Motion of individual red blood cells in a concentrated suspension flowing through micro-channels

In this study, we use a confocal micro-PIV (Particle Image Velocimetry) system to investigate red blood cell motions flowing in micro-channels. This system enables us to visualize the individual RBCs even in the high Hct blood by exciting the labeled RBCs by the laser. We measure individual trajectories of RBCs in a micro-channel with stenosis or bifurcation under high Hct conditions. Our results clearly demonstrate that the trajectories of RBCs strongly depend on the hematocrit, the RBC property and the position in the micro-channel. This information is important for a better understanding of mass transport in the microcirculation

Blood-on-chips: flow through complex geometries

Blood is a complex body fluid, composed of cells and plasma, which holds a massive amount of information about several physiological and pathologic events happening throughout the body. Hence, blood sampling and analysis are used extensively in traditional clinical laboratories for the diagnosis of several diseases. Since the inception of microfluidics, there has been a growing interest, by both microfluidic and biomedical communities, to develop blood-on-chip devices as an alternative tool for the diagnosis of major diseases, such as cancer and cardiovascular diseases. Therefore, it is essential to understand the blood flow behaviour involved in this kind of microfluidic channels in order to design reliable blood-on-a-chip devices able to efficiently treat and diagnose a variety of diseases. The present experimental study shows the effect of micro-scale contractions and expansions, such as those found in an artificial stenosis, on the blood flow and cell behaviour. The micro-channels were fabricated in PDMS using softlithography and the experiments were carried out by using dextran 40 containing different fractions of human erythrocytes. The in vitro blood flow was measured by means of a high-speed video microscopy system composed with an inverted microscope, a high-speed camera and a thermo plate to control the surrounding temperature

Individual motions of red blood cells in high-hematocrit blood flowing in a microchannel with complex geometries

Blood flow in a microchannel with complex geometries has been investigated to develop biomedical microdevices (e.g. Faivre et al., 2006) or to understand pathology in small vessels, such as lacunar infarcts. In a small channel, say 100 μm in diameter, the blood is no longer assumed to be a homogeneous fluid because the size of the red blood cells (RBCs) cannot be neglected compared to the generated flow field (the diameter of a RBC is about 8 μm). In such a case, we must treat the blood as a multiphase fluid, and investigate the motion of individual cells in discussing the flow field. In this study, we investigated the motion of RBCs in a microchannel with stenosis or bifurcation using a confocal micro-PTV system. We measured individual trajectories of RBCs under high Hct conditions (up to 20%), when the interactions between RBCs become significant. We discuss the effect of Hct on the flow field and cell-free layers, as well as the effect of deformability of RBCs on the cell-free layer thickness by hardening RBCs using a glutaraldehyde treatment

Effects of Interval Time of the Epley Manoeuvre

Objective: The Epley maneuver (EM) has an immediate effect: rapid reduction of positional nystagmus. Benign paroxysmal positional vertigo (BPPV) causes BPPV fatigue, which constitutes fatigability of positional nystagmus and vertigo with repeated performance of the Dix-Hallpike test; notably, BPPV fatigability becomes ineffective over time. We hypothesized that the immediate effect of the EM is caused by BPPV fatigue. Therefore, we suspected that performance of the EM with intervals between head positions would worsen the immediate reduction of positional nystagmus in patients with BPPV, because BPPV fatigability would become ineffective during performance of this therapy. Methods: Forty patients with newly diagnosed BPPV were randomly assigned to the following two groups; one group performed the EM without intervals between positions (group A), and the other group performed the EM with 3 min intervals between positions (group B). The primary outcome measure was the ratio of maximum slow-phase eye velocity (MSPEV) of positional nystagmus soon after the EM, compared with that measured before the EM. Secondary outcome included whether a 30 min interval after the EM enabled recovery of MSPEV of positional nystagmus to the original value. This study followed the CONSORT 2010 reporting standards. Results: In both groups A and B, the immediate effect of the EM could be observed, because MSPEV during the second Dix-Hallpike test was significantly smaller than MSPEV during the first Dix-Hallpike test (p < 0.0001 in group A, p < 0.0001 in group B). The primary outcome measure was larger in group B than in group A (p = 0.0029). The immediate effect faded 30 min later (secondary outcome). Conclusions: This study showed that the EM had an immediate effect both with and without interval time in each head position of the EM. Because setting interval time in each head position of the EM reduced the immediate effect of the EM, interval time during the EM adds less benefit. This finding can reduce the effort exerted by doctors, as well as the discomfort experienced by patients with pc-BPPV, during EM. However, this immediate effect may be caused by BPPV fatigue, and may fade rapidly

