System Performance and User Feedback Regarding Wearable Bioimpedance System for Multi-Site Knee Tissue Monitoring: Free-Living Pilot Study With Healthy Adults

Abstract

Knee-focused wearable devices have the potential to support personalized rehabilitation therapies by monitoring localized tissue alterations related to activities that reduce functional symptoms and pain. However, supporting these applications requires reported data to be reliable and accurate which can be challenging in the unsupervised free-living conditions that wearable devices are deployed. This pilot study has assessed a knee-focused wearable sensor system to quantify 1) system performance (operation, rates of data artifacts, environment impacts) to estimate realistic targets for reliable data with this system and 2) user experiences (comfort, fit, usability) to help inform future designs to increase usability and adoption of knee-focused wearables. Study data was collected from five healthy adult participants over 2 days, with 84.5 and 35.9% of artifact free data for longitudinal and transverse electrode configurations. Small to moderate positive correlations were also identified between changes in resistance, temperature, and humidity with respect to acceleration to highlight how this system can be used to explore relationships between knee tissues and environmental/activity context.

Keywords: bioimpedance; knee; multi-modal; multi-site; wearable.

FIGURE 1 ∣

(A) High-level block diagram of the electronics of the wearable sensor system, (B) electrode integration into the commercial brace, and (C) illustration of knee tissue locations that are measured by the wearable system after fitting to a participants body.

FIGURE 2 ∣

MAX30001 development kit (dashed) and wearable system (hatched) (A) resistance measurements from four cases of 2R-1C models and (B) standard deviation of measurements across all analog multiplexer configurations.

FIGURE 3 ∣

(A) Timing of a complete cycle of measurements from the wearable system during run-time and (B) highlight of configuration and settling time required for MAX30001 sensor for single frequency measurement.

FIGURE 4 ∣

Circumference measurements around the knee at three locations.

FIGURE 5 ∣

Average (A,B) and standard deviation (C,D) resistance (8–128 kHz) of on-board 2R-1C model for days 1 and 2 of data collection from study participants.

FIGURE 6 ∣

(A,C) Transverse and (B,D) longitudinal knee tissue resistance and reactance (8 kHz, 128 kHz) of Participant 3 using wearable sensing system over 2 days.

FIGURE 7 ∣

(A) Transverse and (B) longitudinal knee tissue resistance (8 kHz, 128 kHz) collected during free-living across 2 days from 5 healthy adult participants using wearable sensing system.

FIGURE 8 ∣

(A) Transverse and (B) longitudinal knee tissue reactance (8 kHz, 128 kHz) collected during free-living across 2 days from 5 healthy adult participants using wearable sensing system.

FIGURE 9 ∣

(A) Acceleration magnitude and (B) MAD representing activity at participants knee collected using wearable system across days 1 (red) and 2 (blue) of data collection.

FIGURE 10 ∣

(A) Temperature and (B) relative humidity of local wearable environment across day 1 (red) and 2 (blue) of participant data collection.

FIGURE 11 ∣

Comparisons of (A) $\Delta R_{8k}$, (B) $\Delta R_{128Kk}$ for longitudinal knee bioimpedance, (C) temperature, and (D) humidity reported by wearable with acceleration MAD from participants across 2-day data collection.