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 1,009 records · Page 56Linked to original sources

PubMed2002

Determination of particle size by using the angular distribution of backscattered light as measured with low-coherence interferometry.

We employ a novel interferometer to measure the angular distribution of light backscattered by a turbid medium. Through comparison of the measured data with the predictions of Mie theory, we are able to determine the size of the scatterers comprising the medium with subwavelength precision. As the technique is based on low-coherence interferometry, we are able to examine the evolution of the angular distribution of scattered light as it propagates into the medium. The effects of multiple scattering as a function of penetration depth in the medium are analyzed. We also present various considerations for extending this technique to determining structural information in biological tissues, such as the effects of a distribution of particle sizes and the need to average out speckle contributions.

Interferometry↗

PubMed2000

Influence of inspiratory flow rate, particle size, and airway caliber on aerosolized drug delivery to the lung.

A number of studies in the literature support the use of fine aerosols of drug, inhaled at low IFRs to target peripheral airways, with the objective of improving clinical responses to inhaled therapy (Fig. 8). Attempts have been made to separate response due to changes in total administered dose or the surface concentration of the dose from response due to changes in site of deposition--both are affected by the particle size of the aerosol, with IFR additionally influencing the latter. The tools for measuring dose and distribution have improved over the last 10-15 years, and thus we should expect greater accuracy in these measurements for assessing drug delivery to the lung. There are still issues, though, in producing radiolabeled (99m)technetium aerosols that are precise markers for the pharmaceutical product being tested and in quantitating absolute doses deposited in the lung. PET isotopes may provide the means for directly labelling a drug and perhaps can offer an alternative for making these measurements in the future, but deposition measurements should not be used in isolation; protocols should incorporate clinical tests to provide parallel therapeutic data in response to inhalation of the drug by the various patient populations being studied.

Administration, Inhalation↗

PubMed1989

Effect of reactivity rate and particle size of magnesium oxide on magnesium availability, acid-base balance, mineral metabolism, and milking performance of dairy cows.

Four ruminally fistulated Holstein cows were arranged in a 4 x 4 Latin-square design. Treatments consisted of a control diet and three diets containing 4% MgO (DM basis) with increasing reactivity rates (A, B, C). Diets contained corn silage and concentrate at a 40:60 ratio (DM) and were fed at 95% of ad libitum intake. Total acid-consuming capacity and solubility of MgO in vitro paralleled particle size and agreed with the solubilities in the rumen. Milk fat percentage, but not milk yield, was increased by all three MgO diets. Ruminal pH was elevated by the MgO diets across all 8 h postfeeding. MgO, reactivity A diet tended to increase ruminal acetate, total VFA production, milk yield, milk fat yield, and milk fat percentage. Effect of time postfeeding on acetate and propionate production was significant; 2 to 6 h postfeeding was the period most responsive to the diets. No significant influence on blood acid-base balance was observed. On the basis of urinary excretion of Mg, MgO sources with smaller particles are more available to cattle. Both Ca and Cl metabolism appeared to be affected by reactivity rate of MgO.

Acid-Base Equilibrium↗

PubMed1990

The effects of nicotinic acid treatment on high density lipoprotein particle size subclass levels in hyperlipidaemic subjects.

Twenty-three consecutive hyperlipidaemic patients were treated with 4 g nicotinic acid daily for 6 weeks. The treatment resulted in the expected reduction of serum very low density (VLDL) and low density lipoproteins (LDL) and in the increase of high density lipoproteins (HDL). The cholesterol concentration of the latter fraction rose by 45%. The HDL fraction was isolated by ultracentrifugation and then subjected to gradient gel electrophoresis (gge), in order to determine the HDL particle size distribution, before and after treatment. The increase of HDL was almost exclusively confined to the largest HDL (gge) subclass HDL-2b, the protein content of which rose by 183%. In contrast, there was about a 25% decrease in the concentration of the smallest HDL(gge) subclasses, HDL-3b and HDL-3c. The levels of HDL-2b and VLDL triglycerides showed a significant inverse correlation before, as well as after, treatment. Multiple partial correlation analysis demonstrated, however, that the nicotinic acid induced increase in HDL-2b concentration showed a highly significant inverse correlation to the decrease in LDL cholesterol, but not to the decrease in VLDL triglyceride levels. Recent studies, in particular those regarding the negative correlation between both the degree and progression of coronary atherosclerosis and the HDL-2b concentration in young male myocardial infarct patients, suggest that the profound increase of HDL-2b levels by nicotinic acid treatment in hyperlipidaemic patients might be of considerable importance in the protection of coronary atherosclerosis.

