Ventilatory response to carbon dioxide output in subjects with congestive heart failure and in patients with COPD with comparable exercise capacity.

BACKGROUND Patients with congestive heart failure or COPD may share an increased response in minute ventilation (V̇E) to carbon dioxide output (V̇CO2 ) during exercise. The goal of this study was to ascertain whether the V̇E/V̇CO2 slope and V̇E/V̇CO2 intercept can discriminate between subjects with congestive heart failure and those with COPD at equal peak oxygen uptake (V̇O2 ). METHODS We studied 46 subjects with congestive heart failure (mean age 61 ± 9 y) and 46 subjects with COPD (mean age 64 ± 8 y) who performed a cardiopulmonary exercise test. RESULTS The V̇E/V̇CO2 slope was significantly higher in subjects with congestive heart failure compared with those with COPD (39.5 ± 9.5 vs 31.8 ± 7.4, P < .01) at peak V̇O2 < 16 mL/kg/min, but not ≥ 16 mL/kg/min (28.3 ± 5.3 vs 28.9 ± 6.6). The V̇E/V̇CO2 intercept was significantly higher in both subgroups of subjects with COPD compared with the corresponding values in the subjects with congestive heart failure (3.60 ± 1.7 vs -0.16 ± 1.7 L/min, P < .01; 3.63 ± 2.7 vs 0.87 ± 1.5 L/min, P < .01). According to receiver operating characteristic curve analysis, when all subjects with peak V̇O2 < 16 mL/kg/min were considered, subjects with COPD had a higher likelihood to have the V̇E/V̇CO2 intercept > 2.14 L/min (0.92 sensitivity, 0.96 specificity). Regardless of peak V̇O2 , the end-tidal pressure of CO2 (PETCO2 ) at peak exercise was not different in subjects with congestive heart failure (P = .42) and was significantly higher in subjects with COPD (P < .01) compared with the corresponding unloaded PETCO2 . CONCLUSIONS The ventilatory response to V̇CO2 during exercise was significantly different between subjects with congestive heart failure and those with COPD in terms of the V̇E/V̇CO2 slope with moderate-to-severe reduction in exercise capacity and in terms of the V̇E/V̇CO2 intercept regardless of exercise capacity.