Some pressure and fluid dynamic characteristics of the canine epidural space

1977 ◽  
Vol 232 (3) ◽  
pp. H255-H259
Author(s):  
R. G. Bengis ◽  
A. C. Guyton
Keyword(s):  
Epidural Space ◽  
Fluid Dynamic ◽  
Fluid Pressure ◽  
Simultaneous Recording ◽  
Positive Pressure ◽  
Pressure Curve ◽  
Epidural Pressure ◽  
Volume Depletion ◽  
Significant Drop ◽  
Epidural Catheters

Pressure measured in teh epidural space of 50 dogs was consistently negative (subatmospheric). Acutely implanted epidural catheters gave an average reading of -2.72 mmHg (n = 44, SE = 0.18), whereas chronically implanted catheters gave more negative readings, averaging -5.8 mmHg (n = 6, SE = 0.49). Since the chronically implanted catheters permit healing, resolution of hemorrhage, and resealing of the epidural space to take place, resulting in equilibration of microcirulatory forces, these readings are believed to represent more closely the true epidural pressure. Also these results approximate closely the calculated and measured interstitial fluid pressures obtained by different techniques in other loose areolar connective tissue systems. Compliance studies, using a double-lumen catheter for simultaneous recording and infusing in the epidural space, showed increasing compliance as the pressure rose into the positive pressure range, with an eventual plateau of the volume-pressure curve at the level of the concomitantly measured cerebrospinal fluid pressure (avg = +5.73 mmHg, n = 10, SE = 0.48). Intravenous volume loading using Tyrode solution caused a large rise in epidural pressure, and volume depletion with diuretics caused a significant drop in epidural pressure.

scholarly journals Comparison of Epidural Pressure Decrease Pattern According to Different Lumbar Epidural Approaches

2020 ◽  
Vol 2;23 (4;2) ◽  
pp. E202-E210
Author(s):  
Jihee Hong
Keyword(s):  
Epidural Space ◽  
Management Practice ◽  
Epidural Injection ◽  
Epidural Pressure ◽  
Abrupt Decrease ◽  
Interspinous Ligament ◽  
Pressure Decrease ◽  
Significant Difference ◽  
Key Words Epidural ◽  
Midline Approach

Background: During lumbar epidural injection (LEI) using a midline approach, we might encounter failure of identifying the epidural space owing to an equivocal or absent loss of resistance (LOR) sensation. The reason for such absence of LOR sensation has been suggested as paucity of midline ligamentum flavum, paravertebral muscle, and cyst in the interspinous ligament of the lumbar spine. Despite its low specificity, LOR is the most commonly used method to identify the epidural space. Objectives: The purpose of this study was to analyze lumbar epidural pressure decrease patterns and identify factors contributing to this pressure decrease. Study Design: Prospective randomized trial. Setting: An interventional pain management practice in South Korea. Methods: This prospective study included 104 patients receiving LEI due to lumbar radiculopathy. A midline or paramedian approach of LEI was determined with randomization. Among various factors, gender, age, body mass index (BMI), and diagnosis were analyzed using a subgroup that included 60 cases of only a paramedian approach. Results: Grades I, II (abrupt decrease), and III (gradual decrease) were found as patterns of epidural pressure decrease. Abrupt pressure decrease was more frequently observed in the paramedian group (P < 0.001). Age, gender, BMI, and diagnosis did not show any significant difference in frequencies between abrupt and gradual pressure decrease. Limitations: We could not match LOR sensation with epidural pressure decrease shown in the monitor. Conclusions: This study demonstrates that abrupt pressure decrease occurs more frequently with the paramedian approach. However, age, gender, BMI, or diagnosis did not affect the incidence of epidural pressure decrease. Key words: Epidural, paramedian, midline, pressure decrease

Study of Air Inclusion in Lubrication System of CVT Gearbox Transmission With Biphasic CFD Simulation

2016 ◽  
Author(s):  
Cristian Ferrari ◽  
Pietro Marani
Keyword(s):  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Critical Conditions ◽  
Positive Pressure ◽  
Computational Domain ◽  
Lubrication System ◽  
Operation Condition ◽  
Dynamic Simulations ◽  
Lubrication Performance ◽  
Lumped Element Model

