Thematische Bibliographien / Flow shunting

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Auswahl der wissenschaftlichen Literatur zum Thema „Flow shunting“

Autor: Grafiati

Veröffentlicht am 28. Juni 2021

Zuletzt aktualisiert am 1. Februar 2022

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Zeitschriftenartikel zum Thema "Flow shunting"

Smolich, Joseph J., Kelly R. Kenna, Michael M. H. Cheung und Jonathan P. Mynard. „Brief asphyxial state following immediate cord clamping accelerates onset of left-to-right shunting across the ductus arteriosus after birth in preterm lambs“. Journal of Applied Physiology 128, Nr. 2 (01.02.2020): 429–39. http://dx.doi.org/10.1152/japplphysiol.00559.2019.

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Reversal of shunting across the ductus arteriosus from right-to-left to left-to-right is a characteristic feature of the birth transition. Given that immediate cord clamping (ICC) followed by an asphyxial cord clamp-to-ventilation (CC-V) interval may augment left ventricular (LV) output and central blood flows after birth, we tested the hypothesis that an asphyxial CC-V interval accelerates the onset of postnatal left-to-right ductal shunting. High-fidelity central blood flow signals were obtained in anesthetized preterm lambs (gestation 128 ± 2 days) after ICC followed by a nonasphyxial (∼40 s, n = 9) or asphyxial (∼90 s, n = 9) CC-V interval before mechanical ventilation for 30 min after birth. Left-to-right ductal flow segments were related to aortic isthmus and descending aortic flow profiles to quantify sources of ductal shunting. In the nonasphyxial group, phasic left-to-right ductal shunting was initially minor after birth, but then rose progressively to 437 ± 164 ml/min by 15 min ( P < 0.001). However, in the asphyxial group, this shunting increased from 24 ± 21 to 199 ± 93 ml/min by 15 s after birth ( P < 0.001) and rose further to 471 ± 190 ml/min by 2 min ( P < 0.001). This earlier onset of left-to-right ductal shunting was supported by larger contributions ( P < 0.001) from direct systolic LV flow and retrograde diastolic discharge from an arterial reservoir/windkessel located in the descending aorta and its major branches, and associated with increased pulmonary arterial blood flow having a larger ductal component. These findings suggest that the duration of the CC-V interval after ICC is an important modulator of left-to-right ductal shunting, LV output and pulmonary perfusion at birth. NEW & NOTEWORTHY This birth transition study in preterm lambs demonstrated that a brief (∼90 s) asphyxial interval between umbilical cord clamping and ventilation onset resulted in earlier and greater left-to-right shunting across the ductus arteriosus after birth. This greater shunting 1) resulted from an increased left ventricular output associated with a higher systolic left-to-right ductal flow and increased retrograde diastolic discharge from a lower body arterial reservoir/windkessel, and 2) was accompanied by greater lung perfusion after birth.

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Javlé, P., J. Yates, H. G. Kynaston, K. F. Parsons und S. A. Jenkins. „Hepatosplanchnic haemodynamics and renal blood flow and function in rats with liver failure“. Gut 43, Nr. 2 (01.08.1998): 272–79. http://dx.doi.org/10.1136/gut.43.2.272.

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Background—Massive liver necrosis, characteristic of acute liver failure, may affect hepatosplanchnic haemodynamics, and contribute to the alterations in renal haemodynamics and function.Aims—To investigate the relation between hepatosplanchnic haemodynamics, including portal systemic shunting, and renal blood flow and function in rats with acute liver failure.Methods—Liver failure was induced in male Wistar rats by intraperitoneal injection of 1.1 g/kg ofd(+)-galactosamine hydrochloride. The parameters assessed included: systemic, hepatosplanchnic, and renal blood flow (57Co microsphere method); portal-systemic shunting and intrarenal shunting (consecutive intrasplenic, intraportal, or renal arterial injections of 99mTc methylene diphosphonate and99mTc albumin microspheres); arterial blood pressure and portal pressure; renal function; and liver function (liver function tests and 14C aminopyrine breath test).Results—Progressive liver dysfuntion was accompanied by the development of a hyperdynamic circulation, a highly significant decrease in renal blood flow and function, and an increase in intrarenal shunting 36, 42, and 48 hours after administration of d-galactosamine. The alterations in renal blood flow and function were accompanied by significant increases in portal pressure, portal venous inflow, and intrahepatic portal systemic shunting in galactosamine treated rats compared with controls. There was a significant correlation between changes in renal blood flow and changes in portal pressure, intrahepatic portal systemic shunting, and deterioration in liver function (r=0.8, p<0.0001).Conclusions—The results of this study suggest that both increased intrahepatic portal systemic shunting and hepatocyte impairment may contribute to alterations in renal haemodynamics and function.

