Biomedical subjects

Y R Woo

Publications and source records attributed to Y R Woo.

22 records · Page 2Linked to original sources

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

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.

Blood Flow Velocity↗

PubMedDate not supplied

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.

Biophysical Phenomena↗

PubMedDate not supplied

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.

Aortic Valve↗