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At least 289 records · Page 16Linked to original sources
PubMed2005

Pentoxifylline attenuates the increase in whole blood viscosity after transfusion.

BACKGROUND: Pentoxifylline improves tissue oxygenation and intestinal blood flow in models of haemorrhagic shock, and it has been used for the treatment of intermittent claudication due to its beneficial effects on haemorheology. We investigated the effects of pentoxifylline on whole blood viscosity during packed red-blood cell transfusion in critically ill adult patients. METHODS: Twenty critically ill patients were randomly assigned to one of two groups (pentoxifylline group: n = 11, placebo group: n = 9) and prospectively studied. Forty-five minutes before and during the packed red-blood cell transfusion (10 ml min(-1)) over a period of 80 min, 1.5 mg kg(-1) . h(-1) pentoxifylline or placebo were administered intravenously. Haematocrit, plasma fibrinogen concentration, total protein concentration, whole blood viscosity (at a shear rate of 10 s(-1), 50 s(-1), and 100 s(-1)) and plasma viscosity were measured. RESULTS: After the packed red-blood cell transfusion, haematocrit levels increased significantly in both groups (pentoxifylline group: from 26.1 +/- 2.8% to 33.0 +/- 3.2; placebo group: from 24.4 +/- 3.3% to 32.6 +/- 2.6%; means +/- standard deviation). Compared to baseline, whole blood viscosity increased in both groups at all shear rates after the transfusion, but the increase was significantly less in the pentoxifylline group (26 +/- 15% vs. 49 +/- 14%, 23 +/- 11% vs. 39 +/- 12%, and 22 +/- 11% vs. 35 +/- 12% for the pentoxifylline vs. placebo groups at shear rates of 10 s(-1), 50 s(-1), and 100 s(-1), respectively). Plasma viscosity, total protein concentration, and fibrinogen concentration remained unchanged and no significant differences among groups were observed. CONCLUSIONS: These results suggest that pentoxifylline is effective in attenuating the increase in whole blood viscosity after a transfusion of packed red-blood cells. Plasma viscosity is not influenced by pentoxifylline.

Adult↗
PubMed2006

Effects of a new perfluorocarbon emulsion on human plasma and whole-blood viscosity in the presence of albumin, hydroxyethyl starch, or modified fluid gelatin: an in vitro rheologic approach.

BACKGROUND: Artificial oxygen carriers such as perfluorocarbon (PFC) emulsions have reached Phase III clinical trials as alternatives to homologous blood, but their rheologic effects have not been characterized. In this study, the rheologic effects of PFC emulsion in the presence of clinically used volume expanders were investigated. STUDY DESIGN AND METHODS: The effects of a new PFC emulsion (small droplet size with narrow size distribution) at two PFC concentrations (4 and 8 g/dL) on plasma and whole-blood viscosity in the presence of human albumin solution (HAS), hydroxyethyl starch (HES), or modified fluid gelatin (MFG) were investigated. Three hematocrit (Hct) levels were investigated: 30, 20, and 13 percent. Plasma, PFC emulsions, and whole-blood viscosity, with a Couette viscometer, and RBC elongation, with an ektacytometer, were measured for shear rates of 0.2 to 128 per second. RESULTS: The two PFC concentrations increased plasma and whole-blood viscosities. Viscosity values similar to physiologic ones (Hct level, 40%) were observed at: 1) Hct level of 13 percent, with 4 or 8 g per dL MFG-PFC; 2) Hct level of 20 percent, with 4 g per dL MFG-PFC; and 3) Hct level of 30 percent, with 4 g per dL HES-PFC and 4 and 8 g per dL HAS-PFC. RBC deformability was unchanged. CONCLUSION: It is concluded that this new PFC emulsion increases plasma and blood viscosity and that among the three studied volume expanders, the interaction with MFG can result in viscosity values above the physiologic one even at low Hct values. The possible consequences of the increased viscosity at low Hct values are discussed.

Albumins↗
PubMed1982

Effect of plasma exchange on blood viscosity and cerebral blood flow.

