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PubMed1986

Effect of shear rate variation on apparent viscosity of human blood in tubes of 29 to 94 microns diameter.

In order to test the hypothesis that the increase of vascular resistance observed in vivo at low flow rates is due in part to blood rheological properties, the apparent viscosity of human blood was measured in small tubes in a range of shear rates. Pressure-flow relationships were obtained in vertical glass tubes (29 to 94 microns i.d.) perfused with blood at hematocrits between 0.13 and 0.65. Viscosity of blood and plasma was calculated using Poiseuille's law. With the exception of data obtained in the largest tube at a hematocrit of 0.6, relative blood viscosity was found to be independent of shear rate in the range between 1 and 120 s-1. Microscopic observation revealed pronounced red cell aggregation at low shear rates. Velocity profiles obtained by the use of fluorescence-labelled red cells showed increased blunting with decreasing shear rate. The Fahraeus-Lindqvist effect was evident in a reduction of viscosity with tube size at a given feed hematocrit. The observed constancy of apparent blood viscosity with decreasing shear is attributed to the opposing effects of a cell-depleted marginal layer and red cell aggregation or deformation in the cell core. The findings indicate that the increase of vascular resistance at low arterial pressure cannot be explained by shear-dependent changes of apparent blood viscosity observed in macroviscometers.

Blood Flow Velocity↗
PubMed2004

Density-driven instabilities of variable-viscosity miscible fluids in a capillary tube.

A linear stability analysis is presented for variable-viscosity miscible fluids in an unstable configuration; that is, a heavier fluid placed above a lighter one in a vertically oriented capillary tube. The initial interface thickness is treated as a parameter to the problem. The analysis is based on the three-dimensional Stokes equations, coupled to a convection-diffusion equation for the concentration field, in cylindrical coordinates. When both fluids have identical viscosities, the dispersion relations show that for all values of the governing parameters the three-dimensional mode with an azimuthal wave number of one represents the most unstable disturbance. The stability results also indicate the existence of a critical Rayleigh number of about 920, below which all perturbations are stable. For the variable viscosity case, the growth rate does not depend on which of the two fluids is more viscous. For every parameter combination the maximum of the eigenfunctions tends to shift toward the less viscous fluid. With increasing mobility ratio, the instability is damped uniformly. We observe a crossover of the most unstable mode from azimuthal to axisymmetric perturbations for Rayleigh numbers greater than 10(5) and high mobility ratios. Hence, the damping influence is much stronger on the three-dimensional mode than the corresponding axisymmetric mode for large Rayleigh numbers. For a fixed mobility ratio, similar to the constant viscosity case, the growth rates are seen to reach a plateau for Rayleigh numbers in excess of 10(6). At higher mobility ratios, interestingly, the largest growth rates and unstable wave numbers are obtained for intermediate interface thicknesses. This demonstrates that, for variable viscosities, thicker interfaces can be more unstable than their thinner counterparts, which is in contrast to the constant viscosity result where growth rate was seen to decline monotonically with increasing interface thickness.

Models, Theoretical↗
PubMed2005

Box-Behnken experimental design in the development of a nasal drug delivery system of model drug hydroxyurea: characterization of viscosity, in vitro drug release, droplet size, and dynamic surface tension.

The purpose of the research was to investigate the changes in physicochemical properties and their influence on nasal formulation performance using 5-factor, 3-level Box-Behnken experimental design on the combined responses of viscosity, droplet size distribution (DSD), and drug release. Gel formulations of hydroxyurea (HU) with surface-active polymers (hydroxyethylcellulose [HEC] and polyethylene-oxide [PEO]) and ionic excipients (sodium chloride and calcium chloride) were prepared using Box-Behnken experimental design. The rheology and dynamic surface tension (DST) of the test formulations was investigated using LV-DV-III Brookfield rheometer and T60 SITA tensiometer, respectively. Droplet size analysis of nasal aerosols was determined by laser diffraction using the Malvern Spraytec with the InnovaSystems actuator. In vitro drug release studies were conducted on Franz diffusion cells. With PEO gel, calcium chloride increased the viscosity and DSD and retarded drug release, while sodium chloride decreased the viscosity, DST, and DSD and accelerated the release of HU. With HEC gel, the addition of the above salts resulted in less significant changes in viscosity, DSD, and DST, but both salts significantly increased the release of HU. Droplet size data obtained from a high viscosity nasal pump was dependent on type of polymer, polymer-excipient interactions, and solvent properties. The applications of Box-Behnken experimental design facilitated the prediction and identified major excipient influences on viscosity, DSD, and in vitro drug release.

