Commonly used arm positions can overestimate blood pressure readings: study

There's definitely a huge variance in blood pressure readings depending on posture, relaxation, arm position, recent activity, etc. If you buy a blood pressure monitor, it's really interesting to see how "random" a single reading at the doctors' is, and how large your fluctuation throughout the day is.

That being said, it really makes me wonder about studies that correlate blood pressure with other things. Is the blood pressure really being measured "correctly" in all those studies? Or not?

In other words, if your "true correct" blood pressure is lower than what the doctor normally takes, but then a lot of the studies are based on real-life "incorrect" higher blood pressures, then don't you similarly want an "incorrect" higher reading for consistency? Or are the studies always really done with far more accurate blood pressure readings, where the patient sits still for 5 min beforehand, keeps their legs uncrossed, is totally free of stress and anxiety, didn't exercise beforehand, etc.?

> Is the blood pressure really being measured "correctly" in all those studies? Or not?

This is why you do readings three different times a day for several days. And why there’s instructions on how long to dust still before the readings, why you do three repeats with multiple minutes of wait in between, and finally why the averages of those readings aren’t just simple averages. But yes you always have to wonder about every study using self reported home readings if they follow the instructions or not, because it is tedious to do it correctly.

I guess it depends on the study. If it is just comparing between groups, the conclusions probably still hold if they consistently measured blood pressure in the "incorrect" way. If it is something like "85% of Americans have high blood pressure", then probably the conclusions are incorrect because they are comparing the "correct" baseline against an incorrect measurement method. There are also other ways to measure blood pressure, like recent smartwatches - so read the methods section carefully, I guess.

As long as blood pressure variance is randomized then you’re getting a signal, and that happens when everyone is measured in a similar way (or randomized to different ways). You don’t need perfect precision.

What you don’t want is to make everyone who, say, smokes wear the cuff while standing up while everyone else gets cuffed lying down.

> and that happens when everyone is measured in a similar way (or randomized to different ways)

But that's exactly the issue -- that the similarity or randomness is one way for one study, and another way for another study, because of culturally different sets of nurses and/or patients.

In other words, you're right it's not affecting results within a study, but it makes comparison between studies questionable.

And it makes it equally questionable whether a study's results apply to you, if your signal is 10 units off of a study's signal, and occurs across a cutoff that determines whether you should take a medication or not.

The reading process itself is a constant that you can't filter out by doing it repeatedly. Something squeezing your arm with what feels like the force of a hydraulic press surely doesn't have any weird side effects.

Anecdata, but I always get high anxiety from not being sure if the thing is actually still working properly or if it's just gonna keep pumping itself up until it explodes in my face or something. Not exactly rational but these sort of things never are. Looney toons ass machine.

"Something squeezing your arm with what feels like the force of a hydraulic press"

It shouldn't feel that crushing. I know it's common, but it shouldn't be. It's lazy/rushed healthcare professionals who only want to take it one time suing an automated machine and crank it to 200mm. If you actually put it at 140mm or take it with a manual sphig, it would read a "normal" person just fine without the crushing. The problem is, the people who are high around 130-140 need the machine at least 20mm higher and would need a retake, which means more time.

When my heart went to hell, I bought a blood pressure monitor. Before I left the hospital, I had to agree to religiously test my blood pressure three times a day at the exact same time. Anything beyond that was a bonus, but to provide useful data I needed those three readings a day.

As my cardiologist explained, 39 year olds don’t randomly end up spending a week in a cardiac ward so he needed better data to form a holistic treatment plan.

I have an automatic at-home blood pressure device, and it does the same thing. Not 200 mmHg, but high enough that I’d freak out if I didn’t know it was normal and would let up soon enough[1]. Did the product designers do that intentionally while still meeting a spec of “not panicking the user in a way that would elevate blood pressure” and getting approved for sale to non-professionals?

It seems like this is genuinely hard to work around in practice.

[1] I recall it being a staple of 80/90s tv, at least Beavis and Butthead, to have a character use an auto blood pressure device and freak out at being so clamped.

