Rectal adaptation to distention: implications for the determination of perception thresholds

Urethra Sparing With Target Motion Mitigation in Dose-Escalated Extreme Hypofractionated Prostate Cancer Radiotherapy: 7-Year Results From a Phase II Study

Purpose

To explore whether the rectal distension-mediated technique, harnessing human physiology to achieve intrafractional prostate motion mitigation, enables urethra sparing by inverse dose painting, thus promoting dose escalation with extreme hypofractionated stereotactic ablative radiotherapy (SABR) in prostate cancer.

Materials and Methods

Between June 2013 and December 2018, 444 patients received 5 × 9 Gy SABR over 5 consecutive days. Rectal distension-mediated SABR was employed via insertion of a 150-cm3 air-inflated endorectal balloon. A Foley catheter loaded with 3 beacon transponders was used for urethra visualization and online tracking. MRI-based planning using Volumetric Modulated Arc Therapy - Image Guided Radiotherapy (VMAT-IGRT) with inverse dose painting was employed in delivering the planning target volume (PTV) dose and in sculpting exposure of organs at risk (OARs). A 2-mm margin was used for PTV expansion, reduced to 0 mm at the interface with critical OARs. All plans fulfilled Dmean ≥45 Gy. Target motion ≥2 mm/5 s motions mandated treatment interruption and target realignment prior to completion of the planned dose delivery.

Results

Patient compliance to the rectal distension-mediated immobilization protocol was excellent, achieving reproducible daily prostate localization at a patient-specific retropubic niche. Online tracking recorded ≤1-mm intrafractional target deviations in 95% of treatment sessions, while target realignment in ≥2-mm deviations enabled treatment completion as scheduled in all cases. The cumulative incidence rates of late grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxicities were 5.3% and 1.1%, respectively. The favorable toxicity profile was corroborated by patient-reported quality of life (QOL) outcomes. Median prostate-specific antigen (PSA) nadir by 5 years was 0.19 ng/ml. The cumulative incidence rate of biochemical failure using the Phoenix definition was 2%, 16.6%, and 27.2% for the combined low/favorable-intermediate, unfavorable intermediate, and high-risk categories, respectively. Patients with a PSA failure underwent a 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) scan showing a 20.2% cumulative incidence of intraprostatic relapses in biopsy International Society of Urological Pathology (ISUP) grade ≥3.

Conclusion

The rectal distension-mediated technique is feasible and well tolerated. Dose escalation to 45 Gy with urethra-sparing results in excellent toxicity profiles and PSA relapse rates similar to those reported by other dose-escalated regimens. The existence of intraprostatic recurrences in patients with high-risk features confirms the notion of a high α/β ratio in these phenotypes resulting in diminished effectiveness with hypofractionated dose escalation.

Understanding the physiology of human defaecation and disorders of continence and evacuation

The act of defaecation, although a ubiquitous human experience, requires the coordinated actions of the anorectum and colon, pelvic floor musculature, and the enteric, peripheral and central nervous systems. Defaecation is best appreciated through the description of four phases, which are, temporally and physiologically, reasonably discrete. However, given the complexity of this process, it is unsurprising that disorders of defaecation are both common and problematic; almost everyone will experience constipation at some time in their life and many will develop faecal incontinence. A detailed understanding of the normal physiology of defaecation and continence is critical to inform management of disorders of defaecation. During the past decade, there have been major advances in the investigative tools used to assess colonic and anorectal function. This Review details the current understanding of defaecation and continence. This includes an overview of the relevant anatomy and physiology, a description of the four phases of defaecation, and factors influencing defaecation (demographics, stool frequency/consistency, psychobehavioural factors, posture, circadian rhythm, dietary intake and medications). A summary of the known pathophysiology of defaecation disorders including constipation, faecal incontinence and irritable bowel syndrome is also included, as well as considerations for further research in this field.

