A mathematical model for the simultaneous transport of gases to compute blood carboxyhaemoglobin build-up due to CO exposures: application to the end-expired breath technique

A time-dependent model has been formulated for the simultaneous transport of gases O2, CO2, CO and N2 in the lungs to compute carboxyhaemoglobin (COHb) build-up in the blood as a result of exposures to CO. The model takes into account the ventilation rate, cardiac output and interaction of gases in the blood. The nonlinear functions for representing O2, CO2 and CO dissociation curves have been used. The COHb levels computed from the solution of steady state equations of our model are in good agreement with those measured experimentally (Peterson and Stewart, 1970. Archives of Environmental Health 21, 165–170). The transient levels of CO in the alveolar air at the beginning of CO exposure are compared with those measured experimentally (Tikuisis et al., 1987. Journal of Applied Physiology 63, 820–827). The model is applied to analyze the end-expired breath method used for the prediction of blood COHb and it is found that the maximum partial pressure (P) of CO (PACO) with the predicted value of mean capillary partial pressure of oxygen (PO2) gives the accurate value of COHb level in the blood.