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At least 343 records · Page 19Linked to original sources
PubMed1988

Effect of statil (ICI 128436) on erythrocyte viscosity in vitro.

The hypothesis that sorbitol accumulation could contribute to a reduced erythrocyte deformability in diabetes was investigated. Erythrocyte sorbitol and erythrocyte viscosity at high and low shear rates were studied in 20 insulin-dependent diabetic (IDDM) and 20 matched control subjects. An increased erythrocyte sorbitol and an increased low-shear erythrocyte viscosity were found in the IDDM patients, but there was no significant correlation (r = .11, NS) between the parameters. Incubation (3 h, 37 degrees C) in a Krebs buffer containing 33.3 mM glucose resulted in a significant sorbitol accumulation, but erythrocyte viscosity was not affected. Despite this fact, addition of 1 mM statil (ICI 128436) in the 5.5- and 33.3-mM glucose media not only prevented erythrocyte sorbitol accumulation but also improved erythrocyte viscosity in diabetic and control subjects. The effect was more pronounced at the low (approximately 16%) than at the high (approximately 2%) shear rate. The effect on erythrocyte viscosity disappeared by washing the erythrocytes after incubation, although erythrocyte sorbitol remained different. Our results suggest that sorbitol accumulation does not contribute to an increased erythrocyte viscosity in diabetes, and statil shows a positive effect on erythrocyte viscosity independent of its aldose reductase-inhibiting property.

Adult↗
PubMed2002

Characteristic behavior of viscosity and viscoelasticity of Aureobasidium pullulans culture fluid.

Measurements of dynamic viscoelasticity and steady flow viscosity were made for culture fluids obtained by cultivation of Aureobasidium pullulans IAM 5060 with initial pHs of 6 and 7 and for exopolysaccharide (EPS) solutions obtained by removal of microbial cells. The molecular weight of EPS of the pH 6 culture is about 850,000, and that of the pH 7 culture is much larger. In the present study, the complex viscosity shifted to a considerably larger value than that of the steady flow viscosity. This differs from the Cox-Merz experience law which claims that there is a similarity between the angular frequency dependence of complex viscosity and the shear rate dependence of steady flow viscosity. On the other hand, the dynamic viscosity at small strain amplitude practically corresponded to the steady flow viscosity. The storage modulus of the pH 7 samples decreased markedly with a strain amplitude of more than 0.2, indicating that a dense network structure was formed. The linear region of the plot of viscoelasticity against strain amplitude was wider for the pH 6 culture, reflecting the stability of the network structure in this sample. The viscoelastic level of the EPS solution was a little greater than that of the culture fluid. This suggests that the viscoelasticity of the culture fluid is mainly caused by network structure forming among dissolved polysaccharides.

Journal Article↗
PubMed1979

Effect of diet viscosity on the operation of the pharyngeal pump in the blood-feeding bug Rhodnius prolixus.

1. The rate of pumping and total number of pump strokes was recorded whilst Rhodnius prolixus fed on measured amounts of artificial diets. 2. Increasing the viscosity of the diet caused a decline in both the frequency with which the pharyngeal pump operates and the average stroke volume of the pump. 3. In 5th-instar Rhodnius, the stroke volume tends toward a maximum value of about 60 nl at viscosities lower than about 3 cP. 4. Feeding rates (volume per unit time) agree with Poiseuille's law at high viscosities, but are less than predicted at low viscosities. 5. The maximum power output of the pump occurs at a viscosity between 1 and 3 cP, which is probably the range of the effective viscosity of blood in tubes with the dimensions of Rhodnius stylets. 6. These results are inconsistent with a hypothesis of a central nervous system 'oscillator' controlling the pump muscle, independent of feedback, but are consistent with a model involving peripheral feedback from stretch receptors, with an appropriate delay.

Animals↗
PubMed1984

Shear viscosity of the surfactant from dog lungs.

Surface viscosity (eta S) was measured in the pulmonary lavage fluid obtained from 40 mongrel dogs. Two experimental methods were employed to determine surface viscosity: a) Fourt's "torsion pendulum" procedure; and b) the "viscous traction" viscosimeter. A satisfactory correlation (r = 0.88) between these two methods was obtained. The mean value for surface viscosity of the pulmonary lavage fluid was 3.8 X 10(-2) surface-poise (s.p.) with the torsion pendulum procedure, and 4.3 X 10(-2) s.p. with the viscous traction viscosimeter. The implications of surface viscosity in pulmonary mechanics is discussed, as well as the effects of blood plasma addition to the pulmonary lavage fluid. A significant increase of surface viscosity could be observed when blood plasma was added to the hypophase, in concentrations greater than 0.1%. This increase in surface viscosity might be of importance when related to the augmented respiratory work during the evolution of pulmonary edema.

