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At least 1,063 records · Page 59Linked to original sources
PubMed1980

The effect of improvement in diabetic control on plasma and whole blood viscosity.

Rheological studies were made on the blood of 12 diabetic patients after a period of poor diabetic control (HbA1 12.6 +/- 0.7% (mean +/- SD); mean home capillary blood glucose level 11.7 +/- 1.2 mmol/l), and after at least three months of improved control (HbA1 9.1 +/- 0.4%, p < 0.01; mean home capillary blood glucose level 9.2 +/- 0.6 mmol/l). There were significant decreases in plasma fibrinogen levels (4.1 +/- 0.6 to 3.7 +/- 0.6 g/l, p < 0.01), plasma viscosity (1.31 +/- 0.1 to 1.25 +/- 0.04, p < 0.001), and whole blood viscosity at low (22.8 +/- 2.7 to 20.2 +/- 2.9, p < 0.01) and high shear rates (3.4 +/- 0.2 to 3.1 +/- 0.2, p < 0.01). Ten diabetics with clinically evident complications were matched with diabetics of similar age, sex, duration and current control of diabetes. There were no significant differences in plasma or whole blood viscosities between the two groups. Hyperviscosity in diabetes seems strongly related to hyperglycaemia and to be influenced by the quality of diabetic control.

Adolescent↗
PubMed1981

Effects of guar on plasma viscosity and related parameters in diabetic children.

Ten diabetic children supplemented their normal diets with 0.45 g/kg/day guar gum for 4 weeks. They experienced a decrease in (1) plasma fibrinogen, (2) insulin requirement, (3) serum osmolality and (4) plasma viscosity; and an increase in serum albumin and total serum protein concentrations. The decrease in plasma viscosity, which was statistically significant, depended on the increase of albumin and the decrease of fibrinogen and may have some significance to the development of diabetic microangiopathy. The sequence of events eventually leading to a decrease of plasma viscosity is possibly mediated by gip and glucagon, consecutively.

Adolescent↗
PubMed1987

Haemodilution therapy in ischaemic stroke: plasma concentrations and plasma viscosity during long-term infusion of dextran 40 or hydroxyethyl starch 200/0.5.

In 21 patients with ischaemic strokes we have monitored plasma viscosity, total plasma concentration, numeric average molecular weight (Mn), and weight average molecular weight (Mw) of Dextran 40 (dextran) and hydroxyethylstarch 200/0.5 (HES) during 10 days of treatment (days 1-4, 2 X 500 ml; days 5-10, 1 X 500 ml). Plasma concentrations of dextran increased during the first 4 days (8.3 mg X ml-1 on the first day to 18.0 mg X ml-1 on the fifth day), reached an apparent steady state of 17.2 mg X ml-1 during the next 6 days, and declined subsequently with a half-time (t1/2) of 4.03 days. After ten days treatment Mn and Mw were shifted towards higher values. Plasma viscosity increased from 1.26 mPas to 1.69 mPas on Day 10 (p less than 0.01) and was linearly correlated with the total plasma concentration of dextran (p less than 0.001; r = 0.88). Total plasma concentrations of HES averaged 11.7 mg X ml-1 on Day 1 and 12.4 mg X ml-1 on Day 5. The molecular weight distribution did not change during the infusions but decreased in comparison with the administered solution. Plasma viscosity fell from 1.40 mPas to 1.30 mPas at Day 10 (p less than 0.05) and was not related to the concentration of HES. The haemodiluting effect, as indicated by a decrease of the haematocrit, was 22% and 16.8% for dextran and HES respectively. These data suggest several advantages of HES compared with dextran in haemodilution therapy of ischaemic stroke.

Aged↗
PubMed1976

Red cell aggregation in blood flow. II. Effect on apparent viscosity of blood.

The apparent viscosity of blood strongly increases at low shear in rotational viscometers, this phenomenon is based on the reversible formation of red cell aggregates. The magnitude of this increase strongly depends on the hematocrit value, on plasma viscosity and lastly on the microrheological properties of the aggregates. The independent measurement of the microrheological behavior and the effects on viscosity allows a detailed analysis of the hemodynamic effects of red cell aggregates under defined flow conditions in vivo. The comparative analysis shows that the conventional viscometry strongly underestimates the rheological differences between normal and pathologically intensified aggregation. Based on detailed analysis under defined flow conditions in vitro, the biological significance of viscometric results and the hemodynamic relevance of red cell aggregates are discussed.

Adolescent↗
PubMed1990

Neonatal polycythaemia: effect of partial dilutional exchange transfusion with human albumin on whole blood viscosity.

