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At least 1,207 records · Page 67Linked to original sources
PubMed2007

Analysis of effective radiating area, power, intensity, and field characteristics of ultrasound transducers.

OBJECTIVE: To characterize the ultrasound fields produced by a cohort of transducers from a single manufacturer via hydrophone and Schlieren technology. DESIGN: Descriptive study. SETTING: Measurement laboratory. PARTICIPANTS: Seven same-model ultrasound transducers from a single manufacturer. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Effective radiating area (ERA), total power, spatial average intensity (SAI), beam nonuniformity ratio (BNR), and Schlieren beam widths at 1.0 and 3.3 MHz. RESULTS: Values for ERA (1.0 MHz range, 3.62-4.38 cm(2); 3.3 MHz range, 3.74-4.76 cm(2)), total power (1.0 MHz range, 5.0-5.6 W; 3.3 MHz range, 4.7-5.7 W), SAI (1.0 MHz range, 1.2-1.4 W/cm(2); 3.3 MHz range, 1.0-1.5 W/cm(2)), and BNR (1.0 MHz range, 2.79-5.85; 3.3 MHz range, 2.51-4.56) fell within manufacturer's specifications and U.S. Food and Drug Administration (FDA) regulations. Schlieren analysis showed significantly larger beam widths at 3.3 MHz compared with 1.0 MHz and a large degree of variability in the ultrasound fields generated by the different transducers. There were no significant correlations between beam widths and ERA values. CONCLUSIONS: ERA and total power values in a test cohort exist within a range that met FDA regulations. Individual variability in ERA and total power resulted in 50% variability in SAI. This variability may help explain previous reports of heating differences between transducers.

Acoustics↗
PubMed2000

Spatial frequency tuned covariance channels for red-green and luminance-modulated gratings: psychophysical data from human adults.

Both chromatic and luminance-modulated stimuli are served by multiple spatial-frequency-tuned channels. This experiment investigated the independence versus interdependence of spatial frequency channels that serve the detection of red-green chromatic versus yellow-black luminance-modulated stimuli at low spatial frequencies. Contrast thresholds for both chromatic and luminance-modulated gratings were measured within 12 individual subjects using a repeated-measures design. Spatial frequencies ranged from 0.27 to 2.16 c/deg. A covariance structure analysis of individual differences was applied to the data. We computed statistical sources of individual variability, used them to define covariance channels, and determined the number and frequency tuning of these channels. For luminance-modulated gratings, two covariance channels were found, including one above and one below 1 c/deg [cf. Peterzell, & Teller (1996). Individual differences in contrast sensitivity functions: the coarsest spatial pattern analyzer. Vision Research, 36, 3077-3085]. For chromatic gratings, correlations between thresholds for most spatial frequencies were uniformly high, yielding a single covariance channel covering all but the highest spatial frequency tested. A combined analysis of both data sets recovered the same three covariance channels, and showed that detection thresholds for low-frequency red-green chromatic and luminance-modulated stimuli are served by separate, statistically independent processes.

Adult↗
PubMed2005

Subcutaneous insulin: pharmacokinetic variability and glycemic variability.

The therapeutic goal in insulin-treated diabetic patients is to maintain on the long-term a tight glucose control (HbA1, < 6.5-7% or less) through an insulin regimen which "mimic" the physiological insulin profile: a basal insulin secretion to maintain glucose homeostasis and an acute post-prandial secretion in response to meal intake. Such goal represents a challenge for the clinician as conventional human insulins have major drawbacks: slow absorption and too late peak with regular insulins, delayed peak and often occuring at an unwanted time with intermediate and long-acting insulins. Furthermore, these insulins are characterised by a large within- and between-subjects variability, which complicate patients' task to self-adapt their daily doses, even for those well educated and compliants. These limitations and unpredictable variations in insulin action are responsible for an increased risk of hypoglycemic events, between meals as well as during the night period. As a consequence, glucose control is frequently insufficient in type 1 diabetic patients, and these limitations may contribute also to the delayed initiation of insulin therapy in type 2 diabetics when oral antidiabetic agents fail. This variability and the non-reproducibility of the conventional insulin pharmacodynamics are explained by several exogenous and endogenous factors describe in this review. Availability of new short-acting (lispro, aspart and glulisine) and long-acting analogs (glargine, detemir) of human insulin, with improved pharmacokinetic characteristics, and a lesser variability and better reproducibility, should facilitate a tight glucose control in insulin-treated patients. The main pharmacokinetic and pharmacodynamic characteristics of these new insulin analogs are presented and discussed in the light of there intra- and inter-individual variability. Their reduced variability should permit to reinforce near "physiological" insulin regimen such as "basal-bolus" technique and to consider new approaches and therapeutic strategies in type 1 and type 2 diabetic patients.