The effects of plasma exchange using a low viscosity plasma substitute on blood viscosity and cerebral blood flow were investigated in eight subjects with normal cerebral vasculature. Plasma exchange resulted in significant reductions in plasma viscosity, whole blood viscosity, globulin and fibrinogen concentration without affecting packed cell volume. The reduction in whole blood viscosity was more pronounced at low shear rates suggesting an additional effect on red cell aggregation. Despite the fall in viscosity there was no significant change in cerebral blood flow. The results support the metabolic theory of autoregulation. Although changes in blood viscosity appear not to alter the level of cerebral blood flow under these circumstances, plasma exchange could still be of benefit in the management of acute cerebrovascular disease.

Adult↗
PubMed1978

Pus, deoxyribonucleic acid, and sputum viscosity.

On 100 sputum specimens selected from patients suffering from chronic bronchitis, bronchiectasis, asthma, and cystic fibrosis total deoxyribonucleic acid (DNA) content has been related to macroscopic type, to total dry weight yield, and to the apparent viscosity of the secretion at 1350 s-1: since DNA may be present, either as fibres or within cells, in one-third of the specimens the contribution of each form to the apparent viscosity was assessed. The effect on sputum viscosity of the addition of DNA in vitro has also been studied. Whereas between mucoid, mucopurulent, and purulent macroscopic types a significant difference in total DNA and dry weight yield has been found, viscosity was not significantly correlated with purulence. Similarly, the concentration of either cells or fibres correlated significantly with total DNA but not with viscosity. The in vitro addition of DNA to sputum caused a significant increase in its viscosity, and reasons for the differences between the iv vivo and in vitro effect are discussed. Certain constituents of purulent sputum tend to increase viscosity and others to reduce it, and the influence of these varies in the several diseases studied.

Adolescent↗
PubMed1978

Hemodynamic functions and blood viscosity in surface hypothermia.

Hemodynamic functions and blood viscosity changes in hypothermia (core approximately 25 degrees C) were studied in 14 pentobarbital-anesthetized dogs subjected to surface cooling. The viscosity of blood (eta B) increased progressively to 173% of that at 37 degrees C when body temperature was lowered to 25 degrees C. The increase in blood viscosity was caused by: a) the direct effect of low temperature on plasma viscosity, b) hemoconcentration as a result of plasma loss, and c) the low-flow (low-shear) state induced by hypothermia. A larger portion of the increased viscosity was caused by the low-flow state in hypothermia. The systemic flow resistance (SFR) increased to 271% of control, and this was attributable about equally to the increases in blood viscosity and systemic vascular hindrance (SFR/eta B). Similarly, the viscosity of blood contributed significantly to raising the pulmonary flow resistance. The relative constancy of mixed venous O2 saturation suggests that the cardiac output at low body temperature is generally adequate to meet the metabolic needs.

Animals↗
PubMed1987

Blood viscosity in small tubes: effect of shear rate, aggregation, and sedimentation.

Apparent viscosity was determined in vertical glass tubes (ID 30.2-132.3 microns) with suspensions of human red cells in A) serum, B) saline containing 0.5 g/100 ml albumin, C) plasma, and D) plasma containing Dextran 250 at a feed hematocrit of 0.45. Pressure-flow relationships were obtained in a range of pseudo-shear rates (mu) between 0.15 and 250 s-1. Relative viscosities in the nonaggregating suspensions (A and B) were found to increase monotonically with decreasing mu. The Fahraeus-Lindqvist effect was present in the entire range of mu. In the two aggregating suspensions (C and D), viscosities increased initially in larger but not small tubes with declining mu and fell in all tubes at some characteristic mu (usually below 10 s-1). Viscosity reduction was greater in the larger tubes and in suspensions with greater aggregation tendency. With suspension D, the Fahraeus-Lindqvist effect was eliminated in the lowermost shear-rate range. The cell-free marginal zone increased in width (to a maximum of approximately 40% of tube radius) as viscosity declined. Measurements of viscosity and cell-free marginal zone were also performed with suspension C in tubes mounted in horizontal position. In contrast to vertical tubes, a monotonic increase in viscosity was found with decreasing mu, associated with cell sedimentation and development of a cell-free layer only in the upper portion of the tubes.

