Band Electrodes Reduce Simulated Calf Bioimpedance Measurement Errors Due to Muscle Anisotropy

Abstract

Remote monitoring of fluid status via calf bioimpedance measurements could improve the experience of patients with congestive heart failure and reduce readmission rates. Most measurements today use conventional Ag/AgCl electrodes and a short inter-electrode spacing, resulting in current flowing primarily near the electrodes, preventing deeper current penetration and in turn accurate volume estimation. Textile band electrodes may more evenly distribute current throughout the calf. In the present study, simulations were conducted to investigate the impact of inter-electrode spacing/placement and fat tissue on bioimpedance using both Ag/AgCl electrodes and textile band electrodes. Simulation results showed that increasing the inter-electrode spacing can improve current distribution in the tissue, but there are still errors that increase with fat thickness (14.3% error at 10 cm spacing down to 1.7% error at 20 cm spacing for a "nominal" fat thickness, vs.-0.3% and-0.5% error for band electrodes). Band electrodes most closely matched the expected resistance and seem the most suitable regardless of inter-electrode spacing. Clinical relevance-This study suggests that band electrodes should be used for segmental bioimpedance measurements with short conductor lengths instead of spot electrodes.

Characterization and Correction of Low Frequency Artifacts in Segmental Bioimpedance Measurements

“…One is to reduce the difference between χ 3 or χ 4 in some way, but this can be difficult in practice due to limitations of electrode materials. However, there are alternative methods: (1) adjusting the cutoff frequency (increasing the LF or reducing the HF) before fitting to the Cole model and (2) performing the measurement twice, swapping the voltage and current leads 1 For a detailed derivation and discussion on how the resistances and other parameters contribute to overall errors in fluid status estimation, see [8].…”

“…One of the major challenges in bioimpedance research is the lack of electrodes that can be used for long-term monitoring, especially in home environments. Previous research has shown that textile band electrodes are a promising alternative to conventional Ag/AgCl electrodes and can be used for segmental bioimpedance measurements at the calf [1]. However, textile electrodes have artifacts that can prevent accurate volume estimation [2].…”

Evaluating Research Grade Bioimpedance Hardware Using Textile Electrodes for Long-Term Fluid Status Monitoring

“…The wearable compression sock consisted of four band electrodes made from a textile material to ensure uniform current distribution throughout the measured part of the calf. A uniform current distribution is necessary in order to estimate volume based on bioimpedance (see Section 2.1), and to ensure that bioimpedance is not artificially high due to fat on the calf (Delano, 2020). Band electrodes ensure this uniformity by driving current through the calf from around the calf circumference, rather than from a single point as with spot Ag/AgCl electrodes.…”

“…1. Current distribution: The prototype uses band electrodes to distribute current uniformly through the calf, minimizing the impact of calf fat and ensuring accurate calf fluid volume estimation, unlike conventional spot Ag/AgCl electrodes (Delano, 2020).…”