Abstract
Thirteen healthy adults were exposed to isocapnic sustained hypoxia to compare the effect of hypoxia on regional cerebral oxygenation states and to investigate the relation hypoxic ventilatory response (HVR) and deoxygenation level of brain tissue. Regional cerebral oxygenation profiles were monitored with near-infrared spectroscopy applying the probes to scalp at front and back of head. Arterial oxygen saturation declined from 97.6±1.2% (mean±SD) to 80.7±3.1% and HVR was -0.29±0.16L/min/%. Oxyhemoglobin (O2Hb) decreased 4.77±2.53uM at forehead region and 1.45±4.83 uM at suboccipital region. On the other hand, deoxyhemoglobin (HHb) increased 6.45±2.29 uM at front of head and 3.87±3.18 uM at back of head. The changes of O2Hb and HHb at back of head were smaller than front of head, though there was not significant difference. Tissue oxygenation index (TOI=O2Hb/(O2Hb+HHb)×100 (%) ) also decreased 8.8±3.3% at front of head and 2.2±4.7% at back of head. The brain tissue oxygenation levels at suboccipital region was significantly higher than forehead region. HVR correlated significantly to decrease in TOI at suboccipital region, but not at forehead region. These results suggest that suboccipital region is protected from hypoxic risk and we may speculate that local oxygenation level of respiratory center act a potential influence on hypoxic chemosensitivity. [J Physiol Sci. 2008;58 Suppl:S118]
