The effects of autonomic dysfunction and endurance training on cardiovascular control

Abstract

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.

Cardiac homeostasis is independent of calf venous compliance in subjects with paraplegia

“…hemodynamics were similar between the groups at supine rest and during acute HDT and HUT, as previously reported (12,18,20,38). CO during passive tilting is maintained by increases in heart rate, which are compensatory to losses in central filling pressure, venous return, and reduced stroke volume (13).…”

“…These concomitant problems facing individuals with paraplegia suggest that they would be highly susceptible to orthostatic intolerance. Despite significant reductions in muscle mass and sympathetic activity of the lower extremity, resting and orthostatic cardiac hemodynamics, i.e., CO, stroke volume, and heart rate, have been reported as similar in persons with paraplegia and nondisabled controls (11,12,18,20,38). It is unclear how central hemodynamics are maintained during gravitational stress in persons with lower ex-tremity denervation and skeletal muscle atrophy.…”

Autonomic function as a missing piece of the classification of Paralympic athletes with spinal cord injury

“…modulator of resting vagosympathetic cardiac control. 43,44 Athletes with SCI have also demonstrated some ability to improve CV modulation through exercise, 44,45 although not to the extent of athletes with intact ANS. 46,47 To address the question as to how ANS dysfunction relates to Paralympic classification, it is important to look specifically at the response to exercise in SCI athletes.…”

Orthostatic influence on heart rate and blood pressure variability in trained persons with tetraplegia

“…Several studies report orthostatic hypotension in people with tetraplegia (Houtman et al 2000;Illman et al 2000), while it is not clear whether regular physical activity improves autonomic regulation during orthostatic challenges. A lower resting heart rate and higher vagal tone have been reported in endurance-trained able-bodied athletes (Wecht et al 2001). Amano et al (2001) reported that obese individuals, who manifested lower SNS activity against physiological perturbations, improved both the sympathetic and parasympathetic nervous activity after 12 weeks of endurance exercise training.…”