Barostat measurement of rectal compliance and capacity

Constipated patients with functional defecatory disorder have secondary rectal hyposensitivity due to altered rectal biomechanics

BACKGROUND AND AIM

Rectal hyposensitivity (RH) is common in constipation and often coexists with functional defecatory disorder (FDD). Rectal sensory thresholds are routinely evaluated with the anorectal manometry probe; however, the gold standard for the assessment of rectal sensitivity is with a barostat, use of which is limited by time constraints and availability. A novel rapid barostat bag (RBB) may facilitate measurements of rectal sensitivity. The aim is to evaluate the relationship between RH (measured by the RBB) and FDD (defined as any minor disorder of rectoanal coordination by the London classification) in constipated patients.

METHODS

Consecutive constipated patients referred for anorectal function testing underwent anorectal manometry with the 3D-HDAM probe as well as rectal sensation testing with the RBB pump. RH was defined by volume to first sensation >30%, urge to defecate >80%, or discomfort >100% (normalized to rectal capacity).

RESULTS

Fifty-three percent of constipated patients had RH. Patients with FDD had a significantly increased volume to first sensation (134.5 mL vs 102.0, P = 0.02), urge to defecate (187.0 mL vs 149.0, P = 0.04), and rectal capacity (253.5 mL vs 209.0, P = 0.04) compared to constipated patients without FDD. There was no difference in normalized sensory thresholds (percent of rectal capacity) nor the prevalence of hyposensitivity to each sensory threshold nor overall hyposensitivity.

CONCLUSION

Patients with FDD, when measured with the RBB, have increased sensory thresholds on volumetric distension, but RH was not observed when sensory threshold volume were normalized to rectal capacity. This may reflect "secondary" RH due to altered rectal biomechanics.

Novel insights into physiological mechanisms underlying fecal continence

The machinery maintaining fecal continence prevents involuntary loss of stool and is based on the synchronized interplay of multiple voluntary and involuntary mechanisms, dependent on cooperation between motor responses of the musculature of the colon, pelvic floor, and anorectum, and sensory and motor neural pathways. Knowledge of the physiology of fecal continence is key toward understanding the pathophysiology of fecal incontinence. The idea that involuntary contraction of the internal anal sphincter is the primary mechanism of continence and that the external anal sphincter supports continence only by voluntary contraction is outdated. Other mechanisms have come to the forefront, and they have significantly changed viewpoints on the mechanisms of continence and incontinence. For instance, involuntary contractions of the external anal sphincter, the puborectal muscle, and the sphincter of O'Beirne have been proven to play a role in fecal continence. Also, retrograde propagating cyclic motor patterns in the sigmoid and rectum promote retrograde transit to prevent the continuous flow of content into the anal canal. With this review, we aim to give an overview of primary and secondary mechanisms controlling fecal continence and evaluate the strength of evidence.

Type of Rectal Barostat Protocol Affects Classification of Hypersensitivity and Prediction of Symptom Severity in Irritable Bowel Syndrome

Background/Aims

Visceral hypersensitivity is an important pathophysiologic mechanism in irritable bowel syndrome (IBS). We compared 2 barostat distension protocols and their ability to distinguish between IBS patients and healthy controls, identify subjects with rectal hypersensitivity, and their associations with gastrointestinal symptom severity.

Methods

We retrospectively reviewed all patients at our unit that had undergone barostat investigations 2002-2014. Protocol 1 (n = 369) used phasic isobaric distensions with stepwise increments in pressure and protocol 2 (n = 153) used pressure controlled ramp inflations. Both protocols terminated when subjects reported pain or maximum pressure was reached. Thresholds for first sensation, urgency, discomfort and pain were established. Age- and gender-matched controls were used for comparison. The gastrointestinal symptom rating scale-IBS, and the hospital anxiety and depression scale were used for symptom reports.

Results

A significantly higher proportion of patients was classified as having hypersensitivity in protocol 1 vs protocol 2 for all thresholds (P < 0.001). Patients with visceral hypersensitivity, defined based on rectal pain thresholds in protocol 1 had more severe gastrointestinal symptoms overall as well as anxiety, whereas these associations were weaker or in most cases absent when visceral hypersensitivity was defined based on rectal pain thresholds in protocol 2.

Conclusion

Our study indicates that a rectal barostat protocol using phasic isobaric distensions with stepwise pressure increments is more sensitive in IBS patients with respect to identifying subjects with rectal hypersensitivity and a link with IBS symptoms.

