Contribution of lung function to exercise capacity in patients with chronic heart failure

Background: The importance of exercise capacity as an indicator of prognosis in patients with heart disease is well recognized. However, factors contributing to exercise limitation in such patients have not been fully characterized and in particular, the role of lung function in determining exercise capacity has not been extensively investigated. Objective: To examine the extent to which pulmonary function and respiratory muscle strength indices predict exercise performance in patients with moderate to severe heart failure. Methods: Fifty stable heart failure patients underwent a maximal symptom-limited cardiopulmonary exercise test on a treadmill to determine maximum oxygen consumption (VO2max), pulmonary function tests and maximum inspiratory (PImax) and expiratory (PEmax) pressure measurement. Results: In univariate analysis, VO2max correlated with forced vital capacity (r = 0.35, p = 0.01), forced expiratory volume in 1 s (r = 0.45, p = 0.001), FEV1/FVC ratio (r = 0.37, p = 0.009), maximal midexpiratory flow rate (FEF25-75, r = 0.47, p < 0.001), and PImax (r = 0.46, p = 0.001), but not with total lung capacity, diffusion capacity or PEmax. In stepwise linear regression analysis, FEF25-75 and PImax were shown to be independently related to VO2max, with a combined r and r(2) value of 0.56 and 0.32, respectively. Conclusions: Lung function indices overall accounted for only approximately 30% of the variance in maximum exercise capacity observed in heart failure patients. The mechanism(s) by which these variables could set exercise limitation in heart failure awaits further investigation.