Haematocrit (HCT) and viscosity of whole blood were measured in ten polycythaemic hyperviscous newborn infants both before and after dilutional partial exchange transfusion with 5% albumin. This was performed in order to evaluate the effect on the lowering of HCT and whole blood viscosity. Mean umbilical HCT values decreased from 68.7% before, to 54.4% post transfusion. This decrease in HCT and viscosity was highly significant (P less than 0.001). Safety and lack of complications make human albumin solution superior to human plasma for exchange transfusion in neonatal polycythaemia.

Blood Proteins↗
PubMed1983

Transport in QSAR VIII. The influence of viscosity on transport rate constants in two-phase systems organic solvent-water.

In the system cyclohexane-water transport rate constants and partition coefficients of nine sulfonamides are determined at six temperatures. Kinematic viscosities of the organic and aqueous layer are determined at the same temperatures. Experimentally bilinear relationships between transport rate constants and partition coefficients are obtained in good agreement with theory. According to this theory convection and diffusion are important features in the overall transport process. Using the experimental data, the influence of viscosity on transport rate constants is established and expressed in terms of the relationships between maximum transport rate constants and viscosities. These relationships correspond with laminar flow at both sides of the interface.

Biological Transport↗
PubMed1988

Hypocholesterolemic action of chitosans with different viscosity in rats.

The relationship between hypocholesterolemic efficacy and average molecular weight of chitosan was studied in rats fed a cholesterol-enriched (0.5%) diet. Several chitosan preparations with a comparable degree of deacetylation but differing widely in average molecular weight, as demonstrated by viscosity, almost completely prevented the rise of serum cholesterol at the 5% dietary level. At the 2% level, chitosans with viscosities at both extremes exerted a comparable cholesterol-lowering action. The glucosamine oligomer composed mainly of three to five aminosugar residues was not effective. The results indicate that the hypocholesterolemic action of chitosans is independent of their molecular weight within the tested viscosity range.

Animals↗
PubMedDate not supplied

Effects of posture on plasma and serum viscosity.

This study demonstrates the importance of defining normal reference population ranges for P- and S-viscosity with respect to posture. The normal ranges determined for P-viscosity are not acceptable as a reference range for a hospitalized population that is predominantly in a supine position. Mean percentage changes of P- and S-viscosity in the recumbent posture as compared to the same population in the upright posture were 7.51 and 5.88, respectively.

Adult↗
PubMed2001

Intrinsic viscosity of bead models for macromolecules and bioparticles.

A new method based on the fractal dimension dependence of the hydrodynamic radius is proposed for calculation of the intrinsic viscosity of bead models. The method describes properly the viscosity increment except for elongated structures such as linear aggregates and ellipsoids. It is expected to be useful for very compact structures, for which the volume correction does not improve the results calculated by the modified Oseen tensor. The results obtained for the viscosity increment lie between the volume corrected ones and those determined by the cubic substitution procedure. They are close to the values recalculated from the falling velocities of the models analyzed.

Biophysical Phenomena↗
PubMed1999

[Corneal endothelial protection in phacoemulsification of high risk eyes with cornea guttata. Intra-individual comparison of 2 visco-elastic substances of different viscosity and molecular size].

BACKGROUND: We compared the endothelial protective function of two hyaluronic acid viscoelastics (Healon GV, Provisc) of different molecular weight and viscosity during phakoemulsification in high-risk eyes. MATERIALS AND METHODS: This prospective, randomized, single-masked clinical trial in 60 eyes was characterized by an intraindividual comparison. For better demonstration of the endothelial protective function provided by the viscoelastics, only patients with bilateral cornea guttata were included. In addition to corneal thickness, central endothelial cell counts, anterior chamber flare, visual acuity and intraocular pressure were recorded preoperatively and postoperatively on the first day and 1-2 weeks after surgery. RESULTS: No differences were observed between the endothelial cell counts in either eye. In contrast, eyes treated with Provisc had a statistically significant higher increase of corneal thickness. Transient corneal decompensation was also noticed only in three eyes of the Provisc group. CONCLUSION: The results do not support the assumption of generally better protection of the corneal endothelium by viscoelastics with lower viscosity compared to viscoelastics with higher viscosity.

Corneal Diseases↗
PubMed2002

Cell ageing for 1 day alters both membrane elasticity and viscosity.

