Showing papers by "Young I. Cho published in 1992"

Intracranial aneurysms: flow analysis of their origin and progression.

Abstract: PURPOSE To explain the origin and growth of intracranial aneurysms using the hemodynamic data obtained from a computer simulation. MATERIALS AND METHODS Pulsatile flow in an intracranial aneurysm cavity was numerically simulated based on physiologic pulsatile flow observed in the aorta. A finite element method was applied to solve the equations of motion and the non-Newtonian viscosity of blood was taken into account in the analysis. An angiogram of a middle cerebral artery segment with aneurysm was used for the computer modeling of blood flow within the aneurysm cavity. Local shear stress and pressure on the wall at the neck of the aneurysm as well as blood flow motions inside the cavity were calculated as a function of time for various stages in the development of the aneurysm. FINDINGS Blood moves into the aneurysm cavity along the proximal wall of the cavity and emerges along the distal wall during the acceleration period of systole; however, during the deceleration period of systole and diastole, blood changes its flow direction, entering along the distal wall of the cavity and leaving along the proximal cavity wall. Rapid changes of blood flow direction result in rapid changes in wall shear stress and pressure at the proximal and distal walls of the cavity, rendering continuous damage to the intima at the cavity neck. These hemodynamic stresses relate to the anatomy of a particular vessel may be responsible for the initiation of aneurysm formation and subsequent progression, thrombosis and/or rupture. CONCLUSION Computer modeling can further our understanding of factors that determine the origin and progression of intracranial aneurysms.

Hydrodynamics of a vertically falling thin cylinder in non-Newtonian fluids

Abstract: The effect of the shear-thinning characteristics of non-Newtonian fluids on the hydrodynamics of a vertically falling thin cylinder in a circular container was investigated. The effects of the aspect ratio, the diameter ratio of the cylinder to the container, and the density of the cylinder were also studied. Glycerin was used as the Newtonian fluid. A neutralized Carbopol 934 (1200 ppm by wt.) solution was used as a purely viscous non-Newtonian fluid, and a polyacrylamide (Separan AP-273 1000 ppm by wt.) solution was used as a viscoelastic non-Newtonian fluid. The final orientation of the thin cylinder in the polyacrylamide solution was vertical, regardless of the initial launching orientation if the concentration was greater than 200 ppm. In contrast, the thin cylinder fell horizontally both in glycerin and in the Carbopol solution, regardless of the initial launch orientation of the cylinder. The dimensionless terminal velocity increased in all test fluids as the aspect ratio increased. In the polyacrylamide solution it increased more rapidly with increasing aspect ratio than in the Carbopol solution. The maximum value of the dimensionless terminal velocity in glycerin and in the Carbopol solution was two. The corresponding maximum value in the polyacrylamide solution was 6.7, which was attributed to the preferred orientation of the long-chain molecules of polyacrylamide along the direction of the falling cylinder. The predictions of the drag coefficient of the thin cylinders based on the inelastic modeling gave good agreement with experimental data in the Carbopol solution when the aspect ratio was greater than 50. However, in the polyacrylamide solution the inelastic modelling showed a relatively large percentage deviation even at a large aspect ratio.

Apparatus and method for determining deformability of red blood cells of a living being

Abstract: Apparatus (20, 100) and methods for determining the deformability of the red blood cells of a living being. In one embodiment the apparatus (20) comprises a sampling unit (22) arranged to be coupled to a blood vessel (26) of the being for withdrawing a portion of the blood of the being at substantially the time that said portion of said blood is flowing through said vessel to calculate the deformability of red blood cells. In another embodiment the apparatus (100) comprises a viewing system (104) to provide direct visualization of the red blood cells and also includes a unit (24) for calculating blood viscosity to correlate that information with the perceived red blood cell deformability.

