PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Particle Size”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources
PubMed1984

Effect of particle size of the calcium source on performance of broiler chicks fed diets with different calcium and phosphorus levels.

Broiler chicks were fed diets differing in calcium (Ca) level, source, and particle size. The basal diet fed in most experiments contained .62% total phosphorus and .49% Ca from sources other than the Ca sources being compared. Performance was not affected by Ca source in diets with .9% Ca. In diets with 1.5% Ca, gain and bone ash were significantly lower with a powdered, USP grade calcium carbonate than with limestone particles passing through a 1,000-mu screen and retained by a 417-mu screen. Crushing these particles to allow them to pass through a 74-mu screen caused them to behave like the powdered calcium carbonate. Particles of this limestone had to at least pass through a 147-mu screen to cause a greater reduction in gain; the finest particles tested (passed a 74-mu screen) reduced performance most. When graded levels of fine and medium particles were fed, the higher levels reduced gain, and less of the fine particles was required to produce a given reduction. In a high Ca-low P diet, fine particles of the Ca source were more deleterious than medium. Apparently, chicks can shunt excess Ca in the form of medium particles (150 to 1,000 mu) through the digestive system better than they can the more reactive, fine particles.

Animals↗
PubMed2003

Particle size of bone graft and method of impaction affect initial stability of cemented cups: human cadaveric and synthetic pelvic specimen studies.

We determined the effect of bone graft particle size and impaction technique on the initial stability of cemented acetabular cups. First, acetabular reconstructions were performed in human cadaveric pelvic bones in which type 2 AAOS cavitary defects were created. Reconstructions were made with small bone grafts (average 2 mm) produced by a bone mill or large bone grafts (average 9 mm) produced by hand with a rongeur. All chips were made from freshly-frozen femoral heads. Impaction was done using acetabular impactors and a hammer. We did a loading experiment with a gradually increasing dynamic load up to 3000 N. We used radiostereometric analysis (RSA) to determine cup stability. The cups were more stable when large bone grafts were used. Because of limitations of the cadaver model, we developed a synthetic acetabular model. For validation of this model, we repeated the experiments using small and large bone grafts. The results with both models were similar. In the synthetic model, we compared impaction with hammer and impactors with the reversed reaming technique using manual compression on the reamer. The latter method resulted in more migration. We recommend firm impaction with a hammer of large bone grafts for optimal stability of the cup.

Acetabulum↗
PubMed2000

Towards a quantitative free flow electrophoresis and its application to particle size separations.

The possibility to quantify free-flow electrophoresis (FFE) data was explored in application to 6 negatively charged polystyrene size standards in the size range of 73 to 762 nm diameter. Peak fraction numbers in FFE were shown to be proportional to mobilities of the particles, determined by capillary zone electrophoresis in the identical buffer. Standard deviations of peak fraction numbers demonstrate a high degree of intra-experimental reproducibility while inter-experimentally, a variability of 1 to 5 peak fraction numbers within 28 fractions was found. A relative mobility (Rf) scale for peak identification in FFE based on the free mobility of the dye, SPADNS, allowed for the utilization of the entire electrophoretic migration path but failed to improve the precision of fraction numbers in view of the substantial zone spreading of the dye. Mobility differences between particles increased upon lowering the ionic strength of the electrophoretic buffer. Peak width increased with particle size in inverse relation to ionic strength.

Buffers↗
PubMed2003

Alloyed semiconductor quantum dots: tuning the optical properties without changing the particle size.

Alloyed semiconductor quantum dots (cadmium selenium telluride) with both homogeneous and gradient internal structures have been prepared to achieve continuous tuning of the optical properties without changing the particle size. Our results demonstrate that composition and internal structure are two important parameters that can be used to tune the optical and electronic properties of multicomponent, alloyed quantum dots. A surprising finding is a nonlinear relationship between the composition and the absorption/emission energies, leading to new properties not obtainable from the parent binary systems. With red-shifted light emission up to 850 nm and quantum yields up to 60%, this new class of alloyed quantum dots opens new possibilities in band gap engineering and in developing near-infrared fluorescent probes for in vivo molecular imaging and biomarker detection.

