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PubMed2007

The role of cement viscosity on cement-bone apposition and strength: an in vitro model with medullary bleeding.

We compared the mechanical and morphological characteristics of cement-bone structures created with either standard- or low-viscosity cement using a human cadaver model that simulated intramedullary bleeding. The goal is to determine if the viscosity of the cement would affect the strength of the cement-bone interface and the degree of apposition between the cement and bone. The tensile strength of cement-bone constructs with standard-viscosity cement (2.42 +/- 1.55 MPa) was 21% stronger than with low-viscosity cement (2.00 +/- 1.51 MPa, P = .034). Cement-bone apposition was positively correlated (r2 = 0.29, P <. 0001) with the strength of the interface. There was 15% greater apposition between cement and bone (P = .036) for standard-viscosity cement. Low-viscosity cement may be less effective in displacing bone marrow and in preventing hemodynamic backflow, resulting in less apposition and a weaker interface.

Aged, 80 and over↗

PubMed2006

Influence of parenteral fat emulsion Intralipos and citric acid on blood viscosity and erythrocyte morphology in vitro.

In most studies fat emulsion had been administered by enteral route. Recently a parenteral soybean-oil emulsion has been developed. In this study we assessed the effects of a parenteral soybean-oil emulsion (Intralipos) and citric acid on blood rheology and erythrocyte morphology in vitro. Porcine blood was incubated in vitro with increasing concentrations of fat emulsion Intralipos and citric acid at 37 degrees C for 1h. Viscosity of plasma and whole blood was measured using a FASCO-2050 digital viscometer. Red blood cell morphology was examined by light microscopy. The viscosity of whole blood represented an ascending dose-dependence for different Intralipos concentrations at high shear rate of 90 and 225 s(-1), however, it decreased with citric acid concentrations. On the other hand, the whole blood viscosity also declined with citric acid concentrations in presence of 30% Intralipos (v/v), and there is a minimal viscosity at 0.67% citric acid (v/v). There are some thorns on the blood membrane at 40% Intralipos as compared with control (no Intralipos addition), which indicates the Intralipos compound may affect blood cell membranes, and resulted in whole blood viscosity increase. We concluded that the intravenous soybean-oil preparation Intralipos interacts with the erythrocyte membrane, and citric acid could alleviate the whole blood viscosity.

Animals↗

PubMed2004

High frequency of (TG)mTn variant tracts in the cystic fibrosis transmembrane conductance regulator gene in men with high semen viscosity.

OBJECTIVE: To evaluate a possible correlation between abnormal semen consistency and cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations and variant tracts. DESIGN: Study of CFTR mutations and variant tracts in men with high semen viscosity as compared with normospermic men. SETTING: University-based centers for andrology, clinical biochemistry, and cystic fibrosis. PATIENT(S): Forty-six male partners from infertile couples with sine causa high semen viscosity compared with 72 normospermic men. INTERVENTION(S): Semen sample collection. MAIN OUTCOME MEASURE(S): We obtained the (TG)mTn polymorphic tracts and a panel of 31 mutations of CFTR, semen viscosity, and semen variables. RESULT(S): The frequencies of the (TG)12 and T5 variant alleles were statistically significantly higher in men with high semen viscosity (17.4% and 7.6%, respectively) than in the normospermic control group (6.9% and 1.4%, respectively). The frequency of the genotypes carrying (TG)12 or T5 was statistically significantly higher in men with high semen viscosity (39.1%) than in the normospermic control group (16.7%). Four men with high semen viscosity showed the variant (TG)12T5 haplotype; one of these men presented variant tracts on both alleles. None of the normospermic controls showed a (TG)12T5 haplotype. CONCLUSION(S): Semen hyperviscosity could be considered a "minimal clinical expression" of cystic fibrosis; CFTR gene sequence variations may constitute the genetic basis for this disease.

Alleles↗

PubMed2004

Release behavior and photo-image of nifedipine tablet coated with high viscosity grade hydroxypropylmethylcellulose: effect of coating conditions.