This study was designed to focus on the influences of ageing on membrane elasticity and membrane viscosity. The method used was that of postfusion red blood cell oscillation, since this does not require contact between the cells and a mechanical device to apply reproducible forces to the membrane. Freshly drawn human red blood cells were compared with cells from the same donors drawn 24 h earlier and stored at 20 degrees C. The measurements of the oscillation's first pump event time constant and the first swell phase duration revealed no significant changes between fresh and aged cells. Geometrical cell parameters alone were insufficient to characterise changes in the mechanical membrane properties, since some did not vary significantly whereas others did. On the other hand, measurement of the rates of change of geometrical parameters showed that both the membrane elasticity and viscosity modules were increased after the ageing period. Elasticity and viscosity influences could be separated because the durations of the two phases of the cell oscillations differ by three orders of magnitude. Further evidence is provided that the measurement of mechanical membrane characteristics of aged red blood cell must incorporate measurements of membrane surface properties rather than cell volume properties.

Cellular Senescence↗
PubMed1997

Elevation of plasma viscosity induces sustained NO-mediated dilation in the hamster cremaster microcirculation in vivo.

We studied whether a flow-independent increase of luminal wall shear stress (WSS) could dilate hamster arterioles in vivo and which endothelial mediators are potentially involved. To this end the plasma viscosity was elevated by exchanging blood for dextran-erythrocyte solution thereby augmenting WSS. Diameters of small and large arterioles as well as red blood cell velocities were measured before and after exchange of blood for solutions of identical haematocrit containing either high- (HMWD) or low-molecular weight dextran (LMWD). The potential role of endothelial autacoids was investigated by local application of the NO-synthase inhibitor NG-nitro-L-arginine (L-NNA), the inhibitor of cyclooxygenase, indomethacin (3 microM), or the K+-channel blocker, tetrabutylammonium (TBA, 0.1 mM) to assess the potential effects of EDHF. HMWD (n = 11 animals) increased plasma viscosity by 64 +/- 3% and dilated arterioles of all branching orders (A1-A4) significantly [by 24 +/- 3% (A1-A2) and 32 +/- 3% (A3-A4)]. This dilation compensated fully for the calculated initial increase of WSS. LMWD (n = 6) did not affect plasma viscosity or arteriolar diameters. Tissue treatment with L-NNA (30-300 microM, n = 12) substantially diminished the HMWD-induced dilation in small arterioles (A3-A4; to 13 +/- 3%; P<<0.05) and virtually abolished it in large ones (A1-A2). Consequently, the calculated WSS increased significantly in these arterioles (by 31 +/- 5%). TBA combined with L-NNA (n = 4) did not reduce further the remaining dilation. Indomethacin (n = 6) had no effect on HMWD-induced dilation. We conclude that an increase of WSS induces a mainly NO-mediated arteriolar dilation. This dilation occurs in all arteriolar branching orders and is of sufficient magnitude to compensate for the initial WSS-increase. Thus, any elevations of WSS fulfil the requirement for a signal to change diameter along the arteriolar tree in a coordinated manner. The fully compensating dilation which we observed indicates that WSS is a controlled variable. It does, however, raise questions as to its role as a continuous endothelial stimulus.

Animals↗
PubMed2005

Role of viscosity and permeability of the erythrocyte plasma membrane in changes in oxygen-binding properties of hemoglobin during diabetes mellitus.

Changes in viscosity and permeability of the plasma membrane and conformation of erythrocyte hemoglobin hematoporphyrin were found in patients with diabetes mellitus. The decrease in oxygen binding and increase in deoxyhemoglobin concentration during diabetes mellitus were accompanied by changes in viscosity and permeability of the membrane for Na+, H+, Ca2+, and K+. Our results suggest that oxygen-binding properties of hemoglobin depend on viscosity and permeability of the erythrocyte plasma membrane.

Calcium↗
PubMed1992

Effect of viscosity and iodine concentration of nonionic radiographic contrast media on coronary arteriography in patients.

To assess the influence of viscosity and iodine concentration, three matched and standardized left coronary arteriograms were obtained in 20 patients using iopamidol (Isovue-370), ioversol (Optiray-320), and iohexol (Omnipaque-350). The order of contrast media was randomized and the administration of contrast was double-blinded. Quantitative densitometric angiographic evaluation of the coronary angiograms was performed in addition to independent operator qualitative assessment. The injection volume of iopamidol (5.4 +/- 1.0 ml) was slightly but significantly less than that of ioversol and iohexol (5.6 +/- 1.0 ml, 5.7 +/- 1.0 ml, both p less than 0.05). The calculated iodine concentration was also lower for ioversol (1.7 +/- 0.32 gm) than for iopamidol (1.98 +/- 0.35 gm) and iohexhol (1.9 +/- 0.35 gm, both p less than 0.05). There were significantly lower contrast syringe injection pressures for ioversol (6.6 +/- 0.8 atm) than for iopamidol (7.5 +/- 0.9 atm) and iohexol (7.2 +/- 1.1 atm, both p less than 0.05). The quantitative densitometric analysis failed to demonstrate significant differences among the contrast media with respect to image density parameters for any individual agent. All coronary angiograms were deemed of diagnostic quality. The data in this study indicated that although differences in iodine concentration exist among the three agents, operator compensation with more rapid contrast delivery (higher volume) and lower viscosity (lower injection pressure) produced equivalent image opacification during coronary angiography. Given the same incidence of adverse hemodynamic and clinical effects, selection of a low viscosity media theoretically provides an advantage during procedures using small diameter catheters or interventional procedures requiring contrast visualization through reduced catheter lumina.

