Blood Cell Flow Research Articles

An immersed boundary method for mass transfer through porous biomembranes under large deformations

In this paper, a novel immersed boundary method for modeling convection and diffusion of mass transfer through porous membranes under large deformations is proposed. An algebraic function consisted of transmembrane velocity and diffusion coefficient of membrane is derived for modeling local concentration jumps across porous membranes. An additional equation is introduced to describe the temporal evolution of diffusive flux. Numerical validations show that the present method is robust to predict the concentration field under various fluid-porous membrane coupling conditions such as membrane oscillations in an elastic force driven flow, tank-treading and swinging motion of red blood cells in simple shear flow, and parachuting motion when cells squeeze in narrow channels down to 4 micrometers. The conservations of mass and volume in single cell are examined, and the relative errors of mass conservation are negligible. Numerical results suggest that the proposed method is capable of predicting mass transfer through porous membranes while providing detailed hydrodynamics around cells in micro-circulatory systems.

Assessment of platelet indices and platelet activation markers in children with Plasmodium falciparum malaria

BackgroundPlasmodium falciparum malaria remains one of the world’s major infectious diseases that cause most morbidity and mortality, particularly in children. In Ghana, most children below the ages of 5 years depending on the severity of the infection often lose their lives. However, it is still debatable why infection with falciparum malaria contributes to thrombocytopenia.MethodsThis study sought to investigate the expression of the various platelet indices and activation markers in children with falciparum malaria. Platelet indices (Platelet count [PLT], Plateletcrite [PCT], Mean Platelet Volume [MPV], Platelet Distribution Width [PDW] and Platelet-Large Cell Ratio [P-LCR]) and platelet surface membrane glycoproteins (GPIIb/IIIa [PAC-1], P-selectin [CD62p] and GPIV [CD36]) expressions were determined in children with falciparum malaria (cases) and healthy children (controls) using automated blood cell analysis and flow cytometry techniques, respectively.ResultsExcept for P-LCR, all the other platelet indices (PLT, MPV, PDW, and PCT) were significantly lower in the cases than the controls (P < 0.05). Also, it was observed that the level of expression of the activation markers; PAC 1 and CD62p showed a significant (P < 0.05) decreased before and after activation in falciparum malaria cases than in the controls. On the contrary, CD36 expression in the controls did not differ significantly (p > 0.05) from the malaria cases. Platelet activation markers were known to be associated with increased risk of falciparum malaria with the mean fluorescence intensity of PAC1 (Odds Ratio [OR] 34.0, Relative Risk [RR] 4.47, 95% Confidence Interval [CI] 4.904–235.7; p < 0.0001) and CD36 (OR 4.2, RR 1.82, 95% CI 0.9824–17.96; p = 0.04). Moreover, the percentage expression of CD62p (OR 4.0, RR 1.80, 95% CI 0.59–27.24; p = 0.19) was also observed to be probably associated with increased risk of falciparum malaria although not statistically significant (p > 0.05).ConclusionPlasmodium falciparum malaria has been known to be associated with platelet activation markers, which probably contributes to thrombocytopenia.

Skeletal Muscle Capillary Hemodynamics in Rats with Heart Failure with Preserved Ejection Fraction

