From Bioimpedance to Volume Estimation: A Model for Edema Calculus in Human Legs

Abstract

Heart failure (HF) is a severe disease and one of the most important causes of death in our society nowadays. A significant percentage of patients hospitalized for decompensation of heart failure are readmitted after some weeks or months due to an expected bad and uncontrolled HF evolution due to the lack of the patient supervision in real time. Herein is presented a straightforward electric model useful for volume leg section calculus based on the bioimpedance test as a way to assist with the acute HF patient’s supervision. The method has been developed for time-evolution edema evaluation in patients’ corresponding legs. The data are picked up with a wearable device specifically developed for acute heart failure patients. As an initial step, a calibration method is proposed to extract the extracellular volume component from bioimpedance measurements done in healthy subjects, and then applied to unhealthy ones. The intra- and extracellular resistance components are calculated from fitted Cole–Cole model parameters derived from BI spectroscopy measurements. Results obtained in a pilot assay, with healthy subjects and heart failure subjects, show sensitivities in leg volume [mL/Ω], with much lower values for healthy than in unhealthy people, being an excellent biomarker to discriminate between both. Finally, circadian cycle evolution for leg volume has been measured from the bioimpedance test as an extension of the work, enabling an alternative parameter for the characterization of one day of human activity for any person.

Design of Wearable Textile Electrodes for the Monitorization of Patients with Heart Failure

“…This lower impedance corresponds to the presence of edema, which was also visually seen by the physician during the clinical visit. These results are in accordance with previous reports [ 2 , 3 ], where a correlation between the decrease in the impedance signal and the fluid accumulation in the interstitial tissue was found due to the facility from the electric current proceeding through the extracellular medium between electrodes in the presence of edema.…”

“…Together, 3 kHz and 50 kHz correspond to the lower and higher frequencies used in the SFB7 device, respectively. The value of 50 kHz corresponds to an intermediate frequency commonly used in bioimpedance measurements [ 2 , 3 ].…”

“…The initial experience of patients with heart failure in the VOLUM project was reported in [ 2 ]. In this work, a printed 3D fixed structure was used to hold the electrodes.…”

“…The most frequently presented symptoms of heart failure, such as dyspnea, asthenia, or edema, are generally a result of one of the following main features of heart failure: volume overload [ 2 ]. This is frequently observed in the lower limbs of the patient.…”

“…Some wearable devices have recently been proposed to monitor impedance spectroscopy and estimate volume overload in patients with heart failure [ 2 ]. In this work, (VOLUM project) the AD5941 chip from Analog Devices (Wilmington, MA, USA) was used to perform impedance spectroscopy measurements.…”