Administration, Intranasal↗
PubMed1991

[Variance, factors of influence and clinical relevance of plasma viscosity].

The problem of measuring plasma viscosity has been solved through the use of capillary and falling-ball viscosimeters which have a determination variance of less than 1%. On account of the influence of overeating, forced thirst, psychological and physical stress plasma viscosity should be determined in the morning; the patient should be fasting and well hydrated. Plasma viscosity is influenced by diseases with alterated plasma protein composition. An elevated viscosity also significantly increases the risk of developing an arterial occlusion. Since the physician can both decrease and increase plasma viscosity, it should be determined parallel to therapy. Accordingly, plasma viscosity is one of the most important rheological parameters.

Adult↗
PubMed2005

Ras diffusion is sensitive to plasma membrane viscosity.

The cell surface contains a variety of barriers and obstacles that slow the lateral diffusion of glycosylphosphatidylinositol (GPI)-anchored and transmembrane proteins below the theoretical limit imposed by membrane viscosity. How the diffusion of proteins residing exclusively on the inner leaflet of the plasma membrane is regulated has been largely unexplored. We show here that the diffusion of the small GTPase Ras is sensitive to the viscosity of the plasma membrane. Using confocal fluorescence recovery after photobleaching, we examined the diffusion of green fluorescent protein (GFP)-tagged HRas, NRas, and KRas in COS-7 cells loaded with or depleted of cholesterol, a well-known modulator of membrane bilayer viscosity. In cells loaded with excess cholesterol, the diffusional mobilities of GFP-HRas, GFP-NRas, and GFP-KRas were significantly reduced, paralleling the behavior of the viscosity-sensitive lipid probes DiIC(16) and DiIC(18). However, the effects of cholesterol depletion on protein and lipid diffusion in cell membranes were highly dependent on the depletion method used. Cholesterol depletion with methyl-beta-cyclodextrin slowed Ras diffusion by a viscosity-independent mechanism, whereas overnight cholesterol depletion slightly increased both protein and lipid diffusion. The ability of Ras to sense membrane viscosity may represent a general feature of proteins residing on the cytoplasmic face of the plasma membrane.

Animals↗
PubMed2006

Stability and viscosity of a flavored omeprazole oral suspension for pediatric use.

PURPOSE: The stability and viscosity of preparations of a commercially available, flavored, immediate-release powder for oral suspension (omeprazole-sodium bicarbonate) during refrigerator and room temperature storage were investigated. METHODS: Omeprazole-sodium bicarbonate 20-mg packets were suspended to initial omeprazole concentrations of 0.6 and 2 mg/mL, and omeprazole-sodium bicarbonate 40-mg packets were suspended to initial omeprazole concentrations of 1.2, 2, 3, and 4 mg/mL. Suspensions were stored at 4 degrees C in darkness (refrigerated) or 22-25 degrees C (room temperature) in light for one week. A third set of suspensions was stored refrigerated for one month. Omeprazole's stability was quantified after 0, 6, 12, 24, 48, and 168 hours in one-week samples and after 0, 7, 14, 21, and 28 days in one-month samples using high-pressure liquid chromatography. Viscosities of refrigerated suspensions were measured after 0, 1, and 7 days. RESULTS: Refrigerated suspensions retained >98% and >96% of their initial omeprazole concentrations after one week and one month, respectively. Stability of room temperature suspensions was concentration dependent. After one week, the 0.6- and 1.2-mg/mL suspensions retained 87.2% and 93.1% of their respective initial omeprazole concentrations, whereas the 2-, 3-, and 4-mg/mL suspensions retained >97% of their initial omeprazole concentrations. Suspension viscosities varied 10-fold over the concentrations studied, but all were within the viscosity ranges of other commercially available oral suspensions. Prolonged refrigeration did not increase the suspensions' viscosities. CONCLUSION: Omeprazole-sodium bicarbonate suspensions of 0.6-4 mg/mL omeprazole were stored at 4 degrees C in darkness for up to 28 days. The viscosities of refrigerated suspensions did not increase over 7 days. Except for the 0.6 mg/mL preparations, suspensions stored at room temperature in the light retained >90% of their initial omeprazole content after 7 days, despite turning yellow.

