Evaluation of sealing properties of 70 degrees C thermoplasticized gutta-percha used as a retrograde root filling.

The efficacy of low temperature (70 degrees C) thermoplasticized gutta-percha used to seal root canals by the retrograde approach following apicectomy was assessed. A dye leakage technique was used, and gutta-percha was compared with amalgam. Two groups of different sized roots were apicected, and their root canals instrumented and filled conventionally with laterally condensed gutta-percha. Each group was randomly divided into four sub-groups; one was the control group in which no further treatment was carried out. In the other three groups the apical 3 mm of gutta-percha was removed, and the apical cavities filled as follows: group I with 70 degrees C thermoplasticized gutta-percha with sealer; group II with 70 degrees C thermoplasticized gutta-percha without sealer; group III with amalgam. The roots were rendered transparent by acid demineralization, and maximum dye penetration was measured. The results showed statistically significant ranking of leakage between the four sub-groups: 70 degrees C thermoplasticized gutta-percha with sealer less than 70 degrees C thermoplasticized gutta-percha without sealer less than amalgam less than control. The larger canals in all four sub-groups also exhibited significantly greater leakage than the smaller ones.

In vitro velocity and turbulence measurements in the vicinity of three new mechanical aortic heart valve prostheses: Björk-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: Björk-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 Björk-Shiley design. Regions of stagnation/flow separation were observed immediately adjacent (ie, distal) to the minor orifice strut and the pivot guards of the Björk-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.

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), Björk-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, Björk-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.

Calibration of color Doppler flow mapping during extreme hemodynamic conditions in vitro: a foundation for a reliable quantitative grading system for aortic incompetence.

If color Doppler imaging is to continue to evolve into a reliable clinical method to noninvasively evaluate regurgitant lesions, then its grading methods must be quantitated and calibrated under extreme hemodynamic conditions. A left heart pulse duplicator was used to provide a completely controllable system to study aortic incompetence jet morphologies as a function of hemodynamic extremes. The system was first used to calibrate the limits of resolution of color Doppler imaging. Next, to define which jet features reliably predict the defect size or the regurgitant fraction and which are primarily influenced by instantaneous hemodynamic variables, we measured the jets' maximal length, width, proximal width, and temporal pattern of color variance during independent variations in the heart rate, cardiac output, and pressure gradient across the incompetent valve. The proximal jet width (immediately below the valve plane) was the only reliable independent predictor of both the defect size and the regurgitant fraction. Jet depth accurately predicted peak velocity (quantitated by laser Doppler velocimetry); it reliably predicted the severity of incompetence only at a known pressure gradient across the valve. Large defects (5 mm) produced jets with maximal color variance in early diastole, whereas small defects produced pandiastolic variance.

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 pulsatile flow measurements in the vicinity of mechanical heart valves in the mitral flow chamber.

A three-beam laser Doppler anemometer system was used to study the flow fields created by various types of mitral heart valve prostheses under conditions of physiological pulsatile flow. The prosthetic valves studied were the Beall caged-disc valve, Björk-Shiley tilting disc valve, Medtronic-Hall tilting disc valve, and St. Jude bileaflet valve. The results indicate that all four prosthetic valve designs studied create very disturbed flow fields, with elevated turbulent shear stresses and regions of flow separation and/or stagnation. The maximum turbulent shear stresses measured were 1900 dynes/cm2 for the Beall valve, 380 dynes/cm2 for the Björk-Shiley valve, 1800 dynes/cm2 for the Medtronic-Hall valve, and 770 dynes/cm2 for the St. Jude valve. These elevated turbulent shear stresses could cause sublethal and/or lethal damage to red cells and platelets. The regions of flow separation and/or stagnation could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on clinically recovered prosthetic valves.

Studies in vitro of the relationship between ultrasound and laser Doppler velocimetry and applicability to the simplified Bernoulli relationship.

