Alveolar-capillary membrane conductance is the best pulmonary function correlate of exercise ventilation efficiency in heart failure patients
In heart failure (HF), changes in lung mechanics and gas diffusion are limiting factors to exercise. Their contribution to an increased exercise ventilation to CO2 production (VE/VCO2) slope is undefined. A total of 67 stable HF patients underwent cardiopulmonary exercise and pulmonary function tests, including forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), maximal voluntary ventilation (MVV), total lung capacity (TLC) and alveolar diffusing capacity with its subcomponents (alveolar-capillary membrane conductance (D(m)) and capillary blood volume (V(c))). Patients showed a mild restrictive pattern (FEV1=85+/-15% and FVC=75+/-13% of normal predicted) and a moderate D(m) reduction (32+/-12 ml min(-1) mm Hg(-1)). Average peak VO(2) was 15.6+/-4.0 ml min(-1) kg(-1) and the VE/VCO2 slope was 39.6+/-11.0. At simple Spearman correlation analysis, all variables, but V(c), correlated with peak VO2; only D(m) correlated with VE/VCO2 slope. At partial Spearman correlation, all variables lost the peak VO2 correlation, and D(m) still inversely correlated with VE/VCO2 slope (r=-0.35; p=0.005). In patients with a high VE/VCO2 slope (cutoff value 34), despite comparable lung volumes, D(m) was significantly more depressed (30+/-13 vs. 35+/-10 ml min(-1) mm Hg(-1); p<0.01). Pulmonary function tests and alveolar gas diffusing capacity poorly correlate with peak VO2. D(m) impairment rather than lung volumes correlates with exercise ventilation efficiency. This finding further adds to the pathophysiological relevance of an abnormal gas exchange in HF patients.