Pulmonary gas exchange during altered density gas breathing

Abstract

The alveolar-arterial O2 partial pressure difference (PAO2 - PaO2) decreased as carrier-gas density increases. This study was designed to confirm or deny the hypothesis that the improvement in O2 exchange is a result of density-dependent changes in the alveolar ventilation-perfusion (.ovrhdot.VA/.ovrhdot.Q) distribution. On changing from heliox breathing to air breathing, there was an improvement in O2 exchange along with a slight worsening of .ovrhdot.VA/.ovrhdot.Q distribution [in dogs]. Changes in .ovrhdot.VA/.ovrhdot.Q distribution due to altered carrier-gas density apparently are not responsible for changes in O2 exchange. A possible explanation is related to the interaction of diffusion and convection on inspiration, which may cause inspired gas distribution to be different from overall ventilation distribution. Gas exchange properties of gases eliminated from the blood and exhaled apparently are not necessarily symmetrical to the properties of gases inhaled and taken up by the blood.