Blood pressure machine woes.

December 4, 2012 3:26 PM

Every single time I have my blood pressure checked by a machine, it's high. If it's manually done, it is always within the optimal range (usually around 110/70). Does anyone else have this problem? How trustworthy are those machines?

I've had my blood pressure checked by three different doctors (OBGYN, GP, sleep doc) in the last six months who all used the manual method and everything was perfect. Anytime I go to Patient First, they use a machine and my readings are CRAZY high. I went in last night and it was something like 158/100 (WTF). The lady came back in 10 minutes later to check it manually and it was fine. And this seriously happens every single time I go to Patient First. I also tried out one of those automatic machines in a drug store and got a high reading. What is going on here?

posted by MaryDellamorte to Health & Fitness (18 answers total)

The machines aren't that reliable, especially for people who are not average in size. The cuff needs to be sized to fit your arm, so if your arm is particularly big or small and the machine cuff is used, the reading will be off. Manual reading is much better.

Sometimes white coat hypertension also improves after you've had some time to sit and calm down, but it doesn't sound like that is the issue for you.
posted by treehorn+bunny at 3:29 PM on December 4, 2012 [1 favorite]

Do the machines make you nervous? Because it could be some odd kind of white coat hypertension.

Since it's happened at numerous machines it does seem that malfunction could be ruled out. It may also be some quirk that the machines aren't able to read you correctly compared to other people.
posted by LionIndex at 3:30 PM on December 4, 2012 [3 favorites]

I have high blood pressure, treated by medication. I noticed this phenomenon too, although the difference was not quite as marked as yours seems to be.

When I was pregnant I was very closely monitored and had BP checks several times a month. I asked the nurses if they could use the manual pumps instead of the electronic machines and they agreed, saying that the manual pumps tend to be more accurate.
posted by DrGirlfriend at 3:32 PM on December 4, 2012

It always happens to me too. My blood pressure is consistently 10-20 points higher on each number if done by the machine than if done manually. Definitely no white coat hypertension for me. I have an especially small arm for an adult, though, so if what treehorn+bunny says about size is accurate then that makes sense.
posted by brainmouse at 3:33 PM on December 4, 2012

Me too. And the machine squeezes my arm so hard its painful enough I have to fight the reflex to yank it out of the cuff. I think its a size issue too.
posted by fshgrl at 3:35 PM on December 4, 2012

My doctor advised me to always get a second reading from the machines, immediately after the first one. The difference is significant, with the second reading always much lower than the first.
posted by synecdoche at 3:40 PM on December 4, 2012

Response by poster: I definitely don't have a big arm but I never considered it especially skinny. If the machines are consistently bad, why the hell do they use them? It really doesn't save on any time.
posted by MaryDellamorte at 3:44 PM on December 4, 2012

People are really fairly different from each other when it comes to anatomy, and while someone who is trained in taking blood pressures can adapt their strategies to allow for that, the machine is designed with a sort of "ideally average patient" in mind, so the results can never be accurate unless you fit that ideal.

Now a machine you monitor with at home is a different creature - it's like using a scale that's constantly 10 lbs. off - it doesn't matter if you -only- use that scale, because it's the constant you're interested in. As long as your bp readings stay in the same area, you have an idea of how your bp is doing as a constant, even if it shows a high diastolic or systolic or what have you. If a home machine suddenly jumps up, you still know there's a problem (or low battery.)

I personally think the ones in drug stores are simply there to amuse people waiting for prescriptions to be filled, or as a way to entice people into the drug store - "hmm, better check my blood pressure... hmm while I sit here I remember I'm out of toothpaste." You'll notice they are always, always, way at the back of the store.

For automated BP machines in clinics? Some of the more expensive machines may be more accurate that the usual ones, but I believe it's simply doctors wanting to seem impressive/just liking machines that go ping.
posted by angerbot at 3:51 PM on December 4, 2012

All our doctor friends say that the machines are not as accurate as a manual reading by a professional.
posted by smoke at 5:04 PM on December 4, 2012

make sure it is high up on your arm. Half way between armpit and inside of arm - not just resting on your arm bend. That was my problem.
posted by couchdive at 5:16 PM on December 4, 2012

The only person (including machines) who ever gets an accurate, not-too-high reading for me is my GP. The nurses always read me high. The machines always read me high. All of them are convinced my blood pressure is much higher than it actually is (which is only slightly elevated).

