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PubMed1994

[The problem of the individual variability of the human brain].

Series of frontal sections, 20 microns thick, were used to study the individual cytoglio-architectonic features of fields 8.8, 39, 40, 41, 43, 44, 45, 47 of the caudate nucleus, dorsomedial nucleus of the thalamus, Meynert's nucleus in 12 persons aged 29 to 89 years. The profile fields of neurons, their density and the density of gliocytes, including perineuronal ones were measured by computed morphometry, the cellular composition was determined from size of neurons, as well as the neuroglial and neuroperineuronal indices were defined. In 6 cases (distinguished, gifted persons), all the formations under study showed structural signs (abundant satellitosis, predominant large neurons, etc.) suggesting that there is a high functioning of nerve cells whose quantitative parameters are greater than those in other cases.

Adult↗
PubMed2002

Inter- and intra-individual variability of paired-pulse curves with transcranial magnetic stimulation (TMS).

OBJECTIVES: Previous studies have evaluated the variability of motor thresholds (MTs) and amplitude of motor-evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) within and across individuals. Here we evaluate the reproducibility and inter-hemispheric variability of measures of cortical excitability using the 'conventional' paired-pulse (PP) TMS technique. METHODS: We studied PP curves of the left and right hemisphere in 10 healthy subjects on two separate days 2 weeks apart. The inter-stimulus intervals studied were 1, 3, 6, 8, 10 and 12 ms with the conditioning stimulus being 80% of the resting MT, and a single test stimulus producing MEPs of approximately 0.8 mV peak-to-peak amplitude. RESULTS: As a group, the PP curves of the left and right hemispheres, and of Day 1 and Day 2 were not significantly different. The intracortical inhibition (ICI), but not the intracortical facilitation, showed a good correlation across days within the individuals. CONCLUSIONS: Cortical excitability, particularly ICI, measured by PP TMS shows no inter-hemispheric asymmetry and is reproducible within individuals.

Adult↗
PubMed1996

Pancreatic islet B-cell individual variability rather than subpopulation heterogeneity.

Isolated rat pancreatic islet B-cells loaded with the Ca2(+)-sensitive fluorochrome Fluo-3 were examined by single-step flow cytometry at increasing concentrations of D-glucose (1.0 to 20.0 mM). The near forward scatter of light was unaffected by changes in hexose concentration. The Fluo-3 fluorescent signal slightly decreased when the glucose concentration was raised from 1.0 to 5.0 mM, and progressively increased at higher hexose concentrations. The fluorescence attributable to endogenous NAD(P)H increased dramatically throughout the full range of D-glucose concentration, with a typical sigmoidal concentration-response relationship. No evidence for a bimodal frequency distribution of these variables was found, whether at low or high D-glucose concentrations. The dispersion of individual NAD(P)H measurements, as judged by either their coefficient of variation or the height of their modal peak, was less pronounced at high than at low D-glucose concentrations. These findings document vastly different concentration-response relationships for metabolic and ionic variables in glucose-stimulated B-cells. They confirm that all B-cells do not display an identical behavior, but argue against the existence of subpopulation heterogeneity in their responsiveness to D-glucose.

Aniline Compounds↗
PubMed1996

Revealing the distinction between perception and cognition through intra-individual variability of visual evoked responses.

Searching for a method to objectively detect the cognitive activity of the brain, the variability of visual evoked responses (ER) was analysed in 75 human subjects and 10 animals. The individual ERs of a normal subject were found typically very scattered in the first approx. 120 ms after stimulation, converging at 160-220 ms and then diverging again progressively. This variability pattern (VP) is event-related and is not attributable to background noise. On the other hand, statistically significant correlation showed that in most patients, with anatomically intact visual structures but with pronounced mental troubles, the VP is absent and the ERs are randomly scattered. Based on these results we consider that the event-related variability reflects the cognition function of the subjects and that it is instrumental in evidencing the distinction between cognitive and perceptive processes. The results are further consistent with the idea that cognition implies the chaotic activity of certain neural populations and that the VP reflects this chaotic, non-repetitive, non-linear and impredictable but effective neural activity.

Aged↗
PubMed2006

Individual variability in brain activations associated with episodic retrieval: a role for large-scale databases.

