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At least 127 records · Page 7Linked to original sources
PubMed2004

Variability of left ventricular ejection fraction and volumes with quantitative gated SPECT: influence of algorithm, pixel size and reconstruction parameters in small and normal-sized hearts.

PURPOSE: Several software packages are commercially available for quantification of left ventricular ejection fraction (LVEF) and volumes from myocardial gated single-photon emission computed tomography (SPECT), all of which display a high reproducibility. However, their accuracy has been questioned in patients with a small heart. This study aimed to evaluate the performances of different software and the influence of modifications in acquisition or reconstruction parameters on LVEF and volume measurements, depending on the heart size. METHODS: In 31 patients referred for gated SPECT, 64(2) and 128(2) matrix acquisitions were consecutively obtained. After reconstruction by filtered back-projection (Butterworth, 0.4, 0.5 or 0.6 cycles/cm cut-off, order 6), LVEF and volumes were computed with different software [three versions of Quantitative Gated SPECT (QGS), the Emory Cardiac Toolbox (ECT) and the Stanford University (SU-Segami) Medical School algorithm] and processing workstations. Depending upon their end-systolic volume (ESV), patients were classified into two groups: group I (ESV>30 ml, n=14) and group II (ESV<30 ml, n=17). Agreement between the different software packages and the influence of matrix size and sharpness of the filter on LVEF and volumes were evaluated in both groups. RESULTS: In group I, the correlation coefficients between the different methods ranged from 0.82 to 0.94 except for SU-Segami (r=0.77), and were slightly lower for volumes than for LVEF. Mean differences between the methods were not significant, except for ECT, with which LVEF values were systematically higher by more than 10%. Changes in matrix size had no significant influence on LVEF or volumes. On the other hand, a sharper filter was associated with significantly larger volume values though this did not usually result in significant changes in LVEF. In group II, many patients had an LVEF in the higher range. The correlation coefficients between the different methods ranged between 0.80 and 0.96 except for SU-Segami (r=0.49), and were slightly worse for volumes than for LVEF values. In contrast to group I, however, inter-method variability was quite large and most mean LVEF differences were significant. LVEF was systematically highest with ECT and lowest with SU-Segami. With QGS, changes in matrix size from 64(2) to 128(2) were associated with significantly larger volumes as well as lower LVEF values. Increasing the filter cut-off frequency had the same effect. With SU-Segami, a larger matrix was associated with larger end-diastolic volumes and smaller ESVs, resulting in a highly significant increase in LVEF. Increasing the filter sharpness, on the other hand, had no influence on LVEF though the measured volumes were significantly larger. CONCLUSION: In patients with a normal-sized heart, LVEF and volume estimates computed from different commercially available software packages for quantitative gated SPECT are well correlated. LVEF and volumes are only slightly sensitive to changes in matrix size. Smoothing, by contrast, is associated with significant changes in volumes but usually not in LVEF values. However, owing to the specific characteristics of each algorithm, software should not be interchanged for follow-up in an individual patient. In small hearts, on the other hand, both the used software and the matrix size or smoothing significantly influence the results of quantitative gated SPECT. LVEF values in the higher range are frequently observed with all the studied software except for SU-Segami. A larger matrix or a sharper filter could be suggested to enhance the accuracy of most commercial software, more particularly in patients with a small heart.

Algorithms↗
PubMed2026

Re-evaluating pediatric laryngoscope blade size recommendations: Comparable intubation performance across blade sizes in pediatric manikin models.