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Shepherd, A. P., und J. W. Kiel. „A model of countercurrent shunting of oxygen in the intestinal villus“. American Journal of Physiology-Heart and Circulatory Physiology 262, Nr. 4 (01.04.1992): H1136—H1142. http://dx.doi.org/10.1152/ajpheart.1992.262.4.h1136.

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This report describes a mathematical model of the countercurrent shunting (CCS) of O2 in the intestinal villus. The anatomic basis for the model is the close proximity of the arteriole and venule between which O2 is free to diffuse. The model divides the villus into four segments from base to tip. Steady-state equations describe the convective and diffusive fluxes of O2 in the arteriolar, capillary, and tissue compartments within each segment. Longitudinal diffusion along the length of the villus is assumed to be negligible. Simulations with the model led to the following observations: 1) CCS shifted the VO2 vs. blood flow curve down and to the right, slightly impairing VO2 at a given blood flow; 2) the base-to-tip PO2 gradient caused by the tissue O2 consumption was reduced by CCS; 3) when blood flow was reduced, the base-to-tip PO2 gradient increased until the tip PO2 fell to zero and then fell with further flow reductions; 4) lowering blood flow initially caused slight increases in shunting but further decreases in flow reduced shunting; 5) in the blood flow range in which VO2 was flow independent, increasing the O2 demand or decreasing the intervascular distance increased shunting because of the greater arteriole-to-capillary O2 concentration gradient and the decreased diffusion distance, respectively; and 6) lowering the hemoglobin's P50 to simulate fetal blood caused slight reductions in shunting and reduced VO2 at a given flow. In summary, the model confirms the potentially deleterious effects of CCS on intestinal oxygenation, and, in contrast to assertions in the literature, it shows that a base-to-tip PO2 gradient is not prima facie evidence of counter-current shunting.

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Zierer, Andreas, Spencer J. Melby, Rochus K. Voeller und Marc R. Moon. „Interatrial shunt for chronic pulmonary hypertension: differential impact of low-flow vs. high-flow shunting“. American Journal of Physiology-Heart and Circulatory Physiology 296, Nr. 3 (März 2009): H639—H644. http://dx.doi.org/10.1152/ajpheart.00496.2008.

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The purpose of the present study was to determine for the first time the qualitative and quantitative impact of varying degrees of interatrial shunting on right heart dynamics and systemic perfusion in subjects with chronic pulmonary hypertension (CPH). Eight dogs underwent 3 mo of progressive pulmonary artery banding, following which right atrial and ventricular end-systolic and end-diastolic pressure-volume relations were calculated using conductance catheters. An 8-mm shunt prosthesis was inserted between the superior vena cava and left atrium, yielding a controlled model of atrial septostomy. Data were obtained 1) preshunt or “CPH”; 2) “Low-Flow” shunt; and 3) “High-Flow” shunt (occluding superior vena cava forcing all flow through the shunt). With progressive shunting, right ventricular pressure fell from 72 ± 19 mmHg (CPH) to 54 ± 17 mmHg (Low-Flow) and 47 ± 17 mmHg (High-Flow) ( P < 0.001). Cardiac output increased from 1.5 ± 0.3 l/min at CPH to 1.8 ± 0.4 l/min at Low-Flow (286 ± 105 ml/min, 15% of cardiac output; P < 0.001), but returned to 1.6 ± 0.3 l/min at High-Flow (466 ± 172 ml/min, 29% of cardiac output; P = 0.008 vs. Low-Flow, P = 0.21 vs. CPH). There was a modest rise in systemic oxygen delivery from 252 ± 46 ml/min at CPH to 276 ± 50 ml/min at Low-Flow ( P = 0.07), but substantial fall to 222 ± 50 ml/min at High-Flow ( P = 0.005 vs. CPH, P < 0.001 vs. Low-Flow). With progressive shunting, bichamber contractility did not change ( P = 0.98), but the slope of the right atrial end-diastolic pressure volume relation decreased ( P < 0.04), consistent with improved compliance. This study demonstrated that Low-Flow interatrial shunting consistently improved right atrial mechanics and systemic perfusion in subjects with CPH, while High-Flow exceeded an “ideal shunt fraction”.

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Smolich, Joseph J., Kelly R. Kenna und Jonathan P. Mynard. „Retrograde lower body arterial reservoir discharge underlies rapid reversal of ductus arteriosus shunting after early cord clamping at birth in preterm lambs“. Journal of Applied Physiology 120, Nr. 4 (15.02.2016): 399–407. http://dx.doi.org/10.1152/japplphysiol.00794.2015.

