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Results for “Individual variability”

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At least 235 records · Page 13Linked to original sources
PubMed2001

Induction of DNA-strand breaks in human peripheral blood lymphocytes and A549 lung cells by sodium dichromate: association with 8-oxo-2-deoxyguanosine formation and inter-individual variability.

Hexavalent chromium [Cr(VI)] is a genotoxic carcinogen for which inhalation is a major potential route of exposure in occupational settings. In the present study, the ability of sodium dichromate to cause DNA strand breaks in three populations of cells, human whole blood cells, isolated human peripheral blood lymphocytes and cultured A549 lung epithelial cells, was investigated. Treatment with non-cytotoxic concentrations of sodium dichromate (for 1 h) resulted in a concentration-dependent increase in the number of DNA strand breaks as measured by the Comet assay. The lowest concentrations of sodium dichromate that resulted in a statistically significant (P < 0.01) increase in the number of DNA strand breaks were 500, 50 and 10 microM, respectively, in these cells. The use of formamidopyrimidine glycosylase increased the sensitivity of detection of strand breaks in A549 cells 10-fold, suggesting a role for DNA base oxidation in the mechanism of dichromate-induced DNA strand breaks. In support of this hypothesis, immunocytochemistry indicated an elevation of 8-oxodeoxyguanosine in A549 cells treated with 10 and 500 microM sodium dichromate for 1 h. We also demonstrated 2.11- and 2.5-fold ranges in the level of control and dichromate (500 microM)-induced DNA strand breaks, respectively, in cells of whole blood within a group of healthy volunteers (n = 26). A statistically significant (P < 0.001) positive Pearson's correlation (r = 0.606) was found between control and treated levels of DNA strand breaks, suggesting that factors responsible for relatively low levels of DNA strand breaks in untreated PBL may also offer protection against the formation of dichromate-induced DNA strand breaks.

8-Hydroxy-2'-Deoxyguanosine↗
PubMedDate not supplied

How do people solve the "weather prediction" task?: individual variability in strategies for probabilistic category learning.

Probabilistic category learning is often assumed to be an incrementally learned cognitive skill, dependent on nondeclarative memory systems. One paradigm in particular, the weather prediction task, has been used in over half a dozen neuropsychological and neuroimaging studies to date. Because of the growing interest in using this task and others like it as behavioral tools for studying the cognitive neuroscience of cognitive skill learning, it becomes especially important to understand how subjects solve this kind of task and whether all subjects learn it in the same way. We present here new experimental and theoretical analyses of the weather prediction task that indicate that there are at least three different strategies that describe how subjects learn this task. (1) An optimal multi-cue strategy, in which they respond to each pattern on the basis of associations of all four cues with each outcome; (2) a one-cue strategy, in which they respond on the basis of presence or absence of a single cue, disregarding all other cues; or (3) a singleton strategy, in which they learn only about the four patterns that have only one cue present and all others absent. This variability in how subjects approach this task may have important implications for interpreting how different brain regions are involved in probabilistic category learning.

Adult↗
PubMed2005

Visual acuity in 5-7-year-old children: individual variability and dependence on observation distance.

Accurate measurements of uncorrected binocular and monocular visual acuity were performed in 65 children aged 5-7 years at five viewing distances in the range 0.5-5.0 m by means of the test charts containing widely spaced E stimuli in four orientations. It was found that, in most children of this age, visual acuity (V) changed with test distance, as had been reported previously with older subjects. Visual acuity could be considered as practically independent of observation distance (Vmax-Vmin<or=0.2 decimal units) in <50% of children. The remaining children demonstrated evident distance dependence of visual acuity but the shape of the acuity-distance curve varied. The acuity-distance curve of most children peaked at an intermediate distance (1-2 m), the typical difference Vmax-Vmin being 0.4 decimal units. To explain the existence of an optimal observation distance in the majority of children, a number of developmental and environmental factors could be proposed that adjust the parameters of the visual system to the parameters of operational visual space and prevailing activity.

