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Journal articles on the topic 'Pressure gradients'

Author: Grafiati

Published: 4 June 2021

Last updated: 25 July 2025

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1

Wright, Stephen P., Alexander R. Opotowsky, Tayler A. Buchan, et al. "Flow-related right ventricular to pulmonary arterial pressure gradients during exercise." Cardiovascular Research 115, no. 1 (2018): 222–29. http://dx.doi.org/10.1093/cvr/cvy138.

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Abstract Aims The assumption of equivalence between right ventricular (RV) and pulmonary arterial systolic pressure is fundamental to several assessments of RV or pulmonary vascular haemodynamic function. Our aims were to (i) determine whether systolic pressure gradients develop across the RV outflow tract in healthy adults during exercise, (ii) examine the potential correlates of such gradients, and (iii) consider the effect of such gradients on calculated indices of RV function. Methods and results Healthy untrained and endurance-trained adult volunteers were studied using right-heart cathet

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Kimmel, R. L. "The Effect of Pressure Gradients on Transition Zone Length in Hypersonic Boundary Layers." Journal of Fluids Engineering 119, no. 1 (1997): 36–41. http://dx.doi.org/10.1115/1.2819115.

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Boundary layer transition was measured in zero, favorable, and adverse pressure gradients at Mach 8 using heat transfer. Models consisted of 7° half angle forecones 0.4826 m long, followed by flared or ogive aft bodies 0.5334 m long. The flares and ogives produced constant pressure gradients. For the cases examined, favorable pressure gradients delay transition and adverse pressure gradients promote transition, but transition zone lengths are shorter in favorable pressure gradient. Results of the effect of adverse pressure gradient on transition zone lengths were inconclusive.

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Fargen, Kyle M., Rebecca M. Garner, Carol Kittel, and Stacey Q. Wolfe. "A descriptive study of venous sinus pressures and gradients in patients with idiopathic intracranial hypertension." Journal of NeuroInterventional Surgery 12, no. 3 (2019): 320–25. http://dx.doi.org/10.1136/neurintsurg-2019-015251.

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ObjectiveTo determine the relationship between normal physiologic and pathologic venous sinus pressures in patients with idiopathic intracranial hypertension (IIH), which is poorly understood.MethodsRetrospective analysis was performed to identify patients with medically refractory IIH who were evaluated by angiography and retrograde venography with venous manometry. Patients were further subdivided into groups based on anatomic factors.Results104 patients met inclusion criteria for the study. In the absence of non-invasive venographic screening, 58% of patients in this series were found to ha

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Kulick, Daniel L., David T. Kawanishi, John Frierson, and Shahbudin H. Rahimtoola. "Pressure gradients." Coronary Artery Disease 1, no. 1 (1990): 51–58. http://dx.doi.org/10.1097/00019501-199001000-00008.

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Klassen, Gerald A., J. Andrew Armour, and J. Barry Garner. "Coronary circulatory pressure gradients." Canadian Journal of Physiology and Pharmacology 65, no. 4 (1987): 520–31. http://dx.doi.org/10.1139/y87-089.

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The pressure gradients of the canine coronary circulation were measured in 37 dogs during control and following eight interventions: left stellate ganglion or left vagosympathetic trunk stimulation, as well as isoproterenol, acetylcholine, noradrenaline, adenosine, phenylephrine, or adrenaline infusions. During control, pressure gradients in the epicardial coronary arteries (measured from the aorta to coronary artery branch) were 15.2 ± 1 mmHg(1 mmHg = 133.32 Pa) during systole and 10.6 ± 1.5 mmHg during diastole. Adrenaline increased this systolic gradient, while acetylcholine and phenylephri

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Konrádsson, Konrád S., Björn I. R. Carlborg, and Joseph C. Farmer. "Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure." Annals of Otology, Rhinology & Laryngology 106, no. 6 (1997): 495–502. http://dx.doi.org/10.1177/000348949710600610.

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Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels

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Corey, Kenneth A., and Zhi Yi Tan. "A MECHANISM FOR TRANSPORT OF SUBSTANCES BY TEMPERATURE-INDUCED PRESSURE GRADIENTS." HortScience 27, no. 6 (1992): 626e—626. http://dx.doi.org/10.21273/hortsci.27.6.626e.

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Diurnal changes in air and soil temperatures lead to temperature gradients between air and soil, between roots and shoots, and within plant organs. In response to these gradients, fluctuations in gas pressures may develop in organs that are resistant to exchange of gases. These fluctuations may regulate mass flow of gases or solutions within plants. Patterns of diurnal temperature changes were generated to illustrate temperature gradients between roots and shoots. Experimental confirmation of pressure changes induced by temperature differences between roots and shoots were measured with water

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VEYNANTE, DENIS, and THIERRY POINSOT. "Effects of pressure gradients on turbulent premixed flames." Journal of Fluid Mechanics 353 (December 25, 1997): 83–114. http://dx.doi.org/10.1017/s0022112097007556.

