Flow characteristics past jellyfish and St. Vincent valves in the aortic position under physiological pulsatile flow conditions

Thrombus formation and hemolysis have been linked to the dynamic flow characteristics of heart valve prostheses. To enhance our understanding of the flow characteristics past the aortic position of a Jellyfish (JF) valve in the left ventricle, in vitro laser Doppler anemometry (LDA) measurements were carried out under physiological pulsatile flow conditions. The hemodynamic performance of the JF valve was then compared with that of the St. Vincent (SV) valve. The comparison was given in terms of mean systolic pressure drop, back flow energy losses, flow velocity, and shear stresses at various locations downstream of both valves and at cardiac outputs of 3.5 L/min, 4.5 L/min, and 6.5 L/min respectively. The results indicated that both valves created disturbed flow fields with elevated levels of turbulent shear stress as well as higher levels of turbulence in the immediate vicinity of the valve and up to 1 diameter of the pipe (D) downstream of the valve. At a location further downstream, the JF valve showed better flow characteristics than the SV in terms of velocity profiles and turbulent shear stresses. The closure volume of the SV valve was found to be 2.5 times higher than that of the JF valve. Moreover, the total back flow losses and mean systolic pressure drop also were found to be higher in the SV than the JF valve.     

Flow patterns in the aortic root and the aorta studied with time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging: implications for aortic valve-sparing surgery

OBJECTIVE: Sparing the aortic valve has become a surgical option for patients who require repair of aortic root ectasia and have normal valve leaflets. Surgical approaches to valve sparing differ with regard to preservation of the native sinuses of Valsalva. The role of the sinuses and the importance of maintaining them remain controversial. METHODS: By using a time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging technique, aortic root and aortic blood velocity data were acquired from 2 patients with Marfan syndrome 6 months after aortic valve-sparing surgery with straight Dacron grafts and contrasted with data from 6 normal volunteers. RESULTS: In normal aortas vortical blood flow became apparent in the individual sinuses after peak systole. The vortices filled the available space behind the valve leaflets and persisted until diastole, expanding and moving inward during aortic valve closure. In contrast, no vortices were observed in the postoperative patients with Marfan syndrome with negligible sinuses. CONCLUSIONS: Changes in supravalvular flow accompany loss of sinus architecture. Whether the presence, size, and velocity of supravalvular vortices affects the function or durability of the preserved aortic valve remains to be studied.     

Potential limitations of center-line pulsed Doppler recordings: an in vitro flow visualization study

In this study an in vitro model that permits visualization of the flow velocity profile has been used to determine if duplex pulsed Doppler recordings made with a small sample volume in the center line of the vessel can determine the severity of a stenosis in the 38% to 75% range of cross-sectional area reduction. Because most Doppler instruments measure the maximum peak frequency and the extent of spectral broadening, observations in the flow model included changes in the center-line maximum velocity and the location and intensity of flow disturbances. The results showed that center-line measurements of maximum velocity (equivalent to peak Doppler frequency) were directly related to the severity of the stenosis as long as the recordings were made from within the throat to about 1.5 to 3 tube diameters downstream, depending on the shape of the stenosis. However, flow disturbances (equivalent to spectral broadening) did not always occur in the center line of the vessel. Stenoses greater than 50% area reduction produced turbulence across the entire vessel in the region 4.5 to 7.5 diameters downstream. The turbulent period started just before peak systole and extended to just less than half the pulse cycle. In the more proximal zone a forward flow jet was present in the central part of the vessel, and reverse flow was present in the outer region. The interfacial layer between these two regions is subjected to high shear rates that resulted in the formation of waves and vortices.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of the hinge and near-hinge flow fields of the St Jude medical hemodynamic plus and regent bileaflet mechanical heart valves

