Effects of acute cardioselective and non-selective beta-adrenergic blockade on left-ventricular volumes and vascular resistance at rest and during exercise

The effects of intravenous metoprolol and propranolol on left-ventricular performance were studied by radionuclide cardiography in eight healthy young men at rest and during exercise. At rest, a fall of 7 to 10 mmHg was recorded in systolic blood pressure after both drugs (p<0.05). The decrease in cardiac output entirely ascribed to relative bradycardia was 18% after propranolol (p<0.01) compared with 6% after metoprolol (p<0.05). Left-ventricular volumes did not change at rest. Systemic vascular resistance increased by 14% after metoprolol and by 28% after propranolol (both p<0.05). During submaximal bicycle exercise the systolic blood pressure fell by 15 mmHg after both drugs (p<0.05). The reduction in exercise heart rate was 17 beats min'1 and 18 beats min−1 (both p<0.01), but propranolol reduced cardiac output by 18% (p<0.01) compared with 5% (p<0.05) after metoprolol, reflecting a reduction in stroke volume induced only by non-selective blockade. A more pronounced left-ventricular end-diastolic dilat...