In the previous grant period, discoveries of CO2 kinetics during non-steady state revealed significant gaps in understanding of O2 kinetics. To this end, a 5-compartment lung model of gas kinetics in the body during non-steady state has been developed, that incorporates complex interactions between O2 and CO2 in the lung, blood, and tissues. This computer model was used to formulate the following hypotheses, and will elucidate mechanisms underlying the subsequent measured data in anesthetized patients.