Eur J Appl Physiol (1992) 65:73-78
European Journalof
Applied
Physiology and Occupational Physiology © Springer-Verlag1992
Cardiovascular responses in paraplegic subjects during arm exercise Maria T. E. Hopman, Berend Oeseburg, and Rob A. Binkhorst Department of Physiology, University of Nijmegen, Geert Grooteplein N 21, NL-6525 EZ Nijmegen, The Netherlands Accepted February 13, 1992
Summary. The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20°70, 40°70 and 60°70 of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (f~) was sigificantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Q¢ between P and C; however, stroke volume (SV) was significantly lower and f~ significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc . . . . . During submaximal exercise, however, this lower SV was compensated for by a higher f¢ and, thus at the same submaximal oxygen uptake, Qo was similar to that in the control group. Key words: Spinal cord injury - S t r o k e volume - Cardiac output - COz Rebreathing method - Maximal and submaximal exercise
Introduction Since cardiopulmonary function and expected life-span are less favourable in sedentary people compared to the physically active, there has been an increasing demand
Offprint requests to: M. Hopman
for sport in rehabilitation as well as in the daily life of people with spinal cord injuries (Hjeltnes and Vokac 1979; Glaser 1985; Shephard 1988; Compton et al. 1989). These physical activities consist mainly of arm exercise. Whereas cardiovascular responses are well established for able-bodied subjects during leg exercise on treadmill and cycle ergometer, much less attention has been focused on cardiovascular responses during arm exercise in subjects unable to perform leg exercise. During exercise in able-bodied subjects, a redistribution of blood takes place to increase cardiac output (Q¢) and to supply the exercising muscles with blood. The increase in Q¢ is caused by an increase in stroke volume (SV) as well as in heart rate (f¢). In paraplegics, vasoregulation in areas below the spinal cord lesion is not effective and, therefore, the redistribution of blood will be disturbed. The lack of sympathetic innervation from below the level of the lesion and the absence of the musculo-skeletal pump may result in a diminished increase in mean systemic filling pressure and in end-diastolic ventricular volume. According to the Frank-Starling mechanism, this would result in a smaller increase in SV compared to able-bodied subjects with effective redistribution of blood (Guyton and Jones 1973). Cardiovascular responses in paraplegics during arm exercise have been described in a few previous investigations. Results are conflicting, however, with regard to Q¢. Hjeltnes (1977) and Davis and Shephard (1988) have reported a lower Qc, whereas Sawka et al. (1980), De Bruin and Binkhorst (1984) and Kinzer and Convertino (1989) have found the same Q.o, and Jehl et al. (1991) have found higher Q¢, in paraplegics compared to ablebodied subjects at the same oxygen uptake (I/O2). The different findings can be partly explained by variety in level and completeness of the spinal cord lesions and differences in physical fitness of the paraplegic subjects among those investigations. Paraplegic subjects with spinal cord lesions above T6 (Jehl et al. 1991) may have a partly disturbed cardiac sympathetic innervation and complete splanchnic sympathetic denervation, both of which would be expected to influence cardiovascular responses during arm exercise. Furthermore, due to the
74 lack o f a c o m p a r i s o n g r o u p o f a b l e - b o d i e d subjects in the studies o f H j e l t e s (1977) a n d Davis a n d S h e p h a r d (1988), it is n o t k n o w n w h e t h e r the results c h a r a c t e r i s e d an u n d e r e s t i m a t i o n in Qc b y the m e t h o d used or w h e t h e r p a r a p l e g i c subjects h a d lower Qo at the s a m e ~rO 2. T h e p u r p o s e o f this s t u d y was to e x a m i n e c a r d i o v a s cular responses (i.e. 1202, Oc, s v , a n d r e ) to a r m - c r a n k ing exercise in a m o r e well-defined g r o u p o f p a r a p l e g i c subjects with c o m p l e t e spinal c o r d lesions between T6 a n d T12, c o m p a r e d to a c o n t r o l g r o u p m a t c h e d for age, physical activity a n d type o f training. I f p o o l i n g o f venous b l o o d does affect c a r d i o v a s c u l a r responses in p a r a plegics, differences in responses to a r m exercise s h o u l d be o b s e r v e d b e t w e e n g r o u p s .
