The effects of autonomic dysfunction and endurance training on cardiovascular control.

The effects of autonomic dysfunction and regular activity on the cardiovascular system were investigated. The 48 participants included 12 subjects with tetraplegia, 12 subjects with paraplegia, 12 sedentary subjects, and 12 endurance-trained able-bodied controls. Central and peripheral autonomic data were obtained at rest to estimate efferent cardiac vagal output and sympathetic vasomotor control, and plasma norepinephrine concentration was determined as a marker of peripheral sympathetic activity. Cardiovascular parameters were obtained using a noninvasive cardiac output maneuver. The group with paraplegia did not differ from the sedentary group for efferent cardiac vagal output, but all other group comparisons were different (p <0.05). Sympathetic vasomotor control and stroke index were also similar between the paraplegia and sedentary groups, whereas both were increased in the endurance-trained group and were significantly reduced in the tetraplegia group. A strong relation between efferent cardiac vagal output and stroke index was established for the total group (r = 0.78, p <0.01), and analysis of covariance determined that the slope of this relation was similar among the groups. Sympathetic vasomotor control correlated significantly with plasma norepinephrine (r = 0.57, p <0.01), and a relation between sympathetic vasomotor control and stroke index was identified for the total group (r = 0.40, p <0.01). These results suggest that vagal control of resting central cardiac function is maintained despite autonomic dysfunction. The comparable findings in the paraplegia and sedentary groups suggest that regardless of peripheral autonomic dysfunction, the absence of regular physical activity has a similar effect on the resting vagal modulation and stroke index.