The cardinal symptom in heart failure with preserved ejection fraction (HFpEF) is severe exercise intolerance. Limited understanding of HFpEF pathophysiology has precluded the development of effective therapies. We examined the effects of HFpEF on nitric oxide (NO)‐mediated regulation of skeletal muscle capillary hemodynamics. The hypothesis was tested that HFpEF would reduce the proportion of capillaries supporting continuous red blood cell (RBC) flow and impair microvascular hemodynamics in perfused capillaries partly via deteriorations in NO‐mediated function.METHODSIntravital microscopy was used to evaluate the resting spinotrapezius muscle in old male Spontaneously Hypertensive Rats (SHR; n=7) and healthy normotensive Wistar‐Kyoto rats (WKY; n=5). Presence of HFpEF in SHR rats was determined using in vivo (echocardiography and micromanometer) and post‐mortem evaluation of cardiac structure and function. Capillary lumen diameter (dcap), %RBC‐perfused capillaries, and RBC flux (fRBC), velocity (VRBC) and hematocrit (Hctcap) were assessed at physiological sarcomere lengths (2.8±0.1 μm) under control (CON) and non‐selective NO synthase blockade (L‐NAME; 1.5 mM) superfusion conditions.RESULTSCompared to WKY, SHR had elevated left ventricular end‐diastolic pressure (LVEDP; SHR: 11.3±1.3, WKY: 6.9±1.1 mmHg; P&lt;0.05), preserved LV ejection fraction (EF; 76±3 and 81±4%; P&gt;0.05) and fractional shortening (FS; 41±3 and 46±4%; P&gt;0.05), and increased LV mass/body mass (2.54±0.09 and 2.01±0.04 mg/g; P&lt;0.05). As expected, mean arterial pressure was higher in SHR compared to WKY under CON (139±14 and 93±5 mmHg, respectively; P&lt;0.05) with no changes produced by L‐NAME (P&gt;0.05). There were no differences in the %RBC‐flowing capillaries between SHR and WKY under CON (88±2 and 92±2%; P&gt;0.05) or L‐NAME (P&gt;0.05). In RBC‐flowing capillaries under CON, SHR had lower fRBC (10.9±1.3 and 13.7±1.4 cells/s) and VRBC (142±14 and 185±11 μm/s) than WKY (P&lt;0.05 for both). L‐NAME reduced fRBC in WKY (7.6±0.6; P&lt;0.05) but not SHR (10.0±1.0 cells/s; P&gt;0.05). Moreover, L‐NAME induced a greater magnitude of VRBC reduction in WKY (42±3%) than SHR (12±5%; P&lt;0.05). No differences in Hctcap were observed between SHR and WKY under CON (0.25±0.01 and 0.23±0.02) or L‐NAME (P&gt;0.05 for all). Similarly, no differences in dcap were seen between SHR and WKY under CON (4.9±0.1 and 5.1±0.1 μm) or L‐NAME (P&gt;0.05 for all).CONCLUSIONSSHR displayed several cardiovascular alterations consistent with HFpEF, including elevated LVEDP, preserved EF and FS, and increased LV mass/body mass. Although not impacting dcap or Hctcap, SHR showed marked reductions in fRBC and VRBC resulting partly from impaired NO‐mediated function. These alterations in microvascular O2 perfusion likely contribute to exercise intolerance in HFpEF. These data thus reveal important mechanistic clues into muscle dysfunction in this disease and identify the skeletal muscle capillary network as a potential therapeutic target in HFpEF.Support or Funding InformationNIH HL‐2‐108328

Dynamic capillary stalls in reperfused ischemic penumbra contribute to injury: A hyperacute role for neutrophils in persistent traffic jams

Ever since the introduction of thrombolysis and the subsequent expansion of endovascular treatments for acute ischemic stroke, it remains to be identified why the actual outcomes are less favorable despite recanalization. Here, by high spatio-temporal resolution imaging of capillary circulation in mice, we introduce the pathological phenomenon of dynamic flow stalls in cerebral capillaries, occurring persistently in salvageable penumbra after reperfusion. These stalls, which are different from permanent cellular plugs of no-reflow, were temporarily and repetitively occurring in the capillary network, impairing the overall circulation like small focal traffic jams. In vivo microscopy in the ischemic penumbra revealed leukocytes traveling slowly through capillary lumen or getting stuck, while red blood cell flow was being disturbed in the neighboring segments under reperfused conditions. Stall dynamics could be modulated, by injection of an anti-Ly6G antibody specifically targeting neutrophils. Decreased number and duration of stalls were associated with improvement in penumbral blood flow within 2–24 h after reperfusion along with increased capillary oxygenation, decreased cellular damage and improved functional outcome. Thereby, dynamic microcirculatory stall phenomenon can be a contributing factor to ongoing penumbral injury and is a potential hyperacute mechanism adding on previous observations of detrimental effects of activated neutrophils in ischemic stroke.

Increased oxidative phosphorylation in lymphocytes does not atone for decreased cell numbers after burn injury.

