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At least 1,585 records · Page 88Linked to original sources
PubMed1991

Treatment of azotemic, nonoliguric, anemic patients with human recombinant erythropoietin raises whole-blood viscosity proportional to hematocrit.

It has been reported that patients with azotemia have reduced red blood cell (RBC) deformability. Since this is a major determinant of whole-blood viscosity (WBV) and rigid RBCs increase WBV disproportionately relative to the level of hematocrit, it is conceivable that sustained improvement of hematocrit with recombinant human erythropoietin (rhEPO) therapy in azotemic patients might result in abnormally raised WBV. To address this concern, WBV and plasma viscosity (PV) were measured in 9 adult patients (4 men, 5 women) with anemia (mean hematocrit 29.2 +/- 2.7%) and azotemia [mean serum creatinine concentration 339.85 +/- 102.44 mumol/l (3.8 +/- 1.1 mg/dl)] before and after 6 months of treatment with rhEPO (50-175 U/kg given intravenously thrice weekly). Baseline and post-treatment hematocrit, WBV and PV were compared to values derived in 50 normal adult subjects with normal renal function [25 women, 25 men; mean serum creatinine concentration 79.56 +/- 8.84 mumol/l (0.9 +/- 0.1 mg/dl), mean hematocrit 42.4 +/- 3.7%]. To compare rheologic factors at subnormal hematocrits, blood from subjects with normal renal function was diluted with autologous plasma to achieve a range of hematocrits from 20 to 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Effects of prolonged oxygen therapy on pulmonary hypertension and blood viscosity in patients with advanced cor pulmonale.

In 16 patients with chronic bronchitis and advanced cor pulmonale admitted to hospital due to heart failure, a controlled 6-weeks oxygen therapy, 17 h a day, was performed. The trial was started when patients were out of the exacerbation of the disease in a respiratory and circulatory steady state. Pulmonary hemodynamics, blood viscosity, packed cell volume and basic lung function data before and after oxygen therapy were compared. A significant fall of mean pulmonary arterial pressure from 42 to 30 mm Hg without a change in the cardiac output was found. Blood viscosity and packed cell volume-significantly decreased. Arterial oxygen tension did not significantly change. It seems that 17-hours per day oxygen therapy is sufficient to induce regression of anatomic changes in pulmonary arteries, a main cause of pulmonary hypertension in hypoxic cor pulmonale.

Adult↗
PubMed1990

Action of guar gums on the viscosity of digestive contents and on the gastrointestinal motor function in pigs.

The apparent viscosity of three test meals containing 6% of different guar gums was measured in the gastric, duodenal and jejunal contents and related with the gastrointestinal myoelectric activity and transit time in pigs. The motility index (mV/min) and the spike burst frequency (number of spike bursts/min) were closely related to the digesta viscosity: they were significantly increased by most viscous contents in stomach and small intestine. This effect was associated with an increase in the orocecal transit time of liquids and solids.

Animals↗
PubMed1975

Plasma viscosity in the elderly.

Plasma viscosity has been measured by a standardised technique in an unselected series of elderly subjects. Results have been grouped according to the severity of clinical disease and are found to give a good statistical differentiation between most groups, although with a wide overlap. Repeated tests show only a fair correlation with the course of an individual patient's illness. These results are compared with those previously reported. In general, values are lower in elderly than in younger subjects with diesease of comparable clinical severity. "Normal' values are, however, slightly higher in the elderly. Further studies are planned to analyse apparently anomalous results in an attempt to determine more exactly the clinical value of plasma viscosity estimation in the elderly.

Aged↗
PubMed1989

Peripheral hemodynamics, blood viscosity, and the renin-angiotensin system in hemodialysis patients under therapy with recombinant human erythropoietin.

Treatment of renal anemia with rhEPO (120 U/kg body weight/hemodialysis) in transfusion-dependent patients on maintenance hemodialysis led to an increase in blood pressure, regional peripheral resistance and whole blood viscosity. Our results are in agreement with earlier findings that partial correction of renal anemia results in hemodynamic changes characterized by a fall in cardiac output together with an increase in blood pressure due to increased vascular resistance. The increase in whole blood viscosity correlated with the increase in regional peripheral resistance but not with the increase in mean arterial blood pressure. Thus, other regulating factors of vascular resistance must be involved. Correction of renal anemia does not influence the reninangiotensin system. However, peripheral responsiveness of vascular smooth muscles may have changed due to improved tissue oxygenation and thus leading to an increase in vasoconstriction.

