Changes in cerebral oxygenation and blood flow during LBNP in spinal cord-injured individuals

Spinal cord-injured (SCI) individuals, having a sympathetic nervous system lesion, experience hypotension during sitting and standing. Surprisingly, t hey experience few syncopal events. This suggests adaptations in cerebrovas cular regulation. Therefore, changes in systemic circulation, cerebral bloo d flow, and oxygenation in eight SCI individuals were compared with eight a ble-bodied (AB) individuals. Systemic circulation was manipulated by lower body negative pressure at several levels down to -60 mmHg. At each level, w e measured steady-state blood pressure, changes in cerebral blood velocity with transcranial Doppler, and cerebral oxygenation using near-infrared spe ctroscopy. We found that mean arterial pressure decreased significantly in SCI but not in AB individuals, in accordance with the sympathetic impairmen t in the SCI group. Cerebral blood flow velocity decreased during orthostat ic stress in both groups, but this decrease was significantly greater in SC I individuals. Cerebral oxygenation decreased in both groups, with a tenden cy to a greater decrease in SCI individuals. Thus present data do not suppo rt an advantageous mechanism during orthostatic stress in the cerebrovascul ar regulation of SCI individuals.