Electrical bioimpedance spectroscopy (EBIS) is a technique that uses a probe to calculate the transfer impedance from tissues. This transfer impedance can give information about the normal or pathological condition of the tissue. To take readings, pressure has to be applied to the probe in order to get a good contact between the electrodes and the tissue. We have been using EBIS to investigate the early diagnosis of dysplasia and cancer in the human cervix, oesophagus and bladder. We have found that, with increasing pressure (range used here was approximately 1 kPa to approximately 50 kPa), the resistivity readings increase in a consistent way up to 80%. In this paper, we show how this is a case in three different tissue types (oesophageal, gastric and vesical samples). These increases can be higher than those associated with the pathological changes that we are investigating (non-inflamed columnar tissue, for instance, shows values 50% higher than dysplastic columnar tissue). Finite-element modelling was also used to investigate the effect of volume reduction in the connective tissue or stroma. This simulation suggests no strong correlation between reduction of this structure and increase in resistivity. We hypothesize therefore that these changes may be mainly associated with the squeezing of water from the extracellular space. Finally, as pressure is difficult to control by hand, we raise the issue of the necessity of considering this variable when making EIS measurements.

Biological tissues undergoing inflammation and dysplasia seem to exhibit changes in the intercellular space that can be sensed using low frequency electrical impedance methods. Basically, low frequency electric current flows through this space and its widening as well as the disruption of the tight junction decrease the resistance, facilitating current flow. The electrical changes accompanying structural changes from columnar tissue to adenocarcinoma in Barrett's metaplastic mucosa and gastric tissue are illustrated using resected tissue from 32 patients. Two hundred and fifty-eight biopsies were analysed, correlating their electrical resistivity (R) at 9.6 kHz and their histopathological interpretation. Compared to non-inflamed non-dysplastic columnar tissue (R = 4.9 ohms m), the results suggest a small but statistically significant decrease of electrical impedance in columnar tissue showing inflammation (R = 4.2 ohms m, p = 0.016) and a larger decrease when dysplasia is present (R = 3.4 ohms m, p = 0.040). If this method is validated further, this technique could be used to obtain guided biopsies from patients undergoing surveillance programmes for Barrett's oesophagus. We aim to refine this technique using a new system with lower frequencies and, possibly, in vitro (cultured cells) and in vivo (rats) models of Barrett's oesophagus.