Respiratory muscle endurance in heart failure--the effect of clinical severity.

In chronic heart failure there is no single explanation for reduced effort tolerance. Recently, abnormalities of skeletal muscles, which include respiratory muscles, have been described in cases of chronic heart failure. The aim of this study was to investigate the effect of clinical severity of heart failure, measured by means of the Boston score, on respiratory muscle performance (strength and endurance).

Methods: Using the Boston score, we compared 20 patients with chronic heart failure and low ejection fraction to 20 normal people, measuring maximal inspiratory mouth pressures (MIPs), maximal expiratory mouth pressures (MEPs) and endurance. Endurance was measured by repeated maximal static contractions of MIP and MEP as well as maximal voluntary ventilation (MVV).

Results: Inspiratory strength (MIP 75 +/- 34 cmH2O) but not expiratory strength (MEP 116.9 +/- 43.7 cmH2O) were reduced in heart failure patients, compared with controls (MIP 96.2 +/- 29.2, MEP 120.4 +/- 31 cmH2O). Endurance of inspiratory muscles was significantly reduced (P < 0.007) but not of expiratory muscles (P > 0.25). Clinical severity did not correlate with reduced endurance.

Conclusions: Endurance of the inspiratory muscles was reduced in chronic heart failure unrelated to clinical severity.