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PubMed2002

Viscosity of two-dimensional suspensions.

Over a range of conditions, lipid and surfactant monolayers exhibit coexistence of discrete solid domains in a continuous liquid. The surface shear viscosity, mu(s), of such monolayers collapses onto a single curve: mu(s)/mu(so) = [1-(A/A(c))](-1), in which mu(so) is the viscosity of the liquid phase, A is the area fraction of the solid phase measured by fluorescence microscopy, and A(c) is a critical solid phase fraction. This scaling relationship is directly analogous to that of three-dimensional dispersion of spheres in a solvent with long-range repulsive interactions, with area fraction replacing volume fraction.

Lipids↗
PubMed2000

Dielectric relaxation of water and water-plasticized biomolecules in relation to cellular water organization, cytoplasmic viscosity, and desiccation tolerance in recalcitrant seed tissues.

To understand the relationship between the organization of cellular water, molecular interactions, and desiccation tolerance, dielectric behaviors of water and water-plasticized biomolecules in red oak (Quercus rubra) seeds were studied during dehydration. The thermally stimulated current study showed three dielectric dispersions: (a) the relaxation of loosely-bound water and small polar groups, (b) the relaxation of tightly-bound water, carbohydrate chains, large polar groups of macromolecules, and (c) the "freezing in" of molecular mobility (glassy state). Seven discrete hydration levels (water contents of 1.40, 0.55, 0.41, 0.31, 0.21, 0.13, and 0.08 g/g dry weight, corresponding to -1.5, -8, -11, -14, -24, -74, and -195 MPa, respectively) were identified according to the changes in thermodynamic and dielectric properties of water and water-plasticized biomolecules during dehydration. The implications of intracellular water organization for desiccation tolerance were discussed. Cytoplasmic viscosity increased exponentially at water content < 0.40 g/g dry weight, which was correlated with the great relaxation slowdown of water-plasticized biomolecules, supporting a role for viscosity in metabolic shutdown during dehydration.

Biopolymers↗
PubMed1979

Serial changes in coagulation and viscosity during sickle-cell crisis.

Coagulation activity and whole-blood viscosity were measured in the steady state, and serially during painful crisis, in eight patients with sickle-cell anaemia. Platelet and coagulation activation occurred in the steady state and became more pronounced early in crisis. Whole-blood viscosity increased during crisis in parallel with plasma fibrinogen. Similar changes were found in a parallel study of 20 patients with localized bacterial or viral infection who did not have sickle-cell anaemia. Reports of platelet activation, hypercoagulability, and hyperviscosity during painful crisis therefore reflect secondary changes arising from vascular stasis, precipitating infection, and an acute-phase protein reaction. Although secondary, these changes may contribute to vascular occlusion by an additive effect in vessels already partially occluded by sickled cells.

Adolescent↗
PubMed1983

Effect of ethanol on blood viscosity and erythrocyte flexibility in healthy men.

The effects of ethanol on blood rheology were studied in twelve healthy male volunteers each serving as his own control. They drank 1.5 g (33 mmol) of ethanol per kg body weight in fruit juice over 2.5 h under controlled laboratory conditions. Blood and plasma viscosity, packed cell volume and erythrocyte flexibility were measured before and 3, 12 and 16 h after ethanol ingestion began, and again during a second session equal volumes of fruit juice were consumed. Packed cell volume varied similarly after ingestion of juice with or without ethanol. Blood viscosity remained almost unchanged after ethanol, while drinking of juice caused an initial decrease followed by a significant (P less than 0.05) increase from 4.04 (SEM 0.06) to 4.32 (SEM 0.18) mPa.s. The juice also caused more significant fluctuations in erythrocyte rigidity (whole blood) than ethanol, which had parallel but insignificant effects. We conclude that a blood ethanol concentration of 28 mmol l-1 failed to induce any marked changes in blood rheology.

Adult↗
PubMed2005

Prognostic impact of low-shear whole blood viscosity in hypertensive men.

