CEREBROCORTICAL OXYGENATION AND VENTILATORY RESPONSE DURING SUSTAINED HYPOXIA

Cerebrocortical oxygenation was monitored in 8 healthy adults during exposure to sustained isocapnic hypoxia. Subjects were maintained at an arterial oxygen saturation (SaO) of 80% for 12 min with a rebreathing circuit while cerebrocortical oxygenation was assessed non-invasively using near-infrared (NIR) spectroscopy to measure changes in the oxidation state of cytochrome a,a3 (Cyt a,a3) and changes in cortical blood volume (tBV). During sustained hypoxia, subjects demonstrated a biphasic ventilatory response. The mean ventilation (V̇E) peak response was 255% of baseline at an average of 3.4±0.5 min (mean±SE) after the initiation of hypoxia. A subsequent significant attenuation of V̇E to 163% (P<0.05) of baseline occurred after an additional 8.6 min. NIR monitoring revealed a significant (P<0.05) decrease in oxidized Cyt a,a3 as well as a significant (P<0.05) increase in tissue blood volume (tBV) at the time of peak V̇E. Both Cyt a, a3 and tBV remained stable during the remainder of the hypoxic period, despite attenuation of V̇E during sustained hypoxia. The data suggest that cerebrocortical oxygenation and blood flow remain constant when the ventilatory attenuation is observed during sustained hypoxia. © 1990.