Nobuo Watanabe

Ratio of surface roughness to flow scale as additional parameter for shear-induced hemolysis

Background In addition to the conventional knowledge that shear stress and its exposure time should have a large impact on hemolysis, it became obvious through Dr. Maruyamas study that surface roughness would be the additional factor for high shear-induced hemolysis. Concerning this new information, we hypothesized that the ratio of surface roughness to the flow scale should play a role as the additional factor for shear-induced hemolysis. The purpose of this study was to develop a constant shear generator as the method to provide a controlled shear flow field with the combination between the controlled surface roughness and the flow scale to the blood cells. Its preliminary application was to validate our hypothesis. Methods We prototyped the constant shear stress generator with the cylindrical cone-cup structure made from the acrylic material. This chamber had 3 flow scales of 1.00, 1.25, and 1.5 mm according to the change of the inner stationary cone, at which the surface roughness was distributed into the several levels between 0.14 and 0.92 micrometers in arithmetic average roughness. Using this shear chamber, we examined what effect the flow scale and the surface roughness had on hemolysis. Results Our experimental data showed the tendency of a positive correlation between the ratio of surface roughness to the flow scale and the induced hemolysis levels, validating our hypothesis. Conclusions The ratio of the surface roughness to the flow scale should be the additional parameter for shear-induced hemolysis.

Intravital Observation of Microvascular Remodeling During Chronic Exposure to Hypoxia in Mice

It is well known that chronic hypoxia elevates hematocrit levels to maintain oxygen supply to tissues. Although such high hematocrit levels might lead to hypertension due to an increase in blood viscosity, the morbidity rate of hypertension is reportedly lower in populations residing at high altitudes. The present study aimed to clarify how chronic hypoxia affects the cardiovascular system by direct observation of the microcirculation. Mouse dorsal skin chamber was used to observe arteriolar responses and capillary angiogenesis during 1-week exposure to hypoxia. Furthermore, total peripheral vascular resistance (TPR) was evaluated by measuring blood pressure (BP) and blood flow (BF) in rat carotid arteries before and after 1-week exposure to hypoxia. After 1-week exposure to hypoxia, TPR showed no significant difference compared with normoxic conditions. Observation of dorsal skin microcirculation after 1-week exposure to hypoxia, showed that the arteriolar diameter increased by 29% and the vascular area expanded by 37% compared with measures before hypoxia. These results suggest that the effects of high blood viscosity on TPR would be modified by inducing microvascular remodeling.

Blood-device interaction

Management of organ failure has improved in recent years in parallel with advancements in interventions, including organ transplant, although the shortage of donor organs remains the rate-limiting step. The advent of mechanical alternatives to biological organs is a burgeoning area available to clinicians in a variety of scenarios, including short-term procedures (e.g., cardiopulmonary bypass), longer and acute management (e.g., extracorporeal membrane oxygenation), and semi-to-permanent therapies (e.g., ventricular assist devices). A paradigm shift has recently effected a transition from “bridge” therapies toward destination therapies, with a resultant increase in clinical utilization. It is clear, however, that while mechanical circulatory and respiratory support devices can sustain life, damage to blood and its constituents, and/or activation of cellular processes, can negatively impact recovery and health. These adverse effects may be broadly related to blood exposure to high shear stress and/or interactions between biological and artificial materials. Only through advances in mechanical circulatory and respiratory support to minimize blood damage will complications be overcome and mechanical devices attain their true potential.

Visualization of erythrocyte deformation induced by supraphysiological shear stress

To elucidate development of shear-induced damage in erythrocytes, it is necessary to visualize erythrocytes under high-shear flow. Therefore, we prototyped a special shear flow chamber with a counter-rotating mechanism consisting of a transparent acrylic cone and a glass plate. The flow chamber was mounted on an inverted microscope and illuminated by a 350-W metal halide lamp. This experimental system made it possible for a digital video camera to record through the microscopes’ objective lens the rheological behavior in shear flow of erythrocytes diluted in highly viscous polyvinyl pyrrolidone. We successfully visualized the blood cells’ ellipsoidal deformation response to an unphysiological, high shear stress of 288u2009Pa, their shift into abnormal rheological behavior, and final collapse. When abnormality first appeared, the membrane surface of some ellipsoidal erythrocytes started undulating and their shape became more asymmetric. Finally, the erythrocytes appeared to fragment, although the fragments continued tumbling together suggesting that they were all still connected. One such abnormal erythrocyte became segmented through collision with other cell. The undulation of the membrane surface when erythrocytes experienced trauma suggests possible detachment of the lipid bilayer from the membrane cytoskeleton. As the damage increased, the morphological abnormality of cells became greater with less tank-treading, and then, the erythrocytes started tumbling. This unstable behavior increases the volume of flow region occupied by the erythrocytes and increases the chance that neighboring cells will hit them and break them into segmented pieces. This study clearly showed that the beginning of erythrocytes’ morphological abnormality was induced by shear stress.