Adult↗

PubMed2001

Particle size distribution of orange juice cloud after addition of sensitized pectin.

The effect of the addition of commercial pectin to orange juice that was de-esterified by alkaline treatment or pectinmethylesterase was evaluated. Pectin at various degrees of esterification (DE) was added to reconstituted frozen orange juice concentrate, and the extent of cloud loss was determined after centrifugation. Of the five pectin treatments, percent transmittance (% T) of juice remained <5%, except for the pectin treatment with a residual methoxyl content (% DE) of <5%. Addition of 100--600 ppm of 5% DE pectin to juice resulted in % T between 36 and 73%. Despite the absence of clarification, increases in cloud particle size were observed and depended on the % DE, the amount of pectin added, and the method used to modify the pectins.

Beverages↗

PubMed2004

Molecular dynamics study of the catalyst particle size dependence on carbon nanotube growth.

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, which contain at least 20 iron atoms, nucleate SWNTs that have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm.

Journal Article↗

PubMed1981

Particle size and concentration adjustments of tomato products for Howard mold count.

The present AOAC method for mold counts of tomato products (44.096) provides no inter-product standardization of concentration among juice, sauce, paste, puree, and catsup; no intra-product standardization of concentration for juice, sauce, and catsup; and no adjustment for degree of comminution. Use of the official method, therefore, could result in an artificially increased mold count for products which have undergone extreme comminution. A new method was developed to adjust all products to the same concentration and grind them to a uniform particle size, thereby ensuring comparable mold counts on products produced by different processes. Collaborative study results showed equal repeatability for both the official and the proposed methods and a lower coefficient of variation for the proposed method.

Food Microbiology↗

PubMed1996

Low density lipoprotein particle size in hypopituitary adults receiving conventional hormone replacement therapy.

Adults receiving conventional replacement therapy for hypopituitarism are known to have increased cardiovascular mortality. The aim of this study was to assess the lipid profiles of 30 hypopituitary adults compared with 2 case control groups, 1 matched for age, sex, and body mass index (BMI) and the second matched for age and sex only with a BMI representative of the general population. Fasting lipids, lipoproteins, and apoproteins (Apo) were determined by routine methods. Low density lipoprotein (LDL) particle size was determined by nondenaturing gradient gel electrophoresis. LDL size was significantly smaller in the hypopituitary group (25.9 +/- 0.1 nm) than in the BMI-matched (26.2 +/- 0.1 nm; P < 0.05) and standard control (26.3 +/- 0.1 nm; P < 0.01) groups. High density lipoprotein cholesterol levels in the hypopituitary group were significantly lower than those in the BMI-matched control group (1.13 +/- 0.06 vs. 1.34 +/- 0.06 mmol/L; P < 0.05) and the standard control group (1.38 +/- 0.06 mmol/L; P < 0.005). Apo A1 levels were also lower compared with those in the BMI-matched (122 +/- 6 vs. 137 +/- 4 mg/dL; P < 0.05) and the standard (143 +/- 4 mg/dL; P < 0.005) control groups. There was a trend toward higher triglyceride levels when the hypopituitary subjects were compared with the standard control group [1.4 (95% CI, 1.3-2.2) vs. 1.0 (95% CI, 0.9-1.4) mmol/L; P = 0.06]. These differences were more marked in the female subjects studied. No significant differences were noted in total cholesterol, LDL cholesterol, or Apo B levels. We conclude that hypopituitary patients receiving conventional replacement therapy have an atherogenic lipid profile characterized by small dense LDL, decreased high density lipoprotein cholesterol, and increased triglyceride levels, which may contribute to the excess cardiovascular mortality in this group.

Adult↗

PubMed2003

Effective velocity and effective dispersion coefficient for finite-sized particles flowing in a uniform fracture.

In this work we derive expressions for the effective velocity and effective dispersion coefficient for finite-sized spherical particles with neutral buoyancy flowing within a water saturated fracture. We considered the miscible displacement of a fluid initially free of particles by another fluid containing particles of finite size in suspension within a fracture formed by two semi-infinite parallel plates. Particle spreading occurs due to the combined actions of molecular diffusion and the dispersive effect of the Poiseuille velocity profile. Unlike Taylor dispersion, here the finite size of the particles is taken into account. It is shown that because the finite size of a particle excludes it from the slowest moving portion of the velocity profile, the effective particle velocity is increased, while the overall particle dispersion is reduced. A similar derivation applied to particles flowing in uniform tubes yields analogous results. The effective velocity and dispersion coefficient derived in this work for particle transport in fractures with uniform aperture are unique and ideally suited for use in particle tracking models.

