New method for the detection of thrombus formation in cardiovascular devices: optical sensor evaluation in a flow chamber model

We proposed a new method of detecting the onset of thrombus formation based upon the backscattered light intensity changes caused by the alteration of blood flow behavior in the cardiopulmonary devices. In an optical senor based upon the First Order Scattering theory, the relationship between the backscattered light intensity and hematocrit exhibited a monotonically decaying curve for the hematocrit level greater than 45%. To distinguish the effect either by thrombus formation or erythrocyte aggregation on the back-scattered light intensity with a flow chamber connected to a rabbit arterial-venous bypass model, we generated an oscillatory flow using a roller pump and analyzed the results using a Fast Fourier Transform (FFT) method. Our hypothesis was that the nonclotting blood flow would yield an unchanged fundamental spectral power density of the oscillation frequency generated by a roller pump, whereas the thrombus formation would attenuate its power. We measured the back-scattered light intensity in the flow chamber of high shear region and low shear region (n = 5). The blood flow rate was 40 ml/min with the roller pump. The activated clotting time and the hematocrit level were adjusted to 170 +/- 10 s with heparin and 35 +/- 5% with a phosphate buffered sulfate solution, respectively. As a result, the backscattered light intensity from the low shear rate region gradually diminished with time (p < 0.05; 0-5 minutes vs. more than 10-15 minutes), whereas that from the high shear rate region remained fairly constant. The experimental finding supported the hypothesis that the decrease of the backscattered light intensity and diminished spectral power density were caused by the aggregation or clotting erythrocytes. In conclusion, we found that the measurement of the average backscattered light intensity level together with FFT analysis of the backscattered light from the flowing blood is a valuable approach in detecting the onset of thrombus formation.     

Étude rhéo-acoustique de la rupture d''agrégates de particules en suspension dans un champ de cisaillement Application à la désagrégation des globules rouges

Rheo-acoustic study of particle aggregate break-up in a shear flow. Application to red blood cell aggregates.Shear-induced disruption of reversible flocs in a concentrated suspension is investigated by ultrasound backscattering in the low shear regime. Fractal flocs are considered as non-Brownian scatterers much smaller than the wavelength, with acoustic properties close to those of the surrounding medium, so that the attenuation of the coherent field is weak and multiple scattering can be neglected. The concept of variance in local particle volume fraction is used to deduce a first order expression of the ultrasound scattering coefficient (cross-section per unit volume) for Rayleigh scatterers in a dense suspension. On the basis of a scaling law for the shear-induced disruption of aggregates, the shear stress dependence of the ultrasonic scattered intensity from a dense suspension of flocs is derived. In a second part, the shear break-up of hardened red blood cell aggregates is investigated in a plane—plane flow geometry by ultrasound scattering. Rheo-acoustical experiments are analysed within the framework of the self consistent field approximation and the scaling laws currently used in microrheological models. Finally, the ability of ultrasonic, light reflectometry and viscometry methods to provide quantitative information about red blood cell aggregation and membrane adhesiveness is discussed.     

红细胞聚集增高与纤维蛋白原的关系及其对心绞痛患者发病的影响

目的 :探讨红细胞聚集改变与纤维蛋白原的关系及其对心绞痛发病的影响。方法 :测定 80例不稳定性心绞痛患者和 40例健康人的红细胞聚集指数 (光密度法 )、红细胞变形指数 (激光衍射法 )、血浆及全血粘度 (旋转式粘度计 )和纤维蛋白原 (双缩脲法 )。结果 :不稳定性心绞痛患者红细胞聚集指数和全血粘度 ( 4 0s- 1 )及纤维蛋白原浓度均高于对照组 (P均 <0 .0 1～ 0 .0 5 ) ,且红细胞聚集指数与纤维蛋白原呈直线正相关 ,与全血粘度 ( 4 0s- 1 )无相关性。结论 :纤维蛋白原含量增加是红细胞聚集增强的主要原因之一 ;红细胞聚集能力增强导致血液高粘滞 ,与心绞痛发作有关 ;选择 10s- 1 以下切变率测定低切全血粘度 ,利于观察全血粘度与红细胞聚集的关系     

Non-invasive imaging and characterisation of human foot by multi-probe laser reflectometry and Monte Carlo simulation

Diffusely backscattered signals from the human foot sole tissues of normal subjects (n=5) were obtained by multiprobe laser reflectometry. The colour-coded images were constructed from data on the variation of normalised backscattered intensity (NBI), after interpolation and median filtering. The maximum and minimum NBI values at the arch and heel regions of the foot sole, respectively, were observed. The mean NBI at the arch region was significantly higher compared with that at other regions (p<0.0001). The images of optical parameters of normal tissues show point-to-point variation, attributed to their compositional changes. The pattern of variation of the NBI of a diabetic subject (glucose level 170 mg dl⁻¹) was associated with highly significant variation at the lateral sides of the fore- and middle-foot compared with that of normal subjects.     

