Barostat and Other Sensitivity Tests

Fig. 13.1
Schematic diagram of a barostat and catheter

Because visceral sensitivity relies on wall pressure and not on volume of the organ [1, 2], sensory thresholds should be expressed as pressure. Moreover, reproducibility of pressure measurements between laboratories and between subjects is better than volumes because the pressure scale compensates for differences in bag shape, smooth muscle compliance, and contractile activity of the organs [3].


Technical recommendations for measurements of sensory threshold and compliance have been published in adults, and the general principles apply to practice in children [3]. However, sensory threshold assessment requires an adequate cooperation for the report of the sensations and feelings by the subject. Children younger than 7–8 years may not be able to relate adequately their sensations during the procedure. Explanation on equipment and sequence of the procedure must be given to the child and the parents. Because psychological state modulation results in changed sensation at a given stimulus in healthy adult subjects [4], environment and sequence of the barostat study should be as quiet as possible in order to minimize the external influences and standardize the procedure.

For rectal sensitivity studies in children, most authors do not clean extensively the colon but rather suggest to the child to go to the bathroom before the study. For study compliance in children with constipation, cleansing of the rectum with enema should be conducted the day before the barostat study. Because meal may interfere with colonic and gastric tone, a 4–6-h fasting period prior to the study is recommended. All medications affecting pain or gastrointestinal motility should be discontinued at least 48 h prior to the barostat procedure.

For rectal studies, the patient lies in the left lateral position and the catheter is gently inserted into the rectum. For gastric studies, the catheter is inserted by mouth. The catheter is secured with a tape and 5–10 min is allowed for adaptation before beginning the procedure. The barostat bag is then slowly inflated with 30 mL of air and the pressure is allowed to equilibrate for 3 min. The average bag pressure during the last 15 s defines the individual operating pressure (IOP) also called the minimal distending pressure (MDP) which is the minimum pressure required to overcome mechanical forces and inflate the bag with 30 mL of air.

Various distension protocols have been described [3]. In children, the ascending method of limits (AML) without [57] or with [813] tracking has been the most applied. In the AML, the barostat is programmed to deliver phasic intermittent stimuli starting at the IOP progressively increased in 2–4 mmHg steps lasting 60 s followed by 60 s deflation. When the first sensation of pain is reported, the study can be stopped (the sensory threshold is determined) or can be prolonged (tracking) by subsequent distensions randomly adjusted up or down depending on the response of the previous distension (if the subject reports pain, the next distension will be decreased or kept the same; if the subject reports no pain, the next distension will be increased or kept the same). The threshold is determined by averaging the pressures at which pain had been indicated after a series of measures (usually three) (Fig. 13.2). A four- to five-point scale [6, 10] is used as a verbal descriptor for sensation felt during the barostat procedure. The AML is vulnerable to psychological biases (fear of pain) because the stimuli are predictable to the subject. The tracking technique is believed to be more reliable because it is less vulnerable to psychological bias (the stimuli is unpredictable) and because there are multiple determinations of the threshold. On the other hand, the tracking technique necessitates delivering multiple painful stimuli that can be less acceptable in children. However, the tracking method has been used successfully without any adverse event by several pediatric groups [813]. Of note the majority of children tested report that the pain sensation felt during the barostat is notably lower than the pain felt in the real life.


Fig. 13.2
Ascending method of limits with tracking. Rectal barostat tracing in an 11-year-old girl with irritable bowel syndrome (IBS). Verbal scale: (1) gas or first sensation, (2) need to go to the bathroom, (3) urge to go to the bathroom, (4) pain


Sensory Thresholds

The visceral sensory threshold can be separated into two components: the perceptual sensitivity (the ability to detect intraluminal distension) and the response bias (how the sensation is reported). The perceptual sensitivity allows to discriminate between two distensions and reflects the ability of the organ to detect and transduce the stimulus to the central nervous system. The response bias (or perceptual response) is the reporting behavior (intensity, painfulness) that is a cognitive process influenced by past experience and psychological state. Actually, the tools currently used (distending protocols, methods for reporting subjects’ response) are not able to accurately measure separately the two components. Adult studies have shown that the threshold measurement is responsive to changing environments or perturbations and psychological modulation results in changed sensation at a given stimulus in healthy subjects [4]. In children, there are few data regarding the influence of psychological state or trait on sensory threshold assessment. One pediatric study found that rectal sensory threshold did not correlate with the state of anxiety, suggesting that the anxiety generated by the procedure itself is not sufficient to bias the child’s response to distension [10]. However, visceral sensitivity study should be conducted in a neutral and quiet environment in order to avoid any external interference with the measurements. Results can be expressed as sensory thresholds, i.e., the first pressure that triggers a given sensation (urge to defecate, pain), or in intensity of sensation triggered by stimuli at fixed pressure.


