Igor Blazek

1st Prize for the BME Diploma Thesis Winner

Igor Blazek was born in Zagreb, Croatia in 1977. After finishing technical high school, he transferred to Faculty of Electronic Engineering and Computing in Zagreb. He received his B.Sc. in 2003. The thesis of his B.Sc. is entitled

"Accuracy and repeatability of measuring skeletal muscles impedance".

Multi frequency method of measuring impedance is used to determine accuracy and repeatability of measuring skeletal muscles impedance. That method could be a possible solution for detecting ishemic conditions in skeletal muscles.

To determine if this method has any practical use in the thesis, the structure of muscular tissue, different measuring methods and problems which emerge during measuring are discussed. Special care is taken to analyze bipolar and tetrapolar measuring methods. For that purpose simulation and practical measurement on four people are made.

Simulation of biological impedance measuring has been done with the EMAS^TM, a program for simulating electrical and magnetic fields. Frequency change of tissue impedance is approximated with frequency change of electrical permittivity and resistance; parameters which are changed prior to simulation on defined frequency.

For practical measuring purposes, a HP-LCR Meter 4284A linked with a personal computer was used. To determine sensitivity to electrode distance, measurements were made on the left and right legs of four healthy people. Module and phase of impedance was measured with a frequency of 100Hz to exclude influence of electrodes. Measurement itself was taken in a frequency range from 5kHz to 500kHz, with measuring current of 2mA.

Measuring results show that the tetrapolar (4 electrode) measuring method is more accurate, in a sense that values of impedance module are almost the same for the right and left leg of the same person on same distance. That is not the case for the bipolar (2 electrode) measuring method, where results differ on the same leg on different distance almost like on different leg on same distance.

The decision of which method (2 of 4 electrode) to use will depend on what we want to accomplish. If the goal is to find out the exact value of biological impedance, then the bipolar technique could be better, because it is less sensitive to distance between electrodes. If it is necessary to compare the left and right leg of the same person, then the 4 electrode method could be considered better. In the later case it is recommended that the distance between electrodes for current and voltage is much smaller than the distance between two voltage electrodes. Unfortunately, bipolar measurement includes skin-electrode impedance, which is the main disadvantage of this method. That influence can be reduced by assuming that on very low frequencies measuring results include only skin-electrode impedance, which can be than considered in the results.