The study investigated device removal for 3 leading commercially available FMD systems — DnS, InstaFlo (IsF) Bowel Catheter System (Hollister Inc, Libertyville, IL), and F-S — using simulated clinical conditions that mimicked realistic clinical situations as closely as possible. F-S employs an opaque, donut-shaped, collapsible, silicone balloon, and IsF employs an opaque, spherical, foldable, silicone balloon; DnS has a green, trumpet-shaped, foldable, silicone cuff, all of which are inflated for retention, and deflated before removal (see Figure 1).
A simulated rectum was made from soft rubber with a 15 mm-diameter model sphincter; internal dimensions were based on the average rectal physiologies from full-body, magnetic resonance imaging data.13 Simulated fecal effluent, based on Bristol Stool Grade14 6-7 (mushy/liquid stool), was prepared from Reinforced Clostridial Medium (LabM), 0.4% bacteriological agar (Oxoid, Basingstoke, UK), with Browning (Sarson’s, London, UK) added for color.15
Removal force and extension. The catheter tube section of each device was trimmed to a length of 150 mm from the base of the balloon/cuff end. This enabled the samples to be accommodated in a Universal Test Machine (UTM; Zwick, Leominster, UK), a tensile test machine capable of measuring the yield or compressive strength of materials in terms of force (applied by the machine in newtons [N], the International System of Units-derived unit of force) and distance (travelled by the machine grip; mm) (see Figure 2a). For F-S and DnS, the inflation and irrigation tubing were left in place and functional, with just the main catheter trimmed off. This was not necessary for IsF because the inflation and irrigation tubes were close to the balloon end.
The simulated rectum was clamped in a polycarbonate frame and bolted to the UTM. The rectum was filled with simulated fecal effluent via the sphincter. Using the syringe provided with each device, residual air was removed from the balloon/cuff. Six (6) mL of lubricant (KY Jelly; Reckitt Benckiser, Slough, UK) was spread evenly over the deflated balloon/cuff and 1 mL was applied around the simulated sphincter, as would be done in clinical practice. The balloon/cuff then was inserted into the sphincter as per the device instructions for use. Once correctly situated within the simulated rectal cavity and immersed in the simulated fecal effluent, the balloon/cuff was inflated with the appropriate volume of water. The balloon/cuff then was deflated as described in device instructions for use. The trimmed end of the catheter tube was subsequently clamped in the jaws of the UTM, 50 mm above the sphincter, and the UTM jaws were raised at a fixed rate of 100 mm/minute. The maximum forced required to remove the deflated balloon/cuff (in N) and the extension distance (mm) travelled by the UTM jaws were automatically measured and recorded by the UTM as an electronic and printable report; the test stopped when the balloon/cuff had been pulled fully through the sphincter. The simulated rectum, simulated fecal effluent, and device insertion, inflation, and deflation processes test was performed 3 times for each device; each device was cleaned and dried between replications.
Splash capture. Similar to the removal force and extension study, the catheter tube section of each device was trimmed, but to a length of 430 mm from the base of the balloon/cuff end and, for F-S and DnS only, the inflation and irrigation tubing were left in place. Fabric-backed adhesive tape (AT200 Matt Gaffa; Advance Tapes, Leicester, UK) was wrapped around the catheter tubes below the insertion depth markers to support the catheter tube and to prevent the elastic-stretching effect of tube extension (see Figure 1). To capture any dispersal of simulated fecal effluent during the automated removal of the deflated balloon/cuff, the trimmed end of the catheter tube was threaded through a 16-cm outer diameter annular paper disc (standard white 80-gsm paper) with a 6 cm-diameter centralized hole, so the paper rested on top of the simulated rectum. The vertically held catheter tube was sheathed in a 35-cm tall plastic cylinder (external diameter 15.2 cm; internal diameter 14.5 cm) lined internally with A3 paper. The top of the cylinder then was covered with a second annular paper disc so the catheter tube was completely enclosed in a splash-capture cylinder (see Figure 2b). The trimmed end of the catheter tube was clamped in the jaws of the UTM where it exited the splash-capture cylinder, 350 mm above the sphincter. The UTM jaws then were raised at a fixed rate of 100 mm/minute, and the test was stopped when the balloon/cuff had been pulled fully through the sphincter. Care was taken to ensure the catheter tube did not stretch and did not touch the paper. The test was performed 3 times for each device, and each device was cleaned and dried between replications. The quantities and distances of splash were analyzed by placing dried splash-capture papers (an A3 sheet and 2 annular discs per test replication) on an A3-sized photographic light box and covering with a Perspex sheet. A tripod-mounted digital camera was placed at a fixed distance of 100 cm above the papers. Photograph exposure limits were set to obtain maximum illumination and contrast, and images of all splash-capture papers were taken. Splash areas were calculated from images (JPG files of 100 MB resolution) processed with Image Pro Analyzer software, version 184.108.40.2061 (Media Cybernetics, Rockville, MD) as follows:
- The raw image was rotated until the bottom edge was horizontal/aligned to the reference grid.
- The area of interest was cropped 1 cm inside the edge of the light box.
- The blue channel was extracted from the red-green-blue image (for the best contrast for brown effluent against white paper; see Figure 3).
- Brightness, contrast, and gamma were manually optimized to obtain a subjectively optimized image.
- Intensity peak was selected in the histogram, eliminating low intensities.
- Intensity area count was calculated and the screen data were captured.
- The total splash area per sheet (cm2) and the relative percentage of stained area to unstained area were calculated.
Two-sample t tests were conducted using Minitab 17 software (State College, PA) to examine differences in removal forces, catheter tube extensions, and splash areas.