Blood Pressure Readings on a Smart Watch
The Verge’s Nicole Wetsman has some really good material on the status of measuring blood pressure on a smart watch with insights from researchers and doctors:
· “We’re not ready for primetime yet,’ says Jordana Cohen, an assistant professor of medicine at the University of Pennsylvania who studies hypertension.
o Right now, there’s only one wearable device cleared by the Food and Drug Administration to measure blood pressure: a device from medical equipment company Omron.
o “Omron’s HeartGuide is extremely specialized. It’s even marketed as ‘a wearable blood pressure monitor in the innovative form of a wristwatch.’” It does the normal squeeze approach you might’ve had via a doctor or nurse to measure blood pressure.
· Devices from Samsung and Fitbit and so on use light sensors, but the FDA is examining them still:
o Samsung’s approach is based on a measure called pulse transit time, which is the time between the contraction of the heart and when the pulse arrives at a particular body part, like the wrist. It’s correlated with blood pressure. “The faster that pulse transit time is, the more the vessels are tightening — that’s what’s making the pulse travel faster,” Mendes says. Optical sensors also check if vessels are tightening or widening. An algorithm then uses those two bits of information, along with heart rate, to estimate blood pressure.
o Fitbit is a few steps further back in the process — it doesn’t have any blood pressure features available but has a handful of studies underway looking at the relationship between the metrics already collected by its devices and blood pressure.
Limitations are that they can only reliably measure relative blood pressure. The devices need calibration to find out a true number to tell rising and falling blood pressures to some “raw number,” not just the number at the time.
Fitbit’s Eric Friedman, vice president of research, says it’s going to be Herculean to solve: “There have been whole books written around why this is an impossible thing to solve,” he says. “I don’t have the hubris to view it as something that’s coming out any day now.”
“High blood pressure is such a major risk factor for stroke, major cardiac events, and kidney disease,” says Jordana Cohen. “It’s so, so important that we get it right, because if devices are giving you an inaccurate reading, you can get very false reassurance that your blood pressure is normal.”