Velocity of CO2 exchange in blood.

The velocity of CO2 exchange in blood is dependent upon a number of interrelated processes, including chemical reactions, diffusion, and con· vective mixing. Both parallel and serial processes are involved, and alteration of one branch of this complex network (Figure I) has repercussions through· out the entire system. Hence, there necessarily is no set velocity of CO2 exchange in blood; the rate of carbon dioxide movement is a function of many variables. From an experimental standpoint, it is not possible to investigate all these factors simultaneously. The usual approach is to study the role of a single variable under conditions in which the other parameters are held relatively constant. Extrapolation of these data to physiological circumstances is accomplished using mathematical models of gas exchange. This approach has led to a substantial improvement in our understanding of CO2 exchange (32) compared to that of two decades previously (40). The major drawback of the synthesis of individual processes in computational models is the potential to fail to include a critical, but unknown, process in the theoretical construct.