The effect of luminal content and rate of occlusion on the interpretation of colonic manometry

Abstract

Background: Manometry is commonly used for diagnosis of esophageal and anorectal motility disorders. In the colon, manometry is a useful tool, but clinical application remains uncertain. This uncertainty is partly based on the belief that manometry cannot reliably detect non-occluding colonic contractions and, therefore, cannot identify reliable markers of dysmotility. This study tests the ability of manometry to record pressure signals in response to non-lumen-occluding changes in diameter, at different rates of wall movement and with content of different viscosities.

Methods: A numerical model was built to investigate pressure changes caused by localized, non-lumen-occluding reductions in diameter, similar to those caused by contraction of the gut wall. A mechanical model, consisting of a sealed pressure vessel which could produce localized reductions in luminal diameter, was used to validate the model using luminal segments formed from; (i) natural latex; and (ii) sections of rabbit proximal colon. Fluids with viscosities ranging from 1 to 6800 mPa s(-1) and luminal contraction rates over the range 5-20 mmHg s(-1) were studied.

Key results: Manometry recorded non-occluding reductions in diameter, provided that they occurred with sufficiently viscous content. The measured signal was linearly dependent on the rate of reduction in luminal diameter and also increased with increasing viscosity of content (R(2) = 0.62 and 0.96 for 880 and 1760 mPa s(-1), respectively).

Conclusions & inferences: Manometry reliably registers non-occluding contractions in the presence of viscous content, and is therefore a viable tool for measuring colonic motility. Interpretation of colonic manometric data, and definitions based on manometric results, must consider the viscosity of luminal content.

Figure 1

Geometry of the COMSOL numerical model used to calculate the effect of localised wall movements on pressure recorded by a manometric sensor located on the axis of the lumen. The model assumes cylindrical symmetry with a larger diameter representing the cannulae and lumen and small diameter tubes representing non-local constrictions. The contractile region of the lumen was located at the mid-point of the lumen. This simplified geometry matched the functional design of the experimental apparatus as shown by the dashed lines in Figure 2.

Figure 2

Schematic of the setup used to generate the localized movement of the wall of a tubular segment of gut or latex. A fluid-filled syringe is used to hydraulically generate the required localized reductions in diameter (monitored by a pressure gauge). This causes the walls of the specimen of gut to move inwards, towards the manometric catheter, in a controlled rate. The gut is filled with a solution of known viscosity (dark blue), from the two reservoirs (dark blue). The region of the apparatus simulated by the in-silico model is indicated by the dashed lines.

Figure 3

Determination of the point of occlusion. A graded series of pressure steps were applied to determine that point where the wall of the tube contacted the pressure sensor on the manometric catheter. At this point, the signal recorded by the manometric sensor starts to increase rapidly. For the rest of the study, pressures were used that were less than 80% of the threshold required for lumen occlusion.

Figure 4

Modelling of sensor recordings during wall movements imposed by increasing pressure in the chamber surrounding the gut. The applied pressure is shown in green, and calculated sensor responses are shown for viscosities of 780 and 5000 mPa.s (blue and red traces).

Figure 5

Measured changes in pressure on the axis of the latex lumen for phasic applied pressure profiles(green trace), using luminal content with viscosities of 795 and 3180 mPa.s (blue and red traces).

Figure 6

Effects of viscosity of filler on initial pressure gradients of measured pressures recorded from the sensor immediately underneath the region of reducing diameter during collapse of the latex lumen

Figure 7

Measured changes in pressure on the axis of the section of rabbit colon lumen for phasic applied pressure profiles, using luminal content with a viscosity of 880 mPa.s.

Figure 8

Measured rate as a function of applied rate for 48 separate contractions using filler viscosities of 880mPa.s and 1760mPa.s. Linear curve fits to the data gives slopes of 0.48 (R²=0.62) and 0.71 (R²=0.96) respectively.