Doc explained that you have to listen for a certain something -- I can't remember what -- and it has to be the very last something, and that all the other people/machines assume they hear the last something when actually there's another something to come.

Hope that helps, or something.
posted by mudpuppie at 5:55 PM on December 4, 2012

Every machine I've ever used has claimed I was somewhere between pre-hypertensive and on-death's-door hypertensive. None has ever given a normal reading. In contrast, every properly-sized manual cuff has shown my ticker to be fit as a fiddle. My working hypothesis is that the machines are set to err on the side of caution for liability purposes.
posted by matlock expressway at 7:45 PM on December 4, 2012

hahaha. mudpuppie, what you're listening for is the pulse. That's what nurses and doctors hear in the stethoscope when they are measuring your blood pressure. As you let the pressure out of the cuff, the number shown on the gauge at the point when you first start hearing the pulse is the systolic blood pressure (the top number). The number shown on the gauge at the point when you last hear the pulse is the diastolic blood pressure (the bottom number). Sometimes if people let the air out too fast while doing a manual pressure they may not hear exactly where the pulse begins and ends, resulting in a faulty reading.

MaryDellamorte, the machine works decently for most people, it's just people with non-average anatomy that it doesn't work well for, because it can't adjust for your size/shape. Just request a manual BP and tell them the machine doesn't work well for you, if the situation arises again.
posted by treehorn+bunny at 7:52 PM on December 4, 2012 [1 favorite]

Those machines give me the fantods and I always read high on them. My pulse goes totally nuts too. Definitely for me it is machine-specific white coat hypertension. I don't know how people *don't* panic as a robot tightens its death grip on their poor helpless little arms. That machine could snap you like a twig, man.
posted by town of cats at 8:20 PM on December 4, 2012 [3 favorites]

Machines are worthless in terms of precision which is why doctors generally take it manually when there's an actual medical indication to gauge blood pressure. You should never make any clinical decisions based off machine readings nor should you let any clinical decisions be made from a machine reading.

Labor saving device for nurses, mostly.
posted by hobo gitano de queretaro at 8:51 PM on December 4, 2012

The cuff size thing is an issue whether you're taking a manual or an automated blood pressure - if the cuff's too small, the blood pressure reading will be artificially elevated. Most sphygmos should come with a few removable cuffs of varying sizes, definitely any used professionally. People often don't change them when they should because they're lazy. Anyway, there's a marker on the cuff to indicate where it should be closing, and if it's outside that range the cuff is too small. Demand an appropriate cuff!
posted by chiquitita at 9:08 PM on December 4, 2012

Here's a guess: a manual BP is done by auscultating the Korotkoff sounds, whereas all modern mechanical BP cuffs work by measuring the expansion of the artery via the pressure it places upon the cuff. The latter method is much more easily disturbed by a variety of factors, largely because it's not directly measuring the systolic and diastolic pressures but rather interpolating for them using oscillometric methods I don't understand well enough to explain. For more information, read the Wikipedia articles on blood pressure, sphygmomanometer, and Korotkoff sounds.

In any case, the order of accuracy is manual BP with a mercury sphygmomanometer > manual BP with an aneroid sphygmomanometer > digital BP using oscillometry.
posted by d. z. wang at 9:35 PM on December 4, 2012 [1 favorite]

I wouldn't throw out blood pressure monitors completely. There is enormous variation in the quality and accuracy of these units.

Other posters are correct in noting that blood pressure readings from machines are often more sensitive to external influences such as posture and arm height position than readings from a physician or nurse using a sphygmomanometer and stethoscope, but very good machines can deliver perfectly good results; if they couldn't, they wouldn't be used in intensive care units.

Certification counts. There's a lot of cheap crap on the market. Machines that have been certified by blood pressure societies are generally precise, though I have found they do read slightly high. Still, when it comes to treating hypertension, it is better to have a slightly high reading and a slightly low one. I certainly wouldn't trust an uncalibrated monitor.

The Welch-Allyn monitors used in clinics are as good as any manual measurement when used correctly, but they are large, not intended for consumer use, and are breathtakingly expensive.
posted by rhombus at 4:18 AM on December 5, 2012 [1 favorite]