The acute systemic inflammatory response syndrome (SIRS) and multiorgan dysfunction (MOD) that occur in large burn injuries may be attributed, in part, to immunosuppressive responses such as decreased lymphocytes. However, the mitochondrial bioenergetics of lymphocytes after severe burn injury are poorly understood. The purpose of this study was to examine mitochondrial function of lymphocytes following severe burns in a swine model. Anesthetized Yorkshire swine (n = 17) sustained 40% total body surface area full-thickness contact burns. Blood was collected at pre-injury (Baseline; BL) and at 24 and 48 h after injury for complete blood cell analysis, flow cytometry, cytokine analysis, and ficoll separation of intact lymphocytes for high-resolution mitochondrial respirometry analysis. While neutrophil numbers increased, a concomitant decrease was found in lymphocytes (P < 0.001) after burn injury, which was not specific to CD4+ or CD8+ lymphocytes. No changes in immune cell population were observed from 24 h to 48 h post-injury. IL 12-23 decreased while a transient increase in IL 4 was found from BL to 24h (P < 0.05). CRP progressively increased from BL to 24h (P < 0.05) and 48h (P < 0.001) post-injury. Routine and maximal mitochondrial respiration progressively increased from BL to 24h (P < 0.05) and 48 h post-injury (P < 0.001). No changes were found in leak respiration or residual oxygen consumption. When considering the reduction in lymphocyte number, the total peripheral lymphocyte bioenergetics per volume of blood significantly decreased from BL to 24h and 48h (P < 0.05). For the first time, we were able to measure mitochondrial activity in intact lymphocyte mitochondria through high-resolution respirometry in a severely burned swine model. Our data showed that the non-specific reduction in peripheral T cells after injury was larger than the increased mitochondrial activity in those cells, which may be a compensatory mechanism for the total reduction in lymphocytes. Additional studies in the metabolic activation of T cell subpopulations may provide diagnostic or therapeutic targets after severe burn injury.

Study on the blood flow in stenosed microvascular model under pulsed magnetic field

It is widely known that abnormal peripheral blood circulation due to intravascular stenosis causes ischemic diseases and blood circulatory disorders. The purpose of this study was to investigate the influence of pulsed magnetic field (PMF) on hemodynamic characteristics in blood vessel with stenosis of 33% with diameter of 15μm, with the change of PMF intensity and hematocrit (Ht) concentration. Stenosed microvascular channels were fabricated using polydimethylsiloxane (PDMS). Our PMF stimulator has the maximum intensity of 2700G at a transition time of 102 μs with pulse intervals of 1Hz. For the Ht altered RBCs suspension, the changes in blood flow and deformation of red blood cells (RBCs) were examined before and after PMF stimulus with various intensity of 200∼2700G. In stenosed channel, threshold intensity for improvement of blood flow seems to be 400G. The higher the Ht, the higher the viscosity and the slower the velocity of RBCs, but after PMF stimulus, RBCs movement overall increased by more than 9∼67% in both Ht 5% and 20% RBCs suspension. Our study shows that PMF plays an important role in in treating cardiovascular diseases with blood circulation disorders caused by narrowing microvascular due to stenosis. In order to extend our results to clinical applications, we need develop more indicators for hemorheologic characteristics such as viscosity and resistance, and need further experiment with diverse PMF condition such as pulse shape, pulse duration, or repetition rate.

Numerical simulations of blood cell flow in non-Newtonian fluid

We investigated how non-Newtonian viscosity behavior affects the flow characteristics of blood cells. Our findings offer insight about how shear thinning affects the dispersion of liposome-encapsulated hemoglobin and red blood cells in blood. The lattice Boltzmann method was used for fluid calculations, and the rheological properties of the non-Newtonian fluid were modeled with power-law relationships. The deformable three-dimensional red blood cell model was applied. First, we investigated the effects of shear thinning on the flow behavior of single blood cell. Simulation results indicate that shear thinning promotes the axial concentration of red blood cells. Next, varied the hematocrit to see how mutual interference between blood cells affects flow. At low hematocrit, shear thinning clearly promotes the axial concentration of red blood cells. As the hematocrit increases, in contrast, mutual interference has a greater effect, which counteracts shear thinning so the red blood cell distribution resembles the distribution within a Newtonian fluid.