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Arterial reservoir (“windkessel”) function, whereby a part of left ventricular (LV) output is stored in elastic arteries during systole and discharged in diastole, is a well-established physiological phenomenon. However, its role in rapid reversal (to left-to-right) and a systolic-to-diastolic shift of shunting across the ductus arteriosus after birth is unknown. To address this question, ductal and aortic isthmus flows were measured with high-fidelity transit-time probes in six anesthetized preterm fetal lambs before and after cord clamping and subsequent early mechanical ventilation and for 30 min postbirth. Descending aortic flow was calculated as the sum of isthmus and ductal flows. Left-to-right ductal flow profiles were related to those of the isthmus and descending aorta, with upper body arterial reservoir discharge indicated by forward diastolic isthmus flow, and retrograde lower body arterial reservoir discharge by negative diastolic descending aortic flow. Left-to-right ductal shunting appeared immediately after cord clamping ( P < 0.001), due entirely to newly emergent retrograde lower body reservoir discharge, and rose with ventilation via increased lower body reservoir discharge ( P < 0.005), supplemented by upper body reservoir discharge after 45 s ( P < 0.025) and LV systolic flow after 3 min ( P = 0.025). The contribution of lower body reservoir discharge to left-to-right ductal shunting fell to 55 ± 8% at ≥15 min ( P < 0.001) but remained higher ( P < 0.002) than LV systolic flow (33 ± 8%) or upper body reservoir discharge (12 ± 5%). These results suggest that retrograde lower body arterial reservoir discharge plays a key role in rapid reversal and a systolic-to-diastolic shift of ductal shunting after cord clamping and early ventilation at birth.

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Diller, Gerhard-Paul, Astrid E. Lammers, Sheila G. Haworth, Konstantinos Dimopoulos, Graham Derrick, Philipp Bonhoeffer, Michael A. Gatzoulis und Darrel P. Francis. „A modelling study of atrial septostomy for pulmonary arterial hypertension, and its effect on the state of tissue oxygenation and systemic blood flow“. Cardiology in the Young 20, Nr. 1 (Februar 2010): 25–32. http://dx.doi.org/10.1017/s1047951109991855.

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AbstractAtrial septostomy is performed in patients with severe pulmonary arterial hypertension, and has been shown to improve symptoms, quality of life and survival. Despite recognized clinical benefits, the underlying pathophysiologic mechanisms are poorly understood. We aimed to assess the effects of right-to-left shunting on arterial delivery of oxygen, mixed venous content of oxygen, and systemic cardiac output in patients with pulmonary arterial hypertension and a fixed flow of blood to the lungs. We formulated equations defining the mandatory relationship between physiologic variables and delivery of oxygen in patients with right-to-left shunting. Using calculus and computer modelling, we considered the simultaneous effects of right-to-left shunting on physiologies with different pulmonary flows, total metabolic rates, and capacities for carrying oxygen. Our study indicates that, when the flow of blood to the lungs is fixed, increasing right-to-left shunting improves systemic cardiac output, arterial blood pressure, and arterial delivery of oxygen. In contrast, the mixed venous content of oxygen, which mirrors the average state of tissue oxygenation, remains unchanged. Our model suggests that increasing the volume of right-to-left shunting cannot compensate for right ventricular failure. Atrial septostomy in the setting of pulmonary arterial hypertension, therefore, increases the arterial delivery of oxygen, but the mixed systemic saturation of oxygen, arguably the most important index of tissue oxygenation, stays constant. Our data suggest that the clinically observed beneficial effects of atrial septostomy are the result of improved flow of blood rather than augmented tissue oxygenation, provided that right ventricular function is adequate.

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Mascalchi, M., G. Arnetoli, D. Inzitari, G. Dal Pozzo, F. Lolli, D. Caramella und C. Bartolozzi. „Cine-MR Imaging of Aqueductal CSF Flow in Normal Pressure Hydrocephalus Syndrome before and after CSF Shunt“. Acta Radiologica 34, Nr. 6 (November 1993): 586–92. http://dx.doi.org/10.1177/028418519303400612.