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In most practical situations, turbulent premixed flames are ducted and, accordingly, subjected to externally imposed pressure gradients. These pressure gradients may induce strong modifications of the turbulent flame structure because of buoyancy effects between heavy cold fresh and light hot burnt gases. In the present work, the influence of a constant acceleration, inducing large pressure gradients, on a premixed turbulent flame is studied using direct numerical simulations.A favourable pressure gradient, i.e. a pressure decrease from unburnt to burnt gases, is found to decrease the flame wr

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9

McDougall, Cameron M., Vin Shen Ban, Jeffrey Beecher, Lee Pride, and Babu G. Welch. "Fifty shades of gradients: does the pressure gradient in venous sinus stenting for idiopathic intracranial hypertension matter? A systematic review." Journal of Neurosurgery 130, no. 3 (2019): 999–1005. http://dx.doi.org/10.3171/2017.8.jns17459.

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OBJECTIVEThe role of venous sinus stenting (VSS) for idiopathic intracranial hypertension (IIH) is not well understood. The aim of this systematic review is to attempt to identify subsets of patients with IIH who will benefit from VSS based on the pressure gradients of their venous sinus stenosis.METHODSMEDLINE/PubMed was searched for studies reporting venous pressure gradients across the stenotic segment of the venous sinus, pre- and post-stent pressure gradients, and clinical outcomes after VSS. Findings are reported according to the PRISMA (Preferred Reporting Items for Systematic Reviews a

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Guerra, M. Mendes-Ferreira P. Adão R. Pereira E. Vieira M. Lourenço AP Brás-Silva C. Bastos P. Vouga L. Leite-Moreira AF. "Improvement in left intraventricular pressure gradients after aortic valve replacement in aortic stenosis patients." Experimental Physiology 102, no. 4 (2017): 411–21. https://doi.org/10.1113/EP086191.

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New Findings <strong>What is the central question of this study?</strong> Normal diastolic and systolic intraventricular pressure gradients are decreased when left ventricular filling and/or emptying are compromised. We hypothesized that in patients with severe aortic valve stenosis, a condition that interferes with ventricular filling and emptying, those gradients would be disturbed. <strong>What is the main finding and its importance?</strong> We showed the existence of intraventricular pressure gradients throughout the cardiac cycle in the human left ventricle. Moreover, we demonstrated, fo

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Linge, Svein O., Kent-A. Mardal, Anders Helgeland, John D. Heiss, and Victor Haughton. "Effect of craniovertebral decompression on CSF dynamics in Chiari malformation Type I studied with computational fluid dynamics." Journal of Neurosurgery: Spine 21, no. 4 (2014): 559–64. http://dx.doi.org/10.3171/2014.6.spine13950.

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Object The effect of craniovertebral decompression surgery on CSF flow dynamics in patients with Chiari malformation Type I (CM-I) has been incompletely characterized. The authors used computational fluid dynamics to calculate the effect of decompression surgery on CSF flow dynamics in the posterior fossa and upper cervical spinal canal. Methods Oscillatory flow was simulated in idealized 3D models of the normal adult and the CM-I subarachnoid spaces (both previously described) and in 3 models of CM-I post–craniovertebral decompressions. The 3 postoperative models were created from the CM mode

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Fike, C. D., and M. R. Kaplowitz. "Effect of airway and left atrial pressures on microvascular and interstitial pressures in adult lungs." Journal of Applied Physiology 74, no. 5 (1993): 2112–20. http://dx.doi.org/10.1152/jappl.1993.74.5.2112.

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The purpose of this study was to determine the effect of lung inflation and left atrial pressure on the hydrostatic pressure gradient for fluid flux across 20- to 80-microns-diam arterioles and venules in isolated perfused lungs of adult rabbits. We used the micropuncture technique and measured microvascular or interstitial pressures at constant airway pressures of 5 and 15 cmH2O with left atrial pressure adjusted above (zone 3 conditions) or below (zone 2 conditions) airway pressure. Only in lungs inflated to the higher airway pressure did a reduction in left atrial pressure below airway pres

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Robberechts, Tom, Alessandro Giudici, Jacek Kadziela, et al. "NON-INVASIVE PRESSURE GRADIENT ESTIMATION OF STENOTIC LESIONS IN RENAL MULTIFOCAL FIBROMUSCULAR DYSPLASIA: A PILOT STUDY." Journal of Hypertension 42, Suppl 1 (2024): e208-e209. http://dx.doi.org/10.1097/01.hjh.0001021568.82711.41.

