Mathematical model for the exchange of gases in the lungs with special reference to carbon monoxide.

A mathematical model has been formulated for the simultaneous exchange of gases O2, CO2, CO and N2 in the lungs. The model takes into account the physiological parameters, such as ventilation rate, diffusing capacity of the lungs, cardiac output, total volume of blood in the body and the interaction of gases in the blood. The nonlinear functions for representing O2, CO2 and CO dissociation curves have been used. The results predicted from the model are in good agreement with those based on the ventilation/perfusion relationships. The COHb build-up in the blood, computed from the model as a function of exposure time, is in good agreement with the experimental values. The consideration of capillary blood pO2 as a constant value, instead of an independent variable, is shown to introduce a maximum error of 0.25 per cent in the blood COHb. The model is applied to analyse the COHb levels at high altitude.