Abstract
Fluid overload is a chronic medical condition that affects over six million Americans with conditions such as congestive heart failure, end-stage renal disease, and lymphedema. Remote management of fluid overload continues to be a leading clinical challenge. Bioimpedance is one technique that can be used to estimate the hydration of tissue and track it over time. However, commercially available bioimpedance measurement systems are bulky, expensive, and rely on Ag/AgCl electrodes that dry out and can irritate the skin. The use of bioimpedance today is therefore limited to clinical and research settings, with measurements performed at daily intervals or over short periods of time rather than continuously and long-term. This paper proposes using wearable calf bioimpedance measurements integrated into a compression sock for long-term fluid overload management. A PCB was developed using standard measurement techniques that measures the calf bioimpedance using a custom analog front-end built around an AD8302 gain-phase detection chip. Data is transmitted wirelessly via Bluetooth Low Energy to an iOS device using a custom iOS app. Bioimpedance data were collected both from the wearable system and a commercial measurement system (ImpediMed SFB7) using RRC networks, Ag/AgCl electrodes, and the textile compression sock. Bioimpedance data collected from the wearable system showed close agreement with data from the SFB7 when using RRC networks and in five healthy human subjects with Ag/AgCl electrodes. However, when using the textile compression sock the wearable system had worse precision than the SFB7 (4% run to run compared to <1% run to run) and there were larger differences between the two systems than when using the RRC networks and the Ag/AgCl electrodes. Wearable system precision and agreement with the SFB7 was improved by pressure or light wetting of the current electrodes on the sock. Future research should focus on reliable elimination of low-frequency artifacts in research grade hardware to enable long-term calf bioimpedance measurements for fluid overload management.
Highlights
Millions of Americans suffer from chronic fluid overload (Adamson, 2009; Zoccali et al, 2017; Schwaiger et al, 2020), costing the US healthcare system more than $30 billion in 2012 (Virani et al, 2021)
We found that the research grade hardware had comparable results to the SFB7 when using RRC networks and Ag/AgCl electrodes, but had more low frequency artifacts when compared with the SFB7 when using the custom textile compression sock that impacted both precision and agreement between the two tested systems
4.3.1 Presentation Our results show that using standard research grade bioimpedance measurement circuits (in this case, a voltage controlled current source and commercially available instrumentation amplifiers, a common topology used in portable and wearable bioimpedance spectroscopy systems, see e.g., Yang et al (2006); Bonnet et al (2016); Hersek et al (2017); Dheman et al (2020)), results in low frequency artifacts when using textile electrodes
Summary
Millions of Americans suffer from chronic fluid overload (Adamson, 2009; Zoccali et al, 2017; Schwaiger et al, 2020), costing the US healthcare system more than $30 billion in 2012 (Virani et al, 2021). Chronic fluid overload can occur due to conditions such as congestive heart failure (CHF), cirrhosis and end-stage renal disease (ESRD). Despite affecting over six million Americans, managing patient fluid status remains a clinical challenge today (Lukaski et al, 2019; La Franca et al, 2020; Virani et al, 2021). There is a need for a reliable, affordable, and clinically relevant home fluid status monitoring system that can readily integrate into patients’ daily lives
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