Administration, Oral↗
PubMed1993

Fluid flow during percutaneous drainage procedures: an in vitro study of the effects of fluid viscosity, catheter size, and adjunctive urokinase.

OBJECTIVE: An in vitro study was performed to determine the range of flow times of different bodily fluids through catheters of different diameters and to test the hypothesis that urokinase might decrease the viscosity of purulent material. MATERIALS AND METHODS: A standard viscometer was used to measure the viscosities of water, blood, pseudocyst fluid, purulent material, and purulent material with admixed urokinase. For each fluid, Poiseuille's law was used to calculate the kinematic viscosity, from which theoretical drainage times through seven different sizes of catheters were calculated. These theoretical times were compared with the actual measured values to verify that flow was according to Poiseuille's law. RESULTS: The calculated kinematic viscosities (in 10(-6) stokes) were as follows: water, 0.695 +/- 0.006; pseudocyst fluid, 2.185 +/- 0.008; blood, 3.001 +/- 0.049; abscess fluid without urokinase, 5.729 +/- 0.064; and abscess fluid with urokinase, 4.416 +/- 0.070. The viscosity of abscess fluid decreased by 23% with the addition of urokinase. Drainage time was considerably shorter with larger catheters. CONCLUSION: Flow of various bodily fluids, including pus, is according to Poiseuille's law, confirming that for more viscous fluid, larger catheters provide more rapid drainage. Urokinase decreases viscosity of purulent material and increases flow for all sizes of catheters.

Abscess↗
PubMedDate not supplied

High sperm chromatin stability in semen with high viscosity.

This study was designed to determine the effects of high semen viscosity on sperm chromatin stability. Semen samples obtained from men with normal and high viscosity were studied. Sperm chromatin stability was tested by exposure to sodium dodecyl sulfate (SDS) only and SDS together with a zinc-chelating agent, disodium ethylene diamine tetraacetate (SDS+EDTA). After SDS incubation, stable sperm was 61.36 +/- 3.0 and 54.71 +/- 3.42% for normal and high semen viscosity, respectively (P:NS), and after SDS+EDTA, it was further reduced to 12.48 +/- 0.99% in semen samples with normal consistency and in a less magnitude in semen samples with high viscosity (25.6 +/- 5.2). Comparing values obtained in SDS+EDTA, a high sperm stability was observed in samples with hyperviscosity (p < .02). In samples with normal viscosity the percentage of grossly swollen sperm increased 5.40 times from the values obtained in sperm incubated with SDS to the values obtained with SDS+EDTA, whereas in samples with high viscosity the percentage increased only 2.2 times. It is concluded that hyperviscosity is associated with a high sperm chromatin stability in situations when a zinc-chelating agent is present.

Chromatin↗
PubMed1975

Studies on hyaluronic acid. V. Relationship between the protein content and viscosity of rooster comb dermis hyaluronic acid.

Protein accounted for an average of 8.7% w/w of the hyaluronic acid obtained from rooster comb dermis extracts and three types of peptide constituents appeared to be present. A few collagen-like fibers were closely associated with the hyaluronic acid when samples were examined in the electron microscope and collagenase treatment decreased the intrinsic viscosity from 7000-5000 ml/g to 3900-2700 ml/g. The quantities of collagen present, however, were too small to detect chemically with the methods employed. The major peptide consituent was readily separated from the hyaluronic acid by fractionation in a cesium chloride gradient or by treatment with pronase. The viscosity was decreased by the density gradient procedure but not by the pronase digestion. Repeated fractionation in a cesium chloride gradient decreased the intrinsic viscosity still further and a small peptide constituent with a high glycine and serine content remained associated with a hyaluronic acid. The data suggest that an interaction or entanglement with collagen fibers is responsible for the high viscosity of hyaluronic acid in this tissue extract and that the viscosity of purified hyaluronic acid preparations is dependent upon interactions between adjacent polysaccharide chains. Interactions between the major peptide constituent and polysaccharide chains or the small residual peptide component remaining with hyaluronic acid after extensive purification procedures, however, appear to be involved in some organized structure because the presence of the major peptide constituent minimized the decrease in viscosity that occurred when hyaluronic acid samples were lyophilized.

