The association between normal lung function and peak oxygen uptake in patients with exercise intolerance and coronary artery disease

In coronary artery disease (CAD), exercise intolerance with reduced oxygen uptake at peak exercise (VO(2peak)) is assumed to primarily reflect cardiovascular limitation. However, oxygen transport and utilization depends on an integrated organ response, to which the normal pulmonary system may influence overall capacity. This study aimed to investigate the associations between normal values of lung function measures and VO(2peak) in patients with exercise intolerance and CAD. We hypothesized that forced expiratory lung volume in one second (FEV(1)), transfer factor of the lung for carbon monoxide (T(L)CO) and T(L)CO/alveolar volume (T(L)CO/VA) above lower limits of normal (LLN) are associated with VO(2peak) in these patients. We assessed patients with established CAD (n = 93; 21 women) referred for evaluation due to exercise intolerance from primary care to a private specialist clinic in Norway. Lung function tests and cardiopulmonary exercise testing (CPET) were performed. Z-scores of FEV(1), FEV(1)/forced vital capacity (FVC), T(L)CO and T(L)CO/VA were calculated using the Global Lung Function Initiative (GLI) software and LLN was defined as the fifth percentile (z = -1.645). Non-obstructive patients, defined by both FEV(1) and FEV(1)/FVC above LLN, were assessed. The associations of FEV(1Z-score), T(L)CO(Z-score) and T(L)CO/VA(Z-score) above LLN with VO(2peak) were investigated using linear regression models. Mean VO(2peak) ± standard deviation (SD) was 23.8 ± 6.4 ml/kg/min in men and 19.7 ± 4.4 ml/kg/min in women. On average, one SD increase in FEV(1), T(L)CO and T(L)CO/VA were associated with 1.4 (95% CI 0.2, 2.6), 2.6 (95% CI 1.2, 4.0) and 1.3 (95% CI 0.2, 2.5) ml/kg/min higher VO(2peak), respectively. In non-obstructive patients with exercise intolerance and CAD, FEV(1), T(L)CO and T(L)CO/VA above LLN are positively associated with VO(2peak). This may imply a clinically significant influence of normal lung function on exercise capacity in these patients.