Blood Glucose↗
PubMed2003

Open capture-recapture models with heterogeneity: I. Cormack-Jolly-Seber model.

In open population capture-recapture studies, it is usually assumed that similar animals (e.g., of the same sex and age group) have similar survival rates and capture probabilities. These assumptions are generally perceived to be an oversimplification, and they can lead to incorrect model selection and biased parameter estimates. Allowing for individual variability in survival and capture probabilities among apparently similar animals is now becoming possible, due to advances in closed population models and improved computing power. This article presents a flexible framework of likelihood-based models which allow for individual heterogeneity in survival and capture rates. Heterogeneity is modeled using finite mixtures, which have enough flexibility of distribution shape to accommodate a wide variety of different patterns of individual variation. The models condition on the first capture of each animal, and include as a special case the Cormack-Jolly-Seber model. Model selection is done either using Akaike's information criterion or by likelihood ratio tests, making available checks of different influences on survival rates. Bias in parameter estimates is reduced by including individual heterogeneity. Model selection and bias reduction are important in population studies and for making informed management decisions.

Animals↗
PubMed2000

Flicker-photometric electroretinogram estimates of L:M cone photoreceptor ratio in men with photopigment spectra derived from genetics.

Relative proportions of long-wavelength-sensitive (L) to middle-wavelength-sensitive (M) cones were estimated by use of the flicker-photometric electroretinogram (ERG). It has been demonstrated that a major source of error in estimates of cone proportions from spectral luminosity functions is the known variation in the lambda(max) of the photopigments [Vision Res. 38, 1961 (1998)]. To correct for these errors, estimates of cone proportions were derived by use of individualized L-cone spectral sensitivity curves deduced from photopigment gene sequences from each subject. For some individuals this correction made a large difference in the estimated cone proportions compared with the value obtained when a fixed standard L cone was assumed. The largest discrepancy occurred in a man estimated to have 62% L cones (L:M ratio 1.6:1) when a standard L pigment was assumed but a value of 80% L cones (L:M ratio 4:1) when his individualized L-cone spectrum was used. From repeated measurements made with the ERG, it was determined that individual estimates of the relative L-to-M cone contributions, expressed as %L cones, are usually reliable within approximately 2%. The average L:M ratio for 15 male subjects was estimated at 2:1 (67% L cones). Previously, a large range of individual variability was reported for L:M ratios obtained from photometry. An unresolved issue concerns how much of the range might be attributed to error. Here efforts have been taken to markedly reduce measurement error. Nonetheless, a large range of individual differences persists. Estimated L:M ratios for individuals ranged from 0.6:1 to 12:1 (40% L to 92% L).

Adolescent↗
PubMed1987

The relationship of mild hirsutism or acne in women to androgens.

