Effects of different expiratory maneuvers on inspiratory muscle force output

We assessed the effects of two different expiratory maneuvers (fast [F] or slow [S]) on the ability of normal subjects (n = 12, age 35 +/- 6 yr) to ge nerate maximal inspiratory pressures and maximal inspiratory flows near res idual volume (RV). With the F maneuver, the subject exhaled rapidly to RV a nd immediately performed a maximal inspiratory effort, whereas with the S m aneuver the subject exhaled slowly to RV, paused for 4 to 6 s at RV,and the n inspired forcefully. Maximal static inspiratory pressure against an occlu ded airway (PImax) and maximal dynamic inspiratory pressure (PIdyn) and max imal inspiratory flow ((V) over dot I-max) with no added resistance, as wel l as the electromyographic activity of the parasternal muscles, were measur ed during each maneuver. Both maneuvers were initiated from TLC and were pe rformed randomly. In comparison with the S maneuver, the F maneuver yielded values of higher (mean +/- SE) PImax (148 +/- 5 cm H2O versus 135 +/- 7 cm H2O, p < 0.05), PIdyn (33 +/- 2 cm H2O versus 28 +/- 2 cm H2O, p < 0.05), and (V) over dot I-max (12.3 +/- 0.4 L/s versus 114 +/- 0.6 Vs, p < 0.05). In addition, the rate of rise of PImax, the rate of rise of PIdyn, and the integrated peak electromyographic activity of the parasternal muscles were significantly greater with the F than with the S maneuver, suggesting great er inspiratory muscle (IM) activation. The enhanced IM activation may be re lated to a specific inspiratory-expiratory muscle interaction similar to th e agonist-antagonist interactions described for a pair of skeletal muscles.