Cardiovagal baroreflex gain relates to sensory but not neurological level of spinal cord injury

Abstract

The arterial baroreflex is a primary regulator of autonomic outflow to effectively regulate acute blood pressure changes. After a spinal cord injury (SCI), damage to the autonomic nervous system results in cardiovascular dysregulation. Higher level of injury results in greater loss of sympathetic control, while cardiac parasympathetic control remains intact regardless of injury level. Thus, it is possible that those with high level SCI, and hence extensive sympathetic disruption, will require greater cardiac parasympathetic compensation to control blood pressure. However, the effect of an SCI on cardiovagal baroreflex gain remains unclear. Baroreflex control of blood pressure in those with SCI has been reported to be greater, lesser, and no different compared to able‐bodied individuals. Moreover, the effect of injury level on baroreflex gain remains unclear as most studies that examined the effect of lesion level treated it as a discrete variable – high, usually cervical level lesions, and low, usually thoracic level lesions. Therefore, we assessed baroreflex sensitivity using the neck chamber techniques in those with SCI (N = 29) across a range of injury levels (neurological level of injury C1 – T10, sensory score C4 – S4/5), within 2 years of injury, and compared them to able‐bodied (N = 14). Injury level was assessed by both neurological level of injury and sensory score. We assessed baroreflex gain during 5 trials of 4 levels of neck chamber pressure (corresponding to −15, −25, −35, and −45 mmHg). We found no difference in baroreflex gain between those with SCI and able‐bodied (p>0.1). Neurological level of injury was not correlated to baroreflex gain, but sensory score and resting RR‐interval were (r = 0.47, p<0.01; r = 0.57, p<0.01). Multiple regression showed that both sensory score and resting RR‐interval were strongly predictive of baroreflex gain (r2 = 0.47, p<0.01): gain increased with lower sensory score and higher resting RR‐interval. Moreover, baroreflex gain was not different between those with high and low neurological level of injury; but higher in those with lower compared to higher sensory score (both p<0.01). Hence, sensory score is more predictive of baroreflex gain than the widely used neurological level of injury. This might be understood in the context of vagal‐sympathetic accentuated antagonism: those with high level injuries have the lowest likelihood of intact cardiac sympathetic innervation depressing cardiac vagal responsiveness.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.