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 o f gases O-2, CO2, CO and N-2 in the lungs to compute carboxyhaemoglobin (CO Hb) build-up in the blood as a result of exposures to CO. The model takes i nto account the ventilation rate, cardiac output and interaction of gases i n the blood. The nonlinear functions for representing O-2, CO2 and CO disso ciation curves have been used. The COHb levels computed from the solution o f steady state equations of our model an in good agreement with those measu red experimentally (Peterson and Stewart, 1970. Archives of Environmental H ealth 21, 165-170). The transient levels of CO in the alveolar air at the b eginning of CO exposure are compared with those measured experimentally (Ti kuisis et at., 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 oxyge n (PO2) gives the accurate value of COHb level in the blood. (C) 1999 Elsev ier Science Ltd. All rights reserved.