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Biomedical subjects

T Gasser

Publications and source records attributed to T Gasser.

At least 217 records · Page 12Linked to original sources
PubMed1983

Graphical representation of multidimensional EEG data and classificatory aspects.

EEG data are intrinsically multidimensional and this applies also to a set of broad band spectral parameters (6 parameters per derivation). Non-metric multidimensional scaling (MDS) and principal component analysis (PCA) are compared with respect to their capacity to achieve an adequate few-dimensional representation for the graphical comparison of groups and the identification of subgroups. In an application to neurophysiological aspects of mental retardation and learning disability, MDS proved to be somewhat superior to PCA. Both methods profited from the introduction of (1-p)-convex hulls to define a normative region.

Adolescent↗
PubMed1983

The EEG of mildly retarded children: developmental, classificatory, and topographic aspects.

Our investigation was concerned with 25 children, 10-13 years old, with an IQ 50-70 ("mild mental retardation," following the ICD). Among these, 14 attended a school for the mentally retarded and 11 one for the learning disabled. A control group was recruited, matched in age, sex and social class. The unipolar 8-channel record of EEG at rest was subjected to blind clinical rating, and a computerized analysis (broad band spectral parameters delta, theta, alpha 1, alpha 2, beta 1, beta 2). A significantly higher frequency of paroxysms was found by the clinical rating. It also allowed the diagnosis of a maturational lag with respect to the items "maturity" and "prominence of alpha rhythm"). Spectral parameters differentiated the two matched groups particularly in bands and leads of developmental relevance (theta, delta, and fronto-central beta in absolute power and theta, delta occipitally and alpha 2, with the exception of frontal leads for relative power).: As is well known, the mentally retarded constitute a heterogeneous group: this could also be verified with respect to EEG activity for the segment of mild mental retardation. A multivariate classification by nonmetric multidimensional scaling yielded a subgroup of 10 children deviant with respect to its overall EEG activity and a group of 15 children within the normal range. This assignment did not overlap with the assignment to the two schools. By computing ratios of broad band power in antero-posterior and symmetric-interhemispheric leads a reduced topographic differentiation was found for the experimental group in their antero-posterior distribution.

Adolescent↗
PubMed1983

SELAVCO: a method to deal with trial-to-trial variability of evoked potentials.

The possibility and the potential dangers of the inhomogeneity of potentials to repeated stimuli have been recognized for some time. The predominant method of averaging sweeps of brain activity time locked to the stimuli relies on the assumption of an invariant response. In this paper, a method is proposed for dealing more effectively with the variability of single potentials than does averaging. This method operates by weighted averaging and the weights are determined from the data after suitable filtering operations. SELAVCO is validated and compared to the average for real data and in a controlled design close to reality.

Adolescent↗
PubMed1982

Transformations towards the normal distribution of broad band spectral parameters of the EEG.

In this report transformations are evaluated for obtaining normally distributed broad band spectral parameters (both for absolute and relative power) in a sample of healthy individuals. This problem leads automatically to the question of defining a normative sample, both in terms of sampling and recording conditions; as to the latter, the electro-oculogram proved to be crucial. For relative power the transformation log(x/(1-x)) was excellent in all regards, whereas the best transformation for absolute power--log(x)--was not fully satisfactory for all bands.

Adolescent↗
PubMed1981

Novel single-pass exchange of circulating uridine in rat liver.

Evidence is presented that the liver effects an essentially complete degradation of plasma uridine in a single pass and replaces it largely from hepatic pools of acid-soluble uridine nucleotides. The concentration of uridine in the hepatic vein of the rat was essentially the same as that in the arterial circulation and portal vein. However, the isolated perfused rat liver degraded more than 90 percent of infused [5-3H]uridine in a single passage. Similar results were found in vivo when tracer amounts of [3H]uridine and [14C]uridine were infused into the portal vein of an intact rat. Furthermore, less than 2 percent of the infused uridine entered the acid-soluble nucleotide pools of the liver after 30 minutes of infusion. Intraperitoneal injection of [3H]orotate allowed selective labeling of liver (and kidney) pyrimidines. After 3 hours, the specific activity of uridine in the hepatic vein was more than three times that in the arterial circulation. This unusual exchange, which is not saturated even at uridine concentrations as high as 50 microM, contributes to the rapid turnover of plasma uridine and explains its inefficient utilization in peripheral tissues.

