References: Banning et al, 1995
Banning AP, Lewis NP, Northridge DB, Elbom JS, Henderson AH
Perfusion/ventilation mismatch during exercise in chronic heart failure: an investigation of circulatory determinants
Br Heart J 1995; 74: p.27-33.
Department of Cardiology, College of Medicine, University of Wales, Cardiff, UK.
Background-The ventilatory cost of carbon dioxide (CO2) elimination on exercise
(VE/VCO2) is increased in chronic heart failure (CHF). This reflects increased
physiological dead space ventilation secondary to mismatching between perfusion
and ventilation during exercise. The objectives of this study were to
investigate the relation of this increased VE/VCO2 slope to the syndrome ofCHF
or to limitation of the exercise related increase of pulmonary blood flow, or
both.
Patients and methods-Maximal treadmill exercise tests with respiratory gas
analysis were performed in 45 patients with CHF (defined as resting left
ventricular ejection fraction <40% on radionuclide scan); 15 normal controls; 23
patients with coronary artery disease and normal resting left ventricular
function; and 13 pacemaker dependent patients (six with and seven without CHF)
directly comparing exercise responses in rate responsive and fixed rate mode.
Results-Patients with CHF had a steeper VE/VCO2 slope than normal controls: this
was related inversely to peak Vo, below 20 mollminlkg. In patients with coronary
artery disease in whom peak Vo2 (at respiratory exchange ratio 1) was as
limited as in the patients with CHF but resting left ventricular function was
normal, the VE/Vco, slope was normal. In pacemaker dependent patients fixed rate
pacing resulted in lower exercise capacity and peak Vo2 than rate responsive
pacing; the VE/VCO2 slope was normal in patients without CHF but steeper than
normal in patients with CHF; the VEIVCO2 slope was steeper during fixed rate
than during rate responsive pacing in these patients with CHF.
Conclusions-These findings suggest that the perfusion/ventilation mismatch
during exercise in CHF is related to the chronic consequences of the syndrome
and not directly to limitation of exercise related pulmonary flow. Only when the
syndrome of CHF is present can matching between perfusion and ventilation be
acutely influenced by changes in pulmonary flow.