In the normal defecation process, coordinated muscle contractions in colon move the fecal matter toward rectum, which stimulates sensation of urge to defecate. Rectal distension evokes relaxation of the internal anal sphincter and an initial contraction of the external anal sphincter.1 Current thinking is that the Valsalva maneuver performed to initiate defecation results in an increase in the intra-abdominal and rectal pressure, which provides the driving force for the expulsion of rectal contents through the relaxed puborectalis and anal sphincter muscles. However, it is not clear if rectal contractions play a role in the evacuation process.
Using manometric recordings, Kumar and Wingate2 described phasic rectal activity that resembled the intestinal migrating motor complex. Impedance planimetric recordings demonstrated distension-induced rectal contractions in pigs.3 Motor patterns of the colon and rectum have been studied extensively in animals and humans.1 Retrograde rectal contractions were recorded during prolonged high-resolution manometry recordings of the colon using a fiber-optic transducer catheter.4 More recently, pan-colonic pressurization and retrograde contractions of the rectum and distal colon were described.1 These were associated with anal sphincter relaxation but not abdominal wall contractions. In constipated patients, colorectal contractility is increased in the pre-defecatory phase but with less increase in the rectal tone compared to normal subjects (NS).5,6 However, rectal motor events during the expulsion phase were not described in these studies. There are several problems in recording the physiological events involved in the evacuation process: 1) most tests require an operator to be present in the room, 2) high-resolution manometry only simulates the expulsion phase of defecation, and 3) the balloon expulsion test and defecography do not record pressures required to understand the mechanics of evacuation process.
Fecobionics is a simulated stool with the ability to record many physiological parameters that may be important in the defecation/evacuation process.7, 8, 9, 10 The novelty of Fecobionics is that it measures pressures in axial direction and bending of the device (a proxy of the anorectal angle) during rectal distension and expulsion. Fecobionics data are not always consistent with the conventional technologies, which can be explained by differences in the device location in rectum, and technology, for example, direction of pressure measurements, bag vs balloon, and catheter-based vs insertable device.7, 8, 9, 10
Our aim was to determine the presence/absence of rectal contractility at baseline, during rectal distension, and during the expulsion phase of the defecatory process in NS and patients with fecal incontinence (FI) and obstructed defecation (OD) using the Fecobionics device.
In our Fecobionics database, we have access to the recordings obtained with an earlier Fecobionics prototype (wired), which we used to analyze data from 18 NS, 26 patients with FI and 15 patients with OD. Furthermore, we analyzed data from 20 NS studied with an electronically upgraded (wireless with impedance planimetry) Fecobionics (Supplementary Material). The 2 devices have approximately the same geometry (10cm-long and 10–12 mm-diameter), stiffness and functionality.9,10 Fecobionics consists of a bendable core with electronic components surrounded by a thin-walled bag that distends to simulate an artificial stool (Figure). In all studies, the device was inserted into the rectum. The bag was slowly filled with saline up to a volume that induced urge to defecate. The subjects attempted to evacuate the device in privacy. Pressures, the anorectal angle, and bag diameter from the color contour plots were analyzed. X2, Mann-Whitney, and Kruskal-Wallis tests were used for statistics.
Figure.
Sketch of the newest Fecobionics prototype that contained pressure sensors, motion processing units with magnetometer, gyroscope and accelerometer, impedance electrodes for multiple cross-sectional area (diameter) measurements, wireless transmitter, and batteries in the bendable core.
Device placement into the rectum did not induce symptoms but it induced variable degree of rectal contractions in NS and patients. In few subjects, vigorous rectal contractions were recorded by the sensor located cranial to the bag, which was interpreted as that the tip of the device irritated the rectal wall causing reflex contractions. OD patients exhibited rectal contractions more often, and with higher contractions amplitudes compared to NS and FI patients (Table). Furthermore, the anorectal angle was more acute in the OD patient as compared to NS and FI patients.
Table.