Journal Article↗

PubMed2006

In Vitro Comparison of Output and Particle Size Distribution of Budesonide from Metered-Dose Inhaler with Three Spacer Devices during Pediatric Tidal Breathing.

OBJECTIVES: The aim of this in vitro study was to determine the delivered dose of budesonide 200mug via a chlorofluorocarbon-free pressurized metered dose inhaler (pMDI) when administered through different spacers in tidal breathing patterns of young children. METHODS: Tidal breathing was simulated for toddlers and children. Spacers tested were Babyhaler((R)), AeroChamber((R)) Plus small and medium; the pMDI was Budiair((R)) 200microg. Output was measured after one actuation and five inhalations in primed and unprimed spacers. Cumulated output was evaluated after each of five simulated inhalations. Aerosol characteristics - i.e. particle size distribution of the output - were determined in primed spacers with a cascade impactor using high-performance liquid chromatography and UV detection. RESULTS: Total output from primed spacers after five inhalations was determined between 37.9microg and 40.9microg with little differences between spacers and breathing patterns. About 58-79% of this total output was inhaled with the first breath from the AeroChamber((R)) Plus and about 26% from the Babyhaler((R)). The fine particles <5mum ranged between 87% and 92% of the delivered dose for all three spacers. DISCUSSION AND CONCLUSION: The nominal dose (200microg) of the Budiair((R)) 200microg inhaler is reduced to 40microg delivered dose or less by using Babyhaler((R)) and AeroChamber((R)) Plus spacers taking five breaths. With a single breath the delivered dose can be reduced further to a minimum of 10microg using the Babyhaler((R)). Clinical studies are warranted in the future for decisions on 'clinical efficacy', safety, and exact dose adjustment.

Administration, Inhalation↗

PubMed1992

Immunochemical quantification and particle size distribution of airborne papain in a meat portioning facility.

The use of enzymes in industry continues to expand. With this increased use comes a concerted need to better understand potential respiratory health hazards to exposed workers and to quantify exposure levels that cause impaired health. To this end, projects were undertaken by the National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluations Program and Cole Associates whereby this information was collected. Data concerning medical evaluation and aspects of industrial hygiene are the subjects of two separate reports from these respective groups. This method/results report includes a description of (1) a sensitive immunoradiometric assay for the quantification of airborne papain and its particle size distribution, (2) measurement of papain from both general area and personal breathing zone air samples obtained from a meat processing plant that used this immunochemical analysis, (3) a sampling strategy, and (4) an improved air sample processing technique. Airborne papain was measured at levels ranging from low nanogram to microgram per cubic meter concentrations. Approximately half of the papain activity was associated with particles having an aerodynamic diameter of less than 9.4 microns. These data point to a need for containment and controls in the manufacture and use of such compounds. This approach can be considered by the hygienist as an effective tool to be used in conjunction with epidemiologic studies to help set standards that are practical, safe, and maintained.

Air Pollutants, Occupational↗

PubMed2005

Effect of different dietary geometric mean particle length and particle size distribution of oat silage on feeding behavior and productive performance of dairy cattle.

Twenty lactating Holstein cows (5 primiparous and 15 multiparous) were used in a 5 x 5 Latin Square design, with 5 treatments and 3 periods of 21 d each. Diets contained 25% corn silage, 25% oat silage, and 50% concentrate (dry matter basis). The 5 treatments tested in the experiment were long oat silage (LOS), medium oat silage (MOS), fine from long oat silage (FLOS), fine from medium oat silage (FMOS), and half LOS plus half FLOS (LFLOS). The geometric mean particle length (GMPL) of the diets was 6.68, 5.19, 4.46, 4.35, and 5.39 mm for LOS, MOS, FLOS, FMOS, and LFLOS, respectively. The LFLOS was designed to provide dietary GMPL similar to MOS, but with a more bimodal particle size distribution (PSD). Linear and quadratic effects of GMPL were tested, based on the mean GMPL of the feed actually consumed (cGMPL). Contrasts were used to test for the effect of different PSD (MOS vs. LFLOS) and to test for differences between FMOS and FLOS, which would indicate unequal fermentations in the MOS and LOS silos. No differences were detected between FMOS and FLOS in most of the variables measured. Increasing cGMPL linearly decreased dry matter intake, milk production, and milk protein percentage and yield without affecting milk fat percentage, milk fat yield, ruminal pH, and ruminal volatile fatty acid concentration. Although cows fed diets with increasing cGMPL spent more time eating and chewing per day and per kilogram of dry matter intake, there was no effect of cGMPL on rumen pH. Feeding medium oat silage increased milk fat percentage and yield compared with feeding a mixture of long and fine oat silage.

