A two-compartment model of blood acid-base state at constant or variable temperature.

Information available in the literature on the acid-base properties of oxygenated mammalian blood at a constant or variable temperature was put together into a synthetic model; this also aimed at reconciling the single compartment descriptions of acid-base vs temperature relationships in closed ('anaerobic') conditions with the standard dual compartment analysis of isothermal titrations. Experimental values for the concentrations of blood constituents, buffer dissociation constants, etc. were introduced into the set of physicochemical equations governing the steady-state distribution of CO2, electrolytes and water between plasma and red cells. Design of the model was such as to permit monitoring of all variables (e.g. concentrations) throughout any simulated acid-base transformation. A fairly good fit was obtained between model predictions and experimentally-determined relationships or quantities not introduced into the model from the start. Applications to variable temperature titration and to the effects of changes in blood composition or osmolality are presented. The latter underline the implicit assumptions made by neglecting such variables in current presentations of blood acid-base state.