Biomedical subjects

M Eiselt

Publications and source records attributed to M Eiselt.

At least 19 recordsLinked to original sources

PubMed2004

On the spatio-temporal organisation of quadratic phase-couplings in 'tracé alternant' EEG pattern in full-term newborns.

OBJECTIVE: The time courses of quadratic phase-coupling (QPC) of electroencephalographic burst and interburst patterns of the 'trace alternant' (TA) in full-term newborns have been quantified. METHODS: Using the Gabor expansion, a fast Fourier transformation based method, biamplitude, bicoherence and phase-bicoherence time courses of both burst and interburst patterns have been determined (common average reference EEG recordings). With a frequency resolution of 0.25 Hz and a frequency grid of 1-1.5 <==> 3.5-4.5 Hz (region-of-interest), a number of 15 frequency pairs result. These pairs have been investigated. RESULTS: The burst and the interburst patterns are characterized by temporally and topographically different QPC profiles. All differences are dominant at the electrode Fp1 followed by Fp2. There is a significant difference (combined multiple and global test strategy) in the QPC characteristics between both patterns within the time period from 0.75 to 1.5 s after the pattern onset at electrode Fp1. The maximal QPC in burst patterns (especially at Fp1) can be observed during this time period. In contrast to this finding, maximal QPC in interburst patterns (at Fp1) are reached immediately after the onset and at 3 s. Summarising all findings, a QPC-rhythm of 0.1 Hz during TA can be assumed. CONCLUSIONS: It can be assumed that the QPC rhythm of the TA is generated by a pattern-spanning time-variant phase-locking process and there are indications for a possible correspondence between the QPC rhythm and vegetative rhythms. SIGNIFICANCE: This study showed that advanced, time-variant analysis methods quantifying QPC rhythms are able to add new scientific information to the understanding of nature, characteristics and significance of TA in the neonatal EEG.

Algorithms↗

PubMed2002

[Pulmonary plasma catecholamine levels and pulmonary hypertension in congenital heart disease].

Plasma catecholamines may play a role in the pathogenesis of pulmonary hypertension in congenital heart disease with increased pulmonary blood flow. At cardiac catheterization, blood samples were obtained before and after passage of the lung in patients with congenital heart disease with normal pulmonary blood flow (n=39), elevated pulmonary blood flow with normal pulmonary pressure and normal pulmonary vascular resistance (PVR) in patients with atrial septal defect (ASD) (n=57) or ventricular septal defect (VSD) (n=12), and increased pulmonary blood flow, pressure and vascular resistance in patients with ASD, VSD or both (n=22), or in patients with primary pulmonary hypertension (n=4). Plasma catecholamines were determined by reversed phase high performance liquid chromatography and electrochemical detection (HPLC-ECD). In patients with elevated PVR elevated norepinephrine levels (NE) were observed. In contrast, epinephrine levels (E) were not associated with the development of pulmonary hypertension. Patients with primary pulmonary hypertension had the highest levels of NE while patients with associated Down's syndrome had significantly lower epinephrine levels. Pulmonary plasma norepinephrine levels are increased in patients with elevated pulmonary vascular resistance. Whether this phenomena is the cause or sequalae of pulmonary hypertension needs further examination. In the future, plasma catecholamines may serve as a diagnostic feature or may result in further therapeutic options.

Adolescent↗

PubMed2001

Functional interactions within the newborn brain investigated by adaptive coherence analysis of EEG.

To assess functional cortical organization in newborns during quiet sleep we investigated instantaneous interhemispheric coherences in six healthy full-term subjects using linked ear reference and average reference. Tracé alternant was the most frequent EEG pattern during quiet sleep of these newborns and consists of burst and interburst periods. The calculation of coherence was performed by means of time-variant autoregressive models on the basis of Kalman filtering. Coherence changes simultaneously with the appearance of these burst and interburst periods. The highest level of coherence was observed during burst periods in comparison with interburst periods. The lowest level of coherence was observed just before the burst started. During burst, maximal coherence was reached at different moments--late in the low frequency band (0.5-1.5 Hz; about 3 s after the burst started) and earlier in higher frequency bands (> 2 Hz, about 2 s). Interhemispheric coherence depended on the region being investigated. A significant level of coherence could be observed over frontal, temporal and occipital regions. Our data demonstrate significant modification of interhemispheric coherence during quiet sleep of full-term newborns and, irrespective of the immaturity of the brain, these coherences differ significantly between cortical regions.