My wife had a Cryo Chamber Therapy for a few weeks and had to measure pressure and pulse before each session so they let her in. After about a week she was refused entry because her pressure was too high (when she measured it at home - it was normal).

Since then she had problems getting admited every time, and she started to fear the measurement (she had to drive there during work and do overtime later).

She started arguing with the guy and wasted like 5 days driving there and back during work without having another session because the pressure and pulse were too high (despite both being OK at home).

Eventually she went to another person in that hospital to measure her pressure. It was perfect. But when the guy near the entrance to the cryo chamber measured it - it was too high to let her enter.

They tried different instruments and the difference was the same. When the guy measured it - it was too high. When somebody else measured it - it was fine. Finally they let her do the cryo chamber without the guy permission :)

We assumed the difference was just that she was anxious and frustrated when she's seen the guy, but now I wonder if the difference was the position in which he measured the pressure.

There might be a repeatability thing. Always give the full pressure then at least it's one less variable to account for.

Nah. Modern automatic cuffs are adaptive. They tend to first run up pretty low (like 150), see if there is signal. If not then they have to inflate more and more. They tend to determine where to start next time based on the last reading, so if it had the go up to 200 for the last reading it’ll start there next time. If the cuff is a vise, excluding operator error the most likely cause is actually having high blood pressure.

I found that that the measured BP was consistently significantly lower if I didn't look at the device's display while it was doing it's thing. This at home, with a quality device, after doing it many many times.

Had the exact same thing happen when I was doing a Ketamine therapy thing a while back, and I definitely think the anxiousness about the reading had something to do with it.

I've always had perfectly okay blood pressure whenever I have it done at a regular doctor's appointment, so I think knowing that the reading actually matters definitely increases my blood pressure. Ended up getting a doctor's note saying "they don't actually have high blood pressure they are just reacting normally to possibly having to be sent home and reschedule" more or less.

Exactly, this is my concern as well. They say you have to be seated for 5 minutes at least, completely relaxed, not hungry, not having to go the bathroom, in a quiet a room, it must not be too hot or too cold, with both your feet on the ground, before you can have your blood pressure measured, otherwise the reading could be 'artificially' high. Really? It seems to me that if you do all these preparations, the reading will be artificially low, since such conditions are nothing like the conditions that you'll typically find yourself in through the day in your everyday life.

Just to point, it's known that a sizeable segment of the population reacts to the pressure measuring process with increased blood pressure.

Reading around (e.g. [0]) it sounds like variance isn't something researchers care for, probably with the assumption that screening with a higher value is better than missing an issue from a lower value.

We see the same for body temperature (speed and convenience is usually prioritized over accuracy) and weight (2% variation is largely accepted). Afterall guidelines are already off as by definition, as they don't account for individual circumstances, so perhaps aiming for accuracy is useless in most settings.

[0] https://www.mayoclinic.org/diseases-conditions/high-blood-pr...

The goal is to get a clinically relevant measurement, captured at rest under specific conditions, not a measurement that's representative of a random moment during everyday life.

One alternative is a cuff that measures on the upswing, rather than the downswing. It does not tend to squeeze quite as hard, because it stops as soon as it has the systolic reading.

e.g. Omron BP7000

> This is why you do readings three different times a day for several days.

What good is this if my monitor is not as accurate as the one at a doctor's office? It's not like my doctor would take my monitor's readings over his.

You might be surprised. "White coat hypertension" is well-known. Someone with a reliable set of readings from home would be more convincing than someone who says "I get it read at Walmart/CVS once a month and it's ok".

Your doctor's office's monitor isn't incredibly accurate. If you want accurate, you need a mercury sphygmomanometer to measure the pressure. Unless fundamental properties of the universe have changed, it will also be comparable to any other readings taken with mercury.

My doctor was handing me, hypertension, pamphlets, and talking about medication.

Finally realized, that I was habitually late, getting to my appointments and always taking the stairs.

Don’t do that.

Also doctors and nurses are known to do an abject awful job of measuring bp according to the defined procedure. It’s usually way off when taken clinically.

Ars article here but there’s plenty in pubmed too.

https://arstechnica.com/health/2024/10/your-doctors-office-c...