While there has been wide general acceptance of Doppler methods that use the simplified Bernoulii relationship to estimate pressure gradients across stenotic orifices, there is still ongoing controversy related to potential sources of error in the method. In this study we tested accuracy o ultrasound Doppler measurements of flow velocity when compared with the gold standard of laser light Doppler anemometry in a pulsatile flow model of pulmonic stenosis in vitro. We tested two commercially available Doppler systems and examined steered and nonsteered, parallel and off-axis and angle-corrected velocity determinations using continuous-wave and high-pulse repetition frequency (HPRF) methods. We also examined the potential range of error in the simplified Bernoulli method. One hundred and twenty individual flow states were examined with three stenotic valve orifices (3.0, 1.0, and 0.5 cm2 flow area) to measure velocities up to 620 cn/sec. A very high correlation coefficient was obtained for the comparison of laser Doppler anemometric and ultrasound velocity recordings by the nonsteered continuous-wave technique (r= .99, SEE = 17.9 cn/sec), but there was a tendency for underestimation of higher velocities when the transducer was positioned at 30 degrees and the ultrasound beam was steered so as to be parallel to the visualized flow jet (r = .98, SEE = 29.6 cn/sec). The HPRF ultrasound Doppler technique was also highly accurate in this optimized setting for measuring velocities (r = .99, SEE = 17 cm/sec), but also slightly underestimated the highest velocities. Our results also verified the accuracy of the simplified Bernoulli equation for converting instantaneous velocity measurements to estimated peak instantaneous gradient (r = .97, SEE = 8.4 mm Hg).

In vitro fluid dynamic characteristics of aortic bioprostheses: old versus new.

The in vitro fluid dynamic characteristics of a variety of old- and new-generation porcine and pericardial aortic bioprostheses were investigated under pulsatile flow conditions. The pressure drop results indicate that the old valve designs have performance indices in the range of 0.30 to 0.42, while the new, low-pressure fixed designs have performance indices of 0.50 to 0.70. Leaflet photography indicated that the new designs also have superior opening and closing characteristics. Flow visualization, and velocity and turbulent shear stress measurements, conducted with a two-dimensional laser Doppler anemometer system, indicated that all the tissue valve designs create jet-type flow fields. The intensity of the jets and turbulence levels were less severe with the new designs. The old designs created turbulent shear stresses of as little as 1500 dynes/cm2, while the new designs created turbulent shear stresses of as little as 750 dynes/cm2.

An instrument for the measurement of in vitro velocity and turbulent shear stress in the immediate vicinity of prosthetic heart valves.

The measurements of velocity and turbulent shear stress in the immediate vicinity of prosthetic heart valves play a vital role in their design and evaluation. In the past, hot-wire/film and one-component laser Doppler anemometer (LDA) systems have been used extensively. Hot-wire/film anemometers, however, have some serious disadvantages, such as not being able to measure the directionality of the flow, disturbing the flow field with the probe, and requiring frequent calibration. One-component LDA systems do not have these problems, but they cannot measure turbulent shear stresses directly. Since these measurements are essential, and are not available in the open literature, a two-component LDA system was assembled to measure velocity and turbulent shear stress fields under pulsatile flow conditions. The experimental methodology used to create an in vitro data base of velocity and turbulent shear stress fields in the immediate vicinity of various designs of prosthetic heart valve in current clinical use is also discussed in this paper.

Pulsatile flow velocity and shear stress measurements on the St. Jude bileaflet valve prosthesis.

The velocity and turbulent shear stress fields in the immediate vicinity of the St. Jude bileaflet valve were measured under pulsatile flow conditions with a two-dimensional laser Doppler anemometer system. The valve was studied in both aortic and mitral positions. In both positions, the valve created relatively centralized flow fields. However, a major portion of the flow occurred through the two side orifices. Regions of flow separation were observed adjacent to the valve sewing ring in the area of the valve pivot (hinge) mechanism. Elevated turbulent shear stresses were measured in both positions. Peak values of 760 dynes/cm2 and 2 000 dynes/cm2 were observed in the mitral and aortic flow chambers, respectively. Such turbulent shears could cause sublethal and/or lethal damage to blood elements. The regions of flow separation adjacent to the pivot mechanism could lead to tissue overgrowth and/or thrombus formation, which in turn could impede proper motion of the valve leaflets.