Microrheology and light transmission of blood

Summary The well known flow dependence of the optical density of whole blood was studied by measuring light transmission of blood in viscometric flow. A cone-plate chamber (3° cone angle) was transilluminated (=500–800 nm) while under shear (0–460 sec^–1). The transmitted light was monitored with a selenium barrier layer photocell and was continuously recorded. In an identical chamber, the microrheological behaviour of the cells in flow was monitored by microphotography and then correlated to photometric events.Light transmission of human blood showed a biphasic behaviour when plotted as a function of shear rate: between 0 and about 60 sec^–1, the light transmission decreases with shear, corresponding to aggregate dispersion. Above 60 sec^–1, an increase of light transmission with shear occurs, corresponding to red cell deformation, alignment, and orientation. Bovine blood, which does not form aggregates, shows minimum light transmission at rest. Light transmission then rises progressively with shear from the very onset of slow flow. Equine blood (equus zebra) which has very strong aggregation shows a progressive decrease of light transmission with shear due to aggregate persistence up to 460 sec^–1. Amphibia blood (rana esculanta) shows very pronounced increase in light transmission at low shear rates, but no progression with shear. The nucleated amphibia erythrocytes are oriented but not deformed in flow. Rigidified cells which neither aggregate nor become oriented in flow show no flow dependent changes in light transmission. It became evident that in all blood samples minimum light transmission was recorded when the cells were dispersed and randomly oriented; both aggregation and orientation produced increased light transmission. These results explain earlier controversies in the literature, they shed doubt on the existence of a tubular pinch effect in whole blood rheology.Supported by grants from the Deutsche Forschungsgemeinschaft     

Do different ischemic brain lesions have different hemorheological profiles?

Summary The following hemorheological parameters were determined in 68 patients with ischemic brain lesions and in 28 controls: yield shear stress, erythrocyte aggregation, erythrocyte rigidity, plasma viscosity, and hematocrit. The patients were classified into various groups on the basis of etiological criteria. The results revealed differences between certain hemorheological variables (erythrocyte aggregation, plasma viscosity) in some of the stroke groups. Plasma viscosity was significantly higher in patients with Binswanger's disease and significantly lower in the control group compared with values measured in patients with macroangiopathy and microangiopathy. Erythrocyte aggregation was significantly lower in the controls than in the other groups. Discriminant analysis revealed that plasma viscosity, erythrocyte aggregation and hematocrit were the most useful variables for classification.Abbreviations BMDP Biomedical Computer Programs — Series P Dedicated to Professor Dr. K. Poeck on the occasion of his 60th birthday     

Blood Flow and Leukocyte Adhesiveness Are Reduced in the Microcirculation of a Peritoneal Disseminated Colon Carcinoma

Dynamic behavior of leukocytes in the microcirculation of solid tumor tissue was visualized using a fluorescent labeling technique combined with the use of a real-time confocal laser-scanning microscope (CLSM) system. Colon tumor cells (RCN-9) were inoculated into the peritoneal cavity of male Fischer 344 rats. Tumor-free rats were similarly injected with physiological saline (intraperitoneally). Ten days after tumor inoculation, the mesentery was exteriorized and subjected to vital microscopic observation under the CLSM system. Leukocytes were labeled with rhodamine 6G (100 g kg^–1, intravenously), and their behavior within the microvessels (10–30 m in diameter) was analyzed both in the solid tumor tissues and the normal mesentery. Wall shear rate was calculated from the measured values of vessel diameter and erythrocyte flow velocity. In tumor microvasculature of tumor-bearing rats, the centerline erythrocyte velocity (0.73 ± 0.58 mm s^–1, mean±standard deviation) and wall shear rate (210 ± 151 s^–1 were significantly lower than those of the tumor-free rats (1.27 ± 0.83 mm s^–, 344 ± 236 s^–1, respectively). Despite such reduced flow conditions, flux of the rolling leukocytes as well as density of the adhered leukocytes both decreased significantly in tumor microvasculature as compared with normal controls. The methods developed in this work show promise in improving our understanding of tumor biology and pathophysiology. © 1998 Biomedical Engineering Society. PAC98: 8722Fy, 8745Hw, 8745Ft, 8764-t, 4262Be     

