Blood Glucose Measurement Using Bioimpedance Technique

Bioimpedance measurement is gaining importance in wide field of bioresearch and biomedical systems due to its noninvasive nature. Noninvasive measurement method is very important to decrease infection and physical injuries which result due to invasive measurement. This paper presents basic principle of bioimpedance along with its application for blood glucose analysis and effect of frequency on impedance measurement. Input from bioimpedance sensor is given to amplifier and signal conditioner AD5933. AD5933 is then interfaced with microcontroller LPC1768 using I2C bus for displaying reading on LCD. Results can also be stored in database using UART interface of LPC1768. 1. Introduction Impedance of any material can be defined as the opposition offered by material to the electric current flowing through it. It can be formulated as the frequency domain ratio of voltage to current. Impedance can also be represented using resistance and reactance. Every material shows property to dissipate energy and to store energy. Reactance indicates energy storage in material whereas resistance is indicator of energy dissipation [1]. When electricity is passed through body, two types of resistances that is capacitive (reactive) and resistive (resistance) are offered by body, where capacitance arises due to cellular membrane and resistance arises due to body water (intracellular or extracellular water). Cell membrane consists of a layer of nonconductive lipid material sandwiched between two layers of conductive protein molecules. High reactance value indicates good health and cell membrane integrity. Cell membrane structure makes them behave as capacitors when alternating current is applied to it. Hence impedance of tissue varies with frequency. At high frequency, current can flow through both intra- and extracellular water which means that it can penetrate the cellular membrane while at low frequency current cannot penetrate cellular membrane so it flows only through extracellular fluid. As a result, at low frequency, impedance is resistive in nature and at high frequency it has a resistive as well as a reactive component [1] (see Figure 1). Figure 1: Current flow through body: (a) low frequency and (b) high frequency. The incidence of diabetes is increasing worldwide every year [2]. Therefore, it is important to control as well as to treat diabetes. There are various invasive and noninvasive methods available for blood glucose measurement. Glucometer which depends on radio wave transmission uses continuously transmitting and receiving antenna. The transmitting antenna