Major Orifice Research Articles

New Surgical Technique to Induce Reversible Liver Fibrosis by Surgical Closure of Major Duodenal Orifice in Dogs

This study was conducted to induce and evaluate reversible liver fibrosis in dogs by surgical closure of the major duodenal orifice. The study was performed on six healthy local adult dogs. Reversible liver fibrosis was surgically induced in all animals by surgical closure of major duodenal papilla using absorbable suture material for 60 days. Induced liver fibrosis was assessed by clinical, ultrasonographical examination, laboratory and histological methods. The clinical manifestation of the jaundiced dogs showed reduced food intake, pale-yellowish mucus membrane, inflammatory signs of the wound site and severe postoperative pain. Biochemically, there was significantly increased values of the aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, indirect bilirubin, direct bilirubin and total bilirubin especially during the first two days after surgery followed by a gradual decrease of these values until the end of the but still higher than normal values. Ultrasonographic examinations showed abnormal changes in the liver tissue such as an increase in both size and wall thickness of the gall bladder and mottled heterogeneous appearance of the liver during the first two weeks following the surgical induction of the hepatic fibrosis. Histological evaluation of liver samples revealed showed necrosis of hepatocytes and deposition of eosinophilic material, infiltration of inflammatory cells, recent thrombus in the hepatic vein, fatty change. Slight clinical, biochemical, ultrasonographic improvement was observed at 30th post-operative day. In conclusion, surgical induction of reversible liver fibrosis in dogs was an easy technique by surgical closure of major duodenal papilla and the results were confirmed by the clinical, ultrasonographical, laboratory and histological examination.

A Double-Envelope Mitral Inflow Spectral Doppler Profile After MitraClip

A Double-Envelope Mitral Inflow Spectral Doppler Profile After MitraClip

Fenestrated Exclusion of the Right Ventricle for Tricuspid Atresia and Absent Pulmonary Valve

The case of a boy who had an absent pulmonary valve, tricuspid atresia, intact ventricular septum, coronary-to-right-ventricular fistula, and dysplasia of the right ventricular free wall is described. At the bidirectional cavopulmonary shunt procedure, the right ventricular free wall was opened and two major fistula orifices to the cavity were closed with sutures. A fenestrated circular patch was placed in the main pulmonary artery and the right ventricular free wall was plicated. The patient then underwent completion for total cavopulmonary connection. Follow-up catheterization showed that the pulmonary artery was partially excluded with minimal pressure wave conduction from the right ventricle, which significantly shrank. This new approach seems to be effective and reproducible in this particular situation.

Two-Dimensional FSI Simulation of Closing Dynamics of a Tilting Disk Mechanical Heart Valve

The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bi-leaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and the valve housing results in relatively high platelet activation levels whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disc valve with that of a bi-leaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disc valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime and the flow through the gap width is marked by the development of a shear layer which separates from the leaflet downstream of the valve. Zones of re-circulation are observed in the gap between the leaflet edge and the valve housing on the major orifice region of the tilting disc valve and are seen to be migrating towards the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed which sheds in the direction of fluid motion as observed in experiments using PIV measurements. The activation parameter computed for the tilting disc valve, at the time of closure was found to be 2.7 times greater than that of the bi-leaflet mechanical valve and was found to be in the vicinity of the minor orifice region mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase.

Can we interpret the orientation of major or minor orifice in implanted tilting disc mechanical mitral valve on X-ray chest P-A view ? “The Sion Sign”

Introduction Chest X-ray is an important investigation in a patient Following Mitral valve replacement. After Mitral valve replacement in Chest X-Ray Postero-Anterior (P-A) view the Prosthesis in the mitral Position is seen in sagital open position as opposed to a prosthesis in Aortic Position which is seen as coronal slit.

