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• W2056922969 abstract "Perhaps because the oesophagus is relatively accessible and often a source of unexplained discomfort, several new techniques to assess gastrointestinal sensori-motor functions have been initially tested in the oesophagus. Continuing that tradition, this issue of the Journal contains a description of a sophisticated device that incorporates manometric sensors, an ultrasound probe, and a laser Doppler probe for use within the oesophagus.1 Conceptually, it is useful to consider the four physiological domains which can be assessed in the oesophagus by the available techniques. The first domain pertains to propagation of contractions (i.e. peristalsis) and bolus transit, made possible by manometry, as in this device, and intraluminal impedance testing respectively. The second domain is perception, which can be measured by distending an oesophageal balloon with a barostat or by impedance planimetry. A barostat can simultaneously measure pressure–volume relationships, while impedance planimetry can also measure luminal cross-sectional area. The third domain is wall thickness, which can be measured by intra-luminal ultrasound but not by impedance planimetry. Measurements of wall thickness are necessary to calculate stress (stress ≅ tension/wall thickness) and are particularly useful for the oesophagus, because it is not a thin viscus. In addition, ultrasound can also separately assess muscle shortening in the longitudinal and circular layers.2 This device also measures a fourth domain, i.e. visceral blood flow, by laser Doppler flowmetry. Measurements of visceral blood flow have not previously been combined with assessments of gastrointestinal sensori-motor functions. Manometry is extremely useful for identifying peristaltic dysfunction.3 In the oesophagus, the concurrent assessment of two or more domains has substantially enhanced our understanding of normal and disordered functions. Perhaps the most striking example is concurrent videofluoroscopy and manometry, which has provided substantial insights into normal and disordered functions in the oropharynx, oesophageal body and lower oesophageal sphincter.3, 4 Oesophageal flow can also be related to manometric pressure profiles by combined impedance manometry, which revealed functional differences between the proximal and distal oesophagus.5 The addition of impedance to ambulatory pH studies has fostered increased awareness of non-acid reflux.6 By providing a combined assessment of oesophageal biomechanics and sensation, impedance planimetry and intraluminal ultrasound have revealed features suggestive of a disordered oesophageal contractility in non-cardiac chest pain and motor disorders such as nutcracker oesophagus. Thus, Rao et al. used impedance planimetry to demonstrate that during oesophageal distention, the oesophagus was hyperreactive, stiffer (i.e. less compliant) and hypersensitive in patients with atypical chest pain.7 Intraluminal ultrasound has the unique ability to measure thickness of the entire wall, longitudinal and circular smooth muscle thickness and contraction.2 Circular muscle contraction is manifest as changes in luminal calibre, which can be measured directly by impedance planimetry or ultrasound, or indirectly by manometry. Assuming that tissue mass and volume remain constant, oesophageal shortening (reflecting contraction of longitudinal muscle) is associated with a proportional increase in cross-sectional area (i.e. the sum of the areas occupied by the lumen and the wall). Ultrasound-based observations reveal that circular and longitudinal muscle contract synchronously during peristalsis and that the oesophageal musculature is thickened in oesophageal motor disorders.2 These changes are most pronounced in achalasia, intermediate for diffuse oesophageal spasm and least pronounced for nutcracker oesophagus, consistent with the hypothesis that muscle hypertrophy is responsible for the motor disorder. During oesophageal distention, assessments of intra-bag pressure and luminal dimensions have also provided some insights into the mechanisms of normal and abnormal oesophageal perception of balloon distention. Despite several studies, there is no consensus on the precise stimulus (i.e. stretch, pressure or tension/strain) responsible for normal perception of distention. Using intraluminal ultrasound, Mittal et al. reported that a sustained, isolated contraction of longitudinal muscle was associated with 67% of chest pain episodes in patients with atypical chest pain.2 Interestingly, heartburn induced by acid infusion was also associated with similar sustained oesophageal contractions.8 The significance and mechanisms of these findings are the subject of ongoing research. In humans, measurement of gastrointestinal mucosal blood flow by laser Doppler flowmetry has been primarily driven by the concept that insufficient mucosal blood flow during sepsis or haemodynamic stress (e.g. shock, cardiopulmonary bypass) may provoke gut mucosal barrier dysfunction, resulting in bacterial translocation and multiple organ failure. The rationale for measuring oesophageal mucosal blood flow is not obvious because the organ receives a rich dual blood supply and is relatively unaffected by ischaemia. Moreover, relatively severe ischaemia is required to disrupt intestinal motility in animal models.9 It is possible that the device described by Hoff et al. will allow new questions to be answered. For example, Mittal has speculated that a sustained contraction of longitudinal muscle can cause ischaemia of the oesophageal wall and thereby cause oesophageal symptoms.2 Measurements of rectal mucosal blood flow have been used as a surrogate marker of autonomic innervation.10 Measurements of mucosal blood flow may also provide a way to investigate the hypothesis that irritable bowel syndrome is associated with an increased risk of ischaemic colitis.11 Limited data from the study by Hoff et al. suggest that the laser Doppler flowmetry signal declined rather precipitously when the balloon was distended, above a threshold distending pressure of 30 mmHg in one pig and 90 mmHg in another pig. Hoff et al. appropriately emphasize the limitations of laser Doppler flowmetry. Because blood flow is measured in arbitrary units rather than in absolute values and because blood flow can be influenced by a variety of factors (e.g. blood pressure, pressure at site of apposition of the probe to the mucosa), the data are more useful for measuring changes in blood flow in response to interventions during a study, rather than for comparisons between subjects or studies. It is also critical that the degree of apposition between the laser Doppler probe transducer and the mucosa be constant during balloon distention. Another limitation is that the laser Doppler flowmetry probe used in this study assessed perfusion of a localized part of the mucosa rather than the entire mucosal surface or the oesophageal wall. Lastly, the challenges of data analysis and identifying artefact when multiple measurements are being made simultaneously cannot be overemphasized. In general, the shift towards multimodal assessments exemplifies the challenges of understanding oesophageal functions and dysfunctions in an integrated manner. However, at present, it is unclear whether the device described by Hoff et al. will lead to important discoveries, or whether it will merely be utilized to make observations of questionable significance to our understanding of the mechanisms of the disease. The challenge for the clinician-investigator is to exploit the strength of these relatively non-invasive devices and recognize their limitations while conducting studies that fundamentally enhance our understanding of gastrointestinal sensori-motor functions in humans. To paraphrase Socrates, the challenge is to ‘observe objects with the eyes’ while not ‘trying to comprehend them with each of the other senses’; information overload runs the risk of ‘blinding the soul’! The author is supported by grants RO1-HD-41129 and RO1-DK 68055 from the National Institutes of Health. The author is grateful to Drs M. Camilleri and J. A. Murray for reviewing this editorial." @default.
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• W2056922969 date "2006-03-01" @default.
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• W2056922969 title "Dissecting oesophageal sensori-motor functions: the fourth domain" @default.
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• W2056922969 doi "https://doi.org/10.1111/j.1365-2982.2006.00766.x" @default.
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