Does getting arm position just right matter when measuring BP?
July 11, 2020 10:58 AM   Subscribe

A couple guides to taking blood pressure at home say your elbow should be at the same height as your heart (one specifically said right atrium as if I know exactly where mine is but that's beside the point). But in the doctor's office they just flop your arm down on the table regardless of how tall the table is compared to you. So which is it — arm position really matters, or barely matters?

I once asked a medical professional and they said "the difference in pressure from your elbow being a little lower or higher than your heart is so small it doesn't matter", but they didn't go into details and their job doesn't involve taking BP frequently so I wonder if they were really the right person to ask.

I realize BP changes throughout the day depending on time of day, recent exertion, stimulant intake, etc, but since I'll be measuring repeatedly at home if I get the position wrong every time my average will be off.
posted by Tehhund to Health & Fitness (5 answers total) 8 users marked this as a favorite
the people who take BP haphazardly are wrong and this has been known since the 1890s and its a false justification for rushing that is not grounded in research
arm posture differences can change BP measurements nearly as much as drugs can
that said there has been extensive study of this and some of it does disagree on the ideal position and how much difference it makes, but no clinician who knows what they are talking about should glibly dismiss it as something that doesn't make any difference at all, there is a mountain of literature saying otherwise. if you have a home cuff you can prove it to yourself; take your measurements in two different positions, one with the ideal of arm slightly raised and supported, the other the haphazard way, repeat several times a day over several days, note the average difference.
posted by slow graffiti at 11:23 AM on July 11, 2020 [8 favorites]

Getting an accurate and precise blood pressure is incredibly difficult. This exact topic is so controversial that it effectively limits the accuracy and replicability of a lot of large scale trials in cardiology (many methods require that you sit in a quiet room alone for 5-15 minutes before getting your blood pressure checked.....which never happens in a doctor's office as vitals, more often than not, are done immediately after standing up and walking (a big no no) to a weird little cubby hole). Automatic blood pressure cuffs are notoriously unreliable as well. Things like crossing your legs while getting your blood pressure checked can have a marked impact. All this to say that it's one of the reasons why doctors can't diagnose "hypertension" until you've had several independent readings of blood pressure done with a fair bit of time (read days to weeks) between them, and careful technique.

The most important thing for taking blood pressures at home is to do it the same way every time; that means same position, same cuff, same time of day. It allows for a much better comparison (which if you're looking at the delta in terms of the blood pressure is actually what matters). In terms of positioning, practically speaking, the easiest way to do is to sit down and rest your arm on a table and try to not engage any muscles in your arm or shoulder while inflating and deflating the cuff. If you were in the office, someone taking your blood pressure would ideally be holding your arm up with all of the weight in their hand exactly at the level of the heart. But again it's impractical at home and any attempt to hold up your arm with lead to increased muscle tone which will falsely elevate your blood pressure. Cuff size matters, too, and it's amazing how often high blood pressures are falsely elevated because of a cuff that's too small. Cuffs that are too big will falsely lower blood pressures.

As an emergency medicine physician I would also point out that taking your blood pressure at home more often than not can lead to anxiety which inevitably leads to higher blood pressure when taken again which leads to a nasty cycle which often ends ups with people calling their doctor or coming to the emergency department. There's not a ton of documented benefit to taking your blood pressure at home unless you have very specific reasons for doing so, or unless your physician has specifically asked you to do so and document the results.
posted by ghostpony at 11:29 AM on July 11, 2020 [14 favorites]

Readings taken in doctor’s offices are notoriously half-assed. I stopped letting my family practice doc do my vitals as soon as I, a highly anxious person, walked in, since it always led to a discussion about my “hypertension,” which inevitably disappeared by the end of the visit if I had them check again after I had sat and relaxed for a while.

This quick reference lists how much these variables can change the reading, citing studies (that, buyer beware, I did not check). It looks like position is a smaller factor than a lot of other things. I’d aim for consistency, arm slightly supported and middle of the cuff at the midpoint of the sternum, as mentioned here.
posted by charmedimsure at 11:43 AM on July 11, 2020 [4 favorites]

IANAD, but from a patient perspective:

I've monitored my BP at home for the last couple of years (per doctor's orders, as it was verging on hypertensive crisis numbers for a while, and is now well-controlled and normal).

Echoing ghostpony's comment, my doctor has told me that just being consistent in how I'm sitting (relaxed for a while in a chair with arms, or having my arm on a table for a bit before taking the reading, and placing the cuff in the same way each time) is fine.

The way she put it was something like, "We're looking for the long-term trend here, not day-to-day/hour-to-hour fluctuations. Just check it two or three times a week so we have a rough picture of what it's like over time when you're in a comfortable setting without me looming over you." She was also adamant that I not stress out about short-term fluctuations for the reasons ghostpony mentions.

I also run the monitor three times in a row over a couple of minutes just to see if there's a variance. I do this two or three times a week. The thing I've noticed is that within a 10 or so minute window, I can get three very different readings, and since I've been doing it for a while, I don't get stressed about this any more.

I stopped letting my family practice doc do my vitals as soon as I, a highly anxious person, walked in, since it always led to a discussion about my “hypertension,” which inevitably disappeared by the end of the visit if I had them check again after I had sat and relaxed for a while.

When I get it checked during doctor's visits, a nurse leaves me on a chair with a pillow under my arm and runs it on a "BPTru," which reinflates the cuff several times in a row over a ten-minute period. While this is going on, I'm sitting comfortably, alone in the exam room, without anyone hovering over me. They told me that they do this specifically to minimize the chances of a wildly incorrect in-clinic reading because doctor's visits are definitely stressful for some people.
posted by mandolin conspiracy at 12:01 PM on July 11, 2020 [5 favorites]

Wrist blood detectors have a bad rep because it's so much easier to take the reading with the wrist in the wrong position (compared to an upper arm cuff). I bought a wrist blood pressure monitor specifically because it has a feature where it helps you raise your arm to the right level before it takes the reading.
posted by Nelson at 3:27 PM on July 11, 2020

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