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Objective: Currently, there is no validated method to assess the haemodynamic significance of renal artery stenosis in fibromuscular dysplasia (FMD) patients. A translesional pressure gradient >10 mmHg during catheter-based angiography has been proposed as a cut-off for considering angioplasty. However, for reasons of invasiveness, time, accessibility and cost, this approach is seldom used. Therefore, development of a non-invasive method to evaluate the hemodynamic impact of FMD lesions is urgently needed. Design and method: We developed a computer application to quantify FMD-related stenos

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Mei, Fu Liang, and Gui Ling Li. "Increment-Dimensional Precise Integration Method of Oil-Water Coupling Flows in a Low Permeability Reservoir with Capillary Pressure." Applied Mechanics and Materials 580-583 (July 2014): 2883–89. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.2883.

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The simulation of two-phase oil-water coupling flows in a low permeability reservoir with capillary pressure and start-up pressure gradient was carried out. First of all, the state equations with all the oil pressures at grid nodes were established based on lump-centre finite difference method. Secondly, the recurrence formulae of all the oil pressures and water saturations at grid nodes were built up according to IDPIM and an explicit difference method, respectively. Finally, the simulation of two-phase oil-water coupling flows for a typical five point area water injection as an example was c

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Shigenobu, Masaharu, and Shunji Sano. "Detection of Björk-Shiley Mitral Valve Dysfunction via Doppler Echocardiography." Asian Cardiovascular and Thoracic Annals 2, no. 2 (1994): 83–86. http://dx.doi.org/10.1177/021849239400200206.

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Fifty-eight patients with a Björk-Shiley (B-S) mitral valve were examined to study applicability of Doppler echocardiography in diagnosing and predicting the severity of prosthetic valve dysfunction. The effect of valve replacement on the hemodynamic performance at rest and during bicycle exercise was determined from serial echocardiographic data. The high pressure gradient group in which peak pressure gradients were assumed to be more than 15mmHg at rest, showed negative values of percent change in both stroke volume index (%ΔSVI) and left ventricular end-diastolic volume index (%ΔEDVI). All

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Grobler, Lindi, Ryno Laubscher, Johan van der Merwe, and Philip G. Herbst. "Evaluation of Aortic Valve Pressure Gradients for Increasing Severities of Rheumatic and Calcific Stenosis Using Empirical and Numerical Approaches." Mathematical and Computational Applications 29, no. 3 (2024): 33. http://dx.doi.org/10.3390/mca29030033.

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The evaluation and accurate diagnosis of the type and severity of aortic stenosis relies on the precision of medical imaging technology and clinical correlations and the expertise of medical professionals. The application of the clinical correlation to different aortic stenosis morphologies and severities is investigated. The manner in which numerical techniques can be used to simulate the blood flow through pathological aortic valves was analysed and compared to the ground-truth CFD model. Larger pressure gradients are estimated in all severities of rheumatic aortic valves compared to calcifi

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Yang, Q. H., M. R. Kaplowitz, and S. J. Lai-Fook. "Regional variations in lung expansion in rabbits: prone vs. supine positions." Journal of Applied Physiology 67, no. 4 (1989): 1371–76. http://dx.doi.org/10.1152/jappl.1989.67.4.1371.

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We studied the vertical gradient in lung expansion in rabbits in the prone and supine body positions. Postmortem, we used videomicroscopy to measure the size of surface alveoli through transparent parietal pleural windows at dependent and nondependent sites separated in height by 2–3 cm at functional residual capacity (FRC). We compared the alveolar size measured in situ with that measured in the isolated lungs at different deflationary transpulmonary pressures to obtain transpulmonary pressure (pleural surface pressure) in situ. The vertical gradient in transpulmonary pressure averaged 0.48 +

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Lima, Valter C., Evan Zahn, Christine Houde, Jeffrey Smallhorn, Robert M. Freedom, and Lee N. Benson. "Non-invasive determination of the systolic peak-to-peak gradient in children with aortic stenosis: validation of a mathematical model." Cardiology in the Young 10, no. 2 (2000): 115–19. http://dx.doi.org/10.1017/s1047951100006569.

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AbstractDoppler derived systolic pressure gradients have become widely applied as noninvasively obtained estimates of the severity of aortic valvar stenosis. There is little correlation, however, between the Doppler derived peak instantaneous gradient and the peak-to-peak gradient obtained at catheterisation, the latter being the most applied variable to determine severity in children. The purpose of this study was to validate a mathematical model based on data from catheterisation which estimates the peak-to-peak gradient from variables which can be obtained by noninvasive means (Doppler deri

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Chen, Mili, Jinhai Zheng, Linlong Tong, Jisheng Zhang, Mengyan Luo, and Ning Chen. "Experimental Study of Wave-Induced Pore Pressure Gradients around a Sandbar and Their Effects on Seabed Instability." Journal of Marine Science and Engineering 12, no. 9 (2024): 1630. http://dx.doi.org/10.3390/jmse12091630.