An orally applicable nifedipine-loaded core tablets was coated using high viscosity grade HPMC (100,000 cps) in ethanol/water cosolvent. The release of coated tablet was evaluated using USP paddle method in 900 ml of simulated gastric fluid (pH 1.2) for 2 h followed by intestinal fluid (pH 6.8) for 10 h. The surface morphologies using scanning electron microscope and photo-images using digital camera of coated tablet during the release test were also visualized, respectively. The viscosity of hydro-alcoholic HPMC solution largely decreased as the amount of ethanol increased. There was no significant difference in viscosity among plasticizers used. The distinct and continuous coated layer was observed using scanning electron microscope. However, the surface morphologies were highly dependent on HPMC concentration and ratio of coating solvents. The higher ratio of ethanol/water gave a longer lag time prior to drug release. Lag time also increased as a function of the coating levels based on weight gains due to increased thickness of coated layer. Lag time is inversely correlated with HPMC concentration in ethanol/water (5:1) cosolvent. As the HPMC concentration slightly decreased from 3.8 to 3.2% in hydroalcoholic coating solution, a large increase of lag time was observed. As the swelling (mixing) time of high viscosity grade HPMC in ethanol/water cosolvent increased from 1 to 5 h, the release rate was decreased due to enough plasticization of polymer. Based on photo-imaging analysis, the coated tablet was initially swelled and gelled without erosion and disintegration over 5 h. The disintegration of the coated tablet was occurred approximately 7 h after dissolution, resulting in pulsed release of drug. The high viscosity grade HPMC can be applicable for polymeric coating after careful selection of solvent systems. The release behavior and lag time could be controlled by coating conditions such as HPMC concentration, ethanol/water ratio as a coating solvent, coating level and swelling (mixing) time of coating solution. The current time-controlled release tablet coated with high viscosity grade HPMC with a designated lag time followed by a rapid release may provide an alternative to site specific or colonic delivery of drugs. In addition, the release behavior can be matched with body's circadian rhythm pattern in chronotherapy.

Hypromellose Derivatives↗

PubMed2006

The influence of capsule geometry and cement formulation on the apparent viscosity of dental cements.

OBJECTIVES: This work examines the influence of specific aspects of capsule design and cement formulation on the handling properties of the extruded glass polyalkenoate cement (GPC) pastes. METHODS: A commercial metal reinforced GPC, HiDense, and experimental GPCs were extruded using a tensometer at loads and rates maintained within end-user limits and the apparent viscosity of the cement paste was determined by applying Poiseuille's law. The influence of the extrusion procedure (mixing time and ram speed), capillary geometry (length and diameter) and cement composition (powder: liquid (P:L) ratio, tartaric acid content and poly(acrylic acid) molar mass) on the apparent viscosity of the cement paste was evaluated. RESULTS: The examined GPCs behaved as non-Newtonian, pseudoplastic materials and exhibited a yield stress. Variation of the geometry of the capsule capillary resulted in the apparent viscosity of HiDense increasing by 7% as the length increased from 5 to 15mm whilst halving the capillary diameter from 2 to 1mm resulted in a 63% decrease in the apparent viscosity and a 600% increase in the extrusion load. The apparent viscosity of the experimental GPCs was increased by an increase in the P:L ratio and, in general, by the PAA molar mass, whilst the concentration-dependent effect of (+)-tartaric acid (TAA) indicates a working time dependence on TAA content. CONCLUSIONS: Using this approach optimisation of the rheological properties can be achieved by manipulation of the capsule design and cement formulation due to the dependency of the apparent viscosity on the capillary diameter, TAA content, P:L ratio and poly(acrylic acid) molar mass.

Chemistry, Pharmaceutical↗

PubMed2004

Effects of viscosity, taste, and bolus volume on swallowing apnea duration of normal adults.

OBJECTIVE: The effects of viscosity, taste, and nectar-thick liquid bolus volume on swallowing apnea duration (SAD) were examined. STUDY DESIGN AND SETTING: Twenty-two adults, comprised of 10 males and 12 females, participated. SAD was assessed via nasal airflow during swallow conditions of viscosity (thin liquid, thick liquid, and puree), taste (water, apple juice, lemon concentrate), and nectar-thick liquid bolus volumes (5, 10, 15, and 20 mL) across three trials. RESULTS: A significant main effect of nectar-thick liquid bolus volume was found (P < 0.05). Viscosity and taste were not significant. CONCLUSIONS: SAD increased with increases in bolus volume; however, neither changes in bolus viscosity nor changes in taste affected SAD. SIGNIFICANCE: These findings indicate that since viscosity was not significant, the normative data previously published (by this PI) with 60 healthy adults stratified by age and gender can be utilized for comparison to disordered swallowing without regard to the bolus viscosity being used. EBM RATING: D.