Animals↗

PubMed2006

LDL particle size, fat distribution and insulin resistance in obese children.

BACKGROUND: The importance of small dense low-density lipoprotein (sdLDL) cholesterol in coronary heart disease has been demonstrated in many studies. Body fat accumulation, especially abdominal adiposity, is one of the important factors modifying the expression of sdLDL in adults. OBJECTIVE: To determine the prevalence of sdLDL in obese children, and to investigate its relationship with anthropometric and metabolic variables. SUBJECTS: A total of 30 obese children (22 males, 8 females) aged 12.6+/-0.6 years (mean+/-s.e.), who presented to our outpatient clinic with obesity. METHODS: LDL peak particle diameter was determined using gel electrophoresis. LDL subclasses were classified into sdLDL (pattern B; diameter<25.5 nm) and non-sdLDL (pattern A; diameter>or=25.5 nm). Anthropometric and metabolic variables were also determined to identify factors modifying LDL particle size. RESULTS: sdLDL was detected in 11 children (40.0%). In children with sdLDL, waist/height ratio was significantly higher (P=0.0466), and they had significantly higher triglyceride (TG) (P=0.0035) and lower high-density lipoprotein cholesterol (HDLC) levels (P=0.036). Peak LDL diameter as a continuous variable was significantly correlated with HDLC and TG levels. In multiple regression analysis, body mass index and waist/height ratio were significant determinants of the peak LDL diameter variability. CONCLUSIONS: We found a high prevalence of sdLDL in obese children, and a relationship of peak LDL diameter with abdominal fat accumulation, HDLC and TG levels. The presence of sdLDL might be an important risk factor for the metabolic syndrome.

Abdominal Fat↗

PubMed2006

Particle size distribution to design and operate an APT process for agricultural wastewater reuse.

Total suspended solids is a parameter commonly used to operate and design coagulation-flocculation processes. Nevertheless, their application for an advanced primary treatment (a high performance but low dose demand coagulation processes coupled with a high rate sedimentator, sometimes called enhanced primary treatment) is not the best option to produce an effluent for agricultural irrigation. This paper compares the best operating conditions obtained using the TSS or the PSD (particle size distribution) as parameters to follow the efficiency. The treatment objective was to remove particles >20 microm, in such conditions that the effluent can contain organic matter and nutrients necessary for crops with a reduced number of helminth ova (with sizes between 20 to 80 microm). Using the TSS as parameter, the best coagulation (460 s(-1), 60 s contact time and 300 micromolAl/L) and flocculation (20 s(-1) with 15 min) conditions produced an effluent with 1.2 HO/L. To obtain a similar results but using operating conditions determined with the PSD at a three times lower coagulant dose can be employed (diminishing operating costs and reducing the quantity of sludge produced), and a reduction on energy consumption of around eight times can be reached. Best operating conditions defined using the PSD (160 s(-1), 60 s contact time and 100 micromolAl/L) produced an effluent with <0.4 HO/L.

Agriculture↗

PubMed1990

Effects of anaesthesia of human oral structures on masticatory performance and food particle size distribution.

Ten persons with intact dentitions performed a series of 6 masticatory tests, employing 5, 10, 20, 40, 80 and 160 strokes to chew standard quantities of peanuts on their preferred chewing side for each of three test conditions: (1) before anaesthesia: (2) after maxillary anaesthesia; and, (3) after maxillary and mandibular anaesthesia (unilateral). A seventh test employing 20 strokes was also repeated on the non-anaesthetized contralateral side. The chewed food was sieved through 5, 10, 20, 40, 80 and 100 mesh screens. The percentage of the ratio of the volume of peanuts that passed through the sieve and the total volume of recovered food provided the performance score for the given sieve. The performance scores increased significantly with the number of stokes and dropped markedly after anaesthesia. The maximum reduction of 19.6% in the mean masticatory performance and 46% in the mean masticatory efficiency occurred after unilateral anaesthesia at 10 mesh particle size in the 20-stroke test. An average of 40 strokes was required after unilateral anaesthesia to achieve almost the same performance achieved with 20 strokes before anaesthesia. The regression slopes, derived from the 5, 10 and 20 mesh particle distributions showed that coarse particles were ground more rapidly than fine particles before anaesthesia. This preferential comminution became less evident after maxillary anaesthesia and was least evident after unilateral anaesthesia. The regression slope for the control peaked at 10 strokes as compared to 20 strokes after unilateral anaesthesia. Thus peripheral sensory impairment affects masticatory efficiency in dentate persons.

