Biomedical subjects

H Witte

Publications and source records attributed to H Witte.

At least 19 recordsLinked to original sources

PubMed2002

[What influence do size and placement of patella resurfacing have on knee endoprosthesis?].

The aim of this study was to document the changes in retropatellar pressure, contact area and forces due to different sizes and placement of the patella resurfacing in knee arthroplasty. Six cadaver specimens (after Thiel fixation) were examined after the implantation of the total knee arthroplasty Genesis I. The patella sizes "small" and "medium" were placed as the "onlay" version, centered as well as off-centered by 0.4 cm in all four directions. Pressure and area measurements were done with Fuji pressure measuring film, which was placed between the patellar fascia of the femur and the patella in a defined position. The pressure was measured by applying a predetermined force for 5 s. The examinations were done with 60 degrees knee flexion and a force of 280 N. In our results there were no significant differences between, patella sizes. No significant differences for the medial, distal and proximal placement were found for the small patella. The lateral placement led to a significant decrease in the contact area (P = 0.0277), maximum pressure (P = 0.0422) and force (P = 0.0277). The average pressure did not change significantly (P = 0.1159). For the medium size patella there were no significant differences for medial or distal placement. The comparison of lateral and central placement revealed a significant decrease in the contact area (P = 0.0446). Comparing distal and proximal positioning, a significant increase in contact area and significant decrease in force were found (P = 0.0277 and P = 0.0277 respectively). In conclusion, the choice of small or medium patella resurfacing does not seem to have a significant influence. In comparison to the results without patella implants, the implantation of the small patella caused a significant decrease in the retropatellar contact area (P = 0.03) and force (P = 0.03). Average and maximum pressure did not change significantly (P = 0.6 and P = 0.35) even though pressure increased slightly. For the medium size, maximum pressure (P = 0.03) increased significantly and force decreased significantly (P = 0.0277) whereas contact area and average pressure increased slightly. The results of the different placements of the patella implant do not support the recommendation for a medial shift. However, at least the lateralized implantation led to a reduction of contact area and force as well as to a slight increase of pressure which is considered as unfavorable.

Aged↗

PubMed2002

Prediction of movement following noxious stimulation during 1 minimum alveolar anesthetic concentration isoflurane/nitrous oxide anesthesia by means of middle latency auditory evoked responses.

This paper investigates the applicability of generalized dynamic neural networks for the design of a two-valued anesthetic depth indicator during isoflurane/nitrous oxide anesthesia. The indicator construction is based on the processing of middle latency auditory evoked responses (MLAER) in combination with the observation of the patient's movement reaction to skin incision. The framework of generalized dynamic neural networks does not require any data preprocessing, visual data inspection or subjective feature extraction. The study is based on a data set of 106 patients scheduled for elective surgery under isoflurane/nitrous oxide anesthesia. The processing of the measured MLAER is performed by a recurrent neural network that transforms the MLAER signals into signals having a very uncomplex structure. The evaluation of these signals is self-evident, and yields to a simple threshold classifier. Using only evoked potentials before the pain stimulus, the patient's reaction could be predicted with a probability of 81.5%. The MLAER is closely associated to the patient's reaction to skin incision following noxious stimulation during 1 minimum alveolar anesthetic concentration isoflurane/nitrous oxide anesthesia. In combination with other parameters, MLAER could contribute to an objective and trustworthy movement prediction to noxious stimulation.

Anesthetics, Inhalation↗

PubMed2002

[Brief causal relations in EEG based on adaptive Granger causality].

Commonly, coherence and correlation are used to describe interrelations between EEG signals. But, on this basis, the investigation of causality or direction of interrelations is not possible. The general idea of causality between two signals may be expressed in terms of upgrading the predictability of one signal bye the knowledge of the past of the other signal. The best established approach in this context is the so-called Granger causality. The study present an adaptive estimation of Granger causality, which allows to detect dynamic causal relations within time intervals of less 100 ms. The time-variant Granger causality is applied to EEG data of the Stroop task. It could be shown, that conflict situation generates a dense web of directed interactions from posterior to anterior cortical areas.

Adult↗

PubMed2002

[Time variant bispectral analysis based on adaptive recursive Fourier transformation].

