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PubMed1994

Effect of viscosity on oropharyngeal and esophageal emptying in man.

The effect of bolus viscosity on oropharyngeal and esophageal emptying is not known. We investigated this question in 38 healthy volunteers by measuring the transit of five semisolid boluses of varying viscosities across the oropharynx and the esophagus with the aid of scintigraphy. The studies were performed twice on consecutive days. The results show that oropharyngeal and esophageal emptying are reliably reproduced from day to day. Esophageal emptying was inversely related to bolus viscosity; however, oropharyngeal emptying was not influenced by bolus viscosity. We conclude that bolus viscosity has significant, but selective, effect on oropharyngoesophageal emptying.

Adult↗
PubMed1986

Correlation between umbilical vein blood flow and umbilical blood viscosity in normal and complicated pregnancies.

Umbilical vein blood flow (UVBF) was studied during the last 24 h before delivery using a combination of real-time and Doppler ultrasonic equipment in 64 normal and pathological pregnancies and the results were correlated with the values of whole blood viscosity taken from the umbilical vein after delivery. UVBF was reduced in the subgroup with chronic fetal distress (n = 14) (P less than 0.001) and the hypertensive pregnancies (n = 17) (P less than 0.05), whereas umbilical blood viscosity was increased only in the subgroup with chronic fetal distress (P less than 0.01) as compared with the normal pregnancies (n = 24). A significant positive correlation was observed between the umbilical blood viscosity and haematocrit values in all the groups of patients. UVBF and blood viscosity had a significant negative correlation in chronic fetal distress (P less than 0.001) and in hypertensive pregnancies (P less than 0.05), but not in normal or diabetic pregnancies (n = 9). Thus haemoconcentration leading to increased fetal blood viscosity may act as an aetiological factor in the reduction of UVBF in developing fetal distress.

Blood Viscosity↗
PubMed1977

Optimum viscosity of barium suspension for use in the double contrast barium meal.

The effect of viscosity of barium sulphate suspensions on coating was assessed by glass slides as in vitro, and the rat as in vivo models. It was found that below a certain viscosity (as measured by a cup viscometer) coating was impaired. As increasing viscosity is associated with increasing bubble retention and, eventually, when very high viscosities are reached, poor surface flow of suspension, it is recommended that the viscosity of the medium employed should be kept within a narrow range, approximately equal to 70% w/v Baritop, 80% Micropaque, 115% E--Z-paque, 150% Barosperse, or 200% HD 200.

Animals↗
PubMedDate not supplied

Decrease in whole blood viscosity in alloxan diabetic rabbits.

Whole blood and plasma viscosity of normal and alloxan diabetic rabbits were measured by means of cone in cone viscosimeters at different shear rates. Blood behaves like a non-Newtonian fluid, i.e. the viscosity is shear rate-dependent whereas plasma viscosity remains constant over the shear rate range employed, i.e. behaves like a Newtonian fluid. Blood viscosity was found to be statistically significantly decreased in the alloxan diabetic group in comparison to the control group. The decrease is attributed to a slight decrease in mean hematocrit and mean plasma viscosity of the diabetic animals. The possible mechanisms of these changes are discussed.

Animals↗
PubMedDate not supplied

Plasma and serum viscosity in Nigerian diabetics.