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The position and morphology of offshore sandbars are highly dependent on wave conditions; however, the mechanisms driving sand movement by water waves remain elusive to scientists and coastal engineers. This study presents a series of experiments conducted in a wave flume to investigate the impact of wave-induced pore pressure gradients on seabed instability around a sandbar, observed in the Benin Gulf of Guinea. The Froude-Darcy similitude principle was developed to ensure the similarity of hydrodynamics and seepage forces between the experiments and field conditions. Pore pressure gradients

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Patel, Neil D., Patrick M. Sullivan, Cheryl M. Takao, Sarah Badran, Joseph Ahdoot, and Frank F. Ing. "Unmasking the borderline coarctation: the utility of isoproterenol in the paediatric cardiac catheterisation laboratory." Cardiology in the Young 28, no. 6 (2018): 804–10. http://dx.doi.org/10.1017/s1047951118000239.

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AbstractBackgroundOne indication for intervention in coarctation of the aorta is a peak-to-peak gradient >20 mmHg. Gradients may be masked in patients under general anaesthesia and may be higher during exercise. Isoproterenol was given during cardiac catheterisation to simulate a more active physiologic state.ObjectivesWe aimed to describe the haemodynamic effects of isoproterenol in patients with coarctation and the impact of intervention on the elicited gradients.MethodsA retrospective study was performed on two-ventricle patients who underwent cardiac catheterisation for coarctation with

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Loring, S. H., K. Yoshino, W. R. Kimball, and G. M. Barnas. "Gravitational and shear-associated pressure gradients in the abdomen." Journal of Applied Physiology 77, no. 3 (1994): 1375–82. http://dx.doi.org/10.1152/jappl.1994.77.3.1375.

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The abdomen has been variously characterized as a hydrostatic system, in which pressures exhibit a gravitational gradient and pressure fluctuations are spatially uniform, and as a compartment, in which pressure gradients are not simply gravitational and pressure fluctuations differ markedly from place to place. To characterize the pressures acting on the ventral abdominal wall, we used saline-filled catheters and air-filled balloons in anesthetized dogs in various body positions during spontaneous breathing and mechanical ventilation. Pressures were measured in the stomach and at multiple site

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Davis, Michael J., Elaheh Rahbar, Anatoliy A. Gashev, David C. Zawieja, and James E. Moore. "Determinants of valve gating in collecting lymphatic vessels from rat mesentery." American Journal of Physiology-Heart and Circulatory Physiology 301, no. 1 (2011): H48—H60. http://dx.doi.org/10.1152/ajpheart.00133.2011.

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Secondary lymphatic valves are essential for minimizing backflow of lymph and are presumed to gate passively according to the instantaneous trans-valve pressure gradient. We hypothesized that valve gating is also modulated by vessel distention, which could alter leaflet stiffness and coaptation. To test this hypothesis, we devised protocols to measure the small pressure gradients required to open or close lymphatic valves and determine if the gradients varied as a function of vessel diameter. Lymphatic vessels were isolated from rat mesentery, cannulated, and pressurized using a servo-control

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Gostelow, J. P., and A. R. Blunden. "Investigations of Boundary Layer Transition in an Adverse Pressure Gradient." Journal of Turbomachinery 111, no. 4 (1989): 366–74. http://dx.doi.org/10.1115/1.3262281.

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Boundary layer transition was measured on a flat plate for four different turbulence levels. A range of adverse pressure gradients was imposed for one of these. The zero pressure gradient results were in agreement with accepted data for transition inception, length, and turbulent spot formation rate. They were also well represented by Narasimha’s universal intermittency distribution. A surprisingly strong similarity was also exhibited by intermittency distributions under adverse pressure gradients. Dimensionless velocity profiles were reasonable for the zero pressure gradient cases but difficu

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Cohen, Elie, and Xavier Gloerfelt. "Influence of pressure gradients on wall pressure beneath a turbulent boundary layer." Journal of Fluid Mechanics 838 (January 22, 2018): 715–58. http://dx.doi.org/10.1017/jfm.2017.898.

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This study investigates the effects of a pressure gradient on the wall pressure beneath equilibrium turbulent boundary layers. Excitation of the walls of a vehicle by turbulent boundary layers indeed constitutes a major source of interior noise and it is necessary to take into account the presence of a pressure gradient to represent the effect of the curvature of the walls. With this aim, large-eddy simulations of turbulent boundary layers in the presence of both mild adverse and mild favourable pressure gradients are carried out by solving the compressible Navier–Stokes equations. This method

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K. I, Udo, George N. J, Akankpo A. O, Azuoko G. B, and Aka M.U. "Determining Fracture Pressure Gradients from Well Logs." International Journal of Advanced Geosciences 8, no. 1 (2020): 5. http://dx.doi.org/10.14419/ijag.v8i1.29162.