Biophysical Phenomena↗
PubMed1980

Temperature dependence of blood viscosity in frogs and turtles: effect on heat exchange with environment.

The temperature dependence of the viscosity of blood from frogs and turtles has been assessed for temperatures between 5 and 40 degrees C. Viscosity of turtles' blood was, on average, reduced from 3.50 +/- 0.16 to 2.13 +/- 0.10 cP between 10 and 30 degrees C, a decline of 39%. Even larger changes in viscosity were observed for frogs' blood with viscosity falling from 4.55 +/- 0.32 to 2.55 +/- 0.25 cP over the same temperature range, a change of 44%. Blood viscosity was highly correlated with hematocrit in both species at all temperatures. Viscosity of blood from both frogs and turtles showed a large standard deviation at all temperatures and this was attributed to large individual-to-individual variations in hematocrit. Turtles heat faster than they cool, regardless of whether tests are performed at temperatures above or below the range of thermal preference. The effect of temperature dependence of blood viscosity on heating and cooling rates is demonstrated.

Animals↗
PubMed1975

Blood viscosity and cardiac output in acute experimental anemia.

The significance of blood viscosity alterations during anemia was evaluated in dogs under morphine-chloralose anesthesia. In group I, anemia (mean hematocrit 18.1 +/- 1.3 vol %) was produced by exchange transfusion with clinical dextran (avg mol wt 70,000). In group II, anemia was produced (mean hematocrit 19.9 +/- 0.88 vol %) with 500,000 molecular weight dextran, thus preventing the decrease in blood viscosity in group I. The cardiac output increase in group I (93.4%) with low-viscosity anemia was significantly greater than in group II (43.3%) with unchanged blood viscosity. Group III animals were transfused with a clinical dextran-red cell mixture, and group IV animals received a 500,000 mol wt dextran-red cell mixture. In group III, blood viscosity and cardiac output did not change. In group IV, blood viscosity rose and cardiac output fell significantly. The results suggest that a change in blood viscosity exerts a significant effect upon cardiac output, especially during acute dextran-exchange anemia.

Anemia↗
PubMed2003

Neurons in the primate orbitofrontal cortex respond to fat texture independently of viscosity.

The primate orbitofrontal cortex (OFC) is a site of convergence from primary taste, olfactory, and somatosensory cortical areas. We describe the responses of a population of single neurons in the OFC that respond to orally applied fat (e.g., safflower oil) and to substances with a similar texture but different chemical composition, such as mineral oil (hydrocarbon) and silicone oil [(Si(CH3)2O)n]. These findings provide evidence that the neurons respond to the oral texture of fat, sensed by the somatosensory system. Use of an oral viscosity stimulus consisting of carboxymethyl-cellulose in the range 1-10,000 centipoise (cP) showed that the responses of these fat-sensitive neurons are not related to stimulus viscosity. Thus a textural component independent of viscosity and related to the slick or oily property is being used to activate these oral fat-sensitive neurons. Moreover, a separate population of neurons responds to viscosity (produced, e.g., by the carboxymethyl-cellulose series), but not to fat with the same viscosity. Thus there is a dissociation between texture channels used to sense fat viscosity and non-fat-produced viscosity. Further, free fatty acids such as linoleic acid do not activate these neurons, providing further evidence that the oral fat-sensing mechanism through which these OFC neurons are activated is not gustatory but textural. Most of this population of fat-sensitive neurons receive convergent taste inputs. These results provide evidence about how oral fat is sensed and are relevant to understanding the physiological and pathophysiological processes related to fat intake.

Action Potentials↗
PubMed2003

Representations of the texture of food in the primate orbitofrontal cortex: neurons responding to viscosity, grittiness, and capsaicin.

