The regulation of coronary blood flow in man in normal and abnormal conditions

Coronary and Hemodynamic Effects of Temporary Acute Aortic Insufficiency in Intact Anesthetized Dogs

In ten dogs with chronically implanted electromagnetic flowmeter probes, phasic aortic and circumflex coronary artery blood flows were measured before, during, and after 15-120 seconds of aortic insufficiency. The dogs were studied in the intact anesthetized state with a cardiac catheter device that produced graded amounts of temporary aortic insufficiency with 18-68% aortic regurgitation. With the onset of aortic insufficiency, there was an immediate increase in pulse pressure with retrograde aortic diastolic blood flow. During the very first cardiac cycle that demonstrated aortic insufficiency, there was a reduction in diastolic coronary blood flow with an increase in systolic coronary blood flow. Mean coronary blood flow fell very low during the first five to ten cardiac cycles. As severe aortic insufficiency continued, systolic coronary blood flow increased, diastolic coronary blood flow remained low or negative, and mean coronary blood flow returned to the normal range. Before the onset of aortic insufficiency, the ratio of diastolic coronary blood flow to systolic coronary blood flow averaged 2.2; after 2 minutes of aortic insufficiency the ratio of diastolic coronary blood flow to systolic coronary blood flow was 0.15. The amount of reduction in diastolic coronary blood flow was related to the amount of aortic regurgitation. Left ventricular work averaged 3.7 kg m/min before and 8.2 kg m/min after 2 minutes of aortic insufficiency with an average of 63% aortic regurgitation; mean coronary blood flow increased from an average of 51 ml/min before to 60 ml/min after 2 minutes of aortic insufficiency. When aortic insufficiency was terminated, coronary blood flow increased to an average of 123 ml/min.

Effect of propranolol on myocardial oxygen consumption and its hemodynamic correlates during upright exercise

Measurements were made of heart rate, aortic blood pressure, systolic ejection period/beat, myocardial blood flow, and myocardial oxygen consumption in nine normal young men during three bouts of upright bicycle exercise: 1) at the workload which produced a heart rate of 120 beats/minute, 2) at the higher workload necessary to produce a heart rate of 120 beats/minute after administration of intravenous propranolol 0.25 mg/kg, and 3) with infusion of propranolol, at the same workload as the first exercise bout. Comparing exercises 1 and 2, we found a much higher workload was required to produce the same heart rate after propranolol. The blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were the same despite the much greater level of exertion. Comparing exercises 1 and 3, the heart rate, blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were all significantly lower during exercise 3 after propranolol despite the fact that the same degree of exercise was being done. As in previous studies, the heart rate-blood pressure product was an excellent correlate of myocardial oxygen consumption despite the change in contractility induced by propranolol. The systolic ejection period was prolonged significantly altering the tension-time index (TTI), which became an inadequate index of myocardial oxygen consumption. It is concluded that the heart rate-blood pressure product is a good index of myocardial metabolic needs during exercise and the relationship is undistorted by marked changes in contractility, but the tension-time index is a poor correlate. This data emphasizes the fact that the relative metabolic loads for the whole body and for the heart are determined separately and may not change in parallel with a given intervention.