The relationship in women between mild hirsutism or acne to androgen levels has not been well-defined. We investigated this in 62 Caucasian women, aged 18 to 21 years, by relating these pilosebaceous signs to plasma free testosterone (fT), the main circulating determinant of plasma androgenicity. Women with mild hirsutism (n = 13) had a significantly elevated fT (12.7 +/- 5.5, SD, pg/mL [44.1 +/- 19.1 pmol/L]) compared to normal controls (7.4 +/- 2.7 pg/mL [25.7 +/- 9.4 pmol/L]), as did subjects with minor acne (10.7 +/- 4.25 pg/mL [37.1 +/- 14.7 pmol/L]). The most important finding was the striking variability in the relationship between pilosebaceous overactivity and fT levels. In mildly hirsute subjects plasma fT was normal in half of the subjects, and the coefficient of variation of plasma fT was about twice what one would expect from individual variability. We could not demonstrate correlations among the variables of hirsutism, acne, and plasma fT. On the other hand, among 15 women with modest elevations of plasma fT levels (up to twofold), 27% had moderate hirsutism, 40% had mild hirsutism, and 33% had none. However, four of five of the latter patients (without hirsutism) had acne. The relationship of fT to acne severity varied similarly. To define the interactions between androgens and the pilosebaceous apparatus, we propose a model in which variation in apparent skin sensitivity and the level of androgen seem to contribute about equally to the pathogenesis of mild hirsutism and acne. The clinician should suspect that hyperandrogenemia will be found in about half the women with mild cases of hirsutism, and one third with minor acne.

Acne Vulgaris↗
PubMed1993

Do diagnostic algorithms always produce a uniform lung scan interpretation?

Several algorithms have been devised to assist in the interpretation of ventilation-perfusion (V/Q) scans performed to diagnose pulmonary embolism. The degree to which adherence to a single algorithm facilitates diagnostic homogeneity among different readers, however, has been little investigated. We evaluated the individual variability in V/Q lung scan interpretation in a large, academic nuclear medicine division to determine the degree of interpretive heterogeneity among a group of physicians all using the same image interpretation algorithm. Ventilation-perfusion scan interpretive patterns and the diagnostic accuracy of individual physicians were evaluated using quantitative parameters to establish group norms and to detect variations from these norms. The performance of each reader was tracked over a 4 yr period. There was a significant variation in V/Q interpretive patterns and diagnostic accuracy between readers despite the attempted use of a uniform diagnostic algorithm. Subgroups of interpretive styles could be defined based on the percentage of intermediate (including both indeterminate and intermediate categories) scans read. Although there was significant variation in diagnostic accuracy among readers, there was no obvious correlation between accuracy and reading style except that the most nonstandard diagnostic patterns were associated with the most variable diagnostic accuracy. These data show a measurable variation in interpretive patterns and accuracy among multiple readers of V/Q scans despite attempted group adherence to an established diagnostic algorithm.

Algorithms↗
PubMed1987

Quantification of individual sensitivities to ethanol in selective breeding experiments: difference scores versus regression residuals.

Nagoshi et al. (Alcohol Clin Exp Res 10:343-349, 1986) have argued recently that the use of postdrug minus predrug difference scores to assess individual variability in sensitivity or tolerance to ethanol is not to be recommended. Unreliability of variables can result in biased estimates of response to treatment. Instead of difference scores, they recommend using residual scores from the regression of posttreatment on pretreatment measures. We were interested in the consequences of employing difference scores versus regression residuals for a related, but different purpose: the choice of individual animals to be mated for a selective breeding study. The availability of data from such a selective breeding experiment ongoing in the laboratory of one of us (JCC) allowed us to compare directly the effects of use of change and residual scores as criteria for selection. The selection is for maximal hypothermic sensitivity of mice to an acute dose of ethanol. In our sample, difference scores were highly correlated with regression residuals. In practical terms, almost 75% of the individuals chosen for mating by the change score method would also have been chosen by the residual score method. We conclude that for selective breeding experiments, the use of difference scores does not necessarily introduce sampling bias, is unlikely to affect the ultimate outcome of selection, and may be a more meaningful variable for the physiological process studied.

Animals↗
PubMed2003

Predicting repeat self-harm in children--how accurate can we expect to be?

