IEEE and FDA validation
Despite these concerns, several cuffless devices using PWA and PAT have been cleared by the Food and Drug Administration.
Validating cuffless devices is no simple matter. The Institute of Electrical and Electronics Engineers published a validation protocol for cuffless blood pressure devices in 2014 that was amended in 2019 to include a requirement to evaluate performance in different positions and in the presence of motion with varying degrees of noise artifact.
However, Daichi Shimbo, MD, codirector of the Columbia Hypertension Center in New York and vice chair of the American Heart Association Statement on blood pressure monitoring, and colleagues point out limitations, even in the updated standard. These include not requiring evaluation for drift over time; lack of specific dynamic testing protocols for stressors such as exercise or environmental temperatures; and an unsuitable reference standard (oscillometric cuff-based devices) during movement.
Dr. Shimbo said in an interview that, although he is excited about them, “these cuffless devices are not aligned with regulatory bodies. If a device gives someone a wrong blood pressure, they might be diagnosed with hypertension when they don’t have it or might miss the fact that they’re hypertensive because they get a normal blood pressure reading. If there’s no yardstick by which you say these devices are good, what are we really doing – helping, or causing a problem?”
“The specifics of how a device estimates blood pressure can determine what testing is needed to ensure that it is providing accurate performance in the intended conditions of use,” Jeremy Kahn, an FDA press officer, said in an interview. “For example, for cuffless devices that are calibrated initially with a cuff-based blood pressure device, the cuffless device needs to specify the period over which it can provide accurate readings and have testing to demonstrate that it provides accurate results over that period of use.”
The FDA said its testing is different from what the Microsoft Aurora Project used in their study.
“The intent of that testing, as the agency understands it, is to evaluate whether the device is providing useful input based on the current physiology of the patient rather than relying on predetermined values based on calibration or patient attributes. We evaluate this clinically in two separate tests: an induced change in blood pressure test and tracking of natural blood pressure changes with longer term device use,” Mr. Kahn explained.
Analyzing a device’s performance on individuals who have had natural changes in blood pressure as compared to a calibration value or initial reading “can also help discern if the device is using physiological data from the patient to determine their blood pressure accurately,” he said.
Experts interviewed for this article who remain skeptical about cuffless BP monitoring question whether the numbers that appear during the induced blood pressure change, and with the natural blood pressure changes that may occur over time, accurately reflect a patient’s blood pressure.
“The FDA doesn’t approve these devices; they clear them,” Dr. Shimbo pointed out. “Clearing them means they can be sold to the general public in the U.S. It’s not a strong statement that they’re accurate.”