 afterload to the heart i s increased the heart tissue must contract with more vigor i n order to expel the same amount of blood against a greater pressure. For this reason the change i n ICP t e l l s us something about the amount of time which the l e f t v e n t r i c l e spends i n a phase of isometric contraction, whereby the length of the fibers does not change, during which time the inner ventricular tension r i s e s . This rate of tension development (dp/dt) depends on the power of contraction or simply the c o n t r a c t i l e state of the myocardium (74). I f ICP increases with an augmented afterload, as i s produced with IHG exercise, t h i s suggests that the c o n t r a c t i l i t y of the heart i s not enough to produce a large enough dp/dt against the pressure load such that i t spends longer time i n increasing the i n t r a v e n t r i c u l a r pressure to opening of the a o r t i c valve. D. ELECTRICAL ACTIVITY WITHIN THE LEFT VENTRICLE Following the spread of e l e c t r i c a l a c t i v i t y , mechanical a c t i v i t y starts i n the heart after a variable i n t e r v a l which i s referred to as EML. There i s very l i t t l e information available i n the l i t e r a t u r e pertaining to alterations of the EML during bouts of sustained isometric exercise. A possible reason for this absence i n the l i t e r a t u r e could be that EML i s most frequently coupled with ICP to show changes i n PEP. However Franks et a l . (18) strongly suggest that EML and ICP should be analyzed separately because they represent quite different aspects of the cardiac cycle. Quarry and Spodick (65) used the Q-Im i n t e r v a l which i s very similar to the EML and showed that Q-Lm decreased s i g n i f i c a n t i y with a one minute 50% MVC contraction and a t h i r t y second 100% MVC contraction. Coutts (8) 22 however found that EML was not s i g n i f i c a n t l y altered during a ten second 75% MVC i n the supine position. Perhaps ten seconds of contraction was not enough time for the body to produce complete physiological adaptation to the muscular stress' such that alterations i n the e l e c t r i c a l a c t i v i t y of the l e f t v e n t r i c l e were i n s i g n i f i c a n t or completely absent. Kumar and Spodick (36) i n an excellent review of the mechanical events of the l e f t v e n t r i c l e also establish the fact that measurements of EML are rare. The only studies which they c i t e are concerned with changes i n the Q-Im in t e r v a l i n pathophysiological states. I I I . MYOCARDIAL OXYGEN CONSUMPTION The most successful non-invasive method of measuring myocardial oxygen consumption has been to use the product of LVET, BPs and HR. Katz and Feinberg (32) reviewed the relations between cardiac work and i t s oxygen consumption and concluded that an increase i n HR and/or the buildup and maintenance of tension i n the ventricles causes the heart to consume most of i t s available oxygen (O2) supply. Kivowitz et a l . (35) had 22 CHD patients perform an IHG exercise at 25% MVC for f i v e minutes. They found an increase i n coronary blood flow and myocardial oxygen consumption of 45% from resting values. This indicates that an IHG exercise i s severe enough to tax the work output of the heart. However no evidence of myocardial lactate production was present during the bout of s t a t i c work which suggests that the coronary blood flow increase during the IHG exercise was substantial to supply the myocardium with the needed oxygen. Similar findings were reported by Nakhjavan et a l . (59) who studied lactate metabolism of the heart during IHG exercise and pace produced tachycardia. Tension time index (BPs x LVET) and the t r i p l e product were used to measure myocardial 02 consumption. The results showed that both measurements were greater during IHG at 30% MVC for f i v e minutes than right a t r i a l pacing. However the largest consumption of oxygen by the heart occurred during simultaneous a t r i a l pacing and IHG exercise. These authors also found that myocardial lactate production was absent during IHG exercise but was increased during right a t r i a l pacing. Lindquist et al.(42) also used the t r i p l e product to assess myocardial oxygen consumption. These researchers compared the results of dynamic and s t a t i c work i n 22 normal subjects. They showed a larger t r i p l e product during an IHG exercise of 30% MVC for one and one half minutes than during dynamic work. These results suggest that IHG exercise w i l l increase the oxygen consumption of the myocardium but that t h i s requirement i s met by an increased coronary flow which i s substantial to supply the needed oxygen to the working tissue. IV. CIRCULATORY CHANGES WITH STATIC WORK The ci r c u l a t o r y adjustments to sustained s t a t i c work have been well documented i n the l i t e r a t u r e . The most marked changes associated with an IHG contraction of the forearm are acute increases i n BPd, BPs and HR (38, 39, 49, 6 l ) • Both the blood pressure elevation and HR elevation are proportional to the r e l a t i v e force and duration of the contraction. 24 M i t c h e l l and Wildenthal (56) note that neither the absolute tension developednor the size of the muscle group i s the determining factor i n al t e r i n g c i r c u l a t o r y variables during isometric work. Lind et a l . (40) have shown that BP ris e s to a s i m i l a r extent with a 20% MVC of the fore- arm, a 20% MVC of the thigh muscles and a 20% MVC of indiv i d u a l fingers, despite manifold differences i n absolute tension developed and i n the energy requirements of the respective e f f o r t s . According to Lind (37) the amount of blood flow r e s t r i c t i o n caused by isometric muscular contraction i s the main factor which controls the length of time a contraction can be maintained. Lind et a l . (40) have shown that blood flow through the arm i s not completely occluded u n t i l the tension exceeds 70% MVC. For this reason a 50% MVC can be maintained for a maximum time of approximately two minutes while a 100% MVC can be maintained for about t h i r t y seconds. A one minute contraction at 50% MVC would therefore induce a state of 50% absolute fatigue of the forearm while a 100% MVC for t h i r t y seconds would produce complete fatigue of the forearm. Another important variable which increases during an isometric con- traction i s the cardiac output. Lind (41) examined subjects i n the supine position while they performed hand grip contraction at 10% MVC, 20% MVC and 50% MVC. I t was confirmed that sustained hand grip contractions caused an increase i n cardiac output which was a major factor i n producing the increased mean blood pressure. I t was also found that i n the younger subjects (mean age 26) there was no change i n systemic vascular resistance (SVR) while i n one older subject aged 37 there was s i g n i f i c a n t increase i n 25 the SVR with hand grip exercise. In addition the cardiac stroke volume showed no systemic change at 10% MVC or 20% MVC but a consistent and clear reduction i n a l l cases at a tension of 50% MVC, when cardio-acceleration was pronounced. This suggests that i n the younger subjects the major cause of increased BP during isometric work was the augmentation of CO due d i r e c t l y to the cardio-acceleration since increases i n SV and SVR have been shown to be absent. M i t c h e l l and Wildenthal (56) however con- clude that the increased CO present with s t a t i c work results primarily from tachycardia but may also be caused i n part by an increased stroke volume i n some individuals. When isometric exercise i s superimposed upon dynamic exercise, the cardiovascular effects tend to be additive. Nutter et al.(61) describes that when sustained hand grip contraction i s performed by subjects walking on a treadmill with an oxygen consumption of 1.1 L/minute, the increase i n BP i s the same as that produced by an equivalent hand grip alone despite the marked lowering of systemic vascular resistance produced by the. dynamic exercise. However, during an extreme combination of walking at an oxygen consumption of 2.2 L/minute and 50% MVC the pressor response i s less than that produced during less strenuous walking. I t seems that the more vigorous the dynamic phase of the exercise the more extreme w i l l be the muscular vasodilation. In such a condition the pressor response to the isometric exercise w i l l be less pronounced. V. CV CHANGES IN A HOT ENVIRONMENT This subject has very recently been extensively reviewed by Rowell (69) who himself has conducted a number of c l a s s i c studies. I t i s w e l l known that heat exchange between the body and the environment i s determined by the amount of heat brought to or from the skin by the vascular tubing. The o v e r a l l cardiovascular response to direct whole body heating i s a r i s e i n CO i n proportion to the r i s e i n HR. The SV increases very l i t t l e (4%-5%) from normal values and the BPm s i m i l a r l y f a l l s s l i g h t l y . The marked r i s e i n t o t a l limb blood flow measured plethysmographically during indirect heating has been shown to be confined to the skin rather than the muscle mass. Rowell concludes that muscle blood flow i n the leg or forearm, which i s not d i r e c t l y heated, decreases or remains constant with whole body heating. Two separate studies were conducted by Johnson et a l . (29) and Heistad et al.(24) who researched the interaction between thermal cutaneous vasodilator and pressoreceptor reflexes i n the forearm. Johnson used seven normal subjects aged 22-30 years to determine whether skin w i l l respond to increased neurogenic vasoconstrictor a c t i v i t y during direct heating. A l l testing was performed i n a supine resting condition. The results showed that sympathetic vasoconstriction i s unable to overcome the high levels of vasodilation accompanying moderate levels of body heating. Heistad concluded s i m i l a r l y when he found that i n the forearm the vasoconstriction response to lower body negative pressure was less during body heating. Since i t i s known that isometric exercise w i l l increase the amount of catecholamines i n the c i r c u l a t i o n (60) i t may be argued that a s t a t i c contraction of the forearm would increase the pressor response of the skin. However i n a hot environment although the skin retains some a b i l i t y to vasoconstrict, this r e f l e x mechanism may not override the heat-induced vasodilation. CHAPTER I I I METHODS AND PROCEDURES I . SUBJECTS Fourteen male subjects from the Univers i ty of B r i t i s h Columbia aged 20 to 31 (mean age = 25.4) volunteered to be subjects i n th is experiment. P r io r to being accepted into the study each ind iv idua l was asked about the i r health records and i f they were undertaking or had recently completed any kind of physical t r a in ing programme. Only those people who had no previous health problems and who were not t r a in ing or recently completed a t r a in ing programme wi th in the l a s t s i x months were accepted into the study. The subjects were a l l phys ica l education students and maintained a s i m i l a r a c t i v i t y l e v e l throughout the day. Their height and weight were recorded and compared to standard tables. None of the subjects were found to be grossly overweight or obese. I I . EXPERIMENTAL PERIOD Each subject was tested on two separate days with one day of rest between the two tes t ing days. The tes t ing procedure was exactly the same i n both a hot environment and neutral (room) environment. A res t ing measure of a l l var iables was taken to ensure that the equipment was responsive and that the^readings were clear enough for analys is . This i n i t i a l period of adjustment not only permitted the access of the best possible readings for that subject but also gave the subject a chance to get acquainted with the equipment and tes t ing procedures. 