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At least 1,423 records · Page 79Linked to original sources
PubMed1981

Comparative studies on viscosity and concentration of protein and hexosamine in pure pancreatic juice.

In order to investigate the cause of an increase in viscosity of pancreatic juice in patients with chronic pancreatitis, we performed comparative studies on voscosity and concentration of protein, hexosamine, three hydrolytic enzymes (amylase, chymotrypsinogen and lipase), calcium and gamma-Glutamyltranspeptidase in pure pancreatic juice. Pure pancreatic juice (PPJ) was obtained from seven control subjects, 10 patients with probable chronic pancreatitis and six patients with definite chronic pancreatitis by means of endoscopic retrograde catheterization of the papilla. Specimens were collected in ice-cooled tubes during the initial four-minute period and thereafter at two-minute intervals for 20 minutes after a rapid intravenous injection of secretin (Eisai Secrepan, 1 U/kg of body weight) and then at one-minute intervals for 10 minutes after a rapid intravenous injection of pancreozymin (Boots, 1 U/kg of body weight). It was demonstrated that the viscosity of PPJ was closely related to the concentration of hydrolytic enzyme protein, hexosamine and the presence of mucous substance and protein plugs.

Amylases↗
PubMed1980

Blood viscosity and the overnight fast.

A 12-hour overnight fast in 17 subjects did not result in a significant increase in blood viscosity, as occurs after a 24-hour fast. The usual preoperative fast does not therefore appear to have any adverse rheological effect. However, when it is necessary to prolong the fast, intravenous fluids should be given to prevent the expected increase in blood viscosity which then might have clinical effects as a result of decreased organ perfusion.

Adolescent↗
PubMed1998

Thickener viscosity in dysphagia management: variability among speech-language pathologists.

Twenty-three speech-language pathologists (SLPs) experienced with thickening liquids for dysphagia evaluations were asked to mix solutions comparable to their perceptions of nectar, honey, and pudding consistencies. The purpose of the study was to determine if these professionals were able to reliably repeat their relative perceptions of nectar, honey, and pudding over multiple mixings. Each mixed solution was analyzed using a viscometer to determine its actual viscosity. A replication reliability analysis indicated that the professionals were not consistent in their attempts to thicken liquids. Intrasubject results were somewhat better or more consistent than intersubject results. Results of this study indicate the need for a standard protocol during dysphagia management to ensure consistent viscosities across evaluation and treatment.

Deglutition Disorders↗
PubMed2003

Cell spreading on quartz crystal microbalance elicits positive frequency shifts indicative of viscosity changes.

Cell attachment and spreading on solid surfaces was investigated with a home-made quartz crystal microbalance (QCM), which measures the frequency, the transient decay time constant and the maximal oscillation amplitude. Initial interactions of the adsorbing cells with the QCM mainly induced a decrease of the frequency, coincident with mass adsorption. After about 80 min, the frequency increased continuously and after several hours exceeded the initial frequency measured before cell adsorption. Phase contrast and fluorescence microscopy indicated that the cells were firmly attached to the quartz surface during the frequency increase. The measurements of the maximal oscillation amplitude and the transient decay time constant revealed changes of viscoelastic properties at the QCM surface. An important fraction of these changes was likely due to alterations of cytosolic viscosity, as suggested by treatments of the attached cells with agents affecting the actin and microtubule cytoskeleton. Our results show that viscosity variations of cells can affect the resonance frequency of QCM in the absence of apparent cell desorption. The simultaneous measurements of the maximal oscillation amplitude, the transient decay time constant and the resonance frequency allow an analysis of cell adsorption to solid substratum in real time and complement cell biological methods.

Adsorption↗
PubMed2005

Acto-myosin cytoskeleton dependent viscosity and shear-thinning behavior of the amoeba cytoplasm.

