EFFECT OF GAS DENSITY AND VISCOSITY ON THE MAXIMAL EXPIRATORY FLOW-VOLUME RELATIONSHIP

Abstract

Variation of the viscosity and density of expired gas caused unique and consistent changes in the FV [flow-volume] curve. The lower part of the [alpha]-[beta] segment is most strongly influenced by gas viscosity, whereas the upper part is most strongly influenced by gas density. The results agree qualitatively with theoretical predictions based on a simple lung model. This model also predicts that the slope of the [alpha]-[beta] segment of the FV curve would vary inversely with the product of lung compli-ance and a lower airway "resistance constant." Published evidence supports this hypothesis. These considerations suggest that the slope of the FV curve should be a clinically useful index relating lung compliance to airway resistance.