Exercise haemodynamic effects of beta-blockade and intrinsic sympathomimetic activity

Summary Beta-adrenergic blockade with intrinsic sympathomimetic activity (ISA) causes less depression of resting and submaximal heart rate (HR) than non-ISA beta-blockers. The effects of these drugs on exercise haemodynamics have not been well studied. We evaluated effects of pindolol, propranolol and placebo during rest and steady-state exercise on cardiac output, oxygen consumption, calf blood flow, HR and blood pressure in 18 healthy subjects.Pindolol 5 mg and propranolol 80 mg given twice daily, reduced maximal exercise HR by 50 and 52 beats·min^–1 respectively, confirming similarity of beta₁-blockade. Resting cardiac output was unchanged in all three groups after one week of therapy.Cardiac output, measured during steady-state exercise decreased in the propranolol group (18.3 vs 15.6 l·min^–1) with no significant changes in pindolol (15.7 vs 16.0 l·min^–1) or placebo (18.6 vs 17.3 l·min^–1). The rise in cardiac output, from rest to exercise, was similarly attenuated by propranolol but not by pindolol or placebo. Exercise stroke volume increased 12% on pindolol (123–140 cc) and decreased 7% on propranolol (143–133 cc).Neither drug had a detrimental effect on exercise calf blood flow compared to placebo. Thus, unlike propranolol, pindolol with ISA, maintains a normal cardiac output during submaximal exercise.Presented in part at the National meeting of the American Federation for Clinical Research, Washington, D.C., May, 1985