Inspiratory Muscle Strength After Threshold Inspiratory Muscle Training Versus Incentive Spirometry in Patients Undergoing Coronary Artery Bypass Grafting: A Randomized Controlled Trial

Abstract

Respiratory dysfunction after coronary artery bypass grafting (CABG) may reduce inspiratory muscle strength and affect health-related quality of life. This single-center, assessor-blinded randomized controlled trial compared threshold inspiratory muscle training (IMT) with incentive spirometry (IS) in 30 adults undergoing elective CABG. Participants were randomized 1:1 to IMT or IS. IMT was performed for five preoperative days and IS for two days; both interventions were resumed after extubation and continued until discharge. Preoperative Strength Index (S-Index) was analyzed using ANCOVA adjusted for baseline values, while SF-12 Physical and Mental Component Summary scores were assessed at baseline, discharge, and 30 days. After baseline adjustment, preoperative S-Index was significantly higher with IMT than IS (85.85 vs 75.48 cmH₂O; adjusted mean difference 10.37 cmH₂O, 95% CI 2.52–18.22; p=0.012; partial η²=0.214). PCS-12 and MCS-12 changed significantly over time (both p<0.001), but time-by-group interactions were not significant (p=0.621 and p=0.174, respectively). Hospital stay (9.60 vs 11.93 days; p=0.004) and ICU stay [median 2.0 vs 4.0 days; p=0.027] were shorter with IMT, although these were exploratory outcomes. Threshold IMT produced greater short-term preoperative improvement in dynamic inspiratory muscle strength than IS, while health-related quality-of-life trajectories did not differ between groups.