The 12cc Penn State Pulsatile Pediatric Ventricular Assist Device: Fluid Dynamics Associated With Valve Selection

The mortality rate for infants awaiting a heart transplant is 40% because of the extremely limited number of donor organs. Ventricular assist devices (VADs), a common bridge-to-transplant solution in adults, are becoming a viable option for pediatric patients. A major obstacle faced by VAD designers is thromboembolism. Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile VAD are a strong inlet jet, a late diastolic recirculating flow, and a wall shear rate greater than 500 s(-1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two mechanical heart valves: Bjork-Shiley monostrut (BSM) tilting disk valves and CarboMedics (CM) bileaflet valves. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense, which led to better recirculation and wall washing than the three jets produced by the CM valves. Regurgitation through the CM valve served as a significant hindrance to the development of the rotational flow.

A Detailed Fluid Mechanics Study of Tilting Disk Mechanical Heart Valve Closure and the Implications to Blood Damage

Hemolysis and thrombosis are among the most detrimental effects associated with mechanical heart valves. The strength and structure of the flows generated by the closure of mechanical heart valves can be correlated with the extent of blood damage. In this in vitro study, a tilting disk mechanical heart valve has been modified to measure the flow created within the valve housing during the closing phase. This is the first study to focus on the region just upstream of the mitral valve occluder during this part of the cardiac cycle, where cavitation is known to occur and blood damage is most severe. Closure of the tilting disk valve was studied in a "single shot" chamber driven by a pneumatic pump. Laser Doppler velocimetry was used to measure all three velocity components over a 30 ms period encompassing the initial valve impact and rebound. An acrylic window placed in the housing enabled us to make flow measurements as close as 200 microm away from the closed occluder. Velocity profiles reveal the development of an atrial vortex on the major orifice side of the valve shed off the tip of the leaflet. The vortex strength makes this region susceptible to cavitation. Mean and maximum axial velocities as high as 7 ms and 20 ms were recorded, respectively. At closure, peak wall shear rates of 80,000 s(-1) were calculated close to the valve tip. The region of the flow examined here has been identified as a likely location of hemolysis and thrombosis in tilting disk valves. The results of this first comprehensive study measuring the flow within the housing of a tilting disk valve may be helpful in minimizing the extent of blood damage through the combined efforts of experimental and computational fluid dynamics to improve mechanical heart valve designs.

Influence of a tilting prosthetic mitral valve orientation on the left ventricular flow — an experimental in vivo magnetic resonance imaging study

Orientation-related monoleaflet mechanical valve flow and velocity studies in the downstream are limited in mitral valve replacement studies. In five sheep, ventricular blood flow was visualized prior to the implantation of a Medtronic Hall tilting valve model. In six sheep, the implant orientation was either anatomical (disc aligned with the anterior leaflet) or anti-anatomical. The mitral subvalvular apparatus was preserved. Sheep were positioned within an 1.5 T field strength MR scanner (Magnetom Sonata; Siemens) to assess time-dependent three dimensional blood flow. The preoperative ventricular velocity profiles presented negligible individual variances. Streamlines passed homogeneously without any spatial differences in flow velocities into the left ventricle. Starting from the anatomical position, blood entered mainly through the major orifice of the mechanical valve. The single artificial leaflet mimicked the rudder effect of the natural anterior mitral leaflet, preventing blood streaming directly towards the septum. The area with inhomogeneous blood velocities in the ventricle increased but not significantly from the preoperative status. The non-axial inflow not directed directly to the apex converted to a similar helix as observed in the preoperative cases. Anti-anatomical orientation of the prosthesis caused a significant increase in turbulence immediately after passing the mitral prosthesis. The main stream was changed so significantly that the blood flow shifted towards the septum and caused higher velocities of the stream profiles and turbulence apically. To achieve optimal hemodynamics, orientation of the mitral tilting valve has to be considered carefully, as has been long known from aortic valve replacement studies.

