Kozaburo Hayashi

Stress-strain characteristics of in situ frozen and stress-shielded rabbit patellar tendon.

To assess the effects of stress shielding on the stress-strain behaviour of the in situ frozen tendon, which simulates an ideally oriented autogenous graft, patellar tendons (PT) of 26 Japanese white rabbits underwent in situ freezing with and without the stress shielding treatment. The patella-PT-tibia complexes excised at 3 and 6 weeks postoperatively were loaded between 0% and 3% strain. The material constants were computed by fitting the data to a constitutive equation. The material constants showed that the initial slope of the stress-strain curve of the group without stress shielding was significantly steeper than that of the group with stress shielding at 3 weeks, but not at 6 weeks. The increase in the slope of the stress-strain curve of the group without stress shielding was significantly more than that of the group with stress shielding at both 3 and 6 weeks.

Blood rheology in the endotoxin-administered rabbits

The effects of endotoxin on blood rheology were studied in rabbits. Non-treated six rabbits (Group A) were used to obtain control data. Thirteen rabbits who were administered 0.1 mg of endotoxin three times at intervals of 3 days were divided into two groups; seven rabbits (Group B) were injected with 1 ml saline solution as the vehicle for endotoxin at 7 days after the final administration of endotoxin, while the remaining six rabbits (Group C) were administered endotoxin at 0.2 mg/kg on the same day. Blood was sampled from the femoral artery 120 min after the final treatment. Blood viscosity was measured at a shear rate of 150 s-1 at 37 degrees C using a cone-plate viscometer. The passage time for a 5% red blood cell suspension and that for plasma were determined by filtration; the former represents erythrocyte deformability while the latter is related to plasma fluidity. The hematocrit, whole blood viscosity and erythrocyte deformability did not show significant differences among these three groups. The ratio of hematocrit to whole blood viscosity is considered to be an index of oxygen delivery from the hemorheologic point. This index did not show significant difference either. A good correlation was observed between whole blood viscosity and hematocrit in Group A, but not in the endotoxin-treated groups. The plasma fluidity was lower in Groups B and C than in Group A. These data indicate that plasma fluidity and the hematocrit-viscosity relationship are affected in endotoxin-treated rabbits, although blood viscosity, erythrocyte deformability and oxygen delivery hardly changed.

A selective thromboxane synthetase inhibitor, OKY-046, fails to improve blood rheology in endotoxin-shocked rabbits

Effects of a selective thromboxane synthetase inhibitor, (E)-3-[4-(1-imidazolylmethyl) phenyl]-2-propenoic acid hydrochloride monohydrate (OKY-046), were studied hemorheologically in endotoxin shocked-rabbits. The animals were intravenously administrated with 0.1 mg of endotoxin 3 times at intervals of 3 days. At 7 days after the last endotoxin injection, endotoxin (0.2 mg·kg−1) was intravenously administrated to induce a shock. OKY-046 (30 mg·kg−1) was administrated after hypotension was developed by the endotoxin treatment and, then, it was continuously injected at 0.03 mg·kg−1·min−1. Blood pressure remained unchanged and hypotensive was maintained during the treatment with OKY-046. Blood was sampled from the femoral artery 15 (before the administration of OKY-046), 45, and 120 minutes after the final administration of endotoxin. Pao2 increased, and PaCO2, arterial pH, and base excess (BE) decreased during the endotoxin shock. The decrease of pH and BE was prevented by the administration of OKY-046. In the endotoxin-shocked animals, hematocrit, whole blood viscosity, erythrocyte deformability, plasma fluidity, and the ratio of hematocrit to whole blood viscosity showed no significant differences between the OKY-046 treated animals and non-treated ones. These data show that a selective thromboxane synthetase inhibitor (OKY-046) does not improve the blood rheology during endotoxin shock, although it seems to prevent the acidosis in some extent.

Mechanical properties of segmented polyether polyurethanes for blood pump applications

The effects of test environment (cholesterol-lipid solution, saline solution, and room air), temperature (24°, 37°, and 50°C), and cyclic rate (0.8, 2, and 5 Hz) on the fatigue properties of Biomer and Toyobo TM5 polyurethanes were studied to obtain basic data for the design of artificial heart pumps and for the development of accelerated endurance test methods.

Constitutive Law of the Arterial Wall and Stress Distribution

Stress distribution through the wall thickness of the artery was analyzed on the basis of the uniform strain hypothesis which assumes that the wall circumferential strain is constant over the wall cross-section under the physiological loading condition. In contrast with the results calculated using the conventional zero initial stress hypothesis which assumes that there is no stress when all external loads are removed, the uniform strain hypothesis yielded almost uniform distribution of wall stresses under the physiological condition and non-zero residual stresses even when all external forces were removed.