The localization of brain functions using neuroimaging techniques is commonly dependent on statistical analyses of groups of subjects in order to identify sites of activation, particularly in studies of episodic memory. Exclusive reliance on group analysis may be to the detriment of understanding the true underlying cognitive nature of brain activations. In this overview, we found that the patterns of brain activity associated with episodic retrieval are very distinct for individual subjects from the patterns of brain activity at the group level. These differences appear to go beyond the relatively small variations due to cyctoarchitectonic differences or spatial normalization. We review evidence that individual patterns of brain activity vary widely across subjects and are reliable over time despite extensive variability. We suggest that varied but reliable individual patterns of significant brain activity may be indicative of different cognitive strategies used to produce a recognition response. We argue that individual analyses in conjunction with group analyses are likely to be critical in fully understanding the relationship between retrieval processes and underlying neural systems.

Brain↗
PubMed1989

The intra- and inter-individual variability and reliability of transepidermal water loss measurements.

An analysis of variance was conducted to estimate the intra- and inter-individual variations in TEWL on the forearms, by sites (8 measurement sites) and by days (10 different days), in 30 non-exposed healthy individuals. The estimated intra- and inter-individual variations, by sites, were 15.5% and 84.5%, respectively, the sum of the 2 components always being 100%. With the exclusion of the 2 most distal sites near the wrist, which had significantly higher baseline TEWL values and fluctuations in TEWL, an improvement in the intra-individual variation was obtained. Thus, of the 6 sites, the estimated intra- and inter-individual variations were 8.4% and 91.6%, respectively. This finding supports the exclusion of these most distal sites for future investigations. The estimated intra- and inter-individual variations, by days, were 20.6% and 79.4%, respectively. The low site-to-site (8.4%) and day-to-day (20.6%) intra-individual variations, as compared to the large inter-individual variations of the same (91.6% and 79.4%), indicate that baseline TEWL is a stable personal characteristic. Thus, individual susceptible to irritant contact dermatitis (ICD), due to occupational exposure, may be reliably characterized by utilizing their baseline TEWL values, for "prediction" of risk in epidemiological field studies.

Adult↗
PubMed2000

The recognition of isolated words and words in sentences: individual variability in the use of sentence context.

Estimates of the ability to make use of sentence context in 34 postlingually hearing-impaired (HI) individuals were obtained using formulas developed by Boothroyd and Nittrouer [Boothroyd and Nittrouer, J. Acoust. Sco. Am. 84, 101-114 (1988)] which relate scores for isolated words to words in meaningful sentences. Sentence materials were constructed by concatenating digitized productions of isolated words to ensure physical equivalence among the test items in the two conditions. Isolated words and words in sentences were tested at three levels of intelligibility (targeting 29%, 50%, and 79% correct). Thus, for each subject, three estimates of context ability, or k factors, were obtained. In addition, auditory, visual, and auditory-visual sentence recognition was evaluated using natural productions of sentence materials. Two main questions were addressed: (1) Is context ability constant for speech materials produced with different degrees of clarity? and (2) What are the relations between individual estimates of k and sentence recognition as a function of presentation modality? Results showed that estimates of k were not constant across different levels of intelligibility: k was greater for the more degraded condition relative to conditions of higher word intelligibility. Estimates of k also were influenced strongly by the test order of isolated words and words in sentences. That is, prior exposure to words in sentences improved later recognition of the same words when presented in isolation (and vice versa), even though the 1500 key words comprising the test materials were presented under degraded (filtered) conditions without feedback. The impact of this order effect was to reduce individual estimates of k for subjects exposed to sentence materials first and to increase estimates of k for subjects exposed to isolated words first. Finally, significant relationships were found between individual k scores and sentence recognition scores in all three presentation modalities, suggesting that k is a useful measure of individual differences in the ability to use sentence context.

Adult↗
PubMed2004

Dietary vitamin K influences intra-individual variability in anticoagulant response to warfarin.