Adult↗
PubMed1993

Plasma, serum and whole-blood viscosity variations with age, sex, and smoking habits.

To study the influence of age, sex, and smoking habits on rheology, the authors measured plasma (PV), serum (SV), native (NBV), and corrected (CBV) blood viscosity with a computerized rotational viscometer in 152 blood donors (86 men and 66 women) and in 20 healthy persons (4 men and 16 women) attending smoke aversion treatment. None of the viscosity measures or erythrocyte sedimentation rate changed significantly with age, whereas hematocrit (HC) and fibrinogen concentration (FC) both increased with ageing (p < 0.05 and p < 0.001, respectively). Higher (p < 0.001) values of NBV and HC were found in men than in women, whereas higher values were found in women than in men for FC (p < 0.01) and ESR (p < 0.001). In blood donors, moderate smoking (mean twelve cigarettes/day) significantly influenced only ESR, which was higher (p < 0.001) in smokers than in nonsmokers. In heavy smokers (mean twenty-one cigarettes/day), however, higher (p < 0.001) PV, SV, and NBV were found, as well as higher (p < 0.01) FC and HC as compared with nonsmoking blood donors.

Adult↗
PubMed2001

Accommodation to changes in bolus viscosity in normal deglutition: a videofluoroscopic study.

Videofluoroscopic swallow studies were performed on 60 normal adult volunteers. Swallowing variables were measured during swallows of a 3-cm3 paste bolus and a 3-mL liquid bolus and were compared to identify changes in swallow gesture displacement and timing, as well as changes in bolus movement timing. The study revealed that some differences measured by videofluoroscopy appear to be the result of the inherent bolus characteristics, while others likely represent changes in swallow gestures needed to accommodate variations in bolus viscosity. The overall timing of pharyngeal transit did not vary between bolus types. Oropharyngeal transit trended toward being faster for a liquid bolus with a concurrent early elevation of the aryepiglottic folds. The hyoid bone elevated at the same time, at the same rate, and to the same extent irrespective of bolus viscosity. During a liquid bolus swallow, the hyoid bone trended toward a more prolonged elevation, corresponding to prolonged pharyngoesophageal sphincter opening. The pharyngoesophageal sphincter, however, opened to a greater extent with a paste bolus.

Adolescent↗
PubMed1979

Viscosity of dental porcelain as a function of temperature.

A method for viscosity measurement is described and representative data are given for opaque, gingival, and incisal porcelains. The significance of viscosity in annealing and in stress development due to thermal expansion mismatch is discussed. Thermal history of the porcelain is shown to be important only over a relatively small temperature interval in affecting residual stresses.

Dental Porcelain↗
PubMed1980

Apparent viscosities of setting elastomers.

The flow behavior of five elastomeric impression materials was determined by extrusion viscometry. Initial viscosity ranged from 400 to 5,100 poise at a shear rate of 2.2 reciprocal seconds. All of the elastomers showed initial non-Newtonian behavior and increased viscosity with time.

Dental Impression Materials↗
PubMed2005

Mathematical model describing erythrocyte sedimentation rate. Implications for blood viscosity changes in traumatic shock and crush syndrome.

BACKGROUND: The erythrocyte sedimentation rate (ESR) is a simple and inexpensive laboratory test, which is widespread in clinical practice, for assessing the inflammatory or acute response. This work addresses the theoretical and experimental investigation of sedimentation a single and multiple particles in homogeneous and heterogeneous (multiphase) medium, as it relates to their internal structure (aggregation of solid or deformed particles). METHODS: The equation system has been solved numerically. To choose finite analogs of derivatives we used the schemes of directional differences. RESULTS: (1) Our model takes into account the influence of the vessel wall on group aggregation of particles in tubes as well as the effects of rotation of particles, the constraint coefficient, and viscosity of a mixture as a function of the volume fraction. (2) This model can describe ESR as a function of the velocity of adhesion of erythrocytes; (3) Determination of the ESR is best conducted at certain time intervals, i.e. in a series of periods not exceeding 5 minutes each; (4) Differential diagnosis of various diseases by means of ESR should be performed using the aforementioned timed measurement of ESR; (5) An increase in blood viscosity during trauma results from an increase in rouleaux formation and the time-course method of ESR will be useful in patients with trauma, in particular, with traumatic shock and crush syndrome. CONCLUSION: The mathematical model created in this study used the most fundamental differential equations that have ever been derived to estimate ESR. It may further our understanding of its complex mechanism.

