Blood Viscosity

Cerebral vasospasm after aneurysmal subarachnoid hemorrhage is a potentially severe sequel. The induction of hypertension, hypervolemia, and hemodilution is advocated for vasospasm, but it is unclear whether hemodilution confers any benefit. A finite element model of oxygen transport in the proximal middle cerebral artery (MCA) was used to evaluate the complex relationship among hematocrit, viscosity, oxygen content, and blood flow in the setting of vasospasm. A single-phase non-Newtonian finite element model based on three-dimensional incompressible Navier–Stokes equations was constructed of the M1 segment. The model was solved at vessel stenoses ranging from 0% to 90% and hematocrit from 0.2 to 0.6. A small area of poststenotic recirculation was seen with mild (30%) stenosis. Poststenotic eddy formation was noted with more severe (60% to 90%) stenosis. Volumetric flow was inversely related to hematocrit at mild stenosis (0% to 30%). With near-complete stenosis (90%), a paradoxical increase in flow was seen with increasing hematocrit. Oxygen transport across the segment was related to hematocrit at all levels of stenosis with increasing oxygen transport despite a reduction in blood flow, suggesting that with clinically significant vasospasm in the MCA, hemodilution does not improve oxygen transport, but to the contrary, that ischemia may be worsened.

In transport phenomena, precise knowledge or estimation of fluids properties is necessary, for mass flow and heat transfer computations. Viscosity is one of the important properties which are affected by pressure and temperature. In the present work, based on statistical techniques for nonlinear regression analysis and correlation tests, we propose a novel equation modeling the relationship between the two parameters of viscosity Arrhenius-type equation, such as the energy (í µí°¸í µí±Ž) and the preexponential factor (í µí°´í µí±). Then, we introduce a third parameter, the Arrhenius temperature (í µí±‡ í µí°´), to enrich the model and the discussion. Empirical validations using 75 data sets of viscosity of pure solvents studied at different temperature ranges are provided from previous works in the literature and give excellent statistical correlations, thus allowing us to rewrite the Arrhenius equation using a single parameter instead of two. In addition, the suggested model is very beneficial for engineering data since it would permit estimating the missing parameter value, if a well-established estimate of the other parameter is readily available.

In arterial blood flow, the wall shear stress expresses the force per unit area exerted by the wall on the fluid in a direction on the local tangent plane. There is substantial evidence that the wall shear stress induced by the pulsatile blood flow in the arterial system affects the atherogenic process. It is now widely accepted that the vessel segments that appear to be at the highest risk for development of atherosclerosis are those with low wall shear stress or oscillating wall shear stress. The purpose of this article is to define wall shear stress, to introduce relevant concepts of fluid mechanics to nonexperts, and to critically review the various methods that have been used for the assessment of wall shear stress in animal and human blood circulation, paying special attention to the case of coronary arteries.

The association between testosterone-replacement therapy and cardiovascular risk remains unclear with most reports suggesting a neutral or possibly beneficial effect of the hormone in men and women. However, several cardiovascular complications including hypertension, cardiomyopathy, stroke, pulmonary embolism, fatal and nonfatal arrhythmias, and myocardial infarction have been reported with supraphysiologic doses of anabolic steroids. We report a case of an acute ST-segment elevation myocardial infarction in a patient with traditional cardiac risk factors using supraphysiologic doses of supplemental, intramuscular testosterone. In addition, this patient also had polycythemia, likely secondary to high-dose testosterone. The patient underwent successful percutaneous intervention of the right coronary artery. Phlebotomy was used to treat the polycythemia acutely. We suggest that the chronic and recent "stacked" use of intramuscular testosterone as well as the resultant polyc...