28 29 After t h i s session the subjects were put through the entire testing procedure. Between each work load the subject was given f i v e minutes to recover after which time his pulse was taken to ensure that the heart rate had dropped back to a resting l e v e l . When testing i n the heat i n i t i a l subjection to heat was gradual, l a s t i n g from ten to f i f t e e n minutes, u n t i l a l l of the equipment had been adjusted for the subject and clear recordings were attained. During this time, sauna temperature and subsequently the skin temperature rose gradually. Data c o l l e c t i o n did not begin u n t i l the skin temperature had reached 40°C at which time the thermostat for the sauna was dropped i n order to maintain the skin temperature between 40°C - 41°C throughout the testing period. I I I . PRE-EXPERIMENTAL INSTRUCTIONS Subjects were asked to maintain the i r normal a c t i v i t y and rest patterns throughout the i r three experimental days. Testing was not done i n the post absorptive state; however subjects were asked not to eat at least one hour before coming into the laboratory. A l l of the subjects except two did not eat for at least two hours before being tested. The two subjects who ate between one and two hours before the testing had eaten a very l i g h t lunch because they had not eaten any breakfast. During that i n i t i a l period when the subjects were getting acquainted with the testing procedures s p e c i f i c instructions were given to each subject: V 30 a) Try to relax the entire body b) Keep breathing normally and try to eliminate any sudden jerking of the musculature c) When contracting the forearm i s o l a t e the contraction such that no other muscle i n your body i s f a c i l i t a t i n g the work of the forearm. IV. PROCEDURES The complete testing scheme for each subject i s i l l u s t r a t e d below i n Figure 2. Each volunteer was subjected to three levels of contraction i n two different environments t o t a l l i n g s i x different conditions. Figure 2. Rest 50% MVC 100% MVC Neutral Heat N l H l N 2 H 2 Testing Scheme 31 The subject was seated i n a back r e c l i n i n g position of 110°. The l e f t arm lay on a padded arm rest which was inclined s l i g h t l y towards the f l o o r i n order to f a c i l i t a t e the taking of blood pressure. The s t a t i c contractions were performed by the right forearm using a hand dynamometer which was e l e c t r i c a l l y connected to an oscilloscope and gave a continuous v i s i b l e recording to the subject and experimenter of the degree of contraction. Prio r to commencement of any testing the maximal voluntary contraction (MVC) for each subject was i d e n t i f i e d from which both maximal (100% MVC) and submaximal (50% MVC) degrees of contraction were calculated and converted into units on the oscilloscope. The subjects were asked to contract the forearm at 100% MVC for one half minute and at 50% MVC for one minute. A l l subjects were tested i n a neutral environment and a heated environment. The neutral setting as existed i n the physiotherapy room at the University of B r i t i s h Columbia did vary somewhat i n both tempera- ture and humidity from day to day. In the physiotherapy room, the temperature was seen; to fluctuate between 24°C and 26°C throughout the ,two-week experiment while the humidity fluctuated between 51% and 58% saturation. The heated environment was created i n the sauna which was also situated i n the physiotherapy room at the University of B r i t i s h Columbia. The humidity i n the sauna was not regulated but was l e f t to vary i n accordance with the natural humidity i n the a i r on any one day. Such a procedure was used because i t was found during a p i l o t investigation that increasing the humidity to 100% saturation caused the subject to 32 perspire profusely which caused poor contact of the equipment to the skin and discomfort to the subject. In view of the fact that the guiding factor for commencement of data c o l l e c t i o n was the skin temperature i t was decided,not to increase the humidity i n the sauna but rather induce a gradual change i n the skin temperature by regulating the a i r temperature of the sauna only. During each of the s i x experimental conditions a number of simultaneous tests were taken on each subject. Skin Temperature Skin temperature readings were taken continuously throughout the testing session i n the sauna. A thermister was attached to the skin surface on the right side of the body two inches beneath the ribcage. The thermister was checked and calibrated every morning and afternoon before testing of subjects i n the sauna. Blood Pressure Blood pressure was taken with a cuff sphygmomanometer whose input was e l e c t r i c a l l y transferred to one channel i n the Sanborn recorder. This system gave a beat to beat graphic recording from which both s y s t o l i c and d i a s t o l i c pressures could be read. The sphygmomanometer was calibrated for each experimental condition before each of the work bouts. The pressure recording was taken during the l a s t f i v e seconds of contraction for each work load. Heart Sounds A phonocardiogram (PCG) was used to detect the f i r s t and second heart sounds. The microphone head of the PCG apparatus was situated on the skin 33 surface within the fourth or f i f t h i n t e r c o s t a l space, adjacent to the sternum on the l e f t side of the body, depending on which p o s i t i o n gave the stronger s i g n a l . The PCG was connected to a second channel of the Sanborn recorder. Carotid Pulse Wave Carotid pulse waves were registered from a pressure s e n s i t i v e instrument strapped to the skin on the top of the c a r o t i d artery on the l e f t side of the neck. Recordings were found to be strongest when the head was t i l t e d to the r i g h t allowing the c a r o t i d artery on the l e f t side of the neck to be u p l i f t e d closer to the skin surface. The subject was asked not to swallow during the f i v e second period i n which the simul- taneous recordings were taken. The beat to beat recordings were also e l e c t r i c a l l y transferred to one of the four active channels on the Sanborn recorder which produced graph recordings of the pulse waves. Electrocardiogram A CM5 lead was used for the electrocardiogram (ECG) which was taken simultaneously on the fourth channel of the Sanborn recorder along with BP, PCG, and CPW. Precautions were taken to eliminate the Valsalva manoeuver by explaining the importance of maintaining normal breathing during contraction of the forearm to each subject. An analysis of the simultaneous recordings of ECG, PCG, and CPW per- mitted the c a l c u l a t i o n of the s y s t o l i c time i n t e r v a l s i n milliseconds. A graphic representation of the s y s t o l i c time i n t e r v a l s i s shown i n Figure 3. A recording of these i n t e r v a l s was taken only during the l a s t f i v e seconds 34 Figure 3. S y s t o l i c Time Intervals S y s t o l i c Time Intervals measured from simultaneous recordings of e l e c t r o c a r d i o - gram, phonocardiogram, and c a r o t i d pulse wave. Also blood pressure recording e l e c t r i c a l l y transmitted from cuff sphygmo- manometer. LVET, l e f t v e n t r i c u l a r e j e c t i o n time; Q-S_, preisovolumetric contraction period; PEP, pre- eje c t i o n period. S i S 2 35 of each contraction period. From these only the three strongest and clearest cycle tracings closest to the end of the contraction period were used for analysis. A l l subjects were tested under s i x different conditions. One half of the subjects were tested f i r s t i n the sauna and secondly i n the neutral environment while the other half did the reverse. The order by which the work load was administered was randomly assigned by picking the assorted loads from a hat. The work loads were administered i n the same order i n both environmental conditions for each subject. From the i n i t i a l fourteen recordings only twelve of these which gave the sharpest tracings were used i n the computer analysis. The two poorest tracings were discarded p r i o r to computer analysis of the raw data. This guaranteed that the data were of good quality and decreased the chances of fa u l t i n g the experiment by production of poor quality tracings i n a few subjects. V. STATISTICAL CONCERNS As was mentioned above only the l a s t f i v e seconds of each test condition were recorded on the Sanborn. This period was ample to assure that the effects of the test condition were maximally represented on the recording and also allowed enough time to record the a r t e r i a l pressure. Of this five-second tracing only the l a s t three clearest cardiac cycles were used i n the computer analysis. From these three cycles a mean was computed for s i x s y s t o l i c i n t e r v a l s , BPs and BPd. These means were 36 then transformed by the computer re s u l t i n g i n fourteen dependent variables. The names of the dependent and independent variables are as follows: Independent variables A. Environment (2 levels) Heat A^ Neutral B. Workload (3 levels) B 1 Rest B 2 50% MVC B 3 100% MVC The fourteen dependent variables can be broken down into separate categories: a) Blood Pressure BPs and BPd b) Heart Rate c) Ventricular Systole LVET, TS, MS, and ETI d) Ventricular Diastole Diastole and CT e) Sympathoadrenergic a c t i v i t y ICP, PEP, and PEP/LVET f) Electromechanical Lag (EML) g) Myocardial Oxygen Consumption TRIP { The test design i s i l l u s t r a t e d below i n Figure 4. Test Design. Heat Neutral V i X i X i v 2 x 2 X 2 v 3 x 3 x 3 '. Xtt v 5 x 5 x 5 v 6 x 6 x 6 Vy Xy Xy v 8 x 8 x 8 V 9 Xg Xg Vio Xio XlO V n X n X l l V i z ^ X12 x 1 2 Vl3 Xl3 Xl3 Xm V i X l X l v 2 x 2 x 2 v 3 x 3 x 3 V H x 4 xk v 5 x 5 x 5 v 6 x 6 x 6 Vy Xy Xy v 8 x 8 x 8 Vg Xg Xg Vio Xio x i o V n X n X n Vl2 X12 X12 Vl3 Xl3 X l 3 Vm Xli» x14 V l X l X l V 2 X 2 X 2 v 3 x 3 x 3 v 4 x 4 X H v 5 x 5 x 5 v 6 x 6 x 6 Vy Xy Xy v 8 x 8 x 8 Vg Xg Xg Vio X10 X10 V n X n X l l V i 2 X12 Xl2 Vl3 X l 3 X l 3 Vm X 1 4 x i i + Figure 4. 