Adult↗

PubMed1993

Cytoplasmic viscosity near the cell plasma membrane: measurement by evanescent field frequency-domain microfluorimetry.

The purpose of this study was to determine whether the unique physical milieu just beneath the cell plasma membrane influences the rheology of fluid-phase cytoplasm. Cytoplasmic viscosity was evaluated from the picosecond rotation of the small fluorophore 2',7'-bis-(2-carboxyethyl)-5-carboxyfluorescein (BCECF) by parallel-acquisition Fourier transform microfluorimetry (Fushimi and Verkman, 1991). Information about viscosity within < 200 nm of cell plasma membranes was obtained by selective excitation of fluorophores in an evanescent field created by total internal reflection (TIR) of impulse-modulated s-plane-polarized laser illumination (488 nm) at a glass-aqueous interface. Measurements of fluorescence lifetime and time-resolved anisotropy were carried out in solutions containing fluorescein or BCECF at known viscosities, and monolayers of BCECF-labeled Swiss 3T3 fibroblasts and Madin-Darby canine kidney (MDCK) cells. Specific concerns associated with time-resolved fluorescence measurements in the evanescent field were examined theoretically and/or experimentally, including variations in lifetime due to fluorophore proximity to the interface, and the use of the s and p polarized excitation. In fluorescein solutions excited with s-plane polarized light, there was a 5-10% decrease in fluorescein lifetime with TIR compared to trans (subcritical) illumination, but no change in rotational correlation time (approximately 98 ps/cP). Intracellular BCECF had a single lifetime of 3.7 +/- 0.1 ns near the cell plasma membrane. Apparent fluid-phase viscosity near the cell plasma membrane was 1.1 +/- 0.2 cP (fibroblast) and 1.0 +/- 0.2 cP (MDCK), not significantly different from the viscosity measured in bulk cytoplasm far from the plasma membrane. The results establish the methodology for time-resolved microfluorimetric measurement of polarization in the evanescent field and demonstrate that the cell plasma membrane has little effect on the fluid-phase viscosity of adjacent cytoplasm.

3T3 Cells↗

PubMed1998

Effect of viscosity on mechanics of single, skinned fibers from rabbit psoas muscle.

Muscle contraction is highly dynamic and thus may be influenced by viscosity of the medium surrounding the myofilaments. Single, skinned fibers from rabbit psoas muscle were used to test this hypothesis. Viscosity within the myofilament lattice was increased by adding to solutions low molecular weight sugars (disaccharides sucrose or maltose or monosaccharides glucose or fructose). At maximal Ca2+ activation, isometric force (Fi) was inhibited at the highest solute concentrations studied, but this inhibition was not directly related to viscosity. Solutes readily permeated the filament lattice, as fiber diameter was unaffected by added solutes (except for an increased diameter with Fi < 30% of control). In contrast, there was a linear dependence upon 1/viscosity for both unloaded shortening velocity and also the kinetics of isometric tension redevelopment; these effects were unrelated to either variation in solution osmolarity or inhibition of force. All effects of added solute were reversible. Inhibition of both isometric as well as isotonic kinetics demonstrates that viscous resistance to filament sliding was not the predominant factor affected by viscosity. This was corroborated by measurements in relaxed fibers, which showed no significant change in the strain-rate dependence of elastic modulus when viscosity was increased more than twofold. Our results implicate cross-bridge diffusion as a significant limiting factor in cross-bridge kinetics and, more generally, demonstrate that viscosity is a useful probe of actomyosin dynamics.

Actin Cytoskeleton↗

PubMed1999

Low high density lipoprotein levels are associated with an elevated blood viscosity.

