Google patent puts a tiny blood pressure sensor in a smartwatch

Google is clearly not finished poking at the blood pressure problem. The company already has Blood Pressure Trends heading to its wearables, but a newly published patent shows something quite different. Instead of looking for longer-term patterns from the sensors already on your wrist, Google is exploring hardware that could actually measure a blood pressure signal through your fingertip. 

The patent was published on September 17 and describes a miniaturized impedance plethysmography sensor (IPG sensor), built into a computing device. The drawings make the wearable angle pretty obvious too. One example is a smartwatch, while others show small finger-worn devices and even other types of electronics.

Your fingertip becomes part of the sensor

The basic idea is quite neat. Google places a set of miniature electrodes underneath the fingertip, with two used to send a tiny electrical excitation signal through the tissue and another two used to measure the resulting electrical response.

Blood flowing through the finger changes its electrical impedance. By tracking those changes, the system can produce a pulsatile waveform that reflects the blood pulse, and Google says that signal can then be used to determine blood pressure or a proxy for blood pressure. The patent’s process diagram boils the whole thing down to generating IPG data, deriving the pulsatile signal and then estimating blood pressure from it. 

And Google clearly has smartwatch use in mind. Figure 6A shows the system incorporated into a watch worn on the wrist, with the sensing area positioned on the watch body where a finger could be placed against it. Earbuds are another option. As well as smartphones.

That’s not the only idea

And this is not even the only recent Google patent dealing with the problem. A separate application published last month describes a small finger cuff containing an inflatable bladder, multiple pressure sensors and optical sensors. 

That system would inflate around the finger while an array of barometric sensors maps pressure around the digital artery. But as you can see from the image below, it’s not exactly a discreet smart ring.

Optical sensors simultaneously measure the pulse, and the device combines those signals to calculate blood pressure. The patent’s flow diagram specifically shows inflation, pressure mapping, optical measurements and the final blood pressure estimate as parts of the process. 

Where this fits with Google’s plans

It is worth noting that neither patent names a Pixel Watch or Fitbit product. Google has been busy around blood pressure lately, though. It ran a Fitbit Hypertension Lab study with Pixel Watch 3 owners last November, and Blood Pressure Trends is coming to the Pixel watches this fall as part of Health Guardian.

We also covered an earlier Fitbit patent that hinted at blood pressure checks from the wrist in April. Put the two finger filings next to that and Google is clearly working on blood pressure from several directions. Patents do not confirm a release though, so treat these as a look at what Google is exploring.

Source USPTO: September patent, August patent