Exercise ventilatory inefficiency in heart failure and chronic obstructive pulmonary disease

Background: Dyspnea on exertion is common to both heart failure (HF) and chronic obstructive pulmonary disease (COPD), and it is important to discriminate whether symptoms are caused by HF or COPD in clinical practice. The ventilatory equivalent for carbon dioxide (V̇_E/V̇CO₂) slope and V̇_E intercept (a reflection of pulmonary dead space) are two candidate non-invasive indices that could be used for this purpose. Thus, we compared non-invasive indexes of ventilatory efficiency in patients with HF and preserved or reduced ejection fraction (HFpEF and HFrEF, respectively) or COPD. Methods: Patients with HFpEF (n = 21), HFrEF (n = 20), and COPD (n = 22) patients performed cardiopulmonary exercise testing to volitional fatigue. V̇_E and gas exchange were measured via breath-by-breath open circuit spirometry. All data from rest to peak exercise were used to calculate V̇_E/V̇CO₂ slope and V̇_E intercept using linear regression. Receiver operating characteristic (ROC) curves were constructed to determine optimized cutoffs for V̇_E/V̇CO₂ slope and V̇_E intercept to discriminate HFpEF and HFrEF from COPD. Results: HFrEF patients had a greater V̇_E/V̇CO₂ slope than HFpEF and COPD patients (HFrEF: 40 ± 9; HFpEF: 32 ± 7; COPD: 32 ± 7) (p < 0.01). COPD patients had a greater V̇_E intercept than HFpEF and HFrEF patients (COPD: 3.32 ± 1.66; HFpEF: 0.77 ± 1.23; HFrEF: 1.28 ± 1.19 L/min) (p < 0.01). A V̇_E intercept of 2.64 L/min discriminated COPD from HF patients (AUC: 0.88, p < 0.01), while V̇_E/V̇CO₂ slope did not (p = 0.11). Conclusion: These findings demonstrate that V̇_E intercept, not V̇_E/V̇CO₂ slope, may discriminate COPD from both HFpEF and HFrEF patients.