Medscape’s Editor-in-Chief Eric Topol, MD, referred to continual noninvasive, cuffless, accurate blood pressure devices as “a holy grail in sensor technology.”
He personally tested a cuff-calibrated, over-the-counter device available in Europe that claims to monitor daily blood pressure changes and produce data that can help physicians titrate medications.
Dr. Topol does not believe that it is ready for prime time. Yes, cuffless devices are easy to use, and generate lots of data. But are those data accurate?
Many experts say not yet, even as the market continues to grow and more devices are introduced and highlighted at high-profile consumer events.
Burned before
Limitations of cuffed devices are well known, including errors related to cuff size, patient positioning, patient habits or behaviors (for example, caffeine/nicotine use, acute meal digestion, full bladder, very recent physical activity) and clinicians’ failure to take accurate measurements.
Like many clinicians, Timothy B. Plante, MD, MHS, assistant professor at the University of Vermont Medical Center thrombosis & hemostasis program in Burlington, is very excited about cuffless technology. However, “we’ve been burned by it before,” he said in an interview.
Dr. Plante’s 2016 validation study of an instant blood pressure smartphone app found that its measurements were “highly inaccurate,” with such low sensitivity that more than three-quarters of individuals with hypertensive blood levels would be falsely reassured that their blood pressure was in the normal range.
His team’s 2023 review of the current landscape, which includes more sophisticated devices, concluded that accuracy remains an issue: “Unfortunately, the pace of regulation of these devices has failed to match the speed of innovation and direct availability to patient consumers. There is an urgent need to develop a consensus on standards by which cuffless BP devices can be tested for accuracy.”
Devices, indications differ
Cuffless devices estimate blood pressure indirectly. Most operate based on pulse wave analysis and pulse arrival time (PWA-PAT), explained Ramakrishna Mukkamala, PhD, in a commentary. Dr. Mukkamala is a professor in the departments of bioengineering and anesthesiology and perioperative medicine at the University of Pittsburgh.
PWA involves measuring a peripheral arterial waveform using an optical sensor such as the green lights on the back of a wrist-worn device, or a ‘force sensor’ such as a finger cuff or pressing on a smartphone. Certain features are extracted from the waveform using machine learning and calibrated to blood pressure values.
PAT techniques work together with PWA; they record the ECG and extract features from that signal as well as the arterial waveform for calibration to blood pressure values.
The algorithm used to generate the BP numbers comprises a proprietary baseline model that may include demographics and other patient characteristics. A cuff measurement is often part of the baseline model because most cuffless devices require periodic (typically weekly or monthly) calibration using a cuffed device.
Cuffless devices that require cuff calibration compare the estimate they get to the cuff-calibrated number. In this scenario, the cuffless device may come up with the same blood pressure numbers simply because the baseline model – which is made up of thousands of data points relevant to the patient – has not changed.
This has led some experts to question whether PWA-PAT cuffless device readings actually add anything to the baseline model.
They don’t, according to Microsoft Research in what Dr. Mukkamala and coauthors referred to (in a review published in Hypertension) as “a complex article describing perhaps the most important and highest resource project to date (Aurora Project) on assessing the accuracy of PWA and PWA devices.”
The Microsoft article was written for bioengineers. The review in Hypertension explains the project for clinicians, and concludes that, “Cuffless BP devices based on PWA and PWA-PAT, which are similar to some regulatory-cleared devices, were of no additional value in measuring auscultatory or 24-hour ambulatory cuff BP when compared with a baseline model in which BP was predicted without an actual measurement.”