Methods Subjects. A group of 11 male paraplegic subjects with complete spinal cord lesions and 11 male control subjects participated in this study. All subjects gave their written informed consent. The study was approved by the Faculty Ethics Committee. The level of the spinal cord lesions of the paraplegics was between T6 and T12 and thus cardiac sympathetic innervation would have been unaffected, suggesting a basically normal regulation of intrinsic cardiac function. The control group consisted of 5 wheelchair-bound individuals, with permanent injury of the knee or foot, and 6 ablebodied subjects. The paraplegics and the wheelchair-bound controls participated at comparable levels in competitive sport and their training statuses with regard to type and duration were almost identical. Both groups used a wheelchair for transport and sport. The disabilities in both groups had existed for at least 4 years. The able-bodied subjects were selected according to training status and age. Since the responses to maximal and submaximal arm exercise were not significantly different between the wheelchair-bound controls and the able-bodied subjects, it was possible to combine these 11 subjects. In other words, this control group was physically matched with the group of paraplegics with the exception of the spinal cord lesion; their physical characteristics are summarized in Table 1. The subjects underwent a comprehensive medical examination which included a 12-lead electrocardiogram, cardiac and pulmonary auscultation, detailed physical and medical history and, for the paraplegics, a brief sensomotoric neurological examination to verify the level and completeness of the lesion as reported in their medical file. From this examination no impediment to participation in this study was found. Protocol. All subjects visited the laboratory twice within 1 week. On both occasions, the temperature in the experimental room was maintained between 21 and 22°C with a 45%-50% relative humidity. At least 2 h prior to each test, the subjects abstained from caffeine, alcohol and nicotine. On the first occasion, the subjects were weighed in the sitting position on a hospital scale, while body length was taken from the medical file. Each subject performed maximal arm-cranking exercise using a continuous multistage protocol, with a frequency of 60 rpm (Washburn and Seals 1983). Power output was increased by 10 W every minute beginning, at 10 W until exhaustion to determine maximal oxygen uptake (VO2m~x; mean 1702 of the last minute) and maximal power output (Win,x). The test was terminated when, even after verbal encouragement by the examiner, the subject was unable to maintain the frequency of 60 rpm. The fo base excess (BE) and respiratory exchange ratio (R) were used as objective criteria for maximal exercise. During the second visit, each subject performed submaximal arm exercise at 20%, 400/0 and 60% of his individual Wm~x.Each period of exercise lasted 7 min with a 5 min recovery period. Stea-
dy-state exercise during the 6th and 7th min was verified by /202, ventilation (12E) and ft.
Apparatus. Exercise was performed, sitting in a wheelchair fixed to the floor, on an electro-magnetic arm-crank ergometer (modified cycle ergometer, Lode, Groningen, The Netherlands). The axis of the crank unit was adjusted to shoulder height. During revolution of the arms they were at no time fully extended. Measurements. During the tests, I202, carbon dioxide output (12CO2), R and I?E were measured continuously and averaged over 30 s-intervals, by an automatic gas analyser (Oxycon IV, Mijnhardt, Bunnik, The Netherlands). This gas analyser included a dry gas-meter with a paramagnetic O2 and infrared CO2 analyser, calibrated daily with gas mixtures analysed by the Scholander technique. A Hans-Rudolph valve was connected to a three-way stopcock used for switching from outdoor air to the rebreathing bag when the rebreathing procedure commenced. The electrocardiogram and fo were recorded continuously using a cardiotachometer. During the last minute of each period of submaximal exercise and 3 min after termination of maximal exercise, blood gases were determined from a capillary ear-lobe blood sample, after rubbing the ear-lobe with a vasodilating ointment. Hydrogen ion activity (pH), partial pressure of carbon dioxide (PCO2) and partial pressure of oxygen (PO2) were measured (IL Blood Gas Analyser, model 1312, Instrumentation Laboratory, Lexington, MA). The BE and percentage of oxygen saturation (%oSO2) were calculated using pH, PCO2, PO2 and concentration of haemoglobin, the latter measured by the Hemocue (Kwant et al. 1987). At each level of submaximal steady-state exercise Qo was determined by the CO2 rebreathing method according to Collier (1956). To obtain partial pressure of CO2 in mixed venous blood (PvCO2) a rapid and linear CO2 analyser (Capnograph Godart type MO, de Bilt, The Netherlands) was used to measure the CO2 plateau during rebreathing. The quality of the PCO2 plateau was verified using a computer algorithm in which both variation of the signal and the length of the plateau were compared to predetermined values (Van Herwaarden et al. 1980). A correction for alveolar-arterial PCO2 differences was applied (Jones et al. 1969). Partial pressure of CO2 in arterial blood (PaCO2) was calculated via the modified Bohr-formula for physiological dead-space. The CO2 concentration was calculated from PCO2 using the CO2 dissociation curve, corrected for changes of pH and BE during exercise. Arterial to mixed venous difference in oxygen content (DO2.,.v) was calculated by dividing Qc into 1202. The SV was calculated by dividing fc into Qc. Statistical analysis. A Student's t-test was applied to assess the significance of differences 1. In physical characteristics 2. In responses to maximal and submaximal arm-cranking exercise between paraplegic and control subjects and 3. In responses between wheelchair-bound and able-bodied subjects within the control group. A probability less than 5% was used to establish statistical significance.
