Inspiratory Maneuver Effects on Peak Expiratory Flow

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Abstract
We investigated the effects of two different inspiratory maneuvers (fast or slow) on the ability of normal subjects to generate peak expiratory flows (PEF) and maximal dynamic expiratory pressures (Pexp) during the performance of a forced vital capacity maneuver. During the fast maneuver (F), the subject inspired rapidly to total lung capacity (TLC) and immediately performed a maximal expiration, whereas in the slow maneuver (S) the subject inspired slowly to TLC, paused for 4-5 s at TLC and then performed a maximal expiration. Ten normal subjects performed a series of such maneuvers. In addition to PEF and Pexp, we measured EMG activity of abdominal (EMGabd) and rib cage muscles, and lung elastic recoil pressure (PesL). Overall, F yielded higher PEF values than S (by approximately 7%); in addition, PesL, Pexp, rate of rise of Pexp (dPexp/dt), and EMGabd were similarly higher with F than with S (p < 0.05 for all). Analysis of individual data showed that the intermaneuver differences in PEF were largely explained by differences in PesL, Pexp or dPexp/dt. Our data suggest that, in comparison with the slow maneuver, the fast maneuver induces a greater change in both the lung elastic recoil and expiratory muscle activation which account for differences in PEF between the two maneuvers. The enhanced expiratory muscle activation with the fast maneuver suggests a specific inspiratory-expiratory muscle interaction analogous to agonist-antagonist interactions described for skeletal muscles.