Our Design

Possible Design Solutions

Length Tension Manometry

This methodology involves creating a length tension curve for the sphincter muscle. This procedure would involve the placement of a probe into the patient’s sphincter. The patient squeezes and the resulting pressure on the probe recorded. Then, the probe was removed and another probe, larger in width, was inserted and force once again recorded. Repeating this process for various sizes of probe, an effective length tension curve can be determined⁴.

Anal Sphincter Electromyography

In this procedure, a small needle electrode is inserted directly into the sphincter of the patient. The needle is used to guide the placement of the electrodes directly into the skin. Then, as the patient is asked to relax, squeeze and push, the variations in the muscle’s electrical activity is recorded. Clinicians and researchers can then use this data in order to determine parts of the sphincter muscle which may not be functioning effectively⁵.

Adapting EndoFLIP Technology

EndoFLIP technology is most commonly used to determine the pressure gradient and radial measurements of an extended catheter bag. Currently, EndoFLIP Technology can be used for an esophageal catheter, to determine the health of the esophageal muscles. The catheter contains 16 electrodes that can measure the radial distention at different portions of the bag, if filled with saline solution.

This software technology allows for real time data collection. This design would use the same technology and adapt the esophageal catheter, such that it could be inserted into the anal canal to measure the strength of the pelvic floor muscles. It would require an existing esophageal catheter to have the catheter bag removed and replaced with a modified version, while the electronics remained intact. The catheter diameter would be increased to facilitate quick filling, and the bag would be adapted so that it could distend to at least 3 cm and fill up to 90 mL of 3% saline solution³.

Custom Catheter System

One design alternative is to create a new anorectal catheter by ourselves without worrying about EndoFLIP compatibility. First, we would have to create our own reading system using Arduino or another method to export data measurements sensed by the electrodes on the catheter. We would also need to determine the best impedance sensors and electrodes to use, as well the material of the bag. Then, we would have to figure out the electronics/wiring that would be needed for assembling the catheter together.

After deliberating over the pros and cons of multiple design options, we decided to adapt current EndoFLIP technology so that Crospon's esophageal catheter could be used for the anal sphincter. Our goals included:

• Creating a new balloon with appropriate sizing such that it met the following endorectal constraints
  • Max volume at 0mmHg: 90mL
  • Max diameter: 30 mm
  • Can withstand pressures up to 100mmHg
• Including a manual filing mechanism to decrease procedure time
• Ensuring balloon is easily removable and exchangeable

Design Solution

Material Choice:

Polyurethane Film (1.5 mm thick)

• Medical grade plastic (biocompatible)
• Cost effective
• Thin and flexible
• Leakproof under large pressures

Sealing:

Hand Impulse Heat Sealer

• Can create strong heat seals for straight edges
• Consistent and reproducible seal strength
• Cost effective

However, many design iterations came from attempting to create a seal between the balloon and the catheter/tubing

Design Iterations

Testing

We performed testing to make sure our 3 specifications were met:

• Max diameter: 30mm
• Max Volume: 90mL
• Pressure: >100mmHg

We created 8 balloons and tested all of them for diameter and volume. We wanted the balloons to have a max volume of 90mL and for it to be 30mm at this volume in order for the physical therapist to be able to have consistent study results and so it would be comfortable in the patient. We also wanted the balloon to withstand over 100mmHg since that was the minimum pressure that would be exerted against the balloon during testing.

The volume and pressure was tested with a water manometry machine where we measured the maximum volume as how much water filled the balloon before the pressure would spike up from 0. We then measured the diameter using a caliper. We also used the EndoFLIP system for our best prototypes to guarantee that our balloons were filling to the correct diameter and withstanding enough pressure.

Results

Editor: Connie Gean