EFFECTS OF ISOSORBIDE DINITRATE ON EXERCISE CAPACITY IN CARDIAC PATIENTS - RELATIONSHIP BETWEEN OXYGEN-UPTAKE RESPONSES AND HEMODYNAMIC-EFFECTS

Acute effects of oral isosorbide dinitrate on exercise capacity were evaluated in 14 patients with chronic heart disease measuring the anaerobic threshold and left ventricular function during exercise. A symtom-limited exercise test was performed on a bicycle ergometer with work rates increased by 1W every 6 seconds. Left ventricular function was continuously monitored with a computerized cadmium telluride detector following the intravenous injection of technetium-labeled red blood cells. Thirty minutes after the control exercise test, patients were given isosorbide dinitrate, 5 mg orally. The second exercise test was performed 30 min later. Isosorbide dinitrate improved the anaerobic threshold from 715.4 +/- 172.9 to 774.9 +/- 173.5 ml/min (p < 0.01) and ejection fraction at peak exercise from 36.7 +/- 11.6 to 39.9 +/- 12.3% (p < 0.05). However, there was no significant change in maximum work rate or peak oxygen uptake. Those patients for whom isosorbide dinitrate resulted in a 10% or greater improvement in the anaerobic threshold had both higher pre-treatment ejection fractions and greater increases in peak exercise ejection fraction following isosorbide dinitrate. Measurements of the anaerobic threshold and left ventricular function during exercise may be useful in the evaluation of the efficacy of vasodilators in cardiac patients.