Aging↗
PubMed1996

Electrophysiological background of individual variability in electrical defibrillation efficacy.

This study was performed to test whether heart-to-heart variability of defibrillation efficacy is attributable to differences in postshock refractory state of nondepolarized myocardium. In 30 anesthetized dogs, a localized potential gradient was created using 1-16 V of stimulus across a pair of platinum plate electrodes on the right ventricle (5-mm interelectrode distance). The postshock recovery interval (PSRI) of the relatively refractory myocardium directly adjacent to the excited area was estimated by measuring the recovery interval after an appropriately timed field stimulus. The transcardiac defibrillation threshold (DFT) was also determined. The results showed that DFT normalized by the weight of the heart was inversely correlated with the PSRI measured with a field stimulus of 6 V (local shock intensity approximately 5 V/cm) or more (6 V: r = -0.502, P < 0.005; 16 V: r = -0.635, P < 0.0005). This observation suggests that variability of defibrillation efficacy in intact hearts is largely due to differences in the postshock refractory state of the nondepolarized myocardium.

Animals↗
PubMed1999

Extended quasi-likelihood is useful for analyzing intra-individual variability in pharmacokinetic regression models.

The method of maximum extended quasi-likelihood (MEQL) can be viewed as an estimation method in the framework of generalized linear models. The method was applied to a pharmacokinetic problem in which the pharmacokinetic model was a nonlinear function of its parameters. The behavior of the method toward the estimation of a variance function was numerically compared with those of the generalized least squares (GLS) and extended least squares methods. In general, the MEQL and GLS methods were equally better. However, the MEQL estimator often showed smaller mean squared errors for the scaling parameter than the other two estimators. Such a generally comparable but partially distinct property of the MEQL method, as compared with the GLS method, is useful to pharmacokinetic analysis.

Least-Squares Analysis↗
PubMed2006

Intra-individual variability of high-sensitivity C-reactive protein: age-related variations over time in Japanese subjects.

BACKGROUND: Prospective studies have demonstrated a direct association between the baseline level of high-sensitivity C-reactive protein (hsCRP) and the risk of developing cardiovascular disease. The potential for hsCRP variability during the follow-up interval is of great interest, so the repeatability of measurements of hsCRP in men and women, and in different age groups, was investigated in the present study. METHODS AND RESULTS: The measurement of hsCRP was performed in 899 male and 780 female Japanese civil servants aged 18-60 years in the spring of 2004 and 2005. Within-subject repeatability and intra-class correlation coefficient of reliability were used to characterize the variation in measurements. Error of the measurement process was negligible, as the analytical variance was 0.0003 [ln(mg/L)] [ln(mg/L)] with a reliability coefficient of 0.997. In contrast, the within-subject variation of hsCRP was considerable with a reliability coefficient of 0.61 in both sexes and repeatability coefficients of 5.25 and 5.38 in men and women, respectively. The variation differed with age, especially in women, as less variation was observed in subjects over 40 years of age during the follow-up interval. CONCLUSIONS: The results suggest that a single measurement of hsCRP is subject to considerable but equal within-subject variation over time in men and women, and this variation differs among the age groups, which may affect the risk assessment of hsCRP in association with future cardiovascular events.

Adolescent↗
PubMed2001

Individual variability in human tibia lead concentration.

Our aims in this study were to determine proximal-distal variability in adult human tibia lead concentration via electrothermal atomization atomic absorption spectrometry (ETAAS) and to determine whether there were any differences between core and surface tibia lead concentrations. We analyzed duplicate core and surface tibia samples for lead at multiple proximal-distal sections on 10 adult human cadaver legs. Dried bone samples were digested in nitric acid using microwave-assisted heating, and lead content was determined by ETAAS with Zeeman background correction. Lead concentrations in nine tibiae (one tibia was excluded because some of the data were compromised) ranged from 3.1 to 27.9 microg lead/g of dry bone. Both core and surface tibia lead concentrations were lower at the proximal and distal ends of the tibia. Surface tibia lead was approximately 5 microg/g greater than core tibia lead in six tibiae with relatively low lead concentration, and 8 microg/g greater in three tibiae with relatively high lead concentration. The difference between core and surface tibia lead was independent of proximal-distal tibia location. We conclude that these nine human tibiae showed a greater surface tibia lead concentration than core tibia lead concentration. This observation has consequences for the noninvasive measurement of tibia lead via K-shell and L-shell X-ray fluorescence.

