SEARCH · Search PubMed

Results for “VISCOSITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources

PubMed2006

Viscosity effects in foam drainage: Newtonian and non-newtonian foaming fluids.

We have studied the drainage of foams made from Newtonian and non-Newtonian solutions of different viscosities. Forced-drainage experiments first show that the behavior of Newtonian solutions and of shear-thinning ones (foaming solutions containing either Carbopol or Xanthan) are identical, provided one considers the actual viscosity corresponding to the shear rate found inside the foam. Second, for these fluids, a drainage regime transition occurs as the bulk viscosity is increased, illustrating a coupling between surface and bulk flow in the channels between bubbles. The properties of this transition appear different from the ones observed in previous works in which the interfacial viscoelasticity was varied. Finally, we show that foams made of solutions containing long flexible PolyEthylene Oxide (PEO) molecules counter-intuitively drain faster than foams made with Newtonian solutions of the same viscosity. Complementary experiments made with fluids having all the same viscosity but different responses to elongational stresses (PEO-based Boger fluids) suggest an important role of the elastic properties of the PEO solutions on the faster drainage.

Journal Article↗

PubMed1980

Viscosity and density dependence during maximal flow in man.

Maximal expiratory flow curves were obtained from ten healthy subjects white breathing air and three other gas mixtures with different densities and viscosities. From these data, the magnitudes of the dependence of maximal flow on gas density and viscosity were obtained. The scaling laws of fluid mechanics, together with a model for the flow-limiting mechanism, were used to obtain a prediction of the relationship between the density dependence and the viscosity dependence of maximal flow. Although the data for individual subjects were too variable to allow a precise comparison with this prediction, the relationship between the mean density dependence and the mean viscosity dependence of all usbjects agreed with the theoretic prediction. This agreement supports the assumption, which is frequently made, that flow resistance rather than tissue visoelasticity is the dominant contributor to peripheral resistance. Information on the relationships between the pressure drop to the flow-limiting segment and flow, gas density and viscosity, and lung volume were also obtained.

Air↗

PubMed1995

Effects of oxygenation and the stress hormones adrenaline and cortisol on the viscosity of blood from the trout Oncorhynchus mykiss

Although the concentrations of the stress hormones adrenaline and cortisol in rainbow trout (Oncorhynchus mykiss) blood increase upon hypoxic exposure, the combined effects of these hormones and O2 lack upon fish blood rheology have not been investigated. Deoxygenated blood taken by caudal puncture exhibited lower viscosities than oxygenated samples at low shear rates, whereas the opposite was true at high shear rates. However, blood from cannulated trout had similar viscosities in its deoxygenated and oxygenated states. In the deoxygenated state, addition of adrenaline lowered viscosity at low shear rates and increased it at high shear rates, resembling the effects of deoxygenation observed in blood taken by venepuncture. In oxygenated blood on the contrary, no marked adrenaline effects were observed. In deoxygenated blood, addition of cortisol lowered viscosity at all measured shear rates compared with blood without cortisol. In oxygenated blood, however, no cortisol effects were observed. The viscosity effects observed in the presence of cortisol could not be attributed to concomitant changes in haematological variables, However, the effects in the presence of adrenaline manifested in deoxygenated 'cannula' blood and in uncannulated blood without added hormones appear to result from parallel increases in haematocrit and cell volume.

Journal Article↗

PubMed2003

Measuring Solution Viscosity and its Effect on Enzyme Activity.

In proteins, some processes require conformational changes involving structural domain diffusion. Among these processes are protein folding, unfolding and enzyme catalysis. During catalysis some enzymes undergo large conformational changes as they progress through the catalytic cycle. According to Kramers theory, solvent viscosity results in friction against proteins in solution, and this should result in decreased motion, inhibiting catalysis in motile enzymes. Solution viscosity was increased by adding increasing concentrations of glycerol, sucrose and trehalose, resulting in a decrease in the reaction rate of the H(+)-ATPase from the plasma membrane of Kluyveromyces lactis. A direct correlation was found between viscosity (eta) and the inhibition of the maximum rate of catalysis (V(max)). The protocol used to measure viscosity by means of a falling ball type viscometer is described, together with the determination of enzyme kinetics and the application of Kramers' equation to evaluate the effect of viscosity on the rate of ATP hydrolysis by the H(+)-ATPase.

