Basal Pressure Variations Induced by a Turbulent Flow Over a Wavy Surface

Turbulent flows over wavy surfaces give rise to the formation of ripples, dunes and other natural bedforms. To predict how much sediment these flows transport, research has focused mainly on basal shear stress, which peaks upstream of the highest topography, and has largely ignored the corresponding pressure variations. In this article, we reanalyze old literature data, as well as more recent wind tunnel results, to shed a new light on pressure induced by a turbulent flow on a sinusoidal surface. While the Bernoulli effect increases the velocity above crests and reduces it in troughs, pressure exhibits variations that lag behind the topography. We extract the in-phase and in-quadrature components from streamwise pressure profiles and compare them to hydrodynamic predictions calibrated on shear stress data.

P57 MOTILITY DISORDERS OF THE ESOPHAGUS - A RISK FACTOR FOR THE DEVELOPMENT OF BARRETT'S ESOPHAGUS?

Aim This study aims to investigate the extent to which esophageal motility affects the development and progression of Barrett's mucosa in GERD patients. Background and Methods The Barret´s esophagus is becoming even more important against the background of an increasing incidence of adenocarcinoma of the esophagus1. The question as to why only a few patients with gastroesophageal reflux disease (GERD) develop a Barrett's esophagus has not been clarified. A cohort of 315 GERD patients with and without Barrett's esophagus who received High Resolution Manometry (HRM) as part of their regular diagnostics was therefore examined in this study. The evaluation of the HRM results was based on the Chicago classification version 3.02 and was compared with endoscopic and histological findings. Results Out of the 315 GERD patients, 67 had a Barrett's esophagus. The two patient groups (GERD without Barrett and GERD with Barrett) did not differ in demographic data and risk profile (hiatal hernia 71.4% vs 10.2%). In pH metry, both groups achieved a comparable DeMeester score as well as a similar fraction time (49.6 vs 44.2, 13% vs 11.7%). In both groups, approximately 40% of patients showed motility disorders. The mean basal pressure and the mean DCI also showed comparable values (21.2 vs 21.3, 1189.2 vs 1249.2). However, when comparing patients within the Barrett cohort with a long and a short segment Barrett (LSB, SSB), differences in peristalsis and pressure build-up of the distal esophagus become clear. Patients with an LSB showed a lower basal pressure of the lower esophageal sphincter (LES) and lower mean DCI (12.9 vs 25.0, 1230.0 vs 1389.3). In addition, they presented a hypotonic LES more frequently (54.6% vs 17.4%). Patients with LSB also showed motility disorders more often (54.6 vs 39.1), especially ineffective motility and fragmented peristalsis (18.2% vs 10.9%, 9.1% vs 2.2%). Conclusion The differences in motility disorders between Barrett and non-Barrett patients already described in other publications3 could not be confirmed in this study, despite the large cohort of 315 patients. However, the differences between LSB and SSB patients suggest that esophageal motility disorders can at least influence the severity of this disease.

NORMATIVE VALUES FOR A NEW WATER-PERFUSED HIGH RESOLUTION MANOMETRY SYSTEM

ABSTRACT BACKGROUND: Esophageal manometry is the most reliable method to evaluate esophageal motility. High resolution manometry (HRM) provides topographic contour colored plots (Clouse Plots) with simultaneous analysis from the pharynx to the stomach. Both solid state and water-perfused systems are available. OBJECTIVE: This study aims to determinate the normative data for a new water-perfused HRM. METHODS: HRM was made in 32 healthy volunteers after 8 hours fasting. HRM system used consisted of a 24-channel water-perfused catheter (Multiplex, Alacer Biomedica, São Paulo, Brazil). The reusable catheter is made of polyvinyl chloride (PVC) with 4.7 mm of diameter. Side holes connected to pressure transducers are spaced 2 cm for the analysis from the pharynx to the lower esophageal sphincter (LES). Holes are spaced 5 mm and 120° in a spiral disposition in the LES area. The sensors encompass 34 cm in total. Upper esophageal sphincter (UES) parameters studied were basal and relaxation pressures. Esophageal body parameters were distal contractile integral (DCI), distal latency (DL) and break. LES parameters studied were basal pressure, integrated residual pressure (IRP), total and abdominal length. Variables are expressed as mean ± standard deviation, median (interquartile range) and percentiles 5-95th. RESULTS: All volunteers (17 males, aged 22-62 years) completed the study and tolerated the HRM procedure well. Percentiles 5-95th range were calculated: Upper Esophageal Sphincter (UES) basal pressure 16.7-184.37 (mmHg), DL: 6.2-9.1 (s), DCI: 82.72-3836.61 (mmHg.s.cm), break: <7.19 (cm), LES basal pressure: 4.89-37.16 (mmHg), IRP: 0.55-15.45 (mmHg). CONCLUSION: The performance and normative values obtained for this low-cost water-perfused HRM seems to be adequate for clinical use.

Interannual variability of glacier basal pressure from a 20 year record

Basal pressure has been recorded at the Svartisen Subglacial Laboratory, northern Norway, for 20 years, and is measured by load cells installed at the ice–rock interface under ~200m of glacier ice. Synchronous pressure variations between load cells are investigated as evidence of stress redistribution and hydrological bed connectivity. A running Pearson correlation is used to study the temporal variation in the response of several sensors. By studying the nature of this correlation as well as the correlation between sensor pairs, it is possible to investigate the evolution of the degree of synchronous response, and to some extent basal connectivity, at the glacier bed. Persistent seasonal variations associated with the melt season are observed throughout the measurement period, indicating dependence on surface hydrological forcing. Overlying this pattern, specific years with longer periods of positive and negative correlation of pressure between sensors are presented to show contrasting interannual variability in basal pressure. An anticorrelated connectivity is associated with a local increase in the rate of daily subglacial discharge, and is caused by load transfer or passive cavity opening. Stable weather appears to enhance connectivity of the sensors, which is attributed to the development of a persistent drainage system and stress redistribution.

Upper esophageal sphincter resting pressure varies during esophageal manometry

BACKGROUND: The upper esophageal sphincter is composed of striated muscle. The stress of intubation and the need to inhibit dry swallows during an esophageal manometry test may lead to variations in basal pressure of this sphincter. Upper esophageal sphincter is usually only studied at the final part of the test. Was observed during the performance of high resolution manometry that sphincter pressure may vary significantly over the course of the test. AIM: To evaluate the variation of the resting pressure of the upper esophageal sphincter during high resolution manometry. METHODS: Was evaluated the variation of the basal pressure of the upper esophageal sphincter during high resolution manometry. Were reviewed the high resolution manometry tests of 36 healthy volunteers (mean age 31 years, 55% females). The basal pressure of the upper esophageal sphincter was measured at the beginning and at the end of a standard test. RESULTS: The mean time of the test was eight minutes. The basal pressure of the upper esophageal sphincter was 100 mmHg at the beginning of the test and 70 mmHg at the end (p<0.001). At the beginning, one patient had hypotonic upper esophageal sphincter and 14 hypertonic. At the end of the test, one patient had hypotonic upper esophageal sphincter (same patient as the beginning) and seven hypertonic upper esophageal sphincter. CONCLUSION: A significant variation of the basal pressure of the upper esophageal sphincter was observed in the course of high resolution manometry. Probably, the value obtained at the end of the test may be more clinically relevant.