The main objective of the study was to find which variables predict repetition of deliberate self-harm in children. The study is based on a group of children who took part in a randomized control trial investigating the effects of a home-based family intervention for children who had deliberately poisoned themselves. These children had a range of baseline and outcome measures collected on two occasions (two and six months follow-up). Outcome data were collected from 149 (92 %) of the initial 162 children over the six months. Twenty-three children made a further deliberate self-harm attempt within the follow-up period. A number of variables at baseline were found to be significantly associated with repeat self-harm. Parental mental health and a history of previous attempts were the strongest predictors. A model of prediction of further deliberate self-harm combining these significant individual variables produced a high positive predictive value (86 %) but had low sensitivity (28 %). Predicting repeat self-harm in children is difficult, even with a comprehensive series of assessments over multiple time points, and we need to adapt services with this in mind. We propose a model of service provision which takes these findings into account.

Adolescent↗
PubMed1991

A procedure for using proton magnetic resonance imaging to determine stereotaxic coordinates of the monkey's brain.

Because of great inter-individual variability in the sizes and configurations of monkey brains, consistent intracerebral stereotaxic placements are not possible when a general brain atlas is relied upon to derive placement coordinates. We describe a procedure that allows the determination of brain atlases for individual monkeys using proton magnetic resonance imaging and the translation of image coordinates to stereotaxic coordinates. The latter is accomplished by chronically implanting glass beads filled with copper sulfate into the skull to establish a plane horizontal to the stereotaxic plane and to provide reference points for zeroing stereotaxic carriers during intracerebral implants. The efficacy of this procedure was confirmed experimentally.

Animals↗
PubMed2006

Predictors of psychological well-being amongst Korean immigrants to the United States: a structured interview survey.

BACKGROUND: As international migration becomes a common phenomenon in many countries, the health issues of immigrants are becoming an important area of concern among health care professionals worldwide. OBJECTIVE: Adopting the stress-health outcome framework, this study examined risks and resources of both positive and negative affect (i.e., happiness and depression) among Korean Americans who experienced acculturative and recent life stresses. METHODS: Hierarchical multiple regression analyses were performed to examine correlates of positive and negative outcomes in the stress process on a final sample of 147 Korean immigrants from a cross-sectional study. RESULTS: For happiness, lower levels of acculturative stress and recent life stress, a greater sense of mastery, and greater social support were associated with an increased level of happiness. None of the individual characteristics were significant. R(2) for the full model was .53. For negative affect, acculturative stress and recent life stress explained a significant portion (41%) of the total variance associated with depression (R(2)=.51). As with the happiness variable, individual characteristics failed to add to the predictiveness of the equation, while sense of mastery and social support functioned as significant resources in reducing depression. CONCLUSION: Increased mastery and greater social support were consistently predictive of greater happiness and less depression. Implications for future immigrant research are discussed.

Acculturation↗
PubMed1992

Custom cryopreservation of human semen.

OBJECTIVE: To design a protocol to evaluate individual variability in human semen cryoprotection by native seminal plasma. DESIGN: Post-thaw motility from the frozen semen of pregnancy-proven donors (n = 10) and patients referred for infertility screening (n = 10) was examined in three equal aliquots (per original ejaculate) that comprised varying ratios of native seminal plasma to TES and Tris (TEST)-yolk buffer (Irvine Scientific, Irvine, CA) in a dose-titration curve format. All aliquots from the same ejaculate contained final vol/vol 6% glycerol, had equal sperm density, and had undergone centrifugation for 5 minutes at 600 x g before buffer:semen ratio adjustment and standard precooling protocol for submersion in liquid nitrogen. Post-thaw measurement of percent original motility preserved (post-thaw percent motility/original percent motility x 100) was used for standardization of results. RESULTS: In 14 of 20 specimens (70%), the maximal yield of original motility was obtained in 50% seminal plasma, with an average post-thaw motile yield of 50%. In 6 of 20 specimens (30%), the best preservation of original motility was noted at 100% seminal plasma, with an average post-thaw motile yield of 58%. No specimen had a greatest percent motility preserved at 0% seminal plasma. Donor specimens have equal preference for either 50% or 100% seminal plasma, whereas patient specimens have a preference for 50% seminal plasma (P < 0.05). CONCLUSIONS: Native seminal plasma has variable cryoprotectant qualities for which custom cryopreservation can compensate. A simple two-point dose-titration test of cryopreservation buffer:seminal plasma ratio (i.e., 50:50 versus 0:100) can determine the optimal mixture for cryopreservation of a given individual's semen.

