Am. J. Respir. Crit. Care Med., Volume 159, Number 3, March 1999, 892-895

Effects of Different Expiratory Maneuvers on Inspiratory Muscle Force Output

SPYROS ZAKYNTHINOS, THEODOROS VASSILAKOPOULOS, ANTONIOS MAVROMMATIS, CHARIS ROUSSOS, and GEORGE E. TZELEPIS

Pulmonary Services and Intensive Care Units, Evangelismos Hospital and Onassis Cardiac Center; University of Athens Medical School, Athens, Greece; and Wayne State University, Detroit, Michigan

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 generate maximal inspiratory pressures and maximal inspiratory flows near residual volume (RV). With the F maneuver, the subject exhaled rapidly to RV and immediately performed a maximal inspiratory effort, whereas with the S maneuver the subject exhaled slowly to RV, paused for 4 to 6 s at RV, and then inspired forcefully. Maximal static inspiratory pressure against an occluded airway (PI_max), and maximal dynamic inspiratory pressure (PI_dyn) and maximal inspiratory flow ( I_max) with no added resistance, as well as the electromyographic activity of the parasternal muscles, were measured during each maneuver. Both maneuvers were initiated from TLC and were performed randomly. In comparison with the S maneuver, the F maneuver yielded values of higher (mean ± SE) PI_max (148 ± 5 cm H₂O versus 135 ± 7 cm H₂O, p < 0.05), PI_dyn (33 ± 2 cm H₂O versus 28 ± 2 cm H₂O, p < 0.05), and I_max (12.3 ± 0.4 L/s versus 11.4 ± 0.6 L/s, p < 0.05). In addition, the rate of rise of PI_max, the rate of rise of PI_dyn, and the integrated peak electromyographic activity of the parasternal muscles were significantly greater with the F than with the S maneuver, suggesting greater inspiratory muscle (IM) activation. The enhanced IM activation may be related to a specific inspiratory-expiratory muscle interaction similar to the agonist-antagonist interactions described for a pair of skeletal muscles.