Relative plasma (RPV) and serum (RSV) viscosities were determined in 71 Nigerian diabetics, with and without hypertension, and compared with an age and sex matched normotensive non-diabetic control group. Viscosity was measured by a simple capillary viscometer. RPV and RSV were statistically significantly raised in diabetics compared with controls (p less than 0.001). RPV was 5.03% and RSV was 4.82% higher than non-diabetic values. There was no significant difference in either RPV or RSV due to sex. Also, no relation of RPV or RSV to age, duration of diabetes or type of treatment was identified. Plasma fibrinogen concentration correlated positively and significantly (r = 0.46; p less than 0.001) with RPV. However, whereas a significant rise was observed for total serum protein, albumin (p less than 0.001) and serum globulin concentrations (p less than 0.005), only the gamma-globulin fraction correlated significantly with RSV (r = 0.27; p less than 0.05). RPV was significantly raised in hypertensive diabetics compared with normotensive diabetics (p less than 0.02) but there was no significant difference in RSV of diabetics attributable to hypertension. Our findings show that fibrinogen predominantly contributes to the increased plasma viscosity while the gamma-globulin made the greatest contribution to serum viscosity in Nigerian diabetics. We suggest that abnormally raised plasma and serum viscosities, by contributing to disturbances in normal blood flow and metabolism, may play an essential role in the development of both micro-circulatory disorders and hypertension in some Nigerian diabetics.

Adult↗
PubMed2001

Magnesium ions and barium coating of colonic mucosa: is it a simple question of viscosity?

The aim of the present study was to verify whether magnesium-induced increase of barium coating of the colonic mucosa is specifically due to the increase of barium suspension viscosity. One hundred sixty-one patients scheduled for double-contrast barium enema (DCBE) were randomised in one group of 23 patients (control group, CG), and three groups of 23 pairs (G1, G2 and G3), i.e. 138 patients. The DCBE was performed with standard technique using a barium suspension with dynamic viscosity of 280 cPs (CG), or with viscosity increased to 320 cPs (G1), 2500 cPs (G2) or 3200 cPs (G3), by extemporaneous addition of MgSO4 1, 2 or 3 g in one member of the pair, Na2SO4 1, 4.2 or 8 g in the other one. Three radiologists evaluated on an ordinal scale mucosal coating and free fluid. In all magnesium subgroups barium coating was better than in CG (p < 0.008), the highest value being obtained in G2. No difference was observed as regards free fluid. Inside paired groups, mucosal coating was more effective in magnesium than in sodium members (p < 0.0002). Viscosity of barium suspension being equal inside each group, this effect must be attributed to magnesium-specific interactions with additives of the barium suspension inducing events other than viscosity changes.

Aged↗
PubMed1993

The effect of Leboyer delivery on blood viscosity and other hemorheologic parameters in term neonates.

OBJECTIVE: This study was done to compare postnatal alterations in blood viscosity, hematocrit value, plasma viscosity, red blood cell aggregation, and red blood cell deformability in term neonates undergoing both early umbilical cord clamping and delivery according to the Leboyer method. STUDY DESIGN: The umbilical cords of 15 healthy, term infants were clamped within 10 seconds of birth (early cord clamping), and 15 infants delivered according to the Leboyer method were placed on the mother's abdomen, and the umbilical cords were clamped 3 minutes after birth. Hemorheologic parameters were studied in umbilical cord blood at 2 hours, 24 hours, and 5 days from the time of delivery. RESULTS: The residual fetal placental blood volume decreased from 45 +/- 8 ml/kg (x +/- SD) after early cord clamping to 25 +/- 5 ml/kg after delivery by the Leboyer method. After Leboyer-method delivery, the hematocrit value rose from 48% +/- 5% at birth to 58% +/- 6% 2 hours after delivery, 56% +/- 7% at 24 hours, and 54% +/- 8% after 5 days. Blood viscosity in the Leboyer-method group increased by 32% within the first 2 hours but did not change significantly during the following 5 days. Plasma viscosity, red blood cell aggregation, and red blood cell deformability were not affected by the mode of cord clamping. CONCLUSIONS: Delivery by the Leboyer method leads to a significant increase in blood viscosity as a result of increasing hematocrit value, whereas other hemorheologic parameters are similar to those of infants with early cord clamping.

Blood Viscosity↗
PubMed1984

Kinetics of carbonic anhydrase catalysis in solvents of increased viscosity: a partially diffusion-controlled reaction.

