I don't understand something about blood pressure.....
I've got an engineering (fluid) background and am struggling with something.
Let's say you've got a system with a pump and some pipework. If you attach a larger more powerful pump to the system and don't change any of the pipework, the average pressure within the system when the pump pumps will be higher until the fluid makes its way through the system. I know this is true. I saw it happen when I worked on a oil rig once when somebody attached the wrong pump to the system and sprayed drilling fluid all over the place.
So, if you have an averagely fit person (i.e. one with a decent set of veins and arteries etc. to start with), who undergoes a lengthy period of training and improves the size and efficiency of their heart, should this not lead to an increase in their blood pressure (certainly the systolic)? Further to this, I believe that exercise leads to an increase in the blood volume. This will further exacerbate the situation. Or would a commensurate increase in artery diameter be expected which would compensate?
I'm struggling as to why a normal diastolic and elevated systolic blood pressure in a long time runner is considered to be in any way abnormal. Surely it's only to be expected based on the physics?
I'm not saying that a high systolic is a good thing, I don't know enough about it to have an opinion, but surely it's a logical thing?
It puzzles me.
You need to buy Tim Noakes Lore of running as it answers all questions on running physiology
"Sympathetic nervous activity increases blood pressure by stimulating the heart, increasing the heart rate and constricting the blood vessels. Exercise training reduces the resting blood pressure by reducing the activity of the sympathetic nervous system (Grassie et al. 1992; Kingwell et al. 1992)."
I think the Grassi paper is this free to view one:
'Physical exercise in essential hypertension'.
The other paper is probably this one (abstract only unless you have access to journals)
Elstead runner: in very basic terms, what you're not allowing for is that it's a self-regulating system with negative feedback and stuff. It has a variety of systems, which work over different timescales (as seen e.g. with adaptations when you go to a higher altitude). So, as the heart gets stronger, it pumps out more blood per beat, thus it doesn't need so many beats per minute to pump the same amount of blood around the body, so runners etc. end up with a lower resting heart rate than sedentary people. Similar feedback on blood pressure and stuff.
I don't think blood pressure is a simple case of fluid dynamics. With veins, arteries and capillaries we aren't dealing with fluid pressure per se as in pipework of fixed dimension or fluid flow of a particular volume. Blood pressure should really be called arterial and vein expansion and contraction capability. High blood pressure really means there's less elasticity in the pipework. Eat tons of salt, that'll harden things up and raise your blood pressure.
Elstead runner wrote (see)
Hi, I've got an engineering (fluid) background and am struggling with something. Let's say you've got a system with a pump and some pipework. If you attach a larger more powerful pump to the system and don't change any of the pipework, the average pressure within the system when the pump pumps will be higher until the fluid makes its way through the system. I know this is true. I saw it happen when I worked on a oil rig once when somebody attached the wrong pump to the system and sprayed drilling fluid all over the place.
No idea what the answer is, but one thing that crosses my mind is that you've got a closed loop in the body. So If the pump is pumping fluid out with greater force, it's also simultaneously sucking it in with greater force. So you've got the output trying to increase pressure, the inlet trying to decrease it. Net result zero change. Possibly. Just thinking aloud really : )
Hmmm - some interesting theories.
Based upon the body's reaction to exercise, a person who exercised regularly, and had a more efficient heart but a well adjusted systen would have low blood pressure. Should that person stop exercising, their heart would remain relatively large/efficient but their system not be so adjusted and I guess that could cause raised blood pressure.....which would then fall away once regular training was commenced.
With regards the heart beating less often, I get that, but surely when a well trained heart does beat it pushes out a lot of blood at once, hence a raise in systolic pressure?
A heart beating twice as fast but pushing out half as much would have a higher diastolic pressure I reckon as there wouldn't be much by way of "rest" between beats.
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