An appropriate investigation of quadratic phase couplings (QPC) in non-stationary signals requires time-variant methods of bispectral analysis. A new approach for time-variant estimation of power spectrum and bispectrum based on an adaptively, recursively estimated Fourier transform (ADFT) is presented in this paper. A reduced calculation effort and the possibility of the calculation of the bispectrum for selected frequency triples are important advantages of this method. Because of the recursive calculation, the ADFT is convenient for analysing ongoing signals. This will be demonstrated for simulated and real biomedical signals.

Electroencephalography↗

PubMed2002

Pneumatized spaces, sinuses and spongy bones in the skulls of primates.

The earliest attempts to understand the "pneumatized spaces" in the skulls of primates in general were focussed on the hollow spaces and the epithelium which covers their surfaces. More recent approaches consider the sinuses as a means to optimise skull architecture. Still, many attempts to get hold of the meaning of the intriguing pneumatized spaces circle around the air filled volumes they enclose. Here, we would like to reverse the approach and focus our biomechanic interpretation on the walls surrounding the big, empty, or at least not mechanically resistant spaces, and their mechanical properties. As a working hypothesis, we consider not only the walls of the more or less closed cavities, or sinuses, but also the braincase, the orbits, and the nasal channel as thin-walled shells of which we know that they can carry surprisingly large loads with a minimum of material. Details of the wall's profiles fit with this approach. From the same viewpoint, the bubble-like, air-filled cavernous systems in the ethmoid or temporal bones, and the marrow-filled spongy substance in the upper jaw are looked at as honeycomb-structures, which provide mechanical properties that are biologically advantageous and allow the saving of weight.

Animals↗

PubMed2001

Effect of different extraction procedures on the yield and pattern of Se-species in bacterial samples.

Investigations are described to extract Se-species from a bacterial sample. The five extraction methods investigated were: hot water, protease, lysozyme, lysozyme-protease, and HCl hydrolysis. The extraction efficiency was determined by comparing the total amounts of selenium in the sample after pressure digestion with the amounts extracted by the different methods described. Efficiencies were found to be only 1% (hot water), ca. 8% (protease, HCl hydrolysis) or ca. 12% (lysozyme, lysozyme-protease). The Se-peak patterns were compared after investigating the extracts with strong anion exchange chromatography-inductively coupled plasma mass spectrometry (SAX-ICP-MS). Most promising were the lysozyme-assisted procedures, which showed the highest diversity of species. Here, in the protease-lysozyme approach, the protease seemed to break down species that had been extracted by lysozyme from the bacterial wall (murein sacculus). The other approaches seemed not to extract many species. Hot water extraction was completely unsuitable, extracting only low amounts of a single, unknown species.

Bacteria↗

PubMed2001

Instantaneous multivariate EEG coherence analysis by means of adaptive high-dimensional autoregressive models.

This study presents an efficient algorithm for the fitting of multivariate autoregressive models (MVAR) with time-dependent parameters to multidimensional signals. Thereby, the dimension of the model may be chosen to equal the number of signal channels. The autoregressive (AR) parameter matrices are estimated by an extension of the recursive least squares (RLS) algorithm with forgetting factor. The estimation procedure includes a single trial as well as an ensemble mean approach. The latter approach allows the simultaneous fit of one mean MVAR model to a set of single trials, each of them representing the measurement of the same task. A particular advantage of this ensemble mean approach is that it requires only a low computation effort in comparison to well known procedures applied to single trials. Furthermore, the ensemble mean approach is linked with a high adaptation capability. The properties of the estimator are investigated using simulated time series. It can be demonstrated that the adaptation capability of the estimation (measured by its adaptation speed and variance) does not depend on the model dimension. The mean MVAR fit is applied to 19-dimensional EEG data, recorded during an elementary comparison procedure. The calculation of ordinary and multiple coherence is discussed. The sensitivity of the multiple instantaneous EEG coherence will be demonstrated.

Algorithms↗

PubMed2001

Phylogenetic relationships within terrestrial mites (Acari: Prostigmata, Parasitengona) inferred from comparative DNA sequence analysis of the mitochondrial cytochrome oxidase subunit I gene.