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Fracture pressure gradient is one of the essential parameters used in determining mud weight profiles during drilling operations. We have determined fracture pressure gradients from well logs obtained from three producing wells in Onshore Niger Delta using an empirical model. Key logs needed for the prediction were conditioned and quality controlled to meet the standard required for reliable results. The true vertical stress, normal compaction trend and compressional shale velocity trends were generated from the logs (density and sonic logs). Poison’s ratio was obtained from compressional and

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Maass-Moreno, R., and C. F. Rothe. "Distribution of pressure gradients along hepatic vasculature." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 6 (1997): H2826—H2832. http://dx.doi.org/10.1152/ajpheart.1997.272.6.h2826.

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To test the hypothesis that the hepatic sinusoidal pressure is virtually identical to the portal venous pressure (Ppv) or the abdominal vena caval pressure (Pave), microvascular pressures were measured in liver vascular networks supplied by a single portal venule near the liver surface of alpha-chloralose-urethan-anesthetized rabbits. With the use of a servo-null pressure-measuring system, the pressures in terminal portal venules, sinusoids, and initial hepatic venules averaged 5.7 +/- 0.8 (SD), 5.4 +/- 0.7, and 4.7 +/- 0.6 mmHg, respectively, relative to the middle of the right atrium. The me

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Shimada, Ichiro, Hitoshi Okabayashi, Takeshi Nishina, et al. "Doppler Hemodynamics of CarboMedics Prosthetic Valves in Aortic Position at Rest and Exercise." Asian Cardiovascular and Thoracic Annals 4, no. 3 (1996): 146–51. http://dx.doi.org/10.1177/021849239600400305.

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To evaluate the size adequacy of CarboMedics prosthetic heart valves, Doppler pressure gradients after aortic valve replacement were determined at rest and immediately after exercise in 83 patients, at a mean time of 18.8 days after aortic valve replacement with CarboMedics prosthetic heart valves (31 standard and 52 R-series). There were 54 males and 29 females, average age 55 years; 12 had pure aortic stenosis, 47 had aortic regurgitation, and 24 had combined lesions. Exercise significantly increased (p < 0.01) the peak velocity (from 2.50 to 2.88 m/sec), the peak pressure gradient (from

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Jiang, Chaoyang, Con Doolan, Charitha de Silva, and Danielle Moreau. "Aeroacoustics of finite wall-mounted square cylinders in pressure gradient flows." Journal of the Acoustical Society of America 154, no. 4_supplement (2023): A104. http://dx.doi.org/10.1121/10.0022941.

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Flow-induced noise produced by finite wall-mounted cylinders (FWMCs) is a major noise source for aircraft landing gear, rail pantographs and submarine appendages. These applications often encounter flows with various pressure gradients, however, there is little information in the literature on the effects of pressure gradients. Our recent work has demonstrated that the presence of a pressure gradient can significantly affect the near-wake flow structures of a square FWMC with a low aspect ratio of 2.4, thereby suppressing/enhancing the vortex-shedding tones. The current study extends this work

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Sen, Suranjana, Debojyoti Bhattacharyya, Subhojit Chaterjee, Bhuvnesh Kumar, and Madhusudan Pal. "Effect of shod walking on plantar pressure with varying uphill gradients." Asian Journal of Medical Sciences 11, no. 6 (2020): 38–45. http://dx.doi.org/10.3126/ajms.v11i6.29902.

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Background: Uphill walking is biomechanically stressful. Changes in plantar pressure, is one of the important predictors of this stress and increased risk of foot injuries. It has been reported that civilians as well as different occupational workers have to walk over uphill gradient with footwear which may cause changes in plantar pressure. Till date published data on plantar pressure is not available of Indian population during shod walking with uphill gradients. Aims and Objective: The present study was aimed to generation of data base on plantar pressure and find out the effect of sh

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Peters, Joseph, Ian Rice, and Tyson Bull. "Exploring the Influence of Wheelchair-User Interface and Personal Characteristics on Ischial Tuberosity Peak Pressure Index and Gradient in Elite Wheelchair Basketball Players." Adapted Physical Activity Quarterly 37, no. 1 (2020): 56–71. http://dx.doi.org/10.1123/apaq.2019-0030.

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This pilot study investigated the relationship between personal and wheelchair factors on skin pressures at the ischial tuberosity in wheelchair basketball players. Seventeen wheelchair basketball players (7 male and 10 female) were evaluated during static and dynamic propulsive conditions while peak pressure index and peak pressure gradient were recorded with an interface pressure mat. The results showed that greater seat dump angles and backrest heights were negatively associated with the peak pressure index. Therapeutic cushion use was moderately associated with a reduced peak pressure grad

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Jiang, Dawei, Min Cao, Xiaotong Zhang, Yang Gao, and Yonghao Han. "Pressure evolution in a diamond anvil cell without a pressure medium." Journal of Applied Physics 131, no. 12 (2022): 125904. http://dx.doi.org/10.1063/5.0086792.

