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Biomedical subjects

R T Yen

Publications and source records attributed to R T Yen.

23 records · Page 2Linked to original sources
PubMed1978

Effect of velocity of distribution on red cell distribution in capillary blood vessels.

Through the use of simulated model experiments, data on blood cell distribution into a bifurcating capillary blood vessel are obtained. The results show that the movement of red blood cells at a bifurcation point is influenced by the difference in velocities of flow in the daughter branches. If the velocity of flow in one branch is slower than that in the other, the hematocrit decreases in the slower branch and increases in the faster branch. For velocity ratios sufficiently smaller than a certain critical value, the hematocrit ratio can be expressed by a linear relationship, (H1/H2) - 1 = a[v1/v2) - 1], in which v1, v2 and H1 H2 denote the particle velocities and tube hematocritis in the branches 1 and 2, respectively, and a is a dimensionless contant dependent upon a number of factors, the most important of which are the ratio of cell diameter to tube diameter, the shape and rigidity of the pellets, and the hematocrit in the feeding tube. For velocity ratios beyond a critical value, nearly all the cells flow into the faster branch. The smaller the feeding-tube hematocrit is, the smaller is the critical velocity ratio at which this phenomenon occurs.

Blood Flow Velocity↗
PubMed1977

Inversion of Fahraeus effect and effect of mainstream flow on capillary hematocrit.

The well known Fahraeus effect (1929) states that if whole blood is allowed to flow from a large reservoir into a small circular cylindrical tube, the hematocrit in the tube is smaller than that in the reservoir, and the smaller the tube, the smaller will be the tube hematocrit. This is interpreted as a feature of particulate flow. We find that this relationship is not monotonic in a model experiment in which gelatin particles (circular disks) are suspended in a silicone fluid to simulate blood. When the diameter of the underformed cell is equal to or greater than the tube diameter, the volume fraction of the cells in the tubes increases to a value equal to or greater than that in the reservoir. Thus the Fahraeus effect has a point of inversion. Additional experiments show that the hematocrit in the tube could be greatly influenced by the flow condition outside the entrance of the tube. If the tube is perpendicular to the main direction of flow in the reservoir (as is the case of Barbee and Cokelet's experiment, or in most arteriole-capillary junctions), the velocity gradient and the velocity of flow in the reservoir just outside the entrance to the tube affects the hematocrit in the tube.

Blood Flow Velocity↗
PubMedDate not supplied

Comparison of theory and experiment in pulsatile flow in cat lung.

A mathematical model of pulsatile flow in cat lung based on existing morphometric and elastic data is presented and validated by experimental results. In the model, the pulmonary arteries and veins were treated as elastic tubes, whereas the pulmonary capillaries were treated as two-dimensional sheets. The macro- and microcirculatory vasculature was transformed into an analog electrical circuit. Input impedances of the pulmonary blood vessels of every order were calculated under normal physiological conditions. Pressure-flow relation of the whole lung was predicted theoretically. Experiments on isolated perfused cat lungs were carried out. The relation between pulsatile blood pressure and blood flow was measured. Comparison of the theoretically predicted input impedance spectra with those of the experimental results showed that the modulus spectra were well predicted, but significant differences existed in the phase angle spectra between the theoretical predictions and the experimental results. This latter discrepancy cannot be explained at present and needs to be further investigated.

Animals↗