Results T h e p h y s i c a l characteristics for the p a r a p l e g i c a n d control subjects, given in T a b l e 1, were n o t significantly different. C o m p a r e d to o b j e c t i v e criteria for m a x i m a l exercise (fc greater t h a n 1 7 0 b e a t s . m i n - ~ , BE less t h a n - 1 0 m m o l . 1 - 1 , R greater t h a n 1.00; S a w k a 1986), all subjects m e t two o f the three criteria, their efforts thus being c o n s i d e r e d to be m a x i m a l . P a r a p l e g i c s showed a significantly lower 1202m~x c o m p a r e d to the c o n t r o l g r o u p . T h e Wm~x was slightly higher in the c o n t r o l
75 Table 1. Physical characteristics and physiological responses to maximal arm exercise in paraplegic and control subjects Paraplegic subjects
Control subjects
mean
SD
mean
SD
29 181 66 2.14 189 1.12 -11.7 133
8 7 9 0.34 8 0.09 2.6 16
32 179 71 2.78 181 1.11 -11.2 147
6 9 10 0.36* 9* 0.07 2.8 17
Age (years) Height (cm) Body mass (kg) Maximal oxygen uptake (1.min -1) Heart rate (beats'min -1) Respiratory exchange ratio Base excess (mmol'1-1) Power output (W)
Table 2. Physiological responses to submaximal arm exercise at 20°70, 40°70 and 60°70 maximal power output (Wm~x) in the paraplegic subjects and control subjects % Wm~Paraplegic subjects
* P < 0.05
g r o u p a l t h o u g h not significantly so. A t the termination o f the maximal test fc was significantly higher in paraplegics (Table 1). Table 2 gives the physiological responses to submaximal arm-cranking exercise at 2 0 % , 40°7o and 60% Wm~x, for b o t h groups. The lkO2, IPE and fc were not significantly different between the 6th and 7th min, suggesting steady.-state conditions. Due to the higher IkO2 . . . . Qc and VO2 at 20°7o, 40% and 60%, Wm~× were higher in the control group. However, at the same lkO2, Q~ was not significantly different between the two groups (Fig. 1). A l t h o u g h Qc was the same in paraplegics and the control g r o u p during submaximal exercise, this was achieved by m a r k e d differences in the f~ and SV rela-
Oxygen uptake 20°70 (1.min -1) 40070 60o70 Cardiac output 20°70 (1.min -1) 40% 60070 Heart rate 20% (beats.min -1) 40% 60070 Stroke volume 20°70 (ml.beat -1) 40070 60% DOz,a.v 20% (ml. 100 m1-1) 40% 60%
Control subjects
mean
SD
mean
SD
0.73 1.04 1.43 7.2 10.0 12.9 95 113 139 78 88 94 10.1 10.4 11.1
0.06 0.09 0.14 1.1 1.6 1.8 14 15" 13' 15 10" 18" 1.7 1.9 1.9
0.78 1.18 1.67 8.0 10.9 15.8 87 102 126 94 109 127 9.8 10.8 10.6
0.13 0.19 0.26 1.6 2.4 3.5 12 11 12 26 28 32 2.5 2.4 2.7
*P
European Journalof
Applied
Physiology and Occupational Physiology © Springer-Verlag1992
Cardiovascular responses in paraplegic subjects during arm exercise Maria T. E. Hopman, Berend Oeseburg, and Rob A. Binkhorst Department of Physiology, University of Nijmegen, Geert Grooteplein N 21, NL-6525 EZ Nijmegen, The Netherlands Accepted February 13, 1992
Summary. The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20°70, 40°70 and 60°70 of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (f~) was sigificantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Q¢ between P and C; however, stroke volume (SV) was significantly lower and f~ significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc . . . . . During submaximal exercise, however, this lower SV was compensated for by a higher f¢ and, thus at the same submaximal oxygen uptake, Qo was similar to that in the control group. Key words: Spinal cord injury - S t r o k e volume - Cardiac output - COz Rebreathing method - Maximal and submaximal exercise
