Ventilation-perfusion lines and gas exchange in liquid breathing: theory.

Alveolar exchange of a gas is governed by the ventilation-perfusion ratio (VA/Q) and the Ostwald partition coefficient for that species. We altered the Ostwald coefficients for O2 and CO2 by considering an animal breathing water or a fluorocarbon (FC-80) and studied the effects on gas exchange. Among our conclusions are the following. 1) When the ratio of the CO2 to O2 solubility in the inspirate exceeds the ratio of the O2 to the CO2 slope of the blood dissociation curve, as in water breathing, the VA/Q line becomes concave upward, and elements having a low VA/Q differ from each other more in terms of CO2 than of O2. 2) As the ratio of the CO2 to O2 solubility in the inspired medium increases, CO2 elimination becomes more dependent on perfusion. 3) At times, the same R will prevail in areas having different VA/Q values. 4) The alveolar-to-arterial O2 and CO2 differences resulting from a given VA/Q distribution do not depend on the O2 and CO2 solubility coefficients of the inspired medium, but on the inspired and mixed venous concentrations necessary to maintain adequate arterial gas levels in the presence of different inspired media.