Effects of DBcAMP on exercise capacity in patients with and without chronic heart failure

Abstract

The acute effects of vasodilation on exercise capacity in cardiac patients with (group 1) and without (group 2) congestive heart failure were studied using dibutyryl cyclic AMP (DBcAMP). Exercise was performed on an upright bicycle ergometer using a graded protocol. DBcAMP increased cardiac output and decreased pulmonary capillary wedge pressure and systemic vascular resistance both at rest and during maximal exercise in these two groups. However, before and after DBcAMP neither exercise duration (371 ± 52 seconds vs. 388 ± 44, NS, in group 1, 645 ± 148 vs. 635 ± 143 seconds, NS, in group 2, respectively) nor maximal oxygen consumption (12.8 ± 2.3 ml/kg/min vs. 13.1 ± 1.6, NS, in group 1, 20.3 ± 1.4 vs. 20.1 ± 1.5, NS, in group 2, respectively) was improved. In both groups the arteriovenous oxygen differences were lower at rest and during exercise performed while on DBcAMP than in the control state. In group 2 patients excess vasoconstriction mediated by abnormally increased neurohormonal activities or edema were absent. Failure of the vasodilator to increase exercise capacity is probably due to nonspecific vasodilation and maldistribution of increased cardiac output, and not to tight vasoconstriction or narrowed arteriolar lumen.