This Key Health Metric Still Evades Gadget Makers

Measuring blood pressure has been around for more than a century, but is proving tricky to digitize.

Tim Culpan

28 May 2023, 11:22 AM IST

DORCHESTER, MA - APRIL 11: Dr. Elizabeth Maziarka reads a blood pressure gauge during an examination of patient June Mendez at the Codman Square Health Center April 11, 2006 in Dorchester, Massachusetts. Massachusetts Governor Mitt Romney is scheduled to sign a health care reform bill April 12 that would make it the first state in the nation to require all its citizens have some form of health insurance. (Photo by Joe Raedle/Getty Images)

(Bloomberg Opinion) -- Advances in software, hardware, semiconductors and medical research have put a virtual laboratory on the wrists of millions of consumers around the world, improving health and saving lives. Yet one of the oldest and most fundamental metrics — blood pressure — has proven too tricky to capture with digital technology.

Real-time heart-rate measurements have been cheaply available for half a century. Better sensors add heart-rate variability (HRV), a gauge of stress, while watch-based electrocardiograms give unprecedent insight into cardiac function. Apple Inc., Whoop Inc., Oura Health Oy, and Alphabet Inc.’s Fitbit all offer to track body temperature that can be used to estimate sleep quality and ovulation. We can even monitor the blood’s oxygen saturation, called SPO2, with a matchbox-sized reader.

For more than 200 years, doctors have known that changes in pressure that result from pumping blood through the body are an indicator of health, with one enterprising researcher improvising an ingenious way to measure it: He stuck a glass tube into the artery of a horse. A less cruel method followed, and has been the standard for more than a century.

Today we still pump air into a cuff wrapped around a limb — usually the upper arm — to produce an audible pause in blood flow, and take note of the pressure. A higher-than-normal figure indicates a patient has hypertension, which the World Health Organization estimates is a major cause of premature death globally, especially in low and middle-income nations.

HR and HRV are based on tracking electrical signals emitted by the heart, which is relatively easy. A traditional ECG also measures these pulses, but new methods coupled with highly-sensitive optical sensors allow us to see blood flow through the skin and accurately gauge these three sets of data.

Apple has made healthcare a centerpiece of its Watch, touting the numerous times its ECG function may have saved lives by helping detect atrial fibrillation — a form of irregular heart beat. This groundbreaking technology received clearance from the Federal Drug Administration, but doesn’t end the US company’s research into cardiac health.

Blood pressure may be next, and the race is on to overcome numerous obstacles involved in taking this measurement on the wrist. At the core of the problem is getting accurate data that is actually relevant. Heart rate is relatively easy because the sensor need only detect a specific event — a beat of the heart — and measure the time between subsequent occurrences.(1)Apple utilizes a one-lead technique to take an ECG, requiring the user to touch a finger to the crown of the watch to create an electric circuit. This gives a good-enough proxy to the gold-standard reading that uses 12 wires across the torso.

There are already devices on the market that claim to analyze from a watch, yet they mostly combine real-time pulse data with sophisticated algorithms to a value for blood pressure. Despite marketing claims, medical groups such as the European Society of Hypertension, “do not recommend cuffless devices for the diagnosis and management of hypertension.”

A recent Australian medical study published by the American Heart Association of 532 wristband wearable devices which purported to track blood pressure found that none was validated or proven accurate to international standards. Among the challenges is calibrating the watch’s measurement against known-accurate equipment, such as a cuff, and then updating that adjustment on a regular basis.

Researchers say this amounts to blood pressure rather than it, the difference being that this approach charts changes from a baseline and is liable to drifting over time.

This lack of fidelity is important and Apple appears to be taking its time. The company’s plan to add a blood-pressure feature to its series of smartwatches has hit some snags and the technology isn’t expected to be ready until next year at the earliest. Accuracy is the major stumbling block, according to a Bloomberg News report.

There are a few ways scientists hope to solve the problem. One is to mimic the operations of a cuff but on a finger instead of the arm. This method involves the ring tightening in order to apply pressure, and then taking measurements similar to a traditional approach. Yet researchers warn this could cause numbness with long-term use.

A more-recent alternative outlined in a paper published in February is to deploy a microphone to supplement readings taken by the optical sensor that measures blood flow. By hearing the sounds of the pulse, researchers believe they can more accurately estimate blood pressure without requiring calibration against a cuff. The South Korean team behind this novel approach admits that their results are only a proof of concept taken from one subject, yet further studies are likely to prove whether it’s viable.

It’s also possible that other groups in academia and industry have come up with better ways to improve readings using existing light monitors, or have invented new sensors that can accurately gauge blood pressure. Doing so is crucial.

With hundreds of devices already claiming to provide this fundamental health metric, and those being largely inaccurate, there’s an increasing risk that consumers are making decisions based on false data. While this could be largely harmless, people may become needlessly anxious from incorrect high readings or lulled into a false sense of security by low ones.

Scientists understand that no data is better than bad data, but in the age of numerous health-tech gadgets and constant connectivity a breakthrough in wrist-based blood pressure monitoring would be a welcome advance.