Journal Article↗

PubMed2000

On-line dynamic measurement of blood viscosity, hematocrit and change of blood volume.

OBJECTIVE: To develop an on-line system for the measurement of blood viscosity and hematocrit. The dynamic changes of the macrovascular blood volumes, microvascular blood volumes and the total blood volume were observed by means of calculating from the testing result. METHODS: Applying traditional viscosity measurement principle and specific wavelength optic density measurement method, an on-line system for the measurement of blood viscosity and hematocrit was developed, and the A/D multifunctional board and the testing circuit were designed by ourselves. The system was validated by experiments both in vitro and in vivo. Therapeutic effects of hypertonic saline dextran solution (HSD) and Lactatic Ringer's solution at the early stage after burn-blast combined injury were compared by this method. RESULTS: The results showed that the system has attained the goal of the design. The changes of the blood viscosity and hematocrit could be detected effectively and continuously. The changes of macrovascular, microvascular and total blood volume could be calculated approximately. CONCLUSIONS: The system and the method can continuously on-line test the blood viscosity and hematocrit, and reveal the change and distribution of blood volumes more accurately and clearly in the therapy process by estimating changes of the macrovascular, microvascular and total blood volumes, respectively. It has confirmed that HSD treatment could increase blood pressure and attenuate tissue edema by significantly increasing total blood volume, improving macrocirculatory and microcirculatory blood volumes. This study suggested that it could be desirable to develop an experiment technique based on the method mentioned above.

Journal Article↗

PubMed1985

Alteration of red cell membrane viscoelasticity by heat treatment: effect on cell deformability and suspension viscosity.

The membrane shear elastic modulus (mu) and the time constant for extensional shape recovery (tc) were measured for normal, control human red blood cells (RBC) and for RBC heat treated (HT) at 48 degrees C. Three separate methods for the measurement of mu were compared (two used a micropipette and one employed a flow channel), and the membrane viscosity (n) was calculated from the relation n = mu. tc. The deformability of HT and control cells was evaluated using micropipette techniques, and the bulk viscosity of RBC suspensions at 40% hematocrit was measured. The shear elastic modulus, or "membrane rigidity", was more than doubled by heat treatment, although both the absolute value for mu and the estimate of the increase induced by heat treatment varied depending on the method of measurement. Heat treatment caused smaller increases in membrane viscosity and in membrane bending resistance, and only minimal changes in cell geometry. The deformability of HT cells was reduced: 1) the pressure required for cell entry (Pe) into 3 micrometers pipettes was increased, on average, by 170%; 2) at an aspiration pressure (Pa) exceeding Pe, longer times were required for cell entry into the same pipettes. However, when Pa was scaled relative to the mean entry pressure for a given sample (i.e, Pa/Pe), entry times were similar for control and HT cells. Bulk viscosity of HT RBC suspensions was elevated by approximately 12% on average (shear rates 75 to 1500 inverse seconds). These findings suggest that alteration of RBC membrane mechanical properties, similar to those induced by heat treatment, would most affect the in vivo circulation in regions where vessel dimensions are smaller than cellular diameters.

Adult↗

PubMed1987

Erythrocyte deformation in shear flow: influences of internal viscosity, membrane stiffness, and hematocrit.

The effect of shear force (depending on shear rate and viscosity of extracellular medium) and hematocrit of RBC suspension on RBC deformation was studied quantitatively using a cone-plate rheoscope with various kinds of cells, ie, partially hemolyzed (PH) cells, density-fractionated intact cells, and diamide-treated cells. The deformation index (DI) of ellipsoidally deformed cells was shown to be a function of beta gamma eta ex(eta ex/eta in)alpha, where gamma eta ex is applied shear stress, eta ex and eta in are external and internal viscosities, respectively, and alpha and beta are adjustable parameters related to the membrane viscoelastic properties. The increase of suspension viscosity at higher hematocrits (Hts) generally enhanced the ellipsoidal deformation of cells, in the same manner as increasing the suspending medium viscosity of a diluted cell suspension. The suppressing effect on cell deformation appeared above a certain Ht. When intact cells were mixed with glutaraldehyde-treated, hardened cells, the ellipsoidal deformation of intact cells was disturbed. The suppression of deformation probably occurred through disturbance of laminar flow-lines around intact cells.

