Blood-gas equilibrium of carbon dioxide in lungs: a continuing controversy

This review presents the experimental evidence that has been published in recent years both against and in support of the occurrence of negative blood-gas CO2 partial pressure differences (delta PCO2) in lungs in rebreathing equilibrium and during steady-state gas exchange in hypercapnia. Although some sources of potential experimental error can be pointed out, the reasons for the remarkably pronounced disagreement between the experimental data of the different studies cannot be definitely identified. Since a consistent and reproducible occurrence of negative blood-gas delta PCO2 in lungs in gas-blood equilibrium is not convincingly proved, it appears to be justified to continue accepting the validity of the conventional concept of equal PCO2 in blood and gas in equilibrium. Because the issue is of considerable importance in the analysis and understanding of alveolar gas exchange, pertinent evidence is expected from future work.