Animals↗
PubMed1996

Nutritional antioxidants, red cell membrane fluidity and blood viscosity in type 1 (insulin dependent) diabetes mellitus.

The study was designed to evaluate whether the antioxidant nutrients selenium, vitamin A, and vitamin E are associated with alterations of blood viscosity in patients with insulin-dependent (Type 1) diabetes mellitus (IDDM). We assessed selenium concentrations in plasma and red blood cells (RBC), glutathione peroxidase activity in RBC, vitamin A and vitamin E, and the viscosity of whole blood and plasma in 20 patients with IDDM and 20 sex, age and body mass index-matched healthy controls. While selenium was not altered in plasma in IDDM, it was markedly decreased in RBC of IDDM (1.24 +/- 0.32 vs 0.92 +/- 0.38 mumol l-1, p = 0.006) correlating negatively with the elastic and viscous component of whole blood viscosity. Plasma viscosity increased with stage of retinopathy. Mean glutathione peroxidase activity in RBC was reduced in IDDM (5.78 +/- 0.77 vs 5.13 +/- 1.03 U gHb-1, p = 0.029). In IDDM with normal renal function (creatinine < or = 97.2 mumol l-1, no albuminuria) vitamin A was significantly reduced (1.26 +/- 0.62 vs 1.89 +/- 0.56 mumol l-1, p = 0.005). Vitamin A levels increased with impaired renal function. They strongly correlated with plasma creatinine (r = 0.86, p < 0.001) and plasma viscosity (r = 0.71, p = 0.001). However, in vitro experiments with different vitamin A plasma concentrations indicated that this particular correlation may not represent a causal one. No changes in vitamin E were found in IDDM. We conclude that reduced selenium concentrations in RBC contribute to impaired haemorheology in IDDM patients. Plasma viscosity was not affected by the plasma concentrations of vitamins A and E.

Adult↗
PubMed1997

Formation of plasma advanced glycosylation end products (AGEs) has no influence on plasma viscosity.

Plasma viscosity is mainly determined by large non-spherical proteins. In Type 1 diabetes mellitus, plasma viscosity increases with deterioration of diabetic control. Since protein glycation and formation of advanced glycosylation end products (AGEs) alter the structural and functional properties of proteins, AGEs might influence the rheological properties of plasma proteins. Therefore, we investigated the influence of plasma-AGEs on plasma viscosity in 34 normoalbuminuric diabetic patients (17 Type 1, 17 Type 2) with normal renal and liver function. In an additional experiment, 6 ml plasma of 9 healthy volunteers were incubated under sterile conditions for 14 days at 37.5 degrees C in the presence of 5.2 and 32.9 mmol l(-1) glucose. In diabetic patients, plasma-AGE levels were not correlated with plasma viscosity. Plasma-AGE levels in healthy controls (246 +/- 37 U ml[-1], mean +/- SD) were raised significantly (p<0.001) after the incubation at 37.5 degrees C (392 +/- 57 U ml[-1] and 552 +/- 58 U ml[-1], respectively). However, no difference was found in plasma viscosity pre- and post-incubation (pre-incubation: 1.25 +/- 0.04 mPas, post-incubation: 1.23 +/- 0.03 and 1.24 +/- 0.03, respectively). We conclude that there is no influence of plasma-AGEs on plasma viscosity.

Adult↗
PubMed1997

Viscosity and elasticity during collagen assembly in vitro: relevance to matrix-driven translocation.