Adult↗

PubMed1998

Effects of a cardioselective beta-blocker on postprandial triglyceride-rich lipoproteins, low density lipoprotein particle size and glucose-insulin homeostasis in middle-aged men with modestly increased cardiovascular risk.

Beta-adrenergic receptor-blocking agents are commonly used for treatment of hypertension, angina pectoris and arrhythmias and as secondary prevention after myocardial infarction. The modest protection against myocardial infarction conferred by these compounds in primary-preventive studies has suggested that beneficial effects of beta-blockade are counteracted by known adverse influences on lipid and glucose metabolism. As most beta-blockers increase plasma triglycerides and decrease the high density lipoprotein (HDL) cholesterol concentration, a randomized, double-blind, cross-over study was conducted to evaluate whether a 12-week treatment with metoprolol (100 mg o.d.) or placebo affected the metabolism of postprandial triglyceride-rich lipoproteins in 15 middle-aged men with a modestly increased cardiovascular risk. Metoprolol treatment significantly increased the postprandial responses of very low density lipoprotein (VLDL) and VLDL remnants to a mixed meal-type of oral fat tolerance test. The effect was particularly prominent for larger (Svedberg flotation rate (Sf) > 400 and Sf 60-400) particle species (P < 0.001 in repeated measures ANOVA), whereas the smaller (Sf 20-60) particles were less affected (P < 0.05). The changes in the postprandial responses of the different VLDL species were mainly related to an effect on the fasting plasma concentrations, with limited or no influences on VLDL catabolism during the postprandial state. In contrast, metoprolol treatment did not significantly influence the postprandial responses of chylomicrons and chylomicron remnants. Notably, the enhanced fasting and postprandial triglyceridaemia during metoprolol treatment was neither accompanied by a rise in fasting or postprandial free fatty acid concentrations, nor by alterations of the glucose and insulin responses to a standard oral glucose challenge. The ensuing shift in the LDL particle size distribution towards smaller particles was limited (fraction small LDL: metoprolol 22.8 +/- 15.7% versus placebo 19.3 +/- 15.0%, P < 0.05). In conclusion, metoprolol treatment primarily enhances fasting and postprandial triglyceridaemia in middle-aged men by increasing the basal hepatic production of VLDL.

Adrenergic beta-Antagonists↗

PubMed1989

Particle size and composition of composite dusts.

Inhalation of respirable crystalline silica dusts (sized between 0.5 and 5.0 micrograms) causes silicosis. Crystalline silica fillers are used in some composites and fine dusts/aerosols generated during high-speed finishing of these materials may be regularly inhaled by clinical dental personnel. Due to the widespread use of composites, the potential of these dusts/aerosols for causing silicosis warrants concern. Six composites were polymerized, then abraded with diamond and carbide finishing burs to produce dusts in a manner simulating the clinical finishing of esthetic veneers. Dusts were collected on 0.8 micron filters using an air sampling pump. Six hundred particles of each dust sample were counted and measured using a light microscope. The respirable fraction of dust particles ranged between 57.2 and 85.7%. The diamond bur created more respirable particles than the carbide bur for each composite tested. The elemental composition of particles of each composite was determined by energy dispersive x-ray analysis. Silicon was detected in amounts ranging from 71-100%. Based on the composition and particle size distribution only, dusts generated during simulated finishing of composite resins containing quartz filler have the potential for causing silicosis in dental personnel.

Air Pollutants, Occupational↗

PubMedDate not supplied

The size distribution of thyroid follicles in single thyroid glands, a peculiar problem of particle size distribution in stereology.

Follicle sections vary in size according to their inclination mainly in hypertrophied thyroids. Sagittal sections elicit a shift to small classes, while transversal sections, to large classes. There is no mathematical transformation able to convert data obtained by sections into "true" sizes of follicles, as may be achieved by isolation. All papers emphasizing only section diameters and inferring about follicle size must be cautiously interpreted, and even discarded, if they tend to establish differences in follicle size solely on that basis. Follicle isolation is necessary if we need to establish follicle size and shape. Although proportions are almost stable for rats of the same age and weight, the proportions of follicle size may vary, as dependent on age and other internal and external conditions. The situation is most complicated by colloid accumulation; but despite these impedimenta, TSH secretion enlarges the follicles, a situation hitherto not well established. Cell enlargement is consequently followed by follicle enlargement, despite colloid resorption.

Animals↗