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Old 11-03-2015, 10:00 AM
The Great Sun Jester The Great Sun Jester is offline
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Explain to a doofus the mechanics of hypertension

So one fine evening while hanging out in the grocery store with the missus, I found my arm in one of those blood pressure testing contraptions. Long story short, I'm right on track for keeping up a generations-old family tradition of hypertension, arteriosclerosis, and strokes--pushed a BP of 139/98. Resting heart rate was still down around 63, so I got that going for me.

Anyways, I'm not really wondering what to do about the numbers, but I am curious about the mechanics behind blood pressure in general. Seems to me it the numbers should be 0 when the heart ain't squeezin', and whatever the systolic reading is when it IS squeezin'. My WAG is that I'm correct about the systolic number, and the reason it doesn't go down to 0 is because the pressure gradually drops between squeezes, and then the squeezy happens again raising the pressure. So if my resting pulse was closer to 53 (ah the good old days!) my diastolic would be quite a bit lower. Am I close?
Old 11-03-2015, 10:12 AM
puddleglum puddleglum is offline
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Think of a tire. Nothing is pushing air through the tire but the air pressure is not zero. That is because there is air inside the tire pushing against the sides of the tire to keep it inflated. Likewise in Blood pressure what is being measured is not the pressure of the blood going through the blood vessels but the pressure the blood is pushing against the sides of the blood vessels. That would only be zero if something was really wrong. 98 means your pressure is high and you need to see a doctor to start medication.
Old 11-03-2015, 01:21 PM
Kevbo Kevbo is offline
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For whatever reason the automatic pressure cuffs seem to read about 8-12mm higher than taking it with a manual cuff and a stethoscope.

Yes, I my hypertension is being treated, my consumer grade cuff matches what they use at the doctor's pretty well, but it always looks a lot better when they read it the old fashioned way.
Old 11-03-2015, 01:47 PM
Really Not All That Bright Really Not All That Bright is offline
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If you walked into the grocery store, it wasn't really measuring your resting heart rate. Resting rates are correctly taken as long as possible after exercise.
Old 11-03-2015, 03:08 PM
lance strongarm lance strongarm is offline
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Originally Posted by The Great Sun Jester View Post
Seems to me it the numbers should be 0 when the heart ain't squeezin', and whatever the systolic reading is when it IS squeezin'.
That would only work if your blood vessels were drained entirely of blood between each heartbeat.

The heart pushes blood through them, causing increases in pressure right after, but the blood is always under pressure even when the heart isn't pushing it.
Old 11-03-2015, 03:19 PM
Morgenstern Morgenstern is offline
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My Cardiologist would always have my BP taken while I was standing, and in both arms. He claimed it was far more representative that way.
Old 11-03-2015, 04:53 PM
jtur88 jtur88 is offline
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Doofus here. Nobody has answered the question, and few have even tried.

If blood pressure is too high, what part of the body is working wrongly, and what is it doing wrong?
Old 11-03-2015, 05:21 PM
leahcim leahcim is offline
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Originally Posted by jtur88 View Post
If blood pressure is too high, what part of the body is working wrongly, and what is it doing wrong?
One cause can be kidney disease. If the arteries to the kidneys narrow, the decreased fluid flow is interpreted incorrectly as dehydration, so they try to retain water and the additional fluid increases blood pressure.
Old 11-03-2015, 05:41 PM
engineer_comp_geek engineer_comp_geek is offline
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First of all, I'm an engineer, not a doctor.

There's a whole bunch of things that factor into your blood pressure. The main things are how hard your heart is pumping, how much fluid is in your blood, and how much the blood vessels are restricting the flow (the more restrictive the more they drive up the pressure, and the harder the heart has to work to push the blood around).

If you are overweight, then the heart has to work harder to circulate the blood, increasing the pressure.

If you smoke, that constricts the blood vessels and drives up the pressure.

Stress can cause the blood vessels to constrict and drive up the pressure.

You could just be unlucky with genetics and could have blood vessels that are naturally more restrictive.

If you are sensitive to salt, ingesting salt will make you retain more fluids, driving up the pressure.

If you have too much fluid in your body, then the kidneys should extract it and you should pee it out. If your kidneys aren't working well, they won't extract the fluid as well and the pressure could rise.

One of our medical dopers can give you a better answer, but that should give you a rough idea of some of the things that your body can be doing wrong.

