NaCl-based blood phantom analysis for in vitro bioimpedance measurement

Daily monitoring of blood glucose levels is vital for managing diabetes; however, invasive blood sampling is a burden on patients. To improve patients’ quality of life, bioimpedance-based noninvasive blood glucose monitoring (BI-NIBGM) that involves wearable electrodes on the wrist has been proposed. In this study, we investigated the validity of applying a simple NaCl solution to a blood phantom for in vitro evaluation of BI-NIBGM. The electrical properties of cow blood and various blood phantoms with different NaCl concentrations were measured based on the parallel-plate method at frequencies from 200 kHz to 100 MHz. The following observations were made: (1) the conductivity of blood can be mimicked accurately with simple NaCl solutions, and the optimal concentration of the phantom depends on the operating frequency and (2) it is challenging to mimic the relative permittivity of blood with simple NaCl solutions because NaCl lacks a cellular structure. Furthermore, the relationship between the bioimpedance and electrical properties of the phantom was examined using a simplified arm model. The results indicate that the relative permittivity of the blood layer has little effect on the bioimpedance and that only the conductivity determines the bioimpedance. Therefore, the NaCl concentration of the phantom can be adjusted from the viewpoint of conductivity for BI-NIBGM.