Inspiratory Muscle Strength as a Determinant of Functional Capacity Early After Coronary Artery Bypass Graft Surgery

Abstract 

Stein R, Maia CP, Silveira AD, Chiappa GR, Myers J, Ribeiro JP. Inspiratory muscle strength as a determinant of functional capacity early after coronary artery bypass graft surgery.

Objective

To evaluate the effects of a 6-day postoperative in-hospital cardiopulmonary rehabilitation program on inspiratory muscle strength and its potential association with improved functional capacity after coronary artery bypass graft (CABG) surgery.

Design

Prospective, randomized controlled trial.

Setting

Tertiary public hospital in Brazil.

Participants

Men (N=20) after CABG were randomized to cardiopulmonary rehabilitation (n=10; age, 64±8y) or to usual care (n=10; age, 63±7y).

Interventions

Ten subjects underwent a 6-day postoperative in-hospital program, which included the use of expiratory positive airway pressure mask and bronchial hygiene techniques, coupled with progressive distance walking and calisthenics as well as cardiopulmonary training. Ten controls were followed by their own physicians and received routine nursing assistance but were not exposed to any specific respiratory or motor physical intervention.

Main Outcome Measures

Maximal inspiratory and expiratory pressure were measured by a pressure transducer, and the highest pressure obtained in 6 measurements was used for analysis (before surgery, and 7 and 30d after surgery). The six-minute walk test (6MWT) was performed 7 days after surgery, and maximal cardiopulmonary exercise testing was performed 30 days after CABG.

Results

After randomization, clinical and functional characteristics were similar in the 2 groups. Rehabilitation resulted in maintenance of maximal inspiratory pressure (PImax) measured at 7 and 30 days postoperatively, respectively (from 68±19% at baseline to 58±22% and to 61±22% predicted), while it was significantly reduced in the control group. 6MWT distance was longer 7 days after CABG in rehabilitation subjects (416±78m) than controls (323±67m). Peak oxygen uptake (Vo₂peak) at day 30 was also higher (28%) in the rehabilitation group and was correlated with PImax (r=.90).

Conclusions

A 6-day rehabilitation program attenuated the postoperative reduction in respiratory muscle strength and also improved the recovery of functional capacity after CABG. The correlation between PImax and Vo₂peak during the late postoperative period suggests that inspiratory muscle strength is an important determinant of functional capacity after CABG.

Key Words: Exercise, Rehabilitation

List of Abbreviations: CABG, coronary artery bypass graft, CPET, cardiopulmonary exercise testing, EPAP, expiratory positive airway pressure, FEV₁, forced expiratory volume in 1 second, FVC, forced vital capacity, PEmax, maximal expiratory pressure, PImax, maximal inspiratory pressure, 6MWT, six-minute walk test, Vo₂peak, peak oxygen uptake