VENTILATION-PERFUSION MATCHING IN CHRONIC HEART-FAILURE

Background: The exercise limitation of patients with chronic heart fai lure is associated with an increased ventilatory response during exerc ise, This is thought to be due, at least in part, to excessive dead sp ace ventilation. Methods: To assess ventilation perfusion matching, 20 patients with chronic heart failure and eight controls with asymptoma tic left ventricular dysfunction underwent symptom limited treadmill e xercise with arterial blood sampling. Metabolic gas exchange was deter mined by expired gas analysis. Fractional dead space ventilation and t he alveolar arterial oxygen difference were derived, Results: There wa s a fall in fractional dead space ventilation (0.43 to 0.28; P < 0.001 ), more marked in the controls (peak dead space fraction 0.19(controls ), 0.32 (patients); P = 0.002). There was a rise in alveolar arterial difference in all patients (1.59 to 2.55 kPa; P = 0.006) with no diffe rence between patients and controls. Arterial carbon dioxide tension f ell during exercise (4.89 to 4.63 kPa; P < 0.001), with no difference between patients and controls, There was no significant change in arte rial oxygen tension. Conclusions: The fall in arterial carbon dioxide was the same in both patients and controls, The modest increase in alv eolar-arterial oxygen difference tension was the same in both groups, which, coupled with the stable arterial oxygen tension makes it unlike ly that a primary change in ventilation-perfusion matching is the caus e of increased ventilatory response to exercise in chronic heart failu re.