So what are the blood pressure responses to aerobic exercise? Here, we have the same boxes.
We have systolic blood pressure on the top, diastolic blood pressure on the bottom and mean
arterial pressure as the line in between. During light to moderate exercise, there is an increase
in systolic blood pressure but a little decrease in diastolic pressure and the same thing happens
as you move to moderate to hard exercise. There's an increase in systolic blood pressure and
a decrease in diastolic pressure. You may ask yourself why are you getting this separation.
Remember with isometric exercise, both systolic and diastolic increased. Well systolic is
increasing for probably the reasons you're thinking of. The heart is contracting harder, i.e.,
there's more inotropy. The reason why diastolic blood pressure falls a little bit is because now
you're vasodilating vascular beds. So something like the muscle vasculature is a great
example. If you vasodilate the muscle vasculature, you drop systemic vascular resistance and
that is observed now as a decrease in diastolic blood pressure. Mean arterial blood pressure
does climb a little bit but not in the same trajectory as resistance exercise. Again, because
mean arterial blood pressure is waited more so for diastolic than systolic blood pressure.
So what happens if you exercise using a different modality? For example, what happens if you
are swimming versus running? Does that change your cardiovascular response to exercise? It
sure does. If you're in the supine position, you have an increase in preload and stroke volume,
meaning you have more blood returning to the heart than you do in the upright position. This
means that the heart rate responses are going to be lower because remember that it is heart rate
times stroke volume to yield us a cardiac output. So if you're exercising and you already have
a higher stroke volume you don't need as high of a cardiac output. We contrast that to the
upright position. There is a decrease in preload and stroke volume while there is an increase in
heart rate. That is because if you don't have as much preload and your stroke volume is lower,
you need a higher heart rate to maintain the same cardiac output.