Rheological properties of blood in patients with ischemic stroke in selected clinical groups]

Hemorheological parameters have been analysed in 34 patients with the acute ischemic stroke. The patients have been divided into two clinical subgroups: with accompanying arterial hypertension (group HA), and free of other diseases (group NHA). Comparative studies have not revealed the significant differences between both groups. However, blood viscosity has been significantly higher in the hypertensive patients. It was related to the decrease in the erythrocyte ability to elastic deformation Group NHA has been characterized by the high fibrinogen levels and by the decrease of the cerebral blood flow.     

Rheological properties of the blood influencing selectin-mediated adhesion of flowing leukocytes

We studied how the rheological properties of blood influenced capture and rolling adhesion of leukocytes as well as their margination in the bloodstream. When citrated, fluorescently labeled blood was perfused through glass capillaries coated with P-selectin, leukocytes formed numerous rolling attachments. The number of attached leukocytes increased as the hematocrit was increased between 10% and 30% and was essentially constant from 30% to 50%. In EDTA-treated blood, adhesion was absent, and the flux of marginated cells varied little with increasing hematocrit. However, the velocity of marginated leukocytes increased monotonically, whereas the volumetric flow rate was constant, implying that the flow velocity profile became blunted and wall shear rate increased. Thus increasing hematocrit promoted attachment for a given total flow rate, without increasing margination, even though wall shear rate and blood viscosity increased. Blood was diluted to 20% hematocrit with plasma, 40-kDa dextran (to reduce red blood cell aggregation), or 500-kDa dextran (to enhance aggregation). Increasing aggregation correlated with increasing leukocyte adhesion and with more slow-flowing leukocytes near the wall. Thus flowing erythrocytes promote leukocyte adhesion, either by causing margination of leukocytes or by initiating and stabilizing attachments that follow.     

Rheological and flow properties of blood investigated by ultrasound

Ultrasonic waves of 1-15 MHz frequencies easily propagate through soft biological tissues, thus providing qualitative and quantitative information on mechanical and flow properties of blood and red blood cell (RBC) suspensions. Two types of techniques allow to investigate blood behaviors: echographic devices via amplitude detection and Doppler effect based devices via frequency detection of the ultrasonic signal. When ever B mode serves to construct images of tissue slabs from the ultrasonic backscattering coefficient and can give qualitative information on the mechanical properties of blood, A-mode allows to quantify the ultrasonic backscattering coefficient. Ultrasonic Doppler modes also provide both qualitative and quantitative information on blood flow velocity: continuous and pulsed Doppler modes provide curves of blood flow versus time when color Doppler and power Doppler imaging visualize blood flowing in human vessels. Association of echographic and Doppler modes to investigate simultaneously structure and velocity of blood is commercially available. Some examples of results given by such ultrasonic techniques that contribute to characterize, both in vitro and in vivo, structure and flow properties of blood or red blood cell (RBC) suspensions are presented.     

Rheological properties of the blood and erythrocyte suspension after exposure to zootoxins

The rheological properties of blood (viscosity, suspension stability and deformation of red blood cells) have been studied under the influence of zootoxins. It has been shown that the toxins Apis mellifera, Mesobuthus eupeus, Agkistrodon blomhoffii in vitro exert essential effect on haemorheological indexes.     

Rheological properties of synovial fluids

Synovial fluid is the joint lubricant and shock absorber [Semin. Arthritis Rheum. 32 (2002), 10-37] as well as the source of nutrition for articular cartilage. The purpose of the present paper is to provide a comprehensive review of the rheological properties of synovial fluid as they relate to its chemical composition. Given its importance in the rheology of synovial fluid, an overview of the structure and rheology of HA (hyaluronic acid) is presented first. The rheology of synovial fluids is discussed in detail, with a focus on the possible diagnosis of joint pathology based on the observed differences in rheological parameters and trends. The deterioration of viscoelastic properties of synovial fluid in pathological states due to effects of HA concentration and molecular weight is further described. Recent findings pertaining to the composition and rheology of periprosthetic fluid, the fluid that bathes prosthetic joints in vivo are reported.     

Rheological properties of cashew gum

Solubilities and rheological properties of dissolved fractions of cashew gum from Anacardium occidentale were investigated. A fraction of gum (64.2%) dissolved in water at 30 °C. A further 13.4% dissolved when the remaining suspension was heated. The fraction that dissolved at 30 °C produced greater solution viscosity than the other fraction or the whole gum. When the pH was raised above 5.5, the solution viscosity dropped sharply.     

Change in the rheologic properties of blood during the early postreanimation period]

Experiments were conducted on nembutal-anesthetized cats; a study was made of the dynamic viscosity of the blood, and also of an aggregation capacity of the blood formed elements for two hours of the postresuscitative period. There was established an increase in the viscosity both in the zone of a low (1.82 dynes/cm2) and high (10.94 dynes/cm2) sear stress. A definite role in increase of the blood viscosity is played by a rise in the hematocrite index and by enhanced aggregation capacity of the blood formed elements.     

Rheological properties of the human lumbar spine ligaments

The purpose of this study is to provide a better understanding of the rheological properties of the lumbar spinal ligaments under subfailure physiological loads. Non-destructive tests including an hysteresis experiment, stress-relaxation and stepwise load-relaxation tests were used to investigate the time-dependent properties of the interspinous-supraspinous ligament complex. Using a reduced relaxation function, the viscoelastic behaviour over the experimental time-scale was described by a linear function of the logarithm of time. Internal damping of ligament substance dissipates about 36% of the mechanical energy applied during physiological loading. Local elastic stiffness is found to be two to four times global stiffness of the bone-ligament-bone complex. These physical parameters (stiffness, energy dissipation, hysteresis, relaxation, etc) can be used to improve computer models of the lumbar spinal column.     

Rheological properties of dairy cattle manure

Rheological properties are important for the design and modelling of handling and treating fluids. In the present study, the viscosity of liquid manure (about 10% total solids) was measured at different shear rates (2.38-238 s(-1)). The effect of temperature on the viscosity at different shear rates was also studied. The results showed that manure has non-Newtonian flow properties, because the viscosity strongly depended on the applied shear rate. The results showed also that manure behaves like real plastic materials. The power-law model of the shear stress and the rate of shear showed that the magnitude of the consistency coefficient decreased while increasing the temperature, with high values of the determination coefficient. Moreover, the results showed that the Arrhenius-type model fitted the temperature effect on manure viscosity very well (R2 at least 0.95) with calculated activation energy of 17.0+/-0.3 kJ mol(-1).