The best peak expiratory flow is flow-limited and effort-independent in normal subjects

Recently, it has been suggested that peak expiratory flow (PEF) may be determined by the wave speed flow-limiting mechanism. In six normal male subjects (age = 33 +/- 8 years) performing expiratory forced vital capacity (FVC) maneuvers, a negative expiratory pressure (NEP) of -10 cm H2O was randomly applied at the beginning of maximal expiration to assess changes in PEF as compared with baseline. During FVC maneuvers, the expiratory effort was measured by changes in esophageal pressure (Pes), as either peak expiratory Pes-Pes at end expiratory lung volume (DeltaPes(peak)) or maximal rate of rise of Pes (dPes/dt(max)). In each experimental condition, at least three FVC maneuvers with comparable expiratory effort were selected for analysis for each subject. With similar DeltaPes(peak) (107.2 +/- 34.9 versus 111.7 +/- 40.5 cm H2O) and dPes/dt(max) (1181 +/- 518 versus 1177 +/- 546 cm H2O/second) PEF amounted to 10.84 +/- 1.08 L/second and to 10.82 +/- 1.03 L/second with and without NEP, respectively. These data show that PEF obtained by normal subjects to the best of their abilities (best PEF) does not increase with NEP and indicate that the best PEF is a flow-limited and effort-independent parameter, reflecting only lung and airways mechanics as the other subsequent maximal expiratory flows achieved during the FVC maneuver.