Key Data Obtained During Rectal Distension
| Device | Procedure | Parameter | Normal subjects (n = 18) | FI patients (n = 26) | OD patients (n = 15) | Statistical significance between groups (1) or between devices (2) |
|---|---|---|---|---|---|---|
| 1 | Insertion | Percentage of subjects with contractions | 94% | 73% | 100% | Normal to FI: NS (borderline) Normal to OD: NS |
| Number of contractions (if contractions) | 1.8 ± 0.2, 2 (1–2) | 2.4 ± 0.4, 2 (1–3) | 3.7 ± 0.5, 4 (2–5) | Normal to FI: NS Normal to OD. P < .01 (U-value 47.5, z-score −2.66052. |
||
| Contractions per minute (if contractions) | 6.4 ± 0.3, 6 (6–7) | 6.4 ± 0.3, 6 (6–7) | 6.1 ± 0.3, 6 (6–7) | NS | ||
| Maximum contraction amplitude (if contractions) | 23.0 ± 2.7, 20 (16–28) | 27.4 ± 3.7, 21 (16–34) | 67.9 ± 10.5, 55 (37–91) | Normal to FI: NS Normal to OD. P < .0001 (U-value 16.5, z-score −3.9492. |
||
| Rear baseline pressure | 43.4 ± 4.5, 42 (33–50) | 38.0 ± 2.5, 40 (33–45) | 40.4 ± 2.5, 40 (36–48) | NS | ||
| Bend angle | 138.6 ± 7.0, 138 (117–159 | 139.0 ± 7.4, 150 (130–164) | 115.3 ± 8.7, 123 (89–137) | Normal to FI: NS Normal to OD. NS (borderline) |
||
| Distension | Urge volume | 36.3 ± 5.5, 28 (20–50) | 54.7 ± 4.1, 60 (40–70) | 51.3 ± 5.7, 40 (38–73) | Normal to FI. P < .05 (z-score 2.48253, Normal to OD: NS |
|
| Flow rate during filling | 0.71 ± 0.05, 0.66 (0.61–0.78) | 0.69 ± 0.05, 0.66 (0.57–0.79) | 0.83 ± 0.07, 0.74 (0.67–0.79) | NS | ||
| Percentage of subjects with contractions | 61% | 50% | 73% | Normal to FI: NS Normal to OD: NS |
||
| Number of contractions (if contractions) | 2.7 ± 0.5, 3 (1–4) | 3.6 ± 1.0, 2 (2–4) | 3.1 ± 0.3, 3 (2–4) | NS | ||
| Contractions per minute (if contractions) | 4.8 ± 0.4, 5 (4–6) | 6.4 ± 0.5, 6 (5–8) | 4.6 ± 0.4, 5 (4–6) | Normal to FI. P < .05 (U-value 35, z-score 2.08572). Normal to OD: NS |
||
| Maximum contraction amplitude (if contractions) | 20.2 ± 2.0, 20 (17–20) | 21.5 ± 1.9, 21 (17–25) | 44.9 ± 7.1, 40 (25–60) | Normal to FI: NS Normal to OD. P < .01 (U-value 18, z-score is −2.75793). |
||
| Rear baseline pressure | 38.5 ± 4.7, 31 (30–38) | 38.3 ± 2.1, 38 (32–47) | 41.3 ± 3.5, 38 (32–51) | NS | ||
| Bend angle | 135.6 ± 6.5, 145 (115–160) | 136.5 ± 7.2, 150 (123–159) | 126.4 ± 6.6, 122 (109–150) | NS. | ||
| 2 | Insertion | Normal subjects (n = 20) | ||||
| Percentage of subjects with contractions | 45% | P < .01 | ||||
| Number of contractions (if contractions) | 2.3 ± 0.5, 2 (2–2) | NS | ||||
| Contractions per minute (if contractions) | 5.4 ± 0.6, 6 (4–6) | NS | ||||
| Maximum contraction amplitude (if contractions) | 15.3 ± 1.4, 15 (12–19) | NS (borderline) | ||||
| Rear baseline pressure | 35.3 ± 2.7, 36 (26–46) | NS | ||||
| Bend angle | 109.3 ± 10.7, 126 (72–151) | NS (borderline) | ||||
| Distension | Urge volume | 77.5 ± 4.9, 83 (68–96) | P < .00001 (z-score 4.16603). | |||
| Flow rate during filling | 0.42 ± 0.02, 0.43 (0.36–0.46) | P < .00001 (z-score −4.54608). | ||||
| Percentage of subjects with contractions | 26% | NS (borderline) | ||||
| Number of contractions (if contraction) | 1.8 ± 0.3, 2 (1–2) | NS | ||||
| Contractions per minute (if contractions) | 3.2 ± 0.2, 3 (3–3) | P < .05 (U-value 8, z-score 2.46234). | ||||
| Maximum contraction amplitude (if contractions) | 18.0 ± 2.3, 18 (15–22) | NS | ||||
| Rear baseline pressure | 27.8 ± 2.1, 28 (21–37) | NS (borderline) | ||||
| Bend angle | 147.8 ± 6.7, 160 (141–166) | NS |
