Abstract
[Background/Purpose]
Impaired peripheral muscles and respiratory muscles reportedly deteriorate exercise intolerance in patients with chronic heart failure (CHF). Cardiac rehabilitation (CR) has been known to improve exercise tolerance and peripheral muscle function. However, the relationship between change in respiratory muscle strength and exercise tolerance is still unclear. We aimed to examine the impact of change in respiratory muscle strength following CR on exercise tolerance in CHF patients.
[Methods]
We studied 115 patients with compensated CHF who continued 5-month CR during hospitalization and after hospital discharge. Isometric quadriceps strength (QS) and maximal inspiratory pressure (PImax) were measured as peripheral muscle and respiratory muscle strength, respectively. We also measured peak oxygen uptake (VO2) during cardiopulmonary exercise test to assess exercise tolerance. All variables were measured at baseline and after the 5-month observation period. We compared the %changes of peak VO2 among 4 groups based on the median of %changes in QS and PImax: group A (%change QS <13.0% and %change PImax <12.6%), group B (%change QS ≥13.0% and %change PImax <12.6%), group C (%change QS <13.0% and %change PImax ≥12.6%) and group D (%change QS ≥13.0% and %change PImax ≥12.6%).
[Results]
In all the patients, %change peak VO2 showed significant positive correlations to %change QS (r = 0.324, P <0.001) and %change PImax (r = 0.352, P <0.001). The group D showed significantly higher %change peak VO2 as compared with group A even after adjustment for clinical confounding factors (mean difference: 10.693, 95% CI: 2.434 ‒ 18.952, P = 0.004).
[Discussion/Conclusion]
Increased respiratory muscle strength as well as peripheral muscle strength contributed to improvement of exercise tolerance following CR in CHF patients.
[Ethical consideration]
The study protocol was approved by the Ethics Committee of Kitasato University Hospital (KMEO B16-107).