The physiology of human defecation

Human defecation involves integrated and coordinated sensorimotor functions, orchestrated by central, spinal, peripheral (somatic and visceral), and enteric neural activities, acting on a morphologically intact gastrointestinal tract (including the final common path, the pelvic floor, and anal sphincters). The multiple factors that ultimately result in defecation are best appreciated by describing four temporally and physiologically fairly distinct phases. This article details our current understanding of normal defecation, including recent advances, but importantly identifies those areas where knowledge or consensus is still lacking. Appreciation of normal physiology is central to directed treatment of constipation and also of fecal incontinence, which are prevalent in the general population and cause significant morbidity.

Rectal visceral sensitivity in women with irritable bowel syndrome without psychiatric comorbidity compared with healthy volunteers

Background. Psychiatric comorbidity and visceral hypersensitivity are common in patients with irritable bowel syndrome (IBS), but little is known about visceral sensitivity in IBS patients without psychiatric disorders. Aim. We wanted to examine rectal visceral sensitivity in IBS patients without comorbid psychiatric disorders, IBS patients with phobic anxiety and healthy volunteers. Methods. A total of thirty-eight female, non-constipated IBS patients without psychiatric disorders and eleven female IBS patients with phobic anxiety were compared to nine healthy women using a barostat double random staircase method. The non-psychiatric patients were divided into those with diarrhoea predominant symptoms and those with alternating stool habits. Results. The IBS patients without psychiatric disorders had normal visceral pressure thresholds. However, in the diarrhoea predominant subgroup, the volume discomfort threshold was reduced while it was unchanged in those with alternating stool habits. The phobic IBS patients had similar thresholds to the healthy volunteers. The rectal tone was increased in the non-psychiatric IBS patients with diarrhoea predominant symptoms and in the IBS patients with phobic anxiety. Conclusions. Non-constipated IBS patients without psychiatric disorders had increased visceral sensitivity regarding volume thresholds but normal pressure thresholds. Our study suggests that the lowered volume threshold was due to increased rectal tone.

Influence of naloxone on rectal sensorimotor function in health

Abnormal rectal motor physiology and visceral hypersensitivity are implicated in the pathogenesis of irritable bowel syndrome. Endogenous opioids are involved in both the regulation of gut motility and the processing of sensory information. Our aim was to study the effect of suppression of endogenous opioid function by naloxone on rectal sensorimotor function in health. Eighteen healthy subjects participated in a rectal barostat study. Sensorimotor function was evaluated during two consecutive stepwise distensions separated by 30 min of basal tone recording, and with perception scoring on a 0-6 graded scale. Naloxone was administered, after 15 min of basal tone measurements, as an intravenous bolus (0.4 mg), followed by continuous infusion (20 microg kg(-1) h(-1)) in a placebo-controlled, single-blinded and randomized fashion. Naloxone did not alter rectal sensitivity. Comparison of visual analogue scale scores between naloxone and saline did not reveal altered intensities of pain or discomfort. Compared to the baseline distension, a significant adaptive increase in compliance occurred during the second distension after saline (7.8 +/- 0.7 vs 11.0 +/- 0.6 mL mmHg(-1), P = 0.0016). This dynamic change in rectal compliance did not occur after naloxone administration (8.8 +/- 0.7 vs 10.1 +/- 0.8 mL mmHg(-1), ns). Low intensity tonic distension induced a rectal adaptive relaxation, which was absent after naloxone. Naloxone does not alter rectal sensitivity but abolishes rectal adaptation in response to repeated balloon distention. These observations suggest that the endogenous opioid system is involved in control of rectal tone rather than rectal sensitivity.

Manometric, sensorimotor, and neurophysiologic evaluation of anorectal function

With advances in diagnostic technology, it is now accepted that in the field of functional bowel disorders, symptom-based assessment is unsatisfactory as the sole means of directing therapy. A robust taxonomy based on underlying pathophysiology has been suggested, highlighting a crucial role for physiologic testing in clinical practice. A wide number of complementary investigations currently exist for the assessment of anorectal structure and function, some of which have a clinical impact in patients with functional disorders of evacuation and continence by markedly improving diagnostic yield and altering management. The techniques, limitations, measurements, and clinical use of manometric, sensorimotor, and neurophysiologic tests of anorectal function are presented.