Neuronal coding of linear motion in the vestibular nuclei of the alert cat

Summary The aim of the present study was to investigate some aspects of the central processing of otolith information during linear motion. For this purpose, the response characteristics of 69 vestibular nuclei units to sinusoidal otolith stimulation in the vertical Z axis were analysed in the alert cat. Among this population of neurons which responded to a 0.05 Hz, 290 mm translation, 47 units (70%) displayed a firing rate modulation which followed the input frequency (H1 units). The majority of these neurons exhibited an increase in discharge rate during upward displacement, with a response phase close to the motion velocity or slightly leading downward acceleration. The acceleration related units were divided into two groups according to whether they showed clear increases or only a slight change in discharge rate when the stimulus frequency was increased. The former group was characterized by an average –16.3 dB drop in gain (from 43.9±1.8 dB, S.D. to 27.6±7 dB, S.D.) within the 0.05 Hz–0.5 Hz frequency range, while the latter group displayed an average –31.2 dB gain attenuation (from 45.1±1.1 dB, S.D. to 13.9±0 dB) within the same decade. In contrast to differences in response gain, all the units tested exhibited a relatively stable phase lead of about 20° with respect to downward peak acceleration. Conversely, units whose response was close to motion velocity in the lower frequency range (0.05 Hz–0.10 Hz) displayed a strong phase lead of about 100° when the stimulus frequency was increased (up to 0.50 Hz). These neurons were thus characterized by an acceleration related response in the higher frequency range. At the same time, an average –24.8 dB gain attenuation (from 47.7±3.4 dB to 22.9±3.7 dB) was found in the 0.05 Hz–0.5 Hz decade. The remaining 22 neurons (30%) were called H2 units since they displayed a response waveform double that of the input frequency, a response already described during sinusoidal rotation. Unit discharge reached a peak approximately in phase with maximum upward and downward velocity. Asymmetrical change in unit firing rate about the resting discharge level and different dynamic behavior of the upward and downward response components were usually found. These response characteristics suggest that the H2 patterns are centrally constructed and could result from convergence of otolith afferents having opposite polarization vectors. Other evidence suggests that these units which behave like motion-detectors can exert an influence on the neck musculature. Our results corroborate, at least in part, the findings of previous studies on the dynamic responses properties of otolith-dependent central neurons during roll tilt, or pure linear acceleration in the horizontal plane.This research was supported by U.A.-C.N.R.S. 372, INSERM (PRC no 133019) and Ministère de la Recherche et de la Technologie (84.C.1311)     

Influence of Agonist, Shear Rate, and Perfusion Time on Nitric Oxide Inhibition of Platelet Deposition

Nitric oxide (NO) is a physiological species involved in inhibition of platelet adhesion and aggregation. A novel NO delivery device was utilized to quantitatively assess the effects of gaseous NO on platelet deposition to agonist-coated biomaterials in the presence of a platelet suspension. Platelet deposition was evaluated as a function of agonist (collagen, fibrinogen, or IgG), shear rate (250, 500, and 750 s^–1), and perfusion time (5, 7.5, and 15 min). The minimal aqueous surface NO concentrations and fluxes necessary for significant inhibition of platelet deposition were quantified. Platelet deposition was completely inhibited at a gaseous NO exposure of 0.1 ppm, irrespective of the platelet agonist, shear rate, and perfusion time. The corresponding aqueous surface NO concentration was 0.09 nM at 250 s^–1 as predicted by a validated model. Surface fluxes ranged between 0.3 and 0.6 femtomoles cm^–2 s^–1. The results of this study are useful for establishing generalized guidelines (i.e., NO flux requirements in the presence of agonists, shear rate, and perfusion time) for the design and development of suitable biomaterials incorporating NO to reduce platelet deposition. Further studies incorporating blood, rather than platelet suspensions, are required to provide a more complete assessment of the required NO flux necessary to inhibit platelet deposition. © 2000 Biomedical Engineering Society. PAC00: 8717-d, 8719Tt     

