The effect of applied pressure on the electrical impedance of the bladder tissue using small and large probes

There are a number of studies using electrical impedance spectroscopy, a minimally invasive technique, as a tissue characterizing method with different probe sizes (usually with larger probe diameters than that used in this work). In urinary bladder studies the probe size are limited to 2 mm diameter, in order to pass through the working channel of the cystoscope to measure the impedance inside the urinary bladder. Thus, bio-impedance of the human urothelium can only be measured using a small sized probe for in vivo studies. Different pressures were applied with this probe and it was demonstrated that increasing the applied pressure over the probe would increase the measured electrical impedance of the bladder tissue. Therefore, the effect of applied pressure on the resulting electrical impedance was considered in this study (all of the measurements were taken on points that had benign histology). An excessive amount of the applied pressure beyond the first visible indentation (first recordable reading) pressure has a significant effect on the impedance of the bladder tissue (p < 0.001). Then, to reduce the effect of pressure on the measured bio-impedance, the effect of a larger probe (10 mm diameter) was considered (p < 0.001). Increasing the probe contact area is one way to reduce the pressure effect on measurements; however this is difficult in practice in the in vivo situation.