Blood pressure is notoriously tricky to measure, whether in a doctor’s office or at home. Now, several wearables—including the Oura Ring and the latest Apple Watch—say they can help people track their blood pressure without an inflatable cuff. WSJ personal tech columnist Nicole Nguyen explains how these devices held up to real-life testing. Danny Lewis hosts.
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[00:00:03] Welcome to WSJ Tech News Briefing. It's Wednesday, October 14th. I'm Danny Lewis for The Wall Street Journal. Blood pressure measurements are an important part of tracking people's health. But the tools and methods used to take those readings are notoriously finicky. I can't count the number of times I've been sitting in my doctor's office with the inflated cuff wrapped around my arm, wondering what the results could be, and then worrying about whether my worries are making my blood pressure rise. What a loop.
[00:00:31] But what if your Apple Watch or Oura Ring could monitor your blood pressure at home? No cuff required. Wall Street Journal personal tech columnist Nicole Nguyen wrote about some of the wearables that are launching new insights into blood pressure trends. She joins us now. Nicole, first off, why is blood pressure so tricky to measure? Blood pressure is very fickle. It changes a lot. It can spike when you're exercising and go up to, you know, 200 millimeters of mercury.
[00:00:59] And then when you're resting and in bed, it can be as low as in the 90s. And so a one-time reading, which is just this like very quick snapshot of your life, isn't entirely representative of your blood pressure on average. And so when you're sitting in the doctor's office, there's something called white coat syndrome, which is when people frequently get higher readings in the doctor's office than they would at home because they're like a little bit nervous about getting their blood pressure taken by the doctor.
[00:01:29] That's a real thing. And also people have anxiety. Like as soon as the cuff starts to inflate, they become a little bit claustrophobic and that can cause higher readings. So blood pressure in general is a tough thing to track and measure. How do wearables take blood pressure readings without the inflatable cuff? Wearables have what's called a PPG sensor, which are LED lights that shine a bright light onto the skin. And there are photo detectors that can read that light back into the system.
[00:01:56] And so when a wearable is measuring your heart rate, they're looking at how your blood vessels are contracting and filling up as your heart is pumping blood through your body. And so that's how, you know, they can read your heart rate. This reading also captures what's called a pulse waveform. So as blood enters the artery, the waveform goes up. As blood volume decreases, the waveform goes down.
[00:02:20] And they've been able to look at those waveforms and look at blood pressure readings at the same time and make an estimation, an inference of what your blood pressure might be based on those waveforms. Gotcha. So it's not like it's directly making a reading on your blood pressure, but sort of more like, oh, like here's what this data suggests about what it is. Right. The most direct measurement of blood pressure would be a needle into your artery, which is invasive and sounds really painful.
[00:02:49] So no one wants that. And a cuff is in a sense and inference also, but because cuffs have been globally recognized and there's an international standard to clinically validate them. Cuffs are the most accepted form of blood pressure monitoring. And how often would you get a reading from some of these wearables? I tested five wearables, which is too many. Don't recommend. But each wearable gives you a different frequency of reading.
[00:03:17] So one wearable called the Hilo Core, which just came out in January, is a tiny little wristband that's fabric and it's very comfortable. It's super lightweight. It works with a cuff that comes included within the system. And for four days, you use the cuff to calibrate the device. So one time a day for four days, you sit, you make sure you're not crossing your legs, you make sure you haven't had any coffee, you make sure you haven't exercised within 30 minutes. It's a whole list of things.
[00:03:47] It's actually like a lot of trouble to find a time in your day when you've been sitting relaxed for 30 minutes. You take a reading. And then once the system is calibrated, you can just wear this wristband and it takes blood pressure readings throughout the day. When you open the Hilo app, you can see those two numbers, which are the systolic on top and the diastolic on the bottom about every two hours, except when you are physically active, which is by design.
[00:04:14] When you're active, the company isn't quite confident enough in the blood pressure reading. And also it distorts your average. So you only get readings when you are sitting and relaxed for long enough. Gotcha. And how about some of the other ones you looked at? There's the Apple Watch 9, the Oura Ring, Google Pixel, right? Yeah, it would be much more convenient if that technology in the Hilo Core was already built into a tracker that people are already using.