Blood Physiological Phenomena↗
PubMed1983

A comparison of blood viscosity between the adult sheep and newborn lamb. The role of plasma and red blood cell type.

Adult sheep and newborn lamb blood viscosity (Vc) have been compared by taking into account not only the hematocrit, but also the type of the red cells (adult or fetal) in the circulation and the plasma Vc. At all shear rates studied the whole blood Vc of the adult was higher than that of the newborn. Plasma Vc was 1.58 +/- 0.18 centipoises in the adult compared to 1.21 +/- 0.19 in the newborn group (P less than 0.001). The mean relative apparent viscosity (whole blood Vc/plasma Vc) was higher in the newborn although the difference was not significant.

Animals↗
PubMed2004

Overexpression of myosin IB in living Entamoeba histolytica enhances cytoplasm viscosity and reduces phagocytosis.

The human parasite Entamoeba histolytica is an ancient protozoan that expresses only one unconventional myosin, which has homology with myosin IB from other amoebae. Myosin IB is involved in phagocytosis of human cells by E. histolytica. In this work, we developed a microrheological technique, analysing magnetic phagosomes, which allowed us to probe the density of the F-actin network in living cells. Using this technique, we showed that overexpression of myosin IB led to an increase in cytoplasm viscosity, which correlated with a delay in initiating human cell phagocytosis. To investigate which myosin IB domains sustain cell viscosity changes, we overexpressed truncated forms of the protein. Our results demonstrate that both actin-binding sites that are present in the heavy chain but not the SH3 domain are required to modulate the density of the actin network. These data suggested that, as well as the motor activity, myosin IB in E. histolytica plays a structural role on the actin network owing to its ability to cross-link filaments. The gelation state of cell cytoplasm and the dynamics of cortical F-actin during phagocytosis seem to be modulated by the myosin IB structuring cytoskeleton activity.

Actins↗
PubMed1991

Blood viscosity measurement for screening of affecting blood circulation.

An in vitro screening test for drugs that decrease blood viscosity was carried out on many pharmacologically active compounds such as Ca-antagonists, alpha-antagonists, beta-antagonists, alpha, beta-antagonists, alpha-agonists, beta-agonists, alpha, beta-agonists, autacoids and others. The results revealed that various types of microcirculatory-improving drugs, vasodilators, and antagonists decreased blood viscosity, while the agonists and autacoids had no significant effect. These findings suggest that this assay is useful for screening compounds related to hemorheology.

Animals↗
PubMed2003

Measuring microscopic viscosity with optical tweezers as a confocal probe.

We demonstrate, what is to the best our knowledge, a new method for studying the motion of a particle trapped by optical tweezers; in this method the trapping beam itself is used as a confocal probe. By studying the response of the particle to periodic motion of the tweezers, we obtain information about the medium viscosity, particle properties, and trap stiffness. We develop the mathematical model, demonstrate experimentally its validity for our system, and discuss advantages of using this method as a new form of scanning photonic force microscopy for applications in which a high spatial and temporal resolution of the medium viscosity is desired.

Microscopy, Confocal↗
PubMed1982

The interaction of calf thymus DNA with mercuric acetate and 3,6-bis-(acetatomercurimethyl)-dioxane. Small-angle X-ray scattering and viscosity studies.

The binding of Hg2+ and 3,6-bis-(acetatomercurimethyl)-dioxane (BAMD) to sonicated calf thymus DNA was studied by small-angle X-ray scattering and viscosity measurements. The scattering experiments with DNA complexed by different amounts of mercurials (for Hg2+ rb=0-0.79, for BAMD rb=0-0.86 mol of mercurial bound per mol of base pairs) established that the rod-like character of the DNA molecules is maintained up to high binding ratios. They revealed further a steady decrease of the cross-section radius of gyration Rc for the DNA X Hg2+ complex and a similar decrease of Rc for the DNA X BAMD complex up to Rb=0.35. This behaviour is certainly caused by the incorporation of both mercurials near the axis of the DNA helix. Binding of BAMD at rb greater than 0.35 led to an increase of Rc which behaviour obviously reflects the location of mercury atoms at large distances from the axis, possibly on the surface of the helix. The increase of the mass per unit length Mc upon binding of the mercurials was found to be much higher than expected. This finding established that the length of the DNA helix decreases by 0.10 +/- 0.01 nm per bound mercurial at low binding ratios (i.e. up to rb=1/3 for BAMD, up to possibly rb=0.5 for Hg2+). A similar conclusion was also drawn from the observed decrease of intrinsic viscosity [n] with increasing rb. The analysis of Mc at high binding ratios suggests that every BAMD molecule bound beyond rb=1/3 decreases the length of the DNA by 0.21 +/- 0.05 nm whereas Hg2+ when bound beyond rb=0.5 causes no change of the length.