BACKGROUND: Pediatric airway management traditionally emphasizes strict adherence to age-based laryngoscope blade size recommendations, despite limited empirical validation. OBJECTIVES: To evaluate whether intubation performance varies across a range of blade sizes, and whether a Macintosh 2 blade performs comparably across multiple pediatric age groups in a simulation setting. METHODS: We conducted a randomized crossover simulation study using three pediatric airway manikins (neonate, infant, and child age groups). Emergency medicine residents and faculty physicians performed intubations using multiple laryngoscope blade types and sizes, including standard and nonstandard options. Primary outcomes were intubation time and first-attempt success. Secondary outcomes included complications and operator-rated ease of glottic view and tube passage. Between-blade differences were estimated with 95% confidence intervals. RESULTS: Across manikin sizes and blade types, intubation times were short and first-attempt success rates exceeded 98% in most conditions. Performance remained consistent even with blade sizes outside conventional age-based recommendations. Between-blade differences in intubation time were small, and complication rates were low across conditions. The Macintosh 2 blade performed comparably across all manikin sizes, with similar intubation times, high success rates, and favorable ease ratings. CONCLUSIONS: Intubation performance in pediatric manikin models was similar across a wide range of blade sizes. These hypothesis-generating findings warrant prospective clinical evaluation of simplified blade selection strategies for pediatric intubation.

Manikins↗
PubMed2001

Unequal cluster sizes for trials in English and Welsh general practice: implications for sample size calculations.

Cluster randomized trials are often used in primary care settings. In the U.K., general practices are usually the unit of allocation. The effect of variability in practice list size on sample size calculations is demonstrated using the General Medical Services Statistics for England and Wales, 1997. Summary statistics and tables are given to help design such trials assuming that a fixed proportion of patients are to be recruited from each cluster. Three different weightings of the cluster means are compared: uniform, cluster size and minimum variance weights. Minimum variance weights are shown to be superior to uniform, particularly when clusters are small, and to cluster size weights, particularly when clusters are large. Where there are large numbers of participants per cluster and cluster size weights are used, the power actually falls as more patients are recruited to large clusters. When minimum variance weights are used the increase in the design effect due to variation in list size is small, regardless of the size of intracluster correlation coefficient or the number of participants per cluster, provided there is no loss of randomized units. When the expected number of participants per practice is low a greater loss in power comes from practices which fail to recruit patients. A method to estimate the likely effect and allow for it is presented.

Accidental Falls↗
PubMed2004

Production of offspring using current income and reserves: size-number trade-off and optimal offspring size.

To analyse the effects of current income on the nature of size-number trade-off and optimal offspring size, we developed a model in which offspring grow by absorbing current income and reserves. The offspring continue to grow while the current income is available or the reserves exist, and they cease to grow when the reserves are depleted and the current income ceases. We showed that the size-number trade-off is nonlinear in the region where the number of offspring is smaller than the critical number and linear in the region where the number of offspring is greater than the critical number. In the former region, the reserves are not depleted by the time the current income ceases and the offspring cease to grow when the reserves are depleted, whereas in the latter region, the reserves are depleted before the current income ceases and the offspring production is completed when the current income ceases. The optimal offspring size is the same as that shown in Sakai and Harada (Evolution 55 (2001) 467) if this optimal size is realized in the region of nonlinear trade-off, whereas the optimal offspring size is the same as that shown in Smith and Fretwell (Am. Natur. 108 (1974) 499) if this optimal size is realized in the region of linear trade-off.

Animals↗
PubMed1991

Sex differences in human brain size and the general meaning of differences in brain size.

Contrary to commonly held convictions, there is no clear association between brain size and body parameters in humans. Within sexes, once age and health status are controlled for, there is no significant association between brain size and body height for females. For males, body height accounts for no more than .04% of the variance in brain size. The relation between brain weight and body weight is even less clearly defined. Nevertheless, there are large and significant differences in brain size between the sexes. If no adequate body parameters can be found that scale to brain size within the sexes, the marked dimorphism between males and females makes it even more difficult to find a common set of parameters that allow evaluation of brain size differences between sexes. Within and across sexes, there is no convincing link between a limited measure of behavioural capacity (IQ) and brain size. This leads to the more general question: Why would one expect such a link, and, if it is not found, what does this mean in the context of general theories of cortical function?

Animals↗
PubMed2000

Particle size determination of a three-component suspension using a laser-scattering particle size distribution analyzer.