Preliminary MRI study on hemodynamics after prosthetic cardiac valve implantation

目的 应用MRI测量人工心脏瓣膜远端血流野及三维图像的描绘,来评价人工心脏瓣膜功能,并为长期随访瓣膜血栓等并发症的出现和发展提供原始资料.方法27例人工主动脉瓣膜置换患者进行MR血流速度测量检查,置换双叶机械瓣20例,单叶机械瓣7例.于升主动脉内距主动脉瓣环0.5、1.0及2.0个人工瓣环直径处进行血流速度测量.应用血流分析及Matlab 6.5软件进行二维及三维血流图形重组.结果16例置换Sorin双叶机械主动脉瓣患者,三维血流图人工心脏瓣膜的形状特点为近似对应于2个瓣孔及2个瓣叶之间缝隙的3个喷射峰;4例置换Sorin双叶机械主动脉瓣患者,出现对应于2个瓣孔的双喷射峰.20例置换双叶机械主动脉瓣患者,血流速度在加速射血相及最大射血相血流速度图变成倾斜.7例置换单叶机械主动脉瓣患者在收缩加速相见对应单叶瓣口的1个主喷射峰.26例反向血流出现在人工瓣膜侧孔的位置.MR血流速度三维图反映了人工心脏机械瓣膜的设计形状.距主动脉瓣环1.0人工瓣环直径处的轴向血流速度图较远端(2.0人工瓣环直径处)及近端(0.5人工瓣环直径处)的轴向血流速度图能更详细反映人工瓣膜的设计形状.结论MR可以无创、直观、在体地了解瓣膜功能,为发现术后并发症奠定基础。

Near Field Flow Characteristics of the Bjork-Shiley Monostrut Valve in a Modified Single Shot Valve Chamber

In certain mechanical heart valves, cavitation has been shown to develop during closure and rebound, leading to valve damage, blood damage, and strokes. Whereas it is uncertain what causes mechanical heart valve related strokes, some evidence suggests that stable bubbles may be the culprits. Previous work has indicated that vortex cavitation may contribute to stable bubble growth. Therefore, in an effort to understand the vortex cavitation, laser Doppler velocimetry data are collected in a plane parallel to and 3 mm away from the major orifice during closure and rebound of a Bjork-Shiley Monostrut mechanical heart valve. A modified single shot chamber is used that incorporates a more realistic near valve geometry than those used in previous studies. The results show the formation of a vortex during closure, which intensifies during rebound and dissipates during the final closing cycle. A regurgitant jet with mean velocities up to 3 m/s through the clearance gap of the valve provides energy to the vortex. During the final closing cycle, the vortex breaks up into asymmetrical, small scale flow patterns. This study provides further evidence that stable bubble formation may stem from the intense vortex cavitation occurring during valve closure and rebound.

Different Tilting Disc Valves Show Similar Rotation-Dependent Impairment in Hemodynamic Performance under a Tilted Implantation Position

Aortic annulus calcification can promote tilted implantation of mechanical valves. This study evaluates the hemodynamics of tilting disc valves under this condition. 23 mm and 25 mm Ultracor (UC) and Medtronic-Hall-Easy-Fit (MH) valves were investigated in a pulse-duplicator under physiological conditions. Mean pressure gradient (dP(mean)), systolic energy loss (dW(sys)), effective orifice area (EOA), closure (V(Cl)), leakage (V(L)), and total regurgitation volume (V(R)) were assessed. Valves were independently positioned at five axial rotations (0 - 180 degrees , zero defined as major orifice facing the top of the "tilt-ramp") and three tilt angles (0 degrees, 10 degrees, 20 degrees) by lifting the prosthesis in the noncoronary sinus. Diameter-enhanced MH valves exhibited a better systolic performance but a higher regurgitation than corresponding UC valves. Moderate tilting showed a rotation-independent increase in dP(mean) and dW(sys) and a decrease in V (R) and EOA with no fundamental differences between valve types. Further tilting caused small additional changes at 90 - 180 degrees rotation. At 0 degrees rotation, however, dramatic regurgitation occurred throughout. Tilting worsened systolic performance regardless of valve type. It should therefore be avoided. Due to extensive regurgitation at 0 degrees rotation, this position should be corrected whenever tilting is inevitable.