Steady-state kinetic studies of the bovine carbonic anhydrase B-catalyzed hydration of CO2, dehydration of HCO3-, and hydrolysis of p-nitrophenylacetate were made in glycerol/water solvents of increased viscosity in order that the effect of diffusion-control on the substrate association reactions could be determined. The minimum association rate constants (kmin = V/(Km[E0])) were obtained at low substrate concentrations. The esterase activity did not depend upon the solvent viscosity. However, both the CO2 hydration and HCO3- dehydration reactions depended upon the solvent viscosity consistent with partial diffusion control. Thus both chemical activation and diffusion control processes contribute to the observed kmin. In low-viscosity aqueous solutions both hydration and dehydration are largely controlled by chemical activation. However, at higher viscosities, equal to that found in the interior of the erythrocyte, both reactions are largely diffusion controlled. This result can be interpreted to mean that carbonic anhydrase is a highly evolved enzyme that has approached its maximum efficiency. The extent of diffusion control observed rules out H2CO3 as a significant reactant with the enzyme. Several models that yield minimum steric requirements for access of substrate to the active site are examined. Minimum steric constraints are less for the smaller CO2. The slower esterase reaction is not influenced by diffusion.

Animals↗
PubMed1981

Elevation of apparent membrane viscosity in ovarian granulosa cells by follicle-stimulating hormone.

Continued exposure of cultured granulosa cells to follicle-stimulating hormone (FSH) induced: (i) a rise in apparent membrane microviscosity, as reflected by an increase in fluorescence polarization of the lipid-soluble probe, 1,6-diphenyl-1,3,5,-hexatriene; and (ii) a progressive decline in the cyclic AMP response to renewed challenge with the same hormone. Both changes were reduced or prevented by pretreatment of the cells with oleic or linoleic acid, agents which reduce membrane viscosity, but not by elaidic or palmitic acid which increase the rigidity of membrane lipids. Other agents that inhibited FSH-induced changes in membrane fluidity (gonadotropin-releasing hormone, actinomycin D and cycloheximide) also prevented desensitization to FSH. Cyclic AMP and cyclic GMP derivatives did not mimic the effects of FSH on apparent membrane viscosity or desensitization. Changes in membrane fluidity are unlikely to be the sole cause of desensitization since (i) pretreatment of the cells with fatty acids that increase lipid viscosity did not induce desensitization to FSH, and (ii) desensitization of granulosa cells to lutropin and prostaglandin E2 by exposure to the homologous hormone was not attended by increased membrane viscosity. The experiments described provide the first example of a hormonally induced increase in the target cell apparent membrane viscosity.

Animals↗
PubMed1976

The effect of cholesterol on the viscosity of protein-lipid monolayers.

The addition of cholesterol to a layer of lipids in a membrane structure is generally believed to result in an increase in the viscosity of the layer. We have shown that cholesterol and two other monolayer-forming lipids markedly decrease the viscosity of a serum albumin monolayer at the decane-water interface, a model membrane system. However, when the protein monolayer already has a surface active lipid component present, the effect of added cholesterol depends upon the other substance. When the albumin monolayer contains tristearin, added cholesterol increases the viscosity. When the lipid is octadecanol, cholesterol decreases the viscosity. The dependence of the change in interfacial viscosity due to cholesterol upon the original composition of the interfacial layer may be useful for characterizing the composition of layers of unknown composition, e.g. some natural membranes.

Cholesterol↗
PubMed1989

Influence of infusate viscosity on intestinal absorption in the rat. An explanation of previous discrepant results.

Previous studies of the influence of increased luminal viscosity on intestinal absorption have yielded conflicting results ranging from no effect to a marked diminution. We measured the absorption of three probes (carbon monoxide, [14C]warfarin, 5.5 mM glucose) from a saline infusate or from saline containing 0.6% guar, which yielded a 20-fold increase in viscosity. Two animal models were used: (a) conscious nonlaparotomized rats with chronically implanted cannulas and (b) anesthetized laparotomized rats. In the anesthetized laparotomized rats, absorption was independent of perfusate viscosity. In the conscious nonlaparotomized rats, the absorption of each of the three probes was significantly greater than in the anesthetized laparotomized rats and increased viscosity caused a 60%-70% decrease in the clearance of the three probes. In anesthetized laparotomized rats, we have shown that fluid moves with laminar flow, and increased infusate viscosity cannot further reduce luminal stirring (or absorption). In conscious, nonlaparotomized rats, laminar flow is disrupted by normal gut motility causing better luminal stirring. Such stirring is inhibited by a viscous infusate resulting in decreased absorption. We conclude that the conflicting results seen in previous studies can be attributed to the model used. In conscious animals where luminal stirring was good, a viscous infusate caused decreased absorption.

