EFFECTS OF ISOSORBIDE DINITRATE ON OXYGEN-UPTAKE KINETICS IN CARDIAC PATIENTS

Purpose: Although nitrates are known to improve indices oi exercise ca pacity in patients with coronary artery disease, their effects on oxyg en uptake kinetics during the onset of exercise have not been clarifie d. We evaluated the acute effects of isosorbide dinitrate on the kinet ics or oxygen uptake during the onset of exercise at a constant work r ate in patients with coronary artery disease. Methods: We studied 14 p atients with coronary artery disease who performed 6 min of low-intens ity exercise at a constant work rate on a cycle ergometer 30 min after oral administration of 10 mp of isosorbide dinitrate or placebo in a double-blind, crossover manner. Oxygen uptake was calculated from brea th-by-breath analysis of respired gases. The time constant of oxygen u ptake kinetics during the onset of exercise was determined by fitting a single exponential function to the oxygen uptake response. Results: Heart rate was significantly increased al rest, and systolic blood pre ssure was significantly decreased both at rest and during exercise aft er administration of isosorbide dinitrate. The time constant of oxygen uptake was significantly shorter (the kinetics were faster) after adm inistration of isosorbide dinitrate (39.4 +/- 10.1 vs 44.5 +/- 10.5 s, P = 0.038). Conclusions: Isosorbide dinitrate was found to speed the kinetics of the increase in oxygen uptake during constant work-rate ex ercise. The time constant of oxygen uptake. which reflects the rapidit y of cardiovascular adaptation at the onset of exercise, seems to be a useful parameter of the effectiveness of therapy in patients with cor onary artery disease.