A study on thrombus influenced red blood cell flow in microvasculature using moving particle semi-implicit method

Microvasculature plays a decisive role on the normal operation of the human body. Previous studies have shown that the causes of microvascular hemolytic anemia and other diseases are closely related to the interaction between micro-thrombi and RBCs. The movement and deformation of Red Blood Cells (RBCs) in microvasculature with hemicyclic micro-thrombi of different sizes on the wall are simulated based on the Moving Particle Semi-implicit method (MPS) and the spring network model of RBCs membrane. Simulation of a single RBC passing the straight blood vessel indicates the strong squeeze of the RBC caused by the thrombus, which leads to a 38.5% increasing of the RBC velocity and a greater deformation, and such squeeze effect is positively related with the size of the thrombus. When two RBCs pass through the straight blood vessel with two thrombi on the both sidewalls, the deformation of the RBCs first increases and then decreases. Results show that when the axial position between the two thrombi is 10 × d0 different, the deformation of RBCs reaches the maximum of 3.10 (upper) and 2.79 (lower), respectively. When two side-by-side RBCs pass through a bifurcated blood vessel with a sidewall thrombus, the velocity and deformation of RBCs are greatly affected by the thrombus. When the thrombus radius changes from 0 × d0 to 20 × d0, the peak velocities of the two cells increase by 51.6% (upper) and 67.9% (lower), respectively.

Effect of Preconditioned Mesenchymal Stromal Cells on Early Microvascular Disturbance in a Mouse Sepsis Model.

Septic patients often die in a context of multiple organ dysfunction syndrome (MODS), despite the macro-hemodynamic parameters being normalized and after the onset of antibiotic therapy. Microcirculation injury during sepsis affects capillary permeability and leukocyte-endothelium interactions and is thought to be instrumental in organ injury. Several studies have demonstrated a beneficial effect of mesenchymal stromal cells (MSCs) injection on survival and organ dysfunctions in sepsis models. In vivo activity of MSCs also appears to be very much dependent on the information provided before injection. Indeed preconditioning by interferon γ (IFNγ; MSC-IFNγ) increases immunosuppressive capacity of MSCs in vitro and in vivo. Therefore, the objective was to evaluate the effect of MSC naive or IFNγ preconditioned on leukocyte-endothelium interactions in a polymicrobial sepsis model by intraperitoneal feces injection. Six hours (H6) after this induction, we used intravital microscopy in mice cremaster muscle venules to study the flow behavior of leukocytes. Plasmas were harvested to evaluate inflammation level and endothelial activation. We showed that MSC-IFNγ have a beneficial effect on microcirculation, by increasing the flow of white blood cells (WBCs) and the percentage of venules containing flowing WBCs, by significantly reducing the adhesion of WBCs and by increasing the average red blood cell velocity (VRBC). In conclusion, our results suggest that intravenous injection of preconditioned MSC-IFNγ improves microvascular hemodynamics in early phases of sepsis.

Red Blood Cell Deformability, Vasoactive Mediators, and Adhesion.

Healthy red blood cells (RBCs) deform readily in response to shear stress in the circulation, facilitating their efficient passage through capillaries. RBCs also export vasoactive mediators in response to deformation and other physiological and pathological stimuli. Deoxygenation of RBC hemoglobin leads to the export of vasodilator and antiadhesive S-nitrosothiols (SNOs) and adenosine triphosphate (ATP) in parallel with oxygen transport in the respiratory cycle. Together, these mediated responses to shear stress and oxygen offloading promote the efficient flow of blood cells and in turn optimize oxygen delivery. In diseases including sickle cell anemia and conditions including conventional blood banking, these adaptive functions may be compromised as a result, for example, of limited RBC deformability, impaired mediator formation, or dysfunctional mediator export. Ongoing work, including single cell approaches, is examining relevant mechanisms and remedies in health and disease.

Combinatorial Immunophenotyping of Cell Populations with an Electronic Antibody Microarray.

Immunophenotyping is widely used to characterize cell populations in basic research and to diagnose diseases from surface biomarkers in the clinic. This process usually requires complex instruments such as flow cytometers or fluorescence microscopes, which are typically housed in centralized laboratories. Microfluidics are combined with an integrated electrical sensor network to create an antibody microarray for label-free cell immunophenotyping against multiple antigens. The device works by fractionating the sample via capturing target subpopulations in an array of microfluidic chambers functionalized against different antigens and by electrically quantifying the cell capture statistics through a network of code-multiplexed electrical sensors. Through a combinatorial arrangement of antibody sequences along different microfluidic paths, the device can measure the prevalence of different cell subpopulations in a sample from computational analysis of the electrical output signal. The device performance is characterized by analyzing heterogeneous samples of mixed tumor cell populations and then the technique is applied to determine leukocyte subpopulations in blood samples and the results are validated against complete blood cell count and flow cytometry results. Label-free immunophenotyping of cell populations against multiple targets on a disposable electronic chip presents opportunities in global health and telemedicine applications for cell-based diagnostics and health monitoring.

