Chronic colonic motility disorders are treated or undergo surgical intervention, most often without proper diagnosis of motor dysfunction, yet all consensus reports indicate that colonic manometry is essential for diagnosis of colon motor dysfunction ( 11 , 19 , 43 , 47 ). Colonic manometry is considered to be of uncertain usefulness because of our limited knowledge of normal colon motor patterns and normal reaction to stimuli. Diagnosis of esophageal dysfunction has changed due to high-resolution manometry, from measurements of isolated points along the esophagus due to a low number of sensors, to a detailed characterization of esophageal motility. This, among other improvements, led to increased sensitivity to detect achalasia, and it allowed for subclassification of achalasia leading to improved guidelines for treatment ( 27 , 57 ). The equivalent of esophageal peristalsis in the colon is the high-amplitude propagating pressure wave (HAPW) ( 22 , 44 ), also known as high- amplitude propagating contraction (HAPC) ( 1 , 6 ), or high-amplitude propagating sequence (HAPS) ( 19 , 23 ). Guidelines for colonic manometry indicate that the most important feature that should be achieved is the ability to conclude that a patient’s motor function is normal ( 11 ). However, we do not yet have criteria to confidently identify normal HAPWs, and no consensus exists as to which protocol to use to elicit HAPWs for diagnostic purposes. Also, an adequate healthy control data set is essential for interpreting an abnormal test ( 11 ), and such a data set is not yet available. High-resolution colonic manometry (HRCM) may achieve this, and the present study provides an important advance toward this goal. Previous studies have demonstrated the relevance of appreciating the regional distribution of propagating waves in the colon. It was found that in the early predefecatory phase, the origin of HAPWs shifts distally ( 1 ). This coordinated spatiotemporal pattern has been suggested to play an important role in the shifting of colonic content in the rectal direction to prepare for defecation, as most individual HAPWs do not span the entire colon ( 9 ). The innervation of the colon also shows regional differences ( 9 , 58 ), and functional differences related to transit and storage are well documented ( 5 , 7 , 41 ). There have also been indications in the pediatric literature that HAPWs are not normal unless they span the entire colon ( 47 ), which makes it important to study regional HAPWs. Therefore, the first objective of this study was to characterize HAPWs in healthy subjects using 84 sensors throughout the colon based on the site of origin and site of termination and quantify their features, so as to assess in future studies potential regional dysfunction in patients. HAPWs generally occur between 4 and 10 times per 24 h in the unprepared colon ( 23 , 35 , 45 ). In a short manometric study, they may not happen without a stimulus and are usually evoked by various stimuli, including a meal and proximal bisacodyl. However, in healthy subjects, a meal may not evoke HAPWs, and, rarely, bisacodyl may not either ( 6 ). Hence the second objective was to identify optimal stimuli that will reliably evoke HAPWs in healthy subjects. A third objective was to develop a quantitative assessment of normal HAPW activity.

METHODS

Study Subjects Nineteen healthy subjects (aged 21–54 yr; 9 women, 10 men) were recruited by local advertising. All participants gave written informed consent, and all procedures were approved by the Hamilton Integrated Research Ethics Board. Exclusion criteria included abdominal surgery, hepatic, kidney, or cardiac diseases, connective tissue disorders, central nervous system disorders, thyroid diseases, prostate diseases, or any malignancies. All subjects reported normal stool consistency (Bristol type IV) and normal bowel frequency: between one bowel movement every 3 days and three bowel movements per day. None had defecation difficulties, and none were taking medication that might influence bowel movements. Before the start of the study, subjects were briefed on details of the study, and informed that there may be discomfort due to water expulsion by motor activity.

High-Resolution Colonic Manometry High-resolution colonic manometry (HRCM) was performed on a custom-made platform [Medical Measurement Systems (MMS); Laborie, Toronto, Canada]. A two-balloon catheter was used in the first 13 subjects, which included balloons between sensors 10 and 11 and 40 and 41. All other volunteers had one balloon between sensors 10 and 11. All balloons were 10 cm in length. The water perfusion rate was 0.1 ml/min via each sensor, resulting in a maximum total of 0.5 L/h when all pressure sensors were inside the colon; the perfusion pressure was 1,000 mbar (100 kPa). Each manometry study lasted 6–8 h, resulting in 3–4 L of water being delivered into the colon. Water was expelled via propulsive motor patterns and through a drainage tube (3.3 mm × 91 cm; Salem Sump, Covidien) placed in the rectum that diverted 1–2 L of water. Water will also have been absorbed. The intraluminal pressure between motor patterns did not change for the duration of the 6–8-h manometry session, measured by baseline pressure readings at the start and end of the procedures; thus, the inflow of water did not cause passive tonic pressure changes that might have evoked motor activity. The catheter was inserted with minimal sedation (fentanyl 50–100 µg iv and midazolam 2–5 mg iv) with the assistance of a colonoscope after a bowel-cleaning procedure using an inert osmotic laxative (PEG-Lyte; Pendopharm, Quebec, ON, Canada) but no stimulant laxatives, such as bisacodyl. Three liters of PEG (70 g/L) were taken between 4 and 6 PM the day before the procedure, with more water consumed as needed so that all solids would be removed. The next morning, 1 L was taken at 4 AM. The tip of the catheter was clipped to the mucosa via a fish line tied to the tip of the catheter, a few centimeters distal to the cecum. The anal sphincter was recorded across 2–4 sensors; therefore, although catheter displacement was rare, movement of the catheter could be detected through a shift in those sensors. The catheter was made of 100% silicone; after use, a hospital-approved cleaning procedure was executed, including sterilization with an autoclave. All subjects were in the supine position during the entire recording, with the exception of the intake of the meal when they were seated upright at a 45° angle. The subjects were instructed to report all events, such as gas or liquid expulsion, cramping, and nausea. The subjects were asked to refrain from preventing or promoting gas or liquid expulsion by increasing abdominal pressure or contracting the external anal sphincter should an urge arise. All body movements, such as changing body position, talking, coughing, laughing, and urination were noted immediately into the data acquisition files to remove pressure artifacts.

