Normal brain function is dependent on stable cerebral blood flow and autoregulation. Even when blood pressure fluctuates, cerebral blood flow is maintained. However, the microcirculation of the cortex has not been thoroughly investigated during rapidly induced hypotension. This study aimed to determine oxyhemoglobin (O2Hb) levels, indicative of cortical blood flow changes, during hypotension induced by thigh cuff release. Twenty-one healthy students participated in this study. Each participant was seated in a recumbent position in a quiet room for 5 minutes. Cuffs of digital tourniquets were placed on both thighs and inflated to 250 mmHg for 5 minutes. Following sudden deflation, the participants were observed for 5 minutes. Right (R) and left (L) prefrontal cortex (PFC) O2Hb levels were measured using a multichannel near-infrared spectroscopy system. Using photoplethysmography, the beat-to-beat mean arterial pressure (MAP) was recorded by finger pulse volume. O2Hb and MAP were averaged 1-second epoch throughout the study. MAP decreased from 95.2 ± 9.9 mmHg to 63.5±9.0 mmHg after cuff release. The time from release to the lowest O2Hb was significantly slower than the time from release to the lowest MAP (p < 0.01); time difference, 3.6 ± 2.2 s in the L-PFC and 3.5 ± 1.8 s in the R-PFC. These results suggest that hypotension induced by thigh cuff release decreases the O2Hb levels in both L and R-PFC with a 3.5–3.6 s delay.
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