Physioligal response to hypoxia exposure at rest. Ventilatory (a) and Alveolar PO2 (b) response to step change from room air to 9% O2 for 10 minutes, followed by a return to room air. Alveolar CO2 is held constant via external supply (isocapnic hypoxia). Data from Reynolds ; experimental data presented as circles, model prediction is a solid line. Experimental alveolar O2 is approximated to be equal to end-tidal O2.