Red blood cell motions in high-hematocrit blood flowing through a stenosed microchannel

We investigated the behaviour of red blood cells (RBCs) in a micro-channel with stenosis by using a confocal micro-PIV system. We could successfully measure individual trajectories of RBCs in a concentrated suspension up to 20% hematocrit (Hct). The results show that the trajectories of healthy RBCs become asymmetric before and after the stenosis, though trajectories of tracer particles in pure water are almost symmetric. The asymmetry is larger in a 10% Hct case than in a 20% Hct case. We also investigated the effect of deformability of RBCs on the trajectories by hardening RBCs by glutarardehyde treatment. The results indicate that the deformability is the key factor in the asymmetry of trajectories and the thickness of cell-free layer. We think that the present results give fundamental knowledge for better understanding blood flow in microcirculations

Dispersion of red blood cells in microchannels : a confocal micro-PTV assessment

Blood in large arteries may be treated as a homogenous fluid from a macroscopic prospective. However, in reality blood is a suspension of deformable cells in viscous fluid plasma. In microcirculation, which comprises the smallest arteries and veins, the flow behavior of individual blood cells and their interactions provide the microrheological basis of flow properties of blood at a macroscopic level. Hence, in microcirculation it is fundamental to study the flow behavior of blood at cellular level. Several studies on both individual and concentrated RBCs have already been performed in the past. However, all studies used conventional microscopes and also ghost cells to obtain visible trace RBCs through the microchannel. The present study is concerned in providing further insights into the microscale blood flow behavior through microchannels by applying an emerging optical technique known as confocal micro-PIV/PTV. The technique consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser combined with a single particle tracking (SPT) software (MtrackJ). Detailed measurements on the motions of RBCs were measured at different haematocrits (Hct) and the correspondent radial dispersion coefficient was determined

Lubrication Tests to Support Optimal Performance Design Guidelines for Thrust Slide-Bearings in Scroll Compressors

This study focuses on the role of lubrication in the optimal performance design guidelines for the thrust slide-bearings in scroll compressors. The theoretical analysis of Ishii et al. showed that the minimum friction power loss in the thrust slide-bearing occurs at a certain outer radius of the friction surface. In the theoretical development, the physical thrust slide-bearing was modeled as a cylindrical thrust plate, representing the orbiting scroll, and the flat plate, representing the fixed scroll, with the same friction area as the physical bearing. The outer radius of the friction surface was varied for a fixed inner radius, where the fluid wedge angle between the sliding surfaces, due to axial loading on the thrust plate, was assumed to be constant at a small value. The average Reynolds equation by Patier & Cheng and the solid contact theory by Greenwood & Williamson were applied to calculate the resultant lubrication performance and finally the friction power loss at the sliding surface. The model showed that the friction power loss drastically decreases and then gradually increases, with increasing outer radius of the sliding surface.  The minimum value of friction power loss was about 80% lower than that of the conventional design thrust slide-bering. In order to confirm experimentally this predicted optimal lubrication performance, a thrust slide-bearing cylindrical-model submerged in a refrigerant oil SUNISO-RB68A was operated under pressurized conditions using R410A as the pressurizing gas. The pressure difference across the friction surface of the thrust bearing was fixed at 0.6 MPa, corresponding to the rated operation condition of a small cooling capacity scroll compressor. In the experiments, a special device was fabricated to maintain a constant fluid wedge angle between the friction surfaces due to the net pressure-induced elastic deformation of the thrust plate. The friction power loss at the friction surface was measured over a wide range of orbiting speeds from 1200 rpm up to 6000 rpm for a fixed orbiting radius of 3.0 mm. The resulting measured data exhibited showed the predicted tendency that the lubrication of the thrust slide-bearing is substabtially by increasing the outer radius. The friction power loss decreased with increasing outer-to-inner radii ratio of friction surface. The minimum loss occurred at an outer-to-inner radii ratio of about 2.1 for an operating speed of 3600 rpm, a significant 80% reduction relative to the usual conventional design ratio