The relationship between dietary intake of vitamin K, fat, plasma vitamin K concentrations and anticoagulation response to warfarin within individuals, as well as the contribution of dietary vitamin K to differences in warfarin dose requirements between individuals were investigated in 53 patients on warfarin therapy who had stably controlled anticoagulation. Each patient completed a dietary record of all foods consumed on a daily basis for 4 weeks. Each week a blood sample was taken for measurement of the international normalized ratio (INR), plasma vitamin K, triglycerides and warfarin enantiomer concentrations. The patients' genotype for CYP2C9 was also determined. Regression analysis of the data showed that, for each increase of 100 microg in the daily dietary intake of vitamin K averaged over 4 d, the INR was reduced by 0.2. There was no correlation between warfarin daily dose and average daily dietary vitamin K intake when calculated over 28 d. The regression model for warfarin dose showed that, while dietary vitamin K had no effect, CYP2C9 genotype (P = 2%) and age (P < 1%) significantly contributed to inter-patient variability in warfarin dose requirements. A consistent intake of vitamin K could reduce intrapatient variability in anticoagulation response and thus improve the safety of warfarin therapy.

Adult↗
PubMedDate not supplied

Patient safety during medication administration: the influence of organizational and individual variables on unsafe work practices and medication errors.

Medication errors are a leading cause of unintended harm to patients, both in Australia and internationally, and there is now a concerted attempt to identify and correct individual and workplace factors that encourage medication errors. The current study used structural equation modelling to measure organizational climate and to test a model with hypothesized links between climate and unsafe medication administration behaviours. The study also examined the possible mediating role of stress and morale. Data were collected from 176 nurses working in rural areas in Australia. The model provided a reasonable fit to the data with organizational climate accounting for 39% of the variance in individual distress, which in turn explained 7% of the variance in self-reported violations. The only variable that made a direct contribution to errors was violations, which accounted for 24% of the variance in medication errors. These findings highlight the importance of monitoring the state of the whole health system. Deficiencies at the organizational level affect the psychological well-being of hospital employees, and distressed employees are more likely to engage in substandard work practices that ultimately endanger the patients under their care.

Ergonomics↗
PubMed2003

Individual variability in cyclosporin A sensitivity: the assessment of functional measures on CD28-mediated costimulation of human whole blood T lymphocytes.

The quantitative analysis of cyclosporin A (CsA) effects might be helpful for optimizing immunosuppressive treatment after allogeneic organ transplantation in individual patients, as rejection can occur despite the existence of CsA blood levels within therapeutic ranges. Previous investigations found that costimulation of the CD28 pathway generally mediates CsA-resistant proliferation of T cell receptor (TCR)-activated T lymphocytes. However, here we describe considerable interindividual variation regarding the immunosuppressive effects of CsA (1000 microg/L) on anti-CD3/CD28 T cell costimulation in a human whole blood assay. In the in vitro study, we found a significant reduction of T cell proliferation, activation marker expression (CD25, CD69) on the T cell surface, and interleukin-2 (IL-2) protein expression in whole blood samples of all healthy subjects (n = 11). However, the investigation of cytokine mRNA profiles revealed variable results of in vitro CsA sensitivity. Whole blood samples of 3 of 11 healthy individuals demonstrated a marked suppression of IL-2 mRNA expression (>50%) and a partial inhibition of IL-4, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) mRNA expression on addition of CsA. In contrast, the remaining 8 healthy individuals had cytokine mRNA expression levels that were unaffected or even increased when CsA was administered in vitro. In patients undergoing CsA monotherapy (ex vivo study, n = 9), we found a significant suppression of IL-2 mRNA levels in 4 of 9 patients ex vivo. Thus, we cannot confirm a universal CsA resistance of T cells on anti-CD3/CD28 costimulation. Instead, our results suggest an individual degree of CsA sensitivity that might be more consistent with clinical experience. Prospective studies are necessary to determine if individual degrees of CsA sensitivity correlate with clinical events and are associated with a low or high risk of transplant rejection.

Adult↗
PubMed1980

[Individual variability of sources of blood supply to the diencephalon].

As a result of investigations performed on 119 cerebral preparations of human corpses injected with roentgenopaque masses, variants of individual changeability have been determined in the cavernous and supraclinoid parts of the internal carotid artery, anterior and posterior cerebral, anterior and posterior connective, anterior villose arteries. As the criteria for determination the variants have been used: 1) degree of embryonic development; 2) source of origin; 3) twistity; 4) ratio of diameters of the interconnected arteries. The results obtained are of interest for anatomists, neurosurgeons, neuropathologists, roentgenologists.

