Baroreflex function after spinal cord injury

Significant cardiovascular and autonomic dysfunction occurs after spinal cord injury (SCI). It is now recognized that cardiovascular disease is a leading cause of morbidity and mortality in SCI. Patients with SCI may also suffer severe orthostatic hypotension and autonomic dysreflexia. Baroreflex sensitivity (i.e., the capability of the autonomic nervous system to detect and respond effectively to acute changes in blood pressure) has been recognized as having predictive value for cardiovascular events, as well as playing a role in effective short-term regulation of blood pressure. The purpose of this article is to review the mechanisms underlying effective baroreflex function, describe the techniques available to measure baroreflex function, and summarize the literature examining baroreflex function after SCI. Finally, we describe the potential mechanisms responsible for baroreflex dysfunction after SCI and propose future avenues for research. Briefly, although cardiovagal baroreflex function is reduced markedly in those with high-level lesions (above the T6 level), the reduction appears to be partially mitigated in those with low-level lesions. Although no studies have examined the sympathetic arm of the baroreflex in those with SCI, despite this being arguably more important to blood pressure regulation than the cardiovagal baroreflex, nine articles have examined sympathetic responses to orthostatic challenges; these findings are reviewed. Future studies are needed to describe whether dysfunctional baroreflex sensitivity after SCI is due to arterial stiffening or a neural component. Further, measurement of forearm vascular conductance and/or muscle sympathetic nerve activity is required to directly evaluate the sensitivity of the sympathetic arm of the baroreflex in those with SCI.