Animals↗
PubMed1994

The effect of a shear load on the viscosities of 10 vinyl polysiloxane impression materials.

The viscosities of 10 vinyl polysiloxane impression materials with and without the effect of a shear load were studied. Samples of each impression material were divided into two groups. An initial shear load of 5.12 rpm was applied to group A samples for 10 seconds. No shear load was applied to group B samples during the same interval of time. The viscosities of two groups of samples were compared at 60 seconds. Results indicated that there were statistically significant differences among the group A or B samples of the impression materials. There were no statistically significant differences between the group A and B samples of five impression materials. The group A samples displayed significantly lower viscosities than group B samples for two impression materials. The group A samples also displayed significantly higher viscosities than group B samples for three impression materials. It was concluded that the effect of a shear load had no consistent effect on the viscosities of a group of vinyl polysiloxane impression materials.

Analysis of Variance↗
PubMed1983

Effect of viscosity on enzyme-ligand dissociation. II. Role of the microenvironment.

A theoretical treatment, describing a novel viscosity effect on decomposition of enzyme-ligand complexes, recently appeared (Somogyi et al., 1978). From this approach emerged a mechanistic picture of the manner in which increased viscosity lowers the value of the decomposition rate constant. A refined version of this model is presented herein. The analysis is extended to the molecular microenvironment ultimately responsible for mediating the "viscosity effect." Consideration is given to two major factors: (1) the role of viscosity in attenuating the excess chemical energy and (2) the statistical features of the microviscosity. In view of spatiotemporal inhomogeneity in the liquid structure, the concept of averaged microviscosity is introduced to parametrize the enzyme-ligand recombination probability. Quantitative predictions are consistent with models of liquid structure and with results from enzyme studies. The "viscosity effect" may contribute to substrate compartmentation in organized multi-enzyme systems in vivo.

Enzymes↗
PubMed1989

Kinetics of the lactate dehydrogenase reaction in high-viscosity media.

The effect of the medium viscosity on kinetics parameters of lactate dehydrogenase reaction was studied. The viscosity increase results in a sharp decline in the catalytic rate for both the pyruvate reduction and lactate oxidation reactions. It is shown that the catalytic step and its associated conformational motions is the only step which is considerably retarded when the viscosity increases. The reaction is not sensitive to changes in the dielectric properties of the medium. An inverse power function observed between the rate constant and viscosity cannot be explained by the theory of absolute reaction rates. However, it can easily be interpreted on the basis of the Kramers theory dealing with the transition over the activation barrier as a diffusional motion in the field of random forces. The influence of the medium's viscosity on the kinetic parameters indicates the existence of strong coupling between the dynamics of the solvent and the conformational motions of the protein molecule, which are correlated with the catalytic step.

Animals↗
PubMed1991

Relation between blood viscosity and hematocrit in rabbits subjected to repeated treatment with endotoxin.