OBJECTIVE: The most widely implanted prosthetic valves are the mechanical bileaflets, most of which have good forward flow hemodynamics. However, recent clinical experiences illustrate the importance of understanding the flow structures generated within the hinge. The purpose of this study was to evaluate the hinge-flow dynamics of two new variations of a 17-mm St Jude Medical bileaflet valve: the Hemodynamic Plus and the Regent (St Jude Medical, Inc, St Paul, Minn). METHODS: Clinical quality reproductions of the valves were manufactured with clear housings. Laser Doppler velocimetry velocity and turbulent shear stress measurements were conducted within the hinge and thumbnail regions of the valves. RESULTS: In the 17-mm Hemodynamic Plus hinge, a rotating flow structure developed in the inflow pocket during forward flow. During systole, velocities through the hinge pocket reached 0.70 m/s, and the turbulent shear stress reached 1000 dynes/cm(2). In the thumbnail, forward flow velocities ranged from 1.4 m/s to 1.7 m/s. In the 17-mm Regent hinge, a rotating flow structure partially developed in the inflow pocket during forward flow. During systole, velocities through the hinge pocket reached 0.75 m/s, and the turbulent shear stress reached 1300 dynes/cm(2). In the thumbnail, forward flow velocities ranged from 1.0 m/s to 1.3 m/s. CONCLUSIONS: The active leaflet motion through the St Jude Medical hinge creates a washout pattern that restricts the persistence of stagnation zones and thus may be a contributing factor to its successful clinical performance. The hinge and thumbnail flow dynamics of the 17-mm Regent valve are at least equivalent to, and possibly superior to, those of the 17-mm Hemodynamic Plus valve.     

Computational evaluation of platelet activation induced by a bioprosthetic heart valve

It is known that bioprosthetic heart valves (BHVs) have better hemodynamics and lower thromboembolic events compared with their mechanical counterparts; however, patients implanted with BHVs still face the potential of such complications. The risk of a clinical thromboembolism is on average 0.7% per year in patients with tissue valves in sinus rhythm. In this study, we developed a computational fluid dynamic (CFD) model of a BHV implanted in an aortic root and investigated the BHV-induced platelet activation using a damage accumulation model previously applied to mechanical valves. The CFD model was validated against published experimental data, including the flow velocity profile across the valve and the transvalvular pressure drop, and close matches were obtained. Hemodynamic performance measures such as flow velocity, turbulent kinetic energy, and wall shear stress were explored. Lagrangian particle tracking was used to calculate the extent of platelet activation for central bulk flow and flow in the vicinity of the leaflets. A peak flow of 2.22 m/s was observed at 40 msec after peak systole in the vicinity of a fold at the base of the leaflets. With the platelet activation expressed as 0-100% of activation threshold levels, mean damage on one pass was 2.489 × 10(-7)% and maximum damage on one pass was 8.778 × 10(-4)%. Our results suggested that the potential for BHV-induced platelet activation was low and that the leaflet's fully open geometry might play a role in the extent of blood element damage.     

Unsteady Fluid Dynamics of Several Mechanical Prosthetic Heart Valves Using a Two Component Laser Doppler Anemometer System

Abstract: Five typical mechanical heart valves (Starr-Edwards, Björk-Shiley convexo-concave (c-c), Björk-Shiley monostrut, Bicer-Val, and St. Jude Medical) were tested in the mitral position under the pulsatile flow condition. The test program included measurements of velocity and turbulent stresses at 5 downstream locations. The study was carried out using a sophisticated cardiac simulator in conjunction with a highly sensitive 2 component laser Doppler anemometer (LDA) system. The continuous monitoring of parametric time histories revealed useful details about the complex flow and helped to establish the locations and times of the peak parameter values. Based upon the nondimensional presentation of data, the following general conclusions can be made. First, all the 5 valve designs created elevated turbulent stresses during the accelerating and peak flow phases, presenting the possibility of thromboembolism and perhaps hemolysis. Second, the difference in valve configuration seemed to affect the flow characteristics; third, the bileaflet design of the St. Jude valve appeared to create a lower turbulence stress level.     

