The increased ventilatory response to exercise in chronic heart failure: Relation to pulmonary pathology

Objective: To assess the exercise limitation of patients with chronic heart failure (CHF) and its relation to possible pulmonary and ventilatory abnormalities. Setting: A tertiary referral centre for cardiology. Methods: The metabolic gas exchange responses to maximum incremental treadmill exercise were assessed in 55 patients with CHF (mean (SD) age 57.9 (13.0) years; 5 female, 50 male) and 24 controls (age 53.0 (11.1) years; 4 female, 20 male). Ventilatory response was calculated as the slope of the relation between ventilation and carbon dioxide production (V̇E/V̇CO₂ slope). Results: Oxygen consumption (V̇O₂) was the same at each stage in each group. Ventilation (V̇E) was higher in patients at each stage. Patients had a lower peak V̇O₂ and a steeper V̇E/V̇CO₂ slope than controls. Dead space ventilation as a fraction of tidal volume (VD/VT) was higher in patients at peak exercise, but dead space per breath was greater in controls at peak exercise (0.74 (0.29) v 0.57 (0.17) litres/breath; P = 0.002). End tidal CO₂ was lower in patients at all stages, and correlated with peak V̇O₂ (r = 0.58, P <0.001). Alveolar oxygen tension was higher in patients at each stage than in controls. Conclusions: Patients with CHF have an increased ventilatory response at all stages of exercise. Although this is accompanied by an increase in VD/VT, there is hyperventilation relative to blood gases. It is more likely that the excessive ventilation is not due to a primary pulmonary pathology, but rather, the increase in dead space is likely to be a response to increased ventilation.