In this study, a rapid and accurate particle size determination method using a light-scattering particle size analyzer was developed to measure the particle size and size distribution of a suspension containing three solid components: clotrimazole, triamcinolone, and sarafloxacin, which have different refractive indices. To ensure that data represent the size distribution of the primary particles of the suspension, the optimal sonication prior to and during measurement was determined. It was found that the results obtained using the average relative refractive index (RRI) of the three components agreed with the results obtained using three individual RRIs. In addition, the results from two analysts demonstrated good reproducibility of this method. The size distribution data of the suspension were also compared to those of the bulk drugs. The results showed that the median particle size of this three-component suspension is relatively close to that of clotrimazole, which accounts for 80% of solid particles in the suspension. Furthermore, the results obtained using the light-scattering technique were comparable to those obtained using a polarized light microscope equipped with an image analyzer, indicating acceptable accuracy of this technique.

Anti-Infective Agents↗
PubMed2006

Analysis of litter size and days to lambing in the Ripollesa ewe. II. Estimation of variance components and response to phenotypic selection on litter size.

A performance data set from 376 Ripollesa purebred ewes of the experimental flock of the Universitat Autònoma of Barcelona was analyzed using a bivariate Bayesian threshold-linear model. The data set contained 1,598 litter size records and 1,699 days-to-lambing records. The model included the additive genetic effect of each animal and 3 nongenetic sources of variation: ewe age, year of lambing, and the permanent environmental effect characterized by the ewe. The flock was phenotypically selected for litter size since 1986, and replacement ewes and rams were selected from the progeny of the more prolific ewes, which had at least 3 deliveries recorded. The phenotypic trend for litter size was positive, whereas days to lambing followed an unclear pattern. Both traits had low heritabilities; 0.13 for litter size and 0.11 for days to lambing. Response to selection was evaluated through (a) the average breeding value of the ewe lambs chosen annually, and (b) the average breeding value of the overall flock. The first measurement suggested a positive trend for litter size, although it showed important oscillations. On the other hand, the average breeding value for the overall flock showed a stable positive tendency after yr 4 of selection, with estimates clearly different from zero after yr 11 of selection. A significant increase in the incidence of multiple births was observed, with a mode of approximately 10%. The correlated response in days to lambing did not show a significant trend. The effect of year of lambing also positively influenced both litter size and days to lambing, although important oscillations were observed between years. Results indicated that litter size in sheep can be effectively improved through phenotypic selection, even in small flocks; moreover, days to lambing could also be genetically improved, given the estimate obtained for its heritability.

Animals↗
PubMed1998

Particle size determination of a flocculated suspension using a light-scattering particle size analyzer.

Microscopy is a useful and direct method for measuring the particle size of a suspension because, in addition to the particle size and size distribution, it provides visual detection of the shape and state of aggregation of the particles in the suspension. However, this method suffers from the shortcomings of being tedious and time consuming. In this study, a light-scattering particle size analyzer was used to determine the particle size and size distribution of a flocculated suspension. The sonication of the sample prior to and during measurement was found to be critical in ensuring that data are representative of the size distribution of the primary particles of the suspension. The light-scattering results were further confirmed by data generated using a polarized light microscope equipped with an image analyzer.

Benzocaine↗
PubMed2001

Estimating relative population sizes from simulated data sets and the question of greater African effective size.