Device 1 is the wired Fecobionics device. Device 2 is the upgraded wireless device. Units are mL, cmH2O, and mL/sec for volume, pressure, and flow rate, respectively. The contraction analysis does not include values for subjects who did not show contractions. Mean and standard error of the mean as well as median and quartiles are provided. Statistical values listed for device 1 are for comparison between the normal and patient groups. Statistical values listed for device 2 are for comparison with device 1.
The key data obtained during rectal distension are listed in Table. The volume at urge sensation was higher in both patient groups compared to NS. Greater than 50% of all subjects exhibited distension-induced rectal contractions. Rectal distension in the OD patients was associated with higher amplitude contractions compared to the other groups. The frequency of rectal contractions was not different between the groups. Studies with the newer version probe in NS were associated with larger urge volume than with the earlier version, which is likely due to the lower rate of filling in the upgraded probe (Table). The newer probe made it possible to analyze the contractions in more detail (Figure A1). The diameter color contour plots revealed rectal contractility, which was not obvious on the manometric recordings. Contractions were retrograde in some cases and antegrade in others. We could not discern the temporal relationship between rectal contractions and the level of sensation.
During the evacuation of the device, no signs of rectal contractions were observed, that is, the bag pressure and rear (cranial) pressure waveforms resembled each other; the bag pressure was 5%–10% higher than the rear pressure (Figure A1). Rectal contractility was not observed in the diameter color contour plots, immediately before and during the expulsion phase.
In conclusion, rectal contractions are seen frequently during the device insertion and distension in the rectum, and the OD patients were most sensitive. The data did not indicate that rectal contractions contributed to the evacuation of the Fecobionics device. The abdominal/rectal pressure generated by the Valsalva maneuver was the major force for the evacuation of the Fecobionics device. The limitation of our experiments is that we studied the evacuation process of a distended bag from the rectum which does not include the colonic phase of the defecation process.1 We cannot exclude the role of rectal contractions during the normal/spontaneous defecation process and in FI patients who may have unintended leaks. Further studies are planned to reveal if abnormalities of rectal contractions play any role in functional anorectal disorders, for example, on how rectal contractions are associated with symptoms, leakage of fecal content, and dyssynergia.
Acknowledgements:
The Chinese University of Hong Kong team consisting of Drs. K Futaba, A Chen, S Ng and T Mak, Ms. C Wong, and Mr. Leung and the California Medical Innovations and 3DT teams consisting of Y Wang, GS Kassab, and F Field are kindly thanked for helping to collect the data.
Footnotes
Conflicts of Interest: This author discloses the following: Hans Gregersen is the inventor of the Fecobionics technology and has filed patent applications. The remaining author discloses no conflicts. Ravinder K. Mittal is a member of the Board of Editors. Their paper was handled in accordance with our conflict of interest policy. See https://www.ghadvances.org/content/authorinfo#conflict_of_interest_policy for full details.