Introduction Since cardiopulmonary function and expected life-span are less favourable in sedentary people compared to the physically active, there has been an increasing demand
Offprint requests to: M. Hopman
for sport in rehabilitation as well as in the daily life of people with spinal cord injuries (Hjeltnes and Vokac 1979; Glaser 1985; Shephard 1988; Compton et al. 1989). These physical activities consist mainly of arm exercise. Whereas cardiovascular responses are well established for able-bodied subjects during leg exercise on treadmill and cycle ergometer, much less attention has been focused on cardiovascular responses during arm exercise in subjects unable to perform leg exercise. During exercise in able-bodied subjects, a redistribution of blood takes place to increase cardiac output (Q¢) and to supply the exercising muscles with blood. The increase in Q¢ is caused by an increase in stroke volume (SV) as well as in heart rate (f¢). In paraplegics, vasoregulation in areas below the spinal cord lesion is not effective and, therefore, the redistribution of blood will be disturbed. The lack of sympathetic innervation from below the level of the lesion and the absence of the musculo-skeletal pump may result in a diminished increase in mean systemic filling pressure and in end-diastolic ventricular volume. According to the Frank-Starling mechanism, this would result in a smaller increase in SV compared to able-bodied subjects with effective redistribution of blood (Guyton and Jones 1973). Cardiovascular responses in paraplegics during arm exercise have been described in a few previous investigations. Results are conflicting, however, with regard to Q¢. Hjeltnes (1977) and Davis and Shephard (1988) have reported a lower Qc, whereas Sawka et al. (1980), De Bruin and Binkhorst (1984) and Kinzer and Convertino (1989) have found the same Q.o, and Jehl et al. (1991) have found higher Q¢, in paraplegics compared to ablebodied subjects at the same oxygen uptake (I/O2). The different findings can be partly explained by variety in level and completeness of the spinal cord lesions and differences in physical fitness of the paraplegic subjects among those investigations. Paraplegic subjects with spinal cord lesions above T6 (Jehl et al. 1991) may have a partly disturbed cardiac sympathetic innervation and complete splanchnic sympathetic denervation, both of which would be expected to influence cardiovascular responses during arm exercise. Furthermore, due to the
74 lack o f a c o m p a r i s o n g r o u p o f a b l e - b o d i e d subjects in the studies o f H j e l t e s (1977) a n d Davis a n d S h e p h a r d (1988), it is n o t k n o w n w h e t h e r the results c h a r a c t e r i s e d an u n d e r e s t i m a t i o n in Qc b y the m e t h o d used or w h e t h e r p a r a p l e g i c subjects h a d lower Qo at the s a m e ~rO 2. T h e p u r p o s e o f this s t u d y was to e x a m i n e c a r d i o v a s cular responses (i.e. 1202, Oc, s v , a n d r e ) to a r m - c r a n k ing exercise in a m o r e well-defined g r o u p o f p a r a p l e g i c subjects with c o m p l e t e spinal c o r d lesions between T6 a n d T12, c o m p a r e d to a c o n t r o l g r o u p m a t c h e d for age, physical activity a n d type o f training. I f p o o l i n g o f venous b l o o d does affect c a r d i o v a s c u l a r responses in p a r a plegics, differences in responses to a r m exercise s h o u l d be o b s e r v e d b e t w e e n g r o u p s .