Clinical introduction of a novel prosthesis for valve-preserving aortic root reconstruction for annuloaortic ectasia

OBJECTIVE: Most patients with annuloaortic ectasia are young. They are at risk for complications related to a lifetime of anticoagulation when composite grafts containing mechanical valves are used for reconstruction. The majority of patients have near normal valve cusps. Valve-preserving techniques have been developed to maintain valve function and avoid anticoagulation. The eddy currents occurring within the sinuses of Valsalva in the natural aortic root have been shown to be important in the smooth, gradual, and gentle closure of the valve. Compliance of the sinuses is important in reducing stress in the leaflets. A novel ascending aortic prosthesis with "built in" compliant sinuses (Robicsek-Thubrikar graft) was developed for clinical aortic root replacement. METHODS: Woven Dacron tubes were used to make the prostheses. Three precisely measured square pieces were cut to make the expandable, individual sinuses. Sewing the individual neo-sinuses to a scalloped end of the Dacron tube graft created the neo-sinotubular junction and sinotubular ridge. Five patients with annuloaortic ectasia underwent valve-preserving aortic root reconstruction. RESULTS: All intraoperative transesophageal echocardiographic images after the valve-preserving procedure showed a normal appearing root with 10% radial expansion of each sinus in systole. The space between the cusps and neo-sinus wall in systole was normal. No patient has more than mild aortic regurgitation. CONCLUSIONS: Valve-preserving aortic root reconstruction with a novel Dacron prosthesis with compliant "built in" sinuses re-establishes normal aortic root geometry with near normal valve motion. This may enhance the durability of the valve-preserving operation.     

Aortic flow after valve sparing root replacement with or without neosinuses reconstruction

Objectives

This study applied advanced 4-dimensional flow magnetic resonance imaging processing to assess differences in aortic flow dynamics after valve sparing root replacement, with and without reconstruction of the Valsalva sinuses.

Turbulent Stresses Downstream of Porcine and Pericardial Aortic Valves Implanted in Pigs

Because late valve-related complications such as hemolysis and thromboembolic events are considered related to flow disturbances caused by the inserted valve, velocity fields downstream of aortic valve prostheses were studied in pigs. Acute hemodynamic evaluation of size 25-mm porcine and pericardial aortic valve prostheses 1 diameter downstream of the valve ring was performed using dynamic three-dimensional visualization of velocity profiles and spatial distribution of turbulence. Point blood velocity signals obtained with a 1-mm hot-film anemometer needle probe were used to compute Reynolds normal stresses (RNS) by calculation of the turbulent velocity energy of the axial velocity component in the systole. The porcine valves caused a skewed velocity and turbulence profile revealing mean spatial systolic RNS at 70 nm-2 +/- 35 nm-2 (+/- SD). The spatial maximum RNS was 275 +/- 139 nm-2. Corresponding values for the pericardial valves were 20 +/- 11 nm-2 and 72 +/- 46 nm-2. The pericardial valves revealed plug-shaped velocity profiles and turbulent profiles with slightly higher RNS values at the stent posts. From a hemodynamic point of view, these acute studies indicate superiority of the pericardial valves compared to the porcine valves. The turbulent stresses found in this study are of a magnitude that may cause blood corpuscular and endothelial damage.     

In Vitro Investigation of the Hemodynamics of Transcatheter Heterotopic Valves Implantation in the Cavo‐Atrial Junction

Severe tricuspid regurgitation (TR) is life‐threatening but is often undertreated. Many patients with severe TR are denied heart valve replacement surgery because their old age or comorbidities predispose them to a higher risk of surgical complications associated with open‐heart surgery. With the advent of transcatheter technology, it is now possible to deliver the valve to the desired location without the need for open‐heart surgery. However, presently, there is no commercially available transcatheter tricuspid valve. This may be due to the complex tricuspid valve anatomy, which lacks an anchorage zone for the percutaneous valves. In view of this drawback, we have recently developed and tested two percutaneous caval heart valves that are designed to deploy at the vena cava and atrium junction. The hemodynamic characteristics of these valves are tested in a mock circulatory system with patient‐specific silicone atrium and vena cava, which emulates the physiological pressure and flow conditions at the right side of the human heart. Particle imaging velocimetry results showed that flow velocity and the associated Reynolds shear stress (RSS) and the turbulent kinetic energy (TKE) downstream of the valves increased after the implantation of the valves. A maximum flow velocity of 0.94 m/s was observed at the region downstream of the percutaneous valve at the superior vena cava (SVC). Maximum RSS value of 2076.1 dynes/cm² was observed downstream of the valve at the inferior vena cava during the deceleration phase while maximum TKE measured was 572.6 J/m³ at the upstream of the valve in the SVC during the peak flow phase. While these values appear high, they are significantly lower than those reported in prosthetic mitral and aortic valves. Hence, caval stented valves can be potentially considered as a minimally invasive option to treat TR.     