Mitral Prosthesis Opening and Flow Dynamics in a Model of Left Ventricle: An In Vitro Study on a Monoleaflet Mechanical Valve

A complete understanding of the flow past a mitral valve prosthesis require a new generation of pulse duplicators and more realistic flow conditions. The objective of this study is to describe the opening kinetics of a monoleaflet Medtronic Hall 27-mm mechanical valve in mitral position and to determine the flow pattern within the left ventricle using particle image velocimetry (PIV) for different instants during the cardiac cycle. At the onset of diastolic phase, the flow goes through the major orifice and then through the minor orifice. The two jets generated induce two counterclockwise vortices within the ventricle, which can lead to a partial closure of the valve during mitral E wave deceleration. During diastasis and mitral A wave, only one vortex persists in the ventricle and pushes the valve disk backward at the end of the diastolic phase. The valve disc never reached its maximum opening (65∘ vs.75∘). This study underscores that the flow past a monoleaflet valve in mitral position is highly dependent on the complex interaction between the inflow, the vortices development within the left ventricle, and the gravity. Such a complex interaction can only be highlighted using new generation of pulse duplicators.

MECHANICAL HEART VALVE CAVITATION FLUID MECHANICS

In vitro high speed videography (HSV) studies of mechanical heart valve IMHV) closure and rebound have revealed the development of bubble and vortex cavitation, which contributes to valve and blood element damage. The local fluid mechanics during closure play an essential role with MHV cavitation, thus necessitating the fundamental understanding for cavitation development and promoting efforts to minimize the impact in vivo. A Bjork-Shiley Monostrut (BSM) MHV was modified to investigate flow structures using HSV and laser Doppler velocimetry (LDV). LDV studies were conducted 1 mm upstream of the valve around the major orifice. Subsequently, the valve housing was modified by removing a rectangular window of titanium from pivot joint to pivot joint along the major orifice while retaining part of the valve housing. Consequently, a modified single shot chamber that included filling the window with acrylic was constructed to retain valve geometry and most of the structural integrity. LDV studies confirmed minimal flow changes due to the modification. The HSV and LDV studies demonstrated the development of vertical structures during closure, which continued through the initial rebound. The structure began 'it the onset of valve closure and decreased in size until it became a tight vortex at valve impact. It briefly enlarged during rebound before finally dispersing clue to the regurgitant jet, In addition, flow velocities up to 18 m/s were measured in the clearance gap suggesting a potential hemolytic cause. The flow measurements determined from within the MHV housing suggest a mechanism for cavitation.

A new approach to detection of the cavitation on mechanical heart valves.

The cavitation on the mechanical heart valves (MHVs) is thought to be a cause of the mechanical failure of the occluder; also, the free radicals that would be generated when the cavitation bubbles implode might affect the patients chemically. These cavitation effects are attributed to the bubble collapse. Therefore, it is important to detect the bubble implosion behavior to analyze the cavitation on MHVs. The cavitation bubbles induce the generation of free radicals at their implosion, and the excited hydroxyl radicals emit the faint light. Based on this fact, we have tried to observe the faint light emission from a MHV to specifically capture the implosion of the cavitation bubbles. A highly sensitive CCD (charge coupled device) camera (C2400-35 VIM camera, Hamamatsu Photonics, Hamamatsu, Japan) was adopted in this study. This camera can observe low light down to the single photon counting range, and it gives two-dimensional mapping of the light. A 20 mm Björk-Shiley valve was submerged in the water tank of 10 L deionized water with luminol as a light enhancer, and then the pressure difference of 150 mm Hg was exerted on the valve at a rate of 60 bpm with a pulse duplicator. The camera and the water tank were settled in the lightproof configuration. After 2 hours of exposure, faint light images have been obtained successfully. The light emits mostly from the edge of the occluder on the inflow side in the major orifice of the valve. Therefore the results suggest that the bubbles would implode around this region and that free radicals caused by cavitation might be produced on MHV, which has coincided with our preliminary result by an electron spin resonance spectrometry.