Buffers↗
PubMed2003

Vaccines against drugs of abuse: a viable treatment option?

Drug addiction is a chronically relapsing brain disorder. There is an urgent need for new treatment options for this disease because the relapse rate among drug abusers seeking treatment is quite high. During the past decade, many groups have explored the feasibility of using vaccines directed against drugs of abuse as a means of eliminating illicit drug use as well as drug overdose and neurotoxicity. Vaccines work by inducing drug-specific antibodies in the bloodstream that bind to the drug of abuse and prevent its entry into the brain. The majority of work in this area has been conducted with vaccines and antibodies directed against cocaine and nicotine. On the basis of preclinical work, vaccines for cocaine and nicotine are now in clinical trials because they can offer long-term protection with minimal treatment compliance. In addition, vaccines and antibodies for phencyclidine, methamphetamine and heroin abuse are currently under development. An underlying theme in this research is the need for high concentrations of circulating drug-specific antibodies to reduce drug-seeking and drug-taking behaviour when the drug is repeatedly available, especially in high doses. Although vaccines against drugs of abuse may become a viable treatment option, there are several drawbacks that need to be considered. These include: a lack of protection against a structurally dissimilar drug that produces the same effects as the drug of choice;a lack of an effect on drug craving that predisposes an addict to relapse; and tremendous individual variability in antibody formation. Forced or coerced vaccination is not likely to work from a scientific perspective, and also carries serious legal and ethical concerns. All things considered, vaccination against a drug of abuse is likely to work best with individuals who are highly motivated to quit using drugs altogether and as part of a comprehensive treatment programme. As such, the medical treatment of drug abuse will not be radically different from treatment of other chronic diseases.

Amphetamine-Related Disorders↗
PubMed1999

[Diagnosis of hepatic enzyme activities of drug metabolizing enzymes-phenotyping and genotyping].

Drug metabolizing enzymes (DMEs) play an important role in the biotransformation of various xenobiotics, generally by detoxifying and eliminating substrates by converting them to more hydrophilic derivatives, or in some cases, activating substrates by conversion to intermediates that are highly reactive with biological macromolecules. It is widely accepted that the enzymatic activities of hepatic DMEs are one of the most important determinants of the concentration of drugs at their site of action or in the blood. Wide inter-individual variability in drug concentrations in the blood has been demonstrated even after the administration of the same doses on the basis of body weight, and in many cases the wide differences in plasma drug concentrations have been attributed to the individual differences in the enzymatic activities of DMEs. Attempts have therefore been made to estimate the hepatic DME activities of each individual before administration of drugs clinically. Three different approaches were taken to estimate patients' hepatic DME activities: 1) the use of probe drugs (phenotyping); 2) molecular diagnosis of genetic DME deficiency (genotyping); 3) examination of DME levels/activities in peripheral blood leukocytes/lymphocytes on the assumption that their activities in leukocytes/lymphocytes are well correlated with hepatic enzyme activities. A great number of data have been accumulated concerning the specificity of certain DME for candidate probe drugs, and searches have been made for mutated alleles of DME genes that indicate whether an individual is deficient in DMEs. Gene expression is measured by sensitive methods such as the reverse-transcriptase polymerase chain reaction and/or immunochemical methods in peripheral blood leukocytes/lymphocytes, which are less invasive tissues. Knowledge is being accumulated that will allow the development of useful methods of predicting the activities of hepatic DMEs that affect individual pharmacokinetics/pharmacodynamics. In this article, various reported methods of assessing hepatic DME activities are reviewed for the purpose of maximizing the efficacy and safety of pharmacotherapy.