The anorectal defaecation reflex: a prospective intervention study

AIM

Our hypothesis is that there may be a neural pathway with sensory afferent neurons in the anal canal that leads to rectal contraction to assist defaecation. We aimed to compare rectal motility between healthy participants with or without anal anaesthesia.

METHOD

This prospective intervention study consisted of two test sessions: a baseline session followed by an identical second session. During each session we performed the anal electrosensitivity test, the rectoanal inhibitory reflex test and rapid phasic barostat distensions. Prior to the second session, participants were randomly assigned to receive either a local anal anaesthetic or a placebo.

RESULTS

We included 23 healthy participants aged 21.1 ± 0.5 years, 13 of whom received an anal anaesthetic and 10 a placebo. All participants showed a transient rectal contraction during the first test session, which decreased significantly after anal anaesthesia (18.6 ml vs. 4.9 ml, p = 0.019). The maximum rectal contraction was comparable to the baseline results in the placebo group. Furthermore, the electrosensitivity at the highest centimetre of the anal canal correlated with the maximum rectal contraction (r = -0.452, p = 0.045).

CONCLUSION

All healthy study participants display an involuntary, reproducible rectal reflex contraction that appears to be innervated by afferent nerves in the proximal anal canal. The rectal reflex contraction appears to play a role in defaecation and we therefore refer to this phenomenon as the anorectal defaecation reflex. Knowledge of the anorectal defaecation reflex may have consequences for the diagnostics and treatment of constipation.

Chronic constipation in adults: Contemporary perspectives and clinical challenges. 1: Epidemiology, diagnosis, clinical associations, pathophysiology and investigation

BACKGROUND

Chronic constipation is a prevalent disorder that affects patients' quality of life and consumes resources in healthcare systems worldwide. In clinical practice, it is still considered a challenge as clinicians frequently are unsure as to which treatments to use and when. Over a decade ago, a Neurogastroenterology & Motility journal supplement devoted to the investigation and management of constipation was published (2009; 21 (Suppl.2)). This included seven articles, disseminating all themes covered during a preceding 2-day meeting held in London, entitled "Current perspectives in chronic constipation: a scientific and clinical symposium." In October 2018, the 3rd London Masterclass, entitled "Contemporary management of constipation" was held, again over 2 days. All faculty members were invited to author two new review articles, which represent a collective synthesis of talks presented and discussions held during this meeting.

PURPOSE

This article represents the first of these reviews, addressing epidemiology, diagnosis, clinical associations, pathophysiology, and investigation. Clearly, not all aspects of the condition can be covered in adequate detail; hence, there is a focus on particular "hot topics" and themes that are of contemporary interest. The second review addresses management of chronic constipation, covering behavioral, conservative, medical, and surgical therapies.

Anal and rectal function after intensity-modulated prostate radiotherapy with endorectal balloon

BACKGROUND AND PURPOSE

Late anorectal toxicity influences quality of life after external beam radiotherapy (EBRT) for prostate cancer. A daily inserted endorectal balloon (ERB) during EBRT aims to reduce anorectal toxicity. Our goal is to objectify anorectal function over time after prostate intensity-modulated radiotherapy (IMRT) with ERB.

MATERIAL AND METHODS

Sixty men, irradiated with IMRT and an ERB, underwent barostat measurements and anorectal manometry prior to EBRT and 6 months, one year and 2 years after radiotherapy. Primary outcome measures were rectal distensibility and rectal sensibility in response to stepwise isobaric distensions and anal pressures.

RESULTS

Forty-eight men completed all measurements. EBRT reduced maximal rectal capacity 2 years after EBRT (250 ± 10 mL vs. 211 ± 10 mL; p < 0.001), area under the pressure-volume curve (2878 ± 270 mL mmHg vs. 2521 ± 305 mL mmHg; p = 0.043) and rectal compliance (NS). Sensory pressure thresholds for first sense and first urge (both p < 0.01) increased. Anal maximum pressure diminished after IMRT (p = 0.006).

CONCLUSIONS

Rectal capacity and sensory function are increasingly affected over time after radiotherapy. There is an indication that these reductions are affected less with IMRT + ERB compared to conventional radiation techniques.

