Hideyuki Niimi

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.

Increased capillary vascularity in the femur of aged rats by exercise training

During aging, bone loss occurs in association with alteration of blood perfusion in the tissue. A number of studies have shown that repaired blood perfusion in various organs was improved by regular exercise, but the effect of exercise on bone microcirculation has not been studied fully yet. This study aimed to investigate the effect of exercise training on capillary vascularity in rat femur by directly observing the bone microcirculation under a laser scanning confocal microscope. Male Wistar rats were divided into three groups: sedentary-young (aged 4-6 months), sedentary-aged (aged 20-22 months) and trained-aged (aged 20-22 months). The exercise program included swimming training 5 days/week for 8 weeks. Using our newly devised window chamber, we directly observed the femur microcirculation of each group under a laser scanning confocal microscopic system. Based on the fluorescent image of microvasculature recorded at the surface of the femur, bone capillary vascularity (CV) was measured using computer software. Liver malondialdehyde (MDA) level was also measured to examine the relationship between CV and oxidative stress in aged rats. In the sedentary-aged group, the CV significantly decreased, but the MDA level significantly increased, compared with sedentary-young group. In the trained-aged group, CV was significantly higher, whereas the MDA level was significantly lower, compared with the sedentary-aged group. In both sedentary-young and sedentary-aged rats, the CV was linearly correlated with the MDA level. In conclusion, the swimming exercise could attenuate aged-induced suppression of CV, closely related to exercise-ameliorated oxidative stress in aged.

Response of cerebral neocapillaries to acetylcholine: an intravital microscopic observation

Abstract The purpose of this study was to examine the response of cerebral neocapillaries to acetylcholine (ACh) in mice. Wild type male mice were used. After anesthesia, a small area of the bone over the parietal cortex was removed to expose the cerebral cortex. The gel–nylon mesh sandwich system was placed over the exposed area. The growth factors bFGF and PDGF were used at a concentration of 6 ng/ml. After the surgical area was covered with a polyurethane biomembrane, the skin was closed with sutures. After 28 days of incubation, the neocapillaries were topically suffused with ACh and the responses of the vascular diameter and red blood cell (RBC) velocity were evaluated using intravital video microscopy. A control group was included to examine the responses of the pial vessels to ACh. A significant increase in vascular diameter and RBC velocity was observed in the control group, while the neocapillaries failed to show anything significant in the bFGF group. However, a significant increase in RBC velocity from the baseline value was observed in the PDGF group. It is suggested that the neocapillaries might have matured in the PDGF group with the formation of pericytes/smooth muscle cell function (SMC), leading to relaxation via the cGMP pathway.

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.

In vivo observation of leukocyte adherence in asthmatic rats

Inflammation of the airway is thought to be one of the main factors contributing to the bronchial hyperresponsiveness which is characteristic for allergic asthma. Leukocyte adhered to vascular endothelium, which is caused by the interaction of adhesion molecules, is necessary for inflammatory cells infiltration. To elucidate the mechanism of leukocyte infiltration in asthma, we developed an animal model of asthma by using Wistar rats. In this model the leukocyte adhered to tracheal venular endothelium was assessed by in vivo microscopic observation. The results showed that the number of leukocytes adhered to tracheal venular endothelium increased significantly in asthmatic rats, as compared with those of controls, and it was accompanied by a significant inflammatory cell infiltration in lung tissue. It is concluded that the increase of leukocyte adhered to venular endothelium is pivotal in inflammatory cell infiltration in asthmatic rats. Copyright

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.

Blood Flow Velocity Measurement in the Microcirculation Using Highly Accurate Iterative PIV (2nd Report, Analysis of Ensemble Averaged Velocity in Rat Mesenteric Arterioles)

Blood flow in microvessels, such as arterioles, capillaries and venules, whose diameter ranges from 5 to 50 μm, is responsible for the maintenance of tissue and organ functions. The measurement of microvascular blood flow velocity with high measurement accuracy is essential for basic and clinical studies in the assessment of flow shear stress at the vascular wall in relation to substance exchange between blood and tissue. This paper aimed to evaluate the velocity field of blood flow in microvessels with high spatial and temporal resolution. By using micro PIV system, the velocity distributions of red blood cells flowing in rat mesenteric arterioles, including near the wall in the axisymmetric plane, were obtained. Ensemble averaged time-series of velocity profiles in the cross-sections were calculated for comparison. It was shown that the arteriole velocity profile was blunt in the center region of the vessel cross-section while it was steep in the near wall region.Blood flow in microvessels, such as arterioles, capillaries and venules, whose diameter ranges from 5 to 50 μm, is responsible for the maintenance of tissue and organ functions. The measurement of microvascular blood flow velocity with high measurement accuracy is essential for basic and clinical studies in the assessment of flow shear stress at the vascular wall in relation to substance exchange between blood and tissue. This paper aimed to evaluate the velocity field of blood flow in microvessels with high spatial and temporal resolution. By using micro PIV system, the velocity distributions of red blood cells flowing in rat mesenteric arterioles, including near the wall in the axisymmetric plane, were obtained. Ensemble averaged time-series of velocity profiles in the cross-sections were calculated for comparison. It was shown that the arteriole velocity profile was blunt in the center region of the vessel cross-section while it was steep in the near wall region.

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].