Assessment of stratified inhomogeneity within distal alveolar space with respect to oxygen uptake

Investigations were made as to whether or not there is a limitation of oxygen transport by stratified inhomogeneity in distal alveolar gas. Experiments were performed on 2 subjects. Single breath manoeuvres were carried out with similar phases of inspiration and expiration but varying breath-hold times. The inspiratory gas contained a small amount of oxygen labeled carbon dioxide, C18O2. End-expiratory gas was analysed on its residual C18O2 partial pressure by mass spectrometry. For evaluating a stratificational conductance, compartment model analysis was applied on the breath-hold data. Stratificational conductance has been found to be higher than 553 ml.mmHg-1. min-1. When transferred to oxygen transport, this means that stratificational conductance is more than 10 times higher than oxygen diffusing capacity. It can be concluded that (i) stratified inhomogeneity in distal alveolar space does not exhibit a limiting factor of oxygen uptake in lungs, (ii) a contribution of stratificational effects to sloping alveolar plateau is expected to be of minor importance.