Methods Subjects. A group of 11 male paraplegic subjects with complete spinal cord lesions and 11 male control subjects participated in this study. All subjects gave their written informed consent. The study was approved by the Faculty Ethics Committee. The level of the spinal cord lesions of the paraplegics was between T6 and T12 and thus cardiac sympathetic innervation would have been unaffected, suggesting a basically normal regulation of intrinsic cardiac function. The control group consisted of 5 wheelchair-bound individuals, with permanent injury of the knee or foot, and 6 ablebodied subjects. The paraplegics and the wheelchair-bound controls participated at comparable levels in competitive sport and their training statuses with regard to type and duration were almost identical. Both groups used a wheelchair for transport and sport. The disabilities in both groups had existed for at least 4 years. The able-bodied subjects were selected according to training status and age. Since the responses to maximal and submaximal arm exercise were not significantly different between the wheelchair-bound controls and the able-bodied subjects, it was possible to combine these 11 subjects. In other words, this control group was physically matched with the group of paraplegics with the exception of the spinal cord lesion; their physical characteristics are summarized in Table 1. The subjects underwent a comprehensive medical examination which included a 12-lead electrocardiogram, cardiac and pulmonary auscultation, detailed physical and medical history and, for the paraplegics, a brief sensomotoric neurological examination to verify the level and completeness of the lesion as reported in their medical file. From this examination no impediment to participation in this study was found. Protocol. All subjects visited the laboratory twice within 1 week. On both occasions, the temperature in the experimental room was maintained between 21 and 22°C with a 45%-50% relative humidity. At least 2 h prior to each test, the subjects abstained from caffeine, alcohol and nicotine. On the first occasion, the subjects were weighed in the sitting position on a hospital scale, while body length was taken from the medical file. Each subject performed maximal arm-cranking exercise using a continuous multistage protocol, with a frequency of 60 rpm (Washburn and Seals 1983). Power output was increased by 10 W every minute beginning, at 10 W until exhaustion to determine maximal oxygen uptake (VO2m~x; mean 1702 of the last minute) and maximal power output (Win,x). The test was terminated when, even after verbal encouragement by the examiner, the subject was unable to maintain the frequency of 60 rpm. The fo base excess (BE) and respiratory exchange ratio (R) were used as objective criteria for maximal exercise. During the second visit, each subject performed submaximal arm exercise at 20%, 400/0 and 60% of his individual Wm~x.Each period of exercise lasted 7 min with a 5 min recovery period. Stea-
dy-state exercise during the 6th and 7th min was verified by /202, ventilation (12E) and ft.
Apparatus. Exercise was performed, sitting in a wheelchair fixed to the floor, on an electro-magnetic arm-crank ergometer (modified cycle ergometer, Lode, Groningen, The Netherlands). The axis of the crank unit was adjusted to shoulder height. During revolution of the arms they were at no time fully extended. Measurements. During the tests, I202, carbon dioxide output (12CO2), R and I?E were measured continuously and averaged over 30 s-intervals, by an automatic gas analyser (Oxycon IV, Mijnhardt, Bunnik, The Netherlands). This gas analyser included a dry gas-meter with a paramagnetic O2 and infrared CO2 analyser, calibrated daily with gas mixtures analysed by the Scholander technique. A Hans-Rudolph valve was connected to a three-way stopcock used for switching from outdoor air to the rebreathing bag when the rebreathing procedure commenced. The electrocardiogram and fo were recorded continuously using a cardiotachometer. During the last minute of each period of submaximal exercise and 3 min after termination of maximal exercise, blood gases were determined from a capillary ear-lobe blood sample, after rubbing the ear-lobe with a vasodilating ointment. Hydrogen ion activity (pH), partial pressure of carbon dioxide (PCO2) and partial pressure of oxygen (PO2) were measured (IL Blood Gas Analyser, model 1312, Instrumentation Laboratory, Lexington, MA). The BE and percentage of oxygen saturation (%oSO2) were calculated using pH, PCO2, PO2 and concentration of haemoglobin, the latter measured by the Hemocue (Kwant et al. 1987). At each level of submaximal steady-state exercise Qo was determined by the CO2 rebreathing method according to Collier (1956). To obtain partial pressure of CO2 in mixed venous blood (PvCO2) a rapid and linear CO2 analyser (Capnograph Godart type MO, de Bilt, The Netherlands) was used to measure the CO2 plateau during rebreathing. The quality of the PCO2 plateau was verified using a computer algorithm in which both variation of the signal and the length of the plateau were compared to predetermined values (Van Herwaarden et al. 1980). A correction for alveolar-arterial PCO2 differences was applied (Jones et al. 1969). Partial pressure of CO2 in arterial blood (PaCO2) was calculated via the modified Bohr-formula for physiological dead-space. The CO2 concentration was calculated from PCO2 using the CO2 dissociation curve, corrected for changes of pH and BE during exercise. Arterial to mixed venous difference in oxygen content (DO2.,.v) was calculated by dividing Qc into 1202. The SV was calculated by dividing fc into Qc. Statistical analysis. A Student's t-test was applied to assess the significance of differences 1. In physical characteristics 2. In responses to maximal and submaximal arm-cranking exercise between paraplegic and control subjects and 3. In responses between wheelchair-bound and able-bodied subjects within the control group. A probability less than 5% was used to establish statistical significance.
