This study is concerned with hemodynamics of branching flows in the cerebral circulation, which is important in pathogenesis of regional ischemic lesion or hypertensive intracerebral hemorrhage occurring preferentially in the basal ganglia. A series of measurements of energy-loss coefficients at branching sites under laminar steady flow have been conducted in model branches having various geometries. Furthermore, the effect of branching on blood supply to its distal area is described using a lumped-parameter model which was constructed according to the measurement of the vascular architecture in the basal ganglia.
It is emphasized that, in circulation in vivo, the branching loss is important where a small artery divides off from a large trunk. It is also indicated that the effect of such branchings may become more significant when the autoreguratory mechanism is abolished under pathological conditions such as CO-poisoning. (J. Jpn. Soc. Biorheol., 1 (2), 77~85, 1987).

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Hollow microporous (pore size: 0.1~0.2μm) polyvinyl alcohol (PVA) fiber was used for measuring viscosity. After the fiber hole and the micropores were debubbled by flushing with 70%ethyl alcohol, water at a given temperature was infused into the blind-ended hollow fiber at various flow rates. The pressure differences across the micropores were measured by a mercury column when the water was infused into the fiber at various flow rates. The pressure difference (Y)-flow(X) relationship showed good linearity (r=0.99) and the coefficient B_w of the regression lines (Y=A+BX) at the water temperatures corresponded to the water viscosities V_W, also with excellent linearity (r=0.99). Therefore the viscosity (V) of the fluid can be obtained from the resistance characteristics (K=B_w/V_w) obtained by the preceding water infusion and from the coefficient (B) of the pressure-flow relationship for the fluid (V=B/K).
The viscosity of diluted human plasma previously filtered through the same PVA fiber was measured at various temperatures simultaneously by the above method and by a cone-plate viscometer. The values obtained by the former were higher than those by the latter. The lower the plasma temperature, the greater the difference between them. The same procedure was performed on heat treated (52°C) plasma. The viscosity obtained by the new method was higher than that obtained by the cone-plate viscometer at all temperatures.
This method using microporous hollow fiber for viscosity measurement is a new one based on inverse Fåraeus-Lindqvist effect. The results mentioned above suggest that deformability of protein molecules which depends on temperature changes caused the difference between the viscosity values obtained by the two methods. (J. Jpn. Soc. Biorheol., 1 (2), 86~94, 1987).

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Effects of elastase on the vascular wall elasticity and smooth muscle contractility were studied in cholesterol-fed rabbits by pressure-diameter tests on excised common carotid arteries, thoracic aortae, and femoral arteries. Rabbits of group RA and RB were fed 1%cholesterol diet for 14 weeks. In addition, rabbits of group RB were administered elastase for the last 7 weeks by abdominal injection. Rabbits of group RE were fed regular chow for 14 weeks. Pressure-diameter tests were carried out under passive and active conditions to determine the stiffness parameter (apparent stiffness), incremental elastic modulus (inherent modulus), and diameter response (smooth muscle contractility).
The administration of elastase significantly decreased the stiffness parameter in and above the physiologically normal blood pressure ranges. The arterial softening caused by the elastase administration was ascribed to the decrease in the elastic modulus inherent to the wall material. The maximum diameter response to 10^-5M norepinephrine was not changed by the administration of elastase. These results clearly indicate that elastase has some regressive effect on atherosclerosis. (J. Jpn. Soc. Biorheol., 1 (2), 95~103, 1987).

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In the second trimester of normal pregnancy, whole blood viscosity decreases and red cell filterability significantly reduces compared with non-pregnant control. In order to elucidate these mechanisms, sex steroids were administered to female castrated rats and their effects on hemorheology were examined.
Eighty castrated rats of Wistar strain were assigned to the following 4 groups-; E-group administered with 1mg of estradiol dipropionate, P-group administered with 24mg of hydroxyprogesterone caproate, EP-group administered with 1mg of estradiol dipropionate and 6mg of hydroxyprogesterone caproate and C-group (control) administered with 0.2ml of olive oil.
Whole blood viscosities measured at a shear rate of 0.5 sec^-1 by Contraves Low Shear viscometer and at a shear rate of 230 sec^-1 by Wells-Blookfield viscometer significantly decreased in E-group and increased in P-group as compared with C-group. Hematocrit decreased significantly in E-group and increased in P-group. Red cell filterability was significantly lower in EP- and C-groups than those in E-and P-groups.
From these results, it is suggested that the decrease in blood viscosity in normal human pregnancy is affected by estrogen and the decrease in red cell filterability during pregnancy is due to the effects of both estrogen and progesterone. (J. Jpn. Soc. Biorheol., 1 (2), 104~109, 1987).

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