Previous genetic and craniometric studies have suggested greater genetic diversity and a larger effective size in Africa. Several demographic scenarios can explain a larger African effective size, and anthropological geneticists have attempted to obtain better estimates of relative population sizes among continental regions in the Old World. A least-squares approach of estimating relative population weights was developed by Relethford and Harpending ([1994] Am. J. Phys. Anthropol. 95:249-270), who applied it to craniometric and genetic data sets and concluded that the ratio of African, Asian, and European effective sizes was 3:1:1, respectively; another data set of short tandem repeat (STR) markers yielded a similar estimate of 7:1:2. However, an estimate from restriction site polymorphism (RSP, also known as restriction fragment length polymorphism, or RFLP) data yielded a very different estimate of 1:1:8. Thus, the European and not the African effective size was largest. Simulations showed that this was the result of ascertainment bias in which polymorphic markers were originally identified in a small panel of Caucasians, leading to inflated heterozygosity in the European sample and thus an inflated population weight. This paper extends those computer simulations to incorporate not only ascertainment bias but also interpopulation gene flow and demographic expansion in two types of genetic data, single nucleotide polymorphisms (SNPs, which are similar but not precisely identical to RSPs) and STRs. The effects of these three parameters on SNP and STR relative weight estimates are described. Simulations show that the ascertainment scheme affects SNP data but not STR data. Gene flow has a noticeable effect on the bias and efficiency of the estimates in both types of genetic data. Population expansions have a large effect only in one ascertainment scheme in the simulated SNP data and no effect in STR data. Relative population weight estimates from four published STR data sets are also reported. These estimates are similar to each other: all show a larger African weight and a European weight somewhat larger than the Asian weight. Because the STR simulations show that when gene flow is greater than 0.01 migrants per generation the African population weight is biased upward, it is likely that the African weights in the four STR data sets are inflated. However, the simulations suggest that the African effective size is still largest of the three regions and is probably at least as great as the sum of the Asian and European effective sizes.

Africa↗
PubMed1994

Quantification of infarct size by thallium-201 single-photon emission computed tomography using the unfolded map method. Comparison with QRS score and angiographic infarct size at 4 weeks after infarction.

A new technique of data processing, the unfolded map method, was used with thallium-201 single-photon emission computed tomography to quantify infarct size in 35 patients with single-vessel disease at 4 weeks after their first myocardial infarction (24 anterior and 11 inferior infarcts), and the results were compared with those obtained by electrocardiography and contrast left ventriculography. The myocardial borders and the infarcted region were defined using the threshold technique and a cutoff value of 55%. Count profile data for each short-axis slice were unfolded zonally into single planes with the same ratio, and their areas were calculated from the slice thickness and radius. Thus, the size of the unfolded map represented the actual left ventricular myocardial area Infarct size was quantitated from the ratio of pixels in the infarcted region to those in the whole map, and the ratio itself was used as the percent infarct size. Although a defect 1 cm in diameter (0.8 cm2) could not be detected in a phantom study, defects > or = 2 cm in diameter (> or = 3.1 cm2) could be measured satisfactorily. The infarct size and percent infarct size determined by the unfolded map method correlated well with the QRS score (r = 0.841 and r = 0.838), the percentage of abnormally contracting segments on left ventriculography (r = 0.835 and r = 0.877), and the ejection fraction (r = -0.835 and r = 0.856). These data indicate that the unfolded map method provides adequate quantification of infarct size, even in the chronic phase, without complicated data processing.

Adult↗
PubMed1984

Erythrocyte deformability and size measured in a multiparameter system that includes impedance sizing.

A Coulter Counter was modified to allow the photographing of erythrocytes as they exist the sizing orifice. These photographs provide the necessary information to determine the shape of individual cells. This data was combined on a cell-by-cell basis with the corresponding impedance signal to determine accurately both the cell size and deformed state of each cell. The particle shape is required if the size is to be determined accurately. Normal, diabetic and sickle cell samples were used in this study. The cell size was corrected according to theory that relates the impedance signal with cell shape. Although there was no objective test to determine the efficacy of this calculation in terms of improving the size measured, the reduction in the associated distribution width is taken as indicative of an improvement in the measuring process. The data presented represent the first attempt to relate cell size with deformed state on a cell-by-cell basis and indicates the potential usefulness of multiparameter deformability and size measurements.

Anemia, Sickle Cell↗
PubMed2002

A new ecologically valid method to assess body size estimation and body size dissatisfaction.

OBJECTIVE: The primary aim of the present study was to develop an ecologically valid method for assessing the perception of body size (as opposed to the memory of body size). METHOD: Women with clinical eating disorders (N = 14) and no eating disorder (N = 24) estimated their actual and desired body size while looking in a mirror. Estimations were made using projected images that were the same height as the participants' reflections in the mirror. RESULTS: This new method assessed the perception of body size under conditions that resembled the real-life situation of viewing oneself in a mirror. Participants with eating disorders significantly overestimated their body size relative to controls (p <.05) and tended to be more dissatisfied with their body size (p =.07). DISCUSSION: It is argued that the new method assesses the perception of body size, is ecologically valid, and is the most clinically relevant of the methods developed to date.