The mechanical behavior of the human parasite Entamoeba histolytica plays a major role in the invasive process of host tissues and vessels. In this study, we set up an intracellular rheological technique derived from magnetic tweezers to measure the viscoelastic properties within living amoebae. The experimental setup combines two magnetic fields at 90 degrees from each other and is adapted to an inverted microscope, which allows monitoring of the rotation of pairs of magnetic phagosomes. We observe either the response of the phagosome pair to an instantaneous 45 degrees rotation of the magnetic field or the response to a permanent uniform rotation of the field at a given frequency. By the first method, we concluded that the phagosome pairs experience a soft viscoelastic medium, represented by the same mechanical model previously described for the cytoplasm of Dictyostelium discoideum [Feneberg et al. in Eur Biophys J 30(4):284-294 2001]. By the second method, the permanent rotation of a pair allowed us to apply a constant shear rate and to calculate the apparent viscosity of the cytoplasm. As found for entangled polymers, the viscosity decreases with the shear rate applied (shear-thinning behavior) and exhibits a power-law-type thinning, with a corresponding exponent of 0.65. Treatment of amoeba with drugs that affect the actin polymer content demonstrated that the shear-thinning behavior of the cytoplasm depends on the presence of an intact actin cytoskeleton. These data present a physiologic relevance for Entamoeba histolytica virulence. The shear-thinning behavior could facilitate cytoplasm streamings during cell movement and cell deformation, under important shear experienced by the amoeba during the invasion of human tissues. In this study, we also investigated the role of the actin-based motor myosin II and concluded that myosin II stiffens the F-actin gel in living parasites likely by its cross-linking activity.

Actins↗
PubMed2005

Viscosity-mediated motion coupling between pairs of trichobothria on the leg of the spider Cupiennius salei.

Arachnids and insects use long, thin hairs as motion sensors to detect signals contained in the movement of the surrounding air. These hairs often form groups with a small spacing of tens to hundreds of micrometers between them. For air oscillation frequencies of biological interest, the potential exists for viscosity-mediated coupling among hairs in a group affecting their response characteristics. Even a small diameter hair can, in principle, affect the flow field around it and the dynamics of the hairs in its neighborhood. The viscosity-mediated coupling between a pair of hairs is investigated here both experimentally and theoretically. The conditions for the existence of the coupling effect, and its magnitude as a function of relevant parameters, are determined. In the range of biologically relevant frequencies (30-300 Hz), viscous coupling between pairs of hairs is only very small in the case of the spider Cupiennius salei. Theoretical analysis points to the relatively large spacing between hairs (20 to 50 hair diameters) and the tuning of the hairs to the above-mentioned frequencies to explain the practical absence of coupling.

Air Movements↗
PubMed2000

Preventive magnesium supplement reduces ischemia-induced hearing loss and blood viscosity in the guinea pig.

The effect of magnesium (Mg) on ischemia-induced hearing loss was investigated in two groups of adult pigmented guinea pigs of either an optimal or suboptimal (physiologically high or low) Mg status maintained by different diets. Total Mg concentrations of the perilymph, cerebrospinal fluid, blood plasma and red blood cells were found to differ significantly between the two groups, as tested in a previous study. Local vascular impairment was produced by unilateral ferromagnetic thrombosis of cochlear blood vessels. Cochlear blood flow (CBF) and hearing function were measured using laser Doppler flowmetry and auditory brain-stem response audiometry, respectively. Ferromagnetic thrombosis resulted in significant reductions of the mean apical CBF in both experimental groups and of the mean basal CBF in the low Mg group compared to the contralateral ears. In the high Mg group, the basal CBF was not decreased. However, the laser Doppler signals revealed considerable interindividual variations and the differences found between the two experimental groups were not significant. In contrast, the hearing loss in the low Mg group was significantly higher than that in the high Mg group. A correlation was found to exist between the vascular impairment and the hearing threshold shift. In a separate series, we also tested the effect of Mg on hemorheology and found both the blood viscosity and blood viscoelasticity to be significantly lower in the high Mg group than in the low Mg group, depending on the shear rates tested. The present findings show that a preventive oral Mg supplement can significantly reduce the rate of ischemia-induced hearing loss and improve blood viscosity in the guinea pig.

Animals↗
PubMed2001

Laryngeal mucosa elasticity and viscosity in high and low relative air humidity.