Psychophysiology of visceral pain in IBS and health

The psychophysiology of visceral pain as it relates to gastrointestinal motility, visceral sensitivity, and putative mechanisms of the processing of visceral stimuli by the central and peripheral nervous systems are discussed. Peripheral mechanisms may include low-grade mucosal inflammation, and it is likely that central nervous mechanisms such as neuronal plasticity at the level of the spinal cord and attentional bias at the cortical level are relevant for the chronification of visceral pain. From a psychophysiological perspective, visceral pain therefore remains a complex symptom because behavioral variables, such as the way an individual deals with stress, may be as important for the etiology of visceral pain as, for example, a history of inflammation.

Bowel urgency in patients with irritable bowel syndrome

BACKGROUND & AIMS

Bowel urgency is the most bothersome symptom in irritable bowel syndrome patients with diarrhea, but its pathophysiology is poorly understood. Our aim was to assess the relationships among reporting the symptom, the reservoir functions of the colon and rectum, and the patients' psychologic profile.

METHODS

The study involved 28 consecutive patients with irritable bowel syndrome and 17 healthy subjects. The presence or absence of bowel urgency was verified by means of a questionnaire during the 3 days required for the ingestion of radio-opaque markers. On the fourth day, an abdominal x-ray was taken to assess colonic transit time, and rectal sensory and motor responses were measured during rectal distention. The subjects' psychologic profiles were assessed using a psychologic symptoms checklist.

RESULTS

Forty-six percent of the patients reported urgency associated with at least 1 defecation. The multivariate logistic regression analysis showed that colonic transit was the only variable independently associated with reported bowel urgency, but the threshold for the sensation of urgency was not removed from the model since its borderline significance level. Rectal compliance was closely associated with the threshold for the sensation of urgency during rectal distention but was not an independent factor for reporting the sensation. The patients with and without urgency showed altered psychologic profiles.

CONCLUSIONS

The symptom of urgency is associated with objective alterations in the colonic and rectal reservoir of patients with irritable bowel syndrome.

Rectal intussusception: a study of rectal biomechanics and visceroperception

OBJECTIVES

Rectal intussusception (RI) is a significant cause of morbidity amongst those with a rectal evacuatory disorder. The pathophysiology is unknown, but may involve abnormal biomechanics of the rectal wall similar to that previously demonstrated in patients with overt rectal prolapse (RP). Using an electromechanical barostat, this study aimed to investigate the biomechanics and visceroperception of the rectal wall in patients with RI.

METHODS

Twenty consecutive patients (12 females, median age 46 yr (range 24-66)) with symptomatic, full-thickness RI were studied. Patients underwent assessment of rectal compliance, visceroperception, adaptive response to isobaric distension at urge threshold, and assessment of the postprandial response. Results were compared with those obtained in 28 asymptomatic volunteers, 10 with RI (6 females, median age 29 yr (range 21-36)) and 18 (9 females, median age 33 yr (range 21-62)) without.

RESULTS

In the absence of the clinical finding of solitary rectal ulcer syndrome (SRUS), patients with symptomatic RI have normal rectal wall biomechanics, as do asymptomatic volunteers with RI (p < 0.05). Patients with the clinical finding of SRUS had reduced compliance and adaptation. In all three groups, there was a linear relationship between rectal pressure and visceroperception. The postprandial contractile response was similar between groups.

CONCLUSIONS

Patients with RI have normal rectal wall biomechanics. This is in contrast to patients with RP, and suggests that while they may represent different stages of the same disease process, they are physiologically distinct. In patients with RI and SRUS, rectal wall inflammation and fibrosis, perhaps arising secondary to the intussusception, may explain the physiological changes observed.

Stimulation of defecation: effects of coffee use and nicotine on rectal tone and visceral sensitivity

OBJECTIVE

Coffee and cigarette use is believed to induce bowel movements, although the literature is controversial and precise measurements of rectal tone and sensitivity with a barostat have never been performed. The aim of this study was to assess the effects of coffee and nicotine on rectal tone, compliance and sensitivity.