Turbulent shear stress measurements in the vicinity of aortic heart valve prostheses.

A two dimensional laser Doppler anemometer system has been used to measure the turbulent shear fields in the immediate downstream vicinity of a variety of mechanical and bioprosthetic aortic heart valves. The measurements revealed that all the mechanical valves studied, created regions of elevated levels of turbulent shear stress during the major portion of systole. The tissue bioprostheses also created elevated levels of turbulence, but they were confined to narrow regions in the bulk of the flow field. The newer generation of bioprostheses create turbulent shear stresses which are considerably lower than those created by the older generation tissue valve designs. All the aortic valves studied (mechanical and tissue) create turbulent shear stress levels which are capable of causing sub-lethal and/or lethal damage to blood elements.

In vitro pulsatile flow velocity and shear stress measurements in the vicinity of mechanical mitral heart valve prostheses.

A three beam laser Doppler anemometer system was used to study the flow fields created by various types of mitral heart valve prostheses under physiological pulsatile flow conditions. The prosthetic valves studied were: Beall caged disc valve, Bjork-Shiley tilting disc valve, Medtronic-Hall tilting disc valve and St. Jude bileaflet valve. The results indicate that all four prosthetic valve designs studied create very disturbed flow fields with elevated turbulent shear stresses and regions of flow separation and/or stagnation. The observed elevated turbulent shear stresses could cause sublethal and/or lethal damage to red cells and platelets. The regions of flow separation and/or stagnation, could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on clinically recovered prosthetic valves.

Steady flow velocity measurements in a pulmonary artery model with varying degrees of pulmonic stenosis.

Velocity and flow visualization studies were conducted in an adult size pulmonary artery model with varying degrees of valvular stenosis, using a two dimensional laser Doppler anemometer system. Velocity measurements in the main, left and right branches of the pulmonary artery revealed that as the degree of pulmonic stenosis increased, the jet type flow created by the valve hit the distal wall of the LPA farther downstream from the junction of the bifurcation. This in turn led to higher levels of turbulent and disturbed flow, and larger secondary flow motion in the LPA compared to the RPA. The high levels of turbulence measured in the main and left pulmonary arteries with the stenotic valves, could lead to the clinically observed phenomenon of post stenotic dilatation in the MPA extending into the LPA.

In-vitro pulsatile flow visualization studies in a pulmonary artery model.

In-vitro pulsatile flow visualization studies were conducted in an adult-sized pulmonary artery model to observe the effects of valvular pulmonic stenosis on the flow fields of the main, left and right pulmonary arteries. The flow patterns revealed that as the degree of stenosis increased, the jet-type flow created by the valve became narrower, and it impinged on the far (distal) wall of the left pulmonary artery further downstream from the junction of the bifurcation. This in turn led to larger regions of disturbed turbulent flow, as well as helical-type secondary flow motions in the left pulmonary artery, compared to the right pulmonary artery. The flow field in the main pulmonary artery also became more disturbed and turbulent, especially during peak systole and the deceleration phase. The flow visualization observations have been valuable in helping to conduct further quantitative studies such as pressure and velocity field mapping. Such studies are important to understanding the fluid mechanics characteristics of the main pulmonary artery and its two major branches.

In vitro pulsatile flow velocity and turbulent shear stress measurements in the vicinity of mechanical aortic heart valve prostheses.