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The inhomogeneity in pressure inside the sample chamber of a diamond anvil cell (DAC) poses a major challenge to the accurate measurement of the properties of materials under high pressures, especially when the pressure medium solidifies under compression or is prohibited in the experiment. In this paper, the authors systematically investigate the pressure gradient in a DAC sample chamber and its evolution over time with changes in temperature. The results show that pressure gradients were formed along both the radial and the axial directions upon compression, and gradually decayed with time a

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Fargen, Kyle M., Alejandro M. Spiotta, Madison Hyer, et al. "Comparison of venous sinus manometry gradients obtained while awake and under general anesthesia before venous sinus stenting." Journal of NeuroInterventional Surgery 9, no. 10 (2016): 990–93. http://dx.doi.org/10.1136/neurintsurg-2016-012608.

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IntroductionVenous sinus stenting is a popular treatment strategy for patients with high venous sinus pressure gradients across a site of outflow obstruction. Little is known about the effect of anesthesia on venous sinus pressure measurements.ObjectiveTo compare venous manometry performed in patients under general anesthesia and while awake.MethodsA prospective database was accessed to retrospectively identify patients who had undergone venous sinus stenting. Pressure gradients were compared between those patients who underwent manometry while awake and before stenting under general anesthesi

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Wu, H., S. Moreau, and R. D. Sandberg. "Effects of pressure gradient on the evolution of velocity-gradient tensor invariant dynamics on a controlled-diffusion aerofoil at." Journal of Fluid Mechanics 868 (April 17, 2019): 584–610. http://dx.doi.org/10.1017/jfm.2019.129.

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A weakly compressible flow direct numerical simulation of a controlled-diffusion aerofoil at $8^{\circ }$ geometrical angle of attack, a chord-based Reynolds number of $Re_{c}=150\,000$ and a Mach number of $M=0.25$ based on the free-stream velocity relevant to many industrial applications was conducted to improve the understanding of the impact of the pressure gradient on the development of turbulent structures. The evolution equations for the two invariants $Q$ and $R$ of the velocity-gradient tensor have been studied at various locations along the aerofoil chord on its suction side. The sha

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Dutta, Partha P., Alexander C. Benken, Tao Li, John Richard Ordonez-Varela, and Yogesh B. Gianchandani. "Passive Wireless Pressure Gradient Measurement System for Fluid Flow Analysis." Sensors 23, no. 5 (2023): 2525. http://dx.doi.org/10.3390/s23052525.

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Using distributed MEMS pressure sensors to measure small flow rates in high resistance fluidic channels is fraught with challenges far beyond the performance of the pressure sensing element. In a typical core-flood experiment, which may last several months, flow-induced pressure gradients are generated in porous rock core samples wrapped in a polymer sheath. Measuring these pressure gradients along the flow path requires high resolution pressure measurement while contending with difficult test conditions such as large bias pressures (up to 20 bar) and temperatures (up to 125 °C), as well as th

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FARRELL, M. D., and P. E. RICHES. "IONIC OSMOTIC EFFECTS INCREASE FLUID FLOW DURING PERMEATION TESTS." Journal of Mechanics in Medicine and Biology 12, no. 04 (2012): 1250063. http://dx.doi.org/10.1142/s0219519412004995.

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Fluid flow is essential for the transport of metabolites to, from and within the intervertebral disc (IVD). By applying quadriphasic mixture theory experimentally, this study relates fluid flow within the bovine nucleus pulposus (NP) to the applied fluid pressure gradients and fixed charge and mobile ion concentration gradients. 24 plugs of NP tissue (diameter 10 mm, height 1020 ± 122 μm (mean ± SD)), orientated in the axial direction, were harvested from bovine tail discs. The plugs were permeated with either; 0 M NaCl , 0.15 M NaCl or 3 M NaCl solutions by subjecting them to 30, 45 and 60 kP

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Rosemurgy, Alexander S., Mark Bloomston, Poopak Ghassemi, and Francesco Serafini. "Preshunt and Postshunt Portal Vein Pressures and Portal Vein-to-inferior Vena Cava Pressure Gradients Do Not Predict Outcome following Partial Portal Decompression." American Surgeon 68, no. 1 (2002): 70–74. http://dx.doi.org/10.1177/000313480206800116.

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This study was undertaken to determine whether preshunt, postshunt, or changes in portal vein (PV) pressures or portal vein-to-inferior vena cava (PV-IVC) pressure gradients determine outcome following partial portal decompression attained through small-diameter prosthetic H-graft portacaval shunt (HGPCS). Seventy-seven adults underwent HGPCS (Child's class A10%, B 56%, and C 34%) and were prospectively evaluated per protocol. PV pressures and PV-IVC pressure gradients decreased significantly in all patients with shunting ( P < 0.001). Eight (10%) patients died within 30 days of shunting (C

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Lee, InSub, Hong Sun Ryou, Seong Hyuk Lee, Ki Bae Hong, and Soo Chae. "A Numerical Investigation on the Development of an Embedded Streamwise Vortex in a Turbulent Boundary Layer With Spanwise Pressure Gradient." Journal of Fluids Engineering 123, no. 3 (2001): 551–58. http://dx.doi.org/10.1115/1.1378022.