Brain↗

PubMed2001

Technique for the quantification of transient quadratic phase couplings between heart rate components.

A technique for the time-variant analysis of quadratic phase coupling (QPC) in heart rate data is introduced and tested in 6 human neonates during quiet sleep. The set up of the approach is based up on the assumption that QPCs in the heart rate variability (HRV) are related to amplitude modulation effects. The application of the biamplitude deals with the detection of the coupling pattern and the bicoherence is used for the statistical quantification of coupling. By means of the results of bispectral analysis the time-variant processing has been adapted. The frequency-selective complex demodulation of the HRV leads to the envelope of the respiratory sinus arrhythmia (RSA), this has been used as one input for a time-variant coherence analysis. The other input is the low-pass filtered 10-second-rhythm of the HRV. A time-continuous quantification of the QPC, caused by amplitude modulation (10-second-rhythm modulates the RSA), is possible using this approach. According to our observed results in neonatal HRV both a phase co-ordination between the 10-second-rhythm and RSA as well as a non-linear coupling (amplitude modulation) between these HRV components can be seen.

Electrocardiography↗

PubMed2000

Relations between early prespike magnetic field changes, interictal discharges, and return to basal activity in the neocortex of rabbits.

To evaluate possible prespike field synchronizations, its relation to both interictal discharges and postspike return to baseline, penicillin-induced cortical interictal discharges were recorded in anaesthetized rabbits by magnetoencephalography (MEG) and electrocorticography (EcoG). Statistical parameters of spatial (global field power (GFP)) and temporal properties (Z-parameter) of field synchronization were calculated. In our previous report, three types of prespike field synchronization were found before the onset of interictal spike. We report here that the continuous and fluctuating, but not the abrupt prespike increases, were more often associated with a spike and wave pattern of interictal discharge than with a spike alone. Furthermore, the postspike return of these statistical parameters shows the same three patterns as the prespike field synchronizations, but in the inverse time sequence. More often than not pre- and postspike pattern were of the same type. The results suggest an influence of prespike field synchronization upon interictal discharge and subsequent field return dynamics.

Animals↗

PubMed2000

Early magnetic field changes preceding the intracortical penicillin induced spikes.

Events preceding interictal activity were studied using a combination of magnetoencephalography (MEG), electrocorticography (ECoG), and intracortical field potential recordings in rabbits. We measured MEG signals simultaneously with ECoG before and during interictal discharges induced by penicillin injected in the cortex (group 1: n = 12, medial cortex, regio retrosplenialis granularis; group 2: n = 4, cortical convexity, regio retrosplenialis agranularis; control group: n = 5); in group 3 (n = 12) a 16-channel depth electrode array was used to calculate the current source density in the cortical area exhibiting interictal epileptiform discharges. The modified Z-parameter as a lumped measure of magnetic field pattern changes and the global field power as a lumped measure of changes of field amplitude differences were calculated. In almost all recordings of both group 1 and 2, the Z-parameter of intra-individual MEG data became significantly larger than the control condition before the earliest change of the interictal spike recorded at the penicillin injection site (20-310 ms earlier, median: 91 ms, n = 151). The increase in Z-parameter in averaged MEG data of group 1 was significantly correlated with time as early as 790 ms before the spike (Pearson correlation coefficient, P < 0.05). After the start of the early increase of the Z-parameter, the global field power also began to increase before the ECoG spike. These results suggest a prespike field recruitment nearly 1 s before an interictal spike.

Action Potentials↗

PubMed1999

A 16-channel SQUID-device for biomagnetic investigations of small objects.

Biomagnetic investigations in basic physiological research using animals require measurement devices different from commercial biomagnetometers used in human investigations. Two major problems have to be tackled in the design of such biomagnetometers. First, the spatial sampling needs to be much higher. Second, the distance between pick-up coils and the sources needs to be much shorter in order to compensate the worse signal-to-noise ratio (SNR) due to the smaller pick-up coils. We designed and built a 16-channel biomagnetic measurement system meeting these design criteria. The pick-up coil diameter of this new biomagnetometer is 6.7 mm, thus allowing 16 channels on an area of 3.2x3.2 cm2. The pick-up coils are located 3 mm above the dewar outer bottom, hence the closest distance to the cortical surface can be a few millimetres. We provide as an example of first measurements performed with the new biomagnetometer investigations of epileptic spikes in adult rabbits by simultaneous magnetoencephalogram (MEG) and electrocorticogram (ECoG) recordings. The high SNR of the recorded MEG and the simultaneously detected electric potentials allow investigations of the spatio-temporal pattern of neuronal processes of epileptiform spikes with signal strengths of about 3.5 pT.