1219 Usefulness of Blood Flow Rate of Subepithelial Microvessels in Gastric Mucosa Using Magnifying Endoscopy in the Stomach

INTRODUCTION: Magnifying endoscopy simple diagnostic algorithm for early gastric cancer (MESDA-G) is used for qualitative diagnosis based on irregular microvascular architecture and micro-surface structure, but it is a static diagnostic algorithm using still images. On the other hand, magnifying endoscopy (ME) visualizes subepithelial microvascular red blood cell (RBC) flow in real time, but there has been no study focusing on the usefulness of microvascular blood flow in the diagnosis of early gastric cancer. We therefore evaluated microvascular blood flow using ME in the diagnosis of early gastric cancer. METHODS: Patients with early gastric cancer (EGC, n = 5) or patchy redness (PR, n = 5) underwent ME with blue light imaging (M-BLI, EG-L600ZW7, Fujifilm) at our hospital. A scale in 1-mm increments was visualized at 100× (3 frames) to 135× (4 frames) magnifications prior to examination, and gastric subepithelial microvascular blood flow in lesions and background mucosa videoed using M-BLI. Images were split into 30 frames/sec, and the mean blood flow rate was calculated by the mean movement distance of one tagging RBC. The blood flow rates in EGC, PR and background mucosa were compared between them. The ratio of blood flow rate (inside lesion/background mucosa) was compared between EGC and PR. RESULTS: EGC characteristics were as follows: mean age, 74.6 ± 7.8 years; male/female ratio, 2:3; previous history (hypertension: 1); Helicobacter pylori infection (current: 3, eradicated: 2); location (M: 4, L: 1); macroscopic type (IIa: 3, IIc: 2); histology (well- [n = 4] and moderately differentiated [n = 1] adenocarcinoma); and invasion depth (all M). PR characteristics were as follows: mean age, 68.2 ± 10 years; male/female ratio, 4:1; previous history (hypertension: 3); H. pylori infection (eradicated: 5); location (M: 2, L: 4). The mean blood flow rate was significantly slower in EGC (1881.4 μm/s; range 1406–2344) vs. PR (4162.6 μm/s; 3281–4688) or background mucosa (4265.7 μm/s; 3750–5156) (P &lt; 0.01). The ratio of blood flow rate (inside lesion/background mucosa) was significantly lower in EGC (0.46; 0.38–0.50) than in PR (0.94; 0.88–1.10; P &lt; 0.01). CONCLUSION: Early gastric cancer was associated with a significantly slower gastric subepithelial microvascular flow rate compared to patchy redness and background mucosa. Gastric subepithelial microvascular flow using magnifying endoscopy in real time may enable physiological diagnosis of early gastric cancer.

Deformation of human red blood cells in extensional flow through a hyperbolic contraction.

Flow-induced damage to red blood cells has been an issue of considerable importance since the introduction of the first cardiovascular devices. Early blood damage prediction models were based on measurements of damage by shear stress only. Subsequently, these models were extrapolated to include other components of the fluid stress tensor. However, the expanded models were not validated by measurements of damage in response to the added types of stress. Recent investigations have proposed that extensional stress might be more damaging to red cells than shear stress. In this study, experiments were conducted to compare human red cell deformation under laminar extensional stress versus laminar shear stress. It was found that the deformation caused by shear stress is matched by that produced by an extensional stress that is approximately 34 times smaller. Assuming that blood damage scales directly with cell deformation, this result indicates that mechanistic blood damage prediction models should weigh extensional stress more than shear stress.

Irregular dynamics of cellular blood flow in a model microvessel.

