Wearable Bioimpedance Monitoring: Viewpoint for Application in Chronic Conditions

Abstract

Currently, nearly 6 in 10 US adults are suffering from at least one chronic condition. Wearable technology could help in controlling the health care costs by remote monitoring and early detection of disease worsening. However, in recent years, there have been disappointments in wearable technology with respect to reliability, lack of feedback, or lack of user comfort. One of the promising sensor techniques for wearable monitoring of chronic disease is bioimpedance, which is a noninvasive, versatile sensing method that can be applied in different ways to extract a wide range of health care parameters. Due to the changes in impedance caused by either breathing or blood flow, time-varying signals such as respiration and cardiac output can be obtained with bioimpedance. A second application area is related to body composition and fluid status (eg, pulmonary congestion monitoring in patients with heart failure). Finally, bioimpedance can be used for continuous and real-time imaging (eg, during mechanical ventilation). In this viewpoint, we evaluate the use of wearable bioimpedance monitoring for application in chronic conditions, focusing on the current status, recent improvements, and challenges that still need to be tackled.

Keywords: bioimpedance; body composition; imaging; impedance cardiography; impedance pneumography; wearable monitoring.

Figure 1

(A) Low-frequency current travels around the cell, while high frequency current can penetrate cells. (B) Electrical model of the tissue with extracellular resistance (Re), intracellular resistance (Ri), and conductance representing the cell membrane (Cm). (C) Illustration of bioimpedance spectroscopy data visualized in the R-Xc plane. Increasing frequencies of the injected alternating current appear counterclockwise in the plot. (D) Tetrapolar electrode configuration in bioimpedance measurement. ECF: extracellular fluid; ETI: electrode tissue impedance; ICF: intracellular fluid; Iinject: injected current; Vmeasred: measured voltage.

Figure 2

(A) Illustration of body composition consisting of solids (eg, bone, dry cell mass) and fluids. The fluids consist of intracellular fluid (ICF) and extracellular fluid (ECF), with the latter comprising interstitial fluid (ISF) and plasma. (B) Electrode configuration example of respiration monitoring with the measured bioimpedance (bioZ) signal. (C) The measured bioZ signal contains a dynamic component (AC) resulting from physiological changes such as breathing and a baseline component (DC) resulting from tissues (eg, bones, fat and/or muscle).

Figure 3

Example of a wearable device (imec the Netherlands, Eindhoven, the Netherlands). (B) Example impedance pneumography data. The figure shows the similarity between bioimpedance and spirometer data for an increasing respiratory volume protocol.

Figure 4

Left: Electrode configurations for impedance cardiography (ICG) measurement, using either red electrodes or yellow electrodes, with current injection electrodes (I) and voltage electrodes (V). Right: electrocardiogram (ECG) and ICG signals showing characteristic morphology with the B point as an example.