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It is the aim of this article to investigate numerically the effects of spanwise pressure gradient on an embedded streamwise vortex in a turbulent boundary layer. The governing equations were discretized by the finite volume method and SIMPLE algorithm was used to couple between pressure and velocity. The LRR model for Reynolds stresses was utilized to predict the anisotropy of turbulence effectively. The validation was done for two cases: one is the development of a streamwise vortex embedded in a pressure-driven, three-dimensional turbulent boundary layer. The other involves streamwise vorte

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Hu, N., and B. B. Keller. "Relationship of simultaneous atrial and ventricular pressures in stage 16-27 chick embryos." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 4 (1995): H1359—H1362. http://dx.doi.org/10.1152/ajpheart.1995.269.4.h1359.

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Ventricular filling is determined by a dynamic balance between atrial and ventricular load and function. The embryonic cardiovascular system undergoes simultaneous growth and morphogenesis at the cellular, tissue, and organ levels to match the embryo's geometrically increasing metabolic demands. As part of our long-term investigation of atrial/ventricular coupling during primary cardiac morphogenesis, we defined the relationship between simultaneous atrial and ventricular pressures in the stage 16-27 white Leghorn chick embryo. We measured atrial and ventricular blood pressures with servo-null

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Gostelow, J. P., A. R. Blunden, and G. J. Walker. "Effects of Free-Stream Turbulence and Adverse Pressure Gradients on Boundary Layer Transition." Journal of Turbomachinery 116, no. 3 (1994): 392–404. http://dx.doi.org/10.1115/1.2929426.

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Boundary layer measurements are presented through transition for six different free-stream turbulence levels and a complete range of adverse pressure gradients for attached laminar flow. Measured intermittency distributions provide an excellent similarity basis for characterizing the transition process under all conditions tested when the Narasimha procedure for determining transition inception is used. This inception location procedure brings consistency to the data. Velocity profiles and integral parameters are influenced by turbulence level and pressure gradient and do not provide a consist

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Gao, Jianfeng, Yang Wu, Xiaojun Shao, Yanan Han, Bingang Guo, and Jianjun Liang. "Analysis of the inhomogeneous LPG-air flow field in a tube containing mixed obstructions." Journal of Physics: Conference Series 2584, no. 1 (2023): 012018. http://dx.doi.org/10.1088/1742-6596/2584/1/012018.

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Abstract Based on numerical simulation, this paper further investigates the flow field structure near the obstacle during the premixed gas deflagration. In the deflagration flow field, the pressure gradient variation and vortex structure intensity in the upper surface region of the obstacle are larger, indicating that the pressure gradient has a stronger effect on the vortex structure. The changes in density gradients and pressure gradients induced by the combined rectangular, flat barrier configuration will be more pronounced than in the model with only flat barriers. This change in turn acts

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Piersanti, Eleonora, Marie E. Rognes, and Vegard Vinje. "Are brain displacements and pressures within the parenchyma induced by surface pressure differences? A computational modelling study." PLOS ONE 18, no. 12 (2023): e0288668. http://dx.doi.org/10.1371/journal.pone.0288668.

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The intracranial pressure is implicated in many homeostatic processes in the brain and is a fundamental parameter in several diseases such as e.g. idiopathic normal pressure hydrocephalus. The presence of a small but persistent pulsatile intracranial pulsatile transmantle pressure gradient (on the order of a few mmHg/m at peak) has recently been demonstrated in hydrocephalus subjects. A key question is whether pulsatile intracranial pressure and displacements can be induced by a small pressure gradient originating from the brain surface alone. In this study, we model the brain parenchyma as ei

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Mislevy, S. P., and T. Wang. "The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 1—Mean Quantities." Journal of Turbomachinery 118, no. 4 (1996): 717–27. http://dx.doi.org/10.1115/1.2840927.

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The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. The acceleration parameter, K, was kept constant along the test section. Both surface heat transfer and boundary layer measurements were conducted. The boundary layer measurements were conducted with a three-wire probe (two velocity wires and one temperature wire) for two representative cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The surface heat transfer measurements were conducted for K

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Amin, Fatima, Abdul Sattar Shaikh, Sohail Khan Bangash, et al. "Correlation between Intraoperative Direct and Transesophageal Echocardiographic Assessment of Right Ventricular Outflow Tract Pressure Gradient in Patients Undergoing Tetralogy of Fallot Repair." Pakistan Heart Journal 56, no. 1 (2023): 92–96. http://dx.doi.org/10.47144/phj.v56i1.2484.

