Three-dimensional visualization of velocity profiles in the ascending aorta in humans. A comparative study among normal aortic valves, St. Jude Medical and Starr-Edwards Silastic Ball valves

Blood velocities were recorded intraoperatively in the ascending aorta approximately 6 cm downstream of the aortic annulus in eight patients with normal aortic valves (prior to coronary bypass surgery) and in seven patients after implantation of a St. Jude Medical valve (4) or Starr-Edwards Silastic Ball valve (3) in the aortic position by means of constant temperature hot-film anemometry. The velocities were measured during 5-15 heart cycles at 41 predetermined measurement points almost evenly distributed in the cross sectional area. Velocity profiles were visualized three-dimensionally at 100 time intervals during one mean heart cycle. The standard deviation of velocities was correspondingly three-dimensionally visualized. For the patients with normal aortic valves the velocity profiles were generally flat but skew, with the highest velocity closer to the left vessel wall at the start of systole. During systole the skewness turned counter-clockwise with the highest velocities closer to the posterior, right and finally anterior vessel wall at the end of systole. In patients with an artificial heart valve in the aortic position the design of the valve was reflected on the contour of the profiles. The findings correspond well with model studies.     

Numerical comparison of the closing dynamics of a new trileaflet and a bileaflet mechanical aortic heart valve

The closing velocity of the leaflets of mechanical heart valves is excessively rapid and can cause the cavitation phenomenon. Cavitation bubbles collapse and produce high pressure which then damages red blood cells and platelets. The closure mechanism of the trileaflet valve uses the vortices in the aortic sinus to help close the leaflets, which differs from that of the monoleaflet or bileaflet mechanical heart valves which mainly depends on the reverse flow. We used the commercial software program Fluent to run numerical simulations of the St. Jude Medical bileaflet valve and a new trileaflet mechanical heart valve. The results of these numerical simulations were validated with flow field experiments. The closing velocity of the trileaflet valve was clearly slower than that of the St. Jude Medical bileaflet valve, which would effectively reduce the occurrence of cavitation. The findings of this study are expected to advance the development of the trileaflet valve.     

Analysis of velocity in the ascending aorta in humans. A comparative study among normal aortic valves, St. Jude Medical and Starr-Edwards Silastic Ball valves

To analyze velocity spectral energy distribution in humans, blood velocities were recorded by means of hot-film anemometry at 41 predetermined measurement points in the cross-sectional area of the ascending aorta approximately 6 cm downstream of the aortic valves. Measurements were made in 8 patients with normal aortic valves, in 4 after insertion of a St. Jude Medical (SJM) aortic valve and in 3 after insertion of a Starr-Edwards Silastic Ball (SSB) aortic valve. Data analysis based on Fast Fourier Transform demonstrated that turbulence energy was lower in patients with normal aortic valves than in patients after insertion of an artificial valve in the aortic position and probably more pronounced after SSB valves than after SJM valves. The spatial distribution of the turbulence energy above 100 Hz was more irregular than corresponding laminar velocities previously presented. The VER100 (Velocity Energy Ratio at 100 Hz, i.e. the velocity energy above 100 Hz divided by the total velocity energy) proved useful for evaluating differences in flow disturbances downstream of different aortic valves. The mean VER100 in the three categories of patients were respectively 0.3, 1.4, and 2.1%.     

人工心瓣在脉动循环模拟系统上的能量损耗的研究

本文对常用的不同尺寸的５种人工心瓣在脉循环系统的主动脉瓣位，在不同的心率，心输邮量和主动脉平均压下进行能量损耗（Ｅｎｅｒｇｙｌｏｓｓｅｓ）的评价。人工心瓣的能量损耗据所计录的左心室压，主动脉压，前反向的跨瓣流量而计算。结果表明，跨瓣压关（ΔＰ）主输量（ＣＯ）的增加而增加，随心率（ＨＲ）和心瓣尺寸（ＶＳ）的增加而减小；跨瓣反流量（Ｒｅｇ）随ＶＳ的增加而增加，且除笼球瓣外，Ｒｅｇ随ＣＯ的增加而减少；主     