Apparatus and method for determining viscosity of the blood of a living being

Abstract: An apparatus (20) for determining the viscosity of the whole blood of a living being comprises a monitor unit (22) arranged to be coupled to a blood vessel (26) for monitoring the transit time of a portion of the blood when it flows through the vessel. In one embodiment the sampling unit (22) is implantable in the blood vessel (26) and uses a pair of transducers (34, 36) for measuring a pressure drop within the vessel, a device (42) for determining the instantaneous blood velocity therein, and circuitry (24) for calculating the blood viscosity. In another embodiment a sampling unit includes a needle (110) and associated syringe-like body (108), plural pairs of pressure transducers (120-122 and 126-128) and associated calculation circuitry (40) to determine the pressure drop at different flow rates so that blood viscosity can be calculated therefrom.

Computer simulation of blood flow using short te magnetic resonance angiography

Abstract: Using computer simulation of pulsatile blood flow and magnetic resonance angiography (MRA), we investigated the hemodynamic factors leading to the formation and evolution of 1) atherosclerotic plaque in carotid arteries, and 2) aneurysms in the abdominal aorta. Phantom and patients were imaged by MRA, color Doppler and/or digital subtraction angiography (DSA). Computer modelling was carried out by finite element analysis to solve the Navier-Stokes equation. In the analyzed vessels, voxels representing pathology were digitally removed. Local wall shear stress and pressure were also calculated as a function of a cardiac cycle. There was general agreement between MRA, color Doppler, DSA and computer simulation in both phantom and in-vivo experiments. In MRA, the best results were achieved by short TE, thin slice 2D “time-of-flight” technique, which was least susceptible to the changes in velocity profiles, and best correlated with Doppler and computer simulation. The hemodynamic information obtained from analyzed carotid arteries predicted that during late systole, flow separation exists at the exact locations from where the plaque voxels were removed. We were also able to predict the location of abdominal aortic aneurysm and its evolution toward the distal vessel intima. In conclusion, MRA accurately depicted flow disturbances, and computer simulation of blood flow proved to be a good predictor of the development of vascular pathology.

Determining the instantaneous shear stress on the wall of a blood vessel

Abstract: An apparatus (20) for determining the instantaneous shear stress produced on a portion of the inner wall of a blood vessel (26) by the blood flow through that vessel comprises a tube (28) arranged longitudinally within the vessel (26) which has a pair of longitudinally spaced pressure transducers (34, 36) for measuring the pressure drop therein. Electronic circuitry (24) receives a signal from a sampling unit (22), and a signal indicative of the inner diameter of the blood vessel, and a signal indicative of the distance between the longitudinally spaced pressure transducers (34, 36) to calculate the instantaenous shear stress.

Apparatus and method for determining in vivo the instantaneous velocity of the flow of blood in a living being

Abstract: Apparatus (20) and a method of determining in vivo the instantaneous velocity of the blood flowing within the body of a living being. The apparatus (20) basically comprises respective first and second sensors (42, 44) which are arranged to be disposed at spaced apart locations within a blood vessel (26). The sensors (42, 44) are coupled to a control/analysis unit (24) located externally of the body of the being. The first sensor (42) is arranged to provide a heat pulse to the blood flowing thereby and to provide a first signal at that time. The second sensor (44) is located downstream of said first sensor and is arranged for providing a second signal when the first blood portion passes thereby. The control/analysis unit (24) measures the time period between those signals and based on that value and data representative of the distance separating the sensors, calculates the instantaneous blood velocity.

Systeme pour determiner la contrainte tangentielle instantanee exercee sur la paroi d'un vaisseau sanguin

Abstract: Dispositif (20) servant a determiner la contrainte tangentielle instantanee exercee sur une partie de la paroi interne d'un vaisseau sanguin (26) par le sang circulant dans ledit vaisseau. Le dispositif comprend un tube (28) dispose dans le sens de la longueur a l'interieur du vaisseau (22) et possedant une paire de transducteurs de pression (34, 36) espaces dans le sens de la longueur et servant a mesurer une chute de pression a l'interieur du vaisseau. Un circuit electronique (24) recoit un signal emis un element d'echantillonnage (22), un signal indiquant le diametre interieur du vaisseau sanguin et un signal indiquant la distance entre les transducteurs de pression (34, 36) espaces sur la longueur du vaisseau, pour calculer la contrainte tangentielle instantanee.