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Reproducibility of the aqueductal CSF signal intensity on a gradient echo cine-MR sequence exploiting through plane inflow enhancement was tested in 11 patients with normal or dilated ventricles. Seven patients with normal pressure hydrocephalus (NPH) syndrome were investigated with the sequence before and after CSF shunting. Two patients exhibiting central flow void within a hyperintense aqueductal CSF improved after surgery and the flow void disappeared after shunting. One patient with increased maximum and minimum aqueductal CSF signal as compared to 18 healthy controls also improved and the aqueductal CSF signal was considerably decreased after shunting. Three patients with aqueductal CSF values similar to those in the controls did not improve, notwithstanding their maximum aqueductal CSF signals decreasing slightly after shunting. No appreciable aqueductal CSF flow related enhancement consistent with non-communicating hydrocephalus was found in the last NPH patient who improved after surgery. Cine-MR with inflow technique yields a reproducible evaluation of flow-related aqueductal CSF signal changes which might help in identifying shunt responsive NPH patients. These are likely to be those with hyperdynamic aqueductal CSF or aqueductal obstruction.

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Ordia, Joe I., Ronald W. Mortara und Edward L. Spatz. „Audible cerebrospinal fluid flow through a ventriculoperitoneal shunt“. Journal of Neurosurgery 67, Nr. 3 (September 1987): 460–62. http://dx.doi.org/10.3171/jns.1987.67.3.0460.

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Smolich, Joseph J., Kelly R. Kenna und Jonathan P. Mynard. „Antenatal betamethasone augments early rise in pulmonary perfusion at birth in preterm lambs: role of ductal shunting and right ventricular outflow distribution“. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 316, Nr. 6 (01.06.2019): R716—R724. http://dx.doi.org/10.1152/ajpregu.00318.2018.

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The glucocorticosteroid betamethasone is routinely administered via maternal intramuscular injection to enhance fetal lung maturation before anticipated preterm birth. Although antenatal betamethasone increases fetal pulmonary arterial (PA) blood flow, whether this agent alters the contribution of 1) right ventricular (RV) output or 2) left-to-right shunting across the ductus arteriosus to rises in PA blood flow after preterm birth is unknown. To address this question, anesthetized control ( n = 7) and betamethasone-treated ( n = 7) preterm fetal lambs (gestation 127 ± 1 days, means ± SD) were instrumented with aortic, pulmonary, and left atrial catheters as well as ductus arteriosus and left PA flow probes to calculate RV output, with hemodynamics measured for 30 min after cord clamping and mechanical ventilation. Mean PA blood flow was higher in betamethasone-treated than in control lambs over the initial 10 min after birth ( P < 0.05). This higher PA flow was accompanied by 1) a greater pulmonary vascular conductance ( P ≤ 0.025), 2) a larger proportion of RV output passing to lungs ( P ≤ 0.01), despite a fall in this output, and 3) earlier reversal and a greater magnitude ( P ≤ 0.025) of net ductal shunting, due to the combination of higher left-to-right ( P ≤ 0.025) and lesser right-to-left phasic shunting ( P ≤ 0.025). These results suggest that antenatal betamethasone augments the initial rise in PA blood flow after birth in preterm lambs, with this augmented rise supported by the combination of 1) a greater redistribution of RV output toward the lungs and 2) a faster and larger reversal in net ductal shunting underpinned not only by greater left-to-right, but also by lesser right-to-left phasic shunting.

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Hawkins, P. A., M. R. DeJoseph und R. A. Hawkins. „Eliminating metabolic abnormalities of portacaval shunting by restoring normal liver blood flow“. American Journal of Physiology-Endocrinology and Metabolism 270, Nr. 6 (01.06.1996): E1037—E1042. http://dx.doi.org/10.1152/ajpendo.1996.270.6.e1037.

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Portacaval shunting causes a variety of anatomic, metabolic, and physiological changes. However, it has not been determined whether, and to what degree, these changes are permanent after a sustained period of shunting. We prepared three groups of rats for study of the recovery process. One group had side-to-side shunts for 3 wk, one group had side-to-side shunts for 2 wk followed by the restoration of normal liver circulation for 1 wk, and one group (control) had sham operations. Side-to-side shunting causes liver atrophy, increased plasma ammonia, altered plasma and brain amino acid spectra, decreased plasma glucose, and increased transport of neutral amino acids across the blood-brain barrier. After restoration of the normal pattern of liver circulation by shunt repair, the liver regained its normal size within 1 day. All abnormalities associated with liver dysfunction disappeared with the exception of plasma glucose, which remained approximately 15% lower than control values.

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Mehr Quellen

Dissertationen zum Thema "Flow shunting"

Šišmiš, Lukáš. „Optimalizace IDS/IPS systému Suricata“. Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2021. http://www.nusl.cz/ntk/nusl-445503.

