Hemodynamic Method to Predict Whether Hunterian Ligation of the Basilar Artery Will Lead to Thrombosis of Basilar Bifurcation Aneurysms

Neurosurgery ◽  
1987 ◽  
Vol 20 (2) ◽  
pp. 249-253 ◽  
Author(s):  
Jack Chang ◽  
Margot R. Roach
Keyword(s):  
Pressure Gradient ◽  
Basilar Artery ◽  
Diameter Ratio ◽  
Phase Lag ◽  
Maximal Width ◽  
Before And After ◽  
Simple Measurement ◽  
Flow Through ◽  
Stop Flow

Abstract In some cases, basilar artery aneurysms cannot be repaired surgically and the basilar artery is occluded near the neck of the aneurysm to stop flow into the aneurysm. After the operation, the aneurysm can fill only by flow through the posterior communicating arteries (PCoAs). Hemodynamically, if the flow were the same in both PCoAs and there were no phase lag in the pressures, there would be no pressure gradient for flow to go across the neck of the aneurysm and therefore the aneurysm would thrombose. We have assumed that the diameter of the artery is roughly proportional to the flow that goes through it chronically. We measured the diameters of the PCoAs in 25 patients who had hunterian ligation of the basilar artery. We also measured the maximal width, height, and depth of the aneurysms on angiograms obtained before and after operation. Eleven aneurysms thrombosed completely and had a diameter ratio of > 0.6; 10 aneurysms thrombosed partially and had a diameter ratio of 0.46 ˜ 1.0; 4 aneurysms did not change and had a diameter ratio of <0.45. The ratio of the sizes of the PCoAs pre- and postoperatively was comparable in most cases, so we believe that it is possible to predict reasonably accurately from this simple measurement whether the aneurysm is likely to thrombose if the basilar artery is ligated.

Maximal vasodilation does not eliminate the vascular waterfall in the canine hindlimb

1995 ◽  
Vol 79 (5) ◽  
pp. 1531-1539 ◽  
Author(s):  
I. Shrier ◽  
S. Magder
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Critical Pressure ◽  
Perfusion Pressure ◽  
Venous Pressure ◽  
Elastic Recoil ◽  
Recoil Pressure ◽  
Before And After ◽  
Flow Through ◽  
Stop Flow

Previous studies have shown that blood flow through skeletal muscle is regulated by changes in an arteriolar vascular waterfall [critical pressure (Pcrit)] and a proximal (arterial) resistance (Ra) element. To determine whether Pcrit still exists during maximal vasodilation, we pump perfused vascularly isolated canine hindlimbs. We set outflow pressure to zero and measured Pcrit, perfusion pressure (Pper), and regional elastic recoil pressure (Pcl; by a stop-flow technique) and calculated both Ra and venous resistance before and after maximal vasodilation with adenosine and nitroprusside. Pcrit was 56.4 +/- 5.1 mmHg before vasodilation and decreased to 11.0 +/- 0.6 mmHg after vasodilation, which was less than the downstream pressure in the venous compliant region (Pel). Therefore, Pcrit should not have affected flow at normal Pper levels under vasodilated conditions. However, we could still measure Pcrit because our technique allowed Pel to decline and Pcrit becomes apparent once Pel < Pcrit. With vasodilation, Ra decreased to < 8.1 +/- 2.6% and Rv decreased to 41 +/- 6% of control values. In contrast to the nonvasodilated vasculature, increases in venous pressure during maximal vasodilation caused immediate increases in Pper. This also suggests that the vascular waterfall is inactive under conditions of maximal vasodilation. We conclude that a small arteriolar Pcrit is still present in the maximally vasodilated hindlimb but is less than the downstream pressure and does not affect flow under these conditions.

