Authors: Phillips AA, Ainslie P, Krassioukov AV, Warburton DE.
Significant cardiovascular and autonomic dysfunction occurs following a spinal cord injury (SCI). Two major conditions arising from autonomic dysfunction are orthostatic hypotension and autonomic dysreflexia (i.e., severe acute hypertension). Effective regulation of cerebral blood flow (CBF) is essential to offset the potential drastic alterations in cerebral perfusion pressure. In the context of orthostatic hypotension and autonomic dysreflexia, the purpose of this review is to examine systematically the mechanisms underlying effective CBF following SCI and propose future avenues for research. Although only 15 studies have examined CBF control in those with high level SCI (above the 6th thoracic level), it appears that CBF regulation is markedly altered in this population. Cerebrovascular function is comprised of three major mechanisms: 1) cerebral autoregulation, which can be broken down into static cerebral autoregulation (i.e., the relative change in CBF responding to steady-state changes in blood pressure) and dynamic cerebral autoregulation (i.e., relative change in CBF responding to rapid changes in blood pressure); 2) cerebrovascular reactivity to changes in PaCO2 (i.e. relative change in CBF in response to altered blood gas concentration); and 3) neurovascular coupling (i.e., the relative change in CBF in response to altered metabolic demand). While static cerebral autoregulation is appears to be well maintained in high level SCI, dynamic cerebral autoregulation, cerebrovascular reactivity, and neurovascular coupling appear to be markedly altered. Several adverse complications after high level SCI may mediate the changes in CBF regulation including: systemic endothelial dysfunction, sleep-apnea, dyslipidemia, decentralization of sympathetic control, and increased parasympathetic activity. Future studies are needed to describe whether altered CBF responses after SCI aid or impede orthostatic tolerance. Further, simultaneous evaluation of extra- and intra cranial CBF, combined with modern structural and functional imaging, would allow for a more comprehensive evaluation of CBF regulatory processes.
Full text and source: Mary Ann Liebert inc.
J Neurotrauma. 2013 Jun 13.