The Skeptical Cardiologist

Are Wrist Blood Pressure Monitors Accurate? Can We Go Cuffless?

The skeptical cardiologist spruced up and updated The Skeptical Cardiologist’s Guide to Home Blood Pressure Monitoring today. Most of what I wrote then is still accurate and I am still using home-measured BPs (for those capable of doing the measurements) as my primary tool for BP assessment and management.

However, consumer and industry interest in wrist-based BP monitors has grown substantially in the 4 years since that was published I believe we need to reconsider their utility. Until recently, I was in agreement with the AHA recommendation to choose upper arm-based BP cuffs over wrist-based ones unless the arm cuff was too painful or there was a medical contraindication to it.

In 2020 Omron asked me to evaluate their HeartGuide BP “watch” and although it had potential, ultimately I could not recommend it. I wrote a (somewhat) humorous and whimsical post on my initial experience with the device (Omron’s Omron’s HeartGuide Wristwatch Blood Pressure Monitor Allows BP Monitoring During Daily Activities Unobtrusively: Can It Replace Ambulatory BP Monitors? ) followed by in depth analysis here.

In the end, I found this device too big, bulky, and expensive to be practical. In terms of accuracy, it was, like many wrist BP cuffs, also limited:

I found that the HeartGuide systolic blood pressure was on average 10 mm Hg lower than the brachial BP when my blood pressure was high (>140 mm Hg).  When my systolic BP was between 120 and 130 mm Hg the HeartGuide was 5 mm Hg lower than the brachial and when my blood pressure was less than 120 mm Hg the Heart Guide and brachial BPs were identical.

I made similar measurements on other volunteers and found some had consistently identical wrist and brachial SBP whereas others had consistently higher blood pressures by wrist compared to brachial techniques.

Because of this individual variation I highly recommend users calibrate the OHG (or any wrist-based BP cuff) versus a standard BP cuff over a series of days with multiple measurements to see how the two measurements compare. If you find a consistent over or underestimate then the device can be used with this known adjustment.

Consumer Reports also finds the Omron HeartGuide to be inaccurate and gave iHealth’s wrist BP monitor a very low score for accuracy.

I advise patients to buy BP monitors which are approved by the AMA and on the US Blood Pressure Validated Device Listing.

There are lots of arm BP monitors on this listing but only 4 wrist devices, all by Omron (one of which, the BP8000-M is the aforementioned HeartGuide wristwatch.)

The Omron BP 6100 is also on the validated BP device list. You can read about my friend Wally’s (mostly negative ) experience with the Omron BP6100 here.

Note that the AMA Validated BP Device List has this disclaimer on all the approved wrist cuffs:

Going Cuffless

Wouldn’t it be nice if we could dispense with those noisy, slow, bulky cuffs that BP devices employ as part of the oscillometric determination of blood pressure at either the radial (wrist) or brachial (arm) artery? It would be even nicer if those smart wearable devices (smartwatches and fitness trackers) that have appeared on so many wrists to measure steps and heart rate could also measure BP.

These smart wearables utilize photoplethysmography (PPG) to calculate heart rate and detect irregular rhythms. Many vendors have been exploring other cardiovascular physiologic parameters that can be obtained from the PPG signal including blood pressure.

For a summary of the technology involved in converting PPG signals into important physiologic parameters, I recommend Peter Charlton’s article in the Proceedings of the IEEE.

Despite a lack of validation, a 2020 paper found that in Australia these cuffless wearable devices dominated the online home BP monitor marketplace.

Nonvalidated Home Blood Pressure Devices Dominate the Online Marketplace in Australia: Major Implications for Cardiovascular Risk Management

There were 532 wristband wearable devices available online for purchase in Australia in 2020 which claimed to measure blood pressure but none of them were validated.

I am in the process of evaluating a very promising smart wearable made by a European company and not yet available in the US. This device has been validated as accurate and utilizes a calibration process against a simultaneous arm cuff BP measurement, something I felt would enhance the accuracy of all wrist-based BP devices. It utilizes a small lightweight bracelet for continuous and unobtrusive BP monitoring.

This device and others have the potential to improve our management of hypertension by providing the equivalent of 24-hour ambulatory home BP monitoring without the expense and hassle of currently available devices. Ambulatory BP monitoring is considered by some experts to be the gold standard for BP control.

Further studies are clearly needed before we can recommend cuffless monitoring but my sense is that we are very close to a breakthrough in this area.

Sphygmomaniacally Yours,

-ACP

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