In earlier work we showed that low relative humidity (RH) of inhaled air causes acoustic voice parameters such as jitter and shimmer to deteriorate. Other authors have shown negative effects on vocal efficiency. To explain these changes in the mechanical properties of the vocal folds, the effects of changes in RH of the air passing over microdissected mucosa of sheep larynges were studied. The dissected surface of the tissue specimen just touched Ringer solution and air of varying RH was blown over the specimen. The mucosa specimen was subjected to sinusoidal oscillations of length (strain) and the resulting force (stress) was measured. The gain and phase angle between the imposed strain and resulting stress were measured, and elasticity and viscosity were calculated. Two different air conditions were tested: air with high RH (100%) vs air with low RH (0%). Viscosity and stiffness increased significantly in both ambient conditions (P < 0.01). Dry dehydrating air resulted in a stiffer and more viscous cover than humid air (P < 0.001). These changes in mechanical characteristics may contribute to the effects on voice parameters described in earlier work.

Animals↗
PubMed2003

Platelet aggregation, blood viscosity and serum lipids in hypertensive and obese children.

UNLABELLED: A group of 35 patients (median age 15.5 years, range 8-17 years) with juvenile essential hypertension, 15 with body mass index (BMI kg/m(2)) <25 and 20 with BMI >25, as well as 35 age and sex matched controls (BMI <25 n=20; BMI >25 n=15) were investigated to study the role of hypertension and obesity, separately and in combination, on in vitro platelet aggregation, blood and plasma viscosity, plasma lipid concentrations and lipid peroxidation as well as nitric oxide (NO) production. Obese children (hypertensive and controls) had significantly higher concentrations of total cholesterol and triglycerides. The levels of high density lipoprotein (HDL)-cholesterol were lower in obese hypertensive children than their non-obese counterparts. There was a significant increase in platelet aggregation and a decrease in NO levels in hypertensive patients (obese and non-obese) reflecting a significant negative correlation (r=-0.553 and -0.530, n=35; P<0.01, respectively). However, an increased tendency to aggregation was also evident in obese normotensive patients. A significant positive correlation was observed between the platelet aggregation and BMI (r=0.501, n=35; P<0.01). Plasma free thiols were decreased in hypertensive children independent of their BMI. An increased lipid peroxidation and higher blood and plasma viscosity were found only in obese patients with hypertension. Multivariate analysis revealed significant interactions in the effects of obesity and hypertension on platelet aggregation and thiol oxidation. CONCLUSION: in obese children an increased platelet aggregation and oxidative insult contribute to the development of hypertension and to the promotion of vascular damage.

Adolescent↗
PubMed2002

Effects of systematic bolus viscosity and volume changes on hyoid movement kinematics.

Using ultrasonography with head and transducer stabilization, this study examined the effects of maximally controlled, systematic changes in bolus viscosity (thin juice-like, 7 cP; nectar-like, 243-260 cP; honey-like, 724-759 cP; spoon-thick, 2760-2819 cP) and volume (5, 10, 20, 30 cc) on hyoid kinematics in 31 healthy subjects (16 male, 15 female) in three age groups (20-39, 40-59, 60-79 years). Frame-by-frame hyoid displacements were tracked from digitized images of 612 swallows. Measures of movement durations, maximal amplitudes, total distances, and peak velocities were subjected to repeated measures multivariate analyses of variance with viscosity, volume, age, and gender as factors. Results showed that (1) spoon-thick swallows had the greatest preswallow gesture and total movement durations; (2) larger-volume swallows had significantly greater maximal amplitudes, forward peak velocity, and total vertical distance; (3) older subjects had longer start-to-max duration (though shorter preswallow gesture and total movement durations), greater maximal vertical amplitude, longer total vertical distance, and greater backward peak velocity than younger subjects; (4) males had greater values for all kinematic parameters except preswallow gesture, hyoid-at-max, and max-to-end durations. The results illustrate the importance of examining the interrelations among kinematic variables to better understand task accommodation and motor control strategies. The evidence also supports the concept of suprahyoid-infrahyoid functional adaptation and compensation in the healthy elderly.