In order to better understand the gelation process associated with collagen assembly, and the mechanism of the in vitro morphogenetic phenomenon of "matrix-driven translocation" [S.A. Newman et al. (1985) Science, 228, 885-889], the viscosity and elastic modulus of assembling collagen matrices in the presence and absence of polystyrene latex beads was investigated. Viscosity measurements at very low shear rates (0.016-0.0549 s(-1)) were performed over a range of temperatures (6.9-11.5 degrees C) in a Couette viscometer. A magnetic levitation sphere rheometer was used to measure the shear elastic modulus of the assembling matrices during the late phase of the gelation process. Gelation was detected by the rapid increase in viscosity that occurred after a lag time tL that varied between O and approximately 500 s. After a rise in viscosity that occurred over an additional approximately 500 s, the collagen matrix was characterized by an elastic modulus of the order of several Pa. The lag time of the assembly process was relatively insensitive to differences in shear rate within the variability of the sample preparation, but was inversely proportional to the time the sample spent on ice before being raised to the test temperature, for test temperatures > 9 degrees C. This suggests that structures important for fibrillogenesis are capable of forming at 0 degrees C. The time dependence of the gelation process is well-described by an exponential law with a rate constant K approximately 0.1 s(-1). Significantly, K was consistently larger in collagen preparations that contained cell-sized polystyrene beads. From these results, along with prior information on effective surface tension differences of bead-containing and bead-lacking collagen matrices, we conclude that changes in matrix organization contributing to matrix-driven translocation are initiated during the lag phase of fibrillogenesis when the viscosity is < or = 0.1 Poise. The phenomenon may make use of small differentials in viscosity and/or elasticity, resulting from the interaction of the beads with the assembling matrix. These properties are well described by standard models of concentrated solutions.

Animals↗
PubMed1999

Capillary electrophoresis of small solutes in linear polymer solutions: relation between ionic mobility, diffusion coefficient and viscosity.

Electrophoretic mobilities, mu, and diffusion coefficients, D, of a small ion (molecular weight 579) were determined in dependence on the viscosity, eta, of aqueous buffer solutions containing ethylene glycol, or polyethylene glycol (PEG) with average molecular weights of 400, 20000, 100000 or 2000000, respectively, as additives. The values for mu and D are inversely proportional to the viscosity for the solutions with small-sized additives (ethylene glycol and PEG400), in accordance to Walden's rule. In contrast, for the longest polymers the mobilities and the diffusion coefficients approximate the values observed for pure water, and are nearly independent of the viscosity. This result agrees with the model of fractional free volume and the obstruction theory. For solutions with equal viscosity, three ranges can be differentiated for mu and D in relation to the size of the additive: for small additives, on the one hand, and the long-chained polymers, on the other hand, the values for mu and D are nearly independent of the size of the additive. In contrast, a pronounced increase of mu and D is found with increasing polymer size in the molecular weight range between 20000 and 100000. The ratio mu/D, occurring in a number of expressions for the plate height contributions, exhibits a remarkably small change over the entire polymer size and viscosity range (between 1 and 7 cP) under consideration. Consequently, the separation efficiency, expressed by the plate number, is found to be nearly constant, and is independent of viscosity.

Diffusion↗
PubMed2002

Electroosmotic flow in capillary channels filled with nonconstant viscosity electrolytes: exact solution of the Navier-Stokes equation.

The partial differential equation describing unsteady velocity profile of electroosmotic flow (EOF) in a cylindrical capillary filled with a nonconstant viscosity electrolyte was derived. Analytical solution, based on the general Navier-Stokes equation, was found for constant viscosity electrolytes using the separation of variables (Fourier method). For the case of a nonconstant viscosity electrolyte, the steady-state velocity profile was calculated assuming that the viscosity decreases exponentially in the direction from the wall to the capillary center. Since the respective equations with nonconstant viscosity term are not solvable in general, the method of continuous binding conditions was used to solve this problem. In this method, an arbitrary viscosity profile can be modeled. The theoretical conclusions show that the relaxation times at which an EOF approaches the steady state are too short to have an impact on a separation process in any real systems. A viscous layer at the wall affects EOF significantly, if it is thicker than the Debye length of the electric double layer. The presented description of the EOF dynamics is applicable to any microfluidic systems.

Electrochemistry↗
PubMed2003

Intravenous immunoglobulin therapy results in post-infusional hyperproteinemia, increased serum viscosity, and pseudohyponatremia.

Intravenous immunoglobulin (IVIG) therapy is associated with rare reports of thromboembolic events and severe hyponatremia. We hypothesized that IVIG therapy may result in hyperproteinemia, increased serum viscosity, and pseudohyponatremia. We conducted a prospective observational study to evaluate the incidence of hyperproteinemia occurring after IVIG therapy and its relationship to serum sodium, viscosity, osmolality, and the serum osmolar gap. Eighteen IVIG infusions at a standard dose of 2 g/kg administered over 2-5 days were evaluated. Serum glucose, sodium, protein, viscosity, osmolality, and a calculated osmolar gap were obtained prior to therapy, 6 hr after the initiation of therapy, 24 hr after the conclusion of therapy, and on post-treatment day 10. Paired t-testing revealed a statistically significant increase in serum protein and viscosity and decrease in serum sodium and calculated osmolality 24 hr after the completion of IVIG therapy. The calculated serum osmolar gap increased insignificantly. In multivariate analysis, hyperproteinemia at the 6-hr time point predicted hyponatremia (P < 0.000), and hyperproteinemia at the 24-hr time point predicted both hyponatremia and increased serum viscosity (P = 0.024). These data demonstrate that increased serum viscosity occurs following IVIG therapy due to hyperproteinemia, and the rare hyponatremia reported is a pseudohyponatremia also due to hyperproteinemia.