Arylamine N-Acetyltransferase↗
PubMed1993

Host factors in the pathogenesis of arthritis triggered by infectious organisms. Overview.

Individual variability in host immune responses to infectious agents is likely influenced by differences in the repertoires of antigenic peptides bound by self-major histocompatibility complex molecules (MHC) and in the repertoires of T-cell receptors expressed in each individual. Moreover, genes regulating the processing of foreign MHC antigens (for example, peptide pump genes and proteosome constituent genes) may also be important in this regard. Infectious organisms may subvert host immune responses through expression of constituents sharing structure homology with host molecules. Such structural mimicry may serve to either promote induction of potentially harmful cross-reactive autoimmune responses or impede effective host responses, thereby favoring persistence of the organism.

Arthritis, Infectious↗
PubMed1992

Evaluation of a new Recommended Dietary Allowance for folate.

This article analyzes the 1989 Recommended Dietary Allowance (RDAs) for folate, which are approximately 50% less than the amounts recommended previously. The RDA committee used the following types of data to estimate allowances: (a) the quantity of folate required to elicit established physiologic responses or replace daily losses corrected for bioavailability and individual variability and (b) dietary folate intake data related to prevalence of deficiency in population groups. Some studies cited by the committee evaluated the response to synthetic folate, whereas other studies used dietary folate to estimate folate requirements. Responses to these two forms of folate may differ and depend on the individual's state of folate depletion. The correction for bioavailability is an estimate based on limited data determined by various experimental approaches. Estimates of the folate content of food vary as a function of a number of factors in the method of analysis and the specific type of food consumed. Additional variables include food preparation, food losses, and nutrient interactions. For these reasons, estimates of folate intake based on computer databases may not accurately reflect folate consumed or physiologically/metabolically available folate. Assumptions that current dietary intakes of folate are sufficient to maintain status in the US population were based, in some cases, on data from population surveys not designed to assess folate status. The new RDAs for folate may not provide an adequate safety allowance for specific population groups at risk and should be reevaluated as new information evolves.

Adolescent↗
PubMed1992

Behavioral factors in stress-induced immunomodulation.

Individual differences in the exploratory response to novelty were found to be related with the vulnerability to develop stress-induced immunological alterations. We studied the effect of exposure to inescapable shock on antibody formation against sheep red blood cells (SRBC) in rats selected according to their locomotor activity in a novel situation. Interestingly, antibody titers were only enhanced in shocked animals with the highest locomotor activity. These results emphasize the importance of taking into account individual differences for the study of the mechanisms involved in stress-induced immunomodulation, suggesting a behavioral procedure (novelty reactions) to deal with individual variability in the effects of stress on the immune system.

Animals↗
PubMed2002

The significance of inter- and intraspecific variation in bacterivorous and herbivorous protists.

This paper reviews the emerging evidence on the significance of inter- and intraspecific variation in the feeding behaviour of aquatic protists. Small heterotrophic nanoflagellates (HNF) have been identified as the primary bacterial consumers in most aquatic environments. Recent research using novel techniques such as flow cytometry and high resolution video microscopy revealed that their feeding strategies and grazing rates are diverse. There is an important conceptual difference between uptake rates measured in short-term (min to h) experiments and grazing rates averaged over a longer-term (d). This is because the latter are strongly affected by digestion rates which are species-specific, i.e. the same bacterial prey may be digested differently by various grazers, and the same predator may selectively digest variable prey. Planktonic ciliates are the most important algal consumers in many lakes and marine systems. Large species-specific differences in their feeding behaviour and growth rates have been documented for closely related species. Intraspecific variation, which is, most likely, caused by varying clonal composition may be as important as interspecific variation. Finally, there is some evidence that the individual variability within a given population is generally large, both among bacterivorous HNF and among herbivorous ciliates. The consequences of this diversity becoming apparent at the levels of the species, population, clone and individual need to be considered by aquatic ecologists in their conceptual models.

Animals↗