Apple Files New Patent For Updated Apple Watch Heart Rate Monitor

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Shortly after Apple started shipping its long-awaited Apple Watch, user reports began filtering in complaining of issues with its heart rate monitor. First, users began complaining that having a tattoo on the wrist would interfere with Watch’s ability to accurately monitor a user’s heart rate, a complaint that Apple had acknowledged less than a week after it started shipping the devices. Next, wearers noticed that after taking the Watch OS 1.01 update, the device no longer captured a resting heart rate unless the user was completely still. This discovery led to widespread complaints from the customer base and an eventual explanation from Apple.

The Apple Watch heart rate sensor relies on two technologies. The first was designed to provide continuous heart rate monitoring during workouts, while the second provides periodic monitoring of resting heart rate. To accomplish this, Apple relies on a technology called photoplethysmography, or PPG, for its continuous heart rate monitoring. Blood absorbs different colors of light at different rates, and is particularly consistent with the rate at which it absorbs green light. Apple is able to calculate a wearer’s heart rate by shining a constant green LED light into the skin, and then measuring variations in the green light absorption. This technology has worked well in Apple Watch. When a user is not working out, Apple relies on an entirely separate infrared technology to capture resting heart rate every 10 minutes. This feature has not fared nearly as well. There is no explanation for why Apple chose to use two separate methods, but many speculate that battery life was a motivating factor.

At launch, the Apple Watch captured resting heart rate every 10 minutes regardless of what a wearer was doing, and would jump to continuous heart rate monitoring only if the wearer was using the Apple workout app. This changed after Watch OS 1.01, which implemented a change that restricted the infrared system from taking a heart rate if the user, or even the user’s arm, was in motion. While many users thought that the now intermittent heart rate monitoring was a bug, Apple explained that the update was intentional, but failed to explain why it had made the change.  Some speculated that the change was meant to ensure that resting heart rate readings were as accurate as possible, suggesting that there were significant issues with its infrared technology’s ability to capture an accurate heart rate in anything but ideal conditions. Others concluded that it must be yet another battery life-saving effort.

Now, Apple has filed a patent describing a new method for monitoring heart rate that overcomes potential accuracy problems introduced with arm or body motion. The current technology requires that both sensors maintain direct contact with the skin during readings. However, the new patent describes a way of detecting if a diode has separated from the skin, and then overcomes this separation by introducing different algorithms designed to detect light absorption in this case.

It is unclear whether the new technology will require a hardware update, or if an OS update could deliver the fix, but at the very least Watch wearers should expect improved performance in the resting heart rate feature on Watch 2.


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