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Robin Shandas - One of the best experts on this subject based on the ideXlab platform.

  • 795 4 determination of flow rate and orifice area in mitral stenosis by doppler color flow imaging quantitative application of Centerline Velocity distance function of proximal flow field
    Journal of the American College of Cardiology, 1995
    Co-Authors: Takahiro Shiota, Robin Shandas, Michael Jones, Izumi Yamada, Lilliam Valdescruz
    Abstract:

    The objectives of the present experimental study were to develop a simplified algorithm for quantifying the Velocity function for minimally restrictive orifices by using Doppler color flow imaging. An animal model of mitral stenosis was created by replacing the native mitral valve with glutaraldehydepreserved 26 mm porcine aortic valves in 11 sheep. 20 to 34 weeks after the surgery the bioprosthetic valves had become stenotic with orifice areas (A) 0.81 ± 0.25 (mean ± SD) cm2/m2 by pressure half time (PHT) and 0.97 ± 0.32 cm2/m2 by modified Gorlin (G) formula. At follow-up catheterization, high fidelity LA and LV pressures were available for 20 stable hemodynamic states. Epicardial Doppler color flow mapping was performed with a Toshiba SSH 160A system. The lowest (30 ± 7.6 cm/sec) and highest (50 ± 10.7 cm/sec) aliasing velocities that clearly displayed the red to blue alias and the corresponding axial distances from the alias to the center of the orifice were used to generate the Velocity function V = a*D(–b). For each condition, both coefficient “a” and exponent “b” could be determined from only two Velocity/distance points (Figure). The product of “a” and “b” correlated well with the flow rate QG (AG*CWVell and QpHT (ApHT-CW)(r = 0.77 and 0.86, SEE = 40.0 and 26.6 ml/sec respectively), although “a” or “b” alone were not well related to CW Velocity, orifice area or maximal flow rate. In addition, when a*b was normalized by CW Velocity A*B/CW correlated well with the orifice area determined by both Gorlin and Doppler PHT methods (R = 0.75 and r = 0.84, SEE = 0.23 and 0.14 cm2). Our study suggests that a Velocity function generated from merely 2 velocities in the flow acceleration field can be applied to determine forward flow rate and orifice area estimates in mitral stenosis. Download : Download high-res image (63KB) Download : Download full-size image

  • estimation of regurgitant flow volume based on Centerline Velocity distance profiles using digital color m q doppler application to orifices of different shapes
    Journal of the American College of Cardiology, 1994
    Co-Authors: Takahiro Shiota, Dag E Teien, You Bin Deng, Robin Shandas, Scott Holcomb, David J Sahn
    Abstract:

    Abstract Objectives. In this study we investigated the Centerline Velocity profile method for flow computation as applied to noncircular, as well as circular, orifices using digital color flow data. Background. Recently it has been suggested that flow volume through an orifice can be estimated more accurately by computing the axial “Centerline” flow Velocity/distance profile proximal to the orifice. Methods. A total of seven different orifices were mounted in a constant-flow model: four circular orifices, two rectangular orifices with a major/minor axis ratio of 4:1 and 8:1 and an ovoid orifice having a major/minor axis ratio of 2:1. Three different flow rates were examined (1.68, 3.48 and 6.48 liters/min). Digital measurements of flow Velocity at discrete positions along the Centerline progressing toward the orifice were analyzed to yield complete flow Velocity profiles for each orifice at each flow rate. Results. A clear separation of the flow profiles for the three different flow rates was observed independent of orifice size for all of the circular orifices. The Velocity/distance acceleration curves showed highly significant correlations using multiplicative regression fits (y = ax−b, r = 0.94 to 0.99, all p Conclusions. In view of the various sizes and shapes encountered clinically for regurgitant orifices, the simplicity of this method for the estimation of the severity of regurgitant lesions might be of importance for clinical applications of this method.

K Harby - One of the best experts on this subject based on the ideXlab platform.

  • modelling and experimental investigation of horizontal buoyant gas jets injected into stagnant uniform ambient liquid
    International Journal of Multiphase Flow, 2017
    Co-Authors: K Harby, S Chiva, J L Munozcobo
    Abstract:

    Abstract In this article, an experimental and theoretical study on the buoyant non-condensable gas jet that is injected horizontally into a high-density liquid ambient at different initial conditions is performed. Direct and instantaneous global measurements of the interface were performed using a high-speed photography. The position and motion of the entire gas jet were captured by a high-Velocity camera and the images were processed, averaged and analyzed to extract the jet parameters and interface position. In the mathematical model, the rate of entrainment is assumed to be a function of the jet Centerline Velocity, the ratio of the mean jet and the ambient densities, while the entrainment coefficient depends on the local Froude number at the jet region. An interfacial shear stress acting at the interface between the jet flow and the water ambient in the opposed direction to the main jet momentum flux is considered. The results showed that the model is able to accurately predict the jet parameters: trajectory, spread, jet angles and penetration lengths as well as the jet regimes. An overall good agreement was obtained between the simulation and experimental results over a large range of Froude numbers and jet diameters. The developed model has proven to be an adequate tool to predict the different jet parameters.

