Some Wearables Can Track Blood Pressure. Do They Work?

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Danny Lewis (0:24)

Welcome to 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.

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?

Nicole Nguyen (1:11)

Blood pressure is very fickle. It changes a lot. It can spike when you're exercising and go up to 200 millimeters of mercury, and then when you're resting and in bed, it can be as low as in the 90s.

A one-time reading, which is just this very quick snapshot of your life, isn't entirely representative of your blood pressure on average. 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 a little bit nervous about getting their blood pressure taken by the doctor. 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.

Danny Lewis (2:02)

How do wearables take blood pressure readings without the inflatable cuff?

Nicole Nguyen (2:06)

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. 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 they can read your heart rate. This reading also captures what's called a pulse wave form. So as blood enters the artery, the wave form goes up. As blood volume decreases, the wave form goes down. And they've been able to look at those wave forms 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 wave forms.

Danny Lewis (2:54)

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.

Nicole Nguyen (3:02)

Right, the most direct measurement of blood pressure would be a needle into your artery, which is invasive and sounds really painful, so no one wants that. And a cuff is, in a sense, an 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.

Danny Lewis (3:24)

And how often would you get a reading from some of these wearables?

Nicole Nguyen (3:28)

I tested five wearables, which is too many, don't recommend. But each wearable gives you a different frequency of reading. So one wearable called the Hylocore, 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. It's actually 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 Hylo 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. 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.