With one in three American adults estimated to suffer from high blood pressure, putting them at a higher risk of heart attack and stroke, it's a wonder that hypertension so easily goes ignored – often until it's too late.
Today's blood pressure monitors must cut off the circulation to take a reading, limiting the ability of everyday fitness trackers and smartwatches to track this vital stat. Not just that, but blood pressure is different around the body. The upper arm is the gold standard because it's in line with the heart, but move north or south on the body and you must compensate for the difference. That's why wrist monitors require you to elevate your arm to heart level.
Read this: Why Fitbit is trying to tackle sleep apnea
But as wearables become more skilled at watching over our physiological health, will this be something we'll soon hear Fitbit, Apple and others talking more about? It's already on their lips, with Fitbit CEO James Park explicitly mentioning it as far back as 2015. We're seeing more consumer-friendly, at-home cuffs like Nokia's BPM+, but while these make it easier to get a precise reading sans doctor, there's still a problem: you have to put it on and take it off every time you want to use it.
What the docs say
Doctors we've spoken to say the ideal scenario is that people take a pressure reading twice a day, once first thing in the morning and again in the evening just before bed. But without the same automated process we're now used to with heart rate monitors on our fitness trackers and smartwatches, even remembering to do it once a month can be a tall order.
"My physician will say Ranndy I think you're hypertensive, I want you to measure your blood pressure for the next three months and then come back," says Ranndy Kellogg, CEO of Omron Healthcare. "But what happens in the time from leaving his office and three months later?
"What people don't understand is that your blood pressure changes all the time, and there's a consistency to that trend, and if that consistency is rising that's the first sign of a problem."
Making the blood pressure smartwatch
Omron makes at-home blood pressure monitors, but Kellogg says that right now it's focused on the Omrom HeartGuide, previously known as Project Zero 2.0 and due to hit the market later this year – for around $350 – once it gets FDA approval.
It's a more discreet wearable "the size of an Apple Watch" that will track pressure from the wrist, accounting for the difference from the upper arm. "You'll look at it and it doesn't look like a blood pressure monitor," he says. "We got it into a state that will make it very easy for people to use."
The HeartGuide is designed to take oscillometric readings on the spot (i.e. in the morning and evening) and it can also take automatic readings through the night via an inflatable cuff that's good for two weeks or 50 inflations.
Another medical-grade blood pressure monitoring smartwatch that's waiting for FDA approval is the Asus VivoWatch BP, announced in June and beating the likes of Apple and Samsung to it.
It uses a combination of light-based PPG heart monitoring and ECG readings, passed through a HealthAI algorithm built by Asus. There's no inflatable cuff-style design here, which Asus says makes it 70% smaller and 50% lighter than the competition. It remains to be seen whether the VivoWatch BP can provide accurate data with this form factor.
Accessibility is one problem, accuracy is the other; you'll find some non-FDA approved blood pressure trackers that claim to estimate a pressure reading, but that won't be enough to convince your doctor that the information you're sharing is valid – which makes the entire exercise pointless.
Looking ahead, some of the most recent rumours around blood pressure in smartwatches come courtesy of Samsung. A Samsung patent on the subject describes a device called the Samsung Gear X, which uses light technology to take the readings. If Samsung has been pursuing this, it too will be looking for FDA approval.
NIST made a fake wrist for a better visual understanding of blood pressure
Other avenues are being explored. A collaborative team from the National Institute of Standards and Technology and Tufts University's School of Medicine are at work on an answer that measures subtle pressure changes at the surface of the skin. To do this they've built a fake arm, using squishy silicone for human tissue, to get a visual understanding of pressure inside a blood vessel.
The results of the study could form the foundation of a technology able to monitor blood pressure without having to cut off blood flow, opening the door for more mainstream wearables to do the same, and the team hope to have a working prototype by the end of the year.
Blood pressure from around the body
Mainstream, everyday, at home blood pressure monitoring might not even be limited to the wrist. "Non-invasively, the ear is good, the upper arm is good, the temple is good, there's a number of areas that are good, they all have their plusses and minuses." says Kellogg. "I think the ear is probably a better place if you're going to use a light source than the wrist."
We're starting to see more companies like Bragi and Jabra take advantage of the better heart rate precision of the ears, and as the hearables category blows up we expect everyone will pitching towards health and fitness.
Biotech company Valencell has demonstrated a cuffless blood pressure sensor based on its heart tech running on a smartphone, which reads PPG waves through the finger.
Valencell president Dr. Steven LeBoeuf also told Wareable that the ear is a place the company is also looking at closely for blood pressure: "One of the good things that we like about the ear is you can get assessments of blood pressure and other biometrics that you simply can't get on the wrist. That's because the pressure wave is so diminished by the time it gets to the outer skin of the wrist."
He has also revealed that Valencell has developed blood pressure assessment tech which uses optical sensors and is as yet unreleased.
What's next
We're expecting the Apple Watch Series 4 in September and Apple's made several moves, such as patents for wrist based ECGs, to show it's serious about medical grade health tracking via the Watch.
When Apple announced at WWDC 2017 that it was adding native core Bluetooth to the Apple Watch, it opened up an avenue to the much-rumoured smart bands. But it would be tricky to make a blood pressure monitor that could inflate on the wrist without a pump in the watch itself, so that's off the table for now – Omron says it's not something it's able to do with the existing 'bladder' method – but no doubt Apple is looking as closely at cracking blood pressure as it is glucose tracking.
Omron's Kellogg reckons a new commercially viable method will surface between two and five years' time. "It could be light, it could be doppler, it could be something else," he says. "There are a lot of experiments going on with our company, clinicians and other companies, and certainly someone will figure out a way to do it."
How we test
By Hugh Langley
Now at Business Insider, Hugh originally joined Wareable from TechRadar where he’d been writing news, features, reviews and just about everything else you can think of for three years.
Hugh is now a correspondent at Business Insider.
Prior to Wareable, Hugh freelanced while studying, writing about bad indie bands and slightly better movies. He found his way into tech journalism at the beginning of the wearables boom, when everyone was talking about Google Glass and the Oculus Rift was merely a Kickstarter campaign - and has been fascinated ever since.
He’s particularly interested in VR and any fitness tech that will help him (eventually) get back into shape. Hugh has also written for T3, Wired, Total Film, Little White Lies and China Daily.