Effect of vasodilator drugs on exercise performance in cardiac failure. Comparison of hydralazine and prazosin.

Abstract

Although vasodilator drugs cause hemodynamic improvement at rest, their effect on the overall exercise response is uncertain. Nine patients with severe diuretic-dependent cardiac failure were studied before and during upright bicycle exercise, after the double-blind administration of equihypotensive doses of hydralazine (H) 75 mg, prazosin (Pr) 3 mg and placebo (Pl). The ventilatory response and O2 uptake were monitored continuously. Cardiac output was measured during the 3rd min of steady state exercise by the CO2 rebreathing method. At rest when the treatment groups were compared with placebo, there was a 25% increase in cardiac index, placebo 1.9 .+-. 0.1, hydralazine 2.3 .+-. 0.1, prazosin 2.4 .+-. 0.1; and 23% decrease in the arteriovenous O2 content difference, placebo 9.1 .+-. 0.7, hydralazine 7.3 .+-. 0.4 and prazosin 6.9 .+-. 0.7 ml O2/100 ml. After progressive exercise to symptom limited maximum, there was no significant difference in the exercise duration, O2 uptake, peak heart rate or blood pressure. Even during steady state exercise (at 2/3 maximum), heart rate, blood pressure, cardiac index, stroke volume, stroke work and arteriovenous O2 content did not differ in the treatment or placebo periods. After the acute oral administration of hydralazine or prazosin in doses which produce a significant hemodynamic improvement at rest, there were no changes in the cardiorespiratory response during exercise.