CORONARY FLOW, BLOOD PRESSURE, AND HEART RATE DOSE–RESPONSE CHANGES AFTER NITROGLYCERIN ADMINISTRATION

Abstract

Changes in left circumflex coronary flow, femoral blood pressure, and heart rate (ECG-Lead II) were recorded simultaneously in pentobarbitalized artificially respired open-chest dogs. A gated sine wave electromagnetic flowmeter was used for coronary flow measurements. After intravenous nitroglycerin (glyceryl trinitrate) administration in six satisfactory experiments, changes in dose–response patterns were studied. (1) Doses of 0.1 μg/kg were ineffective; doses of 1.0, 10, and 100 μg/kg induced in 10 to 15 seconds maximal increases in mean coronary flow averaging 22, 65, and 100%, respectively; blood pressure concurrently decreased showing a maximum fall (in 20 to 25 seconds) associated with reflex tachycardia; a transient initial increase in pulse pressure also occurred. (2) Coronary flow subsequently decreased, reaching below-control values; the magnitude of this decrease appeared to be related to the degree of fall in blood pressure and to the reflex tachycardia; and pulse pressure markedly decreased below the control values. (3) After intravenous injections of pentobarbitone sodium (1 and 10 mg/kg) brief initial (within 10 seconds) dose-related increases in coronary flow were also observed but associated with less-marked blood pressure decreases and no significant changes in either heart rate or pulse pressure.