Cerebrovascular Responses to Orthostatic Stress after Spinal Cord Injury

Orthostatic hypotension (OH) is a debilitating condition affecting individuals with spinal cord injury (SCI) that may be associated with cerebral hypoperfusion. We studied orthostatic cerebral control in individuals with SCI with different levels and severities of injury to spinal cardiovascular autonomic pathways. We measured beat-to-beat cardiovascular and cerebrovascular responses to passive orthostatic stress in 16 controls and 26 subjects with chronic SCI. Cerebrovascular control was assessed from diastolic cerebral blood flow velocity (CBFVD), and indices of static and dynamic cerebral autoregulation. Severity of autonomic injury was inferred from spectral analyses of systolic arterial pressure, and supine plasma noradrenaline concentrations. Symptoms of OH were evaluated using questionnaires. CBFVD decreased during orthostasis only in individuals with autonomically complete injuries above T6. Orthostatic CBFVD was significantly correlated (p < 0.05) with the severity of autonomic injury. Individuals with injuries above T6 had impaired dynamic autoregulation (p < 0.05) compared to controls, and this was correlated (p < 0.05) with the severity of autonomic injury. Individuals with autonomically complete SCI reported increased severity of symptoms relative to controls (p < 0.05). Symptom severity was correlated with the efficacy of dynamic autoregulation. During orthostatic stress, SCI individuals have impaired cerebrovascular control that is related to the level and severity of autonomic injury.