Functional luminal imaging probe: a new technique for dynamic evaluation of mechanical properties of the anal canal

Abstract

BackgroundThe muscle structures surrounding the anal canal are of major importance in maintaining continence but their anatomy and function vary along its length. Standard manometry does not provide detailed information about mechanical properties of the anal canal. A new functional luminal imaging probe (FLIP) has been developed for this purpose. The aim of our study was to investigate whether FLIP allows detailed evaluation of dynamic biomechanical properties along the length of the anal canal.MethodsThe in vitro validity and reproducibility of the FLIP system were tested. Fifteen healthy volunteers (age 32–65 years, mean 51 years), of whom 12 were females, were investigated. The integrity and dimensions of the anal sphincter apparatus were evaluated with endoanal ultrasonography and standard anal manometry. During standardized distensions with the FLIP, 16 cross-sectional areas of the anal canal were measured at 5-mm intervals. Distensibility of the following three segments was evaluated: upper anal canal (surrounded by the internal anal sphincter and the puborectalis muscle), mid-anal canal (surrounded by the internal anal sphincter and the external anal sphincter) and lower anal canal (surrounded by the external anal sphincter). Color contour plots were generated from the FLIP-based dynamic recordings of serial cross-sections.ResultsIn vitro tests confirmed the validity and reproducibility of the FLIP system. The luminal geometry during distension and the biomechanical properties of the anal canal differed at the three levels. Both at rest and during squeeze the mid-anal canal was significantly less distensible than the upper (p < 0.01) and the lower (p < 0.05) anal canal.ConclusionsFLIP is a promising method for evaluation of the nonhomogeneous biomechanical properties along the length of the anal canal.

Functional lumen imaging of the gastrointestinal tract

“…This is clearly an advantage, since the structure and surrounding tissues are heterogeneously distributed along the longitudinal axis. Variations in distensibility along the sphincter can be explained by the heterogeneous anatomy and active muscle function of the sphincters [39,54,56,57,69]. In addition to assessment of sphincter wall heterogeneity caused by changes in the mechanical properties and muscle tone, FLIP measurement is also capable of showing alterations caused by diseases, such as achalasia [47,68], systemic sclerosis [57], and idiopathic fecal incontinence [56].…”

“…So far, only four studies have been published [54][55][56][57]. In vitro tests have shown FLIP distensibility measurements to have great validity and reproducibility [54].…”

“…Figure 7 shows a simple diagram of pressure versus stretch ratio for three locations in the anal sphincter. Studies done with the FLIP demonstrate the nonlinear pressure (tension)-deformation relationships of GI sphincters [33,54,57,68]. Often the pressure is observed to increase during the beginning of the measurement without much distension of the sphincter, but at some point, which may be termed the ''opening pressure,'' the sphincter starts to yield, after which it becomes much more compliant until a certain point.…”

“…In most of the studies published, the distensibility is evaluated in terms of very simple measures such as simply looking at the magnitude of the CSA or dividing the CSA by the pressure at a given point of distension [33,54,57]. This may easily introduce errors.…”

Emerging Roles of the Endolumenal Functional Lumen Imaging Probe in Gastrointestinal Motility Disorders

“…Luft et al, 14 studied the use of EndoFLIP in assessing anal canal properties in healthy individuals. The authors concluded that the upper part of the anal canal is the most compliant and that the least distensible part is the mid-anal canal region, which contributes the most to resting anal continence.…”