The primate orbitofrontal cortex (OFC) is a site of convergence from taste, olfactory, and somatosensory cortical areas. We describe a population of single neurons in the macaque OFC that responds to the texture of food in the mouth. Use of oral viscosity stimuli consisting of carboxymethylcellulose (CMC) in the range 1-10,000 centipoise showed that the responses of one subset of these neurons were related to stimulus viscosity. Some of the neurons had increasing responses to increasing viscosity, some had decreasing responses, and some neurons were tuned to a range of viscosities. These neurons are a different population to oral fat-sensitive neurons, in that their responses to fats (e.g., safflower oil), to silicone oil [(Si(CH3)2O)n], and to mineral oil (hydrocarbon) depended on the viscosity of these oils. Thus there is a dissociation between texture channels used to sense viscosity and fat. Some of these viscosity-sensitive single neurons were unimodal (somatosensory; 25%) and some received convergent taste inputs (75%). A second subpopulation of neurons responded to gritty texture (produced by microspheres suspended in CMC). A third subpopulation of neurons responded to capsaicin. These results provide evidence about the information channels used to represent the texture and flavor of food in a part of the brain important in appetitive responses to food and are relevant to understanding the physiological and pathophysiological processes related to food intake, food selection, and the effects of variety of food texture in combination with taste and other inputs that affect food intake.

Algorithms↗
PubMedDate not supplied

On-line electrical impedance measurement for monitoring blood viscosity during on-pump heart surgery.

BACKGROUND: The viscosity of blood (eta) as well as its electrical impedance at 20 kHz at high shear rate depends on hematocrit, temperature, concentration of macromolecules and red cell deformability. The aim of our study was to investigate the relation between viscosity and electrical impedance in a heart-lung machine-like set-up, because during on-pump heart surgery considerable viscosity changes occur. METHODS: Blood of 10 healthy volunteers was examined under temperature variation between 18.5 and 37 degrees C at four different levels of hemodilution. Blood viscosity was examined with a golden-standard technique, i.e. a Contraves LS 30 Couette viscometer, and the results were compared with measurements of the electrical resistivity (R) at 20 kHz by a specially designed device in series with the tubing system of a heart-lung machine. All measurements were performed at a shear rate of 87 s(-1). RESULTS: Using stepwise multiparameter regression analysis (SPSS) a highly significant correlation was found (r(2) = 0.882) between viscosity (eta) and resistivity (R). Adding the variables sodium ([Na(+)]) and fibrinogen ([Fibr]) concentration the coefficient of correlation further improved to r(2) = 0.928 and the relation became: eta = -0.6844 + 0.038 R + 0.038 [Na(+)] + 0.514 [Fibr]. All coefficients showed a statistical significance of p < 0. 001. CONCLUSIONS: Electrical impedance measurement is feasible in a heart-lung machine-like set-up and allows accurate continuous on-line estimation of blood viscosity; it may offer an adequate way to record and control viscosity changes during on-pump heart surgery.

Adult↗
PubMed1992

Effect of delmopinol on the viscosity of extracellular glucans produced by Streptococcus mutans.

The surfactant delmopinol, which is a new antiplaque agent with a low anti-microbial profile, was tested for its effects on the viscosity of bacterial extracellular glucans. Glucans were isolated from Streptococcus mutans broth supernatants incubated with 0.15 M sucrose in 50 mM sodium phosphate buffer at pH 6. The viscosity was measured in a shear rate range from 15 to 230 reciprocal seconds. The viscosity of the water-soluble glucan was found to be independent of shear rate whereas the water-insoluble glucan showed a strong shear thinning. The addition of delmopinol to preformed glucans did not affect the viscosity nor the shear rate dependence of the glucans. However, when present during synthesis of the polysaccharides, delmopinol was found to reduce the viscosity of both water-soluble and water-insoluble glucans by approximately 50% at the shear rates investigated. The reduction in viscosity for the water-soluble glucans was obtained at a delmopinol concentration of 0.32 mM (0.01%) and for the water-insoluble glucans at 3.2 mM delmopinol. The observed reduction of viscosity of glucans indicates that the in vivo stability of plaque matrix after delmopinol treatment would be lowered, which may lead to a reduction of plaque cohesion and thus facilitate mechanical plaque removal.

Glucans↗
PubMed1998

Relationship between plasma viscosity and the severity of coronary heart disease.

