References: Clark et al, 1997
Clark AL, Volterrani M, Swan JW, Coats AJS
The increased ventilatory response to exercise in chronic heart failure: relation to pulmonary pathology
Heart 1997; 77: p.138-146.
Department of Cardiac Medicine, National Heart and Lung Institute, London, UK
Objective-To assess the exercise limitation of patients with chronic heart
failure (CHF) and its relation to possible pulmonary and ventilatory
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 (VEIVCO2 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 VEIVCO2 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) liters/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.