Toward more accurate measurements of anorectal motor and sensory function in routine clinical practice: validation of high-resolution anorectal manometry and Rapid Barostat Bag measurements of rectal function

BACKGROUND

Measurements of anorectal function using high-resolution anorectal manometry (HR-ARM) and rectal barostat technology provide more reliable results than standard ARM with an elastic balloon; however, HR-ARM results have not been compared to ARM and standard barostat protocols are impractical in routine clinical practice. The aim of this study was to validate HR-ARM against standard ARM and standard barostat against a novel Rapid Barostat Bag (RBB) measurement and elastic balloon measurements of rectal function.

METHODS

Twenty-six healthy volunteers (15 female, 11 male, 19-52 years) were studied. Measurements of anal function and simulated defecation were compared for 12-sensor HR-ARM and 6-sensor standard ARM using line plots from the same recording. Rectal capacity, compliance, and sensation (volume threshold) were measured by elastic balloon, standard barostat, and RBB methods using stepwise inflation of a 700-mL polyethylene bag to 40 mmHg distension by electronic barostat and handheld syringe monitored by sphygmo-manometer, respectively. Results are reported as mean ± SD. Bland-Altman plots and correlation coefficients (r) for measurements were calculated.

KEY RESULTS

There was excellent agreement between HR- and standard ARM measurements (r > 0.86, <25 mmHg difference) and between standard barostat and RBB measurements of rectal capacity (r = 0.97, <25 mL difference). Correlation coefficients of threshold volumes for initial perception, urgency and discomfort were 0.37, 0.71, and 0.95, respectively. No significant correlation was present with elastic balloon measurements. Time to complete studies was shorter for HR-ARM than standard ARM and for RBB than standard barostat in historical controls.

CONCLUSIONS & INFERENCES

HR-ARM with RBB measurements of anorectal function provides quick and reasonably accurate measurements of continence function suitable for use in routine clinical practice (ClinicalTrial.gov NCT01456442).

Autonomic rectal dysfunction in patients with multiple sclerosis and bowel symptoms is secondary to spinal cord disease

BACKGROUND

Most patients with multiple sclerosis report bowel symptoms, but the underlying pathophysiology is unclear.

OBJECTIVE

We hypothesize that rectal dysfunction in multiple sclerosis is secondary to involvement of the spinal cord by the disease and that this can be measured by assessing rectal compliance.

DESIGN

This was a case-control study.

SETTINGS

The study took place in a neurogastroenterology clinic and tertiary referral center.

PATIENTS

Forty-five patients with multiple sclerosis, 19 with a spinal cord injury above T5, and 25 normal control subjects were included in this study. Patients with multiple sclerosis were subdivided into 2 groups according to the Expanded Disability Status Scale, below 5 (multiple sclerosis minor disability, n = 25) or above 5 (multiple sclerosis major disability, n = 20), as a reflection of spinal cord involvement.

MAIN OUTCOME MEASURES

Rectal compliance, Wexner constipation, and Wexner incontinence scores were measured.

RESULTS

Data are presented as mean and SD. Expanded Disability Status Scale correlated with rectal compliance but not with Wexner constipation or Wexner incontinence scores. Post hoc analysis showed no significant difference in Wexner constipation and Wexner incontinence between the 2 multiple sclerosis groups.

LIMITATIONS

Limitations to this study include the lack of an asymptomatic group with multiple sclerosis and the small sample size to evaluate bowel symptoms.

CONCLUSIONS

Rectal compliance correlates with disability, and observed alterations in the rectal properties are secondary to spinal cord involvement. Our findings suggest that, in patients with neurologic impairment, rectal compliance is a surrogate of reflex activity of the spinal cord regulating rectal function and both a potential predictor of outcome and target for treatment. Multiple sclerosis patient subgroups had similar symptom burden, arguing that bowel dysfunction is multifactorial.

Bloating and distention in irritable bowel syndrome: the role of gas production and visceral sensation after lactose ingestion in a population with lactase deficiency

OBJECTIVES

Bloating and distention are often attributed to dietary factors by patients with irritable bowel syndrome (IBS). This study examined the effects of gas production and visceral hypersensitivity on digestive symptoms after lactose ingestion in a population with lactase deficiency.

METHODS

IBS patients (n=277) and healthy controls (HCs, n=64) underwent a 20-g lactose hydrogen breath test (LHBT) with evaluation of hydrogen gas production and lactose intolerance (LI) symptoms. Abdominal distention (199 IBS, 40 HCs) was measured during LHBT. Rectal sensitivity (74 IBS, 64 HCs) was assessed by barostat studies.

