How does exertion make blood pressure too low?

Factual Questions
1

My grandpa has some heart problems, one of them being low blood pressure.

I talked to him today and he said Wednesday he was working in the yard all day, then Thursday he spent the day feeling miserable and recuperating on the couch, because his blood pressure went down to 119/34 or something. He knows this because he has a blood pressure machine at home.

It’s not a surprise to him that exertion = low blood pressure, and rest = blood pressure going back up to normal. He is under a doctor’s care yadda yadda.

But we were both wondering how physical exertion brings his blood pressure down. People with high blood pressure avoid exertion because it brings your blood pressure up (doesn’t it?) What would be the mechanics behind this?

2

Exertion (particularly doing stuff for hours outside) --> water loss through sweat --> reduction in blood volume --> loss of blood pressure, especially for someone whose heart can’t work hard enough to make up the difference. --> feeling like crap

Hell, I’m young and healthy and 6+ hours of doing stuff without hydrating makes me feel like crap.

3

First of all, blood pressure is relative. In a normal, healthy adult 119/34 is not low, it’s within the “normal” range. If your grandpa is normally hypertensive, then it could be low. When BP drops suddenly, blood flow changes. For example, the brain gets less than required, causing lightheadedness or even fainting.

Exertion causes blood vessels to dilate to regulate temperature and to redistribute blood to the body parts being exerted.
Think about two hoses, one with a 1/2 inch diameter the other with a 1[sub]1/2[/sub] inch diameter. With the same flow rate, the pressure in the smaller hose is higher.

This is a pretty simple explanation, the process is more complicated, but I think you get the idea.

4

Maybe he suffers from orthostatic hypotension?

I have that condition and whenever I stand for long periods of time I feel very tired afterwards and in extreme cases I have fainted.

I have no problem walking or running because the leg muscle contractions move the blood back upwards, but whenever I am in the standing position and relatively still, then I start feeling bad.

5

[QUOTE=picunurse]
First of all, blood pressure is relative. In a normal, healthy adult 119/34 is not low, it’s within the “normal” range.
[/QUOTE]

I defer to your expertise, but isn’t a 34 diastolic pretty darn low?

6

Diastolic readings are very subjective and can vary a fair bit depending how one defines the disappearance of the sounds (i.e. when you listen over the arm while the BP cuff is deflated you first hear the sounds start and then you hear them disappear. That corresponds to systolic and diastolic respectively).

7

What picunurse says doesn’t really account for the observation that blood pressure normally goes up with exercise. So, a low BP during exercise is particularly unexpected. Empirically, it’s known that people in whom that phenomena occurs tend to have a very high risk of serious heart disease.

BP that falls with exercise may reflect underlying heart valve disease (i.e aortic stenosis) which would also account for the low diastolic value if aortic insufficiency is present (it often co-exists with aortic stenosis). More likely though, a drop in BP with exercise signifies severe underlying coronary disease (refs on request).

8

My grandfather had a sextuple bypass and does have a bad valve I believe. He has a pacemaker.

I’m not looking for a diagnosis, btw. He totally is getting all sorts of doctor’s care for his heart. We’re not wondering what conditions he has that would cause this more like what is the mechanics of it. But, I realize you guys probably need to know more about his heart history in order to say why this particular heart is doing this particular thing. Sorry - he’s 84, it’s hard to keep up with what he has had worked on :slight_smile:

KarlGauss are you saying that since his valve is bad, the low BP could be a symptom of the valve not working right because it’s being overworked, and thus bloodflow gets all wonky? That makes sense.

9

Ok, so he’s had heart attacks before, right? Hence the bypasses and the pacemaker.

Here’s an overview of what happens during a heart attack
The end result is that his heart has sections that are damaged and don’t contract like they should. Because it can’t contract like it should, it can’t move the same volume of blood with every beat that it should.

Those same damaged areas of his heart can’t relax open the way they could before either. It is important that the heart relaxes properly so that it can refill with blood. When your grandpa exerts himself, his heart rate goes up, and the fraction of time that the heart is relaxed and able to refill gets shorter. Since his heart isn’t as flexible, it doesn’t refill with as much blood in that split second as it is supposed to. Couple that with the decreased ability to move that blood back out again that we talked about before, and you’ve got some bad mojo.

His blood pressure drops because he can’t fill up his heart with blood correctly or move the blood out to his body.

The hydration is still a factor, though.

10

[QUOTE=KarlGauss]
What picunurse says doesn’t really account for the observation that blood pressure normally goes up with exercise. So, a low BP during exercise is particularly unexpected. Empirically, it’s known that people in whom that phenomena occurs tend to have a very high risk of serious heart disease.

[/QUOTE]

The OP said he had a low BP the day after the exercise, not during exercise, so dehydration or hypovolemia would make sense.

11

He has not had a heart attack. He’s just got a bum heart I guess.

I’ll have to ask him about his hydration during yard work. He is not of the Gatorade generation.

12

[QUOTE=PetW]
The OP said he had a low BP the day after the exercise, not during exercise, so dehydration or hypovolemia would make sense.
[/QUOTE]
Right you are. I missed that. So, best just to ignore my ramblings!

13

[QUOTE=ZipperJJ]
He has not had a heart attack. He’s just got a bum heart I guess.

