Impact of chronic obstructive pulmonary disease on exercise ventilatory efficiency in heart failure

Background: Heart failure (HF) and chronic obstructive pulmonary disease (COPD) coexistence increases morbidity and mortality. The intercept of ventilation (VEint) on the VE vs. carbon dioxide production (VCO<inf>2</inf>) relationship during exercise has been found to vary in proportion with dead space (VD) in HF. Considering that increased VD is the key pathophysiological abnormality in COPD but a secondary finding in HF we hypothesized that a high VEint would be useful in suggesting COPD as HF co-morbidity. Our aim was to assess whether an elevated VEint suggests the presence of COPD in HF. Methods: In a multicenter retrospective study, the VE-VCO2 relationship was analyzed both as slope and intercept in HF (n = 108), HF-COPD (n = 106) and COPD (n = 95). Patients with pulmonary arterial hypertension (PAH) (n = 85) and healthy subjects (HF) (n = 56) served as positive and negative controls relative to VE-VCO<inf>2</inf> abnormalities, respectively. Results: Slope and VEint varied in opposite directions in all groups (p < 0.05) being VE-VCO<inf>2</inf> slope highest and lowest in PAH and healthy subjects, respectively. No slope differences were observed among HF, HF-COPD and COPD (32 ± 7, 31 ± 7, and 31 ± 6, respectively). VEint was higher in HF-COPD and COPD compared to HF, PAH and controls (4.8 ± 2.4 L/min, 5.9 ± 3.0 L/min, 3.0 ±2.6 L/min, 2.3 ± 3.3 L/min and 3.9 ±2.5 L/min, respectively; p < 0.01). A VEint >=4.07 L/min identified patients with high probability of having COPD or HF-COPD (sensitivity of 71.6% and specificity of 72.0%). Conclusion: These data provide novel evidence that a high VEint (>=4.07 L/min) should be valued to suggest coexistent COPD in HF patients.