News and Views from the 16^th International Symposium

on Gastrointestinal Motility

H. Nathan and co-workers in J. Dents group have developed a Laser Doppler Velocimeter for the measurement of intraluminal flow and they have validated this technique against video fluoroscopy in the oesophagus of 7 healthy volunteers. The probe tip of the Laser Doppler was inserted in a 23 lumen manometric assembly allowing concurrent pressure recording. They claim a temporal resolution well below 1 sec and state that this is vital to understand the mechanical significance of intraluminal pressure waves. In the human oesophagus, they found a high intersubject variability in intraluminal flow between swallows and between the lower and upper part of the organ.

Another methodological advance was reported by DB Balaban et al. in Virginia, USA where they used the combination of pH-metry, manometry and high-frequency ultrasonography to monitor for 24 hrs the oesophageal wall-layers and thickness in 10 patients with non-cardial chest pain and 10 additional subjects. This scanning method, using a 12,5 MHz transducer with a diameter of 2 mm appears to be a further refinement of the method reported by Taniguchi and co-workers. In the present study, a unique oesophageal motor pattern (sustained contraction) appeared to be the motor correlate of both spontaneous and induced oesophageal chest pain. Sustained oesophageal contractions was detected by ultrasonography but not by pressure recordings.

Measurement of wall tension in the gut emerges as a more significant measure to obtain compared to pressure-volume and compliance recordings. Tension in tubular organs is a measure of the force the wall is subjected to in circumferential direction, and can be estimated using LaPlace`s law. Mechanoreceptors seem to respond directly not to changes in pressure or volume but rather to changes in tension or strain. The Tensostat developed by the Barcelona-group has now got competition from the computer-controlled Tensiometer developed by H Gregersen and co-workers. The Tensiometer consists of a balloon probe, an impedance planimeter for measurement of cross-sectional area, pressure transducer and amplifier, a peristaltic pump, AD-converter, and a PC with dedicated software. They presented results from in vitro evaluation and real-time measurement of tension in the human oesophagus.

Regarding measurement of tension, there was an interesting work by L Lepionka and CH Malbert where they aimed at quantifying "tension"-receptor characteristics in vivo in anaesthetized pigs during isovolumetric, isobaric, and isotension distensions. Although gastric mechanoreceptors respond clearly to distension, the essential stimuli for these receptors have not been properly defined. They concluded that circumferential tension is not the essential stimuli for fundic "tension"-receptors, and suggest that circumferential strain might be important to activate these receptors.

The term allodynia means perception of pain by a stimuli that previously was non-painful. Primary allodynia occurs when pain is provoked at the site of the injured tissue and secondary allodynia describes pain that is provoked form the surrounding non-injured tissue. S Sarkar and co-workers aimed at demonstrating that secondary allodynia can be induced in the healthy human oesophagus by showing a reduction in pain thresholds proximal to the site of acidification. They found that acidification of the lower oesophagus caused a reduction in pain thresholds both in the lower and upper oesophagus which is consistent with the development of primary and secondary allodynia. They claim that this finding suggests a contribution of central sensitization to visceral hypersensitivity in man.

Based on studies in animals, it is commonly believed that postprandial gastric emptying of non-digestible solids occurs mainly related to the antral phase III when all other gastric contents are emptied. PO Stotzer and co-workers from Sahlgrenska Hospital studied 6 healthy volunteers with manometry and fluoroscopically monitoring of radioopaque markers (1 and 3 mm sizes). They concluded that, contrary to current concepts, gastric emptying of non-digestible solids after a meal occurs unrelated to antral phase III, at least up to a particle size of 3 mm.

J Tack and J Janssens groups in Leuven is engaged in studying the importance of accommodation and pain thresholds in the proximal stomach and presented several studies on this symposium. In one study, they concluded that ingested volume rather than caloric content of a meal is a major determinant of meal-induced satiety in healthy subjects. In patients with functional dyspepsia, they reported that impaired postprandial accommodation of the proximal stomach was present in 19 out of 41 patients. The patients with and without impaired accommodation did not differ in perception or discomfort threshold during gastric distension. They also found that impaired accommodation in functional dyspepsia was associated with symptoms of early satiety and weight loss. In another study, they hypothesized that the impaired accommodation in these dyspeptic patients could also contribute to symptoms in the late postprandial or interdigestive period by enhancing the sensitivity to distension. In 8 of 18 patients impaired accommodation of the proximal stomach after a meal was demonstrated, and these patients experienced discomfort at lower pressure and volume levels when distension was performed 1 hr after the meal compared to those patients who had normal accommodation. They concluded that impaired gastric meal accommodation not only give rise to symptoms in the early postprandial phase but also may contribute to symptom induction in the interdigestive phase. This group has previously presented works on the 5-HT₁ receptor agonist sumatriptan in functional dyspepsia. This time they presented data that indicated that sumatriptan maintains the postprandial increase in transient lower oesophageal sphincter relaxations (TLOSR) and the amount of acid reflux in healthy subjects. They also investigated the effect of another 5-HT₁ receptor agonist, buspirone (5, 10, and 20 mg perorally), on gastric emptying in healthy subjects. They found that buspirone at a high dose profoundly delayed gastric emptying of both liquids and solids and induced a lag phase for liquid emptying, thus confirming previous results using sumatriptan. At lower doses, gastric emptying remained unaffected by buspirone indicating that lower doses should be preferred if used in patients with functional dyspepsia.

RM Stern and co-workers from Pennsylvania used slow diaphragmatic breathing (SDB), previously shown to increase parasympathetic nervous system activity, to investigate its effect on gastric dysrhythmias and symptoms of motion sickness induced by a rotating optokinetic drum. They found that SDB in a situation previously demonstrated to provoke tachygastria, prevented the development of gastric dysrhythmias and decreased symptoms of motion sickness.

M Vu et al. from Leiden evaluated proximal gastric motility using an electronic barostat in 12 patients after successful laparoscopic Nissen funduplicatio due to GERD, 12 patients with GERD (endoscopic oesophagitis I-III), and 12 healthy controls. They found that minimal distending pressure and fasting fundus compliance was similar in the 3 groups. However, postprandial relaxation was significantly reduced in Nissen-operated patients compared to both GERD-patients and controls. The duration of postprandial fundus relaxation was shorter (30 min) in Nissen-operated patients compared to controls (70 min). Interestingly, it was prolonged (>90 min) in patients with GERD.