Amino Acids↗
PubMed1997

Whole blood viscosity, blood pressure and cardiovascular risk factors in healthy blood donors.

Whole blood viscosity contributes to the total peripheral resistance and has been suggested to be a risk factor for cardiovascular disease. Whole blood viscosity was measured using a direct technique in 105 healthy blood donors and in addition to establishing our reference values, the relationship to blood pressure and other cardiovascular risk factors was assessed. Whole blood viscosity correlated with systolic blood pressure (r = 0.29, p = 0.003), cholesterol (r = 0.21, p = 0.034), cholesterol/HDL cholesterol ratio (r = 0.33, p = 0.01), triglycerides (r = 0.37, p < 0.0005), body mass index (r = 0.29, p = 0.003) and waist-hip ratio (r = 0.30, p = 0.002). Subjects with systolic blood pressure > 130 mmHg (n = 16) had higher whole blood viscosity (p = 0.017) than those with lower blood pressure. Whole blood viscosity was significantly lower in women (n = 52) than in men at all shear rates (0.045 > p > 0.001). These results suggest that even in a population of healthy normotensive blood donors of a wide age range and either gender, there are positive correlations between directly assessed whole blood viscosity and a number of the components of the metabolic cardiovascular syndrome including systolic blood pressure, weight and blood lipids.

Adult↗
PubMed1991

Effects of temperature and viscosity on prothrombin times of blood.

Accurate prothrombin time tests are important because they are frequently performed on presurgical patients to evaluate their blood-clotting status. We studied the effect of temperature (27-47 degrees C) on PTs obtained with eight different brands of thromboplastin. We also compared the sensitivities of two types of coagulation timers to changes in blood viscosities between 1 and 16 mPa/s. Viscosities were measured with the Brookfield Digital Viscometer. The MLA Eletra 800 and the BBL fibrometer were used to measure PTs. All eight thromboplastins gave convex curves of PT versus temperature, with optimum values lying between 38 and 39 degrees C. The curves were fitted to 4th-degree polynomials which showed that a mean temperature bias of 2 degrees C can increase PTs. Ortho Brain (7.8% change) was affected the most, while thromboplastin C (4.4% change) was affected the least. Plots of PT versus viscosity showed that the BBL fibrometer, which uses an electromechanical sensor, was more affected by viscosity than the MLA Electra 800, with an optical detector. However, above 8.2 mPa/s, all PTs were significantly elevated. Hence, patients with macroglobulinemia, whose plasma viscosities sometimes exceed 8.2 mPa/s, may have falsely elevated PTs. We conclude that temperature and viscosity are critical factors in the test and significantly contribute to within and between laboratory variations in PT measurements.

Blood Viscosity↗
PubMed2006

Heat treatment of bovine colostrum. I: effects of temperature on viscosity and immunoglobulin G level.

The objective of this study was to identify the critical temperature, at or below which heat-treatment of bovine colostrum would produce no significant changes in viscosity, IgG concentration, or Ig activity. Results of preliminary work, using a Rapid Visco Analyzer (RVA) to heat 50-mL aliquots from 6 unique batches of bovine colostrum at 59, 60, 61, 62, and 63 degrees C, suggested that colostrum could be heated to 60 degrees C for up to 120 min without changing viscosity or IgG concentration. This finding was confirmed by heating 50-mL aliquots from 30 unique batches of colostrum in an RVA for 120 min at 60 and 63 degrees C. Heating colostrum to 63 degrees C resulted in an estimated 34% decrease in IgG concentration and 33% increase in viscosity. However, there was no difference in IgG concentration between preheat-treated (73.4 +/- 26.5 mg/mL) and post-heat-treated (74.5 +/- 24.3 mg/mL) samples after heating colostrum to 60 degrees C in an RVA for 120 min. Similarly, viscosity was unaffected after heating colostrum to 60 degrees C in an RVA for 120 min. High quality colostrum (> or =73.0 mg/mL) suffered greater losses of IgG and greater viscosity changes when heated to 63 degrees C than did moderate quality colostrum (<73.0 mg/mL). However, the effects of colostrum quality were minor if high quality colostrum was only heated to 60 degrees C. The results of a bovine viral diarrhea serum neutralization assay suggested that antibody activity was unchanged after heating colostrum to either 60 or 63 degrees C. However, these results were interpreted as being inconclusive due to a high proportion of missing results because of the congealing of many samples after heat treatment. The results of this study indicate that 50-mL volumes of bovine colostrum can be heat treated at 60 degrees C for up to 120 min in an RVA without affecting IgG concentration or viscosity.