Blood Viscosity↗

PubMed1989

Blood viscosity and hearing levels in the Caerphilly Collaborative Heart Disease Study.

Data from 342 men who are participants in the Caerphilly Collaborative Heart Disease Study were used to replicate a previous report of a significant relationship between measures of whole-blood viscosity and hearing levels in persons with sensorineural hearing impairment. In the unselected data, there were significant relationships between measures of whole-blood viscosity at high shear rates and hearing threshold levels at 2000 and 4000 Hz, even after accounting for the effects of age and socioeconomic group. In a subset of the data containing 124 persons selected on the basis of likely sensorineural hearing impairment, there were significant relationships between whole-blood viscosity and hearing level at all frequencies, with stronger effects at the higher frequencies. The data support the contention of a potentially important relationship between whole-blood viscosity and sensorineural hearing impairment.

Audiometry, Pure-Tone↗

PubMed1990

Blood viscosity and sensorineural hearing loss.

Two groups of 33 subjects each, one experimental and one control, matched one-to-one for age and occupation, were chosen from a large number of subjects who were covered by special insurance for annual medical control at our hospital. The periodical checkups included cardiovascular, nervous, and renal systems, as well as vision and hearing. In addition routine blood tests, including whole blood viscosity, were also performed. The experimental group consisted of subjects in whom a bilateral, slight, and unexplained sensorineural loss of hearing was detected in the routine audiological testing, without any known reason. In the control group, the routine hearing tests demonstrated normal hearing. The differences between the two groups were statistically significant in pure-tone threshold level and in speech discrimination score, when the test was performed at a -5dB signal-to-noise ratio. The results of the vestibular tests were normal in both groups. Hematocrit and whole blood viscosity were slightly but significantly higher in the experimental group if compared with the control group. The number of subjects with abnormal whole blood viscosity results was higher in the experimental group. The whole blood viscosity as the etiological factor responsible for the hearing deterioration is described.

Adult↗

PubMed2000

Blood viscosity and hematological changes during prolonged submergence in normoxic water of northern and southern musk turtles (Sternotherus odoratus).

Musk turtles (Sternotherus odoratus) can survive at least 150 days of submergence in normoxic water at 3 degreesC, during which time there are large increases in packed cell volume (PCV). We investigated the effects of submergence in normoxic water at 3 degreesC on the blood viscosity of musk turtles from northern (Massachusetts) and southern (Alabama) locales. Blood was collected from air-breathing turtles and after 20, 50, 100, and 150 days of submergence in normoxic water at 3 degreesC. Hematological responses to submergence were similar in the two groups, therefore the results were combined. Packed cell volume increased steadily above that of controls after 20, 50, 100, and 150 days of submergence. Hemoglobin concentration also progressively increased above that of controls after 20, 50, and 100 days of submergence but declined to near control values after 150 days. Blood viscosity increased with increasing PCV; however, blood viscosity of musk turtles appears less affected by PCV than is blood viscosity of mammalian species. As such, musk turtles appear to be able to maintain adequate blood flow to tissues while increasing the oxygen carrying capacity of the blood during prolonged submergence. However, after 150 days submergence, oxygen delivery should decrease due to a reduced oxygen carrying capacity of the blood and an increased resistance to blood flow, which may limit the length of time these turtles can remain viable during hibernation.

Alabama↗

PubMed2002

Electrophoresis in the presence of gradients: I. Viscosity gradients.