Turbulence characteristics downstream of a new trileaflet mechanical heart valve

Design limitations of current mechanical heart valves cause blood flow to separate at the leaflet edges and annular valve base, forming downstream vortex mixing and high turbulent shear stresses. The closing behavior of a bileaflet valve is associated with reverse flow and may lead to cavitation phenomenon. The new trileaflet (TRI) design opens similar to a physiologic valve with central flow and closes primarily due to the vortices in the aortic sinus. In this study, we measured the St. Jude Medical 27 mm and the TRI 27 mm valves in the aortic position of a pulsatile circulatory mock loop under physiologic conditions with digital particle image velocimetry (DPIV). Our results showed the major principal Reynolds shear stresses were <100 N/m2 for both valves, and turbulent viscous shear stresses were smaller than 15 N/m2. The TRI valve closed more slowly than the St. Jude Medical valve. As the magnitudes of the shear stresses were similar, the closing velocity of the valves should be considered as an important factor and might reduce the risks of thrombosis and thromboembolism.     

Advances in prosthetic heart valves: fluid mechanics of aortic valve designs

The in vitro hemodynamic characteristics of a variety of mechanical and tissue heart valve designs used during the past two decades were investigated in the aortic position under pulsatile flow conditions. The following valve designs were studied: Starr-Edwards ball and cage (model 1260), Bj?rk-Shiley tilting disc (convexo-concave model), Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Carpentier-Edwards porcine and pericardial (models 2625, 2650 and 2900), Hancock porcine (models 250 and 410) and Ionescu-Shiley standard pericardial. The Starr-Edward ball and cage, Bj?rk-Shiley tilting disc, Carpentier-Edwards porcine (model 2625) and Ionescu-Shiley standard pericardial valves were designed prior to 1975, while the Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Hancock porcine (model 250), Hancock II porcine (model 410), Carpentier-Edwards porcine (model 2650) and Carpentier-Edwards pericardial (model 2900) valves were designed after 1975. The pressure drop results indicated that the valves designed prior to 1975 had performance indices of 0.30 to 0.45, whereas the valves designed after 1975 had performance indices of 0.40 to 0.70. The regurgitant volumes were higher for the mechanical designs (5.0 to 11.0 cm3/beat) compared to the tissue bioprostheses (1.0 to 5.0 cm3/beat). Two-dimensional laser Doppler anemometry studies indicated that the valves designed after 1975 tended to create more centralized flow fields, with reduced levels of turbulent shear stresses. However, none of the current valve designs is ideal: they all create areas of stasis and/or regions of low velocity reverse flow; and regions of elevated turbulent shear stresses that are capable of causing sub-lethal and/or lethal damage to the formed elements of blood.     

Thrombogenic influence of biomaterials in patients with the Omni series heart valve: pyrolytic carbon versus titanium

An opportunity to assess the thromboembolic rates caused by the construction materials on valve replacements is possible with the Omni series of mechanical heart valves. The Omnicarbon and Omniscience valves are identical in form but differ in that the Omnicarbon valve is constructed entirely of pyrolytic carbon, whereas the Omniscience valve uses titanium for its housing, the rest of its structure being pyrolytic carbon. The literature was reviewed and a comparison in similar groups of patients was made between these two model valves for their thromboembolic rates in the mitral and aortic positions. A total of 569 aortic Omnicarbon valves (4,146 patient years [pt yrs.1) had a thromboembolic events (T/E rate) of 0.5% compared with 1.7% for 468 aortic Omniscience (1,552 pt yrs); p < 0.0001. A total of 298 mitral Omnicarbon valves (3,333 pt yrs) had a T/E rate of 1.6% compared with 2.6% for 716 mitral Omniscience valves (2,134 pt yrs), p < 0.001. There was no difference in the anticoagulation management between the two model valves although the Omniscience valve required higher prothrombin or International Normalized Rate maintenance levels, which resulted in higher bleeding rates among patients with Omniscience valves.     

Thrombolytic treatment of thrombosis on the aortic valvular prosthesis complicated by brain embolism

The authors present a case of thrombosis on the St. Jude Medical 19 aortic valve prosthesis. The diagnosis was confirmed by transthoracic and transoesofageal echocardiography, cardiac fluoroscopy revealed restricted movement of the aortic valve prosthesis leaflet. Thrombolytic therapy was complicated with brain embolism that was successfully percutaneously removed from the cerebral artery by the mechanical device. The patient has fully recovered without any neurological residual symptoms. This case report should be instructive to other clinicians who encounter the same complications after thrombolytic treatment.     

