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Biomedical subjects

Y C Fung

Publications and source records attributed to Y C Fung.

At least 145 records · Page 8Linked to original sources
PubMed1970

Plug effect of erythrocytes in capillary blood vessels.

As an idealized problem of the motion of blood in small capillary blood vessels, the low Reynolds number flow of plasma (a newtonian fluid) in a circular cylindrical tube involving a series of circular disks is studied. It is assumed in this study that the suspended disks are equally spaced along the axis of the tube, and that their centers remain on the axis of the tube and that their faces are perpendicular to the tube axis. The inertial force of the fluid due to the convective acceleration is neglected on the basis of the smallness of the Reynolds number. The solution of the problem is derived for a quasi-steady flow involving infinitesimally thin disks. The numerical calculation is carried out for a set of different combinations of the interdisk distance and the ratio of the disk radius to the tube radius. The ratio of the velocity of the disk to the average velocity of the fluid is calculated. The different rates of transport of red blood cells and of plasma in capillary blood vessels are discussed. The average pressure gradient along the axis of the tube is computed, and the dependence of the effective viscosity of the blood on the hematocrit and the diameter of the capillary vessel is discussed.

Blood Flow Velocity↗
PubMed1968

Theory of the sphering of red blood cells.

A rigorous mathematical solution of the sphering of a red blood cell is obtained under the assumptions that the red cells is a fluid-filled shell and that it can swell into a perfect sphere in an appropriate hypotonic medium. The solution is valid for finite strain of the cell membrane provided that the membrane is isotropic, elastic and incompressible. The most general nonlinear elastic stress-strain law for the membrane in a state of generalized plane stress is used. A necessary condition for a red cell to be able to sphere is that its extensional stiffness follow a specific distribution over the membrane. This distribution is strongly influenced by the surface tension in the cell membrane. A unique relation exists between the extensional stiffness, pressure differential, surface tension, and the ratio of the radius of the sphere to that of the undeformed red cell. The functional dependence of this stiffness distribution on various physical parameters is presented. A critique of some current literature on red cell mechanics is presented.

Biophysical Phenomena↗
PubMedDate not supplied

Consequences of pruning in morphometry of coronary vasculature.

There is a paucity of data on the branching pattern and dimensions of the blood vessels in various organs. The reason for the paucity is undoubtedly the tremendous effort needed to obtain the morphometric data. For those organs whose morphometric data have been determined, pruning was introduced: cutting off branches at successive generations, measuring what remained, using the statistical data to estimate what were cut off, and adding the estimated data to the measured data to obtain the final results. Evaluation of the effects of pruning was not possible, however, because a full set of precise data did not exist. Now a complete set of morphometric data on the coronary arteries is presented by Kassab et al. (8). Hence we are in a position to evaluate pruning versus accuracy. Among several pruning protocols tried we found a simple, easy-to-follow scheme that seemed to be reasonable. It reduced the labor by 79% when it was applied to the left anterior descending (LAD) artery of the pig, and it caused the following percentage errors based on comparison with the unpruned data. The largest error incurred in the mean diameters of all orders of tree is 7.6%. The corresponding maximum errors in the length and number of elements in all orders are -9.8% and 30.0%, respectively. The estimated error of the total equivalent Poiseuille's resistance for the LAD artery computed from pruned data was 25.2% when compared with that computed from unpruned data.

Animals↗
PubMedDate not supplied

The pattern of coronary arteriolar bifurcations and the uniform shear hypothesis.

By minimizing the cost function, which is the sum of the friction power loss and the metabolic energy proportional to blood volume, Murray derived an optimal condition for a vascular bifurcation. Murray's law states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. We tested Murray's law against our data of pig's maximally vasodilated coronary arteriolar blood vessels at bifurcation points in control and hypertensive ventricles. Data were obtained from 7 farm pigs, 4 normal controls and 3 with right ventricular hypertrophy induced by stenosis of a pulmonary artery. Data on coronary arteriolar bifurcations were obtained from histological specimens by optical sectioning. The experimental results show excellent agreement with Murray's law in control and hypertensive hearts. Theoretically, we show that Murray's law can be derived alternatively as a consequence of the uniform vessel-wall shear strain rate hypothesis and a fluid mechanics equation based on conservation of mass and momentum. Conversely, the fluid mechanical equation, together with Murray's law, established as an empirical equation of actual measurements implies the uniformity of the shear strain rate of the blood at the vessel wall throughout the arterioles. The validity of these statements is discussed.

Animals↗