Effects of Rib Arrangements on Pressure Drop and Heat Transfer in a Rib-Roughened Channel With a Sharp 180 deg Turn

1997 ◽  
Vol 119 (3) ◽  
pp. 610-616 ◽  
Author(s):  
S. Mochizuki ◽  
A. Murata ◽  
M. Fukunaga
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Equivalent Diameter ◽  
Before And After ◽  
Rib Roughened

The objective of this study was to investigate, through experiments, the combined effects of a sharp 180 deg turn and rib patterns on the pressure drop performance and distributions of the local heat transfer coefficient in an entire two-pass rib-roughened channel with a 180 deg turn. The rib pitch-to-equivalent diameter ratio P/de was 1.0, the rib-height-to-equivalent diameter ratio e/de was 0.09, and the rib angle relative to the main flow direction was varied from 30 ∼ 90 deg with an interval of 15 deg. Experiments were conducted for Reynolds numbers in the range 4000 ∼ 30,000. It was disclosed that, due to the interactions between the bend-induced secondary flow and the rib-induced secondary flow, the combination of rib patterns in the channel before and after the turn causes considerable differences in the pressure drop and heat transfer performance of the entire channel.

A Topological Study of the Genesis of a Horseshoe Vortex in the Symmetry Plane Due to an Adverse Pressure Gradient

2001 ◽  
Author(s):  
Martijn A. van den Berg ◽  
Michael M. J. Proot ◽  
Peter G. Bakker
Keyword(s):  
Pressure Gradient ◽  
Bifurcation Theory ◽  
Nonlinear Differential Equations ◽  
Nonlinear Dynamical System ◽  
Symmetry Plane ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Nonlinear Dynamical ◽  
Separating Flow ◽  
Flow Through

Abstract The present paper describes the genesis of a horseshoe vortex in the symmetry plane in front of a juncture. In contrast to a previous topological investigation, the presence of the obstacle is no longer physically modelled. Instead, the pressure gradient, induced by the obstacle, has been used to represent its influence. Consequently, the results of this investigation can be applied to any symmetrical flow above a flat plate. The genesis of the vortical structure is analysed by using the theory of nonlinear differential equations and the bifurcation theory. In particular, the genesis of a horseshoe vortex can be described by the unfolding of the degenerate singularity resulting from a Jordan Normal Form with three vanishing eigenvalues and one linear term which is related to the adverse pressure gradient. The examination of this nonlinear dynamical system reveals that a horseshoe vortex emanates from a non-separating flow through two subsequent saddle-node bifurcations in different directions and the transition of a node into a focus located in the flow field.

scholarly journals Electrophysiological signatures of acute systemic lipopolysaccharide: potential implications for delirium science

2020 ◽  
Author(s):  
Ziyad W Sultan ◽  
Elizabeth R Jaeckel ◽  
Bryan M Krause ◽  
Sean M Grady ◽  
Caitlin A Murphy ◽  
...  
Keyword(s):  
Ratio Test ◽  
Phase Lag ◽  
Aged Patients ◽  
Monocyte Chemoattractant Protein 1 ◽  
Adenosine Receptor Antagonist ◽  
Electrophysiological Recordings ◽  
Before And After ◽  
Matched Data ◽  
Adenosine Signaling

AbstractBackgroundNovel preventive therapies are needed for postoperative delirium, which especially affects aged patients. A mouse model is presented that captures inflammation-associated cortical slow wave activity (SWA) observed in patients, allowing exploration of the mechanistic role of prostaglandin-adenosine signaling.MethodsEEG and cortical cytokine measurements (interleukin 6 [IL-6], monocyte chemoattractant protein-1 [MCP-1]) were obtained from adult and aged mice. Behavior, SWA, and functional connectivity (alpha-band weighted phase lag index) were assayed before and after systemic administration of lipopolysaccharide (LPS) +/- piroxicam (cyclooxygenase inhibitor) or caffeine (adenosine receptor antagonist). To avoid confounds from inflammation-driven changes in movement, which alter SWA and connectivity, electrophysiological recordings were classified as occurring during quiescence or movement, and propensity score matching used to match distributions of movement magnitude between baseline and LPS.ResultsLPS produces increases in cortical cytokines and behavioral quiescence. In movement-matched data, LPS produces increases in SWA (likelihood-ratio test: χ2(4)=21.51, p=0.00057), but not connectivity (χ2(4)=6.39, p=0.17). Increases in SWA associate with IL6 (p<0.001) and MCP-1 (p=0.001) and are suppressed by piroxicam (p<0.001) and caffeine (p=0.046). Aged animals compared to adult show similar LPS-induced SWA during movement, but exaggerated cytokine response and increased SWA during quiescence.ConclusionsCytokine-SWA correlations during wakefulness are consistent with observations in patients with delirium. Absence of connectivity effects after accounting for movement changes suggests decreased connectivity in patients is a biomarker of hypoactivity. Exaggerated effects in quiescent aged animals are consistent with increased hypoactive delirium in older patients. Prostaglandin-adenosine signaling may link inflammation to neural changes and hence delirium.