A two-dimensional laser Doppler anemometer system was used to study the velocity and turbulent shear stress fields created by various types of mechanical aortic heart valve prostheses under physiological pulsatile flow conditions. The prosthetic valves studied were the Starr-Edwards caged ball valve, Bjork-Shiley tilting disc valve, Medtronic-Hall tilting disc valve, and St. Jude bileaflet valve. The results indicate that all four prosthetic valve designs studied create very disturbed flow fields with regions of flow separation and/or stagnation and regions of elevated turbulent shear stress. The maximum values of the mean turbulent shear stresses measured during peak systole were 1200 dynes/cm2 for the Starr-Edwards valve, 1600 dynes/cm2 for the Bjork-Shiley valve, 1000 dynes/cm2 for the Medtronic-Hall valve, and 1050 dynes/cm2 for the St. Jude valve. The corresponding values during the deceleration phase were about 800, 600, 450 and 800 dynes/cm2, respectively. These elevated turbulent shear stresses could cause sublethal and/or lethal damage to blood elements, and, together with the regions of flow separation and/or stagnation, could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on the clinically recovered prosthetic valves.

Two-component laser Doppler anemometer for measurement of velocity and turbulent shear stress near prosthetic heart valves.

The velocity and turbulent shear stress measured in the immediate vicinity of prosthetic heart valves play a vital role in the design and evaluation of these devices. In the past hot wire/film and one-component laser Doppler anemometer (LDA) systems were used extensively to obtain these measurements. Hot wire/film anemometers, however, have some serious disadvantages, including the inability to measure the direction of the flow, the disturbance of the flow field caused by the probe, and the need for frequent calibration. One-component LDA systems do not have these problems, but they cannot measure turbulent shear stresses directly. Since these measurements are essential and are not available in the open literature, a two-component LDA system for measuring velocity and turbulent shear stress fields under pulsatile flow conditions was assembled under an FDA contract. The experimental methods used to create an in vitro data base of velocity and turbulent shear stress fields in the immediate vicinity of prosthetic heart valves of various designs in current clinical use are also discussed.

An on-line method for evaluation of the in vitro pulsatile pressure drop and regurgitative characteristics of prosthetic heart valves.

An on-line digital method is described for analyzing the pressure drop and regurgitative characteristics of prosthetic heart valves in a pulse duplicator system. The method is based on the Apple II microcomputer system but could be modified to be used with most microcomputers currently available. The digital data collection system is synchronized with the pulse duplicator system, and is programmed to collect the relevant pressure (upstream and downstream) and volumetric flow data for 10 cardiac cycles at a given time. The system is relatively easy to use and gives the scientist a fair amount of flexibility in terms of data collection, storage, and analysis. The on-line method has been used with the pulse duplicator of the Georgia Institute of Technology for the past 3 years.

Bileaflet, tilting disc and porcine aortic valve substitutes: in vitro hydrodynamic characteristics.

The desire for a low profile mechanical valve with better fluid dynamic performance led to the design and development of the St. Jude Medical bileaflet prosthesis. Comparative in vitro flow studies indicate that it has better pressure drop characteristics than the Björk-Shiley (convexo-concave) and Carpentier-Edwards porcine valves in current clinical use, especially in the small sizes. In the 21 to 27 mm aortic valve size range the St. Jude valve has an average performance index of 0.66, compared with 0.46 and 0.32 for the Björk-Shiley and Carpentier-Edwards valves, respectively. In contrast, the St. Jude valve has larger regurgitant volumes than both the Björk-Shiley and Carpentier-Edwards valves. Velocity measurements with a laser-Doppler anemometer indicate relatively centralized flow with small amounts of turbulence downstream of the St. Jude valve. The flow is unevenly distributed between the central and side orifices. The turbulent shear stresses are, however, large enough to cause sublethal or lethal damage to blood elements. Wall shear stresses are smaller than those measured downstream of the Björk-Shiley valve. Regions of flow separation were observed just downstream from the sewing ring, which could lead to excess tissue growth along the sewing ring. The results of this study indicate that overall in vitro fluid dynamic performance of the St. Jude valve is superior to that of the two other commonly used prostheses.

In-vitro fluid dynamic characteristics of the abiomed trileaflet heart valve prosthesis.

The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.