Alloys↗
PubMed1977

Influence of granulation liquid flow rate on particle-size distribution in spray-granulate products.

Granulations were made at various air speeds and various rates of addition of granulating liquid in a spray-granulatin assembly. The ensuring particle sizes were log-normal, and the data substantiate that the process is of the nature previously described. The mean diameter obtained was approximately proportional to the liquid flow rate squared but was independent of air rate. The standard deviation was independent of both parameters.

Drug Compounding↗
PubMedDate not supplied

Theoretical investigation of axial and local particle size distribution on expanded bed adsorption process.

The general rate model was developed and solved to describe protein adsorption in an expanded bed. The model takes into account axial variation of bed porosity, particle size distribution (PSD), external and intraparticle mass transfer, and dispersion in liquid and solid phase. The analysis of the influence of the model parameters on dynamic capacity (DC) was investigated. The simulation results showed that major impact on dynamic capacity is exerted by intraparticle mass transfer (particle diameter and pore diffusivity). The external mass transfer resistance and dispersion parameters have secondary effect on DC. The replacement of axial PSD by the mean particle diameter results in error in calculation of DC, which increases remarkably with the increase of mean particle diameter. The PSD can promote a very slow approaching of plateau concentration by breakthrough curves. It was shown also that axial bed porosity variation could be replaced by average porosity with negligible error for DC calculations.

Adsorption↗
PubMed2001

Low-density lipoprotein particle size, triglyceride-rich lipoproteins, and glucose tolerance in non-diabetic men with essential hypertension.

The aim of the study is to investigate serum lipoproteins abnormalities including low-density lipoprotein (LDL) particle size, and their relationship with other cardiovascular risk factors in men with essential hypertension. Plasma glucose and serum insulin levels during oral glucose tolerance test (OGTT), serum lipoprotein(a), apolipoprotein (apo) A-I. apo B. cholesterol and triglycerides in serum and in lipoproteins, and LDL particle diameter were measured in thirty-eight consecutive newly-diagnosed non-diabetic untreated hypertensive men and 38 healthy male controls. Plasma glucose at baseline, 60 and 120 min during OGTT was significantly higher in patients than controls whereas serum insulin levels did not differ between patients and controls. Serum apo B and triglycerides were significantly raised in patients compared with controls (1.08 +/- 0.17 g/L [mean +/- SD] vs 0.97 +/- 0.22 g/L. p < 0.05, and 1.56 +/- 0.90 mmol/L vs 1.15 +/- 0.57 mmol/L, p < 0.05, respectively). Very-low-density lipoprotein (VLDL) triglycerides and LDL-cholesterol were increased in patients compared with controls (0.89 +/- 0.79 mmol/L and 0.54 +/- 0.35 mmol/L, p < 0.05, and 4.08 +/- 0.85 mmol/L and 3.60 +/- 0.92 mmol/L, p < 0.05, respectively) whereas high-density lipoprotein (HDL) cholesterol was lower in patients compared with controls 0.95 +/- 0.22 mmol/L and 1.07 +/- 0.20 mmol/L, p < 0.05). Adjustment for body mass index, abdominal/hip perimeter ratio and area under the glucose curve did not attenuate the relationship between hypertension and VLDL-triglycerides. Six patients and two controls had a mean LDL diameter < or = 25.5 nm and in the former serum triglycerides ranged from 1.86 mmol/L to 2.37 mmol/L. Mean LDL particle diameter in both patients and controls showed an inverse relationship with log-transformed serum triglycerides (r = - 0.51, p < 0.001 and r = - 0.47, p < 0.005, respectively). Among patients, those with serum triglycerides > or = [corrected] 1.58 mmol/L had a lesser mean LDL diameter than those with triglycerides above this threshold (25.78 +/- 0.47 nm vs 26.30 +/- 0.35 nm, p < 0.001). Higher plasma glucose, serum apo B and LDL-cholesterol as well as the decrease in serum HDL-cholesterol in patients with hypertension are consistent with high coronary heart disease risk. Not only mild hypertriglyceridemia but also high-normal serum triglycerides in themselves or as a surrogate of a predominance of small dense LDL particles in plasma convey an additional risk for cardiovascular disease in hypertensive patients even though routine plasma lipids are within or near normal range.