The focus of this paper is the biphasic phenomena that occurs in a lubrication system of a CVT gearbox transmission of an agricultural tractor, in particular a Method of Analysis is outlined with the aim of mapping and assessing the behavior of the lubrication circuit. The study of the lubrication in gearboxes is an important issue in the design of off-road machines because their reliability depends mostly on the lubrication performance, as well as the machine’s lifetime and overall energy efficiency of the transmission is strongly dependent on the lubrication system behavior. In fact the role of the lubrication system is twofold: firstly to remove the heat generated in the highly loaded rolling bearings and the gears found in the power and accessory gearboxes via heat exchangers; secondly to lubricate these parts. The trend in the development of gearbox transmissions has been towards lower consumption and higher power transmitted, consequently it is necessary to conceive more effective and efficient lubrication systems. Nonetheless the lubrication problem often relies on a trial and error approach and most available scientific literature is based on lumped element model dynamic simulation or one phase thermo-fluid dynamic simulations, overlooking the effects linked to cavitation and air inclusion. One important phenomenon in lubrication systems is that of air suction. This can be seen in particular at high rotational speeds of shafts when the centrifugal force causes a positive pressure drop between inner lubrication pipes and outer radial conduits. In this case the air occupies part of the lubrication conduits, and since the domain is shared by the outflowing liquid phase and the air included, the monophase CFD simulation fails to predict the correct lubrication flow. If this effect is not carefully considered it could cause a lubrication unbalance among the various parts of the gearbox, creating a risk of transmission damage. In this paper the methodology will be presented step by step until in final a complete map of operation condition is created. A preliminary analysis of the circuitry is an essential phase of the project since the tractor’s transmission is an extremely complex assembly composed by hundreds of components therefore the lubrication circuit appears as a large net of moving hydraulic connections and consumers. From this analysis a computational domain is obtained and appropriately meshed. After the pivotal choice of the proper turbulence model and boundary conditions, various runs at different rotating speeds corresponding to the different operating ranges will be performed. The result will be contextualized by commenting on the fluid dynamics phenomena involved and the influence parameters on flow rate distribution, finally evaluating the performances of the lubrication circuit, and in particular highlighting the most critical conditions in terms of speed condition and locating the most critical gearbox parts.

scholarly journals Radiological analysis of the position of epidural catheters in the thoracic epidural space

2014 ◽  
Vol 67 (Suppl) ◽  
pp. S51 ◽  
Author(s):  
Mun Gyu Kim ◽  
Si Young Ok ◽  
Se Kwang Park ◽  
Ho Bum Cho ◽  
Sang Ho Kim
Keyword(s):  
Epidural Space ◽  
Thoracic Epidural ◽  
Epidural Catheters ◽  
Radiological Analysis

Tube Hydroforming (THF): Process Optimization of an Automotive Component

2013 ◽  
Vol 549 ◽  
pp. 141-148
Author(s):  
Aldo Attanasio ◽  
Elisabetta Ceretti ◽  
Giancarlo Maccarini
Keyword(s):  
Fluid Pressure ◽  
Tube Hydroforming ◽  
Experimental Tests ◽  
Side Impact ◽  
Pressure Curve ◽  
Part Geometry ◽  
Italian Government ◽  
Working Solution ◽  
Hydroforming Process ◽  
Good Agreement

This paper reports the results obtained during a research project funded by the Italian Government and involving several Italian Universities (PRIN INTEMA). The activities have been focused on side impact bar manufacturing by means of Tube Hydroforming process (THF). Punch movement paths and fluid pressure curve were optimized by means of FEM software (LS-DYNA) to guarantee tube sealing and material feeding during the tube deformation. The side impact bar geometry was optimized till reaching the shape guaranteeing the obtainment of safe parts with the best compromise in terms of final part geometry and thickness reduction. Different fluid pressure and punch movement paths were investigated. Once accomplished all the simulations and identified the best working solution, experimental tests were performed setting the process parameters according to the values defined during the simulation phase. Good agreement between FEM and experimental results were highlighted.