激光照射治疗对脑性瘫痪患儿临床微循环影响的研究

目的研究低强度半导体激光鼻黏膜照射对脑瘫患儿临床微循环的影响。方法选取50例脑瘫患儿予激光鼻腔照射治疗,观察照射后红细胞聚集及甲襞微循环变化情况。结果激光照射治疗组红细胞聚集改善率为60.47%,远高于对照组的26.83%(P<0.01)。且经激光照射治疗后,脑瘫患儿甲襞微循环有明显改善(P<0.01)。结论低强度激光血液照射疗法可以改善脑瘫患儿红细胞聚集异常,改善脑瘫患儿微循环障碍。     

Computerized analysis of erythrocyte aggregation from sequential video-microscopic images under gravitational sedimentation

The erythrocytes form chain-like aggregates during sedimentation under gravitational field. The dynamic images of these are obtained by video-microscopic system by placing the erythrocyte suspension in plasma at hematocrit 5%, in a glass chamber of thickness 100 μm. The images at intervals of 2 min for 30 s duration are recorded. As the images are associated with high background noise, after digitization they are preprocessed for illumination correction, video de-interlacing, background subtraction, and deblurring, followed by post-processing involving edge enhancement, thresholding, median filtering and edge detection. By processing these images, to quantify the aggregation process, the morphometric parameters—projected aggregate area (PAA), projected aggregate perimeter (PAP) and form factor (FF), and sedimentation completion time (SCT) are obtained. To determine the variability of erythrocyte aggregation during human aging by this technique, blood samples from subjects of various age groups (from 20 to 60 years) are analyzed. The data obtained show the variability in the formation of aggregates in different age groups. The comparison in subjects of different age groups shows that the PAA, PAP and FF, and SCT are decreased significantly compared to that of subjects of age group 20–30 years. In subjects of 51–60 years, the formed aggregates are compact, which sediment faster compared to that of other age groups.     

Diffusion ultrasonore par des suspensions concentrées d'agrégats fractals de globules rouges dans un écoulement de cisaillement

La diffusion ultrasonore en régime de Rayleigh est utilisée pour étudier la dynamique des agrégats fractals et réversibles de globules rouges en suspension concentrée. En considérant une floculation homogène d'objets fractals et sur la base du modèle hybride de diffusion ultrasonore pour des diffuseurs corrélés, en régime de Rayleigh, le concept de variance de la concentration locale en particules est utilisé pour obtenir une expression au premier ordre de la section efficace de rétrodiffusion ultrasonore. À partir de lois d'échelle relatives à la désagrégation réversible d'agrégats en suspension concentrée, une étude rhéo-acoustique en régime de diffusion isotrope est proposée pour décrire la dépendance du coefficient de diffusion (section efficace de diffusion par unité de volume de suspension) avec la contrainte de cisaillement. Le concept de diffusion fractale qui rend compte de l'anisotropie des centres diffuseurs de taille plus importante que la longueur d'onde de l'onde ultrasonore est également présenté. Dans une seconde partie, les mesures rhéo-acoustiques obtenues dans une géométrie de type plan–plan par des suspensions de globules rouges déformables ou durcis, agrégés en présence d'une solution de dextrane, sont présentées et analysées dans le cadre des approximations de self-consistance utilisées dans les modèles rhéologiques. Les capacités de la technique ultrasonore à estimer la contrainte critique de désagrégation et quantifier l'énergie de surface des particules sont finalement discutées.Shear flow dynamics of reversible fractal clusters in dense suspensions were investigated by ultrasound scattering to study shear disruption processes of Rayleigh aggregates and further examine the effective mean field approximation used in the microrheological models. Within the framework of a fractal flocculation process, the concept of variance in local particle volume fraction is used to derive an original expression of the ultrasonic backscattering cross-section for a dense distribution of correlated Rayleigh fractal clusters. Considering the scaling laws for shear break-up of reversible aggregates in concentrated suspensions, a rheo-acoustical model in the Rayleigh scattering regime is proposed to describe the shear stress dependence of the low frequency backscattering coefficient with physical parameters. The anisotropic scattering effects from flocs of size larger than ultrasound wavelength are further discussed. In a second part, we report flow dependent changes of the ultrasonic backscattering coefficient in a plane–plane flow geometry to analyze shear break-up processes of hardened or deformable red cell aggregates in dextran solutions. Rheo-acoustical experiments were examined on the basis of the rheo-acoustial model and the effective medium approximation. The ability of ultrasound scattering to determine the critical shear stress and to give quantitative information on particle surface adhesive energy is analyzed.     