Prediction of Hemolysis in Turbulent Shear Orifice Flow

Abstract
This study proposes a method of predicting hemolysis induced by turbulent shear stress (Reynolds stress) in a simplified orifice pipe flow. In developing centrifugal blood pumps, there has been a serious problem with hemolysis at the impeller or casing edge; because of flow separation and turbulence in these regions. In the present study, hemolysis caused by turbulent shear stress must occur at high shear stress levels in regions near the edge of an orifice pipe flow. We have computed turbulent shear flow using the low-Reynolds number k - ε model. We found that the computed turbulent shear stress near the edge was several hundreds times that of the laminar shear stress (molecular shear stress). The peak turbulent shear stress is much greater than that obtained in conventional hemolysis testing using a viscometer apparatus. Thus, these high turbulent shear stresses should not be ignored in estimating hemolysis in this blood flow. Using an integrated power by shear force, it is optimimal to determine the threshold of the turbulent shear stress by comparing computed stress levels with those of hemolysis experiments of pipe orifice blood flow.     

Coronary flow characteristics after a Bentall procedure with or without sinuses of Valsalva.

OBJECTIVES: The sinuses of Valsalva are known to contribute to the normal function of the aortic valve. Little is known about their role in promoting coronary artery blood flow. The aim of this study was to compare coronary artery flow characteristics among patients undergoing a Bentall operation by means of a conventional cylindrical Dacron conduit or with a new conduit with pseudosinuses of Valsalva or in patients retaining their natural sinuses of Valsalva after aortic valve and supracoronary ascending aorta replacement. METHODS: One year after a Bentall procedure with a standard cylindrical Dacron conduit (7 patients, group A) or with the new conduit (7 patients, group B), or after aortic valve and ascending aortic replacement (control group, 7 patients, group C) coronary flow velocity reserve and diastolic to systolic time integral ratio at baseline and after maximal hyperemia (with 40 microg of adenosine) were assessed by using a 0.014-in. Doppler guidewire positioned in the middle portion of the left anterior descending coronary artery. All patients were in NYHA class I, sinus rhythm and free of coronary disease. RESULTS: Arterial blood pressures and heart rate were comparable among groups. Intracoronary Doppler measurements did not show any significant difference in coronary vascular reserve between the three groups (3.6+/-0.4 vs 3.1+/-0.7 vs 3.7+/-0.5, P = 0.2). A greater diastolic component at baseline was present in group B patients (5.5+/-1.9 vs 3.5+/-0.9 in group A and 3.7+/-0.9 in group C, P = 0.024). After maximal hyperemia the diastolic component increased slightly in group A patients (8%) while both in groups B and C significantly decreased (-15 and -20%, respectively) (P = 0.017). CONCLUSIONS: The presence of pseudosinuses of Valsalva does not influence coronary flow reserve. After maximal coronary vasodilation the increase in the systolic component of coronary flow is more evident in the presence of sinuses or pseudosinuses of Valsalva, thus suggesting that coronary flow pattern may be affected by the presence of sinuses.     