Animals↗
PubMed1991

A semi-empirical model of apparent blood viscosity as a function of vessel diameter and discharge hematocrit.

A semi-empirical model is developed to describe the dependence of apparent viscosity of blood on vessel diameter (2.7 to 500 microns) and vessel discharge hematocrit (5% to 60%). The blood flow is modeled as a cell-rich core and a cell-free marginal layer in the larger vessels and an axial-train in the smaller vessels. Laminar (Poiseuille) flow is assumed in all cases. An equation is derived in which apparent viscosity is a function of vessel diameter, core viscosity, and width of marginal layer. This is then complemented by empirical equations in which core viscosity varies exponentially with discharge hematocrit while the width of marginal layer varies linearly with discharge hematocrit. The model correlates well with several sets of experimental data and behaves according to the Fahraeus-Lindqvist effect. Predicted apparent viscosity tends to the expected finite value for large vessel diameters. Dependence of apparent viscosity on vessel diameter is realistically smooth in the whole diameter range.

Blood Vessels↗
PubMed1991

The effect of pelleting, salt, and pentosanase on the viscosity of intestinal contents and the performance of broilers fed rye.

An experiment was conducted to determine the impact of pelleting of rye, dietary salt (.39 and .57%), and crude pentosanase supplementation (0 and .2%) on the viscosity of intestinal contents and the concomitant performance of broiler chicks fed rye-based diets. Each treatment was replicated six times with six birds per replicate. Test diets were fed from 1 day to 3 wk of age, at which time body weight, feed intake, intestinal viscosity, and molecular weight distribution of carbohydrate complexes were determined in fore and hind gut sections. Enzyme supplementation in all treatment combinations significantly increased weight gains and feed conversion efficiency (FCE). Pelleting and salt did not influence weight gain or FCE, although feed intake was increased through the addition of salt. The viscosity of fore and hind gut contents was significantly reduced with pentosanase supplementation, whereas the effects of salt or pelleting were not as clearly defined. Weight gain and FCE correlated with fore but not hind gut viscosity. The viscosity of gut samples was found to be best described by the concentration of carbohydrate complexes with an average molecular weight greater than 500,000 Da. Pentosanase treatment reduced lumenal concentration of these complexes, thereby reducing viscosity and stimulating improvements in growth and FCE.

Animal Feed↗
PubMed1976

[The viscosity of Thiokol impression material during gelation (author's transl)].

Viscosity behavior of the impression materials is important property which determines the pressure and its distribution to be exerted on oral soft tissues in relation to the tray design and impression technique. The impression material, however, react to gel so fast to measure the viscosity during the reaction that it is still not completely elucidated. It would be able to seize the viscosity behavior of Thiokol impression material during the gelation unequivocally by retarding the oxidative condensation reaction using weak oxidative, lead monoxide. Based on the equal reactivity of SH groups of Thiokol liquid polymer there is no difference in statistic molecular weight distribution at any degree of the reaction between with lead monoxide and with the other oxidatives now in practical use. The viscosity measurement of the mixture of Thiokol LP-2, lead monoxide, and di-butyl phthalate was performed at the rates of shear ranged from 10(1.5) to 10(3.9) sec-1 at 20 degrees C. The viscosity of the mixture progressively increases after spatulation of the materials but yield value does not appear for the time being before setting, that is, the infinite network forming via the pendant SH groups could not take place until the most of SH groups were consumed, attributed to low concentration of poly-functional prepolymer in the liquid polymer. At early stages of the reaciton the viscosity behavior is approximately Newtonian at lower rates of shear and pseudplastic at higher rates of shear. As the reaction proceeds it becomes pseudplastic even at lower rates of shear.

