title: Time dependence of maximum flow as an index of nonuniform emptying.
abstract: Nonhomogeneous lungs are predicted to exhibit time dependence of maximal expiratory flow (Vmax): faster regions would contribute more flow early in the expiration, whatever the initial volume, resulting in different Vmax at a given total lung volume, depending on how long flow limitation has been operating. To test this concept a new technique was developed that permits accurate superimposition of Vmax data over small volume intervals. When quick-release interrupted partial curves with similar volume history but different volume of initiation were compared over their late common-volume segments, the volume-history effects could be differentiated from time dependence of the Vmax. Such time dependence was found in 7 of 7 bronchitics, 3 of 5 smokers, and 0 of 14 nonsmokers tested. We conclude that the emptying during the forced expirations is not uniform even in mild disease states and the time dependence of Vmax is a sensitive test of lung inhomogeneity.
mesh_terms: D000328:Adult; D000368:Aged; D001991:Bronchitis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008449:Maximal Expiratory Flow-Volume Curves; D008875:Middle Aged; D010991:Plethysmography / Q000379:methods*; D012119:Respiration; D012907:Smoking / Q000503:physiopathology*; D013997:Time Factors