RESULTS

Hydrogen production and distention were similar in IBS patients and HCs during LHBT; however, LI was more frequent in IBS (53.8 vs. 28.1%, P<0.001), especially bloating (39.0% vs. 14.1%, P<0.001) and borborygmi (39.0 vs. 21.9%, P=0.010). Only 59.0% of patients with bloating had distention. No correlation was observed between girth increment and bloating (P=0.585). IBS patients had lower rectal sensory thresholds (P=0.001). Multivariate analysis indicated that hydrogen production increased bloating (odds ratio (OR) 2.19, 95% confidence interval (CI) 1.09-4.39, P=0.028) and borborygmi (OR 12.37, 95% CI 3.34-45.83, P<0.001) but not distention (P=0.673). Visceral hypersensitivity was associated with bloating (OR 6.61, 95% CI 1.75-25.00, P=0.005) and total symptom score (OR 3.78, 95% CI 1.30-10.99, P=0.014).

CONCLUSIONS

Gas production and visceral hypersensitivity both contribute to digestive symptoms, especially bloating and borborygmi, in IBS patients after lactose ingestion. Objective abdominal distention is not correlated with subjective bloating.

Impact of late anorectal dysfunction on quality of life after pelvic radiotherapy

PURPOSE

Anorectal dysfunction is common after pelvic radiotherapy. This study aims to explore the relationship of subjective and objective anorectal function with quality of life (QoL) and their relative impact in patients irradiated for prostate cancer.

METHODS

Patients underwent anal manometry, rectal barostat measurement, and completed validated questionnaires, at least 1 year after prostate radiotherapy (range 1-7 years). QoL was measured by the Fecal Incontinence Quality of Life scale (FIQL) and the Expanded Prostate Cancer Index Composite Bowel domain (EPICB)-bother subscale. Severity of symptoms was rated by the EPICB function subscale.

RESULTS

Anorectal function was evaluated in 85 men. Sixty-three percent suffered from one or more anorectal symptoms. Correlations of individual symptoms ranged from r = 0.23 to r = 0.53 with FIQL domains and from r = 0.36 to r = 0.73 with EPICB bother scores. They were strongest for fecal incontinence and urgency. Correlations of anal sphincter pressures, rectal capacity, and sensory thresholds ranged from r = 0.00 to r = 0.42 with FIQL domains and from r = 0.15 to r = 0.31 with EPICB bother scores. Anal resting pressure correlated most strongly. Standardized regression coefficients for QoL outcomes were largest for incontinence, urgency, and anal resting pressure. Regression models with subjective parameters explained a larger amount (range 26-92 %) of variation in QoL outcome than objective parameters (range 10-22 %).

CONCLUSIONS

Fecal incontinence and rectal urgency are the symptoms with the largest influence on QoL. Impaired anal resting pressure is the objective function parameter with the largest influence. Therefore, sparing the structures responsible for an adequate fecal continence is important in radiotherapy planning.

Increased rectal wall stiffness after prostate radiotherapy: relation with fecal urgency

BACKGROUND

  Late anorectal toxicity is a frequent adverse event of external beam radiotherapy (EBRT) for prostate cancer. The pathophysiology of anorectal toxicity remains unknown, but we speculate that rectal distensibility is impaired due to fibrosis. Our goal was to determine whether EBRT induces changes of rectal distensibility as measured by an electronic barostat and to explore whether anorectal complaints are related to specific changes of anorectal function.

METHODS

  Thirty-two men, irradiated for localized prostate carcinoma, underwent barostat measurements, anorectal manometry, and completed a questionnaire prior to and 1 year after radiotherapy. The primary outcome measure was rectal distensibility in response to stepwise isobaric distensions. In addition, we assessed sensory thresholds, anal pressures, and anorectal complaints.