38 The experimental testing for t h i s study consists of a 2x3 f a c t o r i a l design with repeated measures on both variables as i l l u s t r a t e d i n Figure 5. Heat Neutral R 50 100 R 50 100 Si s 2 s 3 s 4 s 5 s 6 s 7 s 8 s 9 s 1 0 S n s 1 2 Figure 5. 2 x 3 F a c t o r i a l Design The data were treated with.a two-way ANOVA for each dependent variable. Also correlations among a l l dependent variables were calculated. CHAPTER IV RESULTS AND DISCUSSION I. RESULTS The means and standard deviations of a l l dependent variables for each of the s i x conditions are given i n Table 1. TABLE 1 Neutral Heat Rest 50% MVC 100% MVC Rest 50% MVC 100% MVC BPs 112 139 144 106 124 132 ± 9.4 ± 13.5 ± 14.0 ±10.8 ± 15.4 ± 16.6 BPd 77 106 110 72 89 96 ± 4.2 ± 9.7 ± 12.0 ± 6.5 ± 13.9 ± 13.1 CT 961 769 663 778 684 593 ±134 ±157 ±103 ±104 ± 99 ± 78 EML 83 78 77 82 77 75 ± 10.4 ± 12.5 ± 10.0 ± 14.2 ± 10.5 ± 12.5 LVET 258 251 241 239 231 220 ± 18.2 ± 18.6 ± 16.7 ± 16.3 ± 15.5 ± 16.8 MS 303 302 281 281 275 257 ± 20.2 ± 16.8 ±11.7 ± 18.2 ±10.1 ± 16.0 TS 386 379 358 364 350 333 ± 21.1 ± 22.1 ±16.7 ±12.7 ± 16.1 ± 20.1 DIAST 574 394 305 413 335 258 ±120.5 ±136.9 ± 89.2 ± 96.2 ± 85.5 ± 60.2 ICP 44.9 51.1 39.8 43.6 42.5 37.8 ± 17.0 ± 9.0 ± 9.8 ±12.9 ± 11.8 ± 14.5 PEP 128.3 128.8 116.8 125.3 119.4 112.2 ± 16.5 ± 10.4 ± 14.8 ± 8.9 ±10.1 ± 11.2 PEP/LVET .50 .52 .49 .53 .52 .5: ± .085 ± .057 ± .084 ± .067 ± .065 ± .01 HR 63.5 80.5 92.3 78.5 89.3 102.7 ± 9.1 ± 13.4 ±12.8 ± 10.4 ±12.8 ± 12.1 TRIP 1825 2813 3205 1964 2551 2969 ±267 ±570 ±617 ±165 , ±410 ±476 ETI 366 387 398 372 383 395 ±11.6 ± 19.0 ±21.3 ±10.3 ±12.3 ±11.5 39 40 S t a t i s t i c a l Results The results of the ANOVA for each variable are grouped according to the cardiovascular function they depict. Testing was conducted for a s i g - n i f i c a n t difference between the heat and neutral (control) environments averaged over the three workloads (rest to 100% MVC). The second test investigated the differences, averaged over environments, among the three workloads. The f i n a l test included the investigation of any interaction between workloads and environments on each of the dependent variables. The sources for the ANOVA tables are termed as follows: E - Environment Eff e c t : Heat vs. Neutral C - Contraction (Workload) Eff e c t : Rest vs. 50% MVC vs. 100% MVC Ci - Workload (Linear change from Rest to 100% MVC) C2 - Workload (Quadratic change from Rest to 100% MVC) EC - Interaction E f f e c t : Environment x Workload Note: Insertion of an asterisk (*) within the ANOVA table s i g n i f i e s s t a t i s t i c a l significance at p < .05 for that p a r t i c u l a r source. Correlation coefficients are included i n the r e s u l t s . These data were used to support or elucidate on the findings. For this reason only those coefficients which were of s t a t i s t i c a l significance ( c r i t i c a l value of the correlation c o e f f i c i e n t at the .01 l e v e l of significance being .658 for df = 10) were included i n the r e s u l t s . However, a complete correlation matrix for each of the s i x test conditions i s presented i n Appendix B. In some cases a post-hoc analysis (Newman-Keuls) was conducted. The prime concern was to show i f s i g n i f i c a n t differences existed from rest to 100% MVC within each environmental condition or between the environments for each s p e c i f i c workload. 41 Blood Pressure Both BPs and BPd (Figures 6 and 7) reacted to isometric work at room temperature and i n a heated environment i n a very similar fashion. The ANOVA data (Tables 2 and 3) indicate that both s y s t o l i c and d i a s t o l i c pressures r i s e s i g n i f i c a n t l y from rest (R) to 100% MVC under the averaged influence of a control and heated environment. However the presence of a si g n i f i c a n t interaction for BPs (p < .05) and BPd (p < .05) does not allow one to concluded that blood pressure increases from rest to 100% MVC i n a simil a r manner for both a neutral and heated environment. Consequently a post-hoc analysis of these comparisons was carried out using the Newman- Keuls method for multiple comparisons. This procedure gives the opportunity to compare the mean differences from R to 100% MVC within each environment. The results for both BPs and BPd are presented i n Table 4. Both BPs and BPd were s i g n i f i c a n t l y greater ov e r a l l from R to 100% MVC i n the control environment than i n the heated environment (Table 2 and Table 3). In order to investigate exactly where this significance between the environments existed a Newman-Keuls analysis was again conducted. Comparisons were made between means of the two environments for each separate workload. The results are presented i n Table 5. Calculation of simple correlation coefficients for BPs and BPd showed significance only for BPs with TRIP (Table 6). 100 . , f Rest 50% MVC 100% MVC Workload Figure 6. Systolic Blood Pressure 43 Workload Figure 7. D i a s t o l i c Blood Pressure 44 TABLE 2 SUMMARY OF ANOVA Blood Pressure (Systolic) Source E * Error C * Error C (1) * C (2) * EC * Error df 1 11 2 22 1 1 2 22 Mean Square 2080.1 81.4 5502.9 102.9 9832.7 1173.1 136.8 36.1 F 25.6 53.5 62.5 24.2 3.8 P <.001 <.001 <.001 <.001 0.038 TABLE 3 SUMMARY OF ANOVA Blood Pressure (Diastolic) Source E * Error C * Error C (1) * C (2) * EC * Error df 1 11 2 22 1 1 2 22' Mean Square 2652.3 113.1 5653.1 93.1 10034.1 12 72.1 243.6 43.2 F 23.4 60.8 85.1 18.6 5.6 P 0.001 <.001 <.001 0.001 0.011 45 TABLE 4 NEWMAN-KEULS ANALYSIS (WORKLOAD EFFECT) BPs and BPd Comparison R vs. 100% MVC R vs. 50% MVC 50% MVC vs. 100% MVC Environment N H N H N H Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 BPs c a l Q 10.92 8.88 9.21 6.14 1.70 2.73 Result p<.05 p<.05 p<.05 p<.05 N.S. N.S. Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 BPd cal Q 12.05 8.78 10.61 6.18 1.43 2.58 Result p<.05 p<.05 p<.05 p<.05 N.S. N.S. From these results i t can be concluded that both BPs and BPd increase from R to 100% MVC i n both the control and heated environment. 46 TABLE 5 NEWMAN-KEULS ANALYSIS (ENVIRONMENT EFFECT) BPs and BPd Comparison H vs. N Rest H vs. N 50% MVC H vs. N 100% MVC Q. 95 3.11 3.11 3.11 BPs c a l Q 2.11 5.77 4.50 Result N.S. p<.05 p<.05 Q. 95 3.11 3.11 3.11 BPd c a l Q 1.63 5.61 3.29 Result N.S. p<.05 p<.05 These results show that both BPd and BPs are not s i g n i f i c a n t l y different at rest between the control and heated environment. However both BPd and BPs are s i g n i f i c a n t l y lower i n the heated environment from the control condition at 50% MVC and 100% MVC. 47 TABLE 6 CORRELATION COEFFICIENTS BPs j Neutral Heat R 50% MVC 100% MVC R 50% MVC 100% MVC TRIP .79 .84 .80 .62 .82 .90 These results support the strong direct association between BPs and myocardial oxygen consumption. Note however that at rest i n the heat the correlation i s not quite s i g n i f i c a n t at the .01 l e v e l . This result i s j u s t i f i a b l e since i n t h i s condition HR plays a greater role than does BPs i n the consumption of the available oxygen to the myocardium. Heart Rate Heart rate increased s i g n i f i c a n t l y from rest to 100% MVC i n a linea r fashion with both environments (Table 7). There were also s i g n i f i c a n t differences between hot and neutral settings when averaged over the work- loads. Such conclusions can be presented from results of the ANOVA only, since there was no s i g n i f i c a n t interaction. This means that any changes i n HR from rest to 100% MVC were uniform i n both environmental conditions That i s to say that the tachycardia induced by isometric work i s additive to the tachycardia induced by thermoregulatory adjustments. Heart rate was s i g n i f i c a n t l y correlated to a number of the s y s t o l i c intervals as i l l u s t r a t e d i n Table 8. 60" : i 1 i Rest 50% MVC 100% MVC. Workload Figure 8. Heart Rate 49 TABLE 7 SUMMARY OF ANOVA Heart Rate Source E * Error C * Error C (1) * C (2) EC Error df 1 11 2 22 1 1 2 22 Mean Square 2323.3 98.8 4216.6 47.2 8426.9 6.2 63.3 28.4 F 23.5 89.4 125.6 0.23 2.2 P 0.001 <.001 <.001 0.641 0.131 Variable CT LVET TS DIAST R .99 .77 .67 .98 TABLE 8 CORRELATION COEFFICIENTS Heart Rate Neutral 50% MVC 100% MVC -.99 -.60 -.83 -.98 -.99 -.43 -.84 -.98 R -.99 -.82 -.73 -.99 Heat 50% MVC -.99 -.84 -.80 -.97 100% MVC -.99 -.83 -.90 -.96 50 These resul ts show that HR i s inversely correlated to the s y s t o l i c and d i a s t o l i c representatives of the cardiac cycle . However LVET does not correlate with HR as highly at 50% MVC and 100% MVC i n the neutral environ- ment as i t does under the other test condit ions. Why LVET should exhibi t a weaker l i nea r re la t ionship with HR during isometric work i n a control environment than i n a heated environment i s not known. I t i s possible that some other phys io log ica l factors , other than HR, which have not been revealed i n th i s study, play a greater role i n determining LVET during isometric stress i n a neutral environment than i n a heated environment. This would cause the t o t a l effect of HR upon LVET to become masked such that the cor re la t ion between them would appear to be d i lu ted . Vent r icu lar Systole (LVET; MS; TS) LVET, MS, and TS are the three variables used to ident i fy a l te ra t ions i n sys to le . A l l three in te rva ls changed i n approximately the same manner. LVET decreased l i n e a r l y from rest to 100% MVC as has been described i n e a r l i e r studies (15, 42, 83). MS and TS also decreased from rest to 100% MVC with s l i g h t l y different slopes than LVET. This i r r e g u l a r i t y can only be due to the changes i n ICP which are incorporated into the MS and TS times. In a l l three cases however the resul ts show a s ign i f i can t difference between environmental conditions and between workloads wi th in each separate environment (Figures 9-11). This i s supported by the presence of a non-signif icant in te rac t ion effect for a l l three variables (Tables 9-11) which s i gn i f i e s that the rate of decrease i n LVET, MS and TS from rest to 100% MVC was very s imi l a r i n both environments. 