[edit] The prep guidance is…

> You must not eat, drink, exercise, or smoke within 30 minutes of a reading. You must have an empty bladder. You must sit straight up in a chair with back support. Your legs must be uncrossed and your feet must be flat on the ground. The arm to be measured must be rested on a flat surface so that it is at the same level as your heart, not lower, not higher. You must sit calmly, without talking for five minutes to relax before the reading. When it's time, an appropriately sized cuff should be wrapped around your bare upper arm, right above the elbow; it should never be wrapped over clothing. At least two readings should be taken, with the average recorded. Ideally, readings should be taken in both arms, with the highest readings recorded.

When was the last time you got it measured properly? Literally never for me in a clinical setting. I don’t know why they bother honestly.

Yes, i experiment with eyes open/closed as well

Probably never, I have really long arms and they usually take it just barely above the elbow also. I have always been on the higher end even when in my 20s and training/dieting for athletic events.

Used to flummox me until I bought my own meter, they can be like $30.

This is why it is better to take three measurements and do an average every time to minimize errors.

The studies on correlation probably have a large enough sample size to become statistically significant - i.e. you have to read the "Method" section to find out how reliable it is, this requires certain kind of statistics and/or scientific background.

Another fun factor I learned about five years ago is temperature. My gym was offering a complimentary fitness evaluation, which among other things included a blood pressure test. The trainer was horrified to see 140-something over something equally terrible, and started explaining how she'd have to refer me to a doctor and advise that I refrain from strenuous physical activity, until I showed her a report from my annual physical a few days prior with 106/70. Turns out that walking to the gym in shorts and a T-shirt in late January causes enough vasoconstriction to really screw with some measurements.

And what's the typical variance (from "actual") for a "usual" reading?

Find one that is accurate enough and crosscheck it with the one at the doctor by taking regular measurements so you get an idea of trends rather than absolute values. Doctors do know about white coat hypertension - it's not a myth. There's no reason you can't do your own experiments with consumer-level blood pressure monitors from reputable manufacturers. In fact, it was my mother's primary care provider who recommended she buy one for home use.

This is what I did with a US$10 pulse oximeter (a Contec CMS50M from China) when my dad ended up in ICU last year, and it was pretty much bang-on with its readings. I've also tested my pulse oximeter on plane trips and know it will drop below 90% when the air is thin (and rise up again if I do some deep breathing), and therefore know it isn't always stuck at a high value.

Search PubMed for "The Accuracy of 6 Inexpensive Pulse Oximeters Not Cleared by the Food and Drug Administration: The Possible Global Public Health Implications".

I once had a similar high outlier blood pressure reading after a somewhat busy day followed by running through the city to my blood donation appointment. Who knew that BP is affected by external factors and doesn't stay constant throughout the day‽‽

Good question, for myself personally (anecdotally) I got systolic of 145-ish in the doctor's office and 120-ish at home. This was validated by a medical take-home 24h cuff.

My doctor did. My blood pressure was slightly elevated in his office and I said it happens at every doctor. He said to get a home monitor, test 3 times in the morning, 3 times in the afternoon for a week and bring in the results at the next appt.

I have a 6-7 year old Omron brand device that doesn't do this. I can always tell right away when my BP is running high because I can feel the machine squeezing harder than normal to get the reading.

> are the studies always really done with far more accurate blood pressure readings, where the patient sits still for 5 min beforehand, keeps their legs uncrossed, is totally free of stress and anxiety, didn't exercise beforehand, etc.?

In situations where blood pressure really matters, we aren't playing around with the cuff and hand positioning. The patient gets an art line.

Doctors recognize that non-invasive BP measurement is an imperfect screening tool. Anybody worth their salt isn't getting worked up about these level of details, because it's largely a waste of time and effort. The solution to an error prone screening tool is not to repeatedly use the screening tool. You move on to more accurate and focused methods of testing.

> Is the blood pressure really being measured "correctly" in all those studies? Or not?

Probably incorrect in most studies, especially large population ones that influence treatment guidelines.