BACKGROUND: The role of blood viscosity as a marker for discriminating cardiovascular risk in essential hypertension remains uncertain. The aim of this study was to assess whether whole blood viscosity (WBV) could be useful in assessing cardiovascular risk in men with a first diagnosis of hypertension. DESIGN: A total of 331 middle-aged men with newly diagnosed essential hypertension (age at entry 40-64 years, average blood pressure 151/95 mmHg) underwent low-shear-rate (0.94 s(-1)) and high-shear-rate (94.5 s(-1)) WBV determination and were then followed for a mean of 4.8 +/- 3 years (range 0-12 years). RESULTS: Cardiovascular event rates in the bottom, middle and top tertiles of the distribution of low-shear WBV were 1.10, 2.13 and 4.43 per 100 patient-years, respectively (log-rank test, P < 0.001). After taking into account several established cardiovascular risk factors in a Cox survival analysis, a raised low-shear WBV conferred an increased risk for cardiovascular events (top vs. bottom tertile hazard ratio = 3.42, 95% confidence interval = 1.4-8.4, P = 0.006; middle vs. bottom tertile hazard ratio = 2.25, 95% confidence interval = 0.9-5.6, P = 0.09). The independent association between high-shear-rate WBV and cardiovascular events bordered statistical significance (P = 0.07). Inclusion in the survival model of low-shear-rate resulted in a significantly greater chi(2) improvement (P < 0.05) than inclusion of high-shear-rate WBV. CONCLUSIONS: In hypertensive men, an increased WBV at low shear rate is a predictor of cardiovascular events independently from the effect of several traditional risk factors. Low-shear WBV is a better discriminator of cardiovascular risk than high-shear WBV.

Adult↗
PubMed1982

Motility initiation of quiescent spermatozoa from rat caudal epididymis: effects of pH, viscosity, osmolality and inhibitors.

Non-motile spermatozoa freshly extruded from the rat caudal epididymis can be initiated to full motility immediately after diluting with 0.9% NaCl. The motility initiation was dependent on the pH, viscosity and osmolality of diluent. Diluent with pH 4 to 8 could optimally initiate the motility. Osmolality of most diluents suitable for the initiation was between 130 to 600 mOsm/kg. The motility initiation was inhibited by Hg2+ greater than Cu2+ greater than Cd2+, chlorpromazine, Triton X-100 and SDS. The following compounds showed essentially no inhibitory effect: EGTA, chlortetracycline, calcein, ruthenium red, phloridzin, myo-inositol and carnitine. The findings suggested that spermatozoa were kept in quiescence in the cauda epididymis not by the pH, osmolality, viscosity, myo-inositol, carnitine, Ca2+ or K+ of the caudal epididymal fluid. It was also suggested that motility initiation did not involve Ca2+, calmodulin and transport of Ca2+ or glucose across sperm membrane.

Animals↗
PubMed1988

Effects of macromolecular adjuvants on the duration of prilocaine. Experimental studies on the effect of variations of viscosity and sodium content and of inclusion of adrenaline.

Sodium hyaluronate (HA) and dextran (Dx) of different molecular weights and concentrations were used as adjuvants to prilocaine for studies of the duration of infraorbital nerve block in the rat (IONB) and spinal anaesthesia in the mouse (SA). A positive relation was found between duration of block on the one hand and the concentration as well as the molecular weight of the adjuvant on the other. A direct relation was found between the duration of block and the viscosity of the anaesthetic solution. Low-sodium-content solutions of plain prilocaine caused a markedly prolonged duration of the most profound degrees of IONB as compared to medium- or high-sodium-content solutions, while no differences between the solutions were found for the weakest intensity of IONB studied or for SA. Solutions of low-sodium-content containing prilocaine and HA were associated with significant prolongations of IONB and SA as compared to corresponding solutions of medium- or high-sodium content. Inclusion of adrenaline, 5 micrograms/ml, in solutions containing prilocaine and Dx significantly prolonged the duration of the most profound degrees of IONB and of SA. By contrast, the inclusion of adrenaline in solutions containing prilocaine and HA did not prolong the duration of IONB or SA. It is concluded that modulations of the viscosity of local anaesthetic solutions by the addition of macromolecular compounds strongly affect the duration of peripheral and central nerve blocks in experimental animals. A further prolongation is accomplished by reducing the sodium content of the solutions and, in the case of Dx-containing solutions, by inclusion of adrenaline in the anaesthetic solution. The possible mechanisms of these actions are discussed.

Adjuvants, Anesthesia↗
PubMed1982

Dynamics of the spin transition in camphor-bound ferric cytochrome P-450 versus temperature, pressure and viscosity.