Adult↗
PubMed1998

The effect of blob size and network dynamics on the size-based separation of polystyrenesulfonates by capillary electrophoresis in the presence of entangled polymer solutions.

This work focuses on the separation of standard polystyrenesulfonates (PSS), with molecular masses (Mr) between 16 and 990 x 10(3) in capillaries filled with semidilute (entangled) linear hydrophilic polymers. Contrary to cross-linked chemical gels, which produce permanent networks, solutions of linear polymers lead to dynamic networks. The analytical performances and migration mechanisms are discussed on the basis of experiments performed in solutions of linear polyethyleneoxides and derivatized celluloses of various molecular masses. The influence of the mesh size and of the lifetime of the obstacles of the separating network has been investigated in detail. The mesh size is assimilated to the blob size of the separating polymer and is a decreasing function of its concentration. The lifetime of the obstacles of the network, identified with the reptation time of the polymer chain, characterizes its dynamics. This characteristic time increases with both the molecular weight of the separating polymer and its concentration. Its impact was first examined at fixed blob size. Then, the influence of the blob size was studied while keeping the reptation time of the network constant. By doing so, the existence of interactions between the solute and the separating polymer or between the solute and capillary wall can be more safely assessed. It appears that the reptation time of the mesh has a large influence on the electrophoretic mobility of the PSSs under a threshold value, which is of the order of magnitude of the time taken by the PSS to migrate on the blob size. Also shown are separations using networks made up with mixtures of polyethyleneoxides of the same nature and same mass concentration, but of very different molecular masses. This latter approach allows one to adapt the viscosity of the solution and the dynamics of the network, keeping the blob size constant.

Electrophoresis, Capillary↗
PubMedDate not supplied

Evidence that host size determines liver size: studies in dogs receiving orthotopic liver transplants.

Orthotopic liver transplantation was performed in two groups of dogs; Group I animals consisted of large dogs that served as recipients of livers obtained from smaller dogs while Group II animals consisted of dogs that received liver from donor dogs of nearly the same size. The small-for-size livers transplanted into the Group I dogs rapidly increased in size over the course of 2 weeks until they achieved a size equal to that originally present in the larger recipient dogs. In contrast, the livers transplanted into dogs of the same size as the donors underwent some degree of atrophy. In both groups of animals, plasma levels of insulin and glucagon and hepatic (graft) activities of thymidine kinase and ornithine decarboxylase were followed serially. The only difference between the two groups of animals for these measures was that the ornithine decarboxylase activity rose to a greater degree in the liver that underwent graft enlargement. These data suggest that recipient size determines, at least in part, liver graft size once it is transplanted. These data also suggest that of the parameters followed, only ornithine decarboxylase activity parallels the finding of growth of the transplanted liver.

Animals↗
PubMed1999

Vessel size-dependent expression of intermediate-sized filaments, calponin, and h-caldesmon in smooth muscle cells of human coronary arteries.

The arterial media is composed of a heterogeneous population of smooth muscle cells (SMCs). Recently, the properties of SMCs were observed to be heterogeneous not only among individual cells but also among arteries of the same vascular bed. To test the hypothesis that a site-specific heterogeneity exists in the SMCs of human coronary arteries, we examined the expression of desmin, vimentin, calponin, and high-molecular-weight (h-) caldesmon in arteries of various sizes. Specimens of arteries were obtained at autopsy from 12 patients: 6 adults (67 +/- 4 years old); 3 younger adults (26 +/- 2 years old); and 3 neonates. The size of the arteries was estimated by the number of SMC layers of the media. The expression was compared in SMCs of large arteries (>10 layers in adults, >5 layers in neonates), medium-sized arteries (5-10 layers in adults, 3-5 SMC layers in neonates), and small arteries (<3 layers). In adults, the percentage of arteries positive for desmin was lower in the small (17% +/- 3%) and medium-sized arteries (44% +/- 12%) than in the large arteries (94% +/- 6%) (P < 0.01). The percentage of arteries positive for calponin was also lower in the small (18% +/- 2%) and medium-sized arteries (66% +/- 5%) than in the large arteries (100%) (P < 0.01). The percentage for vimentin and h-caldesmon did not differ among large, medium-sized, and small arteries. These observations in adults were similar to those in younger adults or neonates. The phenotypes of medial SMCs are vessel size-dependent in human coronary arteries. This finding should be important for understanding the site-specific characteristics of vascular function in the regulation of myocardial perfusion or those of vascular responses to environmental changes.

