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

To assess the exercise limitation of patients with chronic heart failure (CHF) and its relation to possible pulmonary and ventilatory abnormalities.

A tertiary referral centre for cardiology.

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).

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.

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.