Measuring length-tension function of the anal sphincters and puborectalis muscle using the functional luminal imaging probe

Abstract

Functional luminal imaging probe (FLIP) has been used to measure the distensibility of the anal canal. We hypothesized that with increasing distension of the anal canal with FLIP there will be an increase in length of the anal sphincter muscle allowing measurement of the length-tension function of anal sphincter and puborectalis muscles (PRM). We studied 14 healthy nulliparous women. A custom designed FLIP bag (30mm diameter) was placed in the vagina and then in the anal canal, distended in 10ml steps with volumes ranging from 30-90ml. At each volume, subject performed maximal voluntary squeezes. Length tension measurements were also made with a manometric probe system. Tension was calculated (pressure x radius) in Newtons/meter using a custom software program. Peak tensions at different FLIP volumes was compared with the manometric data. No change in the luminal CSA was noted at low fluid volumes; the sphincter muscles were able to fully collapse the FLIP bag within the anal canal/vagina even at rest. At larger volumes, with each squeeze there was an increase in the bag pressure and reduction in the cross-sectional area, which represents concentric contraction of the muscle. Both rest and squeeze tension increased with the increase in volume in the anal as well as vaginal canal indicating that the EAS and PRM produce more tension when lengthened. FLIP device, which has been used to describe the distensibility of the anal canal can also provide information on the length-tension function of the anal sphincters and PRM.

The use of impedance planimetry (Endoscopic Functional Lumen Imaging Probe, EndoFLIP®) in the gastrointestinal tract: A systematic review

“…Several parameters have been suggested from the most complexes (anal canal stiffness defined on the basis of the pressure and diameter changes when the volume increased from 1 to 50 mL, 93‐95 flow resistance of the anal canal defined from the anal canal length, the middle part diameter of the anal canal and the dynamic viscosity of the inflated bag 96 or mechanical work of the anal sphincter muscle, 97 to the most simple (wall tension (T = P.r), 98 anal DI (CSA/P), 99,100 anal compliance (D/P), 97 yield pressure when the most resistant (middle) part of the sphincter begins to distend 93‐95 . More recently, Zifan et al described the use of area‐pressure and area‐tension‐loop analysis of the anal sphincters and puborectalis muscles in normal subjects and fecal incontinent patients, assessing the relationship between changes in muscle length (secondary to anal distension) and muscle function 101,102 . Thus, although 10 studies have reported results of FLIP measurements in the anal canal in HV, 93,95,97‐99,101,103‐105 no reliable normal values are yet available because of the absence of standardized protocols for assessing and analyzing FLIP measurements.…”

“…More recently, Zifan et al described the use of area‐pressure and area‐tension‐loop analysis of the anal sphincters and puborectalis muscles in normal subjects and fecal incontinent patients, assessing the relationship between changes in muscle length (secondary to anal distension) and muscle function 101,102 . Thus, although 10 studies have reported results of FLIP measurements in the anal canal in HV, 93,95,97‐99,101,103‐105 no reliable normal values are yet available because of the absence of standardized protocols for assessing and analyzing FLIP measurements. However, some of these studies have demonstrated that the geometry of the lumen and the biomechanical properties of the anal canal are not uniform during distension.…”

Loop analysis of the anal sphincter complex in fecal incontinent patients using functional luminal imaging probe

“…We recently reported that the FLIP allows one to study the length-tension function of the anal sphincter muscle (32). Cardiologists have used cardiac loops to evaluate the function of myocardium for many decades (5).…”

Functional lumen imaging probe in gastrointestinal motility diseases

“…Recently, a study reported the application of FLIP to the vaginal canal and the anal canal in 14 healthy nulliparous women to provide clinicians with additional knowledge on the relationship between length and tension of the puborectalis muscles and the anal sphincter. 50 Studies with large samples are needed to confirm the abovementioned findings. In the future, FLIP may also be used intraoperatively to identify the phenotypes of FI and to assess the anal sphincter geometry.…”

“…FI diagnosed by HRAM was consistent with the diagnosis achieved using FLIP in more than 70% of patients, which indicates that the anal DI and HRAM results are largely in agreement. Recently, a study reported the application of FLIP to the vaginal canal and the anal canal in 14 healthy nulliparous women to provide clinicians with additional knowledge on the relationship between length and tension of the puborectalis muscles and the anal sphincter . Studies with large samples are needed to confirm the abovementioned findings.…”