Influence of airway geometry on expiratory flow limitation and density dependence.

In a study of individuals of the same sex and similar age and size, between subject variability was noted in lung recoil, lung size, density dependence of maximum expiratory flow, tracheal cross-sectional area, and anatomic dead space. No significance was observed in the relationships to one another of lung size or either estimate of airway size, nor did the magnitude of the change in flow with changes in gas density show a consistent relationship to any of the size variables. The results indicate that there is a dissociation between tracheal dimensions and anatomic dead space as well as between airway size and lung size, suggesting that dysanapsis is a general phenomenon. This introduces additional sources of interindividual variability of maximum expiratory flow and measurements of density dependence of flow.