KEY RESULTS

  External beam radiotherapy reduced maximal rectal capacity (227 ± 14 mL vs 277 ± 15 mL; P < 0.001), area under the pressure-volume curve (3212 ± 352 mL mmHg vs 3969 ± 413 mL mmHg; P < 0.005), and rectal compliance (15.7 ± 1.2 mL mmHg(-1) vs 17.6 ± 0.9 mL mmHg(-1) ; P = 0.12). Sensory pressure thresholds did not significantly change. Sixteen of the 32 patients (50%) had one or more anorectal complaints. Patients with urgency (n = 10) had a more reduced anal squeeze and maximum pressure (decrease 29 ± 11 mmHg vs 1 ± 7 mmHg; P < 0.05 and 31 ± 12 mmHg vs 2 ± 8 mmHg; P < 0.05 respectively) compared with patients without complaints, indicating a deteriorated external anal sphincter function.

CONCLUSIONS & INFERENCES

  Irradiation for prostate cancer leads to reduced rectal distensibility. In patients with urgency symptoms, anal sphincter function was also impaired.

Alternative procedure to shorten rectal barostat procedure for the assessment of rectal compliance and visceral perception: a feasibility study

BACKGROUND

Barostat methodology is widely used for assessing visceral perception. Different barostat protocols are described with respect to the measurement of rectal compliance and visceral perception. The choice of protocols affects the duration, which is normally 60-90 min, and accuracy of the procedure. This study aimed to shorten the procedure by using the semi-random distension protocol for both compliance and visceral perception measurement and a correction based on rectal capacity (RC) instead of minimal distension pressure (MDP).

METHODS

Twelve irritable bowel syndrome (IBS) patients (7 females) and 11 healthy controls (8 females) underwent a barostat procedure. Compliance was determined during both a staircase distension and a semi-random protocol. Visceral perception data were compared as a function of pressure or relative volume, corrected for MDP or RC, respectively.

RESULTS

Compliance measurement using the semi-random protocol instead of the staircase distension protocol resulted in an overestimation in healthy volunteers, but not in IBS patients. The overall conclusion that IBS patients had a lower compliance compared to controls was not different between protocols. Data presentation of the visceral perception scores as a function of corrected volume instead of pressures corrected for MDP did not alter the conclusion that sensation scores in IBS patients were higher as compared to healthy controls.

CONCLUSIONS

This study showed that barostat procedures may be shortened by approximately 20 min, without losing the ability to discriminate between healthy controls and IBS patients. A correction for RC instead of MDP may improve the accuracy of the procedure.

Temporary sacral nerve stimulation alters rectal sensory function: a physiological study

BACKGROUND

The indications for sacral nerve stimulation are increasing, but the mechanism remains poorly understood.

OBJECTIVE

This study aimed to examine the effect of sacral nerve stimulation on rectal compliance and rectal sensory function.

DESIGN

This was a prospective study.

SETTINGS

This study took place at a university teaching hospital.

PATIENTS

Twenty-three consecutive consenting patients (22 female; median age, 49 y) undergoing temporary sacral nerve stimulation for fecal incontinence were prospectively studied. Clinical response was assessed by the use of bowel diaries and Wexner scores.

MAIN OUTCOME MEASURES

Anal manometry, rectal compliance, volume and pressure thresholds to rectal distension (barostat), and rectal Doppler mucosal blood flow were measured before and at the end of stimulation.

RESULTS

Sixteen patients (70%) had a favorable clinical response. Median anal squeeze pressures increased with stimulation from 40 (range, 6-156) cmH2O to 64 (range, 16-243) cmH2O. Median rectal compliance did not significantly change with stimulation (prestimulation: 11.5 (range, 7.9-21.8) mL/mmHg, poststimulation: 12.4 (range, 6.2-22) mL/mmHg, P = .941). Rectal wall pressures associated with urge (baseline: 15.4 (range, 11-26.7) mmHg, poststimulation: 19 (range, 11.1-42.7) mmHg, P = .054) and maximal tolerated thresholds (baseline: 21.6 (8.5-31.9) mmHg, poststimulation: 27.1 (14.3-43.3) mmHg, P = .023) significantly increased after stimulation. Rectal Doppler mucosal blood flow did not significantly change with stimulation (baseline: 125.8 (69.9-346.8), poststimulation: 112.4 (50.2-404.1), P = .735). Changes in anal resting pressure and rectal wall pressures with stimulation were evident only in responders; however, changes in anal squeeze pressures were evident in both responders and nonresponders.

LIMITATIONS

The study reports results following short-term stimulation in a small but homogenous group of patients. A larger long-term study will follow.

CONCLUSION

Temporary sacral nerve stimulation does not change rectal compliance, but is associated with significant changes to the pressure thresholds of rectal distension. This, together with the observation that outcome is not related to sphincter integrity, supports the hypothesis of an afferent-mediated mechanism of action.

