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.