Oguz K. Baskurt

New guidelines for hemorheological laboratory techniques

This document, supported by both the International Society for Clinical Hemorheology and the European Society for Clinical Hemorheology and Microcirculation, proposes new guidelines for hemorheolog ...

Effect of superoxide anions on red blood cell rheologic properties.

The human red blood cell (RBC) is known to be susceptible to oxidant damage, with both structural and functional properties altered consequent to oxidant attack. Such oxidant-related alterations may lead to changes of RBC rheologic behavior (i.e., deformability, aggregability). Two different models of oxidant stress were used in this study to generate superoxide anions either internal or external to the RBC. Our results indicate that generation of superoxide within the RBC by phenazine methosulfate decreases RBC deformability without effects on cell aggregation. Conversely, superoxide generated externally by the xanthine oxidase-hypoxanthine system primarily affects RBC aggregability: the shear rate necessary to disaggregate RBC was markedly increased while the extent of aggregation decreased slightly. Increased disaggregation shear rate (i.e., greater aggregate strength) as a result of superoxide radical damage may adversely affect the dynamics of blood flow in low-shear portions of the circulation, and may also play a role in the no-reflow phenomena encountered after ischemia-reperfusion.

Red blood cell aggregation

Red blood cell aggregation / , Red blood cell aggregation / , کتابخانه دیجیتال جندی شاپور اهواز

Red blood cell aggregation in experimental sepsis

Red blood cell (RBC) aggregation was investigated in a rat model of sepsis with special emphasis on RBC-related factors. Sepsis was produced by cecal ligation/puncture, whereas another group had only laparotomy (sham operation); blood samples also were obtained from control, unoperated-on animals. RBC aggregation was measured in autologous plasma and in 3% dextran 70, 18 hours after the operations, by using a Myrenne Aggregometer system and the zeta sedimentation ratio (ZSR) method. RBC aggregation in autologous plasma was found to be enhanced in both sham-operated and septic animals and was consistent with their increased plasma fibrinogen levels. However, RBC aggregation in dextran was significantly higher than control only in the sepsis group. RBCs from septic animals also aggregated more in septic plasma compared with RBCs from control animals. In the sepsis group, RBC deformability was significantly decreased, whereas RBC lipid peroxidation was significantly increased. Our results thus confirm the known increase of RBC aggregation in septicemia and, in addition, demonstrate marked alterations of intrinsic RBC properties that further enhance red cell aggregation.

Erythrocyte aggregation: Basic aspects and clinical importance

Red blood cell (RBC) aggregate to form two- and three-dimensional structures when suspended in aqueous solutions containing large plasma proteins or polymers; this aggregation is reversible and shear dependent (i.e., dispersed at high shear and reformed at low or stasis). The extent of aggregation is the main determinant of low shear blood viscosity, thus predicting an inverse relationship between aggregation and in vivo blood flow. However, the effects of aggregation on hemodynamic mechanisms (e.g., plasma skimming, Fåhraeus Effect, microvascular hematocrit) may promote rather than impede vascular blood flow. The impact of enhanced RBC aggregation on endothelial function and hemostatic mechanisms adds further complexity, thereby requiring specific attention to the nature, extent and time course of aggregation when considering its overall influence on tissue perfusion. A detailed understanding of aggregation effects is important from a clinical point of view since it may be enhanced during a variety of pathophysiological processes, including infections, circulatory and metabolic disorders, hematological pathologies and several other disease states. Altered RBC aggregation may be an indicator of disease as well as a factor affecting the course of the clinical condition; the prognostic value of RBC aggregation indices has been demonstrated in various diseases. Currently, RBC aggregation is an easily and accurately measurable parameter, and therefore may be expected to have broader clinical usage in the future.

Parameterization of red blood cell elongation index – shear stress curves obtained by ektacytometry

Abstract Measurement of red blood cell (RBC) deformability by ektacytometry yields a set of elongation indexes (EI) measured at various shear stresses (SS) presented as SS-EI curves, or tabulated data. These are useful for detailed analysis, but may not be appropriate when a simple comparison of a global parameter between groups is required. Based on the characteristic shape of SS-EI curves, two approaches have been proposed to calculate the maximal RBC elongation index (EImax) and the shear stress required for one-half of this maximal deformation (SS1/2): (i) linear Lineweaver-Burke (LB) model; (ii) Streekstra-Bronkhorst (SB) model. Both approaches have specific assumptions and thus may be subject to the measurement conditions. Using RBC treated with various concentrations of glutaraldehyde (GA) and data obtained by ektacytometry, the two approaches have been compared for nine different ranges of SS between 0.6–75 Pa. Our results indicate that: (i) the sensitivity of both models can be affected by the SS range and limits employed; (ii) over the entire range of SS-data, a non-linear curve fitting approach to the LB model gave more consistent results than a linear approach; (iii) the LB method is better for detecting SS1/2 differences between RBC treated with 0.001–0.005% glutaraldehyde (GA) and for a 40% mixture of rigid cells but is equally sensitive to SB for 10% rigid cells; and (iv) the LB and SB methods for EImax are equivalent for 0.001% and 0.003% GA and 40% rigid, with the SB better for 0.005% GA and the LB better for 10% rigid.