A General Formulation for Hydroforming of Arbitrarily-Shaped Boxes and Its Application to Hydroforming of an Elliptic-Circular Box

1998 ◽  
Vol 120 (3) ◽  
pp. 481-488 ◽  
Author(s):  
T. S. Noh ◽  
D. Y. Yang
Keyword(s):  
Velocity Field ◽  
Fluid Pressure ◽  
Frictional Coefficient ◽  
Total Power ◽  
Thickness Variation ◽  
Pressure Curve ◽  
Bound Solution ◽  
Total Power Consumption ◽  
Uniform Wall ◽  
Blank Size

A general kinematically admissible velocity field is suggested for the upper-bound solution of hydroforming of arbitrarily-shaped boxes. The suggested formulation is then applied to hydroforming of an elliptic-circular box. From the proposed velocity field, the fluid pressure vs. punch stroke relationship to render uniform thickness and the deformed configuration are determined by minimizing the total power consumption with respect to some chosen parameters. Experiments are carried out in the hydroforming press according to the computed pressure vs. punch stroke curve. The assumption of uniform wall thickness is confirmed by measuring the thickness variation. The effects of various process parameters including blank size, work-hardening exponent and frictional coefficient on the pressure curve are analyzed and discussed. It is thus shown that the proposed method of analysis in the present study can be effectively used for hydroforming of arbitrarily shaped boxes.

scholarly journals Numerical Simulation of Closing Process of Shuttle Check Valve

2015 ◽  
Vol 9 (1) ◽  
pp. 714-720 ◽  
Author(s):  
Xiang Kefeng ◽  
Yao Jin ◽  
Zeng Xiangwei
Keyword(s):  
Pressure Fluctuations ◽  
Fluid Pressure ◽  
Check Valve ◽  
Geometrical Model ◽  
Pressure Curve ◽  
Design And Optimization ◽  
The Core ◽  
Speed Fluctuation ◽  
Fluent Software ◽  
The Moment

For studying the kinetic characteristics of passive shuttle check valve at the moment that it closes its valve core on the condition of high pressure differences, this paper first constructs the equation of motion of the valve core and twodimensional geometrical model by using computation fluid dynamics method, then with the help of the calculation method and physical model provided by Fluent software, employing the dynamic mesh and user-defined functions, simulates the unsteady flow in the valve core’s closing process under the different pressure fluctuations, and obtains the stress nephogram, the velocity vector diagram, the speed curve, and pressure curve of the interior flow field of the valve. The results show that the bigger the value of valve fluctuation is, the larger the fluid pressure that the valve core is subjected to, the openness of the core and the speed fluctuation of the core are, and that in the case of sudden decompression at the entrance, the core can be shut down quickly with the steady speed field and pressure field. The simulation results are conducive to the design and optimization of structure parameter of shuttle check valve.

scholarly journals Quantification of aerosol dispersal from suspected aerosol generating procedures

2021 ◽  
pp. 00206-2021
Author(s):  
Runar Strand-Amundsen ◽  
Christian Tronstad ◽  
Ole Elvebakk ◽  
Tormod Martinsen ◽  
Marius Dybwad ◽  
...  
Keyword(s):  
Test Chamber ◽  
Nasal Cannula ◽  
Low Flow ◽  
Positive Pressure ◽  
Productive Cough ◽  
Significant Drop ◽  
Non Invasive ◽  
Oxygen Treatment ◽  
The Face ◽  
Particle Sizer

BackgroundOxygen delivering modalities like humidified high-flow nasal cannula (HFNC) and non-invasive positive-pressure ventilation (NIV) are suspected of generating aerosols that may contribute to transmission of disease such as COVID-19. We sought to assess if these modalities lead to increased aerosol dispersal compared to the use of non-humidified low-flow nasal cannula oxygen treatment (LFNC).MethodsAerosol dispersal from 20 healthy volunteers using HFNC, LFNC and NIV oxygen treatment was measured in a controlled chamber. We investigated effects related to coughing and using a surgical facemask in combination with the oxygen delivering modalities. An aerodynamic particle sizer measured aerosol particles (APS3321, 0.3–20 µm) directly in front of the subjects, while a mesh of smaller particle sensors (SPS30, 0.3–10 µm) was distributed in the test chamber.ResultsNon-productive coughing led to significant increases in particle dispersal close to the face when using LFNC and HFNC but not when using NIV. HFNC or NIV did not lead to a statistically significant increase in aerosol dispersal compared to LFNC. With non-productive cough in a room without air changes, there was a significant drop in particle levels between 100 cm and 180 cm from the subjects.ConclusionsOur results indicate that using HFNC and NIV does not lead to increased aerosol dispersal compared to low-flow oxygen treatment, except in rare cases. For a subject with non-productive cough, NIV with double-limb circuit and non-vented mask may be a favourable choice to reduce the risk for aerosol spread.

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