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

SUMMARY Although vasodilator drugs cause haemodynamic 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 equi-hypotensive doses of hydralazine (H) 75 mg, prazosin (Pr) 3 mg, and placebo (P1). The ventilatory response and oxygen uptake were monitored continuously. Cardiac output was measured during the third mtnute of steady state exercise by the CO2 rebreathing method. At rest when the treatment groups were compared with placebo, there was a 25 per cent increase in cardiac index, placebo 19 ±091, hydralazine 2-3±0.1, prazosin 2-4±0-1, and 23 per cent decrease in the arteriovenous oxygen content difference, placebo 9 1 ±0.7, hydralazine 7.3±0 4, and prazosin 6-9±0t7 ml 02/100 ml. After progressive exercise to symptom limited maximum, there was no significant difference in the exercise duration, oxygen uptake, peak heart rate, or blood pressure. Even during steady state exercise (at two-thirds maximum), heart rate, blood pressure, cardiac index, stroke volume, stroke work, and arteriovenous oxygen 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 haemodynamic improvement at rest, there were no changes in the cardiorespiratory response during exercise. Vasodilator drugs are effective in both short-and long-term treatment of patients with severe heart failure.1-3 Though their effects on resting haemo-dynamics are well defined, it is not yet clear whether they improve the exercise performance of such patients. Some reports have suggested an improvement in exercise capacity and haemodynamic reserves after the acute administration of a vaso-dilator drug,4 whereas others showed no change in maximal exercise capacity, but improved pump function at submaximal workloads.6 In the present study, we have compared the effects of the predominantly arteriolar vasodilator hydralazine with the arteriolar and venodilator agent prazosin on the cardiac output and ventilatory responses during maximal and steady state exercise and on the time over which such exercise can be tolerated. Patients and methods Nine patients with chronic congestive heart failure and class II to III symptomatology (New York Heart Association criteria) were included in the study. Their ages ranged from 27 to 65 years (mean 47 years); seven were men and two were women. All were taking optimal doses of diuretics and digoxin which were continued in unchanged doses throughout the study. The patients' symptoms …