Blood flow reserve: effects after training with heavy inspiratory exercises: a randomized control trial (BREATHE study)

Abstract Background Inspiratory muscle strength training (IMST) is a resistance-based exercise that strengthens respiratory muscles and may favorably affect vascular health. Purpose We investigated whether high-intensity IMST improves quantitative positron emission tomography (PET) measures of myocardial blood flow (MBF) and flow reserve (MFR) in patients with and without coronary artery disease (CAD). Methods In this single-center, double-blinded, randomized controlled trial, adults were assigned to home-based low- or high-intensity IMST for 6 weeks. Primary outcomes were changes in PET-derived stress MBF, and MFR, analyzed by intention-to-treat. Secondary outcomes included inspiratory muscle strength (PImax), relative perfusion scores, global rest MBF, rest/stress coronary vascular resistance (CVR), and patient-reported health status. Results Forty participants were randomized (low-intensity n=20; high-intensity n=20) (Figure). IMST increased in MFR in both groups (Table). However, there were no significant differences between groups in: stress MBF (−0.08 mL/min/g; 95% CI −0.45 to 0.29; p=0.664) or MFR (−0.14; 95% CI −0.59 to 0.30; p=0.511). PImax tended to improve more with high-intensity IMST (adjusted difference +8.6 cmH2O; 95% CI −0.46 to 17.65; p=0.062). EQ-5D-5L index favored low-intensity training (adjusted difference −0.08; 95% CI −0.15 to −0.01; p=0.023). Conclusions Over 6 weeks, high-intensity IMST did not improve PET-derived stress MBF or MFR compared with low-intensity IMST. Modest within-arm gains in MFR support the need for larger trials to determine whether IMST can meaningfully affect coronary circulation.For image description, please refer to the figure legend and surrounding text. Table. Primary and secondary outcomesFor image description, please refer to the figure legend and surrounding text.