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.