ALVEOLAR TO MIXED VENOUS PCO2 DIFFERENCE UNDER CONDITIONS OF NO GAS EXCHANGE

Under conditions in which no gas exchange occurs across the mammalian lung a steady state difference between alveolar and mixed venous PCO2 (ΔPCO2) was found, the alveolar being higher. The ΔPCO2 appeared to be related to the H+ and HCO3- concentrations of the mixed venous blood and to the pulmonary blood flow rate. A model is presented involving a negatively charged capillary membrane and coupling of viscous and diffusional flows allowing the reaction H+ + HCO3 H2CO3 H20 + CO2 to be shifted toward CO2 and causing the CO2 tension to be higher in the region of the capillary wall than in the bulk phase of capillary blood. Evidence, in support of the theoretical model, that steady state differences of the undissociated form of the weak acid DM0 can occur across the lung and that under certain conditions PCO2 differences can occur across charged artificial membranes, is also presented. © 1969.