Adult↗
PubMed2005

Gradual alteration of mitochondrial structure and function by beta-amyloids: importance of membrane viscosity changes, energy deprivation, reactive oxygen species production, and cytochrome c release.

Intracellular amyloid beta-peptide (A beta) accumulation is considered to be a key pathogenic factor in sporadic Alzheimer's disease (AD), but the mechanisms by which it triggers neuronal dysfunction remain unclear. We hypothesized that gradual mitochondrial dysfunction could play a central role in both initiation and progression of sporadic AD. Thus, we analyzed changes in mitochondrial structure and function following direct exposure to increasing concentrations of A beta(1--42) and A beta(25--35) in order to look more closely at the relationships between mitochondrial membrane viscosity, ATP synthesis, ROS production, and cytochrome c release. Our results show the accumulation of monomeric A beta within rat brain and muscle mitochondria. Subsequently, we observed four different and additive modes of action of A beta, which were concentration dependent: (i) an increase in mitochondrial membrane viscosity with a concomitant decrease in ATP/O, (ii) respiratory chain complexes inhibition, (iii) a potentialization of ROS production, and (iv) cytochrome c release.

Adenosine Triphosphate↗
PubMed2005

Effects of refractive index and viscosity on fluorescence and anisotropy decays of enhanced cyan and yellow fluorescent proteins.

The fluorescence lifetime strongly depends on the immediate environment of the fluorophore. Time-resolved fluorescence measurements of the enhanced forms of ECFP and EYFP in water-glycerol mixtures were performed to quantify the effects of the refractive index and viscosity on the fluorescence lifetimes of these proteins. The experimental data show for ECFP and EYFP two fluorescence lifetime components: one short lifetime of about 1 ns and a longer lifetime of about 3.7 ns of ECFP and for EYFP 3.4. The fluorescence of ECFP is very heterogeneous, which can be explained by the presence of two populations: a conformation (67% present) where the fluorophore is less quenched than in the other conformation (33% present). The fluorescence decay of EYFP is much more homogeneous and the amplitude of the short fluorescence lifetime is about 5%. The fluorescence anisotropy decays show that the rotational correlation time of both proteins scales with increasing viscosity of the solvent similarly as shown earlier for GFP. The rotational correlation times are identical for ECFP and EYFP, which can be expected since both proteins have the same shape and size. The only difference observed is the slightly lower initial anisotropy for ECFP as compared to the one of EYFP.

Bacterial Proteins↗
PubMed1975

Multiple myeloma in a patient with sickel cell anemia. Interacting effects on blood viscosity.

Described here is a case of multiple myeloma in a patient with sickle cell anemia. Viscometric studies were made by comparing the patient's whole blood, plasma and washed red blood cells with those of a normal control subject and a patient with sickle cell anemia. Results showed that the increased viscosity of the patient's whole blood as compared with that of the control patient with sickle cell anemia was mainly due to erythrocytic interaction with the circulating abnormal immunoglobulin. It is postulated that the increased frequency of vaso-occlusive crisis that occurred in our patient in the months before the diagnosis and treatment of multiple myeloma, was due to this cell-protein interaction with the resulting enhancement of whole blood viscosity and the sickling phenomena.

Adult↗
PubMed1984

4-Methylumbelliferyl-glycosides as fluorescence probes of sugar-binding sites on lectin molecules: spectral properties and dependence of fluorescence on polarity and viscosity.

The spectral properties of 4-methylumbelliferyl-glycosides (MeUmb-glycosides) were investigated in order to assess their usefulness as probes of the microenvironment of sugar binding sites on lectin molecules. It was shown that the abnormally high values for fluorescence polarization of free MeUmb-glycosides (from 0.07 to 0.251) were due neither to their molecular size nor to the blockade of their movement, but to the short lifetimes (less than 0.55 ns) of the excited state of these compounds. Working essentially with two MeUmb-monosaccharides and one MeUmb-disaccharide (MeUmb-alpha-D-galactopyranoside, MeUmb-beta-D-galactopyranoside, and MeUmb-2-acetamido-2-deoxy-3-O-(beta-D-galactopyranosyl)-beta-D- galactopyranoside) which were solubilized in various solvents, it was demonstrated that solvent polarity and viscosity definitely affected the fluorescence intensity of MeUmb-glycosides. A low-polarity medium reduced this intensity, and high viscosity enhanced it. The implications of these findings are discussed in relation to the variations in the fluorescence intensity of MeUmb-glycosides when these compounds were bound to lectins.

