CUFFLESS DEVICES CAN OPEN A NEW CHAPTER IN AMBULATORY BLOOD PRESSURE MONITORING ONLY IF VALIDATED RIGOROUSLY: DESIGN OF A CHALLENGING PROTOCOL FOR AKTIIA BRACELET

Abstract

Objective: Cuffless wrist-based blood pressure (BP) monitors have a great potential to make ambulatory monitoring more appealing to patients and provide clinicians with better BP profiling. Investigators must be vigilant to validate these devices properly, as little guidance has been published. We propose a protocol that addresses ambulatory environment challenges, such as body posture changes and variable arm position. In addition to reporting the accuracy, we suggest reporting the number of successful automated measurements – the acceptance rate. Design and method: We tested the Aktiia Bracelet, a cuffless automated device that records optical signals at the wrist and requires an initial calibration, with the proposed protocol on 10 healthy volunteers. We simultaneously recorded the signals from the Aktiia Bracelet and a reference volume-clamp device positioned on the contralateral arm during the following interventions: sitting, lying supine, standing with both arms positioned at heart level; sitting with the Aktiia bracelet wrist positioned 30 cm lower than heart level; isometric leg extension inducing large BP changes. We calculated the mean and standard deviations of the error between Aktiia bracelet and the reference, as well as the acceptance rates in different measurement scenarios. Results: The figure illustrates the mean and standard deviation (STD) of the error between Aktiia bracelet and the reference, as well as the acceptance rate (Acc) for the diastolic BP (DBP). The dashed area illustrates the expected hydrostatic bias. The mean and the standard deviation of the error fell within ISO81060-2 limits. Aktiia bracelet readings were not affected by the hydrostatic bias intervention, even though one could expect an error of more than 20 mmHg. The maximum of the accepted measurements was achieved when patients were lying supine (67%) and sitting (52%). Thus, the user can expect a high density of measurements during night-time. However, when standing, the acceptance dropped (27%). Conclusions: This protocol provides more realistic testing of cuffless wrist-based BP monitors and suggests a way to improve the validation of this new family of devices.