An improved algorithm and a computer program for the analysis of capillary gas exchange.

In most models of capillary gas exchange, the binding curves for O2 and CO2 are represented by simple analytical expressions, and the interactions among the haemoglobin ligands are either neglected or are assigned fixed values independent of PO2, PCO2, pH and red cell DPG. We here present algorithms and a computer program in which the binding curves are described in a near-rigorous manner. This enables solution of a set of typical equations for a unit of blood which undergoes gaseous and proton exchange. We have applied the algorithms to the problem of calculating pulmonary blood flow from the gaseous exchange in the lung by the single-breath method of Kim et al. (1966), where the CO2 binding curves of arterial and mixed venous blood are approximated by straight lines. The application of the algorithms shows that this approximation introduces significant errors in the calculated pulmonary blood flow.