260 51 Neutral Heated 250 \ N \ 1 Rest 1 50% MVC \ 100% MVC Workload Figure 9. Left Ventricular Ejection Time 52 390- Neutral Heated • 380- 370- 360 350 340- 330 h S N N 320 1 Rest 50% MVC Workload Figure 10. Total Systole 100% MVC 310 Figure 11. Mechanical Systole 54 TABLE 9 SUMMARY OF ANOVA Left Ventricular Ejection Time Source E * Error C * Error C (1) * C (2) EC Error df 1 11 2 22 1 1 2 22 Mean Square 7219.9 405.6 1804.5 100.0 3588.0 21.0 5.7 70.0 F 17.8 18.0 26.5 0.32 0.08 . P 0.001 <.001 <.001 0.580 0.922 TABLE L0 SUMMARY OF ANOVA Mechanical Systole Source E * Error C * Error C (1) * C (2) * EC Error df 1 11 2 22 1 1 2 22 Mean Square 10512.5 498.4 3587.5 79.1 6188.0 987.0 43.8 117.8 F 21.1 45.4 65.0 15.7 0.37 P, .001 <.001 <.001 0.002 0.694 55 TABLE 11 SUMMARY OF ANOVA Total Systole Source E * Error C * Error C (1) * C (2) EC Error df 1 11 2 22 1 1 2 22 Mean Square 11806.7 384.2 5484.5 158.2 10620.7 348.4 71.9 127.9 F 30.7 34.7 61.2 2.4 0.56 P <.001 <.001 <.001 0.147 0.578 TABLE 12 SUMMARY OF ANOVA Ejection Time Index Source E Error C * Error C (1) * C (2) EC * Error df 1 11 2 22 1 1 2 22 Mean Square 10.9 324.4 4680.1 109.1 9268.4 91.8 198.2 43.4 F 0.03 42.9 66.0 1.8 4.6 P 0.858 <.001 <.001 0.301 0.022 56 Ejection Time Index The LVET was corrected for effects of HR using the ejection time index as described by Whitsett and Naughton (84) and Martin et a l . (49). This correction eliminates HR as a s i g n i f i c a n t variable influencing the duration of ventricular ejection. I t i s a r e l a t i v e index for which an increase would mean that without the associated effects of HR on LVET the time which the ve n t r i c l e spends i n ejection of blood i s greater. However the actual time spent i n ejection may be s i g n i f i c a n t l y decreased as a result of tachycardia. Figure 12 shows how ETI increases l i n e a r l y from rest to 100% MVC i n both environments. However i n view of the s i g n i f i c a n t interaction (Table 12) conclusions about the increase i n ETI from rest to 100% MVC within each environment could only be made after a post-hoc analysis. The results of the Newman-Keuls multiple comparison for ETI i s presented i n Table 13. TABLE 13 NEWMAN-KEULS ANALYSIS ETI Rest vs. 100% MVC Rest vs. 50% MVC 50% MVC vs . 100% MVC Neutral Heat Neutral Heat Neutral Heat Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 cal Q 10.79 7.64 7.14 3.65 3.65 3.99 Result p<.05 p<.05 p<.05 p<.05 p<.05 p<.05 57 350 i i —i Rest 50% MVC 100% MVC Workload Figure 12. Ejection Time Index 58 The foregoing results conclusively demonstrate that ETI increases s i g n i f i c a n t l y from rest to 100% MVC i n both a neutral and heated environ- ment. This implies that disregarding the effects of tachycardia on the actual ventricular ejection time, an isometric contraction of the forearm causes a r e l a t i v e increase i n the amount of time spent i n l e f t ventricular ejection. There was no s i g n i f i c a n t difference i n the ETI between the two environments as shown by a non-significant environmental (E) e f f e c t . A post-hoc analysis was done to investigate i f there was a s i g n i f i c a n t l y greater ETI at rest i n the heated environment as opposed to a control environment. The results for the Newman-Keuls analysis demonstrated a calculated Q of 1.13 which was below the c r i t i c a l Q value of 3.11 needed for significance at the .05 l e v e l . The s i g n i f i c a n t interaction effect (Table 12) for ETI indicates that without the physiological association of HR, the rate of change i n LVET from conditions of rest to isometric stress i s different for each of the two environments. The interactive nature i n the slopes of the two l i n e s for ETI (Figure 12) i s probably due to the difference i n ETI at rest. This difference, although 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 , was enough to produce a s i g n i f i c a n t EC effect. 59 Diastole and CT Both diastole and CT decreased l i n e a r l y from rest to 100% MVC as i l l u s t r a t e d i n Figure 13 and Figure 14. However i n view of a s i g n i f i c a n t EC (Tables 14 and 15) for both variables a post-hoc analysis was carried out to show s p e c i f i c a l l y where the s i g n i f i c a n t changes occurred. The results of the Newman-Keuls comparison for both diastole and CT are presented i n Table 16. , TABLE 16 NEWMAN-KEULS ANALYSIS Diastole and CT (Workload Effect) Rest vs 100% MVC Rest vs. 50% MVC 50% MVC vs. 100% MVC Neutral Heat Neutral Heat Neutral Heat Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 Diastole c al Q 16.42 i 9.44 5.43 4.69 12.05 4.76 Result p<.05 p< .05 p< .05 p< .05 p< .05 p< .05 Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 CT c a l Q 16.46 10.22 5.86 5.08 10.60 5.17 Result p<.05 p<.05 p< .05 p<.05 p<.05 p<.05 The above results confirm that both diastole and CT decrease s i g n i f i c a n t l y from rest to 100% MVC i n both environmental conditions. 60 Workload Figure 13. Diastole 1000 Neutral — Heated — 500 i j- Rest 50% MVC 100% MVC Workload Figure 14. Cycle Time 62 TABLE 14 SUMMARY OF ANOVA Diastole Source E * Error C * Error C (1) * C (2) EC * Error df 1 11 2 22 1 1 2 22 Mean Square 141778.0 7537.3 273456.3 3235.8 538479.1 8433.4 23499.0 2275.9 F 18.8 84.5 153.1 2.9 10.3 P 0.001 <.001 <.001 0.119 0.001 TABLE 15 SUMMARY OF ANOVA Cycle Time Source df Mean Square F P E * 1 227812.8 22.7 0.001 Error 11 10036.8 C * 2 354486.3 90.4 <.001 Error 22 3919.6 C (1) * 1 701316.4 156.3 <.001 C (2) 1 7656.3 2.3 0.159 EC * 2 22568.6 7.6 0.003 Error 22 2972.0 63 Diastole and CT were also s i g n i f i c a n t l y less i n the heated environ- ment than i n the control environment as shown by a s i g n i f i c a n t E effect i n Table 14 and Table 15. A Newman-Keuls analysis was again conducted to discover at what workloads the environmental difference for both diastole and CT was most s i g n i f i c a n t . The results are presented i n Table 17. TABLE 17 NEWMAN-KEULS ANALYSIS Diastole and CT (Environmental Effect) H vs. N Rest H vs. N 50% MVC . H vs N 100% MVC Q. 95 3.11 3.11 3.11 Diastole . cal Q 6.41 2.35 2.02 Result p<.05 N.S. N.S. Q. 95 3.11 3.11 3.11 CT cal Q 6.32 2.92 2.42 Result p<.05 N.S. N.S. In contrast to the o v e r a l l s i g n i f i c a n t difference demonstrated by the ANOVA data between environments, the post-hoc analysis shows that only at rest was there a difference i n diastole and CT between the heated and control environment. 64 The corre l a t i v e data express extremely strong association between CT, diastole and HR (Table 8). In fact HR has a stronger correlation with CT and diastole than i t does with LVET. In addition CT i s found to be s i g n i f i c a n t l y correlated to a number of other variables (Table 18). TABLE 18 CORRELATION COEFFICIENTS CT EML LVET TS DIAS TRIP Rest .18 .73 .65 .99 -.78 Neutral 50% MVC .85 .57 .77 .99 -.87 100% MVC .74 .45 .85 .99 -.89 Rest -.13 .84 .75 .99 -.41 Heat 50% MVC .64 .82 .79 .99 -.65 100% MVC .55 .82 .87 .98 -.75 The high correlation between CT and diastole support the findings of Franks et a l . (18) who demonstrated that diastole and CT are measures of a simi l a r dynamic function i n the cardiac cycle. The s i g n i f i c a n t correlations between CT and TRIP and CT and systole (LVET and TS) are probably a direct result of production of tachycardia which reduces CT and affects both systole and myocardial oxygen consumption. Of surprising interest however, i s the s i g n i f i c a n t correlation between EML and CT with 50% MVC and 100% MVC 65 especially i n the neutral environment. An explanation for this finding could be that i n stress conditions when the inotropic state of the myocardium i s increasing causing alterations i n myocardial c o n t r a c t i l i t y and rate of contraction, the e l e c t r i c a l a c t i v i t y of the heart i s altered to maintain a l e v e l of e x c i t a b i l i t y needed to cope with the change i n cardiac dynamics. Sympathoadrenergic A c t i v i t y The three variables which most closely represent the contractile state of the myocardium which i n turn i s dependent upon the sympathetic and adrenergic sources of stimulation to the heart tissue are ICP, PEP, and PEP/LVET. Table 19 and Table 20 demonstrate a s i g n i f i c a n t workload (C) effect s i g n i f y i n g that there was an ov e r a l l change i n both ICP and PEP from rest to 100% MVC. ICP increases or remains constant from rest to 50% MVC but decreases i n both environments from 50% MVC to 100% MVC (Figure 14). PEP increases s l i g h t l y from rest to 50% MVC i n the control environment but decreases between the same workloads i n the heat and between 50% MVC and 100% MVC i n both environments. Since there was no s i g n i f i c a n t i n t e r - action effect for either ICP or PEP further post-hoc analysis was not needed. Therefore i t i s concluded that both ICP and PEP change i n a simi l a r fashion during isometric work i n control conditions and i n a heated environ- ment . There was no s i g n i f i c a n t difference throughout the workloads between the two environments for both ICP and PEP. The absence of any EC effect demonstrated that the changes i n these two variables produced by a 66 Neutral • Heated 35 r 30 r Rest 50% MVC 100% MVC Workload Figure 15. Isovolumetric Contraction Period 67 Neutral Heated 100 1— Rest 50% MVC 1 - 100% MVC Workload Figure 16. Pre-ejection Period 68 Neutral Heated .6 - • 55 h .45 f .4 H • i Rest 50% MVC 100% MVC Workload Figure 17. Pre-ejection Period: Left Ventricular Ejection Time (Ratio) 69 TABLE 19 SUMMARY OF ANOVA Isovolumetric Contraction Period Source E Error C * Error C (1) C (2) * EC Error df 1 11 2 22 1 1 2 22 Mean Square 284.0 234.1 405.5 66.1 363.0 448.0 96.3 94.9 F 1.2 6.1 3.7 13.4 1.0 P 0.294 0.008 0.081 0.004 0.379 TABLE 20 SUMMARY OF ANOVA Pre-Ejection Period Source E Error df 1 11 Mean Square 578.0 208.7 F 2.8 P 0.124 C * Error C (1) * C (2) EC Error 2 22 1 1 2 22 1005.7 107.4 1813.0 198.3 67.0 60.4 9.4 11.7 3.3 1.1 0.001 0.006 0.095 0.347 70 TABLE 21 SUMMARY OF ANOVA PEP/LVET Source E Error C Error C (1) C (2) EC Error df 1 11 2 22 1 1 2 22 Mean Square 0.00637 0.00769 0.00239 0.00280 0.00272 0.00206 0.00102 0.00141 F 0.83 0.85 0.62 1.66 0.72 P 0.382 0.439 0.447 0.223 0.497 71 simultaneous subjection to heat and muscular stress was additive i n nature. However a v i s u a l note of the alterations i n ICP from rest to 50% MVC i n the control environments lends one to think that a s i g n i f i c a n t environmental effect may i n fact be present here. To investigate this point a post-hoc analysis was conducted for ICP between the two environmental conditions at 50% MVC. The results of the Newman-Keuls comparison indicated a non- si g n i f i c a n t calculated Q as presented i n Table 22. TABLE 22 NEWMAN-KEULS ANALYSIS ICP (Heat vs. Neutral) Q.95 ca l Q •Result 50% MVC 3.11 1.95 N.S. The above findings c l e a r l y support the ANOVA which showed a non- s i g n i f i c a n t environmental e f f e c t . The t h i r d variable i n this group, PEP/LVET, demonstrated a non- s i g n i f i c a n t workload (C) and environment (E) effect (Table 21). Such results have been reported e a r l i e r for this variable (42, 75). Non- s i g n i f i c a n t changes i n this r a t i o during isometric stress suggests that the myocardium was i n a state of increased c o n t r a c t i l i t y i n response to a greater pressure load. 72 TABLE 23 SUMMARY OF ANOVA Electromechanical Lag Source E Error df 1 11 Mean Square 56.9 78.0 F 0.73 P 0.411 C * Error C (1) * C (2) EC Error 2 22 1 1 2 22 290.0 64.9 533.3 46.7 3.76 57.18 4.47 9.9 0.6 0.07 0.024 0.009 0.449 0.936 Electromechanical Lag EML decreases l i n e a r l y from rest to 100% MVC when averaged over environments (Figure 18). This i s supported by a s i g n i f i c a n t workload (C) effect i n the analysis of variance (Table 23). The absence of an interaction for this variable further complements the o v e r a l l decrease i n EML. However i n order to specify exactly where the s i g n i f i c a n t changes i n EML had occurred subsequent analysis was conducted by the Newman-Keuls method. The results are presented i n Table 24. In contrast to the results of the ANOVA the post-hoc data indicate that EML did not s i g n i f i c a n t l y decrease from rest to 50% MVC, 50% MVC to 100% MVC, or from rest to 100% MVC i n either of the environmental conditions. 