It’s academic and doesn’t practically matter though.

The pathogenesis of hypertension related disorders (kidney failure, heart failure, stroke etc) is well known.

It’s not in doubt that sustained hypertension is bad, that there is increased risk with higher blood pressure and that patients with high blood pressure undergoing treatment suffer less of these bad outcomes.

What's the point of taking your blood pressure if doing any of these things causes significant variance? I'm not meditating at home or out and about all day. So why does it matter what my blood pressure is in one single state? What if I'm in an elevated state all the time? What if I never am? It makes it really hard to believe that blood pressure readings are anything more than nonsense.

Kaiser measures BP on every visit and arm position seems like the least of their worries:

- no rest period before measurement

- measured through a medium-thickness sweatshirt sleeve

- cold hospital hallway

- no back on the chair

- no height adjustment on the chair

- no real surface to rest your arm on (They usually use the handle of the equipment cart that the BP monitor is mounted to)

- Zero attention to cuff positioning/orientation

I've come in at 160/90 but went down to 120/80 after rotating the cuff 1-2cm and resting for a few minutes. Manual measurements from the doctor are usually more accurate.

If you're doing a double leg press (especially in conjunction with a Valsalva maneuver) you can get an instant BP reading as high as 320/250. If that's your idle BP then you're not long for this world lol.

If your BP - measured in a specific and consistent set of conditions - is elevated vs baseline then you are at an increased risk for a set of medical conditions. Researchers could have picked any set of conditions to establish that baseline but I assume that idle is easier to standardize on than e.g. double leg press with 3 RIR. It's not which condition per se but rather that it's the condition researchers aligned on and studied.

The problem is that if the risk is established based on your deviation from the baseline, then you must be measured in the same conditions under which the baseline was established otherwise the results don't mean much if anything at all.

Oddly, at least a decade ago, at least one Bay Area hospital stroke protocol required manual BP readings with a sphygmomanometer. And the patient had an art line.

Not sure if they didn’t have the equipment for art blood pressure or what, but good BP readings were important. And they had all the fancy equipment. Patient presented with an ischemic stroke, and was getting a stent + thinners, so anything problematic was likely due to something immediately life threatening.

They didn’t want an automatic cuff system because it could cause something to burst with the pressure ramp up. At least that is what the surgeon said.

Source: I was the EMT-B on his clinicals who stayed with the patient in the OR while he got stented and took readings every 5 minutes because none of the nurses were ‘current’ on the manual cuff. or so they said. I was pretty fresh, and was pretty good at it at the time, but I think they were just making excuses now haha. I held his hand through the procedure to help calm him down too, which seemed to help a lot.

Patient 20 something that day. Emergency Rooms are quite an experience. I volunteered for Halloween Night, which added to it I’m sure.

PS. Watching the Dr install the arterial catheter (or maybe it was a port?) in the ER was wild. Literal stream-of-blood-shooting-across-the-room-and-spraying-on-the-wall wild. Never seen anything like it before or since. I was glad I had my safety glasses on.

There is another factor that everyone is ignoring here. Some people are just much more sensitive to that kind of pain. If you Lymphadema, or especially Lipodemia, you are much more likely to experience a lot of pain even when a manual sphygmomanometer is being used.

The Omron BP7000 doesn’t hurt me that much, and I measure mine every morning and every evening. But it does hurt my wife, and she has both conditions.

Don't worry, your monitor is good enough for the purpose of screening for hypertension. Truth is the exact values don't matter much for this purpose. Only thing that matters is the fact that people die less and develop less complications when treated based on the results. They are still useful even if the figures have some error in them.

Medicine is just statistics.

Having a full bladder will raise your blood pressure.

Kind of wonder the same thing about BMI and water composition. Your body weight can vary by up to 10 pounds depending on how much water you're retaining. I've never been able to find information about the composition assumed or measured when coming up with BMI numbers.

Granted I don't think the ultimate effect is huge, and you can eliminate it by weighing yourself daily and taking an average. But most people don't do that, and a spot-check at a doctor's office certainly can't do that.

