Comparison of human uterine cervical electrical impedance measurements derived using two tetrapolar probes of different sizes

Abstract

Background: We sought to compare uterine cervical electrical impedance spectroscopy measurements employing two probes of different sizes, and to employ a finite element model to predict and compare the fraction of electrical current derived from subepithelial stromal tissue.

Methods: Cervical impedance was measured in 12 subjects during early pregnancy using 2 different sizes of the probes on each subject.

Results: Mean cervical resistivity was significantly higher (5.4 vs. 2.8 Omegam; p < 0.001) with the smaller probe in the frequency rage of 4-819 kHz. There was no difference in the short-term intra-observer variability between the two probes. The cervical impedance measurements derived in vivo followed the pattern predicted by the finite element model.

Conclusion: Inter-electrode distance on the probes for measuring cervical impedance influences the tissue resistivity values obtained. Determining the appropriate probe size is necessary when conducting clinical studies of resistivity of the cervix and other human tissues.

Figure 1

Mean (SD) impedance spectral data obtained in 12 subjects using the 5 and the 9 mm probe over frequency range 4–819 kHz (p < 0.001).

Figure 2

FE model predicted spectral data using the 5 and the 9 mm probe.

Figure 3

FE model prediction of stromal contribution to cervical impedance for 5 and 9 mm probes, shown as fraction of injected current flowing through cervical tissue stroma.