Binding Sites↗
PubMed1993

Effects of bolus volume, viscosity, and repeated swallows in nonstroke subjects and stroke patients.

This study examined the effects of bolus volume and viscosity and the variability of repeated swallows in ten stroke patients and ten age-matched nonstroke subjects. The ten stroke patients demonstrated single unilateral cortical (three subjects), subcortical (six subjects), or brainstem (one subject) infarcts on computed tomography or magnetic resonance imaging scans at three weeks post-ictus. All subjects underwent videofluoroscopic swallow studies in which seven temporal pharyngeal swallow measures were examined. Despite the dissimilarity in lesion locations, the swallow physiology in the stroke patients was relatively homogeneous, ie, no swallowing disorders severe enough to prevent oral intake. As bolus volume increased, pharyngeal delay time diminished in stroke patients, but not in nonstroke subjects. Increasing bolus volume affected three other pharyngeal swallow measures similarly in nonstroke and stroke subjects: laryngeal closure durations and cricopharyngeal (CP) opening durations increased and duration of tongue base contact to posterior pharyngeal wall decreased. On viscosity comparisons (liquid vs paste), both subject groups displayed longer duration of base of tongue contact to posterior pharyngeal wall. On paste swallows, nonstroke subjects had longer CP opening and lower swallow efficiency, whereas stroke patients did not. This study found no statistically significant learning/repetition effect for repeated swallows in either subject group, or both groups combined.

Adolescent↗
PubMed1979

The effects of suspending medium viscosity on erythrocyte deformation and haemolysis in vitro.

Fresh adult human erythrocytes were suspended in isotonic pH adjusted solutions containing various concentrations of Dextran T.500. The cells were subjected to uniform hydrodynamic shear stress in a Ferranti Shirley Cone and Plate Viscosimeter. The amount of lysis incurred at any given combination of exposure parameters was markedly affected by the viscosity of the suspending medium. Optical diffraction patterns obtained whilst the cells were undergoing shear demonstrated that cellular deformation was also a function of viscosity. Consequently, the distorted shape of the stressed cell may play a crucial role in the haemolytic process.

Adult↗
PubMed1983

Pressure effects on the apparent viscosity of artificial dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine membranes using intramolecular excimer probe.

Emission spectroscopy of intramolecular excimer probes allows the determination of 'equivalent viscosity' of membranes. While increasing the pressure on artificial membrane suspensions, variations in viscosity - essentially related to an increase in the order parameter in the membranes - are observed. In the case of mixed phospholipids, the effect of pressure is amplified, probably due to the existence of holes on the molecular scale between the two lipidic layers.

Dimyristoylphosphatidylcholine↗
PubMed1985

Human erythrocyte spectrin dimer intrinsic viscosity: temperature dependence and implications for the molecular basis of the erythrocyte membrane free energy.

We have determined experimentally the temperature dependence of human erythrocyte spectrin dimer intrinsic viscosity at shear rates 8-12 s-1 using a Cartesian diver viscometer. We find that the intrinsic viscosity decreases from 43 +/- 3 ml/g at 4 degrees C to 34 +/- 3 ml/g when the temperature is increased to 38 degrees C. Our results show that spectrin dimers are flexible worm-like macromolecules with persistence length about 20 nm and that the mean square end-to-end distance for this worm-like macromolecules decreases when the temperature is increased. This implies that the spectrin dimer internal energy decreases when the end-to-end distance is increased and that the free energy increase associated with making the end-to-end distance longer than the equilibrium value for the free molecules is of entropic origin. The temperature dependence of the erythrocyte membrane shear modulus reported previously in the literature therefore appears mainly to be due to temperature dependent alterations in the membrane skeleton topology.

Erythrocyte Membrane↗