Stapled haemorrhoidopexy transiently decreases rectal compliance and sensitivity

AIM

Stapled haemorrhoidopexy may damage the anorectal musculature and its sensorimotor function. Most studies have not used a barostat for the measurement of compliance. This study aimed to investigate the effect of stapled haemorrhoidopexy on rectal compliance and sensitivity.

METHOD

After Ethical Committee approval, we studied 10 male patients (mean age 33.8 years) with third- or fourth-degree haemorrhoids. Rectal compliance and sensitivity were measured with a 600-ml bag and an electronic barostat. Volunteers were submitted to two consecutive rectal distension protocols, including continuous distension at 2, 4 and 6 months after stapled haemorrhoidopexy. Intraluminal volume and pressure were recorded, including the first rectal sensation, desire to defecate and onset of rectal pain. Another group of 10 male control patients (mean age 24.9 years) with pilonidal sinus and no haemorrhoids was also included in the study.

RESULTS

Two months after stapled haemorrhoidopexy, rectal compliance decreased (7.1 ± 0.2 vs 5.3 ± 0.1, 6.4 ± 0.1 vs 5.1 ± 0.1 and 5.6 ± 0.2 vs 4.7 ± 0.1 ml/mmHg for first rectal sensation, desire to defecate and rectal pain, respectively; P < 0.05). The sensitivity threshold volume did not change for the first sensation but decreased significantly for the desier to defecate and pain (p <0.05) (116.8 ± 13.8 vs 148.4 ± 14.61, 251.1 ± 8.9 vs 185.8 ± 8.6 and 293.3 ± 16.6 vs 221.2 ± 6.0 ml for first rectal sensation, desire to defecate and rectal pain, respectively). Four and 6 months after surgery, rectal compliance and sensitivity returned to levels similar to those in the basal period. Muscle tissue was found in only three of the 10 resected doughnuts. Controls remained without any change in rectal compliance and sensitivity.

CONCLUSION

Stapled haemorrhoidopexy transiently decreases rectal compliance and sensitivity threshold in young male patients.

Differences in radiation dosimetry and anorectal function testing imply that anorectal symptoms may arise from different anatomic substrates

PURPOSE

To explore the influence of functional changes and dosimetric parameters on specific incontinence-related anorectal complaints after prostate external beam radiotherapy and to estimate dose-effect relations for the anal wall and rectal wall.

METHODS AND MATERIALS

Sixty patients, irradiated for localized prostate cancer, underwent anorectal manometry and barostat measurements to evaluate anal pressures, rectal capacity, and rectal sensory functions. In addition, 30 untreated men were analyzed as a control group. In 36 irradiated patients, the anal wall and rectal wall were retrospectively delineated on planning computed tomography scans, and dosimetric parameters were retrieved from the treatment plans. Functional and dosimetric parameters were compared between patients with and without complaints, focusing on urgency, incontinence, and frequency.

RESULTS

After external beam radiotherapy, reduced anal pressures and tolerated rectal volumes were observed, irrespective of complaints. Patients with urgency and/or incontinence showed significantly lower anal resting pressures (mean 38 and 39 vs. 49 and 50 mm Hg) and lower tolerated rectal pressures (mean 28 and 28 vs. 33 and 34 mm Hg), compared to patients without these complaints. In patients with frequency, almost all rectal parameters were reduced. Several dosimetric parameters to the anal wall and rectal wall were predictive for urgency (e.g., anal D(mean)>38 Gy), whereas some anal wall parameters correlated to incontinence and no dose-effect relation for frequency was found.

CONCLUSIONS

Anorectal function deteriorates after external beam radiotherapy. Different incontinence-related complaints show specific anorectal dysfunctions, suggesting different anatomic and pathophysiologic substrates: urgency and incontinence seem to originate from both anal wall and rectal wall, whereas frequency seems associated with rectal wall dysfunction. Also, dose-effect relations differed between these complaints. This implies that anal wall and rectal wall should be considered separate organs in radiotherapy planning.

