A Google study suggests an ordinary smartwatch can flag likely high blood pressure without anyone strapping on a cuff first. The paper appeared in Nature, and in a trial with 196 adults the watch picked up more hypertension cases than a single reading at a doctor’s office did.
The numbers are modest, and Google says so. The watch caught 65.8% of the people who truly had hypertension, against 55.3% for the initial office screening, while specificity (correctly clearing healthy people) was 90%. When the watch said “high”, it was right 80.6% of the time, compared with 77.8% for office readings.
The system uses two sensors nearly every smartwatch has: the optical pulse sensor and the accelerometer. Google Research says the accelerometer also picks up tiny vibrations of the wrist caused by each heartbeat. Instead of guessing a number such as 120/80 at one moment, the model averages the patterns over several days and gives a probability that someone is hypertensive. It needs the person’s height as an input, which stands in for the length of the arteries.
To train it, the team used 492,347 hours of sensor recordings from 2,109 volunteers, with no medical labels. The model learned to tell one person’s 15-second slices of signal from another’s, and a simple classifier was fitted on top. The 196-person test ran at five sites in the US, with 24-hour ambulatory monitoring as the reference. Volunteers with known cardiovascular disease or on blood pressure drugs were left out.
The result was better still for people who had already screened high in the clinic. In that group of 48, the watch confirmed sustained hypertension with 78.4% sensitivity and 96.7% positive predictive value, ahead of a repeat office visit at 67.6% and 86.2%. Several days of home monitoring still did better on sensitivity, at 89.2%.
Google stresses this is not a replacement for an arm cuff or a diagnosis. The aim is opportunistic screening that nudges someone to get checked, and the company calls the work early feasibility research that does not by itself promise a product. The work informed “blood pressure trends”, one of four tools in Google’s Health Guardian package for Pixel Watch and Fitbit Air, which reports monthly shifts instead of single readings.
Google puts the number of hypertension sufferers worldwide above one billion and says most are unaware of it, especially people aged 18 to 44. The full results are in the Nature paper.