Blood rheology was studied in rabbits repeatedly treated with endotoxin at a dose of 0.1 mg administered 3 times, at intervals of 3 days. On the 7th day after the last endotoxin injection, blood was sampled 3 times from the femoral artery under anesthesia using pentobarbital sodium. Blood viscosity was determined at a shear rate of 150 s-1 at 37 degrees C using a cone-plate viscometer. Plasma fluidity was determined using the filtration method. Hematocrit and whole blood viscosity showed no significant differences between the untreated rabbits (Group A) and rabbits treated with endotoxin (Group B). Plasma fluidity was significantly lowered in Group B. Whole blood viscosity correlated well with hematocrit in Group A, but there was no correlation in Group B. The ratio of hematocrit to whole blood viscosity, which is considered to be the index of oxygen delivery from the blood rheological point of view, indicated no significant difference between the two groups. The optimal hematocrit to oxygen delivery, however, was higher in Group B than in Group A. These data suggest that the high hematocrit rather becomes an advantage to oxygen delivery in endotoxicosis because the hematocrit-viscosity relation is disturbed.

Animals↗
PubMed1986

Viscosity dependence of the solute quenching of the tryptophanyl fluorescence of proteins.

We have studied the viscosity dependence of the acrylamide quenching of the fluorescence on the internal tryptophan residues in cod parvalbumin and ribonuclease T1, as well as the model systems. N-acetyl-L-tryptophanamide and glucagon. For the latter systems, the apparent rate constant, kq(app), for acrylamide quenching shows a typical diffusion-limited behavior. For parvalbumin and ribonuclease T1, however, the viscosity dependence of kq(app) is quite different. There is little change in the kq(app) values on increasing the bulk viscosity from 1 to 10 cP (by addition of glycerol), but a further increase from 10 to 100 cP results in a significant reduction in the kq(app). Both an unfolding mechanism and a quencher penetration mechanism are considered to explain the results. Only the penetration mechanism is found to be consistent, and our data are interpreted as indicating that the rate-limiting step for quenching goes from being that of diffusion through the protein matrix, at low viscosity, to diffusion through the bulk solvent, at high viscosity. By also considering the Kramers' relationship in fitting our data, we are able to obtain insight regarding the coupling between internal fluctuations in the structure of the protein and motion of the bulk solvent. For parvalbumin and ribonuclease T1, the internal dynamics are found to be very weakly coupled to the bulk.

Acrylamide↗
PubMed1990

Modulation of egg-white lysozyme activity by viscosity intensifier additives.

The activity of egg-white lysozyme was measured in the presence of carbohydrate additives in the reaction medium. These additives show a significant affinity for water. They depress water activity and increase the viscosity of the medium. Solute-solvent interactions in aqueous solutions of the additives are characterized by properties such as the intrinsic viscosity, Huggins constant apparent molar volume and hydration number. It was found that, despite the lowering of enzyme activity when the concentration of additive is increased, the behavior remains Michaelian and neither modification of Km nor inhibition by excess substrate is observed. On the other hand, the effect of the viscosity of the medium on enzyme activity was determined. This effect is independent of the nature of the additive at high viscosities (greater than 4 mPa s-1) for which enzyme activity is very low and appears to vary according to the kind of additive in dilute solution at low viscosities (less than 2 mPa s-1).

Animals↗
PubMed1993

Pellagra--increased viscosity of extracellular matrix.

Pellagra is the result of increased viscosity of extracellular matrix (ECM). The skin changes in pellagra localize at sites of sun exposure or trauma because the mediators which are released cannot diffuse from the area. Edema is reported as the first clinical and microscopic change. Changes in the ECM are not directly visible. Increased viscosity of ECM in the gastrointestinal tract would decrease absorption of fluid and nutrients from the bowel resulting in diarrhea. In the tongue the excess ECM viscosity holds water producing swelling. The effect of climate and seasons relates to the increased demand for ECM repair on sunlight exposed areas. Infections increase the severity of pellagra by requiring increased tissue repair. Local infections are often unusually severe. Infections have a greater inflammatory component at sites of high ECM viscosity. Nicotinic acid reverses the neurologic and gastrointestinal changes of pellagra in 24 h. This suggests a simple rapid mode of action. Nicotinic acid plays a major role in tissue respiration which is essential for tissue repair and degradation of glycosaminoglycans. Altering ECM viscosity is a method of modulating inflammation, immunity, and normal tissue physiology.

Central Nervous System↗