MATERIALS AND METHODS

Sixteen healthy volunteers were recruited for the coffee (n = 8) and nicotine (n = 8) experiments. The experiments were randomly performed in a placebo-controlled crossover design on separate days. In the coffee experiment, 280 ml strong coffee or warm water was drunk and in the nicotine experiment, nicotine (2 mg) or placebo was given sublingually. A rectal barostat procedure was carried out. A flaccid bag, mounted on a catheter, was inserted in the rectum. Continuous pressure distension was exerted to register basal visceral sensitivity and compliance. After rectal adaptation, the stimulus was given. Rectal tone was measured for 1 h, after which continuous pressure distension was repeated.

RESULTS

Rectal tone increased by 45% 30 min after coffee intake (p = 0.031) and by 30% after water intake (p = 0.032), but the effects of coffee and water were not significantly different. Rectal tone did not change significantly after administration of nicotine (7%) or placebo (10%). There was no difference in compliance and visceral sensitivity between coffee and water or nicotine and placebo.

CONCLUSIONS

Both coffee and warm water have an effect on defecation by increasing rectal tone, but nicotine (2 mg) did not affect rectal tone. Coffee and nicotine did not influence sensitivity or compliance.

Characteristics of rectal perception are altered in irritable bowel syndrome

A hallmark symptom of irritable bowel syndrome (IBS) is a lower pain threshold during rectal distension, but the mechanism underlying this disorder remains unclear. Examining the relationship between physiological and perceptual responses to rectal distension can provide insight into the underlying peripheral or central dysfunction in IBS. Therefore, we carried out a study of the rectal sensations of urge to defecate, pain and unpleasantness in relation to the varying states of the rectum. Ten IBS patients and 13 healthy controls underwent six sets of isobaric rectal distensions. The first set was ascending stepwise distensions terminating upon report of moderate pain where verbal ratings of urge, pain, and unpleasantness were acquired. The remaining sets were phasic or tonic distensions at a single pressure eliciting either moderate urge or moderate pain intensity where subjects gave continuous ratings of urge or pain percepts. The McGill Pain Questionnaire (MPQ) was used to assess different qualities of the pain experience during single pressure distensions. Abnormalities in IBS patients included: (1) higher incidence of distensions where unpleasantness is greater than pain intensity, (2) significantly longer persistence of ratings after stimulus termination during phasic distensions eliciting either moderate urge or moderate pain, (3) significantly smaller ratings fluctuations during tonic distensions, and (4) significantly higher MPQ scores for painful tonic distensions. Our study demonstrates that IBS patients have abnormal temporal and intensity properties of rectal sensation. These can be accounted for by either altered peripheral neuromuscular processing and/or processing of ascending rectal input in the central nervous system.

Influence of continuous isobaric rectal distension on gastric emptying and small bowel transit in young healthy women

Patients with slow transit constipation frequently have delayed gastric emptying. In animals rectal distensions inhibit gastrointestinal motility. In healthy volunteers isovolumetric rectal distensions delay upper gut transit. The purpose of this study was to determine the effect of continuous isobaric rectal distension on gastric emptying and oro-cecal transit in young females. Using validated 13C octanoic and lactose-[13C] ureide breath tests gastric half-emptying time and oro-cecal transit time for a meal were measured in 12 volunteers. The tests were repeated in randomized order: during isobaric balloon distension and during sham distension. Isobaric rectal distension was applied using a polyethylene bag connected to a barostat. Intraballoon pressure was kept just below the threshold for the urge sensation. Mean gastric half-emptying time during rectal distension (92.3 +/-5.1 min) was significantly higher than during sham distension (78.8 +/- 4 min; P = 0.015). Mean oro-cecal transit time during rectal distension (391.3 +/-29.1 min) and sham distension (328.8 +/- 38.4 min) were not significantly different. In conclusion, these findings indicate that isobaric rectal distension inhibits gastric emptying, but not small bowel transit in young healthy women. Studies in patients with constipation are indicated.

