Blood Pressure affected by barometric pressure?

Factual Questions
1

My search skills are seriously deficient, and after attempting to find such information through Google and the SD, I ask for your knowledge…

Does the barometric pressure have an impact on the reading of blood pressure? If a person has the same biophysical profile and a blood pressure reading is done during clear weather (high pressure), will it be different than during rainy (low pressure) weather?

My wife is being monitored very closely due to preeclampsia and get varied readings despite continued bedrest. There are serious implications if her BP rises dramatically and suddenly and I want to understand some of the smaller fluctuations and whether they are atmospheric anomolies or indicators of potential trouble.

I’ve not had the opportunity to ask the doctor yet…

2

What an interesting question. My first response was “NOPE” in that the blood is in a closed circuit. There is no air pressure pushing on the “survace” of blood. There is an effect of the air pressure on dissolved gases in the blood (via lungs) as most scuba divers are aware.

Then I thought, “What about the sphygmomanometer (sp?)?” The mercury tube type that one sees in a Dr.'s office has a vacuum above the mercury in the tube thus is not affected by air pressure. Same with the dial types. The “zero” pressure in the top of the tube (one reference) is compared to the other pressure in the cuff. Mathematically, the 130 in the 130 over 70 bp is actually 130 in the cuff - 0 in the reference tube.

Then I thought, “What are the units for the sphygmomanometer?” I figure they must be in mm Hg. If this is the case, we can compare that to the average pressure at sea level (760 mm Hg). If you took your bp at sea level on a 760 day and then on a 750 day, would your bp measured be “off” by 10 mm Hg?

First, we should look at the “average” fluctuation in air pressure. Here in The States, if air pressure deviates from standard by more than 3/4 of an inch, we’re in the middle of a big storm. This would equate to roughly 18 mm Hg. Not a big deal when compared to 760 mm Hg as standard. However, 18 may be a big deal when compared to systolic pressure of 130. Now, the question becomes, “should we be concerned?”

Then I thought, what does the systolic and diastolic pressure actually mean? Well, it’s the pressure required to collapse the vein partially and then completely. The resulting pressures in terms of the blood are the pressures that the blood must exert to begin opening a crushed vein and to completely open the crushed vein. These pressures are exerted by the squeezing of the cuff, above and beyond the ambient pressure. This means that the ambient pressure is subtracted out of both measures.

Whew… In short, I dont’ think it has any effect.
[disclaimer]If it does, it’s certainly teeny.[/disclaimer]

I’ll jot off an email to doctor relatives and ask them, just to be sure.

Se non e vero, e ben trovato.

with heartfelt wishes,
Spritle

3

Just re-read my post and realized that it isn’t real clear, especially the last part.

Atmospheric pressure would affect blood pressure readings if there was a blod/air interface and the blood had a place to “go”. Blood is a liquid and thus darn hard to compress. Pressure on one “side” is carried to the “other side” completely. Since your blood is a liquid inside a rubbery tube surrounded by cells that are mostly liquid, and since there are no air pockets inside you (as far as would relate to blood pressure), and since your entire body is feeling ambient pressure all the way around you (e.g., all around your arm) there is no effect of air pressure on blood pressure.

Better?

4

That bit about sphygmomanometers isn’t right. There’s no vacuum in the Doctor’s mercury filled tube (if they even use one - many use other types with a rotary dial or a digital transducer). And it would be influenced by barometric pressure if it did have a vacuum on only one side, but would not be if it had no vacuum (or a vacuum on both sides of the “U”).
Barometers and sphygmomanometers both measure pressure, and they can use “mmHg” or “in. Hg” as units of pressure, but this does not imply that either influences the other.

The short answer to the question of whether barometric pressure influences blood pressure is, no. Not in the sense that the act of measuring is interfered with somehow. By “blood pressure” is meant the differential pressure inside the blood vessels (typically more specifically the arteries) relative to the outside of the body. As the barometric pressure changes, the absolute pressures in both of these places would change together (or if you like the differential pressures between each of these places and a vacuum). But the difference between them would not. And this makes sense - you can’t really feel barometric pressure, not the fifteen pounds or so on each square inch of any surface.

But the longer answer is, well, maybe it does, a little. Because if the barometric pressure is really low, you have a harder time getting oxygen, and you feel different, and you breathe harder, and for all I know your blood pressure goes one way or the other as a result. This would be relevant at a high altitude. On Everest at 28,000 ft. it’s hard to breathe at all and harder still to function. It’s not what you meant, but many of the poor souls who tried Everest now don’t have any blood pressure at all as a result. Last week in Flagstaff, AZ at 7000 ft. I was frequently winded and out of breath, being used to sea level. The swing of the barometer with weather conditions is smaller than this, though, and I have never heard of anybody noticing the difference.

5

Rummaging around on Google for a while turns up nothing that says to health professionals, “Now, remember, you have to correct this for whether it’s rainy weather or sunny weather.” I take this to mean that the answer to the OP is, “No, the gadget itself isn’t affected that much by atmospheric pressure to affect the results.”

Answering the question you didn’t ask:

The fluctuations in your wife’s blood pressure are due both to the condition of preeclampsia, and probably to the normal daily fluctuations in a person’s blood pressure. It’s nothing to do with defects in the sphyg-- the sphgymon-- aw heck, the blood pressure cuff, or with atmospheric pressure. That’s just wishful thinking on your part, babe, sorry. Wanting to say, “Well, it’s up 10 points today because it’s raining outside” just isn’t supported by the facts. Look for some other reason for her BP to be up 10 points today. Bedrest itself can cause fluctuations.

http://www.dartmouth.edu/~obgyn/mfm/PatientEd/Bedrest.html

Have you seen this website?
http://www.preeclampsia.org/about.htm

Differences in equipment can account for variations.
http://www.preeclampsia.org/symptoms.htm

You say “varied results”. How “varied”? Small daily fluctuations are normal. The idea is to keep the blood pressure down to within certain parameters, not to set a specific numerical goal and to worry if it varies slightly from that goal. It’s normal for a person’s blood pressure to fluctuate during the day; that’s why they tell you to take the readings at the same time every day.

Irritation or annoyance can account for variations.

http://www.webmed.org/ttyh/BCD_hypertension.html

Hope this helps. :slight_smile:

6

cough Oops, ignore the bedrest reference, it doesn’t say what I thought it said. That’s what I get for trying to post and look things up on Google and eat pretzels and watch Superman IV in the other room, all at the same time. Multi-tasking, feh.

7

Here is another article (from the current issue of the British Medical Journal) which details factors affecting the measured blood pressure. Table 1 and Table 2, in particular, are germane to much of this thread.