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 ((V) over dot(E)) to carbon dioxide output ((V) over dot(CO2)) during exercise. The goal of this study was to ascertain whether the (V) over dot(E)/(V) over dot(CO2), slope and (V) over dot(E)/(V) over dot(CO2) intercept can discriminate between subjects with congestive heart failure and those with COPD at equal peak oxygen uptake (V) over dot(O2)).METHODS: We studied 46 subjects with congestive heart failure (mean age 61 +/- 9 y) and 46 subjects with COPD (mean age 64 +/- 8y) who performed a cardiopulmonary exercise test.RESULTS: The (V) over dot(E)/(V) over dot(CO2), 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 (V) over dot(O2) < 16 mL/kg/min, but not >= 16 mL/kg/min (28.3 +/- 5.3 vs 28.9 +/- 6.6). The (V) over dot(E)/(V) over dot(CO2) 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 (V) over dot(O2) < 16 mL/kg/min were considered, subjects with COPD had a higher likelihood to have the. z (V) over dot(E)/(V) over dot(CO2) intercept > 2.14 L/min (0.92 sensitivity, 0.96 specificity). Regardless of peak (V) over dot(O2), the end-tidal pressure of CO2 (P-ETCO2) 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 P-ETCO2.CONCLUSIONS: The ventilatory response to (V) over dot(CO2) during exercise was significantly different between subjects with congestive heart failure and those with COPD in terms of the (V) over dot(E)/(V) over dot(CO2) slope with moderate-to-severe reduction in exercise capacity and in terms of the (V) over dot(E)/(V) over dot(CO2), intercept regardless of exercise capacity.