A consideration of density dependence of maximum expiratory flow.

Density dependence of maximum expiratory flow was considered in terms of equal pressure point and wave speed theories of flow limitation. It appears likely that the sites of flow-limitation, patterns of flow, and airway geometry differ with the density of the gas being expired. Because the conditions which determine maximum expiratory flow for helium-oxygen and for air differ, measurement of density dependence is of questionable value as a test for peripheral airways dysfunction.