Apple Watch Series 7 May Offer Highly Accurate Blood Pressure Measurements

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There’s been no shortage of rumours when it comes to most of Apple’s 2021 product lineup, with reports of Apple’s “iPhone 13” plans already making the rounds, along with redesigned MacBooks, new AirPods, and much more. Despite all of this, however, Apple’s plans for its next-generation Apple Watch remain much more enigmatic.

While it’s a safe bet that Apple has been working steadily to improve the health monitoring capabilities of its popular wearable device, it’s become difficult to predict, or even speculate, on what could possibly be coming next. After all, last year’s Apple Watch added rudimentary sleep tracking capabilities along with a new Blood Oxygen sensor — both things that we’d been hearing about since 2019 — but there’s still one common health monitoring capability that Apple doesn’t seem to have cracked: Blood pressure monitoring.

Despite all the technological marvels that Apple has managed to bake into the Apple Watch, accurately monitoring blood pressure remains something of a holy grail for wearable devices. It’s a health metric that almost everybody wants to measure, yet it’s actually very difficult to do on a wrist-worn device like the Apple Watch.

One of the key challenges is that, as the American Heart Association notes, wrist monitors typically “yield less reliable readings,” and as a result most medical professionals recommend that measurements be taken with devices that use the more traditional blood pressure cuffs that are placed around the upper arm.

Still, it’s a problem that Apple has been trying to figure out for years, and while we’ve been hearing rumours of its impending arrival since before the Apple Watch Series 5, it looks like Apple is getting a lot closer. In fact, a report last summer suggested that Apple had planned it for the Apple Watch Series 6, but was forced to scrap it at the last minute due to serious inaccuracy problems.

Of course, that doesn’t mean that Apple has given up, and contrary to what many rumours implied there’s a good chance that blood pressure monitoring never even made it past the early prototyping stages for the Series 6, as there’s no way that Apple was going to include the technology unless it was accurate enough to be practical.

According to a recently granted patent, however, it looks like Apple may have finally found a way to take accurate blood pressure measurements from the wrist.

The patent in question, Devices and systems for correcting errors in blood pressure measurements, lays out a system for measuring blood pressure from an Apple Watch that is designed to mitigate almost all the factors that the company’s engineers believe are responsible for inaccurate readings.

The Proposed Solution

In broad terms, the researchers behind Apple’s patent outline the use of “one or more correction factors” to adjust the blood pressure measurements that are read by traditional pressure sensors, noting that this would “allow for more compact, convenient, and/or accurate wearable blood pressure measurement devices and methods” — specifically wrist-worn devices like the Apple Watch, of course.

The patent goes on to list some of these “correction factors,” including wrist circumference, target artery depth, tissue density, and hydration, adding that narrower cuffs — those less than 5 cm in width — increase errors even in traditional blood pressure monitoring devices that could be “due in part to variations in physical characteristics of users,” and could therefore be reduced by “using one or more correction factors.”

Reducing the bulkiness of current blood pressure measurement devices may be desirable, but doing so comes with additional challenges. Blood pressure measurement errors tend to increase as the cuff width decreases (e.g., becomes more narrow). For at least this reason, most blood pressure cuffs on the market are at least 5 cm in width and many blood pressure measurement device manufactures and designers have actually avoided narrowing blood pressure cuff widths further.

Apple Patent 10,881,307

The problem, it seems, is that narrower cuffs may not be able to apply enough pressure to reach the necessary arteries for all users, and those with “deeper target arteries” require wider cuffs that can apply sufficient pressure for an accurate measurement. However, Apple’s proposed solution is to estimate the wearer’s tissue density using additional sensors and algorithms to adjust the blood pressure measurement to account for these differences.

Interestingly, the Apple Watch wrist band may also factor into the proposed design, either with sensors to directly estimate the wrist circumference or target artery depth, or simply by determining which notch the band is fastened to. Other approaches include using an ultrasound sensor to measure arterial depth or an actuator with a fluid bladder and magnetic sensors.

In the patent, Apple also outlines its goal for creating an accurate wrist-worn blood pressure monitor in the Apple Watch:

The more convenient blood pressure monitoring may increase the adoption of non-clinical measurements and monitoring of blood pressure by common consumers. This may encourage more frequent blood pressure measurements by users (e.g., daily, weekly, monthly, or the like), thereby increasing the likelihood of detecting hypertension and decreasing risks associated with delayed detection of hypertension.

Apple Patent 10,881,307

While like most patents, Apple doesn’t mention the Apple Watch by name, referring only obliquely to “an electronic watch or the like,” it’s pretty clear that the patent refers to the company’s continuing efforts to add proper blood pressure measuring capabilities to its flagship wearable device.

However, when this is coming remains much more of an open question. Apple’s patent certainly seems to address these problems, and just because the patent was only granted today doesn’t mean that Apple hasn’t already been working on the idea for some time, so while we may have heard this song before, it does seem likely that Apple is at least planning to make another attempt to bring blood pressure monitoring capabilities to the Apple Watch Series 7 later this year, but of course whether we see it materialize or not will almost certainly depend on how the actual field trials of the new sensor systems work with a sufficient degree of accuracy.

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