10-20 mmHg.

https://www.ncbi.nlm.nih.gov/books/NBK482189/

> Smoking within 30 minutes of measurement can raise the systolic blood pressure to 20 mmHg

> a distended bladder can increase systolic and diastolic measurements by 10 to 15 mmHg.

> Sitting in a chair lacking back support can raise systolic blood pressure to 10 mmHg, and a similar increase is observed when both legs are crossed.

> Talking/listening during measurements can increase systolic and diastolic measurements by 10 mmHg.

The major exception is cuff placement over clothing which is noted to vary results by up to 50 mmHg but doing that is stupid anyway and makes you fail medical school.

> I've never been able to find information about the composition assumed or measured when coming up with BMI numbers.

BMI is just weight divided by height squared. No distinction is made between type of mass. Muscle mass, fat, bone, water? BMI couldn't care less. It sums all that stuff up into a single value.

Think of it as a number that roughly correlates to disease. There will always be false positives and false negatives. False positives are acceptable. We want to minimize the number of false negatives.

There are nearly ten billion humans on Earth. It is not possible to fully evaluate every single one of them. Gotta run a SELECT statement. Filter them based on some criteria, and fully evaluate those that match. BMI isn't perfect, but it takes less than one minute to measure the variables and compute it. The equipment required is cheap and easy to use. Speed, efficiency, cheapness and ease are extremely important factors when you're applying this at national scales.

Patient might turn out to be a physically fit 100 kg 1.7 m 34.6 kg/m2 body builder. That's alright. Our objective is to make sure the obese and the malnourished can't escape the sieve.

Either it's accurate enough (most cases) or it is too wrong

Unless it's a wrist model, it should be ok.

My understanding from people who follow the literature is that the studies are done with the recommended procedure, 5 minute wait and all.

> The solution to an error prone screening tool is not to repeatedly use the screening tool.

It can be. Repeated in office blood pressure measurements increase sensitivity and lower specificity. It's not as good as 24 hour monitoring but sometimes that's the best you've got.

You could probably get to a better generalisable number by slapping waist circumfrence in there as well.

I think this is a well-known thing, being apprehensive about having the measurement being taken can influence the result - https://en.wikipedia.org/wiki/White_coat_hypertension

I have omron it has been at least 10 points lower then my other ihealth cuff. I even sent it in, they said was fine. Had the dr check it as well. It was always 10 points lower. I read that omron measures differently than the typical bpm.

I get anxious when taking blood pressure as well. There are techniques your wife can try before entering the cryo-chamber look up the 478 breathing technique. I developed a white coat blood pressure readings over the last several years measuring a stage one or stage two hypertension at my last doctor visit. I use the 478 breathing technique and my blood pressure readings are normal at my last dr visit.

I had a similar trip to the blood bank once: I rode my motorcycle from Palm Springs to San Diego, straight to the blood bank, on a cold January morning. As usual, they took my temperature. It was 95-something. They said, "Are you feeling alright?" I said, "Sure, I should have worn better clothing for the ride down here, but I'm fine." They conferred, then took my cold blood :-)

iOS voice dictation?

For me, the first reading is usually higher (by 20-30, even after a long rest period) and subsequent ones get lower and lower as I calm down from the initial worry about whether I will get a high reading or not.

At the doctor's office / hospital I try to tell them this, but they tend not to care. I think they know it varies a lot, they know about psychological effects, but i) they anyway take it much less seriously than overthinkers like me and some fellow HN-ers would imagine and ii) they may prescribe something and anyway expect it not to do much, and also expect the patient not to follow through with taking it properly etc. Honestly, the whole thing is quite a farce. The painful truth is that generic lifestyle improvements are the biggest bang for your buck, instead of worrying about getting exact and precise blood pressure readings.

The other similar big thing is routine blood tests for deficiencies and cholesterol, iron etc. It can also have huge variance over the year, and often people only do it every one or two years and take it as this extremely solid evidence that you need to take this or that medicine. If we were truly serious about this, we would do several tests, separated by weeks, done with different kit manufacturers at different labs etc.