Animals↗
PubMed1998

[Blood cell count, sodium, potassium, calcium, osmolality and viscosity during pediatric angiocardiography with ioxaglate].

PURPOSE: Children's blood changes during angiocardiography may not be only due to the contrast media (CM). METHODS: We studied the presence and severity of changes in those parameters in 35 pediatric patients undergoing angiocardiography with ioxaglate aiming to identify independent variable responsible for those changes. Blood samples were taken at the beginning of the procedure (SI), at the end (S2) and two hours later (S3). RESULTS: Hematocrit: S1 = 47.3 +/- 6.9%; S2 = 40.7 +/- 7.4% (p < 0.001), (related to the CM volume r=0.37, (p < 0.05). Hemoglobin: S1 = 15 +/- 2.1g%; S2 = 13.2 +/- 2.4g% (p < 0.001), and S3 = 12.7 +/- 2.5g% (NS). White blood cell count: S1 = 7940 +/- 3040 leukocytes/mm3; S2 = 6950 +/- 2700/mm3 (NS); S3 = 10830 +/- 4690 leukocytes/mm3 (p < 0.001). Procedure duration (r = 0.83, p < 0.05) and 5% glucose fluid given between S2 and S3 (r = 0.49, p < 0.05) were isolated. Sodium: S1 = 134.5 +/- 0.4mEq/L, S2 = 130.7 +/- 0.4mEq/L (p < 0.001) (due to 5% glucose fluid injected, r = 0.61, p < 0.01). Potassium: S1 = 4.22 +/- 0.45mEq/L, S2 = 300.6 +/- 13.3mOsm/kg (p < 0.001). Calcium: S1 = 9.13 +/- 1.03mg%; S2 = 8.4 +/- 0.91 mg/dL. (related to the CM, r = 0.43, p < 0.01.) Osmolality: S1= 293.3 +/- 12.5mOsm/kg; S2 = 3.83 +/- 0.4mEq/L (p<0.001). Viscosity: S1 = 3.36 +/- 0.81; S2 = 3.09 +/- 0.74 (p < 0.01); S3 = 3.87 +/- 0.89, p < 0.001. There was an indirect linear regression with the CM. CONCLUSION: There were profound differences among the dependent variables observed but the ioxaglate was partially related to changes in hematocrit/hemoglobin, total calcium and viscosity. We failed to demonstrate significant regression coefficient between CM and changes in leukocytes, sodium, potassium, and osmolality.

Angiocardiography↗
PubMed2004

Concentration and temperature dependence of viscosity of uranium solutions in H2O and 3 mol/L HNO3.

Viscosities of uranium solutions in H(2)O and 3 mol/L HNO(3) medium were measured by Ubbelhode flow viscometer in the concentration range of 0.5%-3.0% from 10 degrees C to 30 degrees C at 5 degrees C interval. Viscosity data were interpreted in terms of an empirical equation; eta =a(o)exp(b(o)M+c(o)M(2)). Values of coefficients a(o), b(o) and c(o) were calculated for all the three systems studied. Flow activation energies and thermodynamic parameters were also evaluated.

Nitric Acid↗
PubMed1977

Penetration of restorative resins into acid etched enamel. I. Viscosity, surface tension and contact angle of restorative resin monomers.

It has been a controversial question whether an intermediate layer of low-viscous, non-composite resin between composite restorative and etched enamel is beneficial. It was the purpose of the present work to investigate some of the factors that govern the penetration of resins into the capillary pores of etched enamel surfaces. Viscosity, surface tension and contact angle on human enamel were measured using monomer mixtures similar to those found in commercial restorative resins. Employing a cylindrical model of relevant dimensions of the capillary pores, and on the basis of Poiseuille's equation the time of penetration was calculated for a relatively high-viscous and a relatively low-viscous monomer mixture. It was concluded that viscosity as such is not a limiting factor for the penetration of restorative resin monomers into the pores of etched enamel surfaces.

Acid Etching, Dental↗