Dental Impression Materials↗
PubMed2000

Relative influence of composition and viscosity of acrylic bone cement on its apparent fracture toughness.

The composition and viscosity of an acrylic bone cement have both been identified in the literature as being parameters that affect the mechanical properties of the material and, by extension, the in vivo longevity of cemented arthroplasties. The objective of the present study was to determine the relative influence of these parameters on a key cement mechanical property; namely, its fracture toughness. Two sets of cements were selected purposefully to allow the study objective to be achieved. Thus, one set comprised two cements with very similar compositions but very different viscosities (Cemex RX, a medium-viscosity brand, and Cemex Isoplastic, a high-viscosity brand) while the other set comprised two cements with similar viscosities but with many differences in composition (Cemex Isoplastic and CMW 1). Values of the fracture toughness (as determined using chevron-notched short rod specimens) [K(ISR)] obtained for Cemex RX and Cemex Isoplastic were 1.83 +/- 0.12 and 1.85 +/- 0.12 MPa square root(m), respectively, with the difference not being statistically significant. The K(ISR) values obtained for Cemex Isoplastic and CMW 1 were 1.85 +/- 0.12 and 1.64 +/- 0.18 MPa square root(m), respectively, with the difference being statistically significant. Thus, the influence of cement composition on its K(ISR) is more marked relative to the influence of cement viscosity. Explanations of this finding are offered, together with comments on the implications of the results for the in vivo longevity of cemented arthroplasties.

Acrylic Resins↗
PubMed2001

No influence of C-peptide, insulin, and glucagon on blood viscosity in vitro in healthy humans and patients with diabetes mellitus.

The influence of the hormones most involved in glucose homeostasis, C-peptide, insulin and glucagon on blood viscosity was tested in vitro. Whole blood (adjusted to haematocrit 45%) from healthy volunteers (n=24) and patients with diabetes mellitus (n=17) was incubated with 10(-7)-10(-10) M C-peptide, insulin or glucagon. None of these peptide hormones, neither at physiological nor at supraphysiological levels, had an influence on high (94.5 s(-1)) or low (0.1 s(-1)) shear rate viscosity. The small group of diabetic patients had a higher plasma viscosity and increased blood viscosity at 94.5 s(-1), which is in agreement with earlier studies, but decreased viscosity at low shear rate. We conclude that C-peptide, insulin and glucagon have no direct effect on blood viscosity in vitro. It is, therefore, unlikely that microvascular disturbances seen with either deficiency or excess of these hormones is due to haemorheological factors.

Adult↗
PubMed2002

Hematological and blood viscosity changes in tail-suspended rats.

BACKGROUND: Fluid shifts during exposure to microgravity result in a decrease in plasma volume which can lead to a transient increase in hematocrit. This transient increase in hematocrit could result in an increased blood viscosity. Yet, hematocrit returns to near normal values within a matter of hours of microgravity exposure as a result of a reduction in red blood cell mass. Rat tail-suspension models mimic the fluid shifts and hematological changes associated with microgravity exposure. METHODS: Tail-suspended rats were monitored for hematological and hemorheological changes over 4, 24, 72, and 168 h of tail suspension. Additionally, hematological and hemorheological changes were followed during recovery periods of 48, 120, and 192 h following 168 h of tail suspension. RESULTS: Although hematocrit increased significantly by 4 h of suspension, blood viscosity did not differ from controls. However, blood viscosity was significantly greater in the 72-, 168-, and 168/48-h suspension groups relative to controls despite no significant differences in hematocrits between groups. Theoretical calculations of blood viscosity at hematocrits of 50 and 60% (values intended to mimic hematocrits that would occur if red blood cell mass did not decrease) show a significant increase relative to the blood viscosities determined for the actual hematocrits in the experimental groups. CONCLUSIONS: The lowering of hematocrit associated with spaceflight may substantially reduce blood viscosity and thereby maintain the hematocrit at an optimal level for oxygen delivery to tissues.

Animals↗