Blood Viscosity↗
PubMed2005

Numerical simulation of the effect of solvent viscosity on the motions of a beta-peptide heptamer.

This report examines the effect of a decrease in solvent viscosity on the simulated folding behaviour of a beta-peptide heptamer in methanol. Simulations of the molecular dynamics of the heptamer H-beta3-HVal-beta3-HAla-beta3-HLeu-(S,S)-beta3-HAla(alphaMe)-beta3-HVal-beta3-HAla-beta3-HLeu-OH in methanol, with an explicit representation of the methanol molecules, were performed for 80 ns at various solvent viscosities. The simulations indicate that at a solvent viscosity of one third of that of methanol, only the dynamic aspects of the folding process are altered, and that the rate of folding is increased. At a viscosity of one tenth of that of methanol, insufficient statistics are obtained within the 80 ns period. We suggest that 80 ns is an insufficient time to reach conformational equilibrium at very low viscosity because the dependence of the folding rate of a beta-peptide on solvent viscosity has two regimes; a result that was observed in another computational study for alpha-peptides.

Computer Simulation↗
PubMed1991

Effect of nifedipine on oxygen delivery in patients with angina pectoris: relation between blood viscosity and hematocrit.

The effect of nifedipine on blood viscosity and hematocrit was investigated. Blood was sampled from eight patients with angina pectoris (mean age: 59 +/- 8 yr) treated with nifedipine (20-30 mg/day) for 5 months. Using a cone-plate type viscometer, blood viscosity was determined at the shear rates of 37.5 and 375 sec-1 at 37 degrees C. Hematocrit was also measured at the same time. Since the ratio of hematocrit to blood viscosity at a shear rate of 375 sec-1 can be considered to reflect oxygen delivery, this ratio (oxygen delivery index) was also calculated. Blood viscosity at a shear rate of 37.5 sec-1 was significantly (P less than .05) decreased by nifedipine treatment, but hematocrit and the blood viscosity at a shear rate of 375 sec-1 were not changed. The oxygen delivery index, however, was significantly (P less than .01) increased after the administration of nifedipine. These results suggest that oxygen delivery increased by the treatment with nifedipine and inhibited erythrocyte aggregation by decreasing blood viscosity at low shear rate.

Aged↗
PubMedDate not supplied

The dermal bioavailability of radiolabelled benzo[a]pyrene from acetone or from oils of differing viscosity, assessed by DNA and protein binding.

Tritium-labelled benzo[a]pyrene ([3H]BaP) was applied to mouse skin in acetone or mineral oils of differing viscosity. Epidermal DNA and protein were extracted after 24 or 48 h and the degree of adduct formation determined by the radioactivity present. When [3H]BaP was applied in acetone, the degree of DNA and protein binding was around 15-20 times greater than that observed when a low-viscosity oil was used as a vehicle. When applied in oils of differing viscosity, however, only a twofold difference was seen across the whole viscosity range (13.5 cSt* at 40 degrees C to 1665 cSt at 60 degrees C). From measurements made of urine and faecal radioactivity and from small-scale investigations using other routes of administration, it was clear that the grooming activity of the animals had a marked effect on skin absorption and macromolecular binding. It is possible that greater grooming activity with low-viscosity oils may explain why oil viscosity did not have a greater effect on binding levels, but further studies are needed to investigate this. These findings may have important implications in the interpretation of long-term skin painting studies and may assist in the interpretation of analytical data and short-term biological assays.

Acetone↗
PubMedDate not supplied

Factors affecting the bioavailability of benzo[a]pyrene from oils in mouse skin: oil viscosity, grooming, activity and its prevention.

