Cardiovascular reactivity after spinal cord injury

Individuals who survive spinal cord injury (SCI) suffer from autonomic cardiovascular abnormalities. In the able-bodied population, a dysfunctional autonomic profile is associated with increased risk for cardiovascular disease (CVD). Cardiovascular disease is a leading cause of death following SCI. Experimental data reveal exaggerated autonomic responses above the level of injury but little is known about what occurs below the injury and how the autonomic nervous system's (ANS) sympathetic and parasympathetic branches respond to stressors in an attempt to restore "sympathovagal balance." Therefore, the purpose of this study was to compare autonomic responses to stressors above and below the injury between individuals with SCI and able-bodied.; Fifteen healthy individuals participated in this study {lcub}7 with paraplegia (PARA); 8 able-bodied controls (CTL){rcub}. Subjects were studied in a laboratory session assessing cardiovascular reactivity to psychological and physiological stressors with continuous heart rate (HR), blood pressure (BP), and respiration monitoring. High frequency heart rate variability (HFHRV) and low frequency blood pressure variability (LFBPV) were used as estimates of parasympathetic activity and sympathetic vasomotor activity respectively. Simultaneous upper and lower body LFBPV measures were used to compare innervated and denervated compartments in the PARA group. Low frequency to high frequency ratio (LF: HF) and alpha index (alpha index) were used as estimates of sympathovagal balance and baroreceptor sensitivity (BRS) respectively.; During both psychological stressors, BRS was less for the PARA group compared to the CTL group: arithmetic {lcub}8.9 +/- 4.9 (ms/mmHg) vs. 18.4 +/- 8.6 (ms/mmHg){rcub} (P < 0.05) and Stroop {lcub}10.9 +/- 4.6 (ms/mmHg) vs. 16.5 +/- 5.1 (ms/mmHg){rcub} (P < 0.05). During the physiological stressor, parasympathetic responses were blunted {lcub}34.6 +/- 14.0 (nu) vs. 57.3 +/- 14.2 (nu){rcub} (P < 0.01) with a trend toward greater sympathetic responses in the lower body {lcub}60.7 +/- 15.1 (nu) vs. 47.0 +/- 13.6 (nu){rcub} (P = 0.09) for the PARA group compared to the CTL group.; These data add to a growing body of evidence that suggests low-level paraplegics demonstrate reduced parasympathetic modulation and impaired baroreflex activity with a trend toward augmented sympathetic modulation in response to stress compared to sedentary able-bodied individuals. These findings may have important clinical implications regarding CVD risk stratification for those with spinal cord injuries.