The kinetics and equilibrium of the low-spin (LS) to high-spin (HS) transition in camphor-bound ferric cytochrome P-450 have been measured versus temperature, pressure and viscosity at selected pH and KCl concentration. The results cannot be described by a single set of delta E degrees, delta V degrees and delta S degrees, since these parameters change with the solvent conditions. A three-state model can explain a large bulk of the data but it is clear that other substates are involved. The activation energy and volume are practically zero for the high to low spin transition, while the low to high spin transition parameters vary from 20 kJ/mol to 80 kJ/mol for delta E psi and from 5 cm3/mol to 80 cm3/mol for delta V psi. The observed relaxation time could be varied from about 10 ms to more than 1000 s by changing temperature, pressure and viscosity. Both kLH and kHL rate coefficients scale roughly as 1/eta, indicating that the slow spin change involves protein motions which are influenced by the solvent viscous forces.

Binding Sites↗
PubMedDate not supplied

The effects of vasectomy on viscosity, pH and volume of semen in man.

The effects of vasectomy on seminal viscosity, volume and pH have been investigated in freshly emitted semen of 21 healthy men before operation and three months later. Viscosity and the pH range were decreased significantly, but the decrease of the seminal volume was not significant. Reasons of changes have been discussed.

Adult↗
PubMed1995

Miniature endplate current kinetics at the mouse neuromuscular junction: effects of temperature and medium viscosity.

The time course of miniature endplate currents (MEPCs), derived by extracellular focal recording, was studied in the mouse neuromuscular junction at different temperatures and medium viscosities, and in eserine-treated endplates. At low temperatures (6-10 degrees C), almost the whole MEPC decay is exponential and the rising phase is not significantly modified by the channel closing process. At physiological temperatures (38-40 degrees C), the early part of the decay is much slower than the later part and the rising phase is made shorter and smaller by channel closing, showing that the channel opening and channel closing processes overlap remarkably. Even at physiological temperatures, however, the late part of the MEPC decay shows an exponential time course. At high temperatures the channel opening process has low temperature sensitivity and slows down when bath solution viscosity is increased, suggesting that at high temperatures channel opening kinetics may mainly be controlled by the time course of acetylcholine diffusion. The lower limit of conformational change rate leading to channel opening was estimated at 10 degrees C (4400 s-1). Experimentally recorded MEPCs were mathematically simulated to obtain a quantitative description of the processes controlling MEPC generation. Mathematical simulation further suggests that (i) acetylcholine diffusion kinetics may affect the onset rate of MEPCs without, however, being rate-limiting; and (ii) partial, transient acetylcholinesterase inhibition operated by acetylcholine may explain the low temperature sensitivity exhibited by the onset rate of MEPCs at high temperatures.

Acetylcholine↗
PubMed1990

Correlation of umbilical cord whole blood viscosity and the presence of fetal distress at birth: a mathematical modelling study.

This study was designed to investigate the relationship between umbilical cord blood viscosity and clinical parameters such as maternal parity, maternal smoking, mode of delivery, sex of infant and the incidence of fetal distress at birth using mathematical modelling. The results demonstrated vaginal delivery, male infants, infants of primigravidas and low cord whole blood viscosity at a high shear rate were covariables and were associated with an increased incidence of fetal distress and low Apgar scores.

Adult↗
PubMed1980

The internal viscosity of the human erythrocyte may determine its lifespan in vivo.

Young red cells obtained by high-speed centrifugation of a normal blood sample had an MCHC of 31.7 g/dl which corresponds to an internal viscocity of about 9 cP. Old red cells from the same blood sample had an average MCHC of 37.5 g/dl which is equivalent to a mean internal viscosity of about 54 cP. This increased internal viscocity of old cells must result in a prolonged transit time through the narrow channels of the splenic microvasculature and consequently an increased probability of contact with a phagocytic macrophage. This probability of contact increases as the internal viscosity of the cell is further increased and may represent one of the major factors associated with the detection and subsequent elimination of senescent cells by the spleen.

Erythrocyte Aging↗
PubMedDate not supplied

Blood viscosity in horses with colic.

