I have to write an exercise prescription for someone for my work, they have hypertension and are taking propranolol which reduces their heart rate and therefore BP. It says they recently did a graded exercise test and max exercise bp is 240/90 but their resting bp is 152/90. So how do they do exercise if their diastolic bp cannot go over 90 when it is already 90 at resting? A scientific answer would be good, thanks.
This is a patient community, so I'm afraid I can't provide a scientific answer. However, as you probably know,BP (mean arterial pressure) is the product of cardiac output and total peripheral (arterial) resistance. Cardiac output is the product of stroke volume and heart rate. But as a cardiac output of, say 10 liter/minute will provide approx. the same MAP regardless of if heart rate is 100 and stroke volume 100 ml, or the heart rate is 50 and stroke volume 200 ml, the same is not true for pulse pressure (sys minus dia). While the first might have a blood pressure of 140/90 and a MAP of 105 mmHg, the latter may have a blood pressure of 180/70 and the same MAP.
Everyone have their unique stroke volume:pulse pressure ratio, depending on arterial compliance/stiffness. In general, a lower number may indicate higher arterial stiffness.
To answer your question, during exercise, large arteries will dilate to allow increased muscular blood flow (adrenal beta-2-receptor-stimulation) causing an isolated effect of lowered blood pressure. Minor arteries will constrict (adrenal alpha-1-receptor stimulation) causing an isolated effect of increased blood pressure. Heart rate and heart contractility will increase (adrenal beta-1-receptor stimulation) causing an isolated effect of increased blood pressure.
So, while the effect of increased heart rate on blood pressure more or less is countered by the arterial dilation, stroke volume increases dramatically, causing a wider pulse pressure. Well-trained individuals may actually experience a drop in diastolic blood pressure during exercise, as their arteries are smooth and well-functioning.
Propranolol is a non-selective beta blocker, which means it also blocks beta-2 receptors. While it does decrease heart rate and contractility, it also prevents arterial dilation in response to adrenaline/noradrenaline, which leaves the alpha-receptor effect unopposed. Some people taking propranolol may experience extreme increases in blood pressure (and compensatory bradycardia) in response to adrenaline, especially if it is injected.
I'm not a doctor, so I'm afraid my answer isn't very scientific, I'm sorry. I hope it was somewhat helpful at least.
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