The physiology of continence and evacuation

Continence is maintained by the coordinated function of the pelvic floor, rectum and anal sphincters. Evacuation occurs through a relaxed pelvic floor. The rectum acts to either store or expel stool both of which require cortical sensory awareness acting in conjunction with intramural and spinal reflexes that ensure timely defecation. The anal sphincters act individually and in unison in response to rectal distension and the sensation of rectal filling. Reflex relaxation of the internal anal sphincter has an additional sensory function in allowing sampling of rectal contents in the upper anal canal. Voluntary control of the external anal sphincter is key in the voluntary deferring of evacuation until a socially opportune moment. This review describes the physiological roles of each of these continence organs in order to understand the complex process of defecation.

Rectal hyposensitivity: pathophysiological mechanisms

Rectal hyposensitivity (RH) relates to a diminished perception of rectal distension. It may occur due to afferent nerve dysfunction and/or secondary to abnormal structural or biomechanical properties of the rectum. The aim of this study was to determine the contribution of these underlying pathophysiological mechanisms by systematically evaluating rectal diameter, compliance and afferent nerve sensitivity in patients with RH, using methodology employed in clinical practice. The study population comprised 45 (33 women; median age 48, range 25-72 years) constipated patients (Rome II criteria) with RH and 20 with normal rectal sensitivity on balloon distension and 20 healthy volunteers. Rectal diameter was measured at minimum distending pressure during isobaric distension under fluoroscopic screening. Rectal compliance was assessed during phasic isobaric distension by measuring the slope of the pressure-volume curve. Electrical stimulation of the rectal mucosa was employed to determine afferent nerve function. Values were compared to normal ranges established in healthy volunteers. The upper limits of normal for rectal diameter, compliance and electrosensitivity were 6.3 cm, 17.9 mL mmHg(-1) and 21.3 mA respectively. Among patients with RH, rectal diameter, but not compliance, was increased above the normal range (megarectum) in seven patients (16%), two of whom had elevated electrosensitivity thresholds. Rectal diameter and compliance were elevated in 23 patients (51%), nine of whom had elevated electrosensitivity thresholds. The remaining 15 patients (33%) with RH had normal rectal compliance and diameter, all of whom had elevated electrosensitivity thresholds. Two-third of the patients with RH on simple balloon distension have elevated rectal compliance and/or diameter, suggesting that impaired perception of rectal distension is due to inadequate stimulation of the rectal afferent pathway. However, a proportion of such patients also appear to have impaired nerve function. In the remaining one-third of the patients, rectal diameter and compliance are normal, while electrosensitivity thresholds are elevated, suggestive of true impaired afferent nerve function. Identification of these subgroups of patients with RH may have implications regarding their management.

Circadian variation of rectal sensitivity and gastrointestinal peptides in healthy volunteers

The aim of our study was to identify diurnal variation of perception of rectal distension and the release of gastroenteropancreatic hormones. In 12 healthy male volunteers (25 years, range 22-32), a rectal balloon distension was performed. Rectal perception thresholds (minimal, urge and pain) and rectal compliance were double-measured with a computer-controlled barostat at seven standardized time points during the day (from 16.00 to 14.00 hours the following day). Blood samples were taken 30 min before and after each rectal distension procedure to determine plasma levels of cholecystokinin (CCK), pancreatic polypeptide (PP) and motilin. Sensory thresholds for urge and pain varied significantly with the time of day, with higher threshold levels in the evening than in the morning hours. Bowel wall compliance showed as well-significant variance at pain threshold and was higher during daytime than in the evening or at night. In contrast to motilin, release of CCK and PP also showed a significant variation depending on daytime. Perception of rectal distension stimuli as well as compliance was independent of intake of food and peptide hormone levels, but CCK and PP levels increased with food, and PP levels decreased with rectal distension. Significant differences in the perception of rectal distension stimuli for urge and pain depending on daytime were found, but the release of gastrointestinal peptides seemed not to be involved. This circadian variation needs to be taken into account in patients and volunteer studies.

Functional gastrointestinal disorders and visceral hypersensitivity in children and adolescents suffering from Crohn's disease

BACKGROUND

Symptoms of abdominal pain are reported by children with active Crohn's disease (CD). During remissions abdominal pain improves in most children but some of them continue to experience pain. We hypothesized that these patients may suffer from protracted abdominal pain related to functional gastrointestinal disorders (FGID) and visceral hypersensitivity. The objective was to characterize the symptoms and to measure the rectal sensory threshold for pain (RSTP) by barostat in CD children and adolescents suffering from abdominal pain despite remission.