Gepulste Doppler-Echokardiographie bei prothetischem Aorten- und Mitralklappenersatz

Summary In 94 subjects with normally functioning heart valve prostheses (51 aortic and 43 mitral valve prostheses) and in 35 patients with intact aortic and mitral valves, blood flow velocity within the heart and the aortic root have been recorded using pulsed Doppler velocity studies in patients with diseased valves of the left heart. In addition, a further 7 patients were investigated using invasive catheter tip velocitometry, pre- and postoperatively. The preversus postoperative changes of maximum velocity and acceleration is characterized as follows: postoperative flow velocity tracings show approximately normal profiles comparable to normal valve function. Turbulence formation is diminished and the steep uptroke of the normal flow pattern is restituted. Differencies in transprosthetic blood flow patterns dependent on the implanted prosthesis model can be defined. Bioprostheses, in particular the Carpentier-Edwards device, reliably approximate normal amplitude-time characteristics. This is also true for the St. Jude Medical prosthesis with central flow properties. Velocitometric signs of valve dysfunction were detected in 9 patients: sensitivity was 100%; specificity ranged from 76% in aortic to 96% in mitral prostheses. Pulsed Doppler echocardiography therefore is a useful complement in the non-invasive haemodynamic tools and can be repeatedly applied to a patient with prosthetic cardiac valve replacement.

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Abkürzungsverzeichnis A Vorwärtsfluß - AI Aorteninsuffizienz - AS Aortenstenose - AV kombiniertes Aortenvitium - B Rückfluß - BS Björk-Shiley-Ventil - CE Carpentier-Edwards-Bioprothese - CTV Katheter-Tip-Velocitometrie - H Strömungsamplitude (mm) - H1/T1 Strömungssteilanstieg (cm/s) - HK Hall-Kaster-Ventil - HPX Hancock-Bioprothese - LE Lillehei-Kaster-Ventil - MAT Maximale Strömungsturbulenz (%) - MI Mitralinsuffizienz - MS Mitralstenose - MV kombiniertes Mitralvitium - O Strömungsnull - PDE gepulste Doppler-Echokardiographie - RF Regurgitationsfraktion (%) - SE Starr-Edwards-Ventil - SJM St. Jude Medical-Prothese - T Zeitabschnitt in der Strömungskurve (s) - U _max maximale Blutströmungsgeschwindigkeit (cm/s) - {ie76-1}_max maximale Strömungsbeschleunigung (g) In memoriam Prof. Dr. A. Vöge     

Bileaflet mechanical heart valve closing sounds: in vitro classification by phonocardiographic analysis

Bileaflet mechanical heart valves, which exhibit hemodynamic performance fairly similar to that of native valves, can be investigated by the analysis of their closing sounds. Signal spectra calculated from the closing sounds are characterized by specific features that are suitable for the functional evaluation of the valves. Five commercial bileaflet mechanical heart valves were studied under different conditions that were simulated in vitro using a Sheffield pulse duplicator for the aortic position. The closing sounds were acquired by means of a phonocardiographic apparatus, analyzed by a specifically implemented algorithm, and were statistically compared. This article was aimed at classifying the investigated valves on the basis of their signal spectra: different profiles were identified, depending on the working conditions; moreover, closing sound reproducibility and intensity allowed the ranking of valve performances with respect to the “noise” produced by valve closure. In particular, results demonstrated which valves were characterized by the lowest noise (i.e., the Medtronic Advantage and St. Jude Regent valves) and which were characterized by the highest reproducibility (OnX, Medtronic Advantage, and St. Jude Regent valves) under the examined experimental conditions.     

Twenty-two year experience with the omniscience prosthetic heart valve

This study was designed to evaluate the long-term clinical results of the Omniscience tilting disc valve. Omniscience valves were implanted in 51 patients (mean age, 50 +/- 10 years); 18 had aortic valve, 24 had mitral valve, and 9 had both aortic and mitral valve replacements. Oral warfarin potassium and dipyridamole were prescribed as our anticoagulant therapy. Preoperatively, 42 patients were in New York Heart Association class III or IV, and 23 of 25 surviving patients were in class I or II after operation. There were 2 (3.9%) early deaths and 23 late deaths (3.5 +/- 0.7% per patient-year). Cardiac related mortality including congestive heart failure, sudden death, and thromboembolism, and hemorrhagic complications were seen in 16 patients. Overall survival at 10, 15, and 20 years was 77 +/- 6%, 62 +/- 7%, and 46 +/- 7%, respectively. Thromboembolic complications were seen in 5 patients, for a rate of 0.8 +/- 0.3% per patient-year; similarly, hemorrhagic complications were also seen in 5 patients. Nonstructural prosthetic valve dysfunction was seen in 4 patients, for a rate of 0.6 +/- 0.3% per patient-year, and sudden death was seen in 2, a rate of 0.3 +/- 0.2% per patient-year. The Omniscience prosthesis demonstrated excellent postoperative clinical status with low rates of valve related complications.     