Low levels of high density lipoprotein (HDL) have been inversely correlated with blood viscosity and plasma viscosity; however, the contribution of concomitant hypertriglyceridemia may confound this association. This study evaluated the relationship between blood viscosity and HDL cholesterol in 70 subjects with fasting levels of total cholesterol <5.2 mmol/l (200 mg/dl) and triglycerides <2.3 mmol/l (200 mg/dl). Viscosity (mPa x s) was measured at 37 degrees C with a coaxial cylinder microviscometer. HDL cholesterol was inversely associated with corrected blood viscosity at 100 s(-1) (beta = -0.49, P<0.00005) and 20 s(-1) (beta = -0.38, P = 0.001) but not at 1 s(-1) (beta = -0.05, P = 0.69) using stepwise multivariate analyses. Low HDL levels are associated with an elevated blood viscosity, and this rheological abnormality may contribute to cardiovascular risk in subjects with isolated low HDL levels.

Adult↗

PubMed1987

Postnatal alteration in hematocrit and viscosity in normal and polycythemic infants.

This study was done to document postnatal alterations in hematocrit and viscosity in the first 18 hours of life in 99 full-term infants, to better understand the age-dependent variations in these measurements that may have a bearing on the diagnosis of neonatal polycythemia. The peripheral venous Hct was highest at 2 hours of age, and dropped to cord blood levels by 18 hours. The whole blood viscosity of peripheral venous samples did not change significantly with age. In infants with peripheral venous Hct greater than or equal to 64%, and therefore considered to have polycythemia, a similar postnatal variation in Hct level was seen. Only 38% of infants with Hct greater than or equal to 64% at 2 hours of age continued to have a high level beyond 12 hours of age. The viscosity level in these infants tended to follow that of the Hct. The mean +/- 2 SD viscosity values obtained from peripheral venous samples was much higher than the upper limits of viscosity used in previous studies in which cord blood viscosity was used as the norm. Cord blood Hct correlated better with peripheral venous Hct than with capillary hematocrit, and provided a noninvasive method for screening. These findings suggest that the postnatal variations in Hct should be taken into consideration in the diagnosis of neonatal polycythemia.

Aging↗

PubMed1985

Regulation of cerebral blood flow in response to changes in blood viscosity.

Cerebral blood flow (CBF) was measured by the non-invasive xenon-133 technique in patients with increased blood viscosity as a result of paraproteinaemia or leukaemia. A highly significant inverse relation was found between CBF and arterial oxygen content in 59 paraproteinaemic patients. There was no significant correlation between CBF and whole blood viscosity, and no significant difference between CBF in paraproteinaemic patients and a matched group of anaemic patients. 7 leukaemic patients with up to threefold increases in whole blood viscosity were also found to have CBF appropriate to their degree of anaemia. The effects of treatment to reduce blood viscosity were studied in 7 paraproteinaemic and 5 leukaemic patients; changes in CBF were significantly related to changes in arterial oxygen content but not to changes in blood viscosity. These studies confirm the importance of arterial oxygen content in the determination of CBF, and demonstrate that regulatory mechanisms can maintain normal cerebral oxygen transport despite increased plasma and whole blood viscosity.

Adult↗

PubMed1986

Blood viscosity as a factor in sensorineural hearing impairment.

The cause of sensorineural hearing impairment is unknown in a high proportion of patients. Since ischaemia is a possible factor, the relation between hearing threshold and blood viscosity, plasma viscosity, and haematocrit was investigated in 49 patients with idiopathic hearing loss, taking into account age, sex, smoking, and socioeconomic group. Hearing thresholds were unrelated to haematocrit or low-shear blood viscosity. Hearing impairment at high frequencies was directly related to high-shear blood viscosity and inversely related to plasma viscosity. The derived measure of red-cell rigidity was significantly related at all frequencies to hearing thresholds. A second study of 92 subjects from a population sample confirmed the inverse relation with plasma viscosity and lack of relation with haematocrit. Increased pure-tone thresholds appear to be related to increased red-cell rigidity; this may be an important factor in sensorineural hearing impairment with implications for diagnosis and prevention.

Adult↗

PubMed1994

Geographical variations in plasma viscosity and relation to coronary event rates.