73 Neutral ' Heated 90 h i I i Rest 50% MVC 100% MVC Workload Figure 18. Electromechanical Lag 74 TABLE 24 NEWMAN-KEULS ANALYSIS EML Rest vs. 100% MVC Rest vs. 50% MVC 50% MVC vs. 100% MVC Neutral Heat Neutral Heat Neutral Heat Q. 95 3.55 3.55 2.94 • ' 2.94 2.94 2.94 c a l Q 2.71 3.27 0.43 1.98 2.28 1.29 Result N.S. N.S. N.S. N.S. N.S. N.S. The reason for t h i s discrepancy i s that the Newman-Keuls method i s a much more conservative test than the ANOVA. I t can therefore be concluded that EML has a tendency to decrease from rest to 100% MVC but that upon further analysis by a more rigorous post-hoc method no s i g n i f i c a n t change i n EML can be found i n either environment. A f i n a l note i s that EML was not s i g n i f i c a n t l y altered from a neutral to a heated environment throughout the workloads. This i s supported by a non-significant E effect (Table 23). EML was s i g n i f i c a n t l y correlated with a number of other variables. This data i s presented i n Table 25. 75 TABLE 25 CORRELATION COEFFICIENTS EML Neutral Heat Rest 50% MVC 100% MVC Rest 50% MVC 100% MVC Diastole .17 .86 .71 -.14 .61 .52 CT .18 .85 .74 -.13 .64 .55 HR -.13 -.82 -.76 .13 -.62 -.52 TABLE 26 SUMMARY OF ANOVA Triple Product Source E Error C * Error C (1) * C (2) * EC * Error df 1 11 2 22 1 1 2 22 Mean Square 257762.0 95456.6 8820472.0 113627.0 17057584.0 583375.4 303208.3 41906.1 F 2.7 77.6 104.4 9.1 7.2 P 0.129 <.001 <.001 0.012 0.004 76 TRIP Analysis of variance results showed an ov e r a l l increase i n TRIP from rest to 100% MVC (Table 26). I t was thought b e n e f i c i a l to the study to inspect the s p e c i f i c changes i n this variable between workloads for each environmental condition. The results of the post-hoc analysis are presented i n Table 27. TABLE 27 NEWMAN-KEULS ANALYSIS TRIP (Workload Effect) Rest vs. 100% MVC Rest vs. 50% MVC ' 50% MVC vs. 100% MVC Neutral Heat Neutral Heat Neutral Heat Q. 95 3.55 3.55 2.94 2.94 2.94 2.94 cal Q 14.19 10.31 10.15 6.02 4.03 4.29 Result p<.05 p<.05 p<.05 p<.05 p<.05 p<.05 The above results confirm those of the ANOVA. TRIP s i g n i f i c a n t l y increases from rest to 100% MVC i n both environmental conditions. There was no s i g n i f i c a n t E effect for TRIP si g n i f y i n g that the changes induced by heat during each workload were 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 when compared to the control environment. However, i n view of the si g n i f i c a n t EC displayed i n Table 26 a post-hoc analysis was again con- ducted to test for s i g n i f i c a n t environmentally induced alterations i n TRIP at each workload. The Newman-Keuls method was again administered, the results of which are presented i n Table 28. 3400 1800 Rest 50% MVC 1 100% MVC Workload Figure 19. Triple Product 78 TABLE 28 NEWMAN-KEULS ANALYSIS TRIP (Heat vs. Neutral) Rest 50% MVC 100% MVC Q.95 3.11 3.11 3.11 cal Q 1.57 2.94 2.66 Result N.S. N.S. N.S. The above data confirm that indeed there i s no s i g n i f i c a n t change i n TRIP for any of the workload conditions between the two environments. Therefore i t seems that the heat stress did not s i g n i f i c a n t l y increase the myocardial oxygen requirements. I I . DISCUSSION Analysis of the results stimulates a variety of conclusions about the cardiovascular dynamics associated with heat stress and s t a t i c exertion. Some of the findings are novel and have created incentive for further research while others seem to support results of e a r l i e r investigations. Blood Pressure As has been demonstrated by many e a r l i e r investigations (26, 33, 37, 45) both BPd and BPs s i g n i f i c a n t l y increase during submaximal and maximal bouts of s t a t i c muscular contraction. This response i s not only present i n a control environment but also when the skin temperature i s elevated to 79 40°C - 41°C. However the presence of a s i g n i f i c a n t interaction effect for BPs and BPd (p < .05) suggests that body heating causes the changes i n blood pressure during each workload condition to be different from those pressures e l i c i t e d i n a control environment. Analysis of variance shows that there i s an o v e r a l l s i g n i f i c a n t decrease i n both BPs and BPd throughout the workloads from a control to a heated environment. Further post-hoc testing demonstrated that BPs and BPd i n a resting state did not s i g n i f i c a n t l y d i f f e r from a control to a heated condition which i s i n support of Hypothesis 4 and e a r l i e r research by Rowell (69) . Of novel interest was the finding that BPs and BPd were s i g n i f i c a n t l y reduced during submaximal and maximal isometric work i n the heat. This result does not support Hypothesis 4 but does encourage discussion about the dominant physiological adjustment during simultaneous subjection of the human body to isometric muscular contraction and thermal } stress. I t seems that although the pressor response to submaximal and maximal s t a t i c exertion i s functional during body heating, i t s dominance as seen during isometric work i n a neutral environment, i s not as powerful when thermoregulatory processes are simultaneously being activated. Such a difference i s undoubtedly due to the vasodilation produced at the skin surface i n response to increasing body temperature. This result i s supported by the findings of Heistad et a l . (24) who used seventeen healthy men and women, 18-25 years of age, to investigate a possible central interaction of thermal and baroreceptors. They found that modification of the baroreceptor r e f l e x by thermal s t i m u l i may occur at a central l e v e l . S p e c i f i c a l l y interaction may occur between efferent 80 messages from the central component of the baroreceptor r e f l e x , the medulla, and the central component of the thermal r e f l e x , namely the hypothalamus. Johnson et a l . (29) used similar methods to determine whether skin w i l l respond to increased neurogenic vasoconstrictor a c t i v i t y during heating. The results' showed that during heating, skin retains the a b i l i t y to vasoconstrict but that this vasoconstriction cannot override heat-induced vasodilation. Heart Rate As expected HR increased l i n e a r l y with submaximal and maximal s t a t i c exertion i n both environmental settings. I t i s a well documented fact that HR r i s e s with isometric exercise (36, 37, 38) and during whole body heating (6, 9). HR was s i g n i f i c a n t l y greater for a l l workloads during body heating. The rate of increase i n HR from rest to 100% MVC was very similar for both environments, as supported by a non-significant EC e f f e c t . This suggests that the tachycardia induced by thermoregulatory processes i s maintained throughout a l l workloads and that the r i s e i n HR induced by isometric work i s additive to the r i s e i n HR due to thermoregulatory adjustments. Ventricular Systole The changes observed i n LVET, TS and MS were very similar to findings reported by other workers (42, 65, 82). A l l three variables decreased s i g n i f i c a n t l y (p < .001) from rest to 100% MVC i n both environmental conditions. These results support Hypothesis 7. 81 LVET, TS and MS were also s i g n i f i c a n t l y less (p < .001) i n the heat than i n the control environment for a l l workloads. This decrease was additive to that induced by isometric exertion which implies that physio- l o g i c a l adjustment to thermal and s t a t i c stress stimulates alterations i n a common factor which d i r e c t l y affects systole. That factor i s probably HR since changes i n LVET and to a lesser extent MS and TS are strongly associated to changes i n the rate of myocardial contraction (81, 82). The o v e r a l l correlation c o e f f i c i e n t (average of the s i x testing conditions) between HR and LVET i n this study was .71 which supports the strong relationship between these two variables. I t seems therefore that changes i n systole are dependent upon the rate of myocardial contraction. Increase i n HR can be e l i c i t e d by both thermoregulation and isometric muscular contraction. During such conditions decreases i n systole are paralleled by simultaneous increases i n HR. Ejection Time Index LVET was "corrected" for HR to allow for the assessment of other factors which may possibly a l t e r the ejection period. I f no factors other than HR had affected LVET, a l l curves for ETI would be e s s e n t i a l l y f l a t , which was not the case i n t h i s study. ETI increased s i g n i f i c a n t l y (p < .001) from rest to 100% MVC i n both environments. Quarry and Spodick (65) reported s i m i l a r results during 30% MVC and 50% MVC i n s i t t i n g p osition. Martin et al.(48) also found the ETI to increase s i g n i f i c a n t l y during a 30% MVC for three minutes. These authors suggest that the augmented ETI during IHG may be i n d i r e c t l y caused by increases i n afterload or d i r e c t l y due to increases i n stroke volume (SV). 82 The effects of independent increases i n systemic pressure and stroke volume on ejection time have been studied but results have not been consistent. Wallace et al.(80), using a right heart bypass preparation i n dogs, found that elevating BPm to 140-160 mm Hg. shortened ejection time. However, augmenting SV separately prolonged LVET. Braunwald et aL. (5) s i m i l a r l y found that an increase i n SV alone would prolong the ejection period but i n contrast to Wallace's findings, augmenting BPm. to 150 mm Hg. did not s i g n i f i c a n t l y a l t e r ejection time. These results suggest that without the influence of HR ejection time may be prolonged by increases i n SV. However, an increase i n SV i s associated with a possible increase i n LVEDP (preLoad) and since i t has been reported that i n normals an IHG contraction produces l i t t l e change i n preload (14, 25, 75) and SV (13, 37) i t i s unlikely that the augmented ETI displayed i n this study i s d i r e c t l y due to an increase i n stroke volume. The effect which an augmented afterload may have on the ETI i s not clear. I t i s suggested by this investigator that an increase i n the contr a c t i l e state of the myocardium induced by an increased afterload, as experienced during s t a t i c exertion, may be reflected i n an increased ETI. Changes i n PEP, ICP and PEP/LVET during submaximal and maximal isometric work suggest that the c o n t r a c t i l e state of the myocardium was augmented i n both environmental conditions. S i m i l a r l y , increases i n ETI from rest to 100% MVC were not s t a t i s t i c a l l y different between the control and heated environment. Therefore both the ETI and the contractile state of the myo- cardium were not affected by the heat. A major contributor to the increase i n the ETI during the IHG contractions may have been the greater sympathetic and adrenergic stimulation of the heart. 