Sensitivity of patient-specific numerical simulation of cerebal aneurysm hemodynamics to inflow boundary conditions

OBJECT: Due to the difficulty of obtaining patient-specific velocity measurements during imaging, many assumptions have to be made while imposing inflow boundary conditions in numerical simulations conducted using patient-specific, imaging-based cerebral aneurysm models. These assumptions can introduce errors, resulting in lack of agreement between the computed flow fields and the true blood flow in the patient. The purpose of this study is to evaluate the effect of the assumptions made while imposing inflow boundary conditions on aneurysmal hemodynamics. METHODS: A patient-based anterior communicating artery aneurysm model was selected for this study. The effects of various inflow parameters on numerical simulations conducted using this model were then investigated by varying these parameters over ranges reported in the literature. Specifically, we investigated the effects of heart and blood flow rates as well as the distribution of flow rates in the A1 segments of the anterior cerebral artery. The simulations revealed that the shear stress distributions on the aneurysm surface were largely unaffected by changes in heart rate except at locations where the shear stress magnitudes were small. On the other hand, the shear stress distributions were found to be sensitive to the ratio of the flow rates in the feeding arteries as well as to variations in the blood flow rate. CONCLUSIONS: Measurement of the blood flow rate as well as the distribution of the flow rates in the patient's feeding arteries may be needed for numerical simulations to accurately reproduce the intraaneurysmal hemodynamics in a specific aneurysm in the clinical setting.     

In vitro hemodynamic characteristics of tissue bioprostheses in the aortic position

The in vitro hemodynamic characteristics of a variety of old and new generation porcine and bovine pericardial bioprostheses were investigated in the aortic position under pulsatile flow conditions. The following valves were studied: Carpentier-Edwards porcine (Models 2625 and 2650), Carpentier-Edwards pericardial, Hancock porcine (Models 242, 250, and 410), Hancock pericardial, and Ionescu-Shiley (standard and low-profile) bioprostheses. The pressure drop results indicated that the old design valves had performance indices in the range of 0.30 to 0.42, whereas the new low-pressure fixed designs have performance indices of 0.50 to 0.70. Flow visualization and velocity and turbulent shear stress measurements, conducted with a two-dimensional laser Doppler anemometer system, indicated that all tissue valve designs created jet-type flow fields. The intensity of the jets and turbulence levels were less severe with the new designs. The old designs created higher peak jet velocities and higher levels of turbulent shear stresses. On the whole, pericardial bioprostheses have better in vitro hemodynamic characteristics than porcine bioprostheses. These observations should have applications regarding the clinical choice of bioprosthetic valves and have implications regarding further improvements in the preparation and design of bioprosthetic valves.     

In vitro velocity and turbulence measurements in the vicinity of three new mechanical aortic heart valve prostheses: Bj?rk-Shiley Monostrut, Omni-Carbon, and Duromedics

The in vitro velocity and turbulent shear stress fields created by three new mechanical valve designs (size 27 mm) were studied in the aortic position under pulsatile flow conditions. The following valves were studied: Bj?rk-Shiley Monostrut tilting disc, Omni-Carbon tilting disc, and Duromedics bileaflet. All three valve designs created low pressure gradients with effective orifice areas in the range of 3.10 to 3.90 cm2. Both tilting disc designs created major and minor orifice jets, which were asymmetric in size. The peak velocities of the major and minor orifice jets were, however, of the same magnitude (200 cm/sec). The Omni-Carbon valve created a more even flow distribution through the minor orifice compared with the Bj?rk-Shiley design. Regions of stagnation/flow separation were observed immediately adjacent (ie, distal) to the minor orifice strut and the pivot guards of the Bj?rk-Shiley and Omni-Carbon valve designs, respectively. The Duromedics valve created relatively centralized flow. However, a major portion of the flow occurred through the two lateral orifices. Regions of flow separation/stagnation were observed adjacent to the valve sewing ring in the area of the valve pivot (hinge) mechanism. All three valve designs did create elevated turbulent shear stresses, with peak values in the range of 1000 to 2000 dynes/cm2 and mean values in the range of 100 to 1000 dynes/cm2. Such elevated shear stresses could cause sublethal and/or lethal damage to cellular blood elements. In an overall analysis, these new-generation low-profile mechanical valves are hemodynamically comparable to the Medtronic Hall and St. Jude Medical mechanical valves and are superior to the older-generation mechanical valves. However, it is unlikely that these valve designs will eliminate the problems of thrombosis, thromboembolic complications, and hemolysis.     

