Can cuffless wearable devices track BP changes?

A cuffless wearable device may help improve hypertension management if it demonstrates accuracy and clinical utility. However, a recent study has found that a commercially available blood pressure (BP) monitoring device does not accurately track night-time BP decline and medication-induced BP changes.

“The commercially available wrist-worn Aktiia cuffless wearable device lacked the key function required for clinical management, namely the ability to track changes in brachial BP during sleep or with drug treatment in a similar fashion as conventional cuff-based methods,” the researchers said.

Forty-one participants (mean age 58 years, 32 percent female, 80 percent hypertensive) were fitted with a wrist-wearable cuffless BP device for 6‒12 days in this study. The researchers performed 24-h ambulatory BP monitoring (ABPM) at the beginning and the end of this period.

Specifically, three hypertensive participants wore the cuffless wearable device and performed home BP monitoring (HBPM) continuously 1 week and 2 weeks after antihypertensive medication uptitration.

Aktiia reported higher average systolic (S)BP for 24-h (difference, 4.9 mm Hg, 95 percent confidence interval [CI], 1.9‒7.9) and night-time (difference, 15.5 mm Hg, 95 percent CI, 11.8‒19.1; p≤0.01 for all), but similar daytime (difference, 1.0 mm Hg, 95 percent CI, ‒1.8 to 3.8; p=0.48), relative to ABPM. [J Hypertens 2023;41:1003-1010]

Average cuffless diastolic (D)BP was also higher for 24-h (difference, 4.2 mm Hg, 95 percent CI, 2.3‒6.0) and night-time (difference, 11.8 mm Hg, 95 percent CI, 9.5‒14.1; p<0.001 for both), but similar during daytime (difference, 1.4, 95 percent CI, ‒0.4 to 3.23; p=0.13).

Additionally, the cuffless wearable device demonstrated a reduced night-time dip for SBP (difference, 14.2 mm Hg, 95 percent CI, 12.1‒16.3) and DBP (difference, 10.2 mm Hg, 95 percent CI, 8.5‒11.9; p<0.001 for both).

After 2 weeks of uptitration, the average medication-induced SBP/DBP decline was ‒1.0/‒0.8 mm Hg with Aktiia compared with ‒19.7/‒11.5 mm Hg with HBPM (p=0.03 for difference).

“We showed that despite comparable daytime BP, the cuffless method did not adequately track the BP decline during night-time sleep when compared [with] conventional cuff-based ABPM,” the researchers said. “Our study results also suggested that the cuffless device did not adequately track antihypertensive medication-induced BP lowering when compared with cuff-based HBPM.”

Accurate or not?

Developers of Aktiia reported in previous studies that their wearable device demonstrated accuracy when validated after cuff BP calibration in the sitting position according to an adapted ISO81060-2 protocol for cuff devices, accuracy in the most common body positions, and accurate tracking of BP changes when taking antihypertensive medications. [Sci Rep 2021;11:20644; Blood Press Monit 2021;26:305-311; Cardiovasc Med 2021;24:w10054]

“Yet, recently, they also reported that conventional ABPM demonstrated a 3.4 times larger night-time dipping than the Aktiia device, which align with our findings,” the researchers noted. [Front Med Technol 2022;4:899143]

Notably, the inability to track BP changes over time is not limited to the Aktiia device alone but is possibly shared among other commercially available cuffless BP devices, according to the researchers.

“One plausible explanation is the reliance of cuffless BP devices on an initial calibration that is often only performed at resting BP using a conventional cuff-based BP device,” they added.

“While awaiting a new ISO standard, which is specific for validating cuffless devices, studies are encouraged to evaluate the ability of wearable devices to track changes in BP, as opposed to just validating the devices at resting or calibration BP,” the researchers said.