Immune and hemorheological changes in Chronic Fatigue Syndrome

BackgroundChronic Fatigue Syndrome (CFS) is a multifactorial disorder that affects various physiological systems including immune and neurological systems. The immune system has been substantially examined in CFS with equivocal results, however, little is known about the role of neutrophils and natural killer (NK) phenotypes in the pathomechanism of this disorder. Additionally the role of erythrocyte rheological characteristics in CFS has not been fully expounded. The objective of this present study was to determine deficiencies in lymphocyte function and erythrocyte rheology in CFS patients.MethodsFlow cytometric measurements were performed for neutrophil function, lymphocyte numbers, NK phenotypes (CD56dimCD16+ and CD56brightCD16-) and NK cytotoxic activity. Erythrocyte aggregation, deformability and fibrinogen levels were also assessed.ResultsCFS patients (n = 10) had significant decreases in neutrophil respiratory burst, NK cytotoxic activity and CD56brightCD16- NK phenotypes in comparison to healthy controls (n = 10). However, hemorheological characteristic, aggregation, deformability, fibrinogen, lymphocyte numbers and CD56dimCD16+ NK cells were similar between the two groups.ConclusionThese results indicate immune dysfunction as potential contributors to the mechanism of CFS, as indicated by decreases in neutrophil respiratory burst, NK cell activity and NK phenotypes. Thus, immune cell function and phenotypes may be important diagnostic markers for CFS. The absence of rheological changes may indicate no abnormalities in erythrocytes of CFS patients.

Activated polymorphonuclear leukocytes affect red blood cell aggregability.

Activated leukocytes can affect adjacent cells by generating oxygen free radicals and secreting proteolytic enzymes, and red blood cells (RBC) exposed to such agents should be susceptible to their effects. This study was thus designed to investigate the effects of activated polymorphonuclear leukocytes (PMN) on RBC aggregability (i.e., on intrinsic RBC aggregation characteristics). PMN were isolated from human blood by density separation and suspended in glucose‐enriched buffer with RBC isolated from the same blood sample (RBC/PMN ratio of 150:1). PMN were then activated in this suspension by adding 1 ng/mL tumor necrosis factor α (TNF‐α) and 10–7 M N‐formyl‐methionyl‐leucyl‐phenylalanine (fMLP) or fMLP alone. After incubation for 2 h at 37°, RBC aggregation behavior in autologous plasma was assessed; RBC deformability and partition coefficients were also measured. RBC aggregation was significantly increased after incubation and deformability and partitioning were decreased; these effects were prevented by phenylmethylsulfonyl fluoride (1 mM) or superoxide dismutase (20 μg/mL) plus catalase (40 μg/mL). TNF‐α and fMLP alone had no effect on RBC aggregation if PMN were not present. Activated PMN can thus markedly affect RBC aggregability, apparently via both proteolytic enzymes and oxygen free radicals; enhanced aggregation seen in clinical states associated with PMN activation or observed during in vivo RBC aging may also involve such PMN‐RBC interactions. J. Leukoc. Biol. 63: 89–93; 1998.

Blood rheology and aging

The flow properties of blood play significant roles in tissue perfusion by contributing to hydrodynamic resistance in blood vessels. These properties are influenced by pathophysiological processes, thereby increasing the clinical relevance of blood rheology information. There is well-established clinical evidence for impaired blood fluidity in humans of advanced age, including enhanced plasma and whole blood viscosity, impaired red blood cell (RBC) deformability and enhanced RBC aggregation. Increased plasma fibrinogen concentration is a common finding in many studies owing to the pro-inflammatory condition of aged individuals; this finding of increased fibrinogen concentration explains the higher plasma viscosity and RBC aggregation in elderly subjects. Enhanced oxidant stress in advanced age is also known to contribute to altered blood fluidity, with RBC deformability being an important determinant of blood viscosity. Several studies have shown that physical activity may improve the hemorheological picture in elderly subjects, yet well-designed observational and mechanistic studies are required to determine the specific effects of regular exercise on hemorheological parameters in healthy and older individuals.

In vivo correlates of altered blood rheology

It is has been known for more than 80 years that compared to in vitro determinations, blood behaves as a less viscous fluid under in vivo flow conditions. The experiments of Whittaker and Winton were among the first dealing with the in vivo effects of altered blood rheology, and experimental studies during the second half of 20th century have provided additional evidence for the complexity of in vivo hemodynamics-hemorheology relationships. Careful studies indicate that the impact of a given blood rheology alteration is determined by the properties of the experimental model (e.g., organ or tissue under investigation), experimental approach (e.g., intravital microscopy, whole organ perfusion) and method used to modify blood rheology. In addition, vascular control mechanisms may play a major role in the resulting hemodynamic effects of a hemorheological alteration: (1) a response simply related to metabolic autoregulation in which there is a compensatory vasodilation due to altered in vivo blood flow and organ/tissue hypoxia; (2) modulation of endothelial function (e.g., NO production) via altering wall shear stress, thereby leading to changes of vascular hindrance. The in vivo effects of altered red blood cell (RBC) aggregation have been investigated in various experimental models. A novel technique for modifying RBC aggregability (i.e., intrinsic tendency of RBC to aggregate) by covalent attachment of specific co-polymers has been used in some studies, and has provided data reflecting the specific effects of RBC aggregation without the influence of altered suspending phase properties. These data indicate that both the magnitude of the hemodynamic effect and the direction of the alteration depend on the intensity of RBC aggregation. Using the same novel technique, RBC aggregation has been shown to be an important determinant of endothelial function through its effects on RBC axial distribution and wall shear stress. These somewhat diverse findings can be explained by considering the contribution of various in vivo hemorheological mechanisms that have opposite effects on in vivo flow resistance.