Flow Characteristics of the St. Jude Prosthetic Valve: An In Vitro and In Vivo Study

The St. Jude cardiac prosthetic aortic valve was evaluated in vitro and in vivo in an attempt to establish flow characteristics and to correlate them with clinical findings. In vitro, a fluid vehicle (6% Polyol V-10, 32°C) with viscosity similar to blood (0.035 dyne-sec/cm²) was used under conditions of steady flow through a flow chamber simulating the aortic root. Gradient, velocity, and shear stress were measured 5.79 mm, 26.79 mm, 44.79 mm, and 77.79 mm downstream from 25-mm and 27-mm valves using a laser-Doppler anemometer. At 417 ml/sec, the valve gradient was 6.2 mmHg with the 25-mm valve, and 5.2 mmHg with the 27-mm prosthesis. Velocity was maximum at the orifice center, and wall shear stress was low (maximum 600 dyne/cm²). In vivo, six patients with 25-mm St. Jude aortic valves were studied within 48 hours after surgery to determine cardiac output, valve flow, and gradient. The gradient was 3.3 ± 1.9 mmHg (M ± SD) at 249 ± 96 ml/sec and the effective valve area was as large as the geometric area (2.58 vs. 3.09 cm²). Thus, flow through the St. Jude valve is unobstructed and central, has low turbulence, and achieves optimal effective valve area for a given available orifice area.     

Effects of Tilting Disk Heart Valve Gap Width on Regurgitant Flow Through an Artificial Heart Mitral Valve

Abstract: While many investigators have measured the turbulent stresses associated with forward flow through tilting disk heart valves, only recently has attention been given to the regurgitant jets formed as fluid is squeezed through the gap between the occluder and housing of a closed valve. The objective of this investigation was to determine the effect of gap width on the turbulent stresses of the regurgitant jets through a Bjork-Shiley monostrut tilting disk heart valve seated in the mitral position of a Penn State artificial heart. A 2 component laser-Doppler velocimetry system with a temporal resolution of 1 ms was used to measure the instantaneous velocities in the regurgitant jets in the major and minor orifices around the mitral valve. The gap width was controlled through temperature variation by taking advantage of the large difference between the thermal expansion coefficients of the Delrin occluder and the Stellite housing of Bjork-Shiley monostrut valves. The turbulent shear stress and mean (ensemble averaged) velocity were incorporated into a model of red blood cell damage to assess the potential for hemo-lytic damage at each gap width investigated. The results revealed that the minor orifice tends to form stronger jets during regurgitant flow than the major orifice, indicating that the gap width is not uniform around the circumference of the valve. Based on the results of a red blood cell damage model, the hemolytic potential of the mitral valve decreases as the gap width increases. This investigation also established that the hemolytic potential of the regurgitant phase of valve operation is comparable to, if not greater than, the hemolytic potential of forward flow, consistent with experimental data on hemolysis.     

The Application of Bileaflet Mechanical Heart Valves in the Polish Ventricular Assist Device: Physical and Numerical Study and First Clinical Usage

The Polish ventricular assist device (Polvad) has been used successfully in clinical contexts for many years. The device contains two single‐disc valves, one at the inlet and one at the outlet connector of the pneumatic pump. Unfortunately, in recent years, a problem has occurred with the availability of single‐disc valves. This article presents the possibility of using bileaflet mechanical heart valve prostheses in the Polvad to avoid a discontinuity in clinical use. The study is based on experimental and numerical simulations and comparison of the distribution of flow, pressure, and stress (wall, shear, and turbulent) inside the Polvad chamber and the inlet/outlet connectors fitted with Sorin Monodisc and Sorin Bicarbon Fitline valves. The type and orientation of the inlet valve affects valve performance and flow distribution inside the chamber. Near‐wall flow is observed for single‐disc valves. In the case of bileaflet valves, the main jet is directed more centrally, with lower shear stress but higher turbulent stress in comparison with single‐disc valves. For clinical usage, a 45° orientation of the bileaflet inlet valve was chosen, as this achieves good washing of the inlet area near the membrane paste surface. The Polvad with bileaflet valves has now been used successfully in our clinic for over a year and will continue to be used until new assist devices for heart support are developed.     