Several studies have indicated that plasma viscosity contributes to cardiovascular risk in men. So far, a significant relationship between plasma viscosity and the severity of coronary heart disease has not been found. Thus, the present study is the first to report on the relationship of plasma viscosity and the severity of coronary heart disease. In a collective of 1142 male myocardial infarction patients, plasma viscosity and additional laboratory parameters were determined. Atherosclerotic changes were quantified by coronary angiography. Patients were divided into groups without any, and with one to three stenosed vessels. We found a positive relationship between plasma viscosity and the severity of coronary heart disease, even after adjusting groups for age, fibrinogen, and use of diuretics. Mean plasma viscosity ranged from 1.141+/-0.035 mPa s in patients without stenosed vessels to 1.162+/-0.044 mPa s in patients who had three coronary vessels with stenoses >50%. Differences between the groups were significant (P<0.001 to 0.05), with two exceptions: differences between patients without any and with one stenosed vessel, as well as between patients with one and two stenosed vessels, did not reach the significance level. On the whole, we can give further support to the hypothesis that cardiovascular risk factors and coronary heart disease may be linked by plasma viscosity.

Blood Viscosity↗
PubMed1993

Blood viscosity during long-term treatment with ticlopidine in patients with intermittent claudication. A double-blind study.

The aim was to test within a randomized, double-blind trial whether the antiaggregant drug ticlopidine might reduce blood viscosity as has been claimed. Sixteen patients with intermittent claudication were studied before and after three years of treatment with ticlopidine, 500 mg/day, or placebo. At baseline, the viscosity values were significantly higher as compared with a reference group of healthy subjects. Whole-blood viscosity, measured at four different shear rates at hematocrit adjusted to a standard 40%, decreased significantly at follow-up, with no difference between ticlopidine treatment and placebo. Hematocrit showed a slight increase in the placebo group. The viscosity parameters were unrelated to lower limb blood flow variables, ankle/brachial index, and walking distances. The mechanism behind the overall decrease in whole-blood viscosity is obscure but could possibly be explained by lifestyle changes. Smoking habits were, however, unaltered. Since plasma viscosity remained increased, it might indicate that some erythrocyte factor, notably red cell aggregability and deformability, had improved. It is concluded that ticlopidine had no long-term effect on blood viscosity.

Aged↗
PubMed1984

Experimental hypervolemic hemodilution: physiological correlations of cortical blood flow, cardiac output, and intracranial pressure with fresh blood viscosity and plasma volume.

Rheological, cerebrovascular, and cardiovascular alterations induced by serial plasma volume (PV) expansion were evaluated in splenectomized dogs. Seven dogs received two infusions of autologous plasma within 120 minutes; each infusion equaled 20% of the respective dog's total blood volume (TBV). The PV increased 31% and then another 26% after the two respective infusions, and the hematocrit (Hct) was obligatorily decreased by 22% during the experiment. The fresh blood viscosity at the shear rate of 10 sec-1 varied inversely with the TBV and the PV and correlated directly with the Hct after these plasma infusions. Cardiac output (CO) increased 71% after the two infusions without significant alterations in mean arterial blood pressure. Additionally, CO was inversely related to both Hct and blood viscosity. Although the 15% rise in regional cortical blood flow (rCoBF) in the territory of the middle cerebral artery did not reach statistical significance, the rCoBF was related inversely to both Hct and blood viscosity and directly to TBV, PV, and CO after the plasma infusions. Cortical vascular resistance (CVR) decreased 18% after the two infusions. The CVR correlated inversely with PV and directly with Hct and blood viscosity. Our data suggest that hypervolemic hemodilution with expansion of PV increases CO more than cerebral blood flow in normal brain. Fresh blood viscosity seems to be a major factor determining CO and cerebral perfusion after IV expansion. This study adds support to the hypothesis that reductions of blood viscosity account for the direct relationship between cerebral blood flow and CO observed after intravascular volume expansion with hemodiluting agents. Hypervolemic hemodilution with plasma reduces CVR, possibly secondary to its effect on blood viscosity, and also raises intracranial pressure.