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V dnešnom svete zrýchľujúcej sa sieťovej prevádzky je potrebné držať krok v jej monitorovaní . Dostatočný prehľad o dianí v sieti dokáže zabrániť rozličným útokom na ciele nachádzajúce sa v nej . S tým nám pomáhajú systémy IDS, ktoré upozorňujú na udalosti nájdené v analyzovanej prevádzke . Pre túto prácu bol vybraný systém Suricata . Cieľom práce je vyladiť nastavenia systému Suricata s rozhraním AF_PACKET pre optimálnu výkonnosť a následne navrhnúť a implementovať optimalizáciu Suricaty . Výsledky z meraní AF_PACKET majú slúžiť ako základ pre porovnanie s navrhnutým vylepšením . Navrhovaná optimalizácia implementuje nové rozhranie založené na projekte Data Plane Development Kit ( DPDK ). DPDK je schopné akcelerovať príjem paketov a preto sa predpokladá , že zvýši výkon Suricaty . Zhodnotenie výsledkov a porovnanie rozhraní AF_PACKET a DPDK je možné nájsť na konci diplomovej práce .

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Ostlin, Janice Christine. „Cardiac shunting and blood flow distribution in the American alligator (ALLIGATOR MISSISSIPPIENSIS)“. Thesis, 1997. http://hdl.handle.net/2429/6562.

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The cardiac and circulatory anatomy of the American alligator (Alligator mississippiensis) is unique in that both the cardiac and systemic circulatory systems display anatomical divisions. This situation may also be of physiological significance to the animal. The purpose of this study was to determine regional blood flow distribution in the alligator, with respect to cardiac blood flow patterns. Animals were instrumented with flow and pressure recorders, and monitored over extended time periods. Fluorescent microspheres capable of being entrapped in tissue capillary beds were introduced into both the right and left aortas under various conditions. Blood flow distribution to tissues during the presence or absence of a pulmonary to systemic (P->S shunt) was of primary interest. Tissue samples depicted a significant separation in the perfusion patterns of the right and left aortas. The right aorta primarily perfused the brain and liver, and to a lesser extent, the digestive system organs. The left aorta perfused the digestive tract organs, including the spleen. Dissection of the circulatory paths of the right and left aortas determined this anatomical division. Possible differences in the left aortic distribution of right ventricular (shunted) blood as compared to left ventricular (not shunted) blood were noted.

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Li, Yi-Jian, und 李宜堅. „Cerebral Blood Flow Velocity and Vasomotor Reactivity before and after Shunting Surgery in Patients with Normal Pressure Hydrocephalus“. Thesis, 1997. http://ndltd.ncl.edu.tw/handle/24831229639771129866.

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Lee, E.-Jian, und 李宜堅. „Cerebral Blood Flow Velocity and Vasomotor Reactivity before and after Shunting Surgery in Patients with Normal Pressure Hydrocephalus“. Thesis, 1997. http://ndltd.ncl.edu.tw/handle/48826035231997811722.

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碩士
國立成功大學
醫學工程學系
86
ABSTRACTOBJECTIVE:The aim of the study was to evaluate the hemodynamic changes and their correlationwith the clinical results by measurement of cerebral blood flow velocity (CBFV) andcerebral vasomotor reserve before and after shunt placement in normal pressurehydrocephalus (NPH).METHODS:Ten demented patients with clinical signs suggestive of NPH received examinationsof blood flow velocity (BFV) and vasomotor reactivity (VMR) of the anterior cerebralartery (ACA) and the middle cerebral artery (MCA) by transcranial Doppler sonographywith carbogen testing before and after shunt treatment. Computerized tomography (CT),clinical assessment and neuropsychological grading were performed prior to and at 3months following surgery. A control group consisting of 7 patients, who underwentlumbar spine surgery, was included to establish baseline data for BFV and VMR values.RESULTS:Compared to the control group, the preoperative CBF studies revealed the NPH patienthad no significant decrease of BFVs in both the MCA and the ACA (P > 0.05), but hadsignificant decrease of carbogen VMR in both those two vessels (P < 0.05). Aftershunting, there were no significant changes of the BFVs in the 2 vessels as comparedto the pre-shunting data (P > 0.05). The post-shunting VMR of ACA was significantlyhigher than the pre-shunting one (p < 0.05), but there was no significance in thatof MCA (p > 0.05). Seven of the ten patients shown mentality or more symptomsimprovement were considered as good results (responsive to shunt). The remaining 3patients, who had consistent symptoms without recognizable problems, were consideredas bad results (shunt failure). Both the value of post-shunting VMR in ACA and thepost-shunting improvement of VMR in MCA of the 7 shunt- responsive patients weresignificantly higher than those of shunt-failure patients (p < 0.05). Within the tenpatients, five patients with gait improvement showed significantly in the value ofpost-shunting VMR of ACA and the post-shunting improvement of VMR for both ACA andMCA by comparing those patients without gait improvement (p < 0.05, respectively).CONCLUSION:Our results support that the patient with NPH did not have decreased BFVs, but hadvarious degrees of impaired vasomotor reserve in both the ACA and the MCA, increasingthe risk of ischemic brain insult. Shunt placement improves the VMR in responsivepatients, consequently preventing from the ischemic insult. Post-shunting increaseof VMR accompanies with the improvement of functional state in shunt-responsivepatients; however, post-shunting increase of VMR in the MCA only, and in both the ACAand the MCA are associated with symptomatic improvement in mentality, and improvementin gait, respectively. These close relationships have implications for prognosticimportance and pathophysiology in NPH.Key Words: Normal pressure hydrocephalus, Cerebral blood flow velocity, Vasomotorreactivity.

