Al. Clark et al., THE INCREASED VENTILATORY RESPONSE TO EXERCISE IN CHRONIC HEART-FAILURE - RELATION TO PULMONARY PATHOLOGY, HEART, 77(2), 1997, pp. 138-146
Objective-To assess the exercise limitation of patients with chronic h
eart failure (CHF) and its relation to possible pulmonary and ventilat
ory abnormalities. Setting-A tertiary referral centre for cardiology.
Methods-The metabolic gas exchange responses to maximum incremental tr
eadmill 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 calculate
d as the slope of the relation between ventilation and carbon dioxide
production VE/VCO2 slope). Results-Oxygen consumption (VO2) was the sa
me at each stage in each group. Ventilation (VE) was higher in patient
s at each stage. Patients had a lower peak VO2 and a steeper VE/VCO2 s
lope than controls. Dead space ventilation as a fraction of tidal volu
me (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 ven
tilatory response at all stages of exercise. Although this is accompan
ied by an increase in VD/VT, there is hyperventilation relative to blo
od gases. It is more likely that the excessive ventilation is not due
to a primary pulmonary pathology, but rather, the increase in dead spa
ce is likely to be a response to increased ventilation.