Wearable Devices Based on Bioimpedance Test in Heart-Failure: Design Issues

Abstract

Heart-failure (HF) is a severe medical condition. Physicians need new tools to monitor the health status of their HF patients outside the hospital or medical supervision areas, to better know the evolution of their patients' main biomarker values, necessary to evaluate their health status. Bioimpedance (BI) represents a good technology for sensing physiological variables and processes on the human body. BI is a non-expensive and non-invasive technique for sensing a wide variety of physiological parameters, easy to be implemented on biomedical portable systems, also called "wearable devices". In this systematic review, we address the most important specifications of wearable devices based on BI used in HF real-time monitoring and how they must be designed and implemented from a practical and medical point of view. The following areas will be analyzed: the main applications of BI in heart failure, the sensing technique and impedance specifications to be met, the electrode selection, portability of wearable devices: size and weight (and comfort), the communication requests and the power consumption (autonomy). The different approaches followed by biomedical engineering and clinical teams at bibliography will be described and summarized in the paper, together with results derived from the projects and the main challenges found today.

Keywords: bioimpedance; bioimpedance vector analysis; electrical impedance; electrocardiography; heart failure; internet of things; total body water; wearable devices.

Fig. 1.

Flow diagram for identifying eligible articles. BI, bioimpedance.

Fig. 2.

General block diagram for the measurement of impedance. Impedances Zx and Zs are found between the excitation circuit and the Instrumentation Amplifier (IA). Final impedance Zabs and phase $\varphi$ are obtained by the processing circuit. Based on [39].

Fig. 3.

Electrical models of skin-electrode interfaces according to material. (A) Ag/AgCl (gel), and (B) dry stainless steel electrode (air) (based on [57]).

Fig. 4.

Block diagram for the Wireless Communication via Bluetooth (Device/Smartphone) and TCP/IP (Smartphone/Server). Different User Interfaces (UI) are provided in the system for patient and medical providers. The protocol TCP/IP (Transmission Control Protocol/Internet Protocol) is commonly used (based on [6]).