Basilar Artery↗
PubMed1988

Evaluation of individual variability in the composition of Agkistrodon contortrix contortrix venom by means of HPLC and two-dimensional PAGE.

Qualitative and quantitative differences of coagulant enzymes in venom samples from individuals of the Agkistrodon c.c. were studied by means of 2D-PAGE and high performance anion-exchange chromatography. A great diversity was found among individual venoms. The two most similar venoms had an identical composition in only about 90%, the least similar ones in about 45% spots. All venoms studied contained more than two fractions with fibrinolytic activity. In three out of the nine analysed venoms two different thrombic proteases were present, one venom contained only one of these enzymes, whereas in five venoms no thrombic activity was detectable.

Animals↗
PubMedDate not supplied

Dose dependency and individual variability in selected clinical, haematological and blood biochemical responses after systemic lipopolysaccharide challenge in cattle.

Previous studies have noted that susceptibility to systemic lipopolysaccharide (LPS) exposure seems to differ between individual cows. However, to date inter-individual variation in the response to intravenous injection of LPS has been reported only as an empirical finding, and its existence or extent has never been backed up by statistical analyses. The aim of the present study was therefore to investigate the dose-dependency of clinical, haematological and blood biochemical responses to intravenous LPS injection in dairy cattle and to determine the extent to which these responses differed between individual cows. Eight dairy cows each received three intravenous injections of Escherichia coli LPS (10, 100, and 1000 ng/kg, consecutively) at three-week intervals. All three LPS doses induced clinical, haematological, and blood biochemical responses lasting up to several days. The strength of all of the responses increased significantly with an increasing LPS dose. A statistically significant inter-individual variation was demonstrated for all clinical, haematological, and blood biochemical responses except for serum calcium concentrations. More than half of the statistical variation in white blood cell and thrombocyte counts could be attributed to the individual. The results of this study show that despite the existence of a dose-response relationship between LPS and ensuing clinical, haematological, and blood biochemical responses, the majority of responses to LPS differ significantly in strength and duration from cow to cow.

Animals↗
PubMed1993

Individual variability in the diurnal intraocular pressure curve.

BACKGROUND: Reduction of intraocular pressure (IOP) is a primary goal of most glaucoma treatments. However, because the IOP varies during the day, single measurements performed in an ophthalmologist's office do not necessarily provide information on the peak level and fluctuation of the IOP. METHODS: Home tonometry was performed to gain more information on the nature of the diurnal IOP curves and on their variability. One hundred seventy-six patients with open-angle glaucoma (OAG), 55 subjects with ocular hypertension (OHT), and 18 control individuals measured their IOP five times daily at home for 4 to 8 consecutive days using a self-tonometer. RESULTS: Well-defined diurnal IOP variations were observed in all three groups with a predominance of curves with morning or mid-day maxima. Erratic IOP curves without a diurnal rhythm were present in OHT (22%) and OAG (16%) patients but not in control subjects. Differences between the curves of the two eyes of an individual were frequent in OHT (33%) and OAG (36%) patients but not in control subjects (6%). Finally, the majority of OHT (72%) and OAG (66%) patients showed a difference in their diurnal curve patterns on repeat home tonometry performed months apart. CONCLUSION: The authors indicate that it is difficult to rely on one eye as a control for the other. They also indicate that changes in IOP observed in the office at different visits often may be due to a shift in the type of diurnal curve rather than to a true change in the mean IOP. Monitoring of the diurnal IOP may be necessary in some cases if the clinician relies, even partially, on the level of IOP when making a decision on patient management.

Circadian Rhythm↗
PubMed1984

[Individual variability of the volume of the amygdaloid body in the human brain].

Measuring the almond nucleus (with the cytoarchitectonic control of its boundaries) on the serial sections of 14 adults of both sexes and different ages (18 cerebral hemispheres), the authors revealed considerable individual spatial differences in its size. In its extremes these differences may be two-fold. As these individual differences in the almond nucleus (AN) were independent of the brain weight of the subjects examined, it is suggested that these differences are determined by the variable functional specificity of the AN in different people.

Adult↗