Plasma viscosity is reported to be predictive of coronary heart disease (CHD) and stroke. To find out whether regional differences in CHD event rates correlate with differences in plasma viscosity, we compared plasma viscosity in a high-risk area for CHD (Glasgow Multinational Monitoring of Trends and Determinants in Cardiovascular Disease [MONICA] and Scottish Heart Health Study population surveys, 1985/86; n = 1166) and in a lower-risk area (MONICA Augsburg survey, 1984/85; n = 3258) in men and women aged 25-64 years. Mean plasma viscosity (37 degrees C) was 1.261 (SD 0.067) mPa s in Augsburg and 1.327 (0.093) mPa s in the west of Scotland for men, and 1.248 (0.066) mPa s and 1.318 (0.087) mPa s, respectively, for women. The unadjusted difference of the means between the west of Scotland and Augsburg was 0.066 (95% CI from weighted regression 0.058-0.073) mPa s for men and 0.070 (0.062-0.078) mPa s for women. Adjustment for age, smoking behaviour, total and high-density-lipoprotein cholesterol, systolic and diastolic blood pressure, and body-mass index had no effect on these differences. Age-standardised coronary event rates in 1985-87 were at least two times higher among men, and four times higher among women, in MONICA Glasgow than in MONICA Augsburg. This large geographical difference in plasma viscosity might partly explain the differences in CHD event rates between these populations. Further studies are needed on the determinants of plasma viscosity, and on its potential roles in atherosclerosis, thrombosis, and ischaemia.

Adult↗

PubMed1987

Adenosine deaminase: viscosity studies and the mechanism of binding of substrate and of ground- and transition-state analogue inhibitors.

We have studied the effects of viscosogenic agents, sucrose and ficoll, on (1) the hydrolysis of adenosine and of 6-methoxypurine riboside catalyzed by adenosine deaminase and (2) the rates of association and dissociation of ground-state and transition-state analogue inhibitors. For adenosine, Vmax/Km is found to be inversely proportional to the relative viscosity with sucrose, an agent affecting the microscopic viscosity, while no effect is found with ficoll, an agent affecting the macroscopic viscosity. Viscosogenic agents have no effect on the kinetic constants for 6-methoxypurine riboside. Thus, the bimolecular rate constant, Vmax/Km = 11.2 +/- 0.8 microM-1 s-1, for the reaction with adenosine is found to be at the encounter-controlled limit while that for the reaction with the poor substrate 6-methoxypurine riboside, 0.040 +/- 0.004 microM-1 s-1, is limited by some other process. Viscosity-dependent processes do not make a significant (less than 10%) contribution to Vmax. The dissociation constants for inhibitors are unaffected by viscosity. The ground-state analogue inhibitor purine riboside appears to bind at a rate comparable to that of adenosine. However, the slower rates of association (0.16-2.5 microM-1 s-1) and dissociation (5 X 10(-6) to 12 s-1) of transition-state analogue inhibitors are affected by the viscosity of the medium to approximately the same extent as the encounter-controlled rates of association and dissociation of adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Deaminase↗

PubMed1988

Origin of viscosity effects in carbonic anhydrase catalysis. Kinetic studies with bulky buffers at limiting concentrations.

In our earlier paper we showed that the rates of CO2 hydration and HCO3- dehydration catalyzed by the high-activity form of mammalian erythrocyte carbonic anhydrase (CA II) were dependent on solution viscosity increase and that the effect was linked to some kind of proton-transfer-related event [Pocker, Y., & Janjić, N. (1987) Biochemistry 26, 2597-2606]. In order to further elucidate the source of the observed viscosity effect, the dependence of kcat and Km for CA II catalyzed HCO3- dehydration at pH 5.90 on sucrose-induced viscosity increase was investigated at several concentrations of 2-(N-morpholino)ethanesulfonic acid (MES) buffer, including the very low buffer concentration region (less than 10 mM) where the proton transfer between the shuttle group on the enzyme and buffer becomes rate limiting. In all examined cases, kcat steadily decreased with added sucrose while Km remained independent of the viscosity increase. The extent to which this reaction was dependent on viscosity was found to be constant, within experimental error, over the entire range of MES buffer concentrations studied (1-20 mM). Furthermore, the viscosity effect was qualitatively and quantitatively the same when an exceptionally large buffer (i.e., bovine serum albumin) was used instead of the more commonly used biological buffer (i.e., MES).(ABSTRACT TRUNCATED AT 250 WORDS)

Bicarbonates↗

PubMed1980

Solvent viscosity and protein dynamics.

