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/V̇CO) slope and V̇ 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 and gas exchange were measured via breath-by-breath open circuit spirometry. All data from rest to peak exercise were used to calculate V̇/V̇CO slope and V̇ intercept using linear regression. Receiver operating characteristic (ROC) curves were constructed to determine optimized cutoffs for V̇/V̇CO slope and V̇ intercept to discriminate HFpEF and HFrEF from COPD.

Results: HFrEF patients had a greater V̇/V̇CO slope than HFpEF and COPD patients (HFrEF: 40 ± 9; HFpEF: 32 ± 7; COPD: 32 ± 7) (p < 0.01). COPD patients had a greater V̇ 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 intercept of 2.64 L/min discriminated COPD from HF patients (AUC: 0.88, p < 0.01), while V̇/V̇CO slope did not (p = 0.11).

Conclusion: These findings demonstrate that V̇ intercept, not V̇/V̇CO slope, may discriminate COPD from both HFpEF and HFrEF patients.