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Buchteile zum Thema "Flow shunting"

Hoekstra, A., und M. Sussman. „Hydrocephalus Management With a Flow-Control Shunt: Overdrainage and Proximal Obstruction: Controllable Complications of Shunting“. In Biomedical and Life Physics, 311–32. Wiesbaden: Vieweg+Teubner Verlag, 1996. http://dx.doi.org/10.1007/978-3-322-85017-1_30.

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Sirakov, Alexander, Marta Aguilar Pérez, Klaus Terstegge, Erich Donauer und Hans Henkes. „Vertebral Artery Junction Aneurysm: Brain Stem Compression due to a Giant Dolichoectatic and Partially Thrombosed Aneurysm Involving the Intradural Segments of Both Vertebral Arteries and the Proximal Trunk of the Basilar Artery; Asymptomatic Thrombosis of the Vertebral Artery Junction After Ventricle Shunting; Endovascular Disconnection of the Vertebrobasilar Junction Using Coil Occlusion of Both V4 Segments and Flow Diverter Stent Deployment from Both Posterior Inferior Cerebellar Arteries to the Afferent V4 Segments; Long-Term Follow-Up Showing Aneurysm Shrinkage and Good Clinical Outcome“. In The Aneurysm Casebook, 1159–74. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-319-77827-3_156.

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Sirakov, Alexander, Marta Aguilar Pérez, Klaus Terstegge, Erich Donauer und Hans Henkes. „Vertebral Artery Junction Aneurysm: Brain Stem Compression due to a Giant Dolichoectatic and Partially Thrombosed Aneurysm Involving the Intradural Segments of Both Vertebral Arteries and the Proximal Trunk of the Basilar Artery; Asymptomatic Thrombosis of the Vertebral Artery Junction After Ventricle Shunting; Endovascular Disconnection of the Vertebrobasilar Junction Using Coil Occlusion of Both V4 Segments and Flow Diverter Stent Deployment from Both Posterior Inferior Cerebellar Arteries to the Afferent V4 Segments; Long-Term Follow-Up Showing Aneurysm Shrinkage and Good Clinical Outcome“. In The Aneurysm Casebook, 1–17. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-319-70267-4_156-1.

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Baird, Lissa C. „Vein of Galen Malformation“. In Pediatric Neurosurgery, 157–64. Oxford University Press, 2019. http://dx.doi.org/10.1093/med/9780190617073.003.0018.

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Vein of Galen malformations consist of multiple arteriovenous fistulas shunting arterial blood into the persistent embryonic prosencephalic vein of Markowski. The mural type are characterized by fewer fistulas and commonly present with progressive hydrocephalus. The choroidal type malformations have more complex and numerous fistulas, have higher flow, and commonly present with severe high-output cardiac failure. Transfemoral transarterial embolization at the fistula sites of the malformation for complete obliteration of arteriovenous shunting is the optimal intervention. An interdisciplinary approach is critical from the time of diagnosis through the post-treatment follow-up period. Sequelae of cardiac failure and end-organ damage may be minimized with early endovascular intervention when indicated and complete embolization when feasible.

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Witschey, Walter RT, und Michael Markl. „Blood flow and phase contrast CMR“. In The EACVI Textbook of Cardiovascular Magnetic Resonance, herausgegeben von Massimo Lombardi, Sven Plein, Steffen Petersen, Chiara Bucciarelli-Ducci, Emanuela R. Valsangiacomo Buechel, Cristina Basso und Victor Ferrari, 146–63. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198779735.003.0018.