I think the reason for not doing more thorough testing is implicitly admitting that the results aren't really all that actionable and improved precision doesn't really improve treatments because we have no idea what to really do with the results. There are studies showing correlations/causations of certain interventions on specific markers, and those markers are in turn correlated to some outcomes, but often the "evidence-based medicine" doesn't follow the full chain towards the actual outcome.

The other big reason for not measuring more times is the same that a man with a watch knows the time, but a man with two watches is never quite sure about it. In other words, if you got a test and had a result, you can document this and all is fine.

It raises my heartrate as well. I know my bladder is full many times due to the heartrate rather than feeling my bladder. I'm not sure if others notice this. I assumed without looking at the anatomy that the arteries to the lower extremities are under pressure from the bladder.

We're also treating people for things like blood pressure somewhat statistically rather than individually.

The studies say, people who have a blood pressure measured this way, that is above X, have an N% higher chance of dying M years sooner of A, B or C than people who measure under Y. If you treat with medication Q it lowers blood pressure, measured this way, by Z points, increasing lifespan by W QALY.

Are you treating people who don't need to be treated and missing people who do? Could you achieve better results with continuous, invasive blood pressure measurements while the patients engage in every day life?

Probably, but then you're increasing the cost of both the study and the public health intervention exponentially for gains in the margin.

Any exercise will raise your BP by quite a bit.

Yes, I was thinking the same. If everyone is measuring heart rate under similar conditions, and then correlating that heart rate with other factors, is that perhaps alright? Can we factor out the "error" to get a working baseline, even if the measurement isn't really heart rate at rest?

I doubt it, frankly. No one is controlling for these conditions. The easiest thing you can do is to wait a few minutes for the patient to relax after entering the examination room to get a reading at rest.

No medical advice should be given on the basis of a single blood pressure test.

I've donated blood about a dozen times, my BP has been high on one or two occasions but only if it was a pattern after two or three times did they flag it up, and since it went back down the next time it was no longer a problem.

They did send me letters about the amount of ferritine in the blood though; the first time it was too high (probably due to having a thing for food that turned out to be high in iron for a while around that time) and they advised I see a doctor for it, but it went down on its own after that. And the last time it was too low, but that's a normal thing if you donate blood a few times (it was every two months for a while), they basically don't summon you again for six months.

TL;DR, a single measurement says nothing.

The idea, in theory, is to measure your "minimum" or baseline blood pressure.

That your activities throughout the day add variable amounts to the baseline but never go below it.

It is a very good question though -- some people have activities/jobs/lifestyles where their BP is significantly elevated all the time. So surely you would think that must matter?

And it has to be in retrograde.

That anxiety is more present in the first of the readings than the last, so you get an indication if that’s affecting the reading too. You don’t have to be able to filter it out entirely to know if the reading has diagnostic value.

It varies of cause, but here the doctor just sends you home with a monitor exactly identical to the one they use at the office. But it’s not like there’s a world of difference to the ones you could buy yourself at a resonable cost.

To my knowledge Omron is considered one of the gold standards for home BP monitoring. Most of their cuffs measure the same old way, the BP7000 is one of the few models that do an upswing measurement. I've had both, along with periodic measurements at the doctor (I also do not get white coat hypertension). The Omrons have been in agreement with all my "official" measurements.

The first time I’ve seen an interrobang used in the wild!

But if the measurement isn't representative of your actual blood pressure what's the point of taking it? It's completely non-informative. Another problem is that even under very controlled conditions, I sometimes find big differences in blood pressure from one minute to the next.

> You move on to more accurate and focused methods of testing

Yes, AFTER the imperfect tool gives you something to worry about. So you still need the imperfect tool, which is what I think a lot of people are missing in this conversation.

Yea. But it’s mostly good except for the commas

With pauses to keep his BP low.

That's a complicating factor, but one that we can usually calculate.

Absolutely. Waist circumference should be and is considered as well, especially when evaluating obesity and its comorbities.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7027970/

The combination of BMI and waist circumference is even better.

I would trust the self-reported home readings more than those taken by professionals, because they're probably happening more often and under less stressful and exceptional circumstances.

what an AWESOME use of "‽"