Partial DNA and amino acid sequences translated from the mitochondrial cytochrome subunit I gene (408 bp) of 17 mite species have been used for analyzing the phylogenetic relationships within the terrestrial Parasitengona (Trombidia). Due to mutational saturation of the third codon position, only first and second codon positions and amino acid sequences were analyzed, applying neighbor-joining, maximum-parsimony, and maximum-likelihood tree-building methods. The reconstructed trees revealed similar topologies of taxa; however, the phylogenetic relationships could be convincingly resolved only within several trombidioid taxa. The proposed basic relationships within the Parasitengona, in particular those of Calyptostomatoidea, Smarididae, and Erythraeidae, were poorly supported in bootstrap tests. A comparison of the presented gene tree with a phylogenetic tree based upon traditional characters revealed only few contradictions in nodes only weakly supported by morphological data. The most astonishing result is the proposed early derivative position of Microtrombidiidae within the terrestrial Parasitengona.

Animals↗

PubMed2001

Pitfalls in the clustering of neuroimage data and improvements by global optimization strategies.

In this paper, we examined three vector quantization (VQ) methods used for the unsupervised classification (clustering) of functional magnetic resonance imaging (fMRI) data. Classification means that each brain volume element (voxel), according to a given scanning raster, was assigned to one group of voxels based on similarity of the fMRI signal patterns. It was investigated how the VQ methods can isolate a cluster that describes the region involved in a particular brain function. As an example, word processing was stimulated by a word comparison task. VQ analysis methodology was verified using simulated fMRI response patterns. It was demonstrated in detail that VQ based on global rather than local optimization of the objective function yielded a higher performance. Performance was measured in statistically relevant series of VQ attempts using several indices for goodness, reliability and efficiency of VQ solutions. Furthermore, it was shown that a poor local optimization caused either an underestimation or an overestimation of the stimulus-induced brain activation. However, this was not observed if the cluster analysis was based upon a global optimization strategy.

Adult↗

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

Identification of the stimulated hemiretina in primary school children and adults based on left and right hemifield pattern reversal visual evoked potentials--a comparative study.

OBJECTIVES: The analysis of left and right hemifield pattern-reversal visual evoked potentials (PVEPs) in children and the identification of the stimulated hemiretina testing different identification procedures previously applied to adults. METHODS: Lateral hemifield PVEPs were recorded in 40 children (6-11 years) and 27 adults (25-40 years) from, at least, 19 standard electrodes. Two procedures were tested for the determination of the stimulated hemifield: firstly, the evaluation of the values of instantaneous frequency at the occipital electrodes at P100 latency (determined by the global field power), and secondly, the application of a generalised dynamic neural network (GDNN) using the PVEP time course at selected electrode positions as the external input. RESULTS: P100 latency as well as P100 amplitude over the contralateral occiput in children were significantly greater than in adults. Contrary to the behaviour in adults, instantaneous frequency is not a robust identifier of left and right hemiretina stimulation in children. The best identification performances were achieved when using group trained GDNNs with the bipolar difference signals of electrodes P3/P4 or T5/T6 as the external input. CONCLUSIONS: The PVEPs at electrodes P3/P4 and T5/T6 contain essential information for the determination of the stimulated hemifield. This should be further considered during the development of on-line procedures for automatic PVEP detection in future studies.

Adult↗

PubMed2001

Time-variant non-linear phase-coupling analysis of EEG burst patterns in sedated patients during electroencephalic burst suppression period.

OBJECTIVES: The quadratic phase-coupling (QPC) within burst patterns during electroencephalic burst suppression has been quantified. METHODS: It can be shown that a QPC exists between the frequency ranges 0-2.5 and 3-7.5 Hz and between the frequency ranges 0-2.5 and 8-12 Hz. By means of time-variant bicoherence analysis, a strong phase-locking between the modulating and the modulated component can be identified. The phase-locking is demonstrable within the first 250 ms after the burst onset and comes up to the maximum between 750 and 1250 ms. RESULTS: The effect is maintained over the whole first part of the burst (2 s) with a decreasing tendency after 1250 ms. All these effects cannot be found in the EEG before entering the burst suppression period (BSP). The transient coupling phenomena in the EEG bursts during BSP can be regarded as indicators for short-term interrelations between the underlying electrophysiologic processes. CONCLUSIONS: It can be suggested that the method introduced for the quantification of the sedation depth should be used.

Cerebrospinal Fluid Pressure↗

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↗

PubMed2001