Animals↗
PubMed1994

Effect of hemodialysis and recombinant human erythropoietin on determinants of blood viscosity.

Blood viscosity (hemorheology) is a major determinant of the rate of blood flow, and increases in viscosity are known to be involved in the etiology of vascular diseases. This placebo-controlled study investigated the independent and combined effects of hemodialysis and recombinant human erythropoietin (rHuEpo) on determinants of blood viscosity in patients with chronic renal failure and related any changes to the normal physiological range. Hemodialysis patients were shown to have a high incidence of rheological abnormalities although the degree of anemia associated with chronic renal failure compensated for these changes. The main effect of both hemodialysis and rHuEPO treatment was an increase in hematocrit associated with a rise in blood viscosity and inconsistent changes in red blood cell (RBC) deformability. The rise in viscosity was significant only following rHuEPO treatment. Hemodialysis-induced increases in blood and plasma viscosity correlated strongly with the degree of hemoconcentration. Although hemodialysis patients have inherent hemorheological abnormalities, correction of renal anemia with rHuEPO to a hematocrit level of < 0.35 in conjunction with dialysis-induced hemoconcentration did not result in adversely high blood viscosity levels in any patient.

Anemia↗
PubMed1993

[Blood viscosity and cerebral blood flow in aged].

It is well known that there is a close correlation between blood viscosity and blood flow. To clarify any relationship between blood viscosity and regional cerebral blood flow (rCBF) in the elderly, we simultaneously studied both CBF with PET (positron emission tomography) and blood viscosity with viscosimeter before and after phlebotomy in the elderly with various kinds of polycythemia. These subjects consisted of five male cases of secondary polycythemia due to pulmonary fibrosis, one male case of essential erythrocytosis (average age 66.6 +/- 4.6 years old) and one female case of stress polycythemia (47 years old). Before phlebotomy an increase in blood viscosity, decrease in rCBF and regional cerebral metabolic rate of oxygen (rCMRO2) were observed in all cases. After phlebotomy (total amount of 800 to 1,000 ml) blood viscosity rapidly decreased, and both rCBF and rCMRO2 tended to increase. There was a significant negative or positive correlation between CBF and blood viscosity or rCMRO2, respectively. However, no increase in cerebral oxygen transport was observed in any subject after phlebotomy. It was noted that cerebral infarction is not infrequent among elderly visitors to Kusatsu spa, which is characterized by high temperature hot spring water. From the authors' observation of 23 cases of cerebral infarction encountered during the last five years, it is noteworthy that the disease tended to occur more frequently during midnight to morning, specially 3:00 to 6:00. Thus, to clarify the pathogenetic mechanism of the cerebral infarction occurring after bathing in hot spring water, we studied the changes in blood viscosity, blood pressure and coagulation-fibrinolytic system after bathing in hot spring water.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Regulation of cell membrane function and secretion by extracellular fluid viscosity.

Plasma viscosity is elevated in various pathological states, due to increased levels of protein and other macromolecules. The possibility that elevation of extracellular fluid viscosity (EFV) affects cellular and biochemical functions was examined in cultured liver cells and in red blood cells. The viscosity was modified by the addition of various macromolecules, which differ in their capacity to increase viscosity and in their chemical nature. It was found that secretion of lipoproteins and lysosomal enzymes by liver cells is inhibited as a function of the medium viscosity. Correspondingly, elevation of plasma viscosity of hyperlipidemic rats reduced lipoprotein levels. In search for the mechanism of this phenomenon we examined the effects of EFV on two cell membrane components which are involved in transmembrane processes: Gangliosides (GMs), and phospholipase A2 (PLA2). It was found that the rate of GMs degradation is decreased with increasing EFV. Of special interest was the finding that the activity of cell membrane PLA2, a key enzyme in secretory processes, is inhibited by increasing EFV. This phenomena was not confined to cell membrane PLA2, as we further found that erythrocyte hemolysis, induced by soluble snake venom PLA2, is inhibited as the EFV is increased. It is proposed that the extracellular fluid viscosity may play an important role in regulation of cellular and biochemical processes in general.

Animals↗