Science Friday - Your Arm Position Can Make Blood Pressure Readings Inaccurate

Episode Date: November 12, 2024

Think back to the last time you went to the doctor’s office. Chances are, at the start of the visit, they took your temperature, pulse, and blood pressure—your “vitals.”But how did they take your blood pressure? The medical literature that describes safe blood pressure ranges is all based on readings taken with the patient sitting with feet flat on the floor, legs uncrossed, back supported, and the testing arm supported by a desk at mid-heart level. But if the blood pressure is measured with the person in a different position—say, perched on the edge of an exam table, legs dangling, and an arm hanging at the side—the readings given by a blood pressure monitor can be distorted. In a recent study published in the journal JAMA Internal Medicine, researchers found that arm position could account for as much as a 7mmHg difference in pressure readings. That difference could be enough to incorrectly classify some people as hypertensive.Dr. Tammy Brady, medical director of the Pediatric Hypertension Program at Johns Hopkins University, joins Ira to talk about the art of blood pressure measurement, how to better track your own blood pressure, how to find blood pressure monitors that have been properly validated, and the importance of advocating for yourself in medical settings.Transcript for this segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

When you go to the doctor's office, are they taking your blood pressure the right way? If those steps aren't adhered to, there could be really substantial measurement and accuracy. Studies have shown that you can overestimate your blood pressure by five to even 30 millimeters of mercury. It's Tuesday, November 12th, and you're listening to Science Friday. I'm sci-fire producer Charles Brookquist. You know, when I go to the doctor, each visit generally starts with me sitting up on the edge of a tall exam table, legs dangling in the air, arm held at a weird angle while an assistant straps on the blood pressure cuff. It turns out that's not right at all.

And it turns out that little things being off when you're having your blood pressure taken can make a big difference in the final numbers. Here's Ira Flato. Joining me now to talk about this is Dr. Tammy Brady. She's medical director of the pediatric hypertension program and professor of pediatrics at Johns Hopkins University in Baltimore. She's one of the authors of a study on this topic recently published in the journal JAMA Internal Medicine. Welcome to Science Friday. Thank you very much.

You're very, very welcome. So I go to my doctor's office, an assistant comes in to take my blood pressure. What do the guidelines say? How should they be doing it? Right. So a lot of people don't recognize that there's a lot more complexity to measuring blood pressure than just putting on a cuff and pushing a button. There are a lot of very important preparatory steps that need to be taken and a lot of important

positions that we need to make sure that patients are in in order to get the most accurate blood pressure. So the first thing that a person should do before measuring their blood pressure is making sure that they have emptied their bladder, make sure that they haven't recently eaten or had any nicotine or alcohol because those things can all lead to an elevated blood pressure. They should really rest for three to five minutes. before a blood pressure measurement. And key to an accurate measurement is making sure that you are using the right size cuff for your arm. Oftentimes, I think there is one cuff that is attached to the

device in the office, and that's the one that goes on the arm. But really, what we should be doing is measuring the person's mid-upper arm circumference and then selecting a cuff that's appropriate for them. And then, of course, there are specific ways in which you should be putting the cuff on the arm. You want it to be snug, but not too snug, and you want it to be positioned on the upper arm. And you want to make sure that the arm is supported and positioned in such a way that the middle of the cuff is at mid-heart level, which is essentially the middle of the bony part of your chest. So your arm should be up there. Yes, absolutely. It needs to be resting. And that's very specific position because if it's not, as we have shown, it can lead to significant inaccuracies.

Those are things that the person giving me the blood pressure reading can do. What am I supposed to be doing while I'm sitting there? Any special positioning? Well, you really need to be in a chair that has back support and allows you to have your feet on the ground. You can make sure that your legs are not crossed. And you know, you really should try to be relaxed and you should certainly not be looking at your phone. And you really should not be talking to the person who is measuring your blood pressure. I think we in health care all want to make people feel comfortable and we'll have a conversation.

But those actions, you know, being an active listener or talking, can elevate your blood pressure. So you want to just be nice and quiet. You know, Dr. Brady, I don't know one patient who does not sit up on the examining table and have their blood pressure taken. And nobody's back is against the wall there ever. I know. I know. And in fact, I've given recently several talks on this. And there's a picture in the Washington Post of somebody doing home blood pressure monitoring

and every single thing is done wrong. Every step is wrong. They're sitting at the edge of the couch. They're holding the device. The cuff isn't even on their upper arm. It crosses the elbow. I mean, the whole thing is terrible. So, yeah, yeah.

