Saburo Yamaguchi

Cell-free plasma layer in cerebral microvessels

Two diameters of vessel and red cell column in cerebral microvessels (> 29.8 microns in diameter) of cat were measured together with red cell velocity, using a two fluorescent tracer method. A fluorescein isothiocyanate (FITC)-labeled red cell was adopted as a flow tracer to measure the cell velocity with a dual window technique. Based on the fluorescence image, the red cell column diameter was measured. Plasma was stained with rhodamine-B isothiocyanate (RITC)-labeled dextran to measure the vessel diameter. The thickness of the cell-free plasma layer could be determined from the difference of the two diameters. The obtained thickness of the cell-free layer was not described by a simple function of vessel diameter or red cell velocity; it was dependent on the pseudo shear rate defined by the ratio of cell velocity to vessel radius. The layer thickness increased with a decrease in the pseudo shear rate.

Experimental study on filtrability of polymorphonuclear leukocyte suspensions.

Filtrability of a suspension of polymorphonuclear leukocytes (PMNs) was examined in a Nuclepore membrane filtration system utilizing a gradually reduced pressure difference with or without an additional negative pressure. The filtration process was continuously recorded using a TV-video system for data analysis. The PMN content in the filtrate was directly measured. The pressure-flow relation was analyzed in terms of the relative resistance of the PMN suspension to that of the suspending medium. The relative resistance of the PMN suspension increased with an increase in the filtered volume until it approached infinity at the level of low pressure difference (2.8 - 0 cmH2O). The remarkable increase in flow resistance was closely associated with the plugging of PMNs in the membrane pores. At high pressure differences (12.8 - 10 cmH2O, 7.8 - 5 cmH2O), the relative resistance increased up to finite values, as the filtered volume increased. The variation in the relative resistance was greatly dependent upon the pressure difference or the flow condition. The amount of filtered cell fraction increased with an increase of additional pressure, indicating that the relative resistance was changed according to the rate of PMN plugging and dislodging in the pores of the membrane.

Changes in Coronary Microcirculation in Acute Ischemia

Blood cells flowing in the coronary microvascular network are responsible for oxygen supply to myocardial cells. Among these cells, white cells (WBCs) are more spherical, larger, and less deformable than red cells (RBCs) [1]. For this reason, WBCs may have an important influence on the microcirculation, especially at a low perfusion pressure. In fact, according to intravital microscopic observation of microcirculation in the s~eletal muscle, one or several WBCs may block the capillary flow during hemorrhagic shock [2]. There is also histological evidence that WBC plugging may cause mechanical obstruction of coronary capillaries in myocardial ischemia [3].

A continuum theory of blood cells filtration at low flow rates

Blood cells filtration with decreasing pressure under gravity was studied for evaluation of the cell fluidity or deformability at a low shear state. A continuum approach was made to the flow and pressure in the filter at the low flow state to relate macro- and micro-scopic quantities. The mass conservation law of each species provided a set of differential equations with respect to the pore fraction and filter resistance. The numerical calculation was made for various values of hematocrit and leukocrit. It was shown that the filter resistance might be increased with decreasing pressure, resulting from both red and white cells. The leukocrit, more than 0.05% white cells, may influence the filtration, depending upon the cell deformation. Even in the absence of the white cell, a decrease in pressure increased the filter resistance markedly. The present result indicates that single red cell shows a nonlinear behavior of flow in pores at the low pressure level.

Long-term oral vitamin C administration improves cerebral microvascular vasodilatory impairment in diabetes: in vivo evidence using diabetic rats

Background: Many clinical reports have indicated that ascorbic acid (vitamin C) improves vasodilatory impairments in patients with diabetes mellitus, but there is very little in vivo evidence to demonstrate its effectiveness on the brain. Objective: To investigate long-term effects of oral vitamin C administration on the cerebral microvascular vasodilation in diabetes, using streptozotocin (STZ)-induced diabetic rats. Materials and methods: Diabetes was induced in male Wistar Furth rats by a single intravenous injection of STZ (55 mg/kg b.w). Ascorbic acid (vitamin C) was administered in drinking water (1g/l). The rats were divided into control and diabetic groups with or without administration of vitamin C. The cerebral microcirculation was observed at different times (12, 24 and 36 weeks) after vitamin C supplementation, using fluorescence videomicroscopy. Responses of cerebral arterioles to acetylcholine (ACh), adenosine-5 diphosphate (ADP) and nitroglycerine (NTG) were studied by measuring diameters of cerebral arterioles before and after topical application on the cortical surface. Results: The vasodilatory responses of cerebral arterioles to ACh and ADP were significantly decreased in diabetic rats, compared with non-diabetic (control) rats. The response to NTG was not altered in diabetic rats, indicating that the vasodilatory impairment involves at the endothelium. The impaired endothelium-dependent vasodilation was prevented by long-term vitamin C administration. Conclusion: Long-term oral vitamin C administration might be of clinical relevance in improving cerebral microvascular vasodilatory impairment in diabetes.

Numerical Simulation of Co-operative Regulation in the Cerebral Microvascular Arcadal Network

Biomathematical models for cat cerebral arteriolar network were developed for numerical evaluation of the significance of arcadal structure in the cerebral microvascular hemodynamics. Heterogeneous distribution of hematocrit and mutual co-operation in the flow regulation in the arcadal network were demonstrated using the numerical simulation.

Microscopic Visualization of Flow in Rat Cerebral Arteries: Biofluid Dynamical Study on Experimentally Induced Aneurysm

Hemodynamic force may be an important factor to develop cerebral aneurysm since its early change often occurs at the cerebral artery bifurcation [1]. In previous studies [2,3], we proved that a cerebral aneurysm could be induced successfully in rats. The scanning electron microscopic observation on the aneurysm showed early changes of the endothelial cell just distal to the apex of the cerebral artery bifurcation [4]. This suggested that the endothelial change might be closely connected with flow near the apex [3].