Monitoring thoracic fluid content using bioelectrical impedance spectroscopy and Cole modeling

Abstract

Heart failure is a chronic disease marked by frequent hospitalizations due to pulmonary fluid congestion. Monitoring the thoracic fluid status may favor the detection of fluid congestion in an early stage and enable targeted preventive measures. Bioelectrical impedance spectroscopy (BIS) has been used in combination with the Cole model for monitoring body composition including fluid status. The model parameters reflect intracellular and extracellular fluid volume as well as cell sizes, types and interactions. Transthoracic BIS may be a suitable approach to monitoring variations in thoracic fluid content.The aim of this study was to identify BIS measures, which can be derived based on the Cole model, that are sensitive to early stages of thoracic fluid accumulation. We simulated this medical condition in healthy subjects by shifting a part of the whole blood from the periphery towards the thorax. The redistribution of blood was achieved non-invasively through leg compression using inflatable leg sleeves. We acquired BIS data before, during and after compression of the legs and examined the effect of thoracic fluid variations on parameters derived based on the Cole model and on geometrical properties of the impedance arc. Indicator dilution measurements obtained through cardiac magnetic resonance imaging were used as a reference for the changes in pulmonary fluid volume.Eight healthy subjects were included in the study. The Cole model parameters of the study group at baseline were: R 0 = 51.4 ± 6.7 Ω, R ∞ = 25.0 ± 7.0 Ω, f c = 49.0 ± 10.5 kHz, α = 0.687 ± 0.027, the resistances of individual fluid compartments were R E = 51.4 ± 6.7 Ω, R I = 50.5 ± 22.9 Ω, the fluid distribution ratio was K = 1.1 ± 0.3, and the radius, area and depression of the arc's center were: R = 15.7 ± 1.3 Ω, X C = −8.5 ± 1.5 Ω, A = 134.0 ± 15.6 Ω 2 . The effect of leg compression was a relatively small, reversible increase in pulmonary blood volume of 90 ± 57 mL. We observed significant changes in parameters associated with intracellular, extracellular and total fluid volume (R 0 : -1.5 ± 0.9 %, p < 0.01; R ∞ : −2.1 ± 1

A Wearable Multimodal Sensing System for Tracking Changes in Pulmonary Fluid Status, Lung Sounds, and Respiratory Markers

“…For the patients with both measurements available ( n = 8), we observed an increasing trend in all but one patient. The magnitude of the average increase in K is consistent with previous work that examined changes in the ratio of the extra- and intracellular resistances in patients with HF and those undergoing pleural effusion [ 34 ]. In general, as the patients experience diuresis and transition to a compensated state, the overload of pulmonary fluid can be assumed to subside as per HF discharge criteria [ 2 ].…”

“…As the BIS measurements encompass the entirety of the thoracic cavity, it is difficult to relate changes in EBI directly to fluid in the lungs, which is typically only possible via segmental EBI, necessitating the use of more electrodes and complex hardware [ 8 , 33 ]. However, variations in K not only indicate the flux of fluid in extracellular spaces, which is associated with edema, but also the redistribution of fluid back into the appropriate intracellular compartments [ 34 , 52 ]. This allows for a more sensitive measure of fluid changes and offers insight regarding the location of fluid accumulation.…”

“…For this work, firmware was developed to enable the main board to alternate between two operational modes: (1) spectroscopy mode, measuring BIS across a logarithmically distributed range of 32 excitation frequencies from 5 to 150 kHz, and (2) continuous mode, concurrently capturing the multi-frequency IP signal at four frequencies (5, 50, 100, 150 kHz). The BIS excitation frequencies were selected to encapsulate the distinctive tissue impedance properties at low and high frequencies, which have previously been employed to assess pulmonary fluid status [ 33 , 34 ], whereas the excitation frequencies for continuous IP measurements were selected in accordance with prior work from our group, which demonstrated strong correlations to respiratory waveforms acquired from gold-standard methods [ 16 ]. The system can perform a sweep of the 32 frequencies every 2 s or sample an individual frequency every ~15.6 ms, dictating a sample rate of 16 Hz for each of the four excitation frequencies in the continuous measurement mode.…”

“…Thus, the resistance at 5 kHz (R5k) and at 150 kHz (R150k) were extracted from the averaged BIS curve. Finally, the ratio of R5k to R150k, denoted hereafter as K , was computed to provide meaningful insight into the distribution and accumulation of fluid between extra- and intracellular spaces, which is often exacerbated in patients with HF [ 34 ]. Comparable whole body BIS methods employ similar rationale when comparing extracellular water (ECW) to total body water (TBW) to detect fluctuations in fluid status for patients with HF [ 47 ].…”

An Instrumented Cochlea Model for the Evaluation of Cochlear Implant Electrical Stimulus Spread

“…The measured SIV signal demonstrated a resistor-capacitor circuit like time course, i.e., not a truly square shape. This can be explained by the complex impedance of the saline and the ground electrode, which normally contain both resistance and capacitance components [30] , [31] . To measure the degree of spread along the cochlea, we extracted the peak-to-peak voltage ( V SI,pp ) from the measured SIV waveforms at all the recording wires ( Fig.…”