Adult↗
PubMed1993

Investigation of the particle size distribution of a model intravenous emulsion.

The size distribution of a model intravenous (iv) emulsion was investigated with special regard to the lower size classes. The special interest in the lower size classes is related to their possible responsibility for a number of side effects as well as their possible influence on pharmacokinetics of incorporated drugs. The particle size distribution of the unfractionated emulsion observed by photon correlation spectroscopy (PCS) showed no particles with diameters < 140 nm. In contrast, a three-dimensional analysis of transmission electron micrographs (TEM) resulted in a mean particle diameter of approximately 68 nm. 31P NMR experiments revealed that approximately 48 mol% of the emulsifier forms particles smaller than approximately 100 nm in diameter. The results from TEM observations and NMR spectroscopy suggest that the majority of particles by number have diameters < 100 nm. PCS measurements of fractionated samples of the emulsion, in combination with their chemical analysis, confirmed the predominance of particles with diameters < 100 nm. The relevance of PCS data analysis for the characterization of unfractionated iv emulsions, consisting of particles differing in structure and showing a broad size distribution by number, seems limited.

Chemical Phenomena↗
PubMed2003

Relationships between low-density lipoprotein particle size, plasma lipoproteins, and progression of coronary artery disease: the Diabetes Atherosclerosis Intervention Study (DAIS).

BACKGROUND: The Diabetes Atherosclerosis Intervention Study showed that treatment with fenofibrate decreases progression of coronary atherosclerosis in subjects with type 2 diabetes. We determined whether on-treatment plasma lipid concentrations and LDL particle size contribute to the favorable effect of fenofibrate on the progression of coronary artery disease (CAD). METHODS AND RESULTS: A total of 418 subjects with type 2 diabetes were randomly assigned to 200 mg micronized fenofibrate daily or placebo. The mean follow-up time was 39.6 months. LDL peak particle diameter (LDL size) was determined by polyacrylamide gradient gel electrophoresis from 405 subjects at baseline and at the end of the study. Progression of CAD was measured with quantitative coronary angiography. LDL size increased significantly more in the fenofibrate group than in the placebo group (0.98+/-1.04 versus 0.32+/-0.92 nm, P<0.001). In the combined group, small LDL size was significantly associated with progression of CAD measured as the increase of percentage diameter stenosis (r=-0.16, P=0.002) and decreases in minimum (r=-0.11, P=0.030) and mean (r=-0.10, P=0.045) lumen diameter. High on-treatment LDL cholesterol, apolipoprotein B, and triglyceride concentrations were also associated with the progression of CAD. In regression analyses, small LDL size added to the effect of LDL cholesterol and apolipoprotein B on the progression of CAD. Similar associations were observed in the fenofibrate group, whereas in the placebo group, lipoprotein variables were not significantly correlated with the progression of CAD. CONCLUSIONS: Changes in LDL size and plasma lipid levels account for part of the antiatherogenic effect of fenofibrate in type 2 diabetes.

Adult↗
PubMed2005

Effects of particle size fractions on reducing heart rate variability in cardiac and hypertensive patients.

It is still unknown whether the associations between particulate matter (PM) and heart rate variability (HRV) differ by particle sizes with aerodynamic diameters between 0.3 microm and 1.0 microm (PM(0.3-1.0)), between 1.0 microm and 2.5 microm (PM(1.0-2.5)), and between 2.5 microm and 10 microm (PM(2.5-10)). We measured electrocardiographics and PM exposures in 10 patients with coronary heart disease and 16 patients with either prehypertension or hypertension. The outcome variables were standard deviation of all normal-to-normal (NN) intervals (SDNN), the square root of the mean of the sum of the squares of differences between adjacent NN intervals (r-MSSD), low frequency (LF; 0.04-0.15 Hz), high frequency (HF; 0.15-0.40 Hz), and LF:HF ratio for HRV. The pollution variables were mass concentrations of PM(0.3-1.0), PM(1.0-2.5), and PM(2.5-10). We used linear mixed-effects models to examine the association between PM exposures and log10-transformed HRV indices, adjusting for key personal and environmental attributes. We found that PM(0.3-1.0) exposures at 1- to 4-hr moving averages were associated with SDNN and r-MSSD in both cardiac and hypertensive patients. For an interquartile increase in PM(0.3-1.0), there were 1.49-4.88% decreases in SDNN and 2.73-8.25% decreases in r-MSSD. PM(0.3-1.0) exposures were also associated with decreases in LF and HF for hypertensive patients at 1- to 3-hr moving averages except for cardiac patients at moving averages of 2 or 3 hr. By contrast, we found that HRV was not associated with either PM(1.0-2.5) or PM(2.5-10). HRV reduction in susceptible population was associated with PM(0.3-1.0) but was not associated with either PM(1.0-2.5) or PM(2.5-10).

