The effects of autonomic dysfunction and endurance training on cardiovascular control

The effects of autonomic dysfunction and regular activity on the cardiovasc ular system were investigated. The 48 participants included 12 subjects wit h tetraplegia, 12 subjects with paraplegia, 12 sedentary subjects, and 12 e ndurance-trained able-bodied controls. Central and peripheral autonomic dat a were obtained at rest to estimate efferent cardiac vagal output and sympa thetic vasomotor control, and plasma norepinephrine concentration was deter mined as a marker of peripheral sympathetic activity. Cardiovascular parame ters were obtained using a noninvasive cardiac output maneuver. The group w ith paraplegia did not differ from the sedentary group for efferent cardiac vagal output, but all other group comparisons were different (p < 0.05). S ympathetic vasomotor control and stroke index were also similar between the paraplegia and sedentary groups, whereas both were increased in the endura nce-trained group and were significantly reduced in the tetraplegia group. A strong relation between efferent cardiac vagal output and stroke index wa s established for the total group (r = 0.78, p < 0.01), and analysis of cov ariance determined that the slope of this relation was similar among the gr oups. Sympathetic vasomotor control correlated significantly with plasma no repinephrine (r = 0.57, p < 0.01), and a relation between sympathetic vasom otor 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 car diac function is maintained despite autonomic dysfunction. The comparable f indings in the paraplegia and sedentary groups suggest that regardless of p eripheral autonomic dysfunction, the absence of regular physical activity h as a similar effect on the resting vagal modulation and stroke index.