Development of artificial neural network-based algorithms for the classification of bileaflet mechanical heart valve sounds

Objectives: As is true for all mechanical prostheses, bileaflet heart valves are prone to thrombus formation; reduced hemodynamic performance and embolic events can occur as a result. Prosthetic valve thrombosis affects the power spectra calculated from the phonocardiographic signals corresponding to prosthetic closing events. Artificial neural network-based classifiers are proposed for automatically and noninvasively assessing valve functionality and detecting thrombotic formations. Further studies will be directed toward an enlarging data set, extending the investigated frequency range, and applying the presented approach to other bileaflet mechanical valves. Methods: Data were acquired for the normofunctioning St. Jude Regent valve mounted in the aortic position of a Sheffield Pulse Duplicator. Different pulsatile flow conditions were reproduced, changing heart rate and stroke volume. The case of a thrombus completely blocking 1 leaflet was also investigated. Power spectra were calculated from the phonocardiographic signals and used to train artificial neural networks of different topologies; neural networks were then tested with the spectra acquired in vivo from 33 patients, all recipients of the St. Jude Regent valve in the aortic position. Results: The proposed classifier showed 100% correct classification in vitro and 97% when applied to in vivo data: 31 spectra were assigned to the right class, 1 received a false positive classification, and 1 was "not classifiable." Conclusion: Early malfunction detection is necessary to prevent thrombotic events in bileaflet mechanical heart valves. Following further clinical validation with an extended patient database, artificial neural network-based classifiers could be embedded in a portable device able to detect valvular thrombosis at early stages of formation: this would help clinicians make valvular dysfunction diagnoses before the appearance of critical symptoms.     

The closing behavior of mechanical aortic heart valve prostheses

Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates regurgitation and water hammer effects that may form cavitations, damage blood cells, and cause thromboembolism. This study analyzes closing mechanisms of monoleaflet (Medtronic Hall 27), bileaflet (Carbo-Medics 27; St. Jude Medical 27; Duromedics 29), and trileaflet valves in a circulatory mock loop, including an aortic root with three sinuses. Downstream flow field velocity was measured via digital particle image velocimetry (DPIV). A high speed camera (PIVCAM 10-30 CCD video camera) tracked leaflet movement at 1000 frames/s. All valves open in 40-50 msec, but monoleaflet and bileaflet valves close in much less time (< 35 msec) than the trileaflet valve (>75 msec). During acceleration phase of systole, the monoleaflet forms a major and minor flow, the bileaflet has three jet flows, and the trileaflet produces a single central flow like physiologic valves. In deceleration phase, the aortic sinus vortices hinder monoleaflet and bileaflet valve closure until reverse flows and high negative transvalvular pressure push the leaflets rapidly for a hard closure. Conversely, the vortices help close the trileaflet valve more softly, probably causing less damage, lessening back flow, and providing a washing effect that may prevent thrombosis formation.     

Bileaflet Aortic Valve Prosthesis Pivot Geometry Influences Platelet Secretion and Anionic Phospholipid Exposure

The clinical histories of the Medtronic Parallel (MP) and St. Jude Medical (SJM) Standard valves suggest pivot geometry influences the thrombogenic characteristics of bileaflet prostheses. This work studied the effects of various pivot geometries on markers of platelet damage in a controlled, in vitro apparatus. The Medtronic Parallel valve, two St. Jude Medical valves, and two demonstration prostheses were used to study the effects of bileaflet pivot design, gap width, and size on platelet secretion and anionic phospholipid expression during leakage flow. A centrifugal pump was used to drive blood through a circuit containing a bileaflet prosthesis. Samples were taken at set time intervals after the start of the pump. These samples were analyzed by cell counting, flow cytometry, and enzyme-linked immunosorbant assay. No significant differences were observed in platelet secretion or anionic phospholipid expression between experiments with the SJM 27 Standard regular leaker, the SJM 20 regular leaker, and the MP 27 valves. Significant differences in platelet secretion and anionic phospholipid expression were observed between a SJM 27 Standard regular leaker and a SJM 27 high leaker valve. These studies suggest that leakage gap width within bileaflet valve pivots has a significant effect on platelet damage initiated by leakage flow. © 2001 Biomedical Engineering Society. PAC01: 8719Uv, 8719Tt, 8380Lz, 8768+z     