  • an experimental study on bubble entrainment and flow characteristics of vertical plunging water jets
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: K Harby, S Chiva, J L Munozcobo
    Abstract:

    Abstract When a vertical liquid jet plunges into a liquid surface after passing through a surrounding gas phase it entrains a large amount of gas bubbles into the receiving pool, and forms a large submerged two-phase region with a considerable interfacial area. At the intersection of the plunging jet and the liquid surface, free-surface instabilities develop, and gas entrainment may be observed. In this study, a set of experiments were performed on plunging water jets injected vertically downward through short circular nozzles l N / d N  ⩽ 5 onto a free water surface. The effect of the operation conditions including initial jet diameters d N , initial jet Velocity V N , and jet length x 1 on the flow characteristics such as the inception Velocity of the gas entrainment V e , the bubble penetration depth H p , the gas entrainment rate Q a , the Centerline jet Velocity V c , and the axial jet Velocity distribution V x below the free water surface were evaluated. A flow visualization technique using a CCD camera, which allowed simultaneous measurements of several magnitudes, was used to investigate such flows. This technique provided a direct measurement of the interfacial behavior between the entrained air bubbles and the liquid ambient. The results obtained showed that the nondimensional bubble penetration depth H p / d N decreased with the dimensionless jet length x 1 / d N up to 25, after this point it was almost constant. Also, the bubble penetration depth was found to increase with the jet Velocity and nozzle diameters. The entrainment rate tended to increase when the jet Velocity increased and its functional dependence was divided into three regions depending on the jet Velocity. The value of Q a was also found to increase as x 1 and d N increased for the same jet flow rate. The jet Centerline Velocity decay V c was measured and found to be a function of: the jet impact Velocity V 1 with the plunge water surface, the jet diameter d 1 and the plunge depth x . The axial Velocity distributions V x / V c were found to be approximately Gaussian distributions for all the cases when plotted against r / b u . Empirical relationships were proposed to predict the jet parameters and when were compared with the available experimental data and correlation of other authors a good agreement was found.

Takahiro Shiota - One of the best experts on this subject based on the ideXlab platform.

  • 795 4 determination of flow rate and orifice area in mitral stenosis by doppler color flow imaging quantitative application of Centerline Velocity distance function of proximal flow field
    Journal of the American College of Cardiology, 1995
    Co-Authors: Takahiro Shiota, Robin Shandas, Michael Jones, Izumi Yamada, Lilliam Valdescruz
    Abstract:

    The objectives of the present experimental study were to develop a simplified algorithm for quantifying the Velocity function for minimally restrictive orifices by using Doppler color flow imaging. An animal model of mitral stenosis was created by replacing the native mitral valve with glutaraldehydepreserved 26 mm porcine aortic valves in 11 sheep. 20 to 34 weeks after the surgery the bioprosthetic valves had become stenotic with orifice areas (A) 0.81 ± 0.25 (mean ± SD) cm2/m2 by pressure half time (PHT) and 0.97 ± 0.32 cm2/m2 by modified Gorlin (G) formula. At follow-up catheterization, high fidelity LA and LV pressures were available for 20 stable hemodynamic states. Epicardial Doppler color flow mapping was performed with a Toshiba SSH 160A system. The lowest (30 ± 7.6 cm/sec) and highest (50 ± 10.7 cm/sec) aliasing velocities that clearly displayed the red to blue alias and the corresponding axial distances from the alias to the center of the orifice were used to generate the Velocity function V = a*D(–b). For each condition, both coefficient “a” and exponent “b” could be determined from only two Velocity/distance points (Figure). The product of “a” and “b” correlated well with the flow rate QG (AG*CWVell and QpHT (ApHT-CW)(r = 0.77 and 0.86, SEE = 40.0 and 26.6 ml/sec respectively), although “a” or “b” alone were not well related to CW Velocity, orifice area or maximal flow rate. In addition, when a*b was normalized by CW Velocity A*B/CW correlated well with the orifice area determined by both Gorlin and Doppler PHT methods (R = 0.75 and r = 0.84, SEE = 0.23 and 0.14 cm2). Our study suggests that a Velocity function generated from merely 2 velocities in the flow acceleration field can be applied to determine forward flow rate and orifice area estimates in mitral stenosis. Download : Download high-res image (63KB) Download : Download full-size image

  • estimation of regurgitant flow volume based on Centerline Velocity distance profiles using digital color m q doppler application to orifices of different shapes
    Journal of the American College of Cardiology, 1994
    Co-Authors: Takahiro Shiota, Dag E Teien, You Bin Deng, Robin Shandas, Scott Holcomb, David J Sahn
    Abstract:

    Abstract Objectives. In this study we investigated the Centerline Velocity profile method for flow computation as applied to noncircular, as well as circular, orifices using digital color flow data. Background. Recently it has been suggested that flow volume through an orifice can be estimated more accurately by computing the axial “Centerline” flow Velocity/distance profile proximal to the orifice. Methods. A total of seven different orifices were mounted in a constant-flow model: four circular orifices, two rectangular orifices with a major/minor axis ratio of 4:1 and 8:1 and an ovoid orifice having a major/minor axis ratio of 2:1. Three different flow rates were examined (1.68, 3.48 and 6.48 liters/min). Digital measurements of flow Velocity at discrete positions along the Centerline progressing toward the orifice were analyzed to yield complete flow Velocity profiles for each orifice at each flow rate. Results. A clear separation of the flow profiles for the three different flow rates was observed independent of orifice size for all of the circular orifices. The Velocity/distance acceleration curves showed highly significant correlations using multiplicative regression fits (y = ax−b, r = 0.94 to 0.99, all p Conclusions. In view of the various sizes and shapes encountered clinically for regurgitant orifices, the simplicity of this method for the estimation of the severity of regurgitant lesions might be of importance for clinical applications of this method.

J L Munozcobo - One of the best experts on this subject based on the ideXlab platform.

  • modelling and experimental investigation of horizontal buoyant gas jets injected into stagnant uniform ambient liquid
    International Journal of Multiphase Flow, 2017
    Co-Authors: K Harby, S Chiva, J L Munozcobo
    Abstract:

    Abstract In this article, an experimental and theoretical study on the buoyant non-condensable gas jet that is injected horizontally into a high-density liquid ambient at different initial conditions is performed. Direct and instantaneous global measurements of the interface were performed using a high-speed photography. The position and motion of the entire gas jet were captured by a high-Velocity camera and the images were processed, averaged and analyzed to extract the jet parameters and interface position. In the mathematical model, the rate of entrainment is assumed to be a function of the jet Centerline Velocity, the ratio of the mean jet and the ambient densities, while the entrainment coefficient depends on the local Froude number at the jet region. An interfacial shear stress acting at the interface between the jet flow and the water ambient in the opposed direction to the main jet momentum flux is considered. The results showed that the model is able to accurately predict the jet parameters: trajectory, spread, jet angles and penetration lengths as well as the jet regimes. An overall good agreement was obtained between the simulation and experimental results over a large range of Froude numbers and jet diameters. The developed model has proven to be an adequate tool to predict the different jet parameters.

  • an experimental study on bubble entrainment and flow characteristics of vertical plunging water jets
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: K Harby, S Chiva, J L Munozcobo
    Abstract:

    Abstract When a vertical liquid jet plunges into a liquid surface after passing through a surrounding gas phase it entrains a large amount of gas bubbles into the receiving pool, and forms a large submerged two-phase region with a considerable interfacial area. At the intersection of the plunging jet and the liquid surface, free-surface instabilities develop, and gas entrainment may be observed. In this study, a set of experiments were performed on plunging water jets injected vertically downward through short circular nozzles l N / d N  ⩽ 5 onto a free water surface. The effect of the operation conditions including initial jet diameters d N , initial jet Velocity V N , and jet length x 1 on the flow characteristics such as the inception Velocity of the gas entrainment V e , the bubble penetration depth H p , the gas entrainment rate Q a , the Centerline jet Velocity V c , and the axial jet Velocity distribution V x below the free water surface were evaluated. A flow visualization technique using a CCD camera, which allowed simultaneous measurements of several magnitudes, was used to investigate such flows. This technique provided a direct measurement of the interfacial behavior between the entrained air bubbles and the liquid ambient. The results obtained showed that the nondimensional bubble penetration depth H p / d N decreased with the dimensionless jet length x 1 / d N up to 25, after this point it was almost constant. Also, the bubble penetration depth was found to increase with the jet Velocity and nozzle diameters. The entrainment rate tended to increase when the jet Velocity increased and its functional dependence was divided into three regions depending on the jet Velocity. The value of Q a was also found to increase as x 1 and d N increased for the same jet flow rate. The jet Centerline Velocity decay V c was measured and found to be a function of: the jet impact Velocity V 1 with the plunge water surface, the jet diameter d 1 and the plunge depth x . The axial Velocity distributions V x / V c were found to be approximately Gaussian distributions for all the cases when plotted against r / b u . Empirical relationships were proposed to predict the jet parameters and when were compared with the available experimental data and correlation of other authors a good agreement was found.

C H C Chan - One of the best experts on this subject based on the ideXlab platform.

  • Centerline Velocity decay of a circular jet in a counterflowing stream
    Physics of Fluids, 1998
    Co-Authors: C H C Chan
    Abstract:

    We use an advection hypothesis to analyze the decay of Centerline Velocity of a circular jet issuing into a counterflowing stream. Working in the Lagrangian frame, we follow the locations and Velocity gradients of jet fluid particles along the jet central axis while the particles are being advected backwards by the counterflow. The spatial Velocity gradient along the jet Centerline is thus obtained and subsequently integrated to describe the spatial decay of axial velocities. Laser-doppler Velocity measurements are performed in the laboratory and the data are well predicted by our analytical expression of Centerline Velocity decay. Looking from another view, our treatment supports that the effect of an external axial flow stream on the jet flow field can be represented by a certain degree of stretching or contracting of the jet in the axial direction.