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Flow-sensitive cardiovascular magnetic resonance (CMR) is a widespread non-invasive imaging method for the clinical evaluation of blood flow in cardiovascular disease. The basic principle of phase contrast magnetic resonance imaging (MRI) is the use of bipolar gradients to encode blood velocity in the magnetic resonance (MR) signal phase. The most common type of flow-encoded scan two-dimensional (2D) cine phase contrast CMR with single-direction velocity encoding is clinically used to quantify cardiovascular flow and velocities. Trade-offs between resolution (temporal and spatial) and acquisition time are illustrated in the context of patient examination, considering high-velocity jet flow, patient breath-hold duration, respiratory motion artefacts, and patient comfort. In addition, the chapter describes how the velocity-to-noise ratio and aliasing behaviour of flow measurements are affected by the velocity-encoding sensitivity (VENC). An advantage of phase contrast MR is that flow encoding may be performed in all three spatial dimensions, improving peak velocity measurement accuracy. Several clinical applications (aortic stenosis, coarctation, and ventricular shunting) and best practices are explained in detail with illustrations. Analysis and post-processing of phase contrast data are summarized. The progressive development of advanced phase contrast techniques is discussed by adding incremental complexity, starting with 2D phase contrast (2D spatial and one-dimensional velocity) and ending with four-dimensional flow encoding (three-dimensional spatial and velocity). Methods to accelerate phase contrast, such as parallel imaging, are briefly discussed. Finally, the chapter concludes with a summary of emerging topics for accelerated scanning and special applications such as compressed sensing, real-time phase contrast, and ultra-short echo time imaging.

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Konferenzberichte zum Thema "Flow shunting"

Zhao, Jun, und Qiyuan Peng. „Integrated Wagon-Flow Allocation and Shunting Locomotive Scheduling Problem at Railyard with Multiple Locomotives“. In Inernational Conference of Logistics Engineering and Management 2012. Reston, VA: American Society of Civil Engineers, 2012. http://dx.doi.org/10.1061/9780784412602.0020.

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Zhang, Yi, und Jun Zhao. „A New Model for Solving Integrated Wagon-Flow Allocation and Shunting Locomotive Scheduling Problem at Railyard“. In Third International Conference on Transportation Engineering (ICTE). Reston, VA: American Society of Civil Engineers, 2011. http://dx.doi.org/10.1061/41184(419)145.

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Mu, Feng, Ciguang Wang und Yun Jing. „Model of Taking-Out and Placing-In Shunting of Non-Through Wagon Flow on Branch-Shaped Sidings“. In Second International Conference on Transportation Engineering. Reston, VA: American Society of Civil Engineers, 2009. http://dx.doi.org/10.1061/41039(345)119.

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Collet, Manuel, Ken A. Cunefare, Massimo Ruzzene, Morvan Ouisse, Benjamin Beck, L. Airoldi und F. Casadei. „Beams and Plates Vibroacoustic Energy Diffusion Optimization by Mean of Distributed Shunted Piezoelectric Patches“. In ASME 2009 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2009. http://dx.doi.org/10.1115/smasis2009-1256.

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The paper proposes a synthesis of different new methodologies for developing a distributed, integrated shunted piezo composite for beams and plates applications able to modify the structural vibro acoustical impedance of the passive supporting structure so as to absorb or reflect incidental power flow. This design implements tailored structural responses, through integrated passive and active features, and offers the potential for higher levels of vibration isolation as compared to current designs. Novel active and passive shunting configurations will be investigated to reduce vibrations such as distributed Resistance Inductance and Resistance with negative Capacitance circuits.

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Biglino, Giovanni, Ethan Kung, Adam Dorfman, Andrew M. Taylor, Edward Bove, Alison Marsden, Tain-Yen Hsia und Silvia Schievano. „A Hemi Fontan Operation Performed by an Engineer: Considerations on Virtual Surgery“. In ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14451.

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Single ventricle circulation, characterized at birth by a rudimentary or absent left or right ventricle, presents a challenging and life-threatening physiological scenario. Surgical palliation aims to restore the balance between systemic and pulmonary blood flow and is staged, each of the three stages presenting the surgeon with different options: - Stage 1 (Norwood procedure) involves different types of shunting to source pulmonary blood flow, or recently a hybrid approach [1]; - Stage 2 can involve a superior cavopulmonary connection (Glenn operation) or patching between the right atrium and the pulmonary arteries (Hemi Fontan operation [2]); - Stage 3 involves a total cavopulmonary connection with extracardiac conduit or lateral tunnel, or with novel alternatives such as the Y-graft [3].

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Collet, Manuel, Morvan Ouisse, Mohammed Ichchou und Roger Ohayon. „Semi-Active Optimization of 2D Wave’s Dispersion Into Shunted Piezocomposite Systems for Controlling Acoustic Interaction“. In ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/smasis2011-5018.