The flow of red blood cells within cylindrical vessels is complex and irregular, so long as the vessel diameter is somewhat larger than the nominal cell size. Long-time-series simulations, in which cells flow 10^{5} vessel diameters, are used to characterize the chaotic kinematics, particularly to inform reduced-order models. The simulation model used includes full coupling between the elastic red blood cell membranes and surrounding viscous fluid, providing a faithful representation of the cell-scale dynamics. Results show that the flow has neither classifiable recurrent features nor a dominant frequency. Instead, its kinematics are sensitive to the initial flow configuration in a way consistent with chaos and Lagrangian turbulence. Phase-space reconstructions show that a low-dimensional attractor does not exist, so the observed long-time dynamics are effectively stochastic. Based on this, a simple Markov chain model for the dynamics is introduced and shown to reproduce the statistics of the cell positions.

Effects of PEGylation on capture of dextran-coated magnetic nanoparticles in microcirculation.

BackgroundMagnetic nanoparticles (MNPs) can be localized against hemodynamic forces in blood vessels with the application of an external magnetic field. In addition, PEGylation of nanoparticles may increase the half-life of nanocomposites in circulation. In this work, we examined the effect of PEGylation on the magnetic capture of MNPs in vivo.MethodsLaser speckle contrast imaging and capillaroscopy were used to assess the magnetic capture of dextran-coated MNPs and red blood cell (RBC) flow in cremaster microvessels of anesthetized rats. Magnetic capture of MNPs in serum flow was visualized with an in vitro circulating system. The effect of PEGylation on MNP-endothelial cell interaction was studied in cultured cells using an iron assay.ResultsIn microcirculation through cremaster muscle, magnet-induced retention of 250 nm MNPs was associated with a variable reduction in RBC flow, suggesting a dynamic coupling of hemodynamic and magnetic forces. After magnet removal, faster restoration of flow was observed in PEG(+) than PEG(–) group, which may be attributed to a reduced interaction with vascular endothelium. However, PEGylation appears to be required for magnetic capture of 50 nm MNPs in microvessels, which was associated with increased hydrodynamic diameter to 130±6 nm in serum, but independent of the ς-potential.ConclusionThese results suggest that PEGylation may enhance magnetic capture of smaller MNPs and dispersion of larger MNPs after magnet removal, which may potentially affect the targeting, pharmacokinetics and therapeutic efficacy.

MicroTools enables automated quantification of capillary density and red blood cell velocity in handheld vital microscopy

Direct assessment of capillary perfusion has been prioritized in hemodynamic management of critically ill patients in addition to optimizing blood flow on the global scale. Sublingual handheld vital microscopy has enabled online acquisition of moving image sequences of the microcirculation, including the flow of individual red blood cells in the capillary network. However, due to inherent content complexity, manual image sequence analysis remained gold standard, introducing inter-observer variability and precluding real-time image analysis for clinical therapy guidance. Here we introduce an advanced computer vision algorithm for instantaneous analysis and quantification of morphometric and kinetic information related to capillary blood flow in the sublingual microcirculation. We evaluated this technique in a porcine model of septic shock and resuscitation and cardiac surgery patients. This development is of high clinical relevance because it enables implementation of point-of-care goal-directed resuscitation procedures based on correction of microcirculatory perfusion in critically ill and perioperative patients.

Haemorheology in dilute, semi-dilute and dense suspensions of red blood cells

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) in a wall-bounded shear flow. The flow is assumed as almost inertialess. The suspension of RBCs, modelled as biconcave capsules whose membrane follows the Skalak constitutive law, is simulated for a wide range of viscosity ratios between the cytoplasm and plasma,$\unicode[STIX]{x1D706}=0.1$–10, for volume fractions up to$\unicode[STIX]{x1D719}=0.41$and for different capillary numbers ($Ca$). Our numerical results show that an RBC at low$Ca$tends to orient to the shear plane and exhibits so-called rolling motion, a stable mode with higher intrinsic viscosity than the so-called tumbling motion. As$Ca$increases, the mode shifts from the rolling to the swinging motion. Hydrodynamic interactions (higher volume fraction) also allow RBCs to exhibit tumbling or swinging motions resulting in a drop of the intrinsic viscosity for dilute and semi-dilute suspensions. Because of this mode change, conventional ways of modelling the relative viscosity as a polynomial function of$\unicode[STIX]{x1D719}$cannot be simply applied in suspensions of RBCs at low volume fractions. The relative viscosity for high volume fractions, however, can be well described as a function of an effective volume fraction, defined by the volume of spheres of radius equal to the semi-middle axis of a deformed RBC. We find that the relative viscosity successfully collapses on a single nonlinear curve independently of$\unicode[STIX]{x1D706}$except for the case with$Ca\geqslant 0.4$, where the fit works only in the case of low/moderate volume fraction, and fails in the case of a fully dense suspension.

