Differential hemodynamic effects of beta-adrenoceptor blockers, Ca antagonists and combined alpha-beta-receptor blockade in ischemic heart disease

Cerebral Blood Flow Assessed with Phase-contrast Magnetic Resonance Imaging during Blood Pressure Changes with Noradrenaline and Labetalol: A Trial in Healthy Volunteers

BACKGROUND

Adequate cerebral perfusion is central during general anesthesia. However, perfusion is not readily measured bedside. Clinicians currently rely mainly on mean arterial pressure (MAP) as a surrogate, even though the relationship between blood pressure and cerebral blood flow is not well understood. The aim of this study was to apply phase-contrast magnetic resonance imaging to characterize blood flow responses in healthy volunteers to commonly used pharmacologic agents that increase or decrease arterial blood pressure.

METHODS

Eighteen healthy volunteers aged 30 to 50 yr were investigated with phase-contrast magnetic resonance imaging. Intra-arterial blood pressure monitoring was used. First, intravenous noradrenaline was administered to a target MAP of 20% above baseline. After a wash-out period, intravenous labetalol was given to a target MAP of 15% below baseline. Cerebral blood flow was measured using phase-contrast magnetic resonance imaging and defined as the sum of flow in the internal carotid arteries and vertebral arteries. Cardiac output (CO) was defined as the flow in the ascending aorta.

RESULTS

Baseline median cerebral blood flow was 772 ml/min (interquartile range, 674 to 871), and CO was 5,874 ml/min (5,199 to 6,355). The median dose of noradrenaline was 0.17 µg · kg-1 · h-1 (0.14 to 0.22). During noradrenaline infusion, cerebral blood flow decreased to 705 ml/min (606 to 748; P = 0.001), and CO decreased to 4,995 ml/min (4,705 to 5,635; P = 0.01). A median dose of labetalol was 120 mg (118 to 150). After labetalol boluses, cerebral blood flow was unchanged at 769 ml/min (734 to 900; P = 0.68). CO increased to 6,413 ml/min (6,056 to 7,464; P = 0.03).

CONCLUSIONS

In healthy, awake subjects, increasing MAP using intravenous noradrenaline decreased cerebral blood flow and CO. These data do not support inducing hypertension with noradrenaline to increase cerebral blood flow. Cerebral blood flow was unchanged when decreasing MAP using labetalol.

EDITOR’S PERSPECTIVE

Systemic and coronary hemodynamics of labetalol in normotensive patients with ischemic heart disease

The systemic and coronary hemodynamic effects of combined alpha- and beta-adrenergic blockade produced by labetalol were assessed in 24 normotensive patients with angina pectoris and an ischemic electrocardiographic response to exercise stress. Both the intravenous (0.5 mg/kg) and oral (200 mg) formulations of labetalol were evaluated. At rest, labetalol produced systemic vasodilation (systemic vascular resistance -16% after intravenous and -8% after oral labetalol, both p less than 0.05) without change in heart rate. Aortic pressure usually was lower and cardiac output preserved or increased. Left ventricular end-diastolic pressure was unchanged. Coronary sinus flow was usually unchanged after either route of administration. Exercise duration was prolonged in 14 of the 20 patients with severe coronary artery disease. During exercise, tachycardia was blunted (-12% after intravenous, -7% after oral labetalol, both p less than 0.05) as was the increase in mean aortic pressure (-12% and -13% intravenous and oral labetalol respectively, both p less than 0.05), left ventricular end-diastolic pressure [-7% and -1%, respectively, both p = not significant (NS)] was unchanged. Coronary sinus flow (-16% and -25%, respectively, both p less than 0.05) was decreased as heart rate and aortic pressure were lower. Cardiac output, systemic vascular resistance, and coronary vascular resistance were similar to control exercise. The hemodynamic effects of intravenous and oral labetalol are, in general, similar. Hemodynamic responses differ from those produced by other beta-blockers and by calcium antagonists.

Systemic and coronary hemodynamic effects of combined oral alpha- and beta-adrenergic blockade (labetalol) in normotensive patients with stable angina pectoris and positive exercise stress tests

The systemic and coronary hemodynamic effects of combined alpha- and beta-adrenergic blockade produced by oral labetalol were assessed in 12 normotensive patients with angina pectoris and an ischemic electrocardiographic response to exercise stress. At rest, labetalol (200 mg, orally) produced systemic vasodilation (systemic vascular resistance -9%, p less than .01) as aortic pressure fell and cardiac output was unchanged. Left ventricular (LV) end-diastolic pressure also fell slightly (17%, p = .05). Systemic vasodilation was not accompanied by reflexly mediated increases in heart rate. Coronary flow and resistance and myocardial oxygen uptake were unchanged. Before labetalol, supine bicycle exercise produced angina in 10 patients. After labetalol, exercise duration was prolonged in 6 of these 10 (average 56%). During exercise, tachycardia was blunted (-7%, p less than .05) as were increases in aortic pressure (-12%, p less than .01) and coronary sinus flow (-25%, p = .03). Cardiac output and LV end-diastolic pressure were similar to control period values. These hemodynamic effects of oral labetalol appeared beneficial, differed from those expected of classic beta-adrenergic blocking agents, and were, in general, similar to those we have observed after intravenous labetalol. The clinical response was good and the drug safe. Labetalol should undergo further evaluation in normotensive as well as hypertensive patients with ischemic heart disease.

Systemic and coronary hemodynamic effects of combined alpha- and beta-adrenergic blockade (labetalol) in normotensive patients with stable angina pectoris and positive exercise stress test responses

The systemic and coronary hemodynamic effects of combined alpha- and beta-adrenergic blockade produced by labetalol were assessed in 12 normotensive patients with angina pectoris and an ischemic electrocardiographic response to exercise stress. When given to the patient at rest, labetalol (0.5 mg/kg intravenously) produced systemic and coronary vasodilation (mean 16% and 13%, respectively, both p less than 0.05); aortic pressure decreased, cardiac output increased and coronary flow and heart rate did not change. Before labetalol treatment, supine bicycle exercise produced angina in all patients. After treatment, exercise duration was prolonged in 8 patients (average 33%). At the same duration of exercise that led to angina during the control period, ST depression in lead V5 was less after labetalol (from 1.2 to 0.4 mm, p less than 0.5). During exercise, tachycardia was blunted (-12%, p less than 0.05) as were the increases in aortic pressure (-12%, p less than 0.05), left ventricular end-diastolic pressure (-7%, difference not significant) and coronary sinus flow (-16%, p less than 0.05). Cardiac output and systemic and coronary vascular resistance were similar to values during control exercise. The hemodynamic effects of labetalol appeared to be beneficial and differed from those of classic beta-adrenergic blocking agents.