In many cases, the resolution provided by capillary electrophoresis systems approaches that predicted for diffusion-limited separations. Once all device-related sources of band broadening have been eliminated or minimized, only thermal diffusion remains. In principle, peaks can be sharpened using gradients of various system characteristics such as gel concentration, buffer viscosity and electric field. However, it is not clear whether this can actually increase the resolution of the system. In this article, we focus our attention on viscosity gradients and we examine both continuous and step-like variations. Our results indicate that the performance of electrophoretic systems cannot be improved by viscosity gradients. They may provide extra stacking, and thus improve the resolution, when the injection width is non-negligible. However, for the systems considered here, the best resolution is obtained when the viscosity is uniform and the stacking is entirely performed at injection. We conclude by discussing the link between these results, the fundamental laws of thermodynamics, the nature of the detection process and the importance of having nonlinear effects in nonuniform systems.

Electrophoresis, Capillary↗

PubMed1992

Conformational analysis of an opioid peptide in solvent media that mimic cytoplasm viscosity.

Many neuropeptides exert their action between the presynaptic vesicles and postsynaptic transmembrane receptors, crossing different layers of specialized cytoplasm. Biomimetic media usually employed to study bioactive peptides do not reproduce the physico chemical environment of cytoplasm--in particular, the high viscosity of this biological fluid. Here we describe a conformational study of a delta-selective opioid peptide, deltorphin I, at variable temperatures in several biocompatible media characterized by varying values of viscosity and dielectric constant. It was found that only viscosity, among these parameters, induces ordered conformations; that is, it acts as a conformational sieve. This finding suggests that the high viscosity of the intersynaptic fluid contributes, in addition to the membrane catalysis proposed by Schwyzer, in overcoming the so-called entropic barrier to the transition state of peptide-receptor interaction by selecting ordered conformations prior to receptor interaction. The folded conformer found in the 80:20 (v:v) DMSOd6/H2O cryoprotective mixture at 265 K has a shape consistent with those of rigid nonpeptidic opiates.

Amino Acid Sequence↗

PubMed1991

Influence of radiographic contrast media viscosity to flow through coronary angiographic catheters.

To assess the influence of viscosity on flow resistance, 4 clinically available contrast media were injected through 12 angiographic catheters of varying dimensions at 20 degrees and 37 degrees C. Seven cc of contrast was injected at a pressure of 200 PSI at 3cc/sec by Medrad Mark IV power injector. The pressure of injection through the manifold was recorded with an electronic pressure transducer. The lowest injection pressure at 37 degrees C occurred with Hexabrix. Differences in contrast media viscosity were apparent with catheters less than 6 French diameter. There were minimal differences in injection pressures with regard to the coronary curve tip configurations for any of the contrast agents. At 20 degrees C, Isovue had lower injection pressures than the other contrast agents. Injection through 5 French catheters demonstrated a greater than 1.5 atmosphere difference, especially between Omnipaque and Hexabrix. The difference in contrast media injection pressure was greater than 2 atmospheres between 8 French guiding and 8 French diagnostic catheters and between 5 French and 6 French diagnostic catheters and less than 2 atmospheres between 8 French and 6 French diagnostic catheters. Injection pressure differences greater than 1 atmosphere were not observed for catheters of the same French size at body or room temperature contrast injection. These data indicate that important temperature related viscosity differences between agents are present and confirm that the largest differences in contrast media are most apparent for the smallest diameter catheters. Given equivalent image opacification and hemodynamic and adverse effects, selection of a low viscosity contrast media theoretically provides an advantage during procedures using small diameter catheters or interventional procedures requiring contrast media visualization through reduced channels.

Angiography↗

PubMedDate not supplied

Effects of exercise on plasma viscosity in athletes and sedentary normal subjects.

