#4657 Comparison of Two Bioimpedance Spectroscopy Devices: A Practical Step Forward on the Way to Daily Bioimpedance Measurements for Dialysis Patients

Background and Aims
Bioimpedance spectroscopy (BIS) is a non-invasive diagnostic tool to assess volume status and body composition through the measurement of voltage drops in alternating currents and subsequent extrapolation of extracellular (R0), intracellular (Ri), and total body (RInf) resistances. Currently available devices mostly rely on disposable electrodes and require supine body position. Here we tested whether a new, more versatile BIS device with reusable electrodes matches an established system in various setups, aiming to enable daily BIS-measurements in the near future.

Method
Two BIS devices (“Cella” and the “Body Composition Monitor” [BCM]) were compared both with four resistance testboxes (circuit boards with resistors and capacitors simulating different body conditions) and in 40 healthy volunteers. In-vivo comparisons included supine hand-to-foot (HF) reference measurements with adhesive disposable electrodes and hand-to-hand (HH) measurements with adhesive disposable and prototype reusable electrode sets (Figure 1).

Results
Analyses of testboxes were reproducible in both devices (intra-device coefficients of variation <1%). Mean differences from testbox components were similar and small for R0 (2-3 Ohm) but not for Ri, where Cella was off by 101 Ohm compared to the BCM's 29 Ohm in a testbox designed with a deliberately low R0/Ri ratio. In-vivo, HF measurements with disposable electrodes differed significantly between both devices (p < 0.001). Prototype reusable HH electrodes exhibited a bias towards larger resistances than HF measurements (R0: 738.36 Ohm vs. 643.09 Ohm; Ri: 1508.18 Ohm vs. 1257.17 Ohm; RInf 500.03 vs. 423.81 Ohm, respectively) and the HH/HF ratio varied between 1.0-1.4 (R0 and RInf) and 0.9-1.6 (Ri).

Conclusion
While the Cella BIS device was shown to produce results with comparable consistency to the BCM in-vivo, the latter measured more accurately under testbox conditions. Accuracy of in-vivo measurements could not be determined for lack of gold-standard measurements. Implementation of HH reusable electrodes will require per-patient calibration against HF measurements due to the large inter-patient fluctuations in the HH/HF ratio. We recommend further longitudinal analyses of intra-patient HH/HF ratios to investigate long-term variabilities.

Figure 1: https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/ndt/38/Supplement_1/10.1093_ndt_gfad063c_4657/4/m_gfad063c_4657_f1.jpeg?Expires=1704272509&Signature=mzHdHma4144-kEJkUK~YKGzpl8ChCs2xeeV7TzElXtpgbYXM2-o8gWq7d7GK85CNrbhv-ehn-kC5hJxbiSud-E5wzLvT0Mvkmp-1DW45rievrjV9nrCrjKz4Va8NPZAigmAhJyzcig9FowvAi0feiP1e2-6Fr9FMSh7rM0YrM00jMdxa~sb0lN6TxAocmnv0r8jc5e2Mguk3k7-cCUW7ij5b4zn8IvBU9DD3EW~nLrB2PDmgFFU7eL806ppF1wsQ7EDzw58Xw4IqBnNqm98nI3tD~~pb~FxaE-H2wHOCAcbGqJ~s2FPnYK~KaKaro7Covs8-cQHso44l9DqeajnH9g__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA 

Setups, Absolute and Normalized Resistances of BIS Measurements. Panels A-E illustrate all in-vivo BIS measurements conducted within this study (Cella: Setups 1, 3 and 5-10; BCM: Setups 2 and 4). Setups 1 and 2 were carried out after participants lay flat on their backs for 10 minutes to achieve fluid equilibrium and were followed by Setups 7 and 8, 5 and 6 and finally 3 and 4. Setups 9 and 10 took place prior to the 10-minute-long supine body positioning right after the participants’ arrival at the study facility. The sequence of setups was rearranged to reflect the increase in normalized error to Setup 1. Panels F-J depict R_Inf, R₀ and R_i in absolute numbers while Panels K-O present normalized R_Inf, R₀ and R_i values, computed by dividing measurements of Setups 2-10 by Setup 1 on an intra-patient basis. Colored points depict mean relative values and error bars delimit mean ±1.96 standard deviations of the mean. BIS, bioimpedance spectroscopy; BCM, Body Composition Monitor; R_Inf, resistance at infinite frequency; R₀, extracellular resistance; R_i, intracellular resistance.