Animals↗
PubMed1979

Statistical handling of EEG-data.

This contribution focusses on the treatment of EEG data as time series. More emphasis is placed on spontaneous activity than on event-related potentials. Smoothing techniques are discussed, both for the nonparametric estimation of regression functions and of densities. Some new promising methods are presented. The fundamentals of time series analysis, and in particular of spectrum analysis, are reviewed. For the difficult area of parameterization of EEG time series, we compare desirable characteristica of parameters with the methods already in use.

Electroencephalography↗
PubMed1978

The computation of EEG bispectra.

This paper presents a FORTRAN program for computation of bispectra of multichannel EEG on a PDP-11/55 computer. Input data are already digitized and file-structured. Output of power spectra, bicoherence and biphases is produced in synoptic form on a line printer.

Computers↗
PubMed1978

Analysis of the adolescent growth spurt using smoothing spline functions.

Height growth velocity curves between 4.5 and 17.75 years were estimated, using smoothing spline functions, for 112 boys and 110 girls from the Zurich Longitudinal Study (1955--1976). Parameters characterizing the growth process, such as peak height velocity and age at peak height velocity, were calculated directly from the estimated curves. The variability of parameters describing the adolescent growth spurt is large, both between and within sexes. Peak height, defined as increase of height velocity during the growth spurt, and age at peak height velocity both characterize the sex difference in growth in a highly significant manner. Peak height of at least 4 cm/year is found in 70% of the boys, but in only 11% of the girls. The age at peak height velocity averages 12.2 years in girls and 13.9 years in boys and has a wide range of 5.7 years and 3.8 years respectively. The sex difference in adult height of 12.6 cm is composed of the following 4 factors: +1.6 cm caused by more prepubertal growth in boys, +6.4 cm by the boys' delay in spurt, +6.0 cm by the more extensive spurt in boys and -1.4 cm by more post-spurt growth in girls. Correlations between parameters indicate that the adult height depends neither on the duration of growth, nor on the duration and height of the peak. Minimal pre-spurt height velocity and peak height velocity, but not peak height, are age- and height-dependent. Partial correlations given adult height reveal two compensating mechanisms between growth in the prepubertal and in the pubertal period. Small prepubertal height and low height velocity with respect to adult height are followed by a late adolescent spurt and vice versa. Small height at the onset of the spurt with respect to adult height is followed by a longer lasting, but not higher spurt and vice versa.

Adolescent↗
PubMed1977

Height correlations between parents and mature offspring in normal subjects and in subjects with Turner's and Klinefelter's and other syndromes.

The correlations for stature between parents and grown-up offspring in 90 normal males and 116 normal females have been compared with similar correlations obtained in 27 adult males with Klinefelter's syndrome, 33 adult females with Turner's syndrome and in 75 adult patients with Down's syndrome. There was close similarity between the findings in the patients with sex chromosomal disorders and in normal subjects, a roughly constant amount of height being gained or lost through the chromosomal abnormalities. However the genetic pattern was lost in patients with Down's syndrome. In males with idiopathic precocious puberty and in untreated females with congenital adrenal hyperplasia, the parent-offspring correlations were not normal. In females with idiopathic precocious puberty they approximated normal values. The first two are pathological conditions of varying severity, whilst the majority of girls diagnosed as suffering from precocious puberty represent the extreme variant of normal.

Adrenocortical Hyperfunction↗
PubMed1977

Studies on EEG activities in the beta band.