In the main study, tritium-labelled benzo[a]pyrene ([3H]BaP) was added to oils of a wide range of viscosity (from 13.5 to ca. 8000 cSt at 40 degrees C) and these were applied once to mouse skin under conditions where grooming was either allowed or prevented. The binding of [3H]BaP to epidermal protein and DNA was assessed. In addition, some studies were conducted to investigate the effect of prior oil exposure on binding levels and to compare binding levels following single and multiple application. It was found in the main study that the binding of [3H]BaP to both DNA and protein was increased as the viscosity of the oil vehicle decreased. Whereas only a twofold difference in DNA binding was found between the lowest and highest viscosity oil vehicle if grooming was allowed, a 14-fold difference was seen if grooming was prevented. This was due to much higher binding levels with low viscosity oils when grooming was prevented. Protein binding showed similar results, although the difference between the grooming and non-grooming situations was slightly less. Whether grooming was prevented or not, both DNA and protein binding of [3H]BaP were found to be inversely proportional to the logarithm of viscosity of the oil vehicle, but when grooming was prevented, the slope for DNA binding was 10 times steeper than when it was permitted. Exposure of the skin to either high or low viscosity oils prior to the application of [3H]BaP in the same oil inhibited the binding to DNA but not to protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Relationship of dissolution rate to viscosity of polymeric solutions.

The influence of viscosity on the dissolution rate of benzoic acid in aqueous solutions of methylcellulose, hydroxypropyl cellulose, and guar gum was investigated. The viscosities were measured by capillary and rotational viscometers and were calculated from experimental diffusion coefficients by means of the Stokes-Einstein equation. The relationship of the dissolution rate to viscosity may be represented by a single curve. An equation is presented relating the dissolution rate of benzoic acid to solubility, diffusion coefficient, and viscosity for these nonionic viscosity-enhancing agents. To demonstrate that additional factors affect the dissolution rate, similar data were determined using solutions of xanthan gum, which is anionic. The electrical effect modified mass transport so the quantitative relationship of dissolution rate and viscosity was not the same as in the nonionic carbohydrate solution.

Benzoates↗
PubMed1977

Changes in blood viscosity and plasma proteins in carcinoma.

Blood viscosity and plasma protein concentrations were measured in 31 patients with a variety of visceral carcinomas. The mean whole blood viscosity was not elevated over normal controls because of a significantly lowered mean hematocrit. However, when hematocrit was eliminated as a variable by adjusting the hematocrit to 45%, the mean whole blood viscosity was significantly elevated in the group with carcinoma. Both the plasma viscosity and the tendency for red cell aggregation were significantly elevated. Since blood is a non-Newtonian fluid, and its viscosity increases markedly at low shear rates, these rheological abnormalities would be most important at the low shear rates characteristic of the venous circulation. It is suggested that these abnormalities in blood viscosity and red cell aggregation may be contributing to the high incidence of venous thromboembolism seen in patients with neoplastic.

Alpha-Globulins↗
PubMed1998

Echo-planar imaging relaxometry to measure the viscosity of a model meal.

A method for measuring noninvasively the viscosity of a polysaccharide model meal using the known relationship between relaxation times and polysaccharide concentration in solution in vitro is presented. The aim is to develop a method for monitoring digesta viscosity in vivo, using EPI to capture the motion of the gastrointestinal lumen. The transverse relaxation rate T-12 of locust bean gum solutions was calibrated against the zero-shear viscosity at 37 degreesC. Differences in viscosity were distinguished significantly using T-12 measurements. T-12 and viscosity were insensitive to exposure to gastric juice and changes in pH, and the model meal was well received by volunteers and provided good contrast in vivo in EPI images. Therefore it would be possible to use this method to monitor the changes in meal viscosity within the gastric lumen in vivo.

Echo-Planar Imaging↗
PubMed1981

Viscosity differences between various guar gums.

Guar gum from four industrial sources was investigated. The viscosity of two preparations of hydrated guar gum in the form of powdered flour and one granulate flour was measured at 22 degrees and 32 degrees C and pH 1.0 and pH 4.0. Viscosity measurements on wax-coated guar granules proved impossible but visual assessment indicated an extremely low viscosity in all conditions. These findings were compared with the ability of the equivalent of 5 g guar gum of the various preparations to modify the absorption of a 50 g liquid glucose load. The mean post-prandial blood glucose curve was not significantly different from the control situation after the incorporation of each preparation. Despite the granulate flour attaining a considerably lower viscosity than the powdered flour they were equally effective in significantly reducing the mean post-prandial insulin curve (area under the curve (0-180 min) reduced by 46 and 50% respectively). The wax-coated granules which achieved minimal viscosity caused significantly less reduction of post-prandial insulin levels (area under the curve reduced by 37%). The viscosity of guar gum upon hydration is of importance in assessing the efficacy of a preparation in clinical use.

Adult↗