A comparative flow study of the Omniscience and the Bj?rk-Shiley cardiac valve prostheses

The pressure-flow rate characteristics of two new convex-concave pivoting disc prosthetic heart valves are evaluated in vitro. The Omniscience and Bj?rk-Shiley prostheses are chosen since both use curved occluders with similar dynamic function, but with different occluder curvature and eccentricity. The Omniscience prosthesis is shown to have consistently less pressure loss, and therefore less energy loss, over a range of steady state and pulsatile flow rates. The enhanced flow characteristics of the Omniscience valve are attributed to the larger opening angle of the occluder, the method of retaining the occluder, in the valve frame, the smaller curvature of the occluder, the smaller pivot-axis eccentricity, and the smaller profile thickness of the occluder. The valves are also tested in the closed position, with steady state pressure gradients causing leakage or backflow. This data is compared with the pulsatile pressure-flow rate data to gain insight into the nature of regurgitation. The total regurgitation of the pivoting disc valves are thought to be strongly dependent upon both the maximal opening angle of the occluder and the radial clearance between the disc and the valve orifice. Both the Omniscience valve and the Bj?rk-Shiley valve are found to have nearly equal volumes of total regurgitation.     

Effects of leaflet geometry on the flow field in three bileaflet valves when installed in a pneumatic ventricular assist device

Our group is currently developing a pneumatic ventricular assist device (PVAD). In this study, in order to select the optimal bileaflet valve for our PVAD, three kinds of bileaflet valve were installed and the flow was visualized downstream of the outlet valve using the particle image velocimetry (PIV) method. To carry out flow visualization inside the blood pump and near the valve, we designed a model pump that had the same configuration as our PVAD. The three bileaflet valves tested were a 21-mm ATS valve, a 21-mm St. Jude valve, and a 21-mm Sorin Bicarbon valve. The mechanical heart valves were mounted at the aortic position of the model pump and the flow was visualized by using the PIV method. The maximum flow velocity was measured at three distances (0, 10, and 30 mm) from the valve plane. The maximum flow velocity of the Sorin Bicarbon valve was less than that of the other two valves; however, it decreased slightly with increasing distance it the X-Y plane in all three valves. Although different bileaflet valves are very similar in design, the geometry of the leaflet is an important factor when selecting a mechanical heart valve for use in an artificial heart.     

Dynamic particle image velocimetry study of the aortic flow field of contemporary mechanical bileaflet prostheses

The characteristics of mechanical bileaflet valves, the leaflets of which open at the outside first, differ significantly from those of natural valves, whose leaflets open at the center first, and this fact affects the flow field down-stream of the valves. The direction of jet-type flows, which is influenced by this difference in valve features, and the existence of the sinus of Valsalva both affect the flow field inside the aorta in different ways, depending on the valve design. There may also be an influence on the coronary circulation, the entrance to which resides inside the sinus of Valsalva. A dynamic particle image velocimetry (PIV) study was conducted to analyze the influence of the design of prosthetic heart valves on the aortic flow field. Three contemporary bileaflet prostheses, the St. Jude Medical (SJM) valve, the On-X valve (with straight leaflets), and the MIRA valve (with curved leaflets), were tested inside a simulated aorta under pulsatile flow conditions. A dynamic PIV system was employed to analyze the aortic flow field resulting from the different valve designs. The two newer valves, the On-X and the MIRA valves, open more quickly than the SJM valve and provide a wider opening area when the valve is fully open. The SJM valve's outer orifices deflect the flow during the accelerating flow phase, whereas the newer designs deflect the flow less. The flow through the central orifice of the SJM valve has a lower velocity compared to the newer designs; the newer designs tend to have a strong flow through all orifices. The On-X valve generates a simple jet-type flow, whereas the MIRA valve (with circumferentially curved leaflets) generates a strong but three-dimensionally diffuse flow, resulting in a more complex flow field downstream of the aortic valve. The clinically more adapted 180 degrees orientation seems to provide a less diffuse flow than the 90 degrees orientation does. The small differences in leaflet design in the bileaflet valves generate noticeable differences in the aortic flow; the newer valves show strong flows through all orifices.     