Aged↗
PubMed1992

Particle size distribution of concentrated perfluorocarbon emulsions by sedimentation field flow fractionation.

Alliance Pharmaceutical Corp's concentrated perflubron (perfluorooctylbromide; PFOB) emulsions are being developed for several medical applications. Sedimentation Field-Flow Fractionation (SdFFF) can provide accurate particle size distribution data when properly calibrated for those emulsions. Since no suitable particle standards are available with the proper density (approximately 1.9 g/cc) and size range (diameter = 0.1-1.0 microns), calibration of the mass distribution was done by comparing the SdFFF detector signal with the actual mass of perflubron extracted from fractions eluted at successive time points and measured by GC. The calibrated mass distribution can then be used to calibrate other instruments such as the photosedimentation instruments used for routine quality assurance measurements.

Blood Substitutes↗
PubMed2005

Comparison of cascade impaction and laser diffraction for particle size distribution measurements.

The Andersen cascade impactor (ACI) and laser diffraction (LD) can be correlated at ambient temperature for aqueous drug formulations atomized by Soft Mist inhalers. A comparison of the two particle size determination methods at different conditions (flow rate, relative humidity) was performed. Under well-defined conditions, the faster LD can substitute the time consuming ACI at least for routine tests. The measurements were performed with three different drug formulations. The aerosol was generated by Soft Mist inhalers, and the droplet distributions were measured simultaneously using a laser diffraction analyzer together with the eight-stage Andersen cascade impactor. The simultaneous measurements ensure that aerosol and air conditions are identical for both LD and ACI. In order to measure the scattered laser light intensity of the aerosol passing the induction port, glass windows were fitted to the induction port. The evaporation effect of the aqueous aerosols on the PSD was investigated at ambient humidity and high humidity (RH > 90%). The simultaneous determination of the droplet size distribution leads to a good correlation between the ACI and LD method only if the measurements were performed at RH of >90%. The humidity of the ambient air had the strongest influence on PSD not only for ACI, but also for LD. In our set-up, the almost saturated air prevents aqueous droplets from drying. The influence of the flow rate on LD was negligible, whereas for ACI, a flow rate dependence is expected. The advantages of LD and the demonstrated compatibility to established EP/USP methods motivate the substitution of the ACI and the use of LD for routine measurements.

Aerosols↗
PubMed2002

Determination of large aerosol particle size by elutriation.

Inhalable dust fraction determination requires aerodynamic size information for large aerosol particles. Operation of cascade impactors at flows that collect these particles leads to jet Reynolds numbers outside the range of established impactor performance. Horizontal elutriators, designed to match earlier respirable dust curves at a single flow rate, may be used to provide aerodynamic size information for particles larger than 50 microm. Operation of these elutriators at higher than design flow rates and angles other than horizontal provides for particle penetration over the size range of the inhalable dust curve. Equations are provided that relate penetration, flow rate, and angle to aerodynamic diameter to allow for bracketing the desired size and distribution. The use of impactor data reduction methods to determine size distributions with the MRE horizontal elutriator is examined with a spreadsheet model. Comparison of elutriator size determination with an impactor in the 10 to 15 microm range, where both methods could be used, resulted in reasonable agreement. This method provides for determination of aerodynamic characteristics of large aerosols in field sampling conditions.

Aerosols↗
PubMed1996

Binding affinity and particle size of LDL in subjects with moderate hypercholesterolemia: relationship with in vivo LDL metabolism.

