Effects of the Buteyko breathing technique on sleep quality, fatigue, and oxygen saturation in patients with acute coronary syndrome: a randomized controlled trial

Introduction Acute coronary syndrome is frequently accompanied by sleep disturbance, fatigue, and hypoxemia; this study aimed to evaluate the effects of Buteyko breathing on these clinical outcomes. Methods This randomized triple-blind clinical trial was conducted in two Iranian hospitals among 92 adults with acute coronary syndrome. Participants were randomly assigned to Buteyko breathing or diaphragmatic breathing for six weeks alongside routine care. Primary outcomes included sleep quality (PSQI), fatigue (MFI-20), and peripheral oxygen saturation (SpO₂), measured at baseline and post-intervention. Between- and within-group comparisons were performed using t-tests with effect-size estimation. ANCOVA was conducted to adjust for baseline characteristics. Results Ninety patients were randomized equally to intervention and control groups with comparable baseline characteristics. Both groups demonstrated significant within-group improvements in PSQI (intervention − 0.82, control − 1.16), MFI-20 fatigue scores (− 2.44 vs. − 3.96), and SpO₂ (+ 0.40 vs. + 0.42; all p < 0.05). However, post-intervention between-group comparisons revealed no significant differences for PSQI (MD = − 0.36, 95% CI − 1.14 to 0.43; p = 0.37), fatigue (MD = 0.40, − 3.47 to 4.27; p = 0.84), or SpO₂ (MD = 0.32, − 0.15 to 0.80; p = 0.18). Effect sizes were uniformly small (Cohen’s d ≤ 0.28). ANCOVA showed no group difference in fatigue (F(1,87) = 0.50, p = 0.483); baseline fatigue significant; R²=0.27, η²=0.006. Conclusion Although modest improvements occurred in sleep, fatigue, and oxygenation, changes were clinically insignificant with no between-group differences; thus, the intervention cannot be recommended over standard evidence-based care. Trial registration IRCT20250607066101N1, Date: 06.15.2025.