Contrast Media↗
PubMed1982

Whole blood viscosity in preeclampsia.

Whole blood viscosity was measured in 41 patients with preeclampsia and in 51 normotensive control subjects. The mean viscosity in the preeclamptic group had a highly significant elevation (t = 9.752, p less than 0.001, at a shear rate of 0.1 sec-1 and t = 4.223, p less than 0.001, at a shear rate of 100 sec-1). The slower shear rate gave the better discrimination between the two groups as only four patients with preeclampsia had a value within 1 SD of the mean of the control group. It is suggested that the measurement of whole blood viscosity may be clinically useful in the management of patients with preeclampsia.

Blood Pressure↗
PubMed1986

Effect of the acute phase reaction on blood viscosity after infrainguinal arterial bypass.

A new method of determining apparent blood viscosity at low shear rates using a porous bed viscometer has been validated in an experimental study of canine blood altered by isovolemic hemodilution. The data confirm the ability of the technique to detect the non-Newtonian behavior of blood at higher hematocrit and fibrinogen values. The technique was then employed in a limited clinical study of nine patients undergoing infrainguinal vascular reconstruction to evaluate the effect of operation and the associated increase in serum fibrinogen levels, resulting from the acute phase reaction, on blood viscosity. Although there was a substantial change in serum glycoprotein levels, the concurrent relative decrease in red cell mass after operation resulted in a decrease in whole blood viscosity. These findings support the beneficial effect of moderate hemodilution as a means of compensating for the potentially detrimental effects of the acute phase reaction on blood rheology.

Animals↗
PubMed1978

Influence of viscosity of enzymatic reactions studied with glucoamylase of Aspergillus niger.

Viscosity can be interpreted in terms of transport of momentum and, therefore, it should influence the kinetics of enzyme reactions. A theory, developed by Somogyi and Damjanovich ((1975) J. Theor. Biol. 51, 393--401), is based on this idea. Transport of momentum must always be accompanied by the transport of mass and this second influence of viscosity is a limiting factor for fast reactions in the liquid phase. A third aspect is, that the chemical potentials of the components of viscous solutions are altered. This paper reports experiments concerning the influence of the viscosigens (compounds that increase the viscosity of solvents), alginate, sucrose, and maltose on the kinetic behaviour of glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3). The observed invariance of V and the decrease of Km are explained by the increase of chemical potentials and restriction of momentum transport.

Aspergillus niger↗
PubMed1985

The effects of dietary omega-3 polyunsaturated fatty acids on erythrocyte membrane phospholipids, erythrocyte deformability and blood viscosity in healthy volunteers.

We have examined, in normal subjects, the effects of a daily dietary supplement of fish oil concentrate ('maxEPA'), providing 3 g of omega-3 fatty acids, on erythrocyte membrane phospholipids, erythrocyte deformability and blood viscosity. After 3 weeks, incorporation of C20:5 omega 3 into erythrocyte phosphatidyl choline (PC) was greater compared to phosphatidyl ethanolamine (PE) and phosphatidyl serine (PS). After 6 weeks, there was no further increase in total erythrocyte C20:5 omega 3, but its distribution amongst phospholipid subclasses had changed. C20:5 omega 3 had increased further in PE and PS, but decreased in PC. Incorporation of C20:5 omega 3 also occurred into PC, PE and PS. omega-3 Fatty acids were incorporated almost entirely at the expense of C18:2 omega 6, but total unsaturation of phospholipids was increased. This is consistent with increased lipid fluidity, which may be an important determinant of erythrocyte deformability. The same dosage of maxEPA also resulted in a significant increase in erythrocyte deformability and a concomitant reduction in whole blood viscosity. Since plasma viscosity and haematocrit were unchanged it seems likely that the effects on blood rheology were mediated by changes in erythrocyte lipid fluidity. Modification of blood rheology by dietary omega-3 fatty acids is of potential value in the treatment of vascular disease.

Blood Viscosity↗