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 VE/VCO2 slope). Results-Oxygen consumption (VO2) was the same at each stage in each group. Ventilation (VE) was higher in patients at each stage. Patients had a lower peak VO2 and a steeper VE/VCO2 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 VO2 (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.