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Pressure Analysis (pressure + analysis)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Experimental Study of a New Method for Early Detection of Vascular Access Stenoses: Pulse Pressure Analysis at Hemodialysis Needle

ARTIFICIAL ORGANS, Issue 2 2010
Koen Van Canneyt
Abstract Hemodialysis vascular access (VA) stenosis remains a frequent complication. However, early detection is challenging and costly. The aim of this in vitro study was to assess a new detection method based on pulse pressure analysis at the hemodialysis needle. A silicon model of a radiocephalic arteriovenous fistula was built in a mock loop. Pressure profiles were measured at the arterial hemodialysis needle and in the proximal feeding artery. Stenoses (50 and 25% diameter reduction) were created proximal to the anastomosis (proximal artery) and distal to the arterial needle (distal vein and proximal vein). The pulse pressure (PP) at the needle was divided by the PP at the feeding artery to obtain a dimensionless ratio, %PP. Experiments were conducted at different blood flow (500,1200 mL/min) and heart rates (60,90 beats/min) to test this new index over a wide range of hemodynamic conditions. In the control model (no stenosis), %PP was 20.26 ± 4.55. A proximal artery 50% stenosis significantly decreased %PP to 7.69 ± 2.08 (P < 0.0001), while the presence of 50% stenosis in the distal (36.20 ± 2.12) and proximal (32.38 ± 2.17) vein led to significantly higher values of %PP (P < 0.0001). For stenosis of 25% diameter reduction in the proximal artery, the %PP decreased to 15.45 ± 2.13 (P = 0.0022) and the %PP increased with a 25% stenosis in the distal vein to 26.71 ± 3.01 (P = 0.0003) and in the proximal vein to 26.53 ± 2.67 (P = 0.0004). This in vitro study shows that the analysis of the PP at the dialysis needle is useful for early detection and localization of hemodialysis VA stenosis, independent of heart rate and flow level. [source]

The use of transient pressure analysis at the Dounreay Shaft Isolation Project.

GEOMECHANICS AND TUNNELLING, Issue 5 2009
Die Verwendung der Analyse instationärer Druckentwicklung am Dounreay Schachtabdichtungsprojekt
Grouting; Innovative methods; Injektionen; Neue Verfahren Abstract This paper provides an assessment of the use of pressure fall-off data during the Dounreay Shaft Isolation Project. The instrumentation controlling the injection of grout monitors and records both the pressure and the flow rate throughout the process, so pressure fall-off data is collected during any pauses to, and at the end of, each grout injection. The shapes of the pressure fall-off vs time curves have been examined qualitatively and categorised. The fall-off data has also been examined using PanSystem well test software, which creates the pressure change and pressure derivative curves, then attempts to simulate the fall-off curve by iteration after selection of a flow and boundary model chosen from the wide range available. The implications that the shapes of the pressure and derivative curves and the flow and boundary models have for the grout curtain have been examined. The caveats that surround the quantitative use of results from Pan-System analyses for a cement grout rather than a Newtonian fluid are discussed. Diese Veröffentlichung handelt von der Beurteilung des Einsatzes und der Analyse von Daten zum Druckabfall im Zuge der Injektion am Schachtabdichtungsprojekt Dounreay, Schottland, UK. Die Instrumentation der Baustelle war darauf ausgelegt, Messwerte von Druck und Injektionsrate anzuzeigen, aufzuzeichnen und als Diagramm darzustellen. Damit war es möglich, in jeder Injektionsunterbrechung (also bei Rate = Null) und zu jedem Passenende Druckabfalldaten aufzuzeichnen. Die Form dieser Druckabfallkurven gegen die Zeit wurde qualitativ untersucht und kategorisiert. Eine weitere Interpretation dieser Daten erfolgte mittels des Programms "PanSystem". Bei dieser Methodik werden die Druckänderungen über kleine Zeitinkremente errechnet und deren Ableitung über die Zeit in Kurvenform dargestellt. Durch iterative Simulation und Eingabe von Randbedingungen ("boundaries") für das jeweilige Strömungsmodell , ausgewählt aus einer weiten Bandbreite von Möglichkeiten , ergibt sich die Möglichkeit, u. a. die Strömungsdimension, Strömungshindernisse und Reichweite der Injektion zu prognostizieren. Die daraus gezogenen Schlüsse für den Injektionsschirm wurden für die qualitative Abnahme der Arbeiten mitverwendet. In dem vorliegenden Artikel wird auch auf die möglichen Vorbehalte eingegangen, die sich aus den rheologischen Abweichungen von Injektionsmischungen gegenüber einer Newtonschen Flüssigkeit ergeben. [source]

Human duodenal phase III migrating motor complex activity is predominantly antegrade, as revealed by high-resolution manometry and colour pressure plots

NEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2002
J. M. Andrews
Abstract,Late phase III migrating motor complex activity has been said to be primarily retroperistaltic but has not been assessed with high resolution manometry or three-dimensional colour pressure plots (pressure/time/distance). Duodenal phase III was examined in healthy young volunteers (seven male, two female) with a 20-lumen assembly. With the most proximal sidehole in the distal antrum, after a 4.5-cm interval 18 sideholes at 1.5-cm intervals spanned the duodenum with a final sidehole 3 cm beyond. Fasting pressures were recorded until phase III occurred. Comparisons were made between proximal (P) and distal (D) duodenum during early (E) (first 0.5,1 min) and late (L) (last 0.5,1 min) phase III. With colour pressure analysis, 121 of 180 pressure wave (PW) sequences were purely antegrade, two purely retrograde and 57 bidirectional. Ten of fifty-seven bidirectional PW sequences were complex, branching to become two separate sequences. Bidirectional sequences occurred more frequently in late than early phase III (L 43 vs. E 14 of 57), but their occurrence did not differ between proximal and distal duodenum (P31 vs. D 24 of 57). Antegrade propagation velocity was faster in late compared with early phase III (L 28.50 vs. E 17.05 mm s,1; P = 0.006), but did not differ between proximal and distal duodenum. Colour pressure analysis also indicated an intermittent segmental pattern to phase III, with each subject exhibiting a change in velocity or direction, or a relative failure of peristalsis somewhere along the duodenum during part of phase III. Duodenal phase III is not homogenous and, in contrast with previous studies, does not primarily constitute a retroperistaltic pump. Colour pressure analysis is useful in interpreting intraluminal pressure profiles and may improve the sensitivity and specificity of clinical studies. [source]