Oxygen toxicity as a function of time and PO2.

The quantification of O2 toxicity as a function of exposure time (t) and PO2 has been based mainly on the empirical rectangular hyperbola. The non-linear response of the O2-damaged physiological variable (DMG) as a function of time at constant PO2 can be related to the dependence of dDMG/dt on the DMG. The kinetics of the O2-derived chemical species suggests a power relationship between the DMG and PO2 rather than a linear relationship. The combination of time and PO2 considerations suggests two models: 1) DMG = a(ebt - 1) PO2c and 2) DMG = a.tbPO2c, where a, b and c are constant. Non-linear regression of the different parameters of O2 toxicity showed a preference for model 2, with b = 2. Possible mechanisms underlying the kinetics of O2 toxicity and the use of the equation for its prediction are discussed.