Protocol A 90-min recording of baseline activity was started 30 min after the colonoscope was withdrawn. The response to a 5-min balloon distension at the proximal colon was investigated. The balloon was initially inflated until the first sensation was reported. This was followed by incremental increases in balloon volume by 60 mL until the maximum tolerated volume was achieved, which was between 250 and 400 ml air. In each of these periods, the volume was sustained for a short period (between 2 and 3 min). The maximum tolerated volume was considered to be when discomfort reached 6–7 on a 10-point scale, as reported by the subject. After the 5-min distention, the balloon was deflated. Analysis of the response to balloon distention was performed on the 5-min period of sustained distention, as well as a 15-min period after deflation. Next, a meal was given to induce the gastrocolonic reflex (500 g of organic vanilla yogurt fortified with organic milk fat (Mapleton Organics, Moorefield, ON, Canada), to reach 800–1,000 kcal). Its effect was observed for 90 min. Next, 4 mg of prucalopride was administered orally, and its effect was observed for 90 min; prucalopride was given to study a possible early effect due to stimulation of the gastric enterochromaffin cells (15, 25), not to study effects of prucalopride after it is absorbed in the bloodstream. Following prucalopride, a 10-mg bisacodyl suspension (Dulcolax; Boehringer Ingelheim, Sanofi Canada, Quebec) was injected in the rectum via a syringe, and its effect was studied for 30 min. The bisacodyl suspension was made in saline by crushing four tablets, 5 mg each, with a pestle and mortar for 5 min. Since it was not possible to keep patients for multiple days and perform separate interventions, all of the stimuli were administered within a 6–8-h time span; therefore, some of the observed effects such as those of prucalopride and bisacodyl may have acted additively. At the end of the study, an X-ray was taken using a portable X-ray machine that was brought into to the study room. Before the X-ray, one or both balloons were slightly inflated so as to make them visible during X-ray and were used along with the catheter clip and metal pieces to visualize the placement of the catheter along the colon. Metal pieces were incorporated in the catheter at the tip and at both sides of the balloon(s) to help identify the position of the catheter.

Analysis The manometric recording was first inspected visually to identify all motor patterns and artifacts. Artifacts due to cough, position change, or straining were removed from analysis. An HAPW was identified as a motor pattern that propagated slower than 2.5 cm/s, has an average pressure of more than 20 mmHg (based on the MMS topographical map pressure scale), and was not part of a cyclic motor pattern (24, 38). HAPWs occurred with or without a subsequent simultaneous pressure wave (SPW) (14). To analyze all of the motor patterns, an Event Series plug-in was used in ImageJ, which converts the data from the manometry scan into a spatiotemporal plot and allowed us to use the tools provided by ImageJ to measure various parameters. To measure HAPW amplitude, the freehand tool was used to outline the general area around the pressure wave. A 20-mmHg isobaric contour line was then set using a Contourer plug-in, to measure the average amplitude of each individual HAPW within this isobar. To measure its velocity, the line tool was used to draw a line from the beginning of the pressure wave to the most distal end. From the line tool, we obtained the length (over how many centimeters of the colon the wave progressed) and its duration (the time difference between the start and end) of the pressure wave. From these data, we also calculated the velocity using length/duration. Pressure waves were categorized according to points of origin and cessation in the colon, as well as the intervention during which they occurred. The exact positioning of the catheter within the colon was determined on the basis of the X-ray taken at the end of the study. HAPWs were paired with their associated percentage anal sphincter relaxation (the colo-anal reflex) which was measured using ImageJ; its rectangular selection tool was used to obtain the mean amplitude of the relaxation, as well as the anal sphincter amplitude 3 min before the relaxation occurred (reference amplitude). To measure the mean amplitude of the relaxation pressure, the plot profile option in ImageJ was used to narrow the selection to only encompass the lowest area of pressure associated with the HAPW, and this area was taken as the area of relaxation. To measure the reference pressure, the area of the anal sphincter 3 min before the relaxation was taken. If HAPWs occurred at a higher frequency, or if there was another motor pattern occurring just before the HAPW, the resting pressure that was available between the two consecutive relaxations was taken as the reference. The percent relaxation was calculated using the formula: 100 − relaxation amplitude reference amplitude × 100 . Twenty percent anal sphincter relaxation was considered clinically relevant as per anorectal manometry guidelines ( Twenty percent anal sphincter relaxation was considered clinically relevant as per anorectal manometry guidelines ( 42 ).

Statistical Analysis Data were expressed as means ± SE, with N as the number of subjects and n as the number of HAPWs. Normal values for each intervention and category were determined using the 95th percentile. GraphPad Prism 8 was used for statistical analysis. The Brown-Forsythe test was used to test for significant differences between the variances of the groups. If the test did show a significant difference in variances, Welch’s one-way ANOVA was used with Games-Howell post hoc test for multiple comparisons. An unpaired t test with or without Welch’s correction was used to compare the percentage of anal sphincter relaxation between independent and HAPW-associated relaxations, as well as differences between HAPWs with and without SPW within each category depending on whether there was a significant difference in variances. Variances for the t test were compared using the F test.

Generation of Symbol Maps The present study devised symbol maps to show the occurrence of HAPWs on a time scale and to illustrate the variability in responses of healthy subjects. Isolated SPWs were also included as characterized in a previous study (13).