Samsung says it has figured out a blood pressure monitoring application for a smartwatch, and the solution will start shipping on the Galaxy Watch Active2, a Tizen watch that launched last year. Samsung says the app “has been cleared by the South Korea’s Ministry of Food and Drug Safety (MFDS), as a Software as a Medical Device (SaMD), making it a government-cleared, over-the-counter and cuffless blood pressure monitoring application.”

The only sensors on the back of a Galaxy Watch Active2 are a photoplethysmography (PPG) heart rate sensor and an electrode for electrocardiograms, but the company says that’s enough to obtain a blood pressure rating. The trick is that you’ll first need to calibrate the sensors with a real blood pressure cuff. The setup process has you wear the watch while taking a blood pressure reading with a cuff, then you enter the cuff reading into Samsung’s software. From there, the software can supposedly take further readings with just the watch hardware.

Traditional automated blood pressure cuffs inflate to restrict blood flow in your arm, and, as the cuff releases the pressure, arterial pulsations are measured with a pressure sensor. There already is a smartwatch with an inflating band that is basically a tiny blood pressure cuff—the Omron HeartGuide—but Samsung’s watch doesn’t work like that. Instead, the company says, “the device measures blood pressure through pulse wave analysis, which is tracked with the Heart Rate Monitoring sensors. The program then analyzes the relationship between the calibration value and the blood pressure change to determine the blood pressure.” It’s a PPG-driven blood pressure reading.

There is actually an entire Nature article on the subject of measuring blood pressure with a PPG sensor. The gist of it is that a PPG sensor measures blood volume and not blood pressure, but the correlation between the two means that once you calibrate with a real blood pressure measurement to a certain volume, you can measure the change in volume and derive a blood pressure reading from that. The downside to this technique is that, for an accurate reading, Samsung says you’ll have to recalibrate the watch with another cuff reading “at least every four weeks.” The company also recommends you have the watch tight on your wrist, and you shouldn’t talk or move while the reading is happening.

It sounds like the test case for this happened in 2018, when Samsung and UFCS launched the “My BP Lab” research project. The project used the Galaxy S9 PPG sensor to measure blood pressure, using the same cuff-calibration plan as today’s smartwatch announcement. At the time, UCSF said the study would let it gather data “from thousands of users in real-world settings.”

The feature will require the “Samsung Health Monitor App,” which Samsung says will be available in Q3 of this year.

https://arstechnica.com/?p=1669857