Myocardial blood flow measurement with 133-Xenon effect of glyceryl trinitrate in dogs.

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Abstract
The use of saline solutions of Xe133 for the measurement of myocardial blood flow in intact dogs is described. Injection of glyceryl trinitrate, 0.01 mg/kg body weight over 1 min., caused an increase in flow up to 3 min., followed by a reduction in flow up to 10 min. Measurements of myocardial blood flow, cardiac output, and myocardial O2 extraction were made at standardized times after giving the drug. At 1/2 min. myocardial blood flow and left ventricular rate of work were both increased. Myocardial O2 consumption was reduced and coronary sinus O2 content rose by 4.4 vol%. At 3 minutes the vasodilator effect was over. There was reduced myocardial blood flow and rate of work; myocardial O2 consumption was reduced further. Measurements at 6 and 10 minutes differed from those at 3 minutes only in degree, with a gradual return to control values. It is suggested that the beneficial effects of glyceryl trinitrate are initial increase in myocardial blood flow, initial increase in external cardiac efficiency, and prolonged reduction in oxygen consumption. These possibilities need to be studied in the ischmic heart.
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