Animals↗

PubMed1999

[High-resolution magnetoencephalography--studies with a small-volume phantom].

To investigate the spatiotemporal organisation of neuronal processes in an animal model using magnetoencephalography (MEG), a high temporal resolution (ms) and an appropriate spatial resolution of about 1 mm is necessary. With the aim of determining the localization error and the resolution power of high-resolution MEG systems, we developed a phantom capable of simulating the characteristics of animal models. The phantom enables us to variably position at least two magnetic field sources to within 0.1 mm. For source localization on the basis of the magnetic field data, a spatial filtering algorithm was used. The investigation of a 16-channel micro SQUID-MEG system with a current dipole orientated tangentially to the phantom surface produced the following localization data (min ... max, x, y--horizontal plane, z--depth); systematic localization error e(x) = 1.16 ... 1.67 mm, e(y) = -1.01 ... -1.28 mm, e(z) = -5.22 ... -7.64 mm, standard deviation of the individual measurements perpendicular to the dipole axis s(perp) = 0.05 ... 0.22 mm, along this axis s(long) = 0.20 ... 1.73 mm, in the depths sz = 0.17 ... 3.17 mm. The "goodness of fit" was > 95%. Separation of two dipoles was still possible for parallel dipoles at a distance apart of d(parallel) = 0.03 mm and for those oriented perpendicularly to each other at a distance apart of d(perp) = 0.10 mm. On the basis of these results we conclude that the MEG system can achieve a resolution sufficient to permit the investigation of neuronal microstructures. The spatial errors detected were related to sensor position in the cryostatic vessel as well as to external low-frequency noise.

Magnetoencephalography↗

PubMed1999

Adaptable preprocessing units and neural classification for the segmentation of EEG signals.

In this contribution, a methodology for the simultaneous adaptation of preprocessing units (PPUs) for feature extraction and of neural classifiers that can be used for time series classification is presented. The approach is based upon an extension of the backpropagation algorithm for the correction of the preprocessing parameters. In comparison with purely neural systems, the reduced input dimensionality improves the generalization capability and reduces the numerical effort. In comparison with PPUs with fixed parameters, the success of the adaptation is less sensitive to the choice of the parameters. The efficiency of the developed method is demonstrated via the use of quadratic filters with adaptable transmission bands as preprocessing units for the segmentation of two different types of discontinuous EEG: discontinuous neonatal EEG (burst-interburst segmentation) and EEG in deep stages of sedation (burst-suppression segmentation).

Coma↗

PubMed1998

Dose-dependent effects of Cerebrolysin on EEG and short-term memory of healthy volunteers during control and hyperventilation induced cerebral ischemia.

Cerebrolysin, a peptidergic nootropic drug, was to be effective on learning and other cognitive functions in animal experiments as well as in clinical studies. Hyperventilation (HV) as a model of brain ischemia induces slowing of the EEG and cognitive impairment. The aim of this study was to examine the potential dose-dependent effects of Cerebrolysin on HV related EEG changes and short term memory during chronic (10 days) application and the time dependency of these effects. In this single centre, double blind, randomized, placebo-controlled, parallel group study 48 healthy males were enrolled and received either 100 ml placebo (NaCl) or Cerebrolysin (10 ml or 30 ml or 50 ml) in a volume of 100 ml (NaCl) for 10 days. EEG at baseline and during HV as well as the cognitive performance was evaluated at Day 1 (baseline, 15 min p.i., 2 h p.i., 4 h p.i., 8 h p.i., 24 h p.i.), Day 10 (baseline, 15 min p.i., 2 h p.i.,) and at day 11 (24 h. after the last infusion). The main effects found during the study can be summarized as follows: At baseline we found an increase of the EEG power ratio (PR) for the grouptrated with 10 ml Cerebrolysin. The effect was most pronounced at the parietal cortex. The effect started after 15 min, was most expressed at 2 h and was kept until 8 h. During HV we found a relative PR decrease of the group (10 ml Cerebrolysin) at 2 hours. For short term memory, there is a trend towards less effective word recall for the baseline situation during the first 4 hours for the placebo. This effect was not observed in the Cerebrolysin treated groups. If chronic effects are concerned, the PR increased over the parietal regions at 24 h for the groups treated with 10 and 30 ml Cerebrolysin. The effect remains at day 10 and 11. But at 10 and 11 days there was also a trend for a relative increase of the PR in the group treated with 50ml Cerebrolysin. Signs of overdosage occurred with the highest concentrations of Cerebrolysin. The events were only mild and caused no harm to the volunteers. The highest concentration caused a small but significant reduction of blood pressure. The effects could be interpreted as those of an atypical nootropic with anti-ischemic properties.