Results T h e p h y s i c a l characteristics for the p a r a p l e g i c a n d control subjects, given in T a b l e 1, were n o t significantly different. C o m p a r e d to o b j e c t i v e criteria for m a x i m a l exercise (fc greater t h a n 1 7 0 b e a t s . m i n - ~ , BE less t h a n - 1 0 m m o l . 1 - 1 , R greater t h a n 1.00; S a w k a 1986), all subjects m e t two o f the three criteria, their efforts thus being c o n s i d e r e d to be m a x i m a l . P a r a p l e g i c s showed a significantly lower 1202m~x c o m p a r e d to the c o n t r o l g r o u p . T h e Wm~x was slightly higher in the c o n t r o l
75 Table 1. Physical characteristics and physiological responses to maximal arm exercise in paraplegic and control subjects Paraplegic subjects
Control subjects
mean
SD
mean
SD
29 181 66 2.14 189 1.12 -11.7 133
8 7 9 0.34 8 0.09 2.6 16
32 179 71 2.78 181 1.11 -11.2 147
6 9 10 0.36* 9* 0.07 2.8 17
Age (years) Height (cm) Body mass (kg) Maximal oxygen uptake (1.min -1) Heart rate (beats'min -1) Respiratory exchange ratio Base excess (mmol'1-1) Power output (W)
Table 2. Physiological responses to submaximal arm exercise at 20°70, 40°70 and 60°70 maximal power output (Wm~x) in the paraplegic subjects and control subjects % Wm~Paraplegic subjects
* P < 0.05
g r o u p a l t h o u g h not significantly so. A t the termination o f the maximal test fc was significantly higher in paraplegics (Table 1). Table 2 gives the physiological responses to submaximal arm-cranking exercise at 2 0 % , 40°7o and 60% Wm~x, for b o t h groups. The lkO2, IPE and fc were not significantly different between the 6th and 7th min, suggesting steady.-state conditions. Due to the higher IkO2 . . . . Qc and VO2 at 20°7o, 40% and 60%, Wm~× were higher in the control group. However, at the same lkO2, Q~ was not significantly different between the two groups (Fig. 1). A l t h o u g h Qc was the same in paraplegics and the control g r o u p during submaximal exercise, this was achieved by m a r k e d differences in the f~ and SV rela-
Oxygen uptake 20°70 (1.min -1) 40070 60o70 Cardiac output 20°70 (1.min -1) 40% 60070 Heart rate 20% (beats.min -1) 40% 60070 Stroke volume 20°70 (ml.beat -1) 40070 60% DOz,a.v 20% (ml. 100 m1-1) 40% 60%
Control subjects
mean
SD
mean
SD
0.73 1.04 1.43 7.2 10.0 12.9 95 113 139 78 88 94 10.1 10.4 11.1
0.06 0.09 0.14 1.1 1.6 1.8 14 15" 13' 15 10" 18" 1.7 1.9 1.9
0.78 1.18 1.67 8.0 10.9 15.8 87 102 126 94 109 127 9.8 10.8 10.6
0.13 0.19 0.26 1.6 2.4 3.5 12 11 12 26 28 32 2.5 2.4 2.7
*P