Let's talk about your study specifically. You looked at different arm positions in the same person. and what did that do to the readings? Tell us about what you found. So with this study, we were really interested to know how important arm position like I described earlier is. Because often in clinical practice, people have their arm in their lap or at their side

and really being able to have their arm positioned at a desk with the middle of the cuff at mid-heart level can take a little bit of extra time and you need to be intentional about it. You need to have the room set up in a certain way. So we wondered, does this even matter? So we conducted a study to see if there was, any over or under estimation of blood pressure when the arms were positioned in the non-guideline-specific

way. And what we found was that there was actually substantial overestimation of blood pressure when the arm was positioned in the lap. So when the arm was in the lap, it overestimated blood pressure by almost four millimeters of mercury systolic. So that's the top number. And four millimeters of mercury diastolic, that's the bottom number. But even more striking was when your arm is at the side, your systolic blood pressure is overestimated by almost seven millimeters of mercury, and the diastolic was almost four and a half millimeters of mercury. And so that, you know, amount of error can lead to someone being inappropriately diagnosed with hypertension and potentially start it on a medicine they don't need. And if the arm position can make the reading really

falsely high, are there other factors that can make the reading falsely low? There are some things that can make the blood pressure low. So some people, if they're standing, when their blood pressure is being measured, their blood pressure can be lower. And then certainly sometimes with other people that can raise their blood pressure, but it definitely can lower blood pressure for certain individuals, as can laying flat.

So laying on your back while you're measuring your blood pressure can lead to a lower blood pressure if you had just eaten. So just having had something to eat can lower your blood pressure by six millimeters of mercury. And even just having some, you know, if you had an acute alcohol consumption, that can actually lower your blood pressure

by almost 24. millimeters of mercury. No kidding. That's a big number. Big jump. I know there are lots of people diagnosed with high blood pressure, hypertension in this country. Do you think the cumulative effects of lots of medical professionals measuring

incorrectly could be skewing that data? That is a great question. And something that I actually wonder myself, I can tell you anecdotally, So I'm a pediatric hypertension specialist, and I have several dedicated clinics for children and adolescents and young adults who have elevated blood pressure in their primary care setting. And many times when they come in and I measure their blood pressure, I measure it three times. I adhere to all of the steps. And I'm very vocal about why I'm doing each thing, why I'm moving them to a certain spot in the room for measurement. And it is really not uncommon for their blood pressure to be stone cold normal when they come into my clinic.

And many of them comment that, wow, nobody's ever done it that way or, well, the last time I was here, they told me to sit up on the examination table. So I do think that this could be potentially happening on a grander scale. And since so much of our research these days is relying on what we call big data, right, taking information from the electronic medical record and using it to estimate prevalences of various disease states, if you use this to estimate hypertension and the blood pressure, that are being put in the chart are the ones that are obtained after suboptimal measurement technique, yeah, we could absolutely be having some inaccurate estimates for disease prevalence. Wow. You know what else? Sometimes I've had my blood pressure taken through my shirt. Yes. It sort of drove me crazy when I first happened. Does it drive you crazy? A little bit, because it doesn't take very much.

in order to make sure that the arm is bare. Now, I will say I did take a look at some of the literature on blood pressure accuracy when you use a cuff over clothing. And it does seem that it might not be terribly inaccurate if the sleeve that you are covering is thin. So I think it might be reasonable. It does need to be systematically studied. I do think that we need some better studies to comment on this.

but what is published says that that might not be so bad. But the cuffs, they really, they rely on the oscillations in the arm. So the blood flowing through the blood vessels, it relies on sensing that. So if there's a lot of clothing between the arm and the cuff, that sense might get a little muffled. And you may, you know, there is potential for inaccuracy there. Should we be proactive and telling, you know, was ever giving us the, that the blood pressure test do it this way? Yes.

So one of the things that I really hope that this study is able to do is to empower patients to remind their healthcare providers about the proper blood pressure measurement steps. I think we're all busy. There's not always, you know, we know that training and certification is essential to make sure that those measuring blood pressure know what they should be doing, but that they're skilled decay over time. And so that should be really repeated every six months. And so my hope is that by this study getting attention,

patients will feel empowered to remind their providers so that when they are in the clinic setting, they're getting the most accurate blood pressure that they can. After the break, extending the conversation from the doctor's office to home blood pressure monitors in those kiosks you might see in stores. All right. I'm going to ask you about a really sticky question because I do this my My cardiologist gave me a home blood pressure monitor, you know, get a personal monitor, check it themselves.

And it actually has a little transmitter that sends it back to his office sometimes. And then I got one myself, and I compared the two. And they were not close many times. Yes. So I have a lot of thoughts on this topic. So first of all, home or out-of-office blood pressure measurement really is. essential to hypertension diagnosis. The white coat effect is real. And what we're trying to do when we give someone a diagnosis of hypertension is identify a person who's at risk for heart disease.

