Building a wristband that can accurately and consistently measure activities like steps taken or biometrics like heart rate is difficult. There are all kinds of issues to take into account, like noise from arm movements, and the ways in which different skin tones or skin translucencies might impact measurements.
Perhaps no one knows this better than the founders of Quanttus. The startup spent several years and millions of venture-capital dollars trying to develop a wrist-worn device that can measure blood pressure. Last week it released its first product, which is nowhere near realizing this dream: an iPhone app for tracking blood-pressure measurements.
Called Q Heart, the free app invites users to log blood-pressure measurements (though you’ll need a blood-pressure measuring cuff), and keep an eye on how they change over time. You can also log your heart rate—unlike some apps, Q Heart won’t measure this for you, either, though—and apply labels to indicate what you were doing in the last 30 minutes (drinking alcohol and being lightly active, for instance) and what you’re doing now, as well as how you’re feeling.
Allison Kelly O’Hair, principal data scientist at Quanttus and leader of the company’s office in Mountain View, California (it has another one in Cambridge, Massachusetts), says the app has been in the works since last year. Quanttus sees it as a way to encourage all kinds of people to monitor their blood pressure, whether or not they have a health condition such as hypertension or hypotension.
Yet it’s far from what Quanttus had spoken about in the past: a smart-watch-like device that can continuously monitor signals like heart rate and blood pressure via ballistocardiogram, or BCG, which is a measure of the itty-bitty movements of your body as your heart pumps blood (see “This Fitness Wristband Wants to Play Doctor”).
The company had said it would do this with an optical sensor on the underside of the wristband, which shines light at the skin to measure how your tissue selectively reabsorbs light in order to measure the volumetric changes in blood vessels that take place each time your heart beats. An accelerometer, meanwhile, could track the resulting small body movements.
The company showed me photos in 2014 of a prototype it used in validation studies at Massachusetts General Hospital and Brigham and Women’s Hospital in Boston; it looked like a digital watch that had no face. A square circuit board covered with electronic components like a battery and green LED sat within a frosted enclosure, placed atop a watchband.
Founded in 2012, the company’s efforts are based on the graduate work of cofounder and chief scientific officer David He (one of MIT Technology Review’s 35 Innovators Under 35 in 2014). The company has reported raising $22 million in funding, $19 million of that through a series A round in February 2014 from venture-capital firms Khosla Ventures and Matrix Partners (a $3 million seed round came prior to that from Khosla founder Vinod Khosla).
As for whether Quanttus is still working on that wristband for measuring blood pressure, and how far along it is, O’Hair says she doesn’t want to comment on where the company is with the device.
“But we are still thinking bigger than the app,” she says.
A former Quanttus employee, speaking on condition of anonymity, says it took more time than the company expected to develop the product. Quanttus isn’t the only company that has struggled to capture reliable, continuous signals at the wrist. Some Apple Watch users have complained that the device offers inaccurate pulse readings during certain exercises, and Apple itself states that activities with “irregular movements” like tennis and boxing won’t yield results as accurately as “rhythmic” ones like running or biking. Apple’s gadget only tracks heart rate continuously while you’re using its Workout app; otherwise, it tries to measure your heart rate every 10 minutes but won’t do so if you’re moving (you can also prompt it to take a measurement).
No matter who’s behind the measurements, the issue may simply be that while the wrist seems like a logical spot for a wearable device—we’re used to wearing watches, after all—it’s actually not a great place on the body to track biological signals (see "The Struggle for Accurate Measurements on Your Wrist"). The ear, for instance, seems to work much better (see “Using Your Ear to Track Your Heart”); and, in fact, He’s graduate work focused on an ear-worn BCG monitor.
Measuring biological signals at the wrist is convenient, but even just gathering heart-rate data is a “non-trivial” problem, says Emil Jovanov, an associate professor at the University of Alabama at Huntsville who studies real-time physiological monitoring. In addition to issues like sorting out the signal you want from the noise of motion artifacts, you can’t get perfect contact with the skin, and different people’s skin can change the quality of the signal that’s collected. Temperature, he says, can play a factor, too.
“You can be inside where it’s room temperature and have a good signal, and then get outside and completely lose your signal because all your blood vessels disappear, or went deeper,” he says.
Reading blood pressure accurately with a wearable on your wrist is even more difficult, he says.
O’Hair, too, agrees that tracking blood pressure in particular, and doing it continuously, is “a tricky problem.” It’s hard to alter the status quo, she says, which currently relies on the kind of arm cuff you’re used to using at your doctor’s office as the gold standard.
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