Adult↗

PubMed1998

Evaluation of microvessel density by computerised image analysis in human renal cell carcinoma. Correlation to pT category, nuclear grade, proliferative activity and occurrence of metastasis.

A high microvessel density is suspected to favour tumour progression and the occurrence of metastasis. To elucidate the significance of abundant vessels for the behaviour of human renal carcinomas, the microvessel density of 110 renal cell carcinomas was correlated to pT category, nuclear grade, proliferative activity, occurrence of metastasis and relapse-free survival interval. The microvessels were quantified using CD31 immunostaining of endothelial cells and computer-aided image analysis. The rules for reproducible microvessel counting, as defined by Weidner, were strictly observed. A statistically significant relationship between the microvessel density and nuclear grade, proliferative activity, occurrence of metastasis and relapse-free survival was found; only for tumour size could no such relation be seen. Perplexingly, there is a diminution of microvessel density in association with increasing nuclear grade, proliferative activity, relapse-free survival interval and frequency of metastasis. This finding is contradictory to the hypothesis that an increasing microvessel density indicates a worsening prognosis.

Antibodies↗

PubMed1998

Intracortical functional heterogeneity in area striate during penicillin-induced spikes in rabbits.

The generation and spread of epileptiform activity within the cortex depend on the functional and anatomical relationships between the focus and its surrounding area. These processes are not completely understood. Thus intracortical current-source-density analysis (CSD) was performed in six rabbits in order to investigate this functional relationship. Electric potential was measured perpendicular to the cortical surface by means of two 16-channel probes, and CSD was calculated within the focus and at various distances of up to 5 mm. The cortical areas surrounding the focus could be subdivided into three regions. The region up to 3 mm from the focus showed similar activity but beyond 4.5 mm no characteristic functional relationship was found with regard to the epileptiform events within the focus. Within the region 3.5-4.5 mm, however, mainly supragranular cells seem to contribute to the electric potential measured at the cortical surface and within the extracellular space. They were activated simultaneously with the initiation of focal spike generation. Taking into account the distribution of the electric potential and the results of CSD analysis, these cells seem mainly involved in the inhibition of the horizontal spread of spike activity.

Action Potentials↗

PubMed1998

Multimodal time-variant signal analysis of neonatal EEG burst patterns.

It can be shown that dominant rhythmic signal components of neonatal EEG burst patterns (discontinuous EEG in quiet sleep) are characterized by a quadratic phase coupling (bispectral analysis), i.e. a multiplicative interaction (connection) between the underlying electrophysiological processes can be assumed. By means of pattern recognition algorithms as well as time-variant spectral and coherence analysis, a so-called "initial wave" (narrow band rhythm within a frequency range of 3-12 Hz) can be demonstrated within the first part of the burst pattern. The detection of this signal component and of the quadratic phase coupling is more successful in the frontal region. By means of amplitude demodulation of the "initial wave" the phase coupling can be attributed to an amplitude modulation. The results were derived from 6 neonates (20 burst patterns for each neonate; 8-channel recordings). A 16-channel EEG-recording was analyzed for one neonate.

Electroencephalography↗

PubMed1997

Analysis of the interrelations between a low-frequency and a high-frequency signal component in human neonatal EEG during quiet sleep.

It can be shown that dominant rhythmic signal components of neonatal EEG burst patterns (discontinuous EEG in quiet sleep) are characterised by a quadratic phase coupling (bispectral analysis). A so-called 'initial wave' (narrow band rhythm within a frequency range of 3-12 Hz) can be demonstrated within the first part of the burst pattern. The detection of this signal component and of the phase coupling is more successful in the frontal region. By means of amplitude demodulation of the 'initial wave' and a subsequent coherence analysis the phase coupling can be attributed to an amplitude modulation, i.e. the envelope curve of the 'initial wave' shows for a distinct period of time the same qualitative course as the signal trace of a 'lower' frequency component (0.75-3 Hz). The results were derived from six neonates (20 burst patterns for each neonate; 8 channel recordings).