Correction of Complete Atrioventricular Canal

Correction of Complete Atrioventricular Canal

In vitro squeeze-flow phenomena at the instant of mechanical valve closure

Cavitation bubble formation associated with mechanical valve closure has been investigated in vitro, and the region of bubble formation has been correlated with large negative pressure transients. The region of cavitation bubbles forms in valve designs where leaflets interact with seat stops. It has been postulated that the fluid is squeezed between the leaflet and the seat stop and radially propelled at high velocities, resulting in further pressure reduction below the vapor pressure of fluid and initiating cavitation bubble formation. We conducted in vitro experiments to visualize and detect the presence of squeeze-flow phenomena associated with valve closure of mechanical heart valves. The closing dynamics were studied by simulating a single closing event of the leaflet with the valve mounted at the mitral position. Squeeze flow was detected at the instant of valve closure, when the valve leaflet interacts with the valve seat stop. The use of a high-speed video camera at 1000 frames per second with strobe light at 16000 pulses per second enabled the visualization of cavitation bubbles and its radial motion from the valve's seat stop due to the squeeze-flow effect. Vapor cavitation bubbles were observed to collapse within 0.5 ms after inception. In mechanical valves without seat stops in the major orifice region, bubbles of duration longer than that of the cavitation bubbles were observed. These microbubbles were present for 4 s before collapsing and are believed to be air bubbles whose presence in vivo has been detected with ultrasound imaging.

7238 Facilitation of pancreatic duct cannulation using synthetic porcine secretin.

INTRODUCTION: Secretin, for diagnostic use, is a gastrointestinal peptide hormone consisting of 27 amino acids. Its primary pharmacologic action is to increase the volume and bicarbonate content of secreted pancreatic juices. Its approved uses are for the diagnosis of chronic pancreatitis and gastrinoma and as an adjunct to obtain pancreatic cells for cytology. Previously, only secretin extracted from porcine duodenums had been available. Recently, a pure synthetic porcine secretin (ChiRhoClin) with an identical amino-acid sequence and structure has been developed. AIM: To assess the pharmacological and clinical efficacy and safety profile of this new synthetic porcine secretin in facilitating cannulation of either the major or minor pancreatic orifice at ERCP. METHODS: In this prospective study, patients were administered 0.2ug/kg IV (max. 16ug) of synthetic porcine secretin if protracted efforts to locate or cannulate the major or minor pancreatic orifice had failed. Exclusion criteria were acute pancreatitis, known sensitivity or adverse reaction to secretin and pregnant or nursing females. RESULTS: Between March and November, 1999, 29 patients were enrolled (M:F 8:21; Average age 52.8 years, range 23-81 years). The indications for secretin injection were: to aid in minor papilla cannulation in patients with pancreas divisum (18), to aid in finding main PD orifice (4), to find PD orifice post biliary sphincterotomy (3), to facilitate intact major papilla cannulation (2), to aid in finding minor papilla (1), and to facilitate minor papilla cannulation in normal PD anatomy (1). Successful cannulation was achieved in 26/29 (89.7%) patients. In one case, cannulation of the minor papilla was still not possible because of its location in a duodenal diverticulum. In the two remaining cases, deep cannulation of the pancreatic duct was not deemed essential and was not pursued. No adverse events were recorded. SUMMARY: A new, pure, synthetic secretin aided successful cannulation of the major or minor pancreatic orifices in 26/29 patients in whom protracted efforts to locate or cannulate the pancreatic duct had failed. These data suggest this new agent is both effective and safe for this clinical indication. CONCLUSIONS: Synthetic porcine secretin is a safe and useful agent, and its administration can be added to the armamentarium of techniques to facilitate pancreatic duct cannulation.

Flow visualization in mechanical heart valves: occluder rebound and cavitation potential.