The aim of this study was to examine relationships between low density lipoprotein (LDL) metabolism, in vitro binding, and particle size. Twenty four study subjects, 17 men and 7 women, had elevated plasma total cholesterol (TC), ranging from 174 to 232 mg/dl, and LDL cholesterol (LDLC) ranging from 113 to 195 mg/dl after 12 weeks on a Step I diet. The fractional clearance rate (FCR) for LDL ranged from 0.233 to 0.619 pools/day (0.366 +/- 0.021) and was significantly correlated with plasma triglycerides (TG) (P < 0.05). Although there was no relation between FCR and binding in the study group as a whole, those subjects with an FCR within the normal range (< 0.45, n = 20), showed a significant negative correlation between FCR and the KD for LDL binding, (r = 0.52). A subset of four subjects with an elevated FCR (> 0.45) had higher production rate (PR) (P < 0.005) and a significant positive correlation between the KD for LDL binding and FCR (P < 0.05). LDL size varied from 240.0 to 265.8 A and was significantly inversely correlated with plasma TG (P < 0.001) but there was no relation between LDL size and metabolism or binding affinity. Thus, there appears to be a correlation between binding affinity and clearance for subjects who had normal LDL production and clearance rates. On the other hand, mechanisms other than binding affinity appear to influence clearance in subjects with elevated rates of production and clearance.

Adult↗
PubMed2000

Reduced LDL particle size in children consuming a very-low-fat diet is related to parental LDL-subclass patterns.

BACKGROUND: A genetically influenced atherogenic lipoprotein phenotype characterized by a predominance of small, dense LDL particles (subclass pattern B) can be induced by low-fat diets in healthy subjects with large LDL particles (pattern A). OBJECTIVE: The aim of this study was to test whether genetic predisposition to subclass pattern B contributes to susceptibility to induction of this trait by a low-fat diet. DESIGN: The prevalence of pattern B in children is relatively low compared with that in older individuals, but genetic susceptibility to this trait in offspring can be inferred by its presence in their parents. Plasma lipoproteins were analyzed 10 d after a change from a usual diet to a very-low-fat (10% fat), high-carbohydrate diet in offspring (mean age: 14 y; range: 7-28 y) of 22 families according to parental LDL-subclass patterns when consuming a low-fat diet: AxA mating (9 families with 19 children), AxB mating (5 families with 10 children), and BxB mating (8 families with 21 children). RESULTS: The very-low-fat, high-carbohydrate diet produced significantly greater decreases in LDL particle size in offspring of BxB parents (f1.gif" BORDER="0"> +/- SE: -0.55 +/- 0.16 nm) and AxB parents (-0.48 +/- 0.19 nm) than in offspring of AxA parents (0.14 +/- 0.20 nm). The number of children expressing pattern B with the 10%-fat diet and the proportion of children converting from pattern A to pattern B was significantly greater in offspring of BxB parents than in those with 1 or 2 pattern A parents. CONCLUSION: A very-low-fat, high-carbohydrate diet can induce expression of LDL-subclass pattern B in genetically predisposed children with low expression of the trait while consuming their usual diets.

Adolescent↗
PubMed1997

Isolation of subcellular-sized particles separated by electrophoresis in dilute polymer solution, using commercial electrophoresis apparatus with intermittent scanning of fluorescence.

Resolution of subcellular-sized particles in electrophoresis employing semi-dilute polymer solutions as "sieving media" improves as the polymer concentration is decreased. Therefore, the previously reported conditions of preparative electrophoresis of microsomes, using concentrated (12%) polyvinylpyrrolidone (PVP) solutions, while solving the problem of non-entrance of large particles into "sieving media", do not provide adequate resolving capacity, as exemplified by failure of the microsome preparation used, to resolve in the manner of gels or dilute solutions. The present report provides the conditions under which the HPGE-1000 apparatus can be preparatively applied when the electrophoretic separation is effectively conducted in a dilute polymer solution. The isolation of three microsome components under those conditions constitutes the first application of "particle sieving", i.e., a separation due preponderantly to size and shape differences, at a preparative scale.

Animals↗