83 Although i t i s unlikely that alterations i n SV were associated with the increases found for the ETI the results of this investigation cannot confirm t h i s . I t i s also possible that the ETI i s determined by changes i n other physiological variables which were not detected i n t h i s study. 84 Diastole The data representing diastole related functions of the cardiac cycle have been presented here for the purpose of supporting and comparing changes i n other variables. As expected both diastole and CT were s i g n i f i c a n t l y reduced with IHG i n both environments. These changes closely paralleled those for HR. The correlative data express extremely high association between CT, diastole and HR. In fact HR has higher correlations for diastole and CT than i t does for LVET. The only puzzling difference between changes i n diastole and CT with those of HR i s that HR displays a non-significant EC effect while diastole and CT do not. That i s to say that while the effects of heat stress and s t a t i c exertion seem to be additive with changes i n HR they are interactive with changes i n diastole and CT. This d i s - crepancy i s further supported by the post-hoc analysis which shows that both diastole and CT are not s i g n i f i c a n t l y different between the environ- ments at 50% MVC and 100% MVC. Such was not the case for HR. The cause of this inconsistency can be explained by the relationship between CT and HR. The transformation from cardiac periods into heart rates i s recognized as being non-linear", that i s , a constant increase i n the R-R i n t e r v a l , at d i f f e r e n t cycle lengths, does not result i n a constant l i n e a r decrease i n HR. This characteristic has been explored by Khachaturian e t a l . (34) i n newborn infants and. Jennings et a l . (27) i n healthy adults. Their results suggest that transformation of CT into HR introduces errors, which are reflected i n the mean, variance and degree of skewness of the basic data. 85 Sympathoadrenergic A c t i v i t y r The three variables which most closely represent the contra c t i l e state of the myocardium, which i n turn i s dependent upon sympathetic and adrenergic sources of stimulation to the heart tissue are ICP, PEP and PEP/LVET. The o v e r a l l tendency for both ICP and PEP was to decrease from rest to 100% MVC. However, i n one condition, 50% MVC i n a control environment, ICP showed a non-significant increase from rest. This abrupt change was incorporated into the PEP such that the PEP showed a plateau effect from rest to 50% MVC. Quarry and Spodick (65) found that ICP and PEP decreased during the f i r s t t h i r t y seconds of a 50% MVC contraction but then returned to s l i g h t l y below control levels at one minute. I t i s conceivable that since the data c o l l e c t i o n for th i s investigation took place during the f i n a l stage of the IHG, i n i t i a l decreases i n ICP and PEP were not detected. The results of ANOVA and Newman-Keuls for environmental effect demonstrate that there was no change i n ICP and PEP between the control and heated conditions. This lack of change was also present for ICP at 50% MVC. I t i s suggested that the contractile state of the myocardium i s not s i g n i f i c a n t l y altered by thermoregulatory processes at rest and during s t a t i c work of the forearm. The ov e r a l l tendency for ICP and PEP to decrease, especially from 50% MVC to 100% MVC, suggests that the c o n t r a c t i l i t y of the heart increased. A decrease or l i t t l e change i n ICP and PEP during IHG has been previously recorded (42, 49, 65). Martin et a l . (48, 49), Metzger et a l . (54) and Talley et al.(78) a l l found a s i g n i f i c a n t inverse r e l a t i o n between PEP or ICP 86 to the rate of tension developed i n the l e f t v e n t r i c l e (dp/dt). I t i s suggested that during a state of increased afterload (BPd) an i n s i g n i f i c a n t change or decrease i n ICP or PEP s i g n i f i e s increased myocardial contract- i l i t y . When the l e f t v e n t r i c l e i s confronted with a greater system pressure load, the myocardial tissue must isometrically contract with increased power i n order to substantially augment the i n t e r n a l pressure of the v e n t r i c l e before the ao r t i c valve w i l l open. The r i s e i n dp/dt against a large afterload can only be achieved i f the contractile state of the myocardium i s increased. No change or a decrease i n PEP/LVET has been associated with augmented myocardial c o n t r a c t i l i t y (19, 21). In this study i t was found that PEP/LVET does not s i g n i f i c a n t l y change during IHG. There was also no change i n PEP/LVET between the two environments. The above results suggest that the contr a c t i l e state of the myocardium was augmented during bouts of isometric contraction of the forearm which i s i n support of Hypothesis 11. However the contractile state of the heart was not s i g n i f i c a n t l y affected by heat i n any of the workload conditions. Electromechanical Lag EML i s indicat i v e of the amount of time which the l e f t v e n t r i c l e spends i n e l e c t r i c a l preparation to commence the isometric phase of systole. The i n i t i a l ANOVA results indicate a linea r decrease i n EML from rest to 100% MVC which support the findings of Quarry and Spodick (65). Subsequent post-hoc analysis revealed that EML did not s i g n i f i c a n t l y change during IHG exercise i n either of the environmental conditions. The reason for this 87 inconsistency i s due to difference i n the s t a t i s t i c a l methods used for analysis. I t i s suggested that EML has a tendency to become reduced with s t a t i c exertion but that upon further analysis by a rigorous post- hoc method, no s i g n i f i c a n t change i n EML can be found between each of the s i x experimental conditions. The absence of a s i g n i f i c a n t environmental effect shows that the increased tachycardia induced by thermoregulation did not affect the e l e c t r i c a l functions i n the l e f t v e n t r i c l e . However Table 25 indicates that EML was s i g n i f i c a n t l y (p < .05) correlated to HR i n an inverse fashion and to CT d i r e c t l y . This implies that alterations i n EML were related to changes i n the rate of myocardial contraction. I t may be that the tachycardia induced by IHG was substantial enough to promote thi s relationship between rate of contraction and CT and that a further increase i n HR due to heat stress did not add further weight to the relationship. 88 Myocardial Oxygen Consumption Myocardial oxygen consumption as reflected by the index TRIP increased with submaximal and maximal IHG contractions i n both environmental conditions. This increase i n myocardial oxygen consumption supports Hypothesis 1 and i s i n agreement with e a r l i e r findings (35, 49, 59). Both the ANOVA and post-hoc analysis confirm that myocardial oxygen consumption as depicted by TRIP did not s i g n i f i c a n t l y change throughout a l l workloads from a control to a heated environment. Therefore i t seems that heat stress did not affect the myocardial oxygen consumption i n addition to those changes e l i c i t e d by a pressure load during IHG. In fact during submaximal and maximal isometric work TRIP was i n s i g n i f i c a n t l y less i n the heated condition. This suggests that an afterload determines the extent of myocardial oxygen consumption to a greater degree than does HR during a simultaneous subjection of thermal and isometric stress. The Interaction (EC) Effect One of the major concerns i n this study was to investigate how the physiological adjustments to isometric work and thermoregulatory processes would interact to produce the f i n a l alterations i n BP, TRIP, HR and the STI. It was hypothesized that a l l variables would react to these two quite d i s s i m i l a r adjustments i n an interactive rather than additive manner. However, the results showed that the variables were not affected i n a simil a r fashion. Some displayed a s i g n i f i c a n t interaction while others did not which i s not i n support of Hypothesis 6. 89 The fourteen variables can be grouped as follows: Interactive Non-Interactive BPs; BPd ETI CT; diastole TRIP HR LVET; MS; TS PEP; ICP; PEP/LVET EML These results simply suggest that i n the case of a s i g n i f i c a n t interaction effect the complete change i n a variable e l i c i t e d by isometric stress was p a r t i a l l y masked by further change i n that variable e l i c i t e d by thermoregulation. With a non-interactive effect of course the opposite i s true. That i s , the changes e l i c i t e d i n any variable by isometric and heat stress were additive and represented i n the t o t a l r e s u l t . Increases i n BPs and BPd during isometric work support Hypothesis 5. The pressor response from rest to 100% MVC was present i n both environ- mental conditions. However the magnitude of the pressor response was less during both submaximal and maximal IHG contraction i n the heat. Hypothesis 4 was p a r t i a l l y supported by a non-significant difference i n BPs and BPd at rest, between the two environmental conditions. During simultaneous subjection of the human body to s t a t i c muscular exertion and heat stress an interaction occurs between the medullary control of blood pressure and the thermoregulatory adjustments directed from the hypothalamus, the f i n a l result being that increase i n blood pressure during IHG contraction i n the heat i s diminished by the thermoregulatory increase i n cutaneous vasodilation. SUMMARY 90 The c o n t r a c t i l i t y of the myocardium was augmented during submaximal and maximal s t a t i c exertion i n support of Hypothesis 11. The increased afterload induced by the IHG contractions i s associated with greater sympathetic stimulation of the heart which causes the myocardial tissue to contract with more power. Such an a l t e r a t i o n i s needed i f the l e f t v e n t r i c l e i s to eject the same amount of blood into the system against an increased a r t e r i a l pressure. However the contractile state of the myocardium was not s i g n i f i c a n t l y affected by the increased volume load produced by tachycardia during thermoregulation i n the heat. This suggests that during a bout of isometric exercise i n a heated environment, where the skin temperature