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Objectives: The objective of this study was to determine the correlation between intraoperative direct (needle) and transesophageal echocardiographic (TEE) assessment of right ventricular outflow tract (RVOT) pressure gradient in patients undergoing Tetralogy of Fallot (TOF) repair. Methodology: A total of 100 patients underwent for TOF repair were included. After completion of surgery and successful weaning from cardiopulmonary bypass, the TEE derived RVOT gradients were obtained from, the midesophageal ascending aortic short axis (AA Sax) view, upper esophageal aortic arch short axis (Arch S

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Thomson, Nicholas, and Joana Rocha. "Semi-empirical wall pressure spectral modeling for zero and favorable pressure gradient flows." Journal of the Acoustical Society of America 152, no. 1 (2022): 80–98. http://dx.doi.org/10.1121/10.0012188.

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Semi-empirical models are used to predict the power spectral density of wall pressure fluctuations in the turbulent boundary layer. Current advancements in power spectral density wall pressure fluctuation prediction have focused on expanding the range of experiments that can be predicted to include adverse pressure gradient flows; however, favorable pressure gradient flows have not received much attention. An experiment was performed to capture the effects of the favorable pressure gradient on the power spectral density. A model was then created to improve upon some of the limitations of exist

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Thyregod, Hans Gustav Hørsted, and Nikolaj Ihlemann. "Measuring Transvalvular Aortic Pressure Gradients." JACC: Cardiovascular Interventions 15, no. 18 (2022): 1849–51. http://dx.doi.org/10.1016/j.jcin.2022.08.021.

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Brill, J. P. "Discontinuities in the Orkiszewski Correlation for Predicting Pressure Gradients in Wells." Journal of Energy Resources Technology 111, no. 1 (1989): 34–36. http://dx.doi.org/10.1115/1.3231398.

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The Orkiszewski correlation is used extensively in the petroleum industry for predicting pressure gradients when gas and liquid flow simultaneously in wells. Unfortunately, the correlation contains a parameter called the liquid distribution coefficient, Γ, that can be discontinuous at a superficial mixture velocity of 10 ft/sec. The liquid distribution coefficient is used to predict both the elevation and friction components of the pressure gradient for slug flow. The accepted trial and error method for integrating the pressure gradient to obtain pressure loss in wells can fail to converge whe

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Dixon, D. A., M. N. Gray, and D. Hnatiw. "Critical gradients and pressures in dense swelling clays." Canadian Geotechnical Journal 29, no. 6 (1992): 1113–19. http://dx.doi.org/10.1139/t92-129.

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Uncertainties exist with regard to the applicability of Darcy's law to dense swelling clays. These clays may not allow water to pass through them when the hydraulic gradient is below a critical value. Preliminary results are presented from a series of constant-head permeability tests on dry, confined, densely compacted bentonite clays. The tests are intended to clarify the applicability of Darcy's law to dense bentonites: these materials may be used for isolation of nuclear fuel wastes in deep geologic disposal vaults. On wetting and with increasing hydraulic gradient, the clays develop swelli

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Scharfschwerdt, Michael, Axel Richter, Kurt Boehmer, Detlef Repenning, and Hans-H. Sievers. "Improved hydrodynamics of a new aortic cannula with a novel tip design." Perfusion 19, no. 3 (2004): 193–97. http://dx.doi.org/10.1191/0267659104pf750oa.

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Background: Reduction of atheroembolic complications during cardiopulmonary bypass remains a major challenge in cardiac surgery. New cannula tip designs may help to attenuate this problem by improved hydrodynamics. Methods: Pressure gradients and back pressures of a new aortic cannula tip design were measured and compared with the Medos X-Flow, Sarns Soft-Flow and Argyle THI cannulae at various flow rates in a mock circulation followed by flow visualization. Results: Pressure gradients were the lowest for the new cannula. Back pressures of the new cannula were up to 84% lower than for the Argy

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Zhou, Gang, Lei Qiu, Wenzheng Zhang, and Jiao Xue. "Simulation Analysis on Water’s Micro Seepage Laws under Different Pressure Gradients Using Computed Tomography Method." Advances in Civil Engineering 2018 (September 6, 2018): 1–26. http://dx.doi.org/10.1155/2018/3401341.

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The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this s

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Penn, Richard D., Max C. Lee, Andreas A. Linninger, Keith Miesel, Steven Ning Lu, and Lee Stylos. "Pressure gradients in the brain in an experimental model of hydrocephalus." Journal of Neurosurgery 102, no. 6 (2005): 1069–75. http://dx.doi.org/10.3171/jns.2005.102.6.1069.

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Object. The goal of this investigation was to establish whether pressure gradients exist between the ventricles, brain tissue, and subarachnoid space when acute or chronic hydrocephalus develops. Such gradients are hypothesized by many models of hydrocephalus, but considerable controversy continues about their existence. Methods. A stereotactic frame was used for surgery in dogs to implant pressure sensors within the right lateral ventricle, the frontal lobe, and forward in the subarachnoid space. The dogs were allowed to recover for 10 to 14 days postoperatively. Then, 800 mg of sterile kaoli

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