Funding:NIH awards R44DK129097, OT2ODO28203, OT2OD025308, and R01DK125657, and RCG grant #14106717 (Hong Kong) and HMRF grant #07180856 (Hong Kong) are acknowledged for financial support.
Ethical Statement: The corresponding author, on behalf of all authors, jointly and severally, certifies that their institution has approved the protocol for any investigation involving humans or animals and that all experimentation was conducted in conformity with ethical and humane principles of research.
Data Transparency Statement: Data and analytic methods will be made available to other researchers upon reasonable request to the corresponding author.
Reporting Guidelines: Helsinki Declaration.
Material associated with this article can be found in the online version at https://doi.org/10.1016/j.gastha.2023.03.002.
Supplementary materials
Recordings with the wired Fecobionics probe (left diagrams A–C) and with the upgraded wireless Fecobionics probe (right diagrams D and E). Diagrams A and B. Pressure data obtained during bag distension in 2 normal subjects. Both recordings show increasing bag pressure and decreasing front pressure during the distension, indicating the bag filling and resultant anal relaxation. The recording in Diagram B shows vigorous rectal contractions in the rear (cranial) pressure channel and some fluctuations in the front (caudal) pressure. The response is less during the bag distension shown in Diagram A. Diagram C shows pressures during evacuation of Fecobionics in a normal subject. Three peaks in the rear and bag pressure are identifiable before the device is evacuated. The front pressure drops already during the first peaks. The evacuation appears to be due to abdominal pressure increase since the rear pressure and bag pressure are identical. Diagrams D and E. The graphical user interface showing diameter color contour plots of the bag and pressures from 2 FI patients. The color scaling in the contour plots is from 10 mm diameter (deep blue) to 50 mm (dark red). Diagram D shows data from the start of the filling of the bag until the device is evacuated. Retrograde contractile waves are observed in the color contour plot. The insert (black arrow) shows magnification of these waves. These contractions are also visible in the rear pressure channel (large red arrow). The second insert show the evacuation process (5 seconds). The green-blue streak from the bottom to top shows the passage through the anal canal (diameter 15–18 mm). Diagram E recordings are obtained during bag filling in a subject who exhibited antegrade and stationary contractions. These were barely recorded by the pressure sensors. The black arrow point to a location where the waves seem to be interrupted. In all diagrams, the front, rear, and bag pressures are shown with blue, green, and red colors, respectively.
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Associated Data
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Supplementary Materials
Recordings with the wired Fecobionics probe (left diagrams A–C) and with the upgraded wireless Fecobionics probe (right diagrams D and E). Diagrams A and B. Pressure data obtained during bag distension in 2 normal subjects. Both recordings show increasing bag pressure and decreasing front pressure during the distension, indicating the bag filling and resultant anal relaxation. The recording in Diagram B shows vigorous rectal contractions in the rear (cranial) pressure channel and some fluctuations in the front (caudal) pressure. The response is less during the bag distension shown in Diagram A. Diagram C shows pressures during evacuation of Fecobionics in a normal subject. Three peaks in the rear and bag pressure are identifiable before the device is evacuated. The front pressure drops already during the first peaks. The evacuation appears to be due to abdominal pressure increase since the rear pressure and bag pressure are identical. Diagrams D and E. The graphical user interface showing diameter color contour plots of the bag and pressures from 2 FI patients. The color scaling in the contour plots is from 10 mm diameter (deep blue) to 50 mm (dark red). Diagram D shows data from the start of the filling of the bag until the device is evacuated. Retrograde contractile waves are observed in the color contour plot. The insert (black arrow) shows magnification of these waves. These contractions are also visible in the rear pressure channel (large red arrow). The second insert show the evacuation process (5 seconds). The green-blue streak from the bottom to top shows the passage through the anal canal (diameter 15–18 mm). Diagram E recordings are obtained during bag filling in a subject who exhibited antegrade and stationary contractions. These were barely recorded by the pressure sensors. The black arrow point to a location where the waves seem to be interrupted. In all diagrams, the front, rear, and bag pressures are shown with blue, green, and red colors, respectively.