Bestimmung der Referenzbereiche rheologischer Parameter: Studie an 653 zufällig ausgewählten Probanden im Kreis Aachen

Summary To determine reference ranges for rheologic parameters (hematocrit, plasma viscosity, erythrocyte aggregation, erythrocyte rigidity) a randomized study involving 653 subjects was carried out. Conditions of sampling, transportation and storing of blood specimens were established prior to the survey. Only 283 subjects met the criteria for enrollment in the study; the others were rejected because of inconspicuous history, normal findings in physical and Doppler-sonographic examination and absence of the risk factors hypertension, diabetes mellitus, overweight, rheumatic diseases, and smoking.The reference range for hematocrit was determined by an impedance-measuring device to equal 39–52% for males and 34–50% for females. The reference range for plasma viscosity, measured by a capillary-tube-plasma viscometer, was found to vary from 1.14 mPas to 1.34 mPas. The reference values for the standardized erythrocyte aggregation index was determined with the mini erythrocyte aggregometer to range from 8 to 21. Erythrocytes measured with the selecting-erythrocyte rigidometer showed a rigidity reference range between 0.83 and 1.19. Analysis of the results revealed that the parameters were independent of age (except in young children) and sex (with the exception of hematocrit).

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Abkürzungsverzeichnis EAS Erythrozytenaggregationsindex - G anscheinend Gesunde ohne Risikofaktoren - Hkt Hämatokrit - M männliche Probanden - PV Plasmaviskosität - SER Erythrozytenrigiditätsindex - W weibliche Probanden - I G unter 30 Jahren - II G zwischen 30 und 50 Jahren - III G älter als 50 Jahre     

Multilayer imaging and compositional analysis of human male breast by laser reflectometry and Monte Carlo simulation

The laser backscattering from biological tissues depends on their composition and blood flow. The onset of abnormalities in tissues is associated with the change in composition at a specific location which may affect laser backscattering. The objective of this work is to study the point-to-point compositional variation of male breast tissues as this site has been prone to cancer development. The normalized backscattered intensity (NBI) profiles at various locations of human chest region of five subjects by multi-probe laser reflectometer are obtained. Based on these data the images of tissue composition, showing the point-to-point changes at various depths from the tissue surface, are reconstructed. The analysis of data shows that the maximum NBI variation is at the pectoralis major muscle and minimum variation is observed at the sternum. The optical parameters, based on the NBI data obtained for five human subjects, show the maximum increase in absorption (p < 0.0001) and minimum change in scattering (p < 0.0001) coefficients compared to that as observed at the sternum. Also the minimum absorption and maximum scattering coefficients are observed at the pectoralis major muscles. The regional variations of NBI and optical parameters further support these findings. The variations in the NBI and optical parameters may indicate the compositional change in tissues, which could be used for diagnostic and therapeutic applications of laser.     

Towards an ideal blood analogue for Doppler ultrasound phantoms.

If a phantom is to produce Doppler spectral waveforms accurately matching those that would be obtained in vivo, it is necessary to use a fluid that behaves like blood in vivo, both acoustically and rheologically. The use of blood itself is undesirable and an analogue is required. Blood exhibits non-Newtonian behaviour as a result of aggregation of erythrocytes at low shear rates. This behaviour affects flow not only in sub-millimetre diameter vessels, but also in large scale structures. An alternative to blood is described that uses finely powdered nylon suspended in a mixture of glycerol and water. The nylon particles used have dimensions and density close to those of erythrocytes and they aggregate at low shear rates to give non-Newtonian behaviour. Viscosity may be varied over a wide range by the addition of liquid detergent. Consideration is given to the importance of haematocrit in modelling pulsatile and disturbed flows as it affects the haemodynamics of flow and the backscattered power of an ultrasound beam. This adaptable blood analogue is suitable for use in models of both large structures and fine vessels.     