The effect of motilin on the rectum in healthy volunteers

AIMS

The role of motilin in the regulation of upper gastrointestinal (GI) motility is well defined. However, little is known about the effects on the distal GI tract. To investigate the effect of exogenous motilin on rectal function, barostat measurements in the rectum were performed and lower abdominal symptoms were scored.

METHODS

Eight fasted, healthy volunteers were infused intravenously with synthetic motilin or placebo over 90 min in a double-blind, randomized, cross-over design. Rectum volume was measured with a barostat device during constant pressure and during isobaric distensions. Lower abdominal symptoms were scored by visual analogue scales. Plasma motilin concentrations were measured by radioimmunoassay.

RESULTS

Baseline rectum volumes were similar between treatments: 185 +/- 62 mL (motilin) and 136 +/- 41 mL (placebo). During the constant pressure procedure, motilin increased rectum volume [area under the effect curve (AUEC)] by 6%[95% confidence interval (CI) -3, 16] of baseline, compared with placebo. During isobaric distensions motilin increased rectum volume (AUEC) by 43 mL (95% CI 0.4, 85; P < 0.05) and compliance by 10 mL mmHg-1 (95% CI 0.3, 20; P < 0.05) relative to placebo. Motilin did not induce changes in the sensation of rectal feelings.

CONCLUSION

Exogenous motilin increased rectal compliance in healthy volunteers, without affecting rectal sensations.

The relationship between rectal pain, unpleasantness, and urge to defecate in normal subjects

Rectal stimulation under normal or pathological conditions evokes numerous sensations. Previous studies have examined rectal stimulation-evoked pain and urge to defecate, but discrepancies in the findings remain because of the different methodologies used in each study and the reporting of sensations only at the end of or after the applied stimuli. Therefore, we conducted a psychophysical study of various aspects of rectal sensation in normal subjects using a variety of distension stimuli and continuous on-line rating of sensation. Ten normal healthy subjects (eight female and two male) were given rectal distension stimuli delivered by a computer-driven barostat. For some experiments, sensation was continuously monitored and rated on a visual analog scale. Subjects first underwent an ascending series of phasic (30 s) distensions to determine how urge, unpleasantness, and pain intensity varied and interrelated as rectal volume and pressure changed. A second series of distensions examined rectal physiology and perception during short phasic (30 s) or long (300 s) distensions at pressures that elicit either moderate urge or moderate pain and while continuously rating these sensations. The McGill Pain Questionnaire was used to assess the multidimensional aspects of rectal pain with each type of distension. The results of the ascending series revealed significant relationships between sensations as pressure and volume increased. The ratings of urge were double that of pain and unpleasantness, whereas unpleasantness and pain ratings were comparable. Isobaric phasic and tonic distensions were associated with an increase in volume (i.e. accommodation) with time. The magnitude of urge with repetitive short isobaric (30 s) distensions was overall not related to the slight increase in rectal volume, while phasic distensions at moderate pain intensity revealed a significant overall relationship between rectal volume and both unpleasantness and pain intensity. Long isobaric distensions evoked sensations that varied over time despite progressive increases in volume, but less variation in sensation was observed during short phasic distensions which also demonstrated a similar increase in rectal volume. Differences in temporal characteristics of sensations evoked by low-pressure distensions eliciting moderate urge versus high-pressure distensions eliciting moderate pain were illustrated by a significantly longer delay to the diminution of non-painful urge versus pain. Therefore, we conclude (1) Differences in the discrimination and the temporal characteristics of urge at subpainful rectal pressures and of pain at noxious pressures suggest that noxious and non-noxious stimuli are processed differently. (2) The overall unpleasantness and pain correlate with rectal volume during accommodation. However, instantaneous evoked sensations can vary independent of volume changes during constant pressure distension. (3) The reported sensation-related responses to tension and stretch will likely be different depending on the degree of accommodation that is occurring. Moreover, the peripheral receptor mechanisms which contribute to controlling this accommodation will also affect the perception of rectal stimuli. (4) Continuous ratings of rectal sensations are valuable in investigating rectal physiology and the multidimensional nature of rectal symptoms.

