Effect of beta‐adrenergic blockade on coronary blood flow during isometric exercise in older adults (875.7)

Abstract

The rise in heart rate (HR) and cardiac contractility during exercise is due to activation of myocardial β‐adrenergic receptors. In animals, β‐adrenergic receptors in the coronary vasculature also mediate a parallel increase in coronary blood flow. However, the role of β‐ adrenergic receptors in the human coronary circulation is unknown. We hypothesized that β‐adrenergic blockade with propranolol would attenuate reflex tachycardia and coronary hyperemia in response to isometric handgrip in healthy older adults. Six men (66 ± 2 yrs) performed isometric handgrip exercise at 40% of maximal voluntary contraction for 2 minutes after receiving intravenous propranolol or no treatment. HR and blood pressure were monitored continuously and rate‐pressure product (RPP) was calculated as an index of myocardial oxygen demand. Coronary blood flow velocity (CBV) was measured by transthoracic Doppler echocardiography and coronary vascular resistance (CVR) was calculated. The coronary supply to demand ratio was calculated as CVR/RPP. Propranolol decreased the HR (8 ± 3 vs. 4 ± 1) and RPP (2580 ± 612 vs. 1520 ± 163) responses to exercise but augmented the CVR/RPP response (‐0.24 ± .09 vs. ‐0.49 ± 0.15). Mean arterial pressure, CVR and CBV were unaltered. β‐adrenergic blockade not only decreased myocardial oxygen demand in response to exercise, it also improved oxygen supply.Grant Funding Source: Supported by NIH P01 HL096570 and UL1 TR000127