[00:04:40] I think one of my gripes with the Hilo Core is that I had to wear yet another thing and I already wear an Oura Ring. But these other devices offer a slightly different kind of data. So WHOOP looks at different metrics that are captured during sleep, including your heart rate and your demographic information and those pulse waveforms that I was talking about. And in the morning, it spits out an estimate of what a resting blood pressure would look like.
[00:05:09] Oura, Google Pixel and Apple Watch give you much less granular data. So Oura just tells you if your nighttime blood pressure has dipped in a normal range, every night our blood pressure dips between 10 and 20%. And if it's beyond that range, it lets you know. And if it is sustained, then that's something to bring up with your doctor. But a one-off isn't that big of a deal. And it also has what's called blood pressure signals.
[00:05:34] So within a 30-day period, if it detects your blood pressure has shifted significantly, it'll alert you. But you'll never see that alert if it hasn't shifted. So it's not a daily or an hourly reading. The Google Pixel once a month sends you this Health Guardian report that tells you whether or not your blood pressure trends are high or not high. So it's just as generic as are they at your baseline or are they elevated?
[00:05:58] And Apple Watch gives you nothing unless it detects you have possible hypertension. And its sensitivity is pretty high. So these are more severe cases of hypertension, I'd say. And so if you don't get an alert, you're not necessarily in the safe zone. But it'll only show you a notification if it detects possible hypertension.
[00:06:20] It's intended to spark a conversation between someone and their physician rather than to alarm them because there are things you can do to lower your blood pressure, like lifestyle changes. Are you tracking your blood pressure with a wearable? If you're a listener on Spotify, let us know why or why not in the comments. Coming up, these wearables are changing the game for some consumers. But what do doctors have to say about them? That's after the break.
[00:06:59] Welcome back. We've been talking about how wearables are adding insights into blood pressure monitoring and how some of them did in real life testing. But Nicole, what do the medical experts say about their accuracy? The American Heart Association last year wrote a statement that said these cuffless devices are very promising and can increase access to a lot of people who don't live close to their physicians or can't physically visit doctors very often. However, there's not yet.
[00:07:28] However, there's not a clinically understood and generally accepted validation standard for this technology. And because physicians can't guarantee their accuracy, there are unanswered questions about their use to guide and diagnose hypertension and hypertension treatment. So I think that means that folks should see these devices as wellness devices. You know, they're intended to support and maintain a healthy lifestyle.
[00:07:57] And if you do get an alert, you should absolutely follow up with your physician to confirm a diagnosis and discuss a treatment plan with your doctor. I mean, what are some of the concerns that doctors and medical experts have about people relying on these devices for blood pressure readings? What they worry about is someone with high blood pressure or hypertension wearing a device and not getting alert and being lulled into a false sense of security.
[00:08:25] And so it is really important, as always, to see your physician regularly and unfortunately get that arm squeeze until the technology is in a place where it's clinical grade, which it's not today. All right. Well, I'm a little bummed that I can't ditch the blood pressure cuff yet then.
[00:08:46] You can't. But, you know, I have to say in wearing these devices, it has made me think about my blood pressure more or really at all, which a lot of doctors say is a good thing. High blood pressure cannot be felt in your body, which is why it's called a silent killer. Awareness in general is a positive trend, according to these physicians. But if these wearables features won't actually replace blood pressure cuffs and people still have to go to the doctor or learn how to take accurate readings at home, what's the point?
[00:09:14] In a surprising twist of events, I was interested in doing this test because hypertension runs in my family. And so blood pressure is something that like my family members and I think about a lot. And I hate the cuff. But in doing this test, I actually sort of learned to love and appreciate the cuff because it's required for calibration for a lot of these devices. I learned how to appropriately fit one onto my bicep and how to take the best reading.
[00:09:41] And it became such a normal part of my life that I no longer have that nervousness, that anxiety around wearing one. All this to say, if you are worried about your blood pressure and you're interested in tracking it and understanding what your long-term trends are, you may actually learn to love the cuff like me. That was WSJ personal tech columnist Nicole Nguyen. And that's it for Tech News Briefing.
[00:10:09] If you're a listener on Spotify, be sure to leave us a comment. Today's show was produced by me with supervising producer Katie Ferguson. I'm Danny Lewis for The Wall Street Journal. We'll be back tomorrow with a new episode. Thanks for listening.