METHODS

Eight patients (median age 14.5 years; range 9.8-17) with quiescent CD but suffering from chronic abdominal pain were studied by rectal barostat. At the same time they completed validated questionnaires to assess FGID, anxiety, and depression. They were compared to 10 control children and 8 children with FGID also investigated in our laboratory.

RESULTS

All patients fulfilled Rome II criteria for irritable bowel syndrome (n = 5), functional abdominal pain (n = 2), and functional dyspepsia (n = 1). RSTP was significantly lower in CD patients compared to the normal controls: median (range) 25 mmHg (15-29) versus 40 mmHg (30-48) (P < 0.01). RSTP was similar in patients and children with FGID. Rectal compliance was similar in patients, children with FGID, and controls. Seven of the 8 patients had scores indicating an anxiety problem.

CONCLUSIONS

Protracted abdominal pain that affects children and adolescents with quiescent CD is related to FGID associated with visceral hypersensitivity and anxiety. The incidence of FGID in children suffering from CD requires further investigation.

Sacral nerve stimulation and rectal function: results of a prospective study in faecal incontinence

The mechanisms of action of sacral nerve stimulation (SNS) to treat faecal incontinence remain poorly understood.

THE AIMS OF OUR STUDY WERE

(i) to measure the effect of SNS on rectal function and (ii) to evaluate rectal function as a predictive factor of clinical response to SNS. Rectal function was studied before and 3 months after permanent SNS in 18 patients (17 women, mean age 58.5 years) with faecal incontinence, using an electronic barostat. Rectal sensitivity and volume variations were recorded during isobaric distensions. Three months after SNS, 14 patients had a significant improvement of faecal incontience symptoms and four had not. Baseline 'maximal tolerated volume' was significantly lower in the positive response group (210 +/- 56 vs 286 +/- 30 mL, P = 0.02). Baseline rectal compliance was lower in patients with a positive response than those without, although this difference did not reach significance (6.2 +/- 3.2 vs 9.2 +/- 2.9 mL mmHg(-1),P = 0.10). Rectal compliance was not significantly modified by SNS. Our results suggest that an increased rectal capacity as measured by the maximal tolerated volume may be a predictive factor of poor response to SNS in faecal incontinence. SNS does not significantly modify rectal function.

Is visceral hypersensitivity correlated with symptom severity in children with functional gastrointestinal disorders?

BACKGROUND

Abdominal pain related to irritable bowel syndrome (IBS) and functional abdominal pain (FAP) is frequent in children and can be of variable severity. Both IBS and FAP are associated with rectal hypersensitivity. We hypothesized that in children with IBS and FAP, the rectal sensory threshold for pain (RSTP) is associated with symptom severity.

PATIENTS AND METHODS

A total of 47 patients (34 girls; median age, 14.2 years) with IBS (n = 29) and FAP (n = 18), according to the Rome II criteria, underwent a rectal barostat examination to determine their RSTP. Gastrointestinal symptom severity was assessed by validated questionnaires. During the rectal barostat exam, symptoms were documented using a visual analog scale and by measuring the area coloured on a human body diagram corresponding to painful sensations.

RESULTS

The median RSTP was 16 mmHg and was similar in IBS and FAP patients. Eighty-three percent of the patients had rectal hypersensitivity (RSTP < or = 30.8 mmHg, the 5th percentile of control children studied in our laboratory). Fifty-one percent and 36%, respectively, reported missing school and social activities at least once per week. Increased frequency of pain, missed days of school, missed social activities, and pain during the barostat examination were not associated with lower RSTP values in either the whole group or in the subset of children with rectal hypersensitivity.

CONCLUSIONS

Rectal hypersensitivity is not proportional to the severity of symptoms in children with IBS and FAP, indicating that symptom severity is influenced by other factors in addition to visceral hypersensitivity.

Compliance and capacity of the normal human rectum--physical considerations and measurement pitfalls

The assessment of parameters which adequately represent rectal and neorectal compliance is complex. Biological properties of the rectum during distension and relaxation show significant departures from in vitro physical compliance measurements; as much dependent upon the viscoelastic charateristics of hollow organ deformation as upon the technique of compliance calculation. This review discusses the pressure/volume characteristics of importance in the rectum during distension from a bioengineering perspective and outlines the disparities of such measurements in living biological systems. Techniques and pitfalls of newer methods to assess rectal wall stiffness (impedance planimetry and barostat measurement) are discussed.