Diffusion and solubility factors in pulmonary inert gas exchanges

¹ Departments of Physiological Chemistry and Medicine, The Johns Hopkins School of Medicine and Medical Division, Baltimore City Hospitals, Baltimore, Maryland

Comparisons have been made in anesthetized dogs of the relative recoveries in arterial blood of pairs of inert gases injected as solutions into the right heart or as gas mixtures into the trachea. The gases differed in their diffusion coefficients or in their solubility. The pairs used were: tritium and Kr⁸⁵; ethylene-C¹⁴ and Xe¹³³. The ratios of the recoveries of the gases approached the ratios of their solubilities and not the ratios of their diffusion coefficients. The site of injection had no significant effect. The concentration-time curves remain proportional during the first passage through the lungs. Diffusion equilibrium is attained within the time of passage of blood through the alveolar capillary. There is no evidence of a diffusion limitation on the exchange of gases with diffusion coefficients as small as that of xenon. Solubility is the limiting factor.