may r i s e to 40°-41°C, the volume load imposed onto the heart by thermoregulatory processes plays a minor role i n augmenting the co n t r a c t i l e state of the myocardium. The major determinant of increased myocardial c o n t r a c t i l i t y seems to be the afterload e l i c i t e d by the pressor response to isometric exercise. Hypothesis 1 i s supported by a s i g n i f i c a n t increase i n TRIP from rest to 100% MVC i n both environmental conditions. Hypotheses 2 and 3 were not supported as TRIP was found not to change s i g n i f i c a n t l y through- out a l l workloads from a control to a heated environment. I t i s well known that HR i s determined primarily by the balance between the in h i b i t o r y effects on the pacemaker of the vagus nerves and the excitatory effects of the release of norepinephrine by the sympathetic nerves. At rest, heat induced tachycardia caused a non-significant increase i n TRIP when compared to the control condition. In contrast TRIP was non-significantly less during isometric work i n the heat when compared to the same workloads 91 i n a control temperature even though heart rates were s i g n i f i c a n t l y greater during s t a t i c work i n the heat. The reason for this reverse change was that BPs was considerably, greater throughout a l l workloads i n the neutral environment. Consequently the increase i n TRIP produced by tachycardia was masked by the lower BPs i n the heat. This suggests that the myocardial oxygen requirements during a bout of s t a t i c exercise i n a heated environment are largely determined by the afterload imposed upon the ventricles rather than the volume load produced by thermo- regulatory processes. Not a l l of the variables were altered during isometric work i n the heat i n an interactive manner as was proposed i n Hypothesis 6. Of the s y s t o l i c time intervals only CT and diastole demonstrated interactive c h a r a c t e r i s t i c s . Of the non s y s t o l i c variables only HR demonstrated additive characteristics. These results suggest that the physiological adjustments to isometric stress and body heating induce opposite changes i n some variables and similar changes i n others. Changes i n systole (LVET; TS; MS), diastole (diastole; CT), ETI and EML were mainly incorporated into this study to supply comparative data. The results show that Hypotheses 7-10 are c l e a r l y supported. Both d i a s t o l i c and s y s t o l i c related intervals s i g n i f i c a n t l y decreased as the HR increased with isometric work and body heating. The EML decreased i n association with a r i s e i n the inotropic state of the myocardium. LVET "corrected" for HR showed a steady increase with submaximal and maximal s t a t i c work. The factor related to the r i s e i n ETI was hypothesized to be either an augmented stroke volume or increased myocardial c o n t r a c t i l i t y . However, the available data could not confirm this theory. CHAPTER V SUMMARY AND CONCLUSIONS The purpose of this study was to investigate the changes i n cardio- vascular dynamics as depicted by s y s t o l i c time i n t e r v a l s , blood pressure, and heart rate during submaximal and maximal isometric work i n a hot environment. A major concern was to determine whether these dynamic changes were additive or interactive i n nature when the cardiovascular system was subjected to an augmented pressure load and volume load simultaneously. A minor concern was to support the findings of previous studies dealing with the alterations i n s y s t o l i c time i n t e r v a l s , HR and BP during sustained exertion of the forearm. Fourteen male volunteers aged 20 to 31 without any previous history of cardiovascular ailments were used as subjects. Simultaneous recordings of the phonocardiogram, electrocardiogram, carotid pulse wave and blood pressure were conducted for each subject i n a seated position during rest and s t a t i c handgrip contractions of 50% MVC and 100% MVC. The subjects were tested i n room temperature and i n a sauna where the skin temperature was raised to 40°C - 41°C. The workloads were randomly rotated for each volunteer and the same ro t a t i o n a l order was used i n both environments. Testing took place on two separate days with one day of rest i n between. Half of the subjects experienced the heated conditions f i r s t and room temperature conditions on the l a s t day of testing. The reverse procedure was used for the remaining subjects. This balanced any day's effect i n the re s u l t s . 92 93 The data from two of the subjects were discarded because of poor quality reproduction of the time i n t e r v a l recordings. This improved the o v e r a l l quality of the data. Of the twelve recordings used only the three clearest cycles closest to the termination of the contraction period were used for s t a t i s t i c a l analysis. The experimental testing consisted of a 2 x 3 f a c t o r i a l design with repeated measures on both variables. The data were treated with a two-way ANOVA for each dependent variable. The s t a t i s t i c a l outputs included means, standard deviations, an ANOVA table for each dependent variable and correlation c o e f f i c i e n t s . In some cases a post-hoc analysis (Newman- Keuls method) was used to determine s p e c i f i c differences between workload or environment effects . The fourteen dependent variables studied were divided into the following groups: a) Systole related variables l e f t ventricular ejection time (LVET) mechanical systole (MS) t o t a l systole (TS) ejection time index (ETI) b) Diastole related variables cycle time (CT) diastole (DIAS) c) Sympathoadrenergic A c t i v i t y ( C o n t r a c t i l i t y ) pre-ejection period (PEP) isovolumetric contraction period (ICP) PEP/LVET (ratio) 94 d) Afterload s y s t o l i c blood pressure (BPs) > d i a s t o l i c blood pressure (BPd) e) Electromechanical Lag (EML) f) Heart Rate (HR) g) Myocardial Oxygen Consumption (Index) t r i p l e product (TRIP) CONCLUSIONS 1. The oxygen consumption of the myocardium as depicted by the t r i p l e product s i g n i f i c a n t l y increased during submaximal and maximal isometric handgrip contraction. This increase was evident at room temperature and during body heating. 2. There was no s i g n i f i c a n t change i n the myocardial oxygen consumption as depicted by TRIP at rest or during isometric forearm contraction between the control and heated environments. This suggests that the heat stress did not s i g n i f i c a n t l y increase the myocardial oxygen requirements. 3. In a state of rest, increasing the skin temperature to between 40°C - 41°C did not s i g n i f i c a n t l y a l t e r either BPs or BPd when compared to a resting state at room temperature. However, BPs and BPd were substantially lower during isometric work i n the heat than during isometric work at room temperature. 95 BPs and BPd s i g n i f i c a n t l y increased during 50% MVC and 100% MVC s t a t i c contractions of the forearm. This increase was demonstrated i n both environmental conditions. A l l variables depicting changes i n l e f t ventricular systole (LVET; MS; TS) and ventricular diastole (diastole and CT) were found to become s i g n i f i c a n t l y reduced with submaximal and maximal s t a t i c contractions of the forearm. These changes were evident i n both environments. A strong inverse correlation was found between HR and LVET, CT and diastole. HR s i g n i f i c a n t l y increased from rest to 100% MVC i n both environmental conditions. Consequently, i t i s suggested that alterations i n LVET, CT and diastole are largely determined by the rate of myocardial contraction. The ejection time index s i g n i f i c a n t l y increased i n both environmental conditions with a 50% MVC and 100% MVC s t a t i c contraction of the forearm. The electromechanical lag showed a general tendency to decrease during an isometric handgrip contraction. 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"Measurement of stroke volume from pulmonary artery pressure record i n man," B r i t i s h Heart Journal, 37: 20-25, 1975. / ) APPENDICES 106 APPENDIX A 107 Raw Scores - Subjects Tested i n Neutral Environment F i r s t Subjects Condition BPs • BPd CT "1 EML ET MS Variables TS DIA PEP ICP PEP/LVET HR TRIP ETI Si N R 1 1 5 . 70 . 840 . 8 3 . 2 5 3 . 2 9 7 . 380 . 4 6 3 . 1 2 7 . 4 3 . 0 . 5 0 1 7 1 . 2 0 8 1 . 0 3 7 4 . 8 N 5 0 1 5 5 . 1 0 5 . 720. 70 . 2 7 0 . 320 . 4 0 0 . 3 7 3 . 1 3 0 . 6 0 . 0 . 4 8 1 8 3 . 3 4 8 7 . 5 4 1 1 . 7 NlOO 1 5 5 . 9 5 . 650 . 70 . 2 5 0 . 2 8 0 . 350 . 3 0 0 . 1 0 0 . 3 0 . 0 . 4 0 0 9 2 . 3 5 7 6 . 9 4 0 6 . 9 H R 110 . 6 0 . 710 . 9 0 . 2 1 3 . 2 5 3 . 343 . 3 5 7 . 1 3 0 . 4 0 . 0 . 6 1 1 8 5 . 1 9 8 3 . 1 3 5 7 . 0 H 5 0 140 . 1 0 0 . 730 . 8 3 . 2 2 3 . 2 7 3 . 347 . 3 7 0 . 1 2 3 . 4 0 . 0 . 5 5 3 8 2 . 2 5 6 9 . 9 3 6 3 . 1 Hi 0 0 1 4 5 . 1 1 0 . 600 . 73 . 2 1 0 . 2 5 3 . 330 . 2 6 3 . 1 2 0 . 4 7 . 0 . 5 7 1 1 0 0 . 3 0 4 5 . 0 3 8 0 . 0 s 2 N R 1 1 0 . 80 . 1 0 1 3 . 7 0 . 2 4 0 . 310 . 380 . 6 2 0 . 1 4 0 . 7 0 . 0 . 5 8 3 5 9 . 1 5 6 3 . 2 3 4 0 . 7 N 5 0 1 4 5 . 1 1 5 . 813 . 8 7 . 2 3 0 . 2 9 3 . 380 . 4 3 3 . 1 5 0 . 6 3 . 0 . 6 5 4 74 . 2 4 6 0 . 2 3 5 5 . 4 NlOO 160 . 1 3 0 . 6 0 7 . 70 . 2 1 3 . 2 7 0 . 340 . 2 6 7 . 12 7 . 5 7 . 0 . 5 9 5 9 9 . 3 3 7 5 . 8 3 8 1 . 5 H R 110 . 6 5 . 8 0 3 . 70 . 2 3 7 . 2 8 7 . 360 . 4 5 0 . 1 2 3 . 5 3 . 0 . 5 2 2 7 5 . 1 9 4 4 . 4 363 .6 H 5 0 1 4 0 . 9 7 . 660 . 7 3 . 2 1 7 . 2 7 3 . 350 . 3 2 3 . 1 3 3 . 6 0 . 0 . 6 1 6 9 1 . 2 7 5 7 . 6 371 .2 HlOO 1 5 5 . 1 1 0 . 550 . 6 7 . 210 . 2 5 7 . 327 . 2 2 7 . 1 1 7 . 5 0 . 0 . 5 5 6 1 0 9 . 3 5 5 0 . 9 395 .5 S 3 N R N 5 0 1 1 5 . 8 0 . 817 . 1 0 0 . 2 3 7 . 2 9 7 . 4 0 0 . 4 2 0 . 1 6 3 . 6 3 . 0 . 6 9 1 7 3 . 1 9 9 9 . 6 3 6 1 . 6 1 5 0 . 1 1 0 . 627 . 7 7 . 2 3 7 . 2 8 3 . 360 . 2 6 7 . 1 2 3 . • 4 7 . 0 . 5 2 2 9 6 . 3 3 9 8 . 9 399 .4 NlOO 1 5 5 . 1 2 7 . 5 9 0 . 77 . 2 4 3 . 2 7 7 . 353 . 2 3 7 . 1 1 0 . 3 3 . 0 .452 1 0 2 . 3 8 3 5 . 6 416 .2 H R 1 2 0 . 80 . 800 . 9 7 . 2 4 0 . 2 7 0 . 370 . 4 3 3 . 1 3 0 . 3 3 . 0 . 542 7 5 . 2 1 6 0 . 0 367 .5 H 5 0 1 4 5 . 8 5 . 6 3 7 . 8 3 . 2 4 0 . 2 6 7 . 350 . 3 0 7 . 1 1 0 . 2 7 . 0 . 4 5 8 9 4 . 3 2 7 9 . 6 4 0 0 . 2 Hi 0 0 1 4 5 . 9 0 . 5 1 7 . 8 0 . 2 1 7 . 2 2 7 . 307 . 2 1 3 . 9 0 . 1 0 . 0 . 4 1 8 1 1 6 . 3 6 4 8 . 4 4 1 4 . 1 Si* N R N 5 0 1 3 5 . 7 5 . 910 . 8 7 . 2 6 0 . 2 7 0 . 350 . 5 4 7 . 9 0 . 3 . 0 . 3 4 6 6 6 . 2 3 1 4 . 3 3 7 2 . 1 1 5 0 . 1 1 0 . 6 4 7 . 70 . 240 . 2 8 3 . 350 . 3 1 0 . 1 1 0 . 4 0 . 0 . 4 5 8 9 3 . 3 3 4 0 . 2 397 .7 NlOO 1 5 0 . 1 1 5 . 5 8 3 . 70 . 2 4 0 . 2 7 0 . 340 . 2 3 7 . 1 0 0 . 3 0 . 0 . 4 1 7 1 0 3 . 3 7 0 2 . 9 4 1 4 . 9 H R H 5 0 1 2 5 . 7 5 . 8 8 3 . 6 3 . 2 5 3 . 310 . 3 7 3 . 5 1 0 . 1 2 0 . 5 7 . 0 . 474 6 8 . 2 1 5 0 . 9 3 6 8 . 8 140 . 1 1 0 . 773 . 9 0 . 2 4 7 . 2 7 7 . 367 . 4 0 7 . 1 2 0 . 3 0 . 0 . 4 8 7 7 8 . 2 6 7 9 . 3 3 7 8 . 6 Hi 00 150 . 110 . 5 6 0 . 5 7 . 2 1 7 . 2 5 7 . 317 . 2 4 7 . 1 0 0 . 4 3 . 0 . 4 6 2 1 0 7 . 