Adult↗
PubMed2003

A haptic size-contrast illusion affects size perception but not grasping.

Object features (e.g. size, shape and orientation) are relevant for recognition and identification, but also for the control of manual actions. Converging evidence suggests a dissociation between the visual systems that mediate object perception and object-directed action. Here we present evidence suggesting that a similar dissociation might exist in the haptic domain. We demonstrate that a haptic variation of a size-contrast illusion influences the perceived size of a target object, but not the degree to which the hand is opened when that object is the target of a grasping movement. This finding is consistent with the view that object perception is "scene-based" and takes into consideration not only the size of the target object but also the sizes of other nearby objects. In contrast, the control of object-directed action is primarily driven by the absolute size of the target object independent of the relative sizes of other objects in the environment, suggesting a "actor-based" frame of reference. The present findings suggest that dissociations between action and perception are not unique to the visual system, but might instead reflect a general organizational principle of sensory processing.

Adult↗
PubMed2001

Quantitative assessment of forearm muscle size, forelimb grip strength, forearm bone mineral density, and forearm bone size in determining humerus breaking strength in 10 inbred strains of mice.

Bone strength is an important clinical endpoint of osteoporosis research. The evaluation of the relative importance of bone and muscle components to bone strength has widespread implications for the understanding and preventing of osteoporosis. The objectives of this study were to understand the interrelationship between the different components of the muscular skeletal system and to determine the effect of forearm muscle size, forelimb grip strength, forearm bone mineral density (BMD), and forearm bone size on the humerus breaking strength among 10 inbred strains of mice. The forearm muscle size was measured using a peripheral quantitative computed tomography (pQCT). The forearm BMD and forearm bone size were measured using a PIXIMUS Densitometer. The forelimb grip strength and humerus breaking strength were measured using an Instron Mechanical Tester. Significant correlations were found among the five regional phenotypes. All variables have a moderately high genetic component with heritability estimates of 0.83 for forelimb grip strength, 0.76 for forearm muscle size, 0.6 for forearm BMD, 0.63 for forearm bone size, and 0.68 for humerus breaking strength. Forward stepwise multiregression analysis showed that the forearm BMD, forelimb grip strength, and forearm bone size were three major determinants of bone strength and explained 61% of the variation in bone breaking strength. These data suggest that evaluation of these three parameters together, rather than BMD alone, is a more effective, noninvasive approach for predicting fracture risk.

Absorptiometry, Photon↗
PubMed2006

Determination of the pore size distribution and porosity of aerobic granules using size-exclusion chromatography.

The pore size distribution and porosity of aerobic granules with different diameters were evaluated using size-exclusion chromatography, in which polyethylene glycols and distilled water were, respectively, used as solute and mobile phase. The porosity of the aerobic granules varied from 68% to 93% and the exclusion limit, expressed as molecular mass, showed a significant difference. For the small-size granules with a diameter of 0.2-0.6mm, molecules greater than 137,000Da could not penetrate the pores, while the exclusion limits of the middle-size granules with a diameter of 0.6-0.9mm and large-size ones with a diameter of 0.9-1.5mm were 76,000 and 29,000Da, respectively. The extracellular polymeric substances of the granules might clog the pores and might be responsible for the reduced porosity. A correlation between the bioactivity and available porosity of the aerobic granules was found. The experimental results show that the size-exclusion chromatography was appropriate for elucidating the pore size distribution and porosity of the aerobic granules.

Aerobiosis↗