Ventilatory Muscle Strength Six Months After Coronary Artery Bypass Grafting in Patients Submitted to Inspiratory Muscular Training Based on Anaerobioc Threshold: A Clinical Trial

Introduction  Coronary artery bypass grafting (CABG) surgery is associated with a decline in ventilatory muscle strength and lung function. Inspiratory muscle training (IMT) based on anaerobic threshold (AT) has been used to minimize the impact of CABG on these parameters, but the long-term impact is unknown.

Objective  To test the hypothesis that AT-based IMT improves inspiratory muscle strength and lung function even six months after CABG.

Methods  This is a randomized controlled clinical trial. In the preoperative period, maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), vital capacity (VC) and peak expiratory flow (PEF) rate were assessed. On the first postoperative day, patients were randomized into two groups: AT-based IMT (IMT-AT) (n=21) where the load was prescribed based on glycemic threshold and conventional IMT (IMT-C) (n=21), with load of 40% of MIP. Patients were trained during hospitalization until the day of discharge and were assessed at discharge and six months later. For within-group comparison, paired Student's t-test or Wilcoxon test was used, and independent Student's t-test or the Mann-Whitney test was used to analyze the different time points. A p<0.05 was considered significant.

Results  At six months after CABG surgery, statistical difference was found between the IMT-AT and the IMT-C groups in MIP (difference between the means of -5cmH2; 95% CI=- 8.21to-1.79) and VC (difference between the means of -2ml/kg;95%CI=-3.87to-0.13). No difference was found between groups in the other variables analyzed.

Conclusion  IMT-AT promoted greater recovery of inspiratory muscle strength and VC after six months of CABG when compared to conventional training.

Muscular Strength; Respiratory Muscles; Anaerobiosis; Breathing Exercises; Myocardial Revascularization/surgery; Hospital Discharge