Spatiotemporal dynamics of red blood cells in capillaries in layer I of the cerebral cortex and changes in arterial diameter during cortical spreading depression and response to hypercapnia in anesthetized mice.

Control of red blood cell velocity in capillaries is essential to meet local neuronal metabolic requirements, although changes of capillary diameter are limited. To further understand the microcirculatory response during cortical spreading depression, we analyzed the spatiotemporal changes of red blood cell velocity in intraparenchymal capillaries. In urethane-anesthetized Tie2-green fluorescent protein transgenic mice, the velocity of fluorescence-labeled red blood cells flowing in capillaries in layer I of the cerebral cortex was automatically measured with our Matlab domain software (KEIO-IS2) in sequential images obtained with a high-speed camera laser-scanning confocal fluorescence microscope system. Cortical spreading depression repeatedly increased the red blood cell velocity prior to arterial constriction/dilation. During the first cortical spreading depression, red blood cell velocity significantly decreased, and sluggishly moving or retrograde-moving red blood cells were observed, concomitantly with marked arterial constriction. The velocity subsequently returned to around the basal level, whileoligemia aftercortical spreading depression with slight vasoconstriction remained. After several passages ofcortical spreading depression, hypercapnia-induced increase of red blood cell velocity, regional cerebral blood flow and arterial diameter were all significantly reduced, and the correlations among them became extremely weak. Taken together with our previous findings, these simultaneous measurements of red blood cell velocity in multiple capillaries, arterial diameter and regional cerebral blood flow support the idea that red blood cell flow might be altered independently, at least in part, from arterial regulation, that neuro-capillary coupling plays a role in rapidly meeting local neural demand.

In vivo cell tracking using speckle image correlation technique employing high frame rate confocal laser scanning microscopy in a mouse skin model

Particle image velocimetry is a technique for analyzing and visualizing collective velocity using sequential images of moving particles. However, there still exist tracer seeding problems in in vivo measurement applications. For overcoming this limitation cell tracking based on speckle image cross-correlation method to confocal microscopy, it is possible to analyze the velocity of cells in blood flow without injecting exogenous particles. Using a standard rate of 30 fps allows tracking of hematocytes near 200μm / sec, but this is insufficient at only moderately higher flow rates due to the inclusion of individual cells moving at velocities well above the average. It is necessary to overcome this limitation by using higher frame rates of imaging for a precise blood stream analysis. We performed in vivo cell tracking based on speckle image cross-correlation acquired at rates of 30, 90 and 180 fps using a confocal microscope. We found that the more than 5-fold increase in frame rate achieves a similar low rate of errors for blood flow containing cells moving at an average speed of up to to 1 mm/sec.

Evaluation of Laser-Doppler-Fluxmetry for the diagnosis of microcirculatory disorders.

The laser Doppler fluxmetry (LDF) is a non-invasive method to assess skin blood perfusion, measuring the flow of blood cells inside a tissue volume without harming the tissue. In the diagnosis of skin circulation disorders, the results of the LDF measurement are generally used in such a way that "normal" (or non-ill) or "pathological" values are achieved by comparison with a reference sample, for example of apparently healthy subjects. In this study, the values of LDF for the diagnosis of microcirculatory disorders in patients with coronary artery disease (n = 20) or in patients with microcirculatory disorders, already diagnosed by capillary microscopy (n = 46), were examined. The mean values of LD amplitudes in the four frequency windows for patients with coronary artery disease were in the reference range. However, some of the patients showed reduced LD values: in eleven of the twenty patients, one or more mean LD amplitudes were below the reference range. Four of the eleven patients had pathologically decreased capillary erythrocyte velocities of very = 0.09-0.21 [mm/s], while the other seven patients had normal blood circulation at rest.For all patients with a proven cutaneous microcirculatory disorder, the mean LD amplitude in at least one of the frequency windows FF2 to FF4 was pathologically reduced. The Laser-Doppler fluxmetry method used in the study allows the reliable diagnosis of cutaneous microcirculatory disorders.