Multifrequency device for measurement of the complex electrical bio-impedance-design and application

A multifrequency device for measurement of the modulus and phase shift of complex electrical impedance of the biological tissue has been designed. Impedance measurement is based on the tetrapolar current method with the current amplitude of 1 mA. Phase is obtained using of the modified “zero-crossing” method. The device operates in the frequency range from 2 kHz to 200 kHz (in two sub-ranges) with manual and automatic frequency control. The impedance device was used for the measurement of the modulus |Z₀| and phase shift φ of the transthoracic impedance by Kubicek´s method in the frequency range of 2 to 200 kHz the mean values of |Z₀| changes from 30.7 to 20.2 Ω and φ respectively from 4.9 to 10.4°. In the narrower range usually used in impedance cardiography (20-100 kHz) the change of φ is 4°. This indicates a necessity to establish a standard for the transthoracic impedance measurement in impedance cardiography method and to use only one chosen frequency. The device can be used for bioimpedance spectroscopic measurements, determination of the extracellular fluids, examination of ΔZ and Δφ due to ventilation or motion of the heart