Spine surgery may be associated with profuse intraoperative bleeding that often requires blood transfusions. In recent years several techniques have been developed to avoid allogenic transfusions and their potential complications to surgical patients. In this study we review and analyse the role of preoperative recombinant human erythropoietin (rHuEPO) administration in spine surgery as a blood conservation strategy. Between 1998 and 2002, a total of 250 patients scheduled for spine surgery were included in our blood-sparing program: 114 patients (group 1), operated on before rHuEPO approval (2000), underwent preoperative autologous blood donation (ABD) alone, and 136 patients operated on after rHuEPO approval (groups 2 and 3) received rHuEPO while undergoing ABD. Adding rHuEPO to ABD resulted in higher haemoglobin and haematocrit values the day of surgery, more ABD units retrieved per patient and, consequently, reduced allogenic transfusion requirements. The effectiveness of rHuEPO as the only preoperative blood conservation technique was evaluated in ten patients with a predicted blood loss of less than 30% of their total volume, scheduled for lumbar surgery. Data from these patients were matched with those from a similar group of patients who had undergone ABD. Patients receiving rHuEPO alone had higher haemoglobin levels the day of surgery than did patients in the ABD program. Neither group required allogenic transfusions. Conclusions: preoperative rHuEPO is useful for reducing allogenic blood requirements in elective spine surgery. In patients with an expected blood loss of around 50% of blood volume, rHuEPO improves ABD, minimising preoperative anaemia and increasing the number of ABD units collected. In patients with expected blood loss below 30% of total volume, rHuEPO administration may replace ABD.

Background: Mechanisms that mediate cocaine- induced cardiovascular events following vasoconstric- tion are incompletely understood. Objective: To examine the effects of cocaine in mod- erate doses on hematologic and hemostatic parameters that influence blood viscosity and thrombotic potential. Methods: Changes in hemoglobin concentration, he- matocrit, and red blood cell counts were measured in hu- man subjects who met Diagnostic and Statistical

The present study in female rats determined the effects of experimental hyperthyroidsm on hemorheological parameters and fibrinogen concentration. To induce experimental hyperthyroidism L-thyroxine (0.4 mg/100 g fodder) was added to the fodder of the experimental group rats for 20 d. After experimental duration, T3, T4, and TSH levels, plasma and blood viscosity, hematocrit, erythrocyte rigidity index, and plasma fibrinogen concentration values of both the control and the experimental group animals were determined and evaluated. In the experimental group, T3 and T4 levels were higher and TSH levels lower than that of the control rats (respectively, p < 0.01, p < 0.001, p < 0.001). Plasma viscosity and fibrinogen concentration of hyperthyroid group were found significantly higher than controls (p < 0.01). However there was no significant difference found in blood viscosity, hematocrit, and erythrocyte rigidity index between control and experimental groups. Thus, hyperthyr...

In arterial blood flow, the wall shear stress expresses the force per unit area exerted by the wall on the fluid in a direction on the local tangent plane. There is substantial evidence that the wall shear stress induced by the pulsatile blood flow in the arterial system affects the atherogenic process. It is now widely accepted that the vessel segments that appear to be at the highest risk for development of atherosclerosis are those with low wall shear stress or oscillating wall shear stress. The purpose of this article is to define wall shear stress, to introduce relevant concepts of fluid mechanics to nonexperts, and to critically review the various methods that have been used for the assessment of wall shear stress in animal and human blood circulation, paying special attention to the case of coronary arteries.

