Assessment of Stratified Inhomogeneity Within Distal Alveolar Space with Respect to Oxygen Uptake
The persistence of longitudinal partial pressure gradients inside the alveolar space during the respiratory cycle, i.e. axial gas mixing deficit, is usually referred to as stratified innomogeneity or stratification. The question whether or not there is a limitation of oxygen transport by stratified inhomogeneity in distal alveolar space has been studied in several experimental and theoretical approaches, but remains a controversial issue. Whereas the results of most theoretical studies (Rauwerda, 1946; Cumming et al., 1971; Paiva, 1973; Pack et al., 1977) suggest that the influence of stratification on gas exchange in lungs can be considered negligible, in some experimental investigations (Sikand et al., 1976; Hlastala et al., 1982), partial pressure gradients within alveolar space were estimated to be significantly higher than zero, indicating a relative importance of stratified inhomogeneity. For quantifying stratificational effects, Okubo and Piiper (1974) introduced a compartment model of the lung including a “stratificational conductance”. There is evidence from all investigations performed up to now that such a stratificational conductance is considerably higher than the pulmonary diffusing capacity of oxygen. A major problem in determining a stratificational conductance is seperating it from the much lower conductances brought about by ventilation, diffusion and blood flow.
KeywordsDioxide Helium Carbon Monoxide Stratification Dura
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