3 4 8 2 . 1 3 9 8 . 8 S 5 N R N 5 0 100 . 7 5 . 1 1 6 7 . 9 7 . 2 7 0 . 3 0 3 . 4 0 0 . 7 6 3 . 1 3 0 . 3 3 . 0 . 482 5 1 . 1 3 8 8 . 6 3 5 7 . 4 1 2 5 . 1 0 5 . 1 0 6 7 . 1 0 0 . 2 7 7 . 3 1 3 . 4 1 3 . 6 5 0 . 1 3 7 . 3 7 . 0 . 4 9 5 5 6 . 1 9 4 5 . 3 3 7 2 . 3 NlOO 1 3 5 . 1 0 5 . 783 . 9 8 . 2 3 7 . 2 8 5 . 3 8 2 . 3 9 7 . 1 4 7 . 5 0 . 0 . 6 2 0 7 7 . 2 4 4 7 . 2 366 .9 H R 9 2 . 70 . 970 . 8 3 . 2 7 0 . 3 0 4 . 387 . 5 8 3 . 1 1 7 . 3 4 . 0 . 4 3 2 6 2 . 1 5 3 6 . 5 3 7 5 . 2 H 5 0 < 1 0 0 . 80 . 837 . 7 7 . 2 5 3 . 2 9 3 . 370 . 4 7 0 . 1 1 7 . 4 0 . 0 . 4 6 1 72 . 1 8 1 6 . 7 3 7 5 . 2 Hi 0 0 1 1 5 . 9 0 . 753 . 8 0 . 2 4 3 . 2 7 0 . 3 5 3 . 3 9 7 . 1 1 0 . 3 0 . 0 . 4 5 3 8 0 . 2 2 2 8 . 8 3 7 8 . 7 S 6 N R 1 0 5 . 8 0 . 9 0 3 . 6 7 . 2 6 3 . 320 . 3 8 7 . 5 1 7 . 1 2 3 . 5 7 . 0 . 4 6 9 6 6 . 1 8 3 6 . 5 3 7 6 . 2 N 5 0 130 . 9 7 . 663 . 5 7 . 2 4 0 . 3 0 3 . 360 . 3 9 7 . 1 2 0 . 6 3 . 0 . 5 0 0 9 0 . 2 8 2 2 . 1 3 9 3 . 8 NlOO 1 5 0 . 1 0 6 . 5 4 3 . 6 0 . 2 5 0 . 2 9 0 . 350 . 2 1 3 . 1 0 0 . 4 0 . 0 . 4 0 0 1 1 0 . 4 1 4 1 . 1 4 3 7 . 7 H R 9 0 . 6 5 . 667 . 6 0 . 2 3 7 . 2 8 3 . 347 . 3 1 0 . 1 1 0 . 5 0 . 0 . 4 6 5 9 0 . 1 9 1 7 . 0 3 8 9 . 7 H 5 0 120 . 6 0 . 6 5 7 . 5 7 . 2 3 3 . 2 8 0 . 330 . 3 2 3 . 9 7 . 4 0 . 0 . 4 1 5 9 1 . 2 5 5 8 . 4 3 8 8 . 7 HlOO 1 2 5 . 7 5 . 5 5 3 . 6 0 . 2 3 0 . 2 7 0 . 327 . 2 2 0 . 9 7 . 3 7 . 0 . 4 2 0 1 0 8 . 3 1 1 7 . 5 4 1 4 . 3 Raw Scores - Subjects Tested i n Heated Environment F i r s t Subjects Condition BPs BPd CT EML ET MS Variables TS DIA PEP ICP PEP/LVET HR TRIP ETI s? NR N 5 0 1 0 0 . 7 8 . 1 1 1 3 . 8 3 . 2 8 0 . 3 2 7 . 4 1 0 . 7 0 7 . 1 3 0 . 4 7 . 0 . 4 6 4 5 4 . 1 5 0 9 . 0 3 7 1 . 6 1 3 0 . 1 1 5 . 7 2 0 . 7 7 . 2 4 7 . 3 0 0 . 3 7 7 . 3 4 7 . 1 3 0 . 5 3 . 0 . 5 2 7 8 3 . 2 6 7 2 . 2 3 8 8 . 3 N 1 0 0 1 4 0 . 1 1 5 . 6 2 7 . 8 0 . 2 2 7 . 2 7 3 . 3 5 7 . 2 7 0 . 1 3 0 . 5 0 . 0 . 5 7 4 9 6 . 3 0 3 8 . 3 3 8 9 . 4 HR H 5 0 1 0 0 . 7 8 . 6 5 3 . 1 1 0 . 2 3 0 . 2 5 0 . 3 6 0 . 2 9 3 . 1 3 0 . 2 0 . 0 . 5 6 5 9 2 . 2 1 1 2 . 2 3 8 6 . 1 1 0 6 . 9 2 . 5 4 3 . 7 0 . 2 1 0 . 2 6 0 . 3 3 0 . 2 1 7 . 1 2 0 . 5 0 . 0 . 5 7 4 1 1 0 . 2 4 5 8 . 2 3 9 7 . 7 Hi nn 9 8 . 8 0 . 5 3 7 . 8 7 . 2 1 3 . 2 4 0 . 3 2 3 . 2 1 0 . 1 1 0 . 2 3 . 0 . 5 1 6 1 1 2 . 2 3 3 7 . 4 4 0 3 . 4 s 8 N R N 5 0 1 0 5 . 8 0 . 9 7 0 . 7 0 . 2 7 7 . 3 2 7 . 4 0 0 . 5 7 0 . 1 2 3 . 5 3 . 0 . 4 4 6 6 2 . 1 7 9 6 . 9 3 8 1 . 8 1 2 5 . 9 6 . 7 2 3 . 7 0 . 2 7 0 . 3 2 0 . 3 9 3 . 3 3 0 . 1 2 3 . 5 3 . 0 . 4 5 7 8 3 . 2 7 9 9 . 5 4 1 1 . 0 N 1 0 0 1 2 0 . 1 0 2 . 6 6 0 . 7 3 . 2 6 3 . 3 0 0 . 3 7 3 . 2 8 0 . 1 1 0 . 3 7 . 0 . 4 1 8 9 1 . 2 8 7 2 . 7 4 1 7 . 9 HR H 5 0 1 0 2 . 8 2 . 6 9 7 . 7 3 . 2 3 0 . 2 8 7 . 3 6 0 . 3 3 7 . 1 3 0 . 5 7 . 0 . 5 6 5 8 6 . 2 0 2 0 . 5 3 7 6 . 4 1 2 0 . 9 0 . 6 0 3 . 7 0 . 2 2 3 . 2 8 0 . 3 5 3 . 2 4 7 . 1 3 0 . 6 0 . 0 . 5 8 5 9 9 . 2 6 6 5 . 2 3 9 2 . 4 Hi nn 1 3 0 . 9 6 . 5 2 7 . 6 7 . 1 9 3 . 2 4 3 . 3 0 7 . 2 2 0 . 1 1 3 . 4 7 . 0 . 5 8 7 1 1 4 . 2 8 6 3 . 3 3 8 7 . 0 Sg % 1 1 5 . 7 5 . 8 9 7 . 8 3 . 2 5 3 . 2 8 7 . 3 7 3 . 5 2 3 . 1 2 0 . 3 7 . 0 . 4 7 4 6 7 . 1 9 4 9 . 4 3 6 7 . 1 N 5 0 1 6 0 . 1 2 5 . 6 8 7 . 7 7 . 2 4 3 . 2 9 3 . 3 6 7 . 3 2 3 . 1 2 3 . 4 7 . 0 . 5 0 7 8 7 . 3 4 0 1 . 9 3 9 1 . 9 - NlOO 1 5 6 . 1 2 5 . 6 1 0 . 7 7 . 2 3 7 . 2 7 0 . 3 4 3 . 2 6 0 . 1 0 7 . 3 0 . 0 . 4 5 2 9 8 . 3 6 3 1 . 5 4 0 3 . 9 HR H 5 0 1 0 5 . 7 2 . 7 9 3 . 8 3 . 2 5 3 . 2 9 3 . 3 8 0 . 4 1 3 . 1 2 7 . 4 3 . 0 . 5 0 1 7 6 . 2 0 1 1 . 8 3 8 1 . 9 1 3 5 . 9 5 . 6 6 7 . 7 0 . 2 3 7 . 2 8 0 . 3 5 0 . 3 1 3 . 1 1 3 . 4 3 . 0 . 4 7 9 9 0 . 2 8 7 5 . 5 3 8 9 . 7 Hi nn 1 3 6 . 1 1 0 . 6 1 7 . 7 0 . 2 2 7 . 2 8 0 . 3 5 0 . 2 5 7 . 1 2 3 . 5 3 . 0 . 5 4 5 9 7 . 2 9 9 9 . 4 3 9 2 . 1 s 1 0 N R N 5 0 N 1 0 0 1 1 0 . 7 5 . 7 3 3 . 8 0 . 2 2 0 . 2 6 7 . 3 4 7 . 3 9 0 . 1 2 7 . 4 7 . 0 . 5 7 6 8 2 . 1 9 8 0 . 0 3 5 9 . 1 1 4 0 . 1 0 8 . 6 6 0 . 7 7 . 2 2 0 . 2 7 7 . 3 5 0 . 3 1 0 . 1 3 0 . 5 3 . 0 . 5 9 3 9 1 . 2 8 0 0 . 0 3 7 4 . 5 1 4 5 . 1 0 8 . 6 1 0 8 0 . 2 1 7 . 2 7 0 . 3 4 7 . 2 6 3 . 1 3 0 . 5 0 . . 0 . 6 0 0 9 8 . 3 0 9 0 . 2 3 8 3 . 9 H R H 5 0 9 6 . 7 0 . 6 4 7 . 8 0 . 2 1 3 . 2 7 7 . 3 5 7 . 2 9 0 . 1 4 3 . 6 3 . 0 . 6 7 3 9 3 . 1 9 0 0 . 2 3 7 1 . 1 1 2 5 . 1 0 2 . 5 4 3 . 7 0 . 2 0 3 . 2 6 0 . 3 2 3 . 2 2 0 . 1 2 0 . 5 0 . 0 . 5 9 1 1 1 0 . 2 8 0 6 . 7 3 9 1 . 1 Hi nn 1 3 4 . 1 0 5 . 5 3 7 . 7 0 . 2 0 0 . 2 5 3 . 3 2 3 . 2 1 7 . 1 2 3 . 5 3 . 0 . 6 1 9 1 1 2 . 2 9 9 6 . 3 3 9 0 . 1 S l l N R N 5 0 1 1 8 . 8 4 . 1 0 4 7 . 9 0 . 2 7 7 . 3 2 0 . 4 1 0 . 6 4 0 . 1 3 3 . 4 3 . 0 . 4 8 2 5 7 . 1 8 7 1 . 5 3 7 4 . 1 1 4 5 . 1 0 0 . 8 0 3 . 7 3 . 2 7 0 . 3 3 0 . 4 0 0 . 4 0 0 . 1 3 0 . 5 7 . 0 . 4 8 1 7 5 . 2 9 2 4 . 1 3 9 7 . 0 N 1 0 0 1 4 0 . 1 0 0 . 8 3 0 . 8 0 . 2 6 7 . 3 0 3 . 3 8 7 . 4 5 0 . 1 2 0 . 4 0 . 0 . 4 5 1 7 2 . 2 6 9 8 . 8 3 8 9 . 6 HR H 5 0 1 1 0 . 7 5 . 8 7 3 . 8 0 . 2 4 7 . 2 8 7 . 3 7 0 . 5 0 3 . 1 2 3 . 4 3 . 0 . 5 0 1 6 9 . 1 8 6 4 . 1 3 6 3 . 5 1 1 4 . 8 8 . 7 3 0 . 8 7 . 2 4 0 . 2 8 7 . 3 7 3 . 3 5 3 . 1 3 3 . 4 7 . 0 . 5 5 6 8 2 . 2 2 4 8 . 8 3 7 9 . 7 Hi nn 1 3 5 . 9 8 . 6 3 0 . 8 0 . 2 3 7 . 2 8 0 . 3 6 0 . 2 7 0 . 1 2 3 . 4 3 . 0 . 5 2 2 9 5 . 3 0 4 2 . 9 3 9 8 . 6 s 1 2 N R N 5 0 1 1 4 . 7 0 . 1 1 2 0 . 9 0 . 2 6 3 . 3 0 7 . 3 9 7 . 7 2 7 . 1 3 3 . 4 3 . 0 . 5 0 7 5 4 . 1 6 0 8 . 2 3 5 4 . 4 1 1 8 . 9 0 . 1 0 9 7 . 1 0 0 . 2 6 3 . 3 0 7 . 4 0 3 . 6 9 0 . 1 4 0 . 4 0 . 0 . 5 3 4 5 5 . 1 7 0 0 . 1 3 5 6 . 3 NlOO HR H 5 0 1 1 6 . 9 6 . 8 6 0 . 9 0 . 2 5 3 . 2 8 3 . 3 7 3 . 4 8 7 . 1 2 0 . 3 0 . 0 . 4 7 6 7 0 . 2 0 5 0 . 2 3 7 1 . 9 1 1 5 . 7 0 . 8 4 0 9 0 . 2 4 0 . 2 7 0 . 3 6 0 . 4 8 0 . 1 2 0 . 3 0 . 0 . 5 0 0 7 1 . 1 9 7 1 . 4 3 6 1 . 4 1 0 8 . 7 0 . 8 3 3 . 9 3 . 2 4 3 . 2 6 7 . . 3 6 0 . 4 7 3 . 1 1 7 . 2 3 . 0 . 4 8 0 7 2 . 1 8 9 2 . 2 3 6 5 . 7 Hi nn 1 1 4 . 8 0 . 7 3 0 . 1 0 3 . 2 4 7 . 2 5 7 . 3 6 7 . 3 6 0 . 1 2 0 . 1 7 . 0 . 4 8 7 8 2 . 2 3 1 1 . 2 3 8 6 . 4 110 Correlation Coefficients - At Rest i n a Neutral Environment BPs BPd CT EML ' LVET MS TS DIAS PEP ICP PEP/LVET HR TRIP ETI BPs 1.000 BPd -0.154 1.000 CT -0.352 0.054 1.000 EML 0.245 -0.213 0.179 1.000 LVET -0.204 0.196 0.731 0.004 1.000 MS -0.592 0.477 0.597 -0.281 0.695 1.000 TS -0.520 0.378 0.652 0.218 0.659 0.869 1.000 DIAS -0.320 -0.011 0.994 0.171 .0.703 0.526 0.572 1.000 PEP -0.440 0.273 0.023 0.281 -0.265 0.340 0.551 -0.049 1.000 ICP -0.585,0.410-0.085-0.352-0.257 0.510 0.403-0.150 0.799 1.000 PEP/LVET -0.249 0.150 -0.314 0.224 -0.649 -0.041 0.143 -0.360 0.904 0.740 1.000 HR 0.305-0.110-0.989-0.127-0.774-0.644-0.671-0.976 0.001 0.076 0.352 1.000 TRIP 0.794 -0.099 -0.779 0.489 -0.348 -0.447 -0.614 -0.765 -0.399 -0.380 -0.148 0.731 1.000 ETI 0.081 0.168 -0.185 -0.080 0.528 0.247 0.146 -0.214 -0.395 -0.356 0.530 0.128 0.138 1.000 Correlation Coefficients - At 50% MVC i n a Neutral Environment BPs BPd CT EML LVET MS TS DIAS PEP ICP PEP LVET HR TRIP ETI BPs 1.000 BPd 0.681 1.000 CT -0.603 -0.428 1.000 EML -0.369 -0.039 0.851 1.000 LVET -0.335 -0.493 0.569 0.244 1.000 MS -0.294 -0.525 0.423 0.013 0.893 1.000 TS -0.406 -0.435 0.776 0.526 0.887 0.844 1.000 DIAS -0.569 -0.406 0.994 0.862 0.535 0.370 0.743 1.000 PEP -0.285 -0.057 0.650 0.699 0.107 0.201 0.554 0.642 1.000 ICP 0.208 0.011 -0.447 -0.584 -0.227 0.198 -0.107 -0.470 0.171 1.000 PEP/LVET 0.018 0.301 0.089 0.362 -0.627 -0.472 -0.197 0.105 0.706 0.310 1.000 HR 0.581 0.401 -0.988 -0.818 -0.604 -0.506 -0.830 -0.976 -0.702 0.343 -0.106 1.000 TRIP 0.837 0.470 -0.870 0.065 -0.271 -0.164 -0.529 -0.853 -0.663 -0.337 -0.315 0.857 1.000 ETI 0.376 0.003 -0.637 -0.768 -0.564 0.344 -0.529 -0.562 -0.126 0.086 -0.751 0.616 0.582 1.000 M ho Correlation C o e f f i c i e n t s - At 100% MVC i n a Neutral Environment BPs BPd CT EML LVET MS TS DIAS PEP ICP PEP/LVET HR TRIP ETI BPs 1.000 BPd 0.631 1.000 CT -0.673 -0.582 1.000 EML -0.525 -0.211 0.744 1.000 LVET -0.474 -0.621 0.446 -0.036 1.000 MS -0.545 -0.623 .0.500 0.039 0.838 1.000 TS -0.732 -0.605 0.846 0.632 0.611 0.790 1.000 DIAS -0.631 -0.579 0.993 0.711 0.418 0.461 0.798 1.000 PEP -0.290 0.022 0.454 0.765 -0.440 -0.057 0.442 0.431 1.000 ICP 0.089 0.245 -0.057 0.162 -0.634 -0.124 0.041 -0.061 0.760 1.000 PEP/LVET -0.023 0.264 0.150 0.567 -0.743 -0.379 0.075 0.145 0.927 0.845 1.000 HR 0.665 0.581 -0.994 -0.759 -0.426 -0.488 -0.845 -0.981 -0.476 0.039 -0.176 1.000 TRIP 0.807 0.499 -0.891 0.165 -0.178 -0.278 -0.764 -0.867 -0.663 0.364 -0.422 0.940 1.000 ETI 0.310 0.094 -0.666 -0.768 0.362 0.251 -0.385 -0.673 -0.848 -0.378 -0.780 0.689 0.581 1.000 Correlation Coefficients - At Rest i n a Heated Environment BPs BPd CT EML LVET MS TS DIAS PEP ICP PEP/LVET HR TRIP ETI BPs 1.000 BPd 0.220 1.000 CT 0.366 0.052 1.000 EML 0.073 0.257 -0.127 1.000 LVET 0.074 0.218 0.840 -0.186 1.000 MS 0.033 0.118 0.630 -0.718 0.721 1.000 TS 0.234 0.441 0.758 0.053 0.854 0.651 1.000 DIAS 0.396 0.021 0.997 -0.138 0.809 0.606 0.713 1.000 PEP 0.053 0.246 -0.474 0.445 -0.636 -0.415 -0.142 -0.481 1.000 ICP -0.045 -0.123 -0.170 -0.813 -0.215 0.516 -0.160 -0.161 -0.160 1.000 PEP/LVET -0.041 -0.019 -0.706 0.334 -0.897 •-(). 606 -0.539 -0.693 0.907 0.226 1.000 HR -0.444 -0.063 -0.993 0.129 -0.821 -0.601 -0.734 -0.994 0.472 0.166 0.701 1.000 TRIP 0.618 0.377 -0.412 0.159 -0.374 0.239 -0.291 -0.402 0.291 -0.272 0.311 0.336 1.000 ETI -0.637 0.236 -0.370 -0.089 0.181 0.077 0.095 -0.422 -0.207 -0.025 -0.227 0.412 -0.109 1.000 Correlation Coefficients - At 50% MVC i n a Heated Environment BPs BPd CT EML LVET MS TS DIAS PEP ICP PEP/LVET HR TRIP ETI BPs 1.000 BPd 0.517 1.000 CT -0.184 -0.233 1.000 EML 0.090 0.241 0.639 1.000 LVET -0.105 -0.333 0.827 0.487 1.000 MS -0.205 -0.216 0.564 0.005 0.664 1.000 TS -0.090 0.042 0.791 0.699 0.792 0.676 1.000 DIAS -0.174 -0.279 0.991 0.614 0.812 -0.498 0.728 1.000 PEP 0.008 0.566 -0.007 0.363 -0.260 0.064 0.383 -0.084 1.000 ICP -0.070 0.283 -0.579 -0.577 -0.656 0.066 -0.284 -0.627 0.549 1.000 PEP/LVET 0.066 0.590 -0.473 -0.028 -0.745 -0.333 -0.184 -0,516 0.838 0.754 1.000 HR 0.094 0.236 -0.990 -0.619 -0.843 -0.608 -0.805 -0.976 0.010 0.563 0.487 1.000 TRIP 0.822 0.413 -0.648 -0.322 -0.364 0.245 -0.426 -0.633 -0.122 0.211 0.124 0.574 1.000 ETI 0.015 -0.023 -0.741 T-0.515--0.261 -0.184 -0.465 -0.735 -0.325 0.167-0.073 0.739 0.545 1.000 Correlation Coefficients - At 100% MVC i n a Heated Environment BPs BPd CT EML LVET MS TS DIAS PEP ICP PEP/LVET HR TRIP ETI BPs 1.000 BPd 0.766 1.000 CT -0.367 -0.179 1.000 EML -0.593 -0.487 0.554 1.000 LVET -0.348 -0.422 0.815 0.495 1.000 MS 0.002 0.163 0.532 -0.155 0.572 1.000 TS -0.324 -0.127 0.870 0.554 0.831 0.723 1.000 DIAS -0.336 -0.174 0.981 0.522 0.755 0.416 0.763 1.000 PEP -0.060 0.404 0.352 0.261 0.011 0.451 0.565 0.249 1.000 ICP 0.465 0.731 -0.213 -0.666 -0.429 0.476 -0.051 -0.263 0.546 1.000 PEP/LVET 0.153 0.566 -0.210 -0.094 -0.606 0.005 -0.062 -0.250 0.787 0.695 1.000 HR 0.324 0.130 -0.994 -0.518 -0.827 -0.600 -0.903 -0.958 -0.394 0.149 0.187 1.000 TRIP 0,895 0.511 -0.643 -0.386 -0.402 0.009 -0.535 -0.620 -0.358 0.103 -0.055 0.607 1.000 ETI 0.075 -0.379 -0.582 -0.175 -0.015 -0.129 -0.397 -0.607 -0.686 -0.471 -0.550 0.574 0.375 1.000 ON

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