Much evidence suggests that blood viscosity (BV) is involved in some pathological processes, such as myocardial ischemia, strokes, and cognitive deficits. In addition, there are data pointing to the higher BV in individuals with sleep apnea, hyperlipidemia and hyperproteinemia, with arterial hypertension, and in dehydrated individuals. 1 Some of the known risk factors that alter BV in pathophysiological processes are diabetes, smoking, aging, and obesity. 2 Blood viscosity is a general measure of intrinsic resistance to blood flow and is determined mainly by hematocrit, plasma viscosity, and the deformation and the aggregation of erythrocytes. Moreover, BV varies with shear rate such as non-Newtonian fluid. Therefore, it is an important property for the regulation of blood rheological conditions (for producing resistance to fluid deformations) to determine blood flow and to determine tissue perfusion. 1,3 Because it is an intrinsic property of blood flow and tissue perfusion, changes in BV and its rheological parameters can promote micro-and macrovascular damage and, as a consequence, major cardiovascular events. 2 The blood represents about 7% of an individual's body weight and consists of plasma (a liquid part of the blood that contains various substances), red blood cells (RBCs), leukocytes (white blood cells), and platelets (cell fragments). Its essential function is the transport of substances, such as hydrogen, oxygen, electrolytes, and nutritional substances, in addition to products of cellular metabolism. RBCs pass through capillaries in the circulatory system and are exposed to various shear stresses in the blood flow. One of the unique features is the ability to change shape in response to external forces. This important phenomenon defines its mechanical behavior and function, since it is known that the reduced deformability

The study provides information on the blood fluidity in healthy, juvenile sheep and rabbits during growth (n = 18), and shows also data from fetal rabbits and cats. In the fetal rabbit (n = 3) and cat (n = 2), whole blood viscosity (WBV; LS30, Contraves, Switzerland) and plasma viscosity (PV; OCR-D, Paar, Austria) was low (WBV (0.7 s(-1)): rabbit: 3.28/3.00/2.44; cat: 7.87/10.88; WBV (94 s(-1)): rabbit: 2.57/2.48/2.39; cat: 2.75/3.73 mPa s) (PV: rabbit: 1.10/1.10/1.05; cat: 1.27/1.39 mPa s), which was associated with a low plasma protein concentration and a low erythrocyte count despite a high erythrocyte volume. After parturition, blood viscosity increased in rabbits in parallel with hematocrit, while MCV decreased (WBV (0.7 s(-1)): 9.28 (8.07/10.88); WBV (94 s(-1)): 3.67 (3.62/3.82); PV: 1.15 (1.15/1.25) mPa s). In contrast, in the sheep, whole blood and plasma viscosity decreased after delivery (WBV (0.7 s(-1)): 1.31 (0.94/1.88); WBV (94 s(-1)): 2.45 (2.43/2.85) PV: 1.24 (1.23/1....

The aim of this study was to evaluate together the main hemorheologic parameters and one of the transmembrane ion transport systems in erythrocytes of subjects with normal and elevated blood pressure. Three sex-, age-, and weight-matched groups consisting of 15 normotensive subjects (NT) with no parental hypertension, 15 patients with essential hypertension (EH) at stage 1-II WHO, and eight patients with secondary hypertension (Sec.H), respectively, were studied. Red blood cell Na+-Li+ countertransport (CTT), blood viscosity (eta B) at shear rates of 230 X S-1, 115 X S-1, and 46 S-1 and plasma viscosity (eta P) at shear rate of 46 X S-1 were measured. Plasma proteins and fibrinogen were also evaluated. CTT was higher in EH than in NT (P less than 0.01), while no significant difference was found between NT and Sec. H patients. eta B at 115 X S-1 and 46 X S-1 was higher in EH, but not in Sec. H, than in NT patients (P less than 0.05). No difference in eta P, plasma proteins and fibrin...

The apparent viscosity of blood in glass tubes declines with decreasing diameter (Fåhraeus-Lindqvist effect) and exhibits a distinctive minimum at 6–7 μm. However, flow resistance in vivo in small vessels is substantially higher than predicted by in vitro viscosity data. The presence of a thick endothelial surface layer (ESL) has been proposed as the primary cause for this discrepancy. Here, a physical model is proposed for microvascular flow resistance as a function of vessel diameter and hematocrit in vivo; it combines in vitro blood viscosity with effects of a diameter-dependent ESL. The model was developed on the basis of flow distributions observed in three microvascular networks in the rat mesentery with 392, 546, and 383 vessel segments, for which vessel diameters, network architecture, flow velocity, and hematocrit were determined by intravital microscopy. A previously described hemodynamic simulation was used to predict the distributions of flow and hematocrit from the assu...