Blood Characterization from Pulsatile Bioimpedance Spectroscopy

The bioimpedance measurements in humans have been receiving considerable attentions during the past two decades because of several advantages, such as low cost, easy application, non-invasiveness and on-line monitoring. The original bioimpedance technique was bioelectrical impedance analysis (BIA). Within a decade, this technique evolved into the more advanced technique known as bioelectrical impedance spectroscopy (BIS), also called multiplefrequency bioimpedance analysis (MFBIA). BIS applies multi-frequency stimulations to measure body impedance. This technique has been widely used for many applications, such as: • Body fluid measurement[1][2]. This method estimates extracellular fluid (ECF), intracellular fluid (ICF) and total body water (TBW); • Tissue volume change. A typical application of this type is the impedance plethysmography[3]. • Tissue characterization. These techniques are mostly based on Cole-Cole model in terms of Cole-Cole impedance parameters[4]. e.g. in [5], normal and ischemic tissues are differentiated by comparing R0 and fc. in [6], Zhao et al. calculated plasma resistance, intracellular resistance and cell membrane capacitance of blood using three measuring frequencies. Characterization of blood bioimpedance properties is of importance for the development of methods estimating some clinical diagnostic indices such as haematocrit, glucose level, hydration, etc. The ability to make in vivo measurements would be a great advance; however, Current bioimpedance spectroscopy measurements of blood are either in vitro[6][7], or are performed on a body appendage and thus represent a combined measurement of all tissues in the measuring field[8], rather than the blood impedance value. In this paper, we propose a novel approach to measure blood impedance in vivo by analyses of data from the cardiac induced pulsatile impedance signal. Pulsatile data are used to fit a non-linear model, from which arterial blood parameters are separated from those of the surrounding tissues.