I’ll have to ask him about his hydration during yard work. He is not of the Gatorade generation.
[/QUOTE]

Well now you’ve got me confused. I can’t think of a good reason for someone to have bypass surgery unless it’s for a heart attack or to avoid a heart attack. Find out the medical name for whatever he has going on and report back. :slight_smile:

14

[QUOTE=Pullet]
Well now you’ve got me confused. I can’t think of a good reason for someone to have bypass surgery unless it’s for a heart attack or to avoid a heart attack. Find out the medical name for whatever he has going on and report back. :slight_smile:
[/QUOTE]

that is correct, but if you’ve had a bypass to AVOID a heart attack, you won’t have any of the damage decribed in your earlier post

15

Yeah he had bypass to avoid a heart attack. He’s a very fit, thin guy and eats like a mouse. 'Cept he is addicted to snack cakes and cookies (his wife bakes with lard) and ended up with extremely clogged arteries and high cholesterol.

He had the bypasses a while ago, like 5 years. Then in the last 2 years or so he still “felt bad” so they put in the pacemaker.

He’s also had a heart murmur his whole life. Forgot to mention that. Not bad enough to “fix” with surgery I don’t think.

Does a heart murmur cause low blood pressure? My dog has a murmur, and she tires easily. No one ever told me it’d make her have low blood pressure, tho. You’d think that if the heart is beating all goofy, pressure would be higher.

16

[QUOTE=ZipperJJ]
Yeah he had bypass to avoid a heart attack. He’s a very fit, thin guy and eats like a mouse. 'Cept he is addicted to snack cakes and cookies (his wife bakes with lard) and ended up with extremely clogged arteries and high cholesterol.

He had the bypasses a while ago, like 5 years. Then in the last 2 years or so he still “felt bad” so they put in the pacemaker.

He’s also had a heart murmur his whole life. Forgot to mention that. Not bad enough to “fix” with surgery I don’t think.

Does a heart murmur cause low blood pressure? My dog has a murmur, and she tires easily. No one ever told me it’d make her have low blood pressure, tho. You’d think that if the heart is beating all goofy, pressure would be higher.
[/QUOTE]

As you mentioned before, a heart murmur is not an irregular beating pattern, it is a valve that is leaking. The valves in the heart are all one way valves, so that the blood is always moving forward. When one of the valves is leaking, blood shoots backwards, creating turbulence and a swooshing sound that you can hear with a stethoscope. The net effect is that not as much blood goes out of the heart with every beat as is supposed to, and the heart has to grow larger to move more volume and work harder to move that volume out to the body.

So in the end, we get the same problem as before: his heart has to work harder than a normal person’s in order to accommodate for when he exerts himself. Exactly how much harder it has to work depends on how bad the leak is.

Since your grandpa has been living his whole life without a big problem from the murmur, it probably isn’t the main thing causing his low blood pressure. Conversely, your dog’s murmur likely was bad enough to give her low blood pressure.

I’m surprised your grandpa needed a 6-way bypass and hadn’t had a heart attack already. Good that they caught it. But, now I’m curious what specific condition he has that requires a pace maker.

The pacemaker is there because the electrical activity of his heart is malfunctioning for one reason or another. Each heart cell is capable of contracting at a specific rhythm, but some cells have a faster rhythm than others. The ones that contract first stimulate the others to contract in a big domino effect. How frequently this happens is what sets your heart rate. The place that the domino effect starts from is important, too. The chambers of the heart have to contract in a specific sequence in order to move blood forward. If the normal rhythm cells get damaged, or if their is a gap in the signal conduction, then the heart either won’t beat frequently enough or it won’t beat in the right sequence. The pacemaker sets the contractions back at normal speed and normal direction.

Your grandfather may have needed a pacemaker because of his heart murmur, or maybe not. Bad murmurs cause the heart to get bigger as it tries to accommodate for all that blood that isn’t moving forward with every beat. Really bad murmurs can dilate the heart so much that it slows down the domino effect of the contracting muscle cells. But again, your grandpa has been living with his murmur for a long time, so it probably isn’t that severe.

I’m not sure how sophisticated human pacemakers are these days so I’m not sure if it is setting his heart rate at a speed that isn’t sufficient for exertion. Maybe one of the human medical folks will help.

Is his heart is only problematic organ?

I still like the dehydration hypothesis. It’s the theory that fits best with his being ok at the exertion while he’s in the midst of it, but feeling crappy afterwards. I know that, when I’m busy working, I will let myself get pretty dehydrated and won’t even feel thirsty. I’ll just get progressively more exhausted and muddle-headed. One time, when I was feverish, I dehydrated myself so badly that my blood pressure plummeted whenever I stood up and I blacked out from lack of blood to my brain. Did that a couple times before I figured what was wrong. Fortunately, I only gave myself a black eye hitting the bathroom counter on the way down instead of cracking my skull open. Scientifically, a neat demonstration of physics and biology. Emotionally, damned scary.

17

Thanks Pullet, and everyone! I think dehydration has got to be a main culprit, if not *the * culprit.

He lives out in the country but he moved there after 60 years in the city, so I’m not sure how much water he drinks since they have well water (and he’s used to city water). He’d never buy bottled water in a million years…I’ll have to see if I can hook him up with a case. I also highly doubt he gives any consideration to electrolyte replacement (it’s what plants crave!) With whatever pills he takes I’m not sure if he can dose up on potassium or not (in banana form).

I’ll see if I can grill him on his water intake, and send him some water from the “city.”

Technically, though, he’s 84 and should really just sit the fuck down. hehe