P4: REDIEM: Renal Extremity Device to Measure Impedance, Edema, Movement

Abstract

Purpose: Advanced and end-stage renal disease (ESRD), is a leading cause of morbidity and mortality. Beyond internal biochemical abnormalities, patients are externally symptomatic of water and electrolyte abnormalities with excess fluid retention, e.g. leg edema; and uncontrolled leg movement, as restless leg syndrome (RLS). Limited methods exist to quantitatively follow leg edema and RLS in patients out of hospital and at home. We report on development of an integrated device capable of monitoring: 1. leg edema, 2. water content/dry weight, and 3. leg movement. Methods: An impedance-edema sensor, with incorporated accelerometer was designed. All components were integrated into a comfortable wearable band, with iOS applicability for ready interpretation (Fig 1). For initial assessment, tissue edema, and leg movement, were measured using facsimiles. Sensor band was placed on hydrated pork belly (leg edema facsimile), current applied (< 10 uA), resistance and impedance determined, and edema and tissue water content calculated via algorithm. Measurements were compared to those made with standardized bioimpedance system. For leg motion, band was placed on limb facsimile oscillated at defined frequency. Results: Initial sensor was able to measure differences in impedance correlating with differing degree of test tissue hydration. Measurements obtained via algorithm correlated closely with standardized bioimpedance system determinations (Fig 2.1, 2.2). The edema algorithm, compared to actual test absorbance, differed on average by 3.4%. Motion sensor was able to detect jerking RLS-like motions with an average of 8.3% error. Slower motion detection was found to be less accurate and is being currently addressed via system design evolution. Conclusion: Combining impedance measuring technology with motion sensing allows for fabrication of a wearable system able to measure leg edema and motion. Use of this system in Renal patients will allow optimization of management as related to water excess/dry weight and RLS and on a serial outpatient basis.