Micropolar Fluid Flow Between Two Inclined Parallel Plates

2017 ◽  
Author(s):  
Abbas Hazbavi ◽  
Sajad Sharhani
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Micropolar Fluid ◽  
Constant Heat Flux ◽  
Hydrodynamic Characteristics ◽  
Parallel Plates ◽  
Governing Equations ◽  
Micropolar Fluid Flow ◽  
Flow Through ◽  
The Magnetic Field

In this study, the hydrodynamic characteristics are investigated for magneto-micropolar fluid flow through an inclined channel of parallel plates with constant pressure gradient. The lower plate is maintained at constant temperature and upper plate at a constant heat flux. The governing equations which are continuity, momentum and energy are are solved numerically by Explicit Runge-Kutta. The effect of characteristic parameters is discussed on velocity and microrotation in different diagrams. The nonlinear parameter affected the velocity microrotation diagrams. An increase in the value of Hartmann number slows down the movement of the fluid in the channel. The application of the magnetic field induces resistive force acting in the opposite direction of the flow, thus causing its deceleration. Also the effect of pressure gradient is investigated on velocity and microrotation in different diagrams.

New Stent for Transapical Mitral Valve Replacement in Acute Swine Experiment

2020 ◽  
Author(s):  
Yu Zou ◽  
Peng Teng ◽  
Liang Ma
Keyword(s):  
Mitral Valve ◽  
Pressure Gradient ◽  
Valve Replacement ◽  
Mitral Valve Replacement ◽  
Mitral Annulus ◽  
The Self ◽  
Purse String ◽  
Transcatheter Mitral Valve Replacement ◽  
Before And After ◽  
The Mean

Abstract Background: Many patients with mitral regurgitation are denied open-heart surgery due to high risk. Transcatheter mitral valve replacement offers an alternative treatment. This study aimed to test the feasibility of a new self-expanding valved stent for transcatheter mitral valve replacement via apex in an acute animal model.Methods: Eight porcine experiments were performed in the acute study. A left thoracotomy was performed. The new self-expanding transcatheter valved stent was deployed under fluoroscopic guidance within the native mitral annulus via apex. Hemodynamic data, before and after implantation, were recorded. Mitral annulus diameter and valve area were measured using echocardiography. Transvalvular and left ventricular outflow tract pressure gradient were measured invasively. Results: Seven animals underwent successful transapical mitral valve replacement; the implantation was unsuccessful in one animal. The mean procedure time, defined from placing the purse-string to tightening the purse-string, was 17.14 ± 7.86 min. Hemodynamic data before and after transapical mitral valve replacement showed no difference in statistical analysis. The mean diameter and mean functional area of the self-expanding device after implantation were 2.58 ± 1.04 cm and 2.70 ± 0.26 cm2, respectively. Trace to mild central and paravalvular leak was detected in 7 valves. Mean pressure gradient across the self-expanding device was 2.00 ± 0.82 mm Hg; the corresponding gradients across the LVOT were 3.28± 1.11 mm Hg. Postmortem examinations confirmed precise device positioning in 7 animals with no signs of LVOT obstruction.Conclusion: Transcatheter mitral replacement of the new valved stent was confirmed feasible in acute preclinical models. The new stent reveals optimal design parameters.

