The Relationship Between Resting Lung-to-Lung Circulation Time and Peak Exercise Capacity in Chronic Heart Failure Patients

Background: Peak exercise capacity (VO_2peak) is a measure of the severity of chronic heart failure (CHF); however, few indices of resting cardiopulmonary function have been shown to predict VO_2peak. A prolonged circulation time has been suggested as an index of increased severity of CHF. The aim of this study was to investigate the relationship between resting lung-to-lung circulation time (LLCT) and VO_2peak in CHF. Methods and Results: Thirty CHF patients (59 ± 13 years, New York Heart Association: 1.9 ± 1.0) undertook the study. Each subject completed resting pulmonary and echocardiography measures and an incremental exercise test. LLCT was measured using the reappearance of end-tidal acetylene (P_ET,C₂H₂) after a single inhalation. Univariate and multivariate stepwise linear regression was used to determine the predictors of VO_2peak. Univariate correlates of VO_2peak (group mean 1.53 ± 0.44 L/min^-1) included LLCT (r = -0.75), inspiratory capacity (r = 0.41), ejection fraction (r = 0.33), peak early flow velocity (r = -0.39), and the ratio of early to late flow velocity (r = -0.31). LLCT was the only independent predictor where VO_2peak = 3.923-0.045 (LLCT); r² = 54%. Conclusions: These results suggest that resting LLCT determined using the soluble inert gas technique represents a simple, noninvasive method that provides additional information regarding exercise capacity in CHF.