Whole blood viscosity (WBV) was measured on six healthy horses and ten horses presented for colic surgery. A Wells-Brookfield cone-and-plate microviscometer at 6 rpm was used to determine WBV and WBV was adjusted for packed cell volume (PCV). The ten colic horses were divided into two groups: five horses that died or were euthanatized (group 1) and five horses that were discharged after surgery and medical therapy (group 2). The mean WBV for each group was compared using analysis of variance followed by Duncan multiple-range tests. Mean WBV of group 2 (5.81 +/- 1.48 centipoise [cp]) and normal horses (7.1 +/- 2.3 cp) was significantly (P less than 0.01) lower than group 1 (17.15 +/- 5.71 cp). This preliminary trial shows that horses that died or were euthanatized had a significantly higher WBV than horses surviving. Since viscosity was adjusted for PCV, the differences may represent changes in other factors such as fibrinogen, rouleaux formation, red blood cell deformability, PaO2, or intracellular calcium ion concentration. Thus, increases in WBV in horses with colic may indicate severely compromised regional perfusion that may lead to significant tissue damage. In this preliminary study, it appears that WBV may be a prognostic aid in horses with colic.

Analysis of Variance↗
PubMed1986

A comparison of the effect of viscosity on the precorneal residence of solutions in rabbit and man.

The precorneal drainage of radiolabelled solutions containing polyvinyl alcohol (PVA) or hydroxypropyl methylcellulose (HPMC) have been measured in rabbit and man by gamma scintigraphy. Concentration of the polymers was varied to produce solutions with a viscosity range between 10.2 and 102 mPas. Solution drainage was faster in man than in the rabbit with a more pronounced effect of viscosity. Significant retardation of drainage in man was noted at the higher polymer concentrations (0.9% HPMC or 5.85% PVA).

Adult↗
PubMed1987

The influence of viscosity on the migration of chloramphenicol and 4-hydroxybenzoic acid through glycerogelatin gels.

Migration of chloramphenicol and 4-hydroxybenzoic acid from solutions in 1-octanol into Glycerol Suppository Base, BP and soft gelatin capsule shells is reported. Rates of migration through the gels, quantified in terms of diffusion coefficients, are given. An electron spin resonance probing technique was used to determine the microscopic viscosity. The latter, rather than the bulk viscosity, was shown to be the major rheological influence on the rate of diffusion.

Chloramphenicol↗
PubMed1987

Determination of the apparent failure viscosity of tablets.

Quantitative differences in the plasticity of several direct compression excipients were found to be distinguishable using normalized work of failure determinations. New parameters were developed to characterize the importance of changes in strain rate application during a diametral crushing test. Failure viscosity was found to have a similar sensitivity to normalized work of failure measurements and was also able to distinguish small changes in plastic behaviour. In cases where it is not possible to measure tablet deformation during tablet crushing, failure viscosity determinations could provide an alternative method for characterizing differences in deformation behaviour.

Chemistry, Pharmaceutical↗
PubMed2006

Effect of viscosity on instilled perfluorocarbon distribution in rabbit lungs.

The effect of viscosity on the distribution of perfluorocarbon instilled into the lungs for liquid ventilation was investigated. Perfluorocarbon (either perfluorodecalin or FC-3283) was instilled into the trachea during ventilation at a constant infusion rate of 40 ml/min and radiographic images were obtained at 30 frames/s. Image analysis was performed and the homogeneity index of the distribution was computed for images at the end of inspiration of each breath to evaluate the evolution of perfluorocarbon distribution during filling. The higher viscosity perfluorocarbon (perfluorodecalin) resulted in a more homogeneous distribution. This was attributed to perfluorodecalin's higher propensity to form liquid plugs in large airways and to those plugs leaving behind a thicker liquid layer as they propagated through the lungs.

Animals↗
PubMed1997

Pulmonary airway reopening: effects of non-Newtonian fluid viscosity.

This paper considers the effects of non-Newtonian lining-fluid viscosity, particularly shear thinning and yield stress, on the reopening of the airways. The airway was simulated by a very thin, circular polyethylene tube, which collapsed into a ribbon-like configuration. The non-Newtonian fluid viscosity was described by the power-law and Herschel-Buckley models. The speed of airway opening was determined under various opening pressures. These results were collapsed into dimensionless pressure-velocity relationships, based on an assumed shear rate gamma = U/(0.5 H), where U and H are the opening velocity and fluid film thickness, respectively. It was found that yield stress, like surface tension, increases the yield pressure and opening time. However, shear thinning reduces the opening time. An increased film thickness of the non-Newtonian lining fluid generally impedes airway reopening; a higher pressure is needed to initiate the airway reopening and a longer time is required to complete the opening process.

Airway Resistance↗