The compliance reflects the ability of a hollow organ to adapt to an imposed distension. It is expressed in mL/mmHg. It is defined as the pressure-volume relationship which sigmoid shape is composed of an initial reflex relaxation followed by a linear section and a final plateau phase. Practically, compliance is calculated according to a nonlinear model fitting the pressure-volume curves. Pressure-volume curves are constructed with average computed volumes during each consecutive pressure step (when equilibration of the volume is reached, typically after 30–45 s). Compliance is calculated as the maximum slope of the pressure-volume curves (Fig. 13.3) [3, 9, 12, 1418]. Normal pediatric values have been published for rectal compliance (22 healthy volunteers 12 ± 2.6 years, 16 mL/mmHg, 12–20 [16]; ten control children mean age 13.7 years, 8.7 mL/mmHg, 6.0–14 [12]). Alteration of gastric compliance has been reported in eight children after Nissen fundoplication [17, 1921].


Fig. 13.3
Normal relationship volume-pressure (compliance = 9.1 mL/mmHg) in the rectum of a 12-year-old IBS patient. The sigmoid curve is composed of an initial reflex relaxation (A) followed by a linear section (B) and a final plateau phase (C). Compliance is calculated as the maximum slope of the curve in the linear section (B)

Tone and Accommodation

The volume of air entering or withdrawn from the balloon is an indirect measurement of tone of the organ. Changes in volume in response to a meal (accommodation) can thus be easily measured by subtracting preprandial to postprandial balloon volumes. Rectal volume response to feeding (decrease of 25 ± 3 % from 88 ± 8 mL before the meal to 66 ± 7 mL after the meal) has been reported in healthy children [6]. In the stomach, no data have been reported in children but in young adults [18].

Qualitative and Quantitative Assessment of the Sensations

Sensations elicited during the barostat, painful or not, must be rated (intensity) and qualitatively reported. Visual analog scale can be used by children aged 6–7 years to rate sensations such as urgency or pain [9, 11, 12] and is easier to use than verbal descriptors in this population. Rating separately pain from unpleasantness is difficult in children. Qualitative evaluation of the pain has been conducted by using validated human body diagrams [10, 22] and questionnaire related to the similarity of the induced pain and the typical pain felt in the real life [9, 13].

Clinical Relevance of Barostat Measurements

Pain-Associated Functional Gastrointestinal Disorders

Rectal Sensitivity Measurement

Using rectal barostat, several independent groups have reported that 75–100 % of children with IBS have rectal hypersensitivity as compared to control children [6, 810, 13]. In adults affected by IBS, the prevalence of visceral hypersensitivity varies from 20 % [23] to 94 % [24] across studies suggesting that rectal hypersensitivity is a more reliable diagnostic marker of IBS in children than in adults. This has been confirmed in a prospective study that included children with abdominal pain for whom rectal sensory threshold was measured prior to any other diagnostic procedures [9]. In the 51 children included, rectal sensory threshold was lower in the FGID group than in the organic disease group (25.4 mmHg vs. 37.1 mmHg; P = 0.0002), and 77 % of the children with FGID had a rectal hypersensitivity. At the cutoff of 30 mmHg, the RSTP measurement for the diagnosis of FGID had a sensitivity of 94 % and a specificity of 77 %. Rectal compliance has not been found different in IBS and control subjects [6, 8, 9, 11, 13]. Children with functional dyspepsia have normal rectal sensitivity suggesting that visceral hypersensitivity is organ specific [10].

Data regarding visceral sensitivity in children with functional abdominal pain (FAP) according to Rome criteria are less clear with discrepancies (sensory threshold similar to controls [6] or similar to IBS [10]) between authors.

Gastric Sensitivity Measurement

Because of the invasiveness of gastric barostat, the pathophysiology of functional dyspepsia (FD) has been scarcely studied in children. A subset of children with recurrent abdominal pain studied by gastric barostat using a latex balloon were reported to present hypersensitivity at the gastric level [13]. More recently, 16 dyspeptic children were extensively studied using gastric barostat [18]. Compliance was similar between patients and controls (69.5 ± 8.9 mL/mmHg). Pressures at the discomfort threshold were significantly lower in dyspeptic children compared with young healthy controls. Accommodation to a meal was significantly lower in dyspeptic children. Hypersensitivity to gastric distension was present in 56 % (9/16) of patients and impaired accommodation in 11 patients (69 %). When studied by gastric barostat, children with IBS have normal gastric sensitivity [13].

Somatic Projections and Reproducibility of the Visceral Pain

Somatic referral induced by rectal distension differs in IBS, FAP, and FD children. In normal children without any gastrointestinal complaints and in dyspeptic patients, rectal distension-induced sensations refer to the S3 dermatome (perineal area). In IBS and FAP, children refer their sensation to aberrant sites compared to the controls, i.e., with abdominal projections to dermatomes T8 to L1 [10]. However, similar results have been obtained in barostat study of children with organic diseases suggesting that subjects with protracted complaints of abdominal pain not related to FGID may have in contrast to “true” controls an abnormal perceptual response to distension (i.e., abnormal interpretation and sensation in response to rectal distension) [9]. The reproduction of pain during rectal distension is frequent in IBS and FAP children but is not predictive of a diagnosis of FGID as compared to organic diseases [9].

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Aug 29, 2017 | Posted by in GASTROENTEROLOGY | Comments Off on Barostat and Other Sensitivity Tests

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