Excretion-retention data of steady state gas exchange in tidal breathing. I. Dependency on the blood-gas partition coefficient.

The aim of this study is to investigate the steady state gas transfer properties of the lungs. These properties can be derived from excretion-retention (E-R) data of inert tracer gases that are infused intravenously. E = PE/Pv and R = Pa/Pv, where PE, Pa and Pv represent the partial pressures of the tracer gases in mixed expired gas, arterial blood and mixed venous blood, respectively. In this paper, special attention is paid to the effects of tidal breathing on E-R data sets of tracer gases with different blood-gas partition coefficients. To that end, E-R data sets have been simulated with a lung model that takes into account tidal breathing, the morphometric geometry of the airways, diffusion limited gas mixing and gas dissolved in superficial lung tissue. The simulated E-R data sets are compared with E-R data sets obtained from anaesthetized dogs. Both the simulated E-R data sets and most of the in vivo determined E-R data sets are incompatible with a model description of pulmonary gas transfer with parallel placed compartments with different ventilation-perfusion ratios. Concerning the simulated E-R data sets, this incompatibility is due to the large buffering capacity of lung tissue for highly soluble gases in combination with the within-breath partial pressure oscillations in the airways.