High density particle image velocimetry, with spatial resolution of O(1 mm), was used to measure the effect of occluder rebound on the flow field near a Bjork-Shiley Monostrut tilting-disk mitral valve. The ability to measure two velocity components over an entire plane simultaneously provides a very different insight into the flow compared to the more traditional point to point techniques (like Laser Doppler Velocimetry) that were utilized in previous investigations of the regurgitant flow. A picture of the effects of occluder rebound on the fluid flow in the atrial chamber is presented. Specifically, fluid velocities in excess of 1.5 m/s traveling away from the atrial side were detected 3 mm away from the valve seat in the local low pressure region created by the occluder rebound on the major orifice side where cavitation has been observed. This analysis is the first spatially detailed flow description of the effects of occluder rebound on the flow field past a tilting-disk mechanical heart valve and further reinforces the hypothesis that the rebound effect plays a significant role in the formation of cavitation, which has been implicated in the hemolysis and wear associated with tilting-disk valves in vivo.

In vitro LDA and flow visualization analysis of the spiral vortex pump: effect of inlet valve orientation

The spiral vortex pump (SV), an innovative, penumatically driven ventricular assist device, was tested using the flow visualization technique and laser Doppler anemometry to study the effect of inlet valve orientation under steady and pulsatile flow conditions in a purposely constructed flow circuit aimed at obtaining flow field data. Qualitative information was obtained using the flow visualization technique. The slit-lighting technique and fluorescent bees provided a clear flow field view at the desired location, and a 200 frames/s high-speed video camera was used, capturing the vortex nature of the flow field. Mean velocity and fluctuating velocity profile were obtained using a Kanomax single-channel FLV system. Three diametrically transverse locations and three vertical locations were selected for measurements. The particle-tracking method was also incorporated to obtain velocity vectors. Based on the experimental data, the following general conclusions can be drawn: (1) The SV pump created a vortex flow field under steady and pulsatile flow conditions. (2) The inlet valve orientation sharply influenced the flow inside the SV pump. (3) A relatively strong circulatory flow field was observed when the major orifice was oriented toward the HD junction under steady flow. (4) A relatively weak circulatory flow field was observed when the major orifice was oriented toward the center under steady flow. (5) The directional flow field was more accentuated under pulsatile flow conditions. (6) A relatively stable flow field was observed when the major orifice was oriented upward (pump outlet direction). (7) Directional flow toward the diaphragm was observed when the major orifice was oriented downward. (8) A strong circulatory flow with possible colliding flow toward the peripheral area was observed when the major orifice was oriented outward. (9) A relatively weak circulatory flow was observed when the major orifice was oriented inward. (10) The strength of the circulatory flow during the peak flow phase under pulsatile conditions was not affected by the orientation of the inlet valve.

Characterization and optimization of the flow pattern inside a diaphragm blood pump based on flow visualization techniques.

We applied two different flow visualization techniques to obtain detailed information on the inside flow of the diaphragm blood pump of our electrohydraulic total artificial heart system to determine the optimum washout effect that would result in better antithrombogenicity. Major orifice directions of the inflow and outflow Bjork-Shiley valves of the left blood pump were independently changed to create 17 varied patterns. The character and velocity of the main flow at the diaphragm-housing junction were acquired using a laser light sheet method with polyethylene tracers. Wall shear flow, a major factor governing washout in the blood pump, was estimated by a newly developed paint erosion method. In this method, quantitative evaluation for an index of washout effect was made by calculating the residual ratio of the paint on the blood pump inner surface at 30 sec of pumping. When a single circular flow was consistently observed by the laser light sheet method, the paint residual ratio become low, indicating washout was relatively good. At the lowest paint residual ratio, the center of the circular flow observed by the laser light sheet method was located at the geometric center of the blood chamber. In conclusion, the flow pattern inside the blood pump could be characterized by combined use of these two flow visualization techniques, and the significant role of circular flow in better washout was clarified.