scholarly journals Grinding Test on Tremolite with Fibrous and Prismatic Habit

Fibers ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 52 ◽  
Author(s):  
Oliviero Baietto ◽  
Mariangela Diano ◽  
Giovanna Zanetti ◽  
Paola Marini
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Health And Safety ◽  
Optical Microscope ◽  
Diameter Ratio ◽  
Grinding Process ◽  
Identification Procedure ◽  
Dimensional Parameter ◽  
Before And After ◽  
Scanning Electron

The main objective of this work is the evaluation of the morphology change in tremolite particles before and after a grinding process. The crushing action simulates anthropic alteration of the rock, such as excavation in rocks containing tremolite during a tunneling operation. The crystallization habit of these amphibolic minerals can exert hazardous effects on humans. The investigated amphibolic minerals are four tremolite samples, from the Piedmont and Aosta Valley regions, with different crystallization habits. The habits can be described as asbestiform (fibrous) for longer and thinner fibers and non-asbestiform (prismatic) for prismatic fragments, also known as “cleavage” fragments. In order to identify the morphological variation before and after the grinding, both a phase contrast optical microscope (PCOM) and a scanning electron microscope (SEM) were used. The identification procedure for fibrous and prismatic elements is related to a dimensional parameter (length–diameter ratio) defined by the Health and Safety Executive. The results highlight how mineral comminution leads to a rise of prismatic fragments and, therefore, to a potentially safer situation for worker and inhabitants.

Cerebrospinal fluid transients induced by hypercapnia

1983 ◽  
Vol 245 (5) ◽  
pp. R701-R705
Author(s):  
M. J. Fisher ◽  
S. R. Heisey ◽  
T. Adams ◽  
D. L. Traxinger
Keyword(s):  
Cerebrospinal Fluid ◽  
Formation Rate ◽  
Tracer Concentration ◽  
Perfusion Studies ◽  
Fluid Redistribution ◽  
Ventriculocisternal Perfusion ◽  
Before And After ◽  
Outflow Rate ◽  
The Times ◽  
Stop Flow

Ventriculocisternal perfusion studies using tracers have shown that hypercapnia causes a transient increase in cerebrospinal fluid (CSF) outflow rate (displaced CSF volume, Vd) and a decrease in CSF effluent tracer concentration (tracer-free CSF, CSFtf). This dilution could be due to an increase in CSF formation rate (Vf) and/or to displacement of unequilibrated CSFtf sequestered in poorly mixed compartments. To facilitate convection in the subarachnoid spaces, we used a “stop-flow” procedure (by clamping the cisternal outflow tube while infusion was constant) in anesthetized cats during ventriculocisternal perfusion with mock CSF containing [14C]dextran. Each animal spontaneously breathed air, then 5% CO2 both before and after stopflow. Although Vd and the times over which Vd and CSFtf were defined were unaffected, CSFtf was decreased by 50% after stop-flow. We conclude that during ventriculocisternal perfusion, mixing is incomplete in CSF spaces, and that unequilibrated CSF contributes significantly to the reduced tracer concentration in Vd during acute hypercapnia. To determine whether Vf transiently increases in response to CO2 breathing, or to any perturbation causing craniospinal fluid redistribution, homogeneity in CSF spaces must be verified.

scholarly journals Relation of coronary artery stenosis and pressure gradient to exercise-induced ischemia before and after coronary angioplasty

1987 ◽  
Vol 10 (2) ◽  
pp. 253-260 ◽  
Author(s):  
Richard J. Peterson ◽  
Spencer B. King ◽  
William A. Fajman ◽  
John S. Douglas ◽  
Andreas R. Grüntzig ◽  
...  
Keyword(s):  
Coronary Artery ◽  
Pressure Gradient ◽  
Coronary Angioplasty ◽  
Coronary Artery Stenosis ◽  
Artery Stenosis ◽  
Before And After ◽  
Exercise Induced
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