Effect of low-intensity laser radiation of the red spectrum on some properties of erythrocytes in Wistar rats

Laser radiation of different power had various effects on the properties of erythrocytes. An increase in the radiation power from 2.2 to 25 mW/cm² was accompanied by a decrease in the erythrocyte sedimentation rate and an increase in erythrocyte filtration index. Radiation of 50 mW/cm² induced abnormal erythrocyte aggregation. Increasing the time of irradiation at power intensity of 2.2 mW/cm² did not potentiate its effect on the blood. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 1, pp. 12–14, January, 2008     

Effect of heat stress on muscle blood flow during dynamic handgrip exercise

Summary During exercise in a hot environment, blood flow in the exercising muscles may be reduced in favour of the cutaneous circulation. The aim of our study was to examine whether an acute heat exposure (65–70°C) in sauna conditions reduces the blood flow in forearm muscles during handgrip exercise in comparison to tests at thermoneutrality (25° C). Nine healthy men performed dynamic handgrip exercise of the right hand by rhythmically squeezing a water-filled rubber tube at 13% (light), and at 34% (moderate) of maximal voluntary contraction. The left arm served as a control. The muscle blood flow was estimated as the difference in plethysmographic blood flow between the exercising and the control forearm. Skin blood flow was estimated by laser Doppler flowmetry in both forearms. Oesophageal temperature averaged 36.92 (SEM 0.08) ° C at thermo-neutrality, and 37.74 (SEM 0.07) ° C (P<0.01) at the end of the heat stress. The corresponding values for heart rate were 58 (SEM 2) and 99 (SEM 5) beats -min^–1 (P<0.01), respectively. At 25° C, handgrip exercise increased blood flow in the exercising forearm above the control forarm by 6.0 (SEM 0.8) ml · 100 ml^–1 · min^–1 during light exercise, and by 17.9 (SEM 2.5) ml · 100 ml^–1 · min^–1 during moderate exercise. In the heat, the increases were significantly higher: 12.5 (SEM 2:2) ml · 100 ml^–1 · min^–1 at the light exercise level (P<0.01), and 32.2 (SEM 5.9) ml · 100 ml^–1·min^–1 (P<0.05) at the moderate exercise level. Skin blood flow was not significantly different in any of the test conditions between the two forearms. These results suggested that hyperthermia of the observed magnitude did not reduce blood flow in active muscles during light or moderate levels of dynamic handgrip exercise.     

Normal indices of the peripheral blood and bone marrow for the monkey macacus rhesus

Summary A study was made of the indices of peripheral blood (45) and of bone marrow (14) in healthy monkeys (Macacus rhesus) in Moscow. The total erythrocyte count in the monkeys observed was 5.5±0.9 million, thrombocyte count –373.66±47 thousand, reticulocyte count 7.78±0.62, leukocyte count –10.95±0.50 thousand, erythrocyte sedimentation rate –4±0.35 mm/h. The total number of the nuclei-containing forms in the bone marrow puncture material averaged 101 thousand. 30.87% of total number of cells were erythroblastoid elements, 58.9% being myeloid and 8.6% lymphoid cells.(Presented by Active Member AMN SSSR P. D. Gorizontov) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 54, No. 11, pp. 106–108, November, 1962     

高脂血症患者血液流变学、血小板聚集的探讨

本文对420例高脂血症患者进行血液流变学和血小板聚集功能的测定。结果表明,老年前期和老年期的高脂血症患者,全血粘度、血浆粘度、红细胞压积、血沉、血沉方程K值、红细胞电泳、纤维蛋白原、血小板最大聚集率和5分钟解聚率与血脂正常者比较,除红细胞压积差异显著(P<0.05)外,其余差异均为极显著(P<0.01);青中年高脂血症患者与血脂正常者比较,低切变全血粘度、红细胞电泳、血小板最大聚集率差异显著(P<0.01)。说明高脂血症造成血液高粘、高凝、高聚状态,尤其是高血脂老年,血液流变学、血小板聚集的指标改变更为严重。     

Effect of hemodynamic forces on platelet aggregation geometry

The shear rate dependence of platelet aggregation geometries is investigated using a combination of in vitro and numerical experiments. Changes in upstream shear rate, γ_Pw, are found to cause systematic changes in mature platelet aggregation geometries. However, γ_Pw is not the only factor determining the shear rate experienced by a platelet moving over, and adhering to, a platelet aggregation: flow simulations demonstrate that naturally occurring variations in platelet aggregation geometry cause the local shear rate on the surface of a mature platelet aggregation to vary between zero and up to eight times γ_Pw. Additionally, as a platelet aggregation grows, systematic changes in geometry are found, indicating that the local shear field over a growing platelet aggregation will differ from that over mature platelet aggregations.