Title : Impedance spectroscopy measurements as a tool for 1 distinguishing different luminal content during bolus transit 2 studies

13 Background: Intraluminal electrical impedance is a well-known diagnostic tool used to 14 study bolus movement in the human oesophagus. However, its use in the human colon it 15 is hindered by the fact that the content cannot be controlled and may include liquid, gas, 16 solid or a mixture of these at any one time. This article investigates the use of complex 17 impedance spectroscopy to study different luminal content (liquid and gas). 18 Methods: An excised section of guinea pig proximal colon was placed in an organ bath 19 with Krebs solution at 37°C degrees and a custom built bioimpedance catheter was 20 placed in the lumen. Liquid (Krebs) and gas (air) content was pumped through the 21 lumen and the intraluminal impedance was measured at five different frequencies (1 22 kHz, 5.6 kHz, 31.6 kHz, 177.8 kHz and 1 MHz) at 10 samples per second. A numerical 23 model was created to model the passage of bolus with different content and compared to 24 the experimental data. 25 Key Results: Differences in mean impedance magnitude and phase angle were found 26 (from 1 kHz to 177.8 kHz) for different contents. The numerical results qualitatively 27 agreed with those in the experimental study. Conductivities of bolus had an effect on 28 detecting its passage. 29 Conclusions & Inferences: Complex impedance spectroscopy can distinguish between 30 different luminal content within a range of measuring frequencies. The numerical model 31 showed the importance of bolus conductivities for bolus transit studies in those where 32 the bolus is controlled. 33