Should You Trust Apple’s New Blood Oxygen Sensor? - IEEE Spectrum
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`5/28/21, 6:35 PM
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`View From the Valley Biomedical Biomedical Devices
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`21 Sep 2020 | 19:00 GMT
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`Should You Trust Apple’s New Blood Oxygen Sensor?
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`In the time of COVID, pulse oximeters are the new thermometers, on the
`shelves of many medicine cabinets. But do they belong in wristwatches?
`
`By Tekla S. Perry
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`Gif: Apple
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`In the early days of the coronavirus pandemic, it wasn’t just face masks and hand
`sanitizer that flew off drugstore shelves. Pulse oximeters were also in short supply, as
`news came out that a drop in blood oxygen could be a sign that a case of the coronavirus
`has taken a bad turn.
`
`These inexpensive and noninvasive electronic devices use LED lights and photodiodes
`to determine the way red blood cells are absorbing light—oxygenated cells absorb more
`infrared light than red light, cells that aren’t carrying oxygen the opposite. With that
`information, algorithms can calculate a level of blood oxygenation; for most healthy
`people that’s in the high 90 percentile, in cases of COVID, the numbers dropped into
`the 80s. So it seemed like a good idea to have one on hand, if you could find one.
`
`Now, six-plus months into the pandemic, it’s not surprising that consumer electronics
`manufacturers are touting the benefits of adding pulse oximeters to wearables. The
`sensors don’t cost much, they don’t use much battery power, and they could attract at
`least a few consumers looking to feel a little safer in this uncertain world.
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`https://spectrum.ieee.org/view-from-the-valley/biomedical/devices/should-you-trust-apples-new-blood-oxygen-sensor
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`Page 1 of 4
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`Masimo Ex. 2016
`Apple v. Masimo
`IPR2020-01714
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`Should You Trust Apple’s New Blood Oxygen Sensor? - IEEE Spectrum
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`5/28/21, 6:35 PM
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` and
`
`Apple is the latest company to bring pulse oximetry to a wrist wearable (Fitbit
` already had products out pre-pandemic, aimed at identifying sleep apnea).Garmin
`
`Announced last week, the
` uses four groups of green, red, andApple Watch Series 6
`
`infrared LEDs along with four photodiodes and what the company says is an advanced
`custom algorithm to determine blood oxygenation. (The red and infrared LEDs are
`involved in the oxygen measurement; the green LED can check pulse rate.) The sensors,
`mounted on the back of the watch and therefore touching the top of the wrist, can be
`used to take readings on demand during the day and automatically during sleep.
`
`Apple is touting the gadget for “fitness and wellness.” Loosely translated, that means
`that this gadget does not have FDA approval to be marketed as a medical device. That
`comes as little surprise—FDA clearance takes time—but without that approval, it’s hard
`to know just how accurate it is.
`
`Photo: Apple
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`Indeed, accuracy remains a question with many of the pulse oximeters on the consumer
`market. Says Steve Xu, a physician-engineer who is medical director for the
`Center for
`Bio-Integrated Electronics at Northwestern University
`, “It is relatively straightforward
`to make a pulse oximeter, even for an undergrad engineering design project, but it is
`really really hard to make a good one that is clinically dependable.”
`
`Is Apple’s a good one? It’s hard to say just yet. Besides the issues of adjusting to
`different skin colors, coping with motion, and other design challenges faced by all pulse
`oximeters, putting the sensors on top of the wrist raises the difficulty level. The devices
`used in hospitals as well as the standalone gadgets sold in drugstores typically clip onto
`a fingertip or, sometimes, an earlobe.
`
`“Those locations have an advantage over the back of the wrist,” Xu says, “because they
`have more capillaries, so provide a better signal to noise ratio.”
`
`Wrist-worn blood oxygen sensors face another disadvantage: while fingertips are thin
`enough to allow light to shine through them, wrist oximeters must rely on reflected
`light, an inherently less precise approach.
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`https://spectrum.ieee.org/view-from-the-valley/biomedical/devices/should-you-trust-apples-new-blood-oxygen-sensor
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`Should You Trust Apple’s New Blood Oxygen Sensor? - IEEE Spectrum
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`5/28/21, 6:35 PM
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`“It’s not necessarily bad,” Xu says, “but all things being equal, isn’t going to be as
`accurate” as a pulse oximeter designed for a more favorable location.”
`
`“I would never put a pulse oximeter on the wrist,” says William McMillan, co-founder,
`president, and chief scientific officer of Profusa, a company developing implantable
`biosensors. “The wrist is subject to a lot of motion, which is bad news for continuous
`measurement.” (Apple’s watches do have motion sensors which could help it identify
`quiet moments.)
`
`Apple can show proof that its watch-based device can provide accurate oxygen
`saturation reading by taking it through FDA’s approval process, says Xu; the testing
`procedure for pulse oximeters is well-established.
`
`Even without such vetting, Apple is launching several health studies using the Apple
`Watch oximeter—one looking at the management of heart failure, one at the
`management of asthma, and one considering blood oxygen level changes as early
`warning signs of COVID-19 and influenza. Both Xu and McMillan are cautiously
`optimistic about such efforts.
`
`“Consumer product companies like Apple and Fitbit have a vastly bigger scale than
`most medical device companies,” Xu says. “Not many technology companies outside of
`the Apples and Fitbits and Samsungs can deploy a million devices in the world and
`manage the data that comes in. So we should do these studies and see how
`prognosticating they are, but we should realize there will be a lot of false positives.
`Maybe it will turn out to be a useful screening tool, but the verdict is still out.”
`
`“Because [the device] isn’t likely terribly accurate, and it won’t involve a control group,
`rather, an uncontrolled situation, they will need a huge sample size to detect any
`phenomena,” says McMillan. “But they end up having millions of data points in which
`to look for insights, and that would be OK.”
`
`This all begs the question—does the average smart watch user actually need to wear a
`pulse oximeter 24/7?
`
`While such a wearable may tell us more about the fluctuations of blood oxygen
`saturation in the broad population, Xu says, “The vast number of healthy people are at
`97 to 99 percent. If we all wear these and freak out whenever it drops to 92, the
`potential to worry people who are well is much higher than the clinical implications,
`which at this point are unknown.”+
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`https://spectrum.ieee.org/view-from-the-valley/biomedical/devices/should-you-trust-apples-new-blood-oxygen-sensor
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`Should You Trust Apple’s New Blood Oxygen Sensor? - IEEE Spectrum
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`5/28/21, 6:35 PM
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`About View From the Valley blog
`
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`and its environs.
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`, Editor
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