Brain Mapping↗

PubMed1997

Exactness of source analysis of biomagnetic signals of epileptiform spikes by the method of spatial filtering: a computer simulation.

On the basis of spatial covariance it is found that, by spatial filtering the localisation of a single dipole source, both parallel and perpendicular to the measurement plane (assuming a signal-noise ratio of 5:1), can be performed with an accuracy of < 0.5 mm. When the signal-noise ratio is increased to 30:1, the resolution of temporally independent current sources separated by 2 mm becomes practicable. This resolution study is carried out by means of a pair of unity current dipoles with the dipole distance as a varying source model parameter. The conclusions, drawn from the results of computer simulation and supported by statistical calculations, refer to the spherical model of the volume conductor of the brain.

Computer Simulation↗

PubMed1997

Quantitative analysis of discontinuous EEG in premature and full-term newborns during quiet sleep.

To assess the spatio-temporal structure of discontinuous EEG tracing in mature and immature newborns, we analysed mean spectral power in frequency bands between 0.8 and 16.8 Hz in 6 full-term newborns and 7 premature newborns < 32 weeks of conceptional age. The most striking results showed a significantly higher mean spectral power for the first half of bursts than for the second half recorded in > 2.8-14.8 Hz frequency bands. This pattern was more pronounced in premature than in full-term newborns. No clear differences were observed in comparisons between the first and the second half of the interburst periods. In addition, as far as mid and high frequency band spectra were considered, the mean spectral power of burst was, in both groups, higher in the right as compared to the left occipital regions.

Brain↗

PubMed1997

Influence of tissue resistivities on neuromagnetic fields and electric potentials studied with a finite element model of the head.

Modeling in magnetoencephalography (MEG) and electroencephalography (EEG) requires knowledge of the in vivo tissue resistivities of the head. The aim of this paper is to examine the influence of tissue resistivity changes on the neuromagnetic field and the electric scalp potential. A high-resolution finite element method (FEM) model (452,162 elements, 2-mm resolution) of the human head with 13 different tissue types is employed for this purpose. Our main finding was that the magnetic fields are sensitive to changes in the tissue resistivity in the vicinity of the source. In comparison, the electric surface potentials are sensitive to changes in the tissue resistivity in the vicinity of the source and in the vicinity of the position of the electrodes. The magnitude (strength) of magnetic fields and electric surface potentials is strongly influenced by tissue resistivity changes, while the topography is not as strongly influenced. Therefore, an accurate modeling of magnetic field and electric potential strength requires accurate knowledge of tissue resistivities, while for source localization procedures this knowledge might not be a necessity.

Adipose Tissue↗

PubMed1997

Glutamine and other amino acid losses during continuous venovenous hemodiafiltration.

Serum amino grams and daily losses of glutamine (Gln) and other amino acids (AAs) into diafiltrate were measured during the first 5 days of continuous venovenous hemodiafiltration (CVVHDF) in 6 ICU patients with acute renal failure (ARF). Four patients had ARF as a part of multiple organ failure (MOF) of septic origin, and 2 patients had isolated ARF because of primary renal disease. During the study, all the patients received defined total parenteral nutrition (TPN). The mean daily AA losses into dialysate were relatively low (0.61 +/- 0.1 gN) and reached 4.5% of the daily AA substitution. Gln represented 32.7 +/- 5.9% of the total AA losses (0.19 +/- 0.04 gN). Serum levels of Gln (p = 0.002) and of most other AAs were significantly lower in the patients than in the control subjects (AA analysis in 16 healthy volunteers). Phenylalanine (Phe) was the only AA that was increased significantly (p < 0.01) in the patients. The mean patient serum concentrations of Phe and tyrosine were significantly higher (p < 0.03) than the correspondent concentrations in dialysate, but the lysine concentration was higher in dialysate (p < 0.03). The serum and dialysate concentrations of other AAs did not differ. Gln in serum decreased significantly (p < 0.03) on the second day of CVVHDF but returned to the baseline levels subsequently. Serum concentrations of Phe increased on the second day of CVVHDF (p < 0.05). Serum concentrations of other AAs remained stable during the whole study. We conclude that Gln losses into dialysate during CVVHDF are relatively low, but CVVHDF itself may induce changes in Gln metabolism and distribution that are reflected by a decrease of serum Gln levels at the institution of this treatment. Therefore, the need for Gln supplementation in ICU patients is even greater in the first days of CVVHDF.

Acute Kidney Injury↗