Microflow fields in the hinge region of the CarboMedics bileaflet mechanical heart valve design

OBJECTIVE: The design of bileaflet mechanical heart valves includes some degree of leakage flow on valve closure for the reverse flow to wash the hinge and pivot region of the valve. It is believed that this reverse flow helps to prevent areas of stasis and inhibit microthrombus formation. However, the magnitude of this retrograde flow may also give rise to unacceptable levels of blood element damage and lead to platelet activation or hemolysis as a result of the increased flow velocities through the hinge region. The purpose of this study was to evaluate the hinge flow dynamics of a 23-mm CarboMedics bileaflet mechanical valve (Sulzer CarboMedics Inc, Austin, Tex) and then to compare the results with those of the St Jude Medical 23-mm Regent (St Jude Medical Inc, Minneapolis, Minn) and Medtronic Parallel (Medtronic, Inc, Minneapolis, Minn) valves studied earlier. This comparison allows new insight into the microflow fields within the hinge region of the CarboMedics bileaflet mechanical valve, which have not been previously assessed during its clinical history. METHODS: Two-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent shear stress fields in the hinge regions. To conduct these measurements, exact dimensional models of the bileaflet hinge regions were cast or machined from transparent plastic materials. The experiment was conducted in a pulsatile flow loop with measurements taken at different levels within the pivot and hinge regions. RESULTS: In the 23-mm CarboMedics valve hinge, the phase-averaged forward velocity obtained at the flat level and levels of 190 microm and 390 microm above flat and 1 mm below flat were 0.54 m/s, 0.77 m/s, 0.3 m/s, and 1.0 m/s, respectively. Corresponding values of the peak phase-averaged leakage velocities were 3.17 m/s, 2.91 m/s, 2.52 m/s, and 0.5 m/s, respectively. Corresponding turbulent shear stresses were 5510 dyne/cm(2), 5640 dyne/cm(2), 4380 dyne/cm(2), and 4810 dyne/cm(2), respectively. CONCLUSIONS: The hinge flow dynamics of the CarboMedics bileaflet design lie somewhere in between those of the St Jude Medical and the Medtronic Parallel valve designs. The fluid dynamics of the investigated valve were found to be similar to those of the St Jude Medical valves, although with slightly higher leakage velocities and turbulent shear stresses. This discrepancy may be a result of the sharper corners associated with the hinge design of the CarboMedics valve. It could also be due to the incremental enlargement of the internal orifice area of the St Jude Medical Regent design.     

Hemodynamic performance of small-size bileaflet valves: pressure drop and laser Doppler anemometry study comparison of three prostheses

Laser Doppler anemometry (LDA) is a single-point technique which is unparalleled to detect accurately the local properties of the velocity field in a turbulent flow, such as that generated by a prosthetic heart valve (PHV). We propose a correlation between the structure of the flow field in three 19 mm bileaflet PHVs (Sorin Bicarbon, St. Jude Standard, St. Jude HP), investigated at peak systole (6 L/min cardiac output [CO]) with LDA, in kinematic and geometric similarity, and the global parameter of transvalvular pressure drop measured in both steady and pulsatile conditions. The pressure transducers of the same apparatus were used to characterize pressure drops at different flow rates whereas the steady-flow case was studied with a highly accurate tester built in our laboratory. The 2 St. Jude models rank according to their internal orifice diameter (ID) with the standard model (with a smaller ID) providing higher pressure drops for each flow rate. Sorin Bicarbon, due to its leaflet geometry, generates a more complex flow field with respect to the 2 St. Jude flat-leaflet models and shows improved hemodynamical behavior in pulsatile conditions with respect to the stationary case due to differences in pressure recovery. This study can provide insights into a PHV's local flow structure and global hemodynamical parameters.