THE USE OF COLE-COLE PLOTS TO COMPARE 2 MULTIFREQUENCY BIOIMPEDANCE INSTRUMENTS

Two commercially available multi-frequency bioimpedance spectrometers (Xitron 4000B and SEAC SFB3) were compared by performing measurements on a set of electronic circuits and by studying 14 healthy volunteers. Output data were plotted as reactance versus resistance and fitted wi th a semicircle using a least squares fitting program. In tests with s ix electronic circuits both instruments produced impedance loci that w ere well described by semicircular Cole-Cole plots, though there were some minor discrepancies using the Xitron instrument at frequencies ab ove 150 kHz. When tested on the volunteers the SEAC instrument gave ve ry good fits (RMSE = 1.5 Omega) to a semicircle from 5-600 kHz on all volunteers. The Xitron instrument gave excellent fits to the semicircl e between 5 and 55 kHz (RMSE = 0.7 Omega) but above 55 kHz the phase m easurements stayed constant or even increased, confirming the anomalou s behaviour reported by other authors. The conclusions to be drawn are that the semicircular plots predicted by the Cole-Cole theory give a very good description of multifrequency impedance data recorded by the SEAC SFB3 instrument, on human subjects, for frequencies between 5 an d 600 kHz. The Xitron 4000B is not able to reproduce the theoretically expected results in humans above 55 kHz.