Rectal visceral sensitivity in healthy volunteers: influences of gender, age and methods

The barostat is a device that maintains a constant pressure within an air-filled polyethylene bag by means of a feedback mechanism. The system measures variations in rectal tone by recording changes in the intrarectal pressure and volume. Different procedures, such as ramp distension or intermittent distension, are used to test visceral sensitivity and rectal wall compliance. It is not quite clear which method is preferable and how the barostat measurements compare with those of the conventional latex balloon. In 28 healthy volunteers (11 males, mean age 36, range 22-67 years) rectal distension was performed in two ways: 1 Pressure-controlled distension, by both intermittent and ramp methods, with measurement on the Visual Analogue Scale (VAS, 0-5) at 8, 12, 16, 20, 24, 28, 32 and 36 mmHg. Hysteresis (comparing area under the curve during deflation and inflation with ramp pressure distension) and compliance were calculated. 2 Volume-controlled distension, with registration of first sensation, urge to defecate and maximal tolerated distension. This procedure was compared to conventional water-filled latex balloon distension. No differences were found between intermittent and ramp distension comparing VAS scores at the same pressures. Gender or age did not affect the VAS score. Males had larger volumes at the same pressures than females. Females had larger hysteresis than males. Older females had larger hysteresis than younger females. The pressure volume curves were S-shaped. Compliance at maximal tolerated distension (V/p) and maximal dynamic compliance (Delta V/Delta p) was higher in males than females. The polyethylene bag had higher MTV and MTP compared to the latex balloon. In conclusion, no differences were found in volumes, compliance or VAS between the intermittent and the ramp pressure-controlled inflation, indicating potential for simplification of the procedure. Males had larger rectal volumes and compliances; females had more pronounced hysteresis. A systemic difference was found between distension with the water-filled latex balloon and with the air-filled polyethylene bag. This should be taken into account when interpreting results.

The role of the barostat in human research and clinical practice

BACKGROUND

The barostat is a recently developed device used to study the physiology and pathophysiology of the motor and sensory functions of the gastrointestinal tract. It can monitor volume changes while maintaining a set constant pressure and deliver controlled distensions of gastrointestinal organs. Simultaneously, motility and visceral perception may be assessed. The barostat has contributed to the understanding of physiological processes in the gastrointestinal tract with regard to regulation of tone, compliance, enteric reflexes, sensation and processing of signals to and from the gut. In addition, the barostat has been used to study various gastrointestinal disorders. In functional bowel disorders, objective abnormalities in visceral sensitivity and enteric reflexes have been demonstrated. Numerous other diseases, gastrointestinal in origin as well as systemic diseases affecting the gut, have been studied. In the near future, the barostat may become a clinically useful tool for the objective diagnosis of motor and sensitivity disorders of the gut and for monitoring the effectiveness of therapy.

Rectal tone, distensibility, and perception: reproducibility and response to different distensions

Increasing interest is focusing on the role of intestinal tone, distensibility, and mechanosensation in the genesis of abdominal symptoms. Experimental approaches usually feature balloon distension of the bowel with measurements of perception, tone, and compliance and/or elastance; however, the methodologies are standardized incompletely. We examined the reproducibility of repeated assessments of sensory perception, basal tone, and compliance and/or elastance of the rectum during distension. We also evaluated the response to inflations that varied in regard to control of pressure or volume, pattern of distension, and rate of inflation. Five healthy volunteers were studied under two separate protocols. The first featured a series of experiments on each of 5 days; the other consisted of 2 separate days of study. Repeated distensions evoked reproducible responses of sensation and compliance and/or elastance on a single day, providing a conditioning distension preceded them. Day-to-day variability was also sufficiently small to allow valid comparisons to be made on different days in healthy persons. The configuration of the distension profile (phasic, staircase, or ramp) and the rate of inflation (from 1 to 40 ml/s) had little effect on distensibility or perception. Perceptions were sometimes transient and sometimes constant, but no relationship was found between these temporal features and the magnitude of the stimulus. These observations help provide a basis as to how the responses to rectal distension can be best studied.