And so if you get a little stress out at the doctor's office and your blood pressure is artificially elevated there, but when you're home and where you spend 99.9% of the time, your blood pressure is normal, that's more important for your cardiovascular disease risk than, say, an elevated blood pressure for five minutes when you're in the doctor's office. So, out-of-office blood pressure measurement is key. However, I will say that essential to accurate blood pressures in the home is making sure that the blood pressure device you're using has actually undergone testing to ensure that it's giving accurate results. And what I mean by that is manufacturers have tools called validation protocols that they can use to test that the

device is accurate in a population. But just because you sell a device, there's a device on Amazon, let's say, or some other marketplace. Just because it's for sale does not mean it's ever been tested. And in fact, 80% of devices that are on the market have never been tested. So you really need to make sure that that first step has been. That you really need to make sure that it's been tested to be accurate before you even start using it for yourself. So I have to just trust them that this has been calibrated and tested.

Well, so I am, I'm very passionate about blood pressure device validation. And I serve as co-chair for the American Medical Association validated device listing committee. And what this committee does is it takes a look at the validation testing for various devices. Manufacturers have to proactively submit their documentation to us. And devices that have undergone the rigorous testing without any protocol violations, they are listed on our site. So if you as a patient or you as a healthcare provider want to be able to find a device that's been tested, you can go to validatebp.org and you can find a variety of devices there that have undergone this testing. So that, for me, is the first step to make sure you get accurate out

of office blood pressure measurement. Validatebp.org. Validatebp.org. Yes. Validatebp.org. That's right. Okay. Now, when I get home and I bring this home blood pressure monitor home, I've got to make sure I'm doing the same things correctly at home that would be happening in the doctor's office. That's right. And so that is absolutely right. And if we as a health care providers can't consistently measure blood pressure properly, how, you know, we need to do a better job also making sure that patients who we are counseling to do these home blood pressures know how to do this. So I think that's really important. I can tell you anecdotally that many of my patients, you know, they wake up and they get out, you know, they sit at the edge of their bed and they put the cuff on and push a button. But, you know, they're, you know, have a full bladder, they're not resting their backs against the wall.

There's many things that are happening that are not consistent with the protocol or the practice guidelines. I plead guilty to one of those. I'm not going to tell you which one. But now that I know, I will do that. What about the kiosks you see in grocery stores or pharmacies, the machines where you can check yourself? Right.

So I also have a lot of thoughts. So the kiosks that are in public places, I think this offers a lot of opportunities to people who want an out-of-office blood pressure measurement but can't afford to get a home blood pressure device for use in their home. I think that this can increase equity and I think it can increase access. So I think that there's a lot of benefits from these devices. But just like I said, home blood pressure devices need to be tested for accuracy. So do these kiosk devices. And in fact, one of the more common devices that, kiosk devices that is, that is used in the United States, has never been validated. So it can be really hard for a consumer, a patient, to know whether or not the machine that's sitting there and their pharmacy has undergone this testing.

Do you have the name of that on your website, too? So we, there is one, there is one kiosk that is on the validatep.org site. but the one that I'm thinking of is Higgy. There's over 10,000 kiosks in the stores in the United States. And this, as Elise says in my last check, which was about a year ago, had not been tested for accuracy. It had been cleared by the FDA, but it had not been tested to see if it was accurate. Well, you are a font of knowledge on this. I'm very happy we're talking to wrap it off.

What can people be doing to advocate for themselves when they go to the doctor's office? Should they be watching out to the things that you do and being an advocate, meaning speaking up if they don't see it being done correctly? Yes. So I tell all of my patients, and again, all of the patients that I take care of, I verbalize what I'm doing, like why I'm moving them, why I'm measuring their arm, why I'm selecting a certain cuff, why they need to be, you know, sitting in the specific chair that I put them in. And then after I'm done, I tell them that they should tell any health care provider who is measuring their blood pressure. that they need to make sure to do all of these things. And so I absolutely think patients should feel empowered to do this. And, you know, and if there's, it's hard to remember all of the steps.

The American Heart Association has some beautiful resources on there. The American College of Cardiology has also some beautiful resources online. So I would encourage you, you know, these are things that you can print out and you can bring with you to your health care provider, you know, as a gentle reminder that these are the ways I would like to have my blood pressure measured. Well, Dr. Brady, this has really been helpful. I want to thank you for taking time to be with us today. I think our audience age group really will benefit from this advice. Great. Well, I'm really glad that you're interested in the study. I'm very, very glad that I can share some of this information with you. You're welcome. Dr. Tammy Brady, medical director of the pediatric hypertension program and professor of pediatrics at Johns Hopkins University in Baltimore, Maryland. That's it for today. Lots of folks help keep sci-fri running, including D. Petersburg,

Melissa Mayors. Emma Gomez. Jackie Hirschfeld. Tomorrow, an update on CAR-T cell therapy and efforts to use it against autoimmune diseases. Plus, what marmots can teach scientists about stress. But for now, I'm Charles Bergquist. Thanks for listening. We'll see you soon.