Effect of Propranolol on Myocardial Oxygen Consumption and Its Hemodynamic Correlates during Upright Exercise

Abstract

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 significaritly 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 tensiontime 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. Additional Indexing Words:Heart rate Blood pressure Heart rate-blood pressure product Tension-time index Triple product Coronary arteriovenous oxygen difference Exercise Angina T HE RELATIONSHIPS between several readily measured hemodynamic variables and both myocardial blood flow (MBF) and myocardial oxygen consumption (MVO2) in normal subjects

Effect of beta‐blockers on exercise double product (systolic blood pressure x heart rate).

“…Despite theoretical limitations, a close correlation (r = 0.90) has been demonstrated between myocardial oxygen consumption and double product during exercise in normal young men (Kitamura et al, 1972;Jorgensen et al, 1973). In these studies a positive correlation was also found between coronary blood flow and double product.…”

The influence of aerobic exercise training on the double product break point in low-to-moderate risk adults

“…The DP has long been used as a non-invasive measure of myocardial oxygen consumption during exercise (Gobel et al 1978;Jorgensen et al 1973;Kitamura et al 1972). The DP has been a useful index in cardiac rehabilitation settings to identify specific workloads at which signs and symptoms of ischemia occur, and improvements in functional capacity relative to the onset of symptomatic ischemia (Arya et al 2005;Durstine and Tanaka and colleagues were the first to identify that the DP increases more rapidly above the LT than below it, and were the first to identify a breakpoint in the double product (DPBP) with incremental exercise in healthy subjects Tanaka and Shindo 1992).…”

Determinants and prediction of transmural myocardial perfusion.

“…An increased heart rate itself is inotropic, but because it tends to decrease left ventricular volume the increase in oxygen consumption is less than would occur in isolated muscle strips. This may be why Jorgensen et al 47 observed equally good prediction of myocardial oxygen consumption during exercise before and after propranolol had been given, and why Krasnow et al 49 showed that myocardial oxygen consumption per unit of SPTI increased by only 25% during maximal stimulation with isoproterenol. The effect that this would have would be to raise the critical DPTI: SPTI ratio from about 0.4-0.5 to about 0.5-0.6.…”