Cardiovascular responses and postexercise hypotension after arm cycling exercise in subjects with spinal cord injury

OBJECTIVE: To examine postexercise hypotension and contributing factors in subjects with spinal cord injury (SCI). DESIGN: Prospective clinical research study. SETTING: Rehabilitation center. PARTICIPANTS: Subjects with chronic cervical-level (n=19) and thoracic-level (n=8) SCI. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Subjects underwent graded arm-cycling with electrocardiogram and oxygen uptake monitoring to exhaustion. Heart rates and blood pressures were measured before and after exercising. Injury to motor and sensory pathways was determined by American Spinal Injury Association grade, and to autonomic pathways by sympathetic skin responses (SSRs) (n=16). RESULTS: Resting blood pressures and heart rates were lower in cervical than thoracic SCI (mean arterial pressure MAP]: cervical, 76.6+/-2 mmHg; thoracic, 93.5+/-3 mmHg; P<.001). Following exercise, heart rate responses were greater in thoracic than cervical SCI; MAP increased in thoracic SCI (8.4+/-5 mmHg) and markedly decreased in cervical SCI (-9.3+/-2 mmHg) (P<.001). No subject had significant electrocardiographic abnormalities at rest or during exercise. There were correlations between SSR and heart rate and blood pressure responses to exercise; the correlation between the SSR and blood pressure response was due to an interaction between the heart rate and blood pressure responses. CONCLUSIONS: Abnormal cardiovascular responses to exercise and transient postexercise hypotension were common in cervical, but not thoracic SCI. This may be partly related to loss of descending sympathetic nervous control of the heart and vasculature following high SCI.