Future Apple Watch could measure blood pressure without extra peripherals

Plans for a new sensor could mean that the regular Apple Watch will be able to accurately measure blood pressure without the need for extras such as a blood pressure cuff.

One of the very first health-related features of the Apple Watch was its ability to measure heart rates in beats per minute. However, it's not been able to accurately measure blood pressure because that requires more sensitive sensors, and also for those sensors to be placed accurately over a vein.

While you can get blood pressure apps for the Apple Watch, they require an extra device, such as a blood pressure cuff, which wraps around the whole wrist. "Pressure measurement designs," US Patent No 10,646,121 describes a way of doing without that cuff and still achieving accuracy in both positioning and data.

This is significant both because it increases the number of people who will be able to check their blood pressure — they only need their Apple Watch, they don't have to buy anything else — but also because of the range of medical benefits that come from regularly recording this data.

"Measuring pressure may be useful in monitoring one or more user parameters," says the patent. "For example, blood pressure measurements may be a helpful user parameter to measure as elevated blood pressure (a.k.a. hypertension) may be an indicator for potential health issues."

"Additionally, pressure measurements may also be indicative of a user's heart rate," it continues. "Further, in some instances, pressure measurements may provide blood pressure waveform morphologies which may be a useful user parameter to monitor."

What Apple proposes is that rather than having sensors arranged through a cuff or other wrist-wrapping extra device, the Watch itself gains a spread of sensors. A combination of hardware and software leverages this array of sensors to calculate accurate readings.

"A sensor array may increase the chance of proper placement of at least one pressure sensing node relative to the target artery," it explains. This increases the "pressure-sensing resolution" to help provide a range of data measurements.

"These devices may help reduce issues with signal processing as one or more preferred pressure sensing nodes of the sensor array may be identified and pressure signals received therefrom may require less error correction or processing," continues the patent. "Such devices may provide a more convenient and accurate blood pressure monitoring device."

The patent does not use the words "Apple Watch," and instead repeatedly describes " a wrist-worn device," so it could be that Apple intends a separate product. But it's unlikely as the patent stresses the point is to "increase the adoption of non-clinical measurements and monitoring of blood pressure by common consumers."

Detail from patent showing one potential sensor array

The invention is credited to Ravi K. Narasimhan, Zijing Zeng, and Zhipeng Zhang. Among Zeng's prior patents is a related one for a "wrist worn accelerometer for pulse transit time (PTT) measurements of blood pressure." Zhang's previous inventor credits include a patent ">in the same field.

Currently-shipping Apple Watches were recently part of an research project into blood pressure and body mass index conducted by the Framingham Heart Study.