Cadaver↗
PubMed2000

Intra-individual variability of the metabolic effect of inhaled insulin together with an absorption enhancer.

OBJECTIVE: To study the metabolic effect and the variability of the effect elicited by inhalation of 87.2 U insulin powder combined with an absorption enhancer. The metabolic effect was compared with that of 10.2 U regular insulin injected subcutaneously and of 5.5 U regular insulin given intravenously RESEARCH DESIGN AND METHODS: In this single-center open euglycemic glucose clamp study 13 healthy male volunteers received 5 insulin administrations on separate study days: once as an intravenous dose, once as a subcutaneous injection, and 3 times by inhalation, in randomized order. Glucose infusion rates (GIRs) necessary to keep blood glucose concentrations constant at 5.0 mmol/l were determined over an 8-h period after administration. RESULTS: After inhalation of the insulin powder aerosol, the onset of action was substantially more rapid than after subcutaneous insulin injection, and maximal action was reached earlier (86+/-47 vs. 182+/-53 min, P<0.0001). The maximal glucose infusion rate after inhalation of insulin was comparable to that after subcutaneous insulin injection (9.2+/-2.6 vs. 8.8+/-2.8 mg x kg(-1) x min(-1), NS). The metabolic effect in the first 2 h after inhalation was significantly greater than that after subcutaneous insulin injection (amount of glucose infused: 0.88+/-0.25 vs. 0.59+/-0.20 g x kg(-1) x 120 min(-1), P<0.0001). However, the total metabolic effect after inhalation and subcutaneous injection was comparable (2.50+/-0.76 vs. 2.56+/-0.69 g x kg(-1) x 480 min(-1), NS). The relative bioefficacy of inhaled insulin calculated in relation to the data from the subcutaneous insulin application was 12.0+/-3.5% (absolute bioefficacy 10.1+/-3.1%) but was highest in the first 2 h after application (18.5+/-3.7%; absolute bioefficacy 8.2+/-4.1%). The intraindividual variability of the metabolic response induced by insulin inhalation was 14+/-9% for the maximal glucose infusion rate, 15+/-10% for the time-to-maximal effect, and 16+/-12% for the total amount of glucose infused. CONCLUSIONS: This feasibility study shows that inhaled insulin with an absorption enhancer has a pronounced metabolic effect compared with the results of a previous study of inhaled insulin without an enhancer. The intraindividual variability of the metabolic effect was comparable with that of inhaled and subcutaneously injected insulin.

Administration, Inhalation↗
PubMedDate not supplied

Contralateral suppression of transient evoked otoacoustic emissions: intra-individual variability in tinnitus and normal subjects.

Contralateral acoustic stimulation reduces the amplitude of the transient evoked otoacoustic emission (TEOAE) in humans. The mechanism is thought to be mediated, at least in part, through the medial olivocochlear efferent system innervating the outer hair cells. To assess its usefulness as a possible clinical test, TEOAE suppression was measured in each ear of 12 subjects over a 6-week period, and these data are shown in detail for four subjects representing extremes of variability in a tinnitus and a non-tinnitus group. Intra-subject test results (n = 18) exhibited a varying extent of suppression values and the variance of each session, consisting of three tests, was not statistically different from one session to another. There was no dependence on variables such as ear (right or left), session, day of testing or their interaction. There was a significant difference in the variability between the tinnitus and the normal group.

Acoustic Stimulation↗