A Finger Worn Ring for On-Demand Measurement of Absolute Blood Pressure

Regular blood pressure (BP) monitoring is needed to manage hypertension. However, cuff devices are not readily accessible, and many adults are living with uncontrolled BP. Furthermore, popular wearable cuffless devices typically require calibration with periodic cuff BP measurements or demographic information. A finger worn ring for cuffless BP measurement without such calibration was investigated.

BP ring concepts were conceived based on the oscillometric cuff principle. The user varies their finger pressures similar to a cuff device by performing ring tightening followed by hand lowering or ring tightening only under visual guidance, while the ring obtains oscillometric measurements from the digital arteries for on-demand BP measurement. A prototype device was built to implement the BP ring concepts. The ring included a mechanical actuator to adjust its diameter and a photoplethysmography sensor, force sensor, and inertial measurement unit to make the measurements. The ring is interfaced to a display via a wired data acquisition system to guide the user in performing the ring tightening/hand lowering. An oscillometric algorithm is applied to compute BP from the measurements. The device was tested in 25 volunteers.

The ring tightening-hand lowering BP measurement could be learned by new users. The device yielded root-mean-square-errors of 7.1 and 6.9 mmHg for systolic and diastolic BP against a validated arm cuff device.

This study demonstrates the feasibility of absolute BP monitoring using a finger worn ring.

The BP ring concepts could potentially be incorporated in smart rings to help improve hypertension control.