Last edited by engineer_comp_geek; 11-03-2015 at 05:42 PM.
Old 11-03-2015, 05:58 PM
lance strongarm lance strongarm is offline
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Originally Posted by jtur88 View Post
Doofus here. Nobody has answered the question, and few have even tried.

If blood pressure is too high, what part of the body is working wrongly, and what is it doing wrong?
That wasn't really the question. You doofus!
Old 11-03-2015, 08:55 PM
jtur88 jtur88 is offline
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Originally Posted by lance strongarm View Post
That wasn't really the question. You doofus!
I thought he asked for the mechanics of hypertension. Like, how the moving parts function to produce the result.
Old 11-03-2015, 09:37 PM
Napier Napier is offline
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I think too much muscle tension in the walls of blood vessels is part of it. And, of course, if you eat too much salt and cause your equilibrium volume of water in your blood to be high, that's gonna increase the fullness of the system.

Note that it would make no sense for a blood pressure in your arm to go down to zero during each heart contraction. What would drive blood all the way up to your brain? Surely you have to maintain a decent pressure there under all reasonable body activities and postures.
Old 11-04-2015, 08:16 AM
Wesley Clark Wesley Clark is offline
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90% of hypertension is called idiopathic which means they don't know the exact cause.

There are other causes of hypertension. Fluid retention can cause it. Stress or anxiety can cause it because noradrenaline attaches to the alpha 1 receptor on blood vessel walls, which causes them to constrict.

I'm not sure I'd the mechanism for hypertension during exercise is the same as stress though. Blood pressure skyrockets during exercise, I saw a study where people's systolic went to 250 during cardio exercise, and that was normal for everyone tested. No idea the mechanism behind it, if it differs from the stress response that is based on adrenaline and noradrenaline.
Old 11-04-2015, 08:59 AM
Francis Vaughan Francis Vaughan is online now
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The thing to keep in mind about the blood flow is that the blood does not flow in rigid pipes. The arteries are strong elastic pipes. When the heart pumps blood, it does so into what is essentially a distributed elastic reservoir. There is a non-return valve at the exit from the heart. That valve is critical, as it stops pressure in the arteries from simply pushing the blood back into the heart after it has contracted.

When the heart beats the pressure in the arterial blood reservoir rises. It reaches a peak as the heart contracts, and once the contraction is done the valve shuts. Blood continues to flow for some part of the cycle through your body as the arteries squeeze the contained blood. During this time your heart is filling with blood at very low pressure (way below the pressure in the arteries) returned via the veins. The pressure in the arteries drops as the blood flows via the capillaries into the venous system. Once the heart is full it beats again, so the dropping arterial pressure is replaced by a new cycle.

Pressure is a funny thing when fluid is flowing. You must have a restriction across which the pressure drops. The restriction in the circulation is mostly the capillaries. Blood needs to flow through them. It is across the capillaries that you see the major pressure drop, and it is this resistance to flow that accounts for the diastolic pressure. The volume flow divided by the resistance is the pressure. Systolic pressure is the peak pressure the heart delivers into the elastic reservoir of arteries. Your near zero pressure is the flow of blood back into the heart via the veins, after it has made it through the capillaries.

So raised pressure is evidence of one or both of - higher flow rate - or - higher resistance in the circulation system. Since arteries will constrict in response to a range of things, higher pressure can be a proxy for that. Higher flow rate must result in higher pressure (or vice versa depending upon how you look at it) and so it is only useful to measure blood pressure for clinical use at rest. What your blood pressure numbers are not, is a measure of overall pressure of blood in your body. The veins account for half the circulatory system, and we are not measuring the pressure in them at all.

Last edited by Francis Vaughan; 11-04-2015 at 09:03 AM.
Old 01-14-2018, 11:46 AM
Irishman Irishman is offline
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The reason it is called "hypertension" is because the tension in the blood vessels (arteries) is considered to be too high. This is caused by the several factors noted previously. Higher arterial tension means the heart has to work harder to pump the blood, driving up the systolic (upper) number.
Old Yesterday, 02:08 PM
bardos bardos is offline
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My doctor's opinion is that the body, being self-regulating and often wise, increases blood pressure only when there is a need for it to rise. In the kidney example above, the body raises blood pressure in order that the kidneys should continue to do their job adequately. If HBP is treated as a "disease" and not a symptom, then through medications, the BP can be lowered but this would actually cause more harm than good.


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