Gadget makers need to focus on key health metric
• Race is on to overcome obstacles involved in taking blood pressure
Advances in software, hardware, semiconductors and medical research have put a virtual laboratory on the wrists of millions of consumers worldwide, 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 watchbased electrocardiograms give unprecedented insight into cardiac function. Apple, Whoop, Oura Health Oy, and Alphabet’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 matchboxsized 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.
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 Organisation estimates is a 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 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 centrepiece 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 does not end the US company’s research into cardiac health.
PULSE DATA
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. Apple uses a onelead 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 analyse from a watch, yet they mostly combine real-time pulse data with sophisticated algorithms to estimate 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”.
An 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 regularly.
Researchers say this amounts to tracking blood pressure rather than measuring it, the difference being that this approach charts changes from a baseline and is liable to drifting over time.
ON FINGER
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 is not expected to be ready until next year at the earliest. Accuracy is the major stumbling block.
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 to apply pressure, and then taking measurements similar to a traditional approach. Yet researchers warn this could cause numbness with longterm 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 its results are only a proof of concept taken from one subject, yet further studies are likely to prove whether it is viable.
It is 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 is a 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 healthtech gadgets and constant connectivity a breakthrough in wrist-based blood pressure monitoring would be a welcome advance.
APPLE’S PLAN TO ADD A BLOODPRESSURE FEATURE TO ITS SERIES OF SMARTWATCHES HAS HIT SOME SNAGS