Variability of the configuration of maximum expiratory flow-volume curves.
With a computer technique variability of the configuration of maximum expiratory flow-volume (MEFV) curves was studied in terms of slope ratio, SR. SR = dV/dV divided by V/V, where V is the instantaneous flow and V is the volume increment above residual volume.) Approximately four SR-V curves, each based on three to five smoothed and averaged MEFV curves, were derived for each of 20 normal subjects (aged 23-55 yr) on a single occasion, and again at least 1 wk later. Individual curves were largely reproducible, the maximum difference in SR at most volumes being 0.3-1 U, but frequently showed substantial yet reproducible fluctuations with volume. These corresponeded to hitherto unrecognized irregularities of maximum expiratory flow that may reflect sudden changes in the location of flow limitation.
D003201:Computers; D005540:Forced Expiratory Flow Rates; D014644:Genetic Variation; D006801:Humans; D008168:Lung / Q000502:physiology*; D008449:Maximal Expiratory Flow-Volume Curves