Results of valve replacement surgery with mechanical prostheses

The clinical study is reported of the results of heart valve replacement surgery with a new pyrolytic carbon tilting disc prosthesis manufactured in Italy. From March 1977 to January 1981, at the "De Gasperis" Cardiosurgery Center, this prosthesis has been implanted in 644 patients: 283 for mitral valve replacement, 240 for aortic valve replacement, and 121 for the replacement of both mitral and aortic valves. To have a sufficiently long period of post-surgery follow-up, we considered the results of 207 patients (124 cases of isolated mitral valve replacement and 83 cases of isolated aortic valve replacement), who underwent surgery consecutively from March 1977 to December 1979. The hospital mortality was 10.5% for mitral valve replacement and 4.8% for aortic valve replacement. All patients who were discharged from hospital, except 2, were subjected to clinical, electrocardiographic, phonocardiographic, echocardiographic and radiological checks. The average follow-up period was approximately 20 months: clinical results were satisfactory. The probability of survival, expressed by actuarial curve, was, three years after surgery, 94% for patients who underwent mitral valve replacement and 97.5% for those who underwent aortic valve replacement. The probability of embolism was, three years after surgery, 8.5% for patients with mitral replaced and 5% for aortic. Even if further confirmations are needed the mortality rate and the probability of embolism related to this new prosthesis, are lower, over the same period of follow-up, than that found in the groups of patients who underwent valve replacement surgery, at the same Center, with Starr-Edwards and Bj?rk-Shiley prostheses. The phonocardiographic and echocardiographic characteristics of this new prosthesis were also investigated.     

Prevalence of pannus formation after aortic valve replacement: clinical aspects and surgical management

Pannus formation after aortic valve replacement is not common, but obstruction due to chronic pannus is one of the most serious complications of valve replacement. The causes of pannus formation are still unknown and effective preventive methods have not been fully elucidated. We reviewed our clinical experience of all patients who underwent reoperation for prosthetic aortic valve obstruction due to pannus formation between 1973 and 2004. We compared the initial 18-year period of surgery, when the Björk–Shiley tilting-disk valve was used, and the subsequent 13-year period of surgery, when the St. Jude Medical valve was used. Seven of a total of 390 patients (1.8%) required reoperation for prosthetic aortic valve obstruction due to pannus formation. All seven patients were women; four patients underwent resection of the pannus and three patients needed replacement of the valve. The frequency of pannus formation in the early group was 2.4% (6/253), whereas it was 0.73% (1/137) in the late group (P < 0.05). Pannus was localized at the minor orifice of the Björk–Shiley valve in the early group and turbulent transvalvular blood flow was considered to be one of the important factors triggering its growth. We also consider that small bileaflet valves have the possibility of promoting pannus formation and that the implantation of a larger prosthesis can contribute to reducing the occurrence of pannus.     

Spatio-temporal Flow Analysis in Bileaflet Heart Valve Hinge Regions: Potential Analysis for Blood Element Damage

Point-wise velocity measurements have been traditionally acquired to estimate blood damage potential induced by prosthetic heart valves with emphasis on peak values of velocity magnitude and Reynolds stresses. However, the inherently Lagrangian nature of platelet activation and hemolysis makes such measurements of limited predictive value. This study provides a refined fluid mechanical analysis, including blood element paths and stress exposure times, of the hinge flows of a CarboMedics bileaflet mechanical heart valve placed under both mitral and aortic conditions and a St Jude Medical bileaflet valve placed under aortic conditions. The hinge area was partitioned into characteristic regions based on dominant flow structures and spatio-temporal averaging was performed on the measured velocities and Reynolds shear stresses to estimate the average bulk stresses acting on blood elements transiting through the hinge. A first-order estimate of viscous stress levels and exposure times were computed. Both forward and leakage flow phases were characterized in each partition by dynamic flows dependent on subtle leaflet movements and transvalvular pressure fluctuations. Blood elements trapped in recirculation regions may experience exposure times as long as the entire forward flow phase duration. Most calculated stresses were below the accepted blood damage threshold. Estimates of the stress levels indicate that the flow conditions within the boundary layers near the hinge and leaflet walls may be more detrimental to blood cells than bulk flow conditions, while recirculation regions may promote thrombus buildup.