To assess the immediate and long-term effects of exercise on factors regulating blood flow, we measured plasma viscosity (eta p) and plasma renin activity (PRA) in 17 trained runners and 16 sedentary healthy subjects before and 10 min after graded treadmill exercise. Resting eta p was lower in runners primarily because of significantly lower fibrinogen concentration. Compared to nonrunners with similar 24-h urine electrolyte excretion rates, runners were characterized by lower PRA at rest. In view of the overall correlation between heart rate and PRA before exercise, reduced adrenergic tone was probably a major factor contributing to the lower PRA in runners. After exercise, plasma viscosity and PRA exceeded control levels, and were similar in magnitude in runners and sedentary subjects. Changes in plasma viscosity were less than expected from the degree of hemoconcentration, primarily because enhanced fibrinolysis maintained fibrinogen level constant. To the extent that plasma viscosity affects viscous flow resistance, the results suggest that tissue perfusion and oxygen delivery rate at rest are greater in trained runners than in sedentary subjects, but these variables become similar after maximum exertion.

Adult↗

PubMedDate not supplied

Validation of viscosity measurements for canine hepatic bile.

This study developed the validated standards for a known viscosity method by obtaining consistent viscosity measurements with defined precision, reproducibility and sensitivity limits for canine hepatic bile. Size 75 Cannon-Manning semimicro viscometers yielded the most precise viscosity measurements. With the development of proper handling methods for fresh bile samples, a precision defined by a coefficient of variation of less than or equal to +/- 0.3% was obtained. To maintain viscometer constancy, the viscometers must be cleaned with chromic acid after each bile test and pass reproducibility tests using defined distilled water viscosity tests.

Animals↗

PubMed1975

Predicting subjective spreadability, viscosity, and stickiness.

Subjective spreadability, viscosity, and stickiness perceived with the fingers were predicted from fluid mechanics. The correlation coefficients of these predictions were 0.95 for spreadability, 0.95 for viscosity, and 0.09 for stickiness. The two important assumptions in the predictions were that spreadability and viscosity were perceived as shear stress and that stickiness was perceived as time. When the finger geometry was approximated as two parallel plates, the predictions only required rheological data for the Newtonian and non-Newtonian liquids used. While these liquids covered a range of 10-6 in apparent viscosity, large variations in other fluid properties such as density and surface tension were not studied.

Acrylamides↗

PubMed1977

Drug migration during drying of tablet granulations II: effect of binder solution viscosity and drying temperature.

The effect of binder solution viscosity and drying temperature on the integranular migration of propoxyphene hydrochloride was studied. Wet granulations containing the drug were prepared using binder solutions with viscosities ranging from 1 to 1000 cps. Temperature studies were conducted using granulations prepared with a 3-cps binder solution and dried at 40, 50, 60, 70, and 80 degrees. Drug migration decreased with increased binder solution viscosity, and insignificant migration occurred in granulations prepared with binder solutions having apparent viscosities above 90 cps. No significant effect on intergranular drug migration was observed within the drying temperature range studied. Tablets compressed from a granulation in which drug migration was high showed a greater tablet-to-tablet drug content variation than a granulation with lower migration, even though each dried granulation was thoroughly mixed before tableting.

Calcium Phosphates↗

PubMed1978

Inlfuence of high-viscosity vehicles on miotic effect of pilocarpine.

Gel formulations containing 2% pilocarpine hydrochloride were prepared from ethylene maleic anhydride, carbomer, hydroxyethylcellulose, polyacrylamide, ethylhydroxyethylcellulose, hydroxypropylcellulose, and poly(methylvinyl ether--maleic anhydride). The viscosity characteristics of each formulation were evaluated from rheograms developed at 37 degrees using a cone and plate viscometer. Single-point viscosities were determined at room temperature using a single-point rotational viscometer. Plastic viscosity parameters correlated to miosis durations in the rabbit following ophthalmic dosing of 50 microliters. Carbomer formulations varying in concentration between 0.9 and 5.0% (w/w) showed a discontinuous relationship when either yield value or plastic viscosity was plotted against miosis durations. At carbomer concentrations above 3%, miosis durations increased 1.5-fold. Above and below this range, plastic parameters did not correlate to miosis duration. It was reasoned that the increased duration was a consequence of the gel's increased yield value such that appreciable in vivo thinning of the gel does not take place with eyelid and/or eyeball movements. As a result, the residence time of the drug in the eye would be expected to increase, thus promoting an increased duration.

Animals↗