A report on first findings of quantitative investigations of beta activity in the frequency domain is presented. Spectral analysis techniques were applied in three parallel still ongoing clinical studies, i.e. (1) an exploration of beta activities in a broad clinical material, (2) a study of the possible use of quantitative beta assessment in antiepileptic drug therapy, and (3) an investigation of special patterns with harmonic components in the beta band. Several clearly distinguishable types of spectral shapes, different coherence characteristics, significant alterations by changes of drug composition and a rich variation of harmonic patterns indicate a large and fascinating new field for clinical EEG research.

Adolescent↗
PubMedDate not supplied

Statistical characterization of the pubertal growth spurt.

BACKGROUND: This is a methodical investigation into the problem of estimating parameters for the pubertal spurt (PS). The variability involved in determining the timing, intensity and duration of the PS for height, leg height and biiliac width is estimated via a realistic simulation. Further, a decomposition of adolescent growth into a component due to the pubertal peak and one due to ongoing prepubertal velocity is evaluated. METHODS: Data for 120 boys and 112 girls are available from 4 weeks to adulthood. The curve-fitting method is kernel estimation for distance, velocity and acceleration. RESULTS: The age of peak velocity and the age of stopping of the PS are well determined. In contrast, the age of onset of the PS is less well determined. Intensity is less variable for the parameter peak velocity than for maximal acceleration. It is feasible to decompose adolescent growth into a component due to the pubertal peak and one due to ongoing prepubertal growth. CONCLUSIONS: Nonparametric curve-fitting methods which do not rely on a parametric growth model can be successfully used to extract individual characteristics of the PS.

Adolescent↗
PubMedDate not supplied

Contribution of growth phases to adult size.

Based on the data of the First Zurich Longitudinal Growth Study we investigate how interindividual differences in adult size arise in the variables leg height, sitting height and standing height, arm length, bi-iliac width and bihumeral width. Specifically, we are also interested in the question of whether across sexes and variables the same growth phases and the same parameters are predictive for achieving a certain adult size. A rather complex pattern emerges, demonstrating that regulation of growth is not the same for boys and girls and moreover is not the same for the six anthropometric variables studied. Prepubertal growth is characterized by its intensity (average velocity) and by its duration. Whereas duration has by itself no appreciable influence on adult size, prepubertal intensity determines adult size to a high degree across all variables and both sexes. The intensity of prepubertal growth determines adult size to a larger degree for boys than for girls. For a given size at the end of the prepubertal period, a small duration enhances the chance of obtaining a large adult size. Compared with prepubertal growth, the amount of variance of adult size explained is small for pubertal parameters, and--with respect to linear measures--significant for girls only. A small duration of prepubertal growth is in the following mainly compensated by a stronger pubertal spurt (PS), to a varying degree across variables. The overall picture which emerges indicates that sitting height--and to a lesser extent bihumeral width--develop in a more irregular fashion than the variables bi-iliac width and leg height.

Adolescent↗
PubMedDate not supplied

Sex dimorphism in growth.

While there is agreement that sex differences in height are small up to the onset of the pubertal spurt in girls, there has been some debate about the question of which, and to what extent, various growth phases contribute to the average adult sex difference of about 13 cm. There has been no consistent agreement between authors as to what extent this difference is due to the late onset of the pubertal spurt (PS) for boys and to what extent it is due to their more intense PS. In this paper, we investigate this question for the variables height, sitting and leg height, arm length, bihumeral and biiliac width. Biiliac width is a special case since both sexes have roughly the same adult size, but girls still have a shorter growing period. The gains for boys, when compared to girls, show a very different pattern across variables: for the legs, the additional growth due to the later spurt is responsible for most of the adult sex difference (64%). On the other hand, for bihumeral width and sitting height, the more intense PS contributes almost 50% to the adult sex difference. An analysis across variables indicates that increments from 1.5 to 6 years largely compensate for deviations in infant morphology from adult morphology.

Anthropometry↗