Effects of inspiratory muscle training for urban patients with chronic heart failure: a randomized controlled trial

Background In chronic heart failure (CHF), respiratory muscle weakness is a key driver of dyspnoea and exercise intolerance. Despite being an independent predictor of adverse clinical outcomes, inspiratory muscle training (IMT) remains underutilised in urban cardiac rehabilitation settings. Purpose To evaluate the efficacy of home-based IMT in enhancing respiratory muscle strength, functional capacity, and quality of life among urban Thai patients with stable CHF Methods This single-blinded randomised controlled trial (RCT) enrolled 40 stable CHF patients (mean age 62.1±12.7 years; 80% male; all NYHA class II). Participants were randomised (1:1) to either 8 weeks of standard cardiac rehabilitation (CR) plus IMT (using a threshold device calibrated at 30% of maximal inspiratory pressure [MIP]) or standard CR alone. Primary outcomes were changes in MIP and maximal expiratory pressure (MEP). Secondary outcomes included 6-minute walk distance (6MWT), EQ-5D-5L, NT-proBNP, and echocardiographic parameters (LVEF, E/E′) at 5 months. Results At 8 weeks, the IMT group showed significantly greater improvement in MIP compared to controls (median change +9.7 [IQR 2.8 to 18.3] vs -2.3 [-21.3 to 10.3] cmH2O; p = 0.033). A positive trend was observed in MEP (median change +6.3 vs 0.7 cmH2O; p = 0.051) and 6MWT. At 5 months, the IMT group demonstrated a favourable shift in diastolic function (median E/E′ 10.9 vs 15.5; p = 0.059). No significant differences were found in LVEF or NT-proBNP, and no adverse events were reported. Conclusion Home-based IMT is safe and effectively enhances respiratory muscle strength and potentially improves diastolic function in urban Thai CHF patients. These findings support the strategic integration of IMT into multidisciplinary cardiac rehabilitation frameworks to optimise functional recovery.