Proteins are dynamic systems. Recent evidence demonstrates that they exist in a large number of conformational substates and can continuously move from one substate to another; motion of a small ligand inside a protein may be possible only through these conformational fluctuations. To test this idea, we study with flash photolysis the binding of CO to protoheme and O2 and CO to myoglobin in many different solvents. The standard evaluation of such experiments yields information only about the protein-solvent system. A novel approach is presented which permits conclusions concerning the protein: Data from all solvents are considered together, and the rates for transitions of the ligand over various barriers are studied as a function of temperature for fixed solvent viscosities. Results show that over a wide range in viscosity the transition rates in heme-CO are inversely proportional to the solvent viscosity and can consequently be described by the Kramers equation. The rates of O2 and CO in myoglobin also depend on the solvent viscosity and are most sensitive to the solvent at the lowest viscosity. Viscosity influences protein reactions even in aqueous solutions. The data dan be interpreted by a dynamic model in which transitions into and inside myoglobin are governed by fluctuations between conformational substates corresponding to closed and open pathways. Ligand motion thus is mainly controlled by gates and not by static potential barriers. Some characteristic parameters for the substates are determined, and they agree approximately with similar parameters found in Mössbauer experiments. As expected, the barrier parameters evaluated in the novel approach deviate markedly from the ones obtained by the conventional procedure. Comparison with model calculations or basic theories will be meaningful only with the new evaluation, and the method may be essential for many or possibly all biochemical reactions.

Carbon Monoxide↗

PubMed1979

Viscosity-dependent structural fluctuations in enzyme catalysis.

The effect of viscosity on the rate of catalysis of carboxypeptidase A has been tested. By use of the tripeptide carbobenzoxy-l-alanyl-l-alanyl-l-alanine [Z(L-Ala)3] as substrate, it was shown that most of the effect on the hydrolysis rate caused by the presence of 30 or 40% methanol or glycerol in aqueous solution can be ascribed to a contribution of viscosity to the catalytic rate constant, kcat. Arrhenius plots of kcat in 30 and 40% glycerol or methanol are linear and almost parallel. When the rate constants are "corrected" for the viscosity of various media, the difference between the various Arrhenius plots is considerably reduced; it vanishes, within experimental error, when the effect of the dielectric constant of the solutions is taken into account as well. It is proposed that the viscosity of the medium can influence the rate-limiting step of the enzymic reaction, which is the rate of transitions over the energy barrier preceding product formation. According to the suggested mechanism, the enzyme--substrate complex can overcome this energy barrier by viscosity-dependent structural fluctuations. The quantitative agreement between the theory and the experimental results suggests that (a) due to the temperature dependence of the viscosity of the solution, the potential energy barrier of the reaction is about 5 kcal/mol lower than the observed activation energy and (b) information about the structural flexibility of the complex can be obtained by kinetic measurements.

Carboxypeptidases↗

PubMed1977

Use of a fluorescent probe to determine the viscosity of LM cell membranes with altered phospholipid compositions.

The phospholipid compostition of LM cells grown in tissue culture was altered by substituting ethanolamine for choline in the growth medium. The plasma membrane isolated from cells grown in medium conatining ethanolamine for 83 h had a sixfold increase in the ratio of phosphatidylethanolamine to phosphatidylcholine, the two major phospholipid classes. This was accompanied by small changes in other lipid components of the membrane. There was also a sixfold increase in the amount of triacylglycerols and alkyldiacylglycerols which were not associated with the membrane fraction of the cell. No significant changes occurred in the lipid composition of cells during growth in choline containing medium. The viscosity of plasma membranes was studied in whole cells and isolated membranes using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Plasma membranes isolated from ethanolamine-supplemented cells had greater viscosities than membranes isolated from choline-supplemented cells. When whole cells were labeled with the fluorescent probe, the opposite trend in the apparent membrane viscosity was observed. This was due primarily to the probe penetrating into nonmembranous neutral lipids rather than remaining localized in the surface membrane of the cells. Since the enthanolamine-supplemented cells contained more low viscosity neutral lipids, the whole cells gave an apparently lower viscosity as compared with choline-supplemented cells, thus, measurements carried out on whole cells gave an inaccurate determination of the viscosity of the surface membrane.

Adenosine Triphosphatases↗