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In this paper, we present an application of the Floquet-Bloch theorem in the context of electrodynamics for vibroacoustic power flow optimization by mean of distributed and shunted piezoelectric patches. The main purpose of this work is first to propose a dedicated numerical approach able to compute the multi-modal wave dispersions curves into the whole first Brillouin zone for periodically distributed 2D shunted piezomechanical systems. By using two specific indicators evaluating the evanescent part of Bloch’s waves and the induced electronic damping, we optimize the piezoelectric shunting electrical impedance for controlling energy diffusion into the proposed semi-active distributed set of cells. Sound radiation efficiency is also analyzed for showing the effects of such smart metamaterial for controlling acoustical noise.

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Cross, Charles J., und Sanford Fleeter. „Shunted Piezoelectric Control of Airfoil Vibrations“. In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-385.

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The application of shunted piezoelectric elements to provide passive structural damping is investigated by means of experiments performed in the Purdue High Speed Axial Compressor Research Facility. Piezoelectric elements are bonded to three airfoils in the stator row. This airfoil is excited by the wakes generated by an upstream rotor. As the wakes drive the airfoil vibrations, the piezoelectrics experience a strain and in response produce an electric field. Tuned electrical circuits connected to the piezoelectrics as shunts dissipate this electrical energy, with multiple shunting techniques utilized. This electrical energy dissipation and the corresponding reduction in the airfoil mechanical energy result in a reduction in the magnitude of the resonant vibrations. Thus, these passive vibration control experiments demonstrate that shunted piezoelectrics have significant damping capability and could be practical for the elimination or minimization of gas turbine blading flow induced vibrations.

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Swim, Benjamin M., Julie A. Reyer, Martin J. Morris und Julian J. Lin. „Development of an Apparatus for the Testing of Hydrocephalic Shunts“. In ASME 2006 Frontiers in Biomedical Devices Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/nanobio2006-18025.

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This abstract summarizes the development of a new apparatus designed to test hydrocephalic shunts. Hydrocephalus is a medical condition most commonly characterized by above-normal intracranial pressure (ICP) that occurs when a patient’s head cannot properly regulate cerebrospinal fluid (CSF) volume in the head. The condition is generally caused by a blockage to flow of CSF in the normal biological pathways. This can result from a birth defect, trauma, or disease. In a hydrocephalic patient, excess fluid builds up in the ventricles resulting in increased mechanical stress and physical deformation of the brain. Untreated, this condition can be quite severe and can lead to brain damage or death. Standard treatment involves implanting an artificial shunt to drain the ventricle and bypass the blockage. The CSF is normally routed to the abdominal cavity. Reducing fluid volume alleviates high ICP and mechanical stress on the brain. Shunting improves the survival rate from 30 to 60 percent for untreated patients to 65 to 95 percent for patients with shunt systems installed [1].

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Tateo, F., M. Collet, M. Ouisse, M. N. Ichchou und K. A. Cunefare. „Design and Experimental Validation of a Metacomposite Made of an Array of Piezopatches Shunted on Negative Capacitance Circuits for Vibroacoustic Control“. In ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/smasis2013-3182.

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In the last few decades, researchers have given a lot of attention to new engineered materials with the purpose of developing new technologies and devices such as mechanical filters, low frequency sound and vibration isolators, and acoustic waveguides. For instance, elastic phononic crystals may come to mind. They are materials with elastic or fluid inclusions inside a matrix made of an elastic solid. The anomalous behavior in phononic crystals arises from interference of waves propagating within an inhomogeneous material. The inclusions inside the matrix cause strong modifications of scattering properties. However, the application of phononic crystals is still limited to sonic frequencies. In fact, band gaps can be generated only when the acoustic wavelength is comparable to the distance between the inclusion. In order to overcome this limitation, a new class of metamaterial has been proposed: meta composite. This new class of material can modify the dynamics of the underlying structure using a bidimensional array of electromechanical transducers, which are composed by piezo patches connected to a synthetic negative capacitance. In this study, an application of the Floquet-Bloch theorem for vibroacoustic power flow optimization will be presented. In the context of periodically distributed, damped 2D mechanical systems, this numerical approach allows one to compute the multimodal waves dispersion curves into the entire first Brillouin zone. This approach also permits optimization of the piezoelectric shunting electrical impedance, which controls energy diffusion into the proposed semiactive distributed set of cells. Experiments performed on the examined structure illustrates the effectiveness of the proposed control method. The experiment requires a rectangular metallic plate equipped with seventyfive piezopatches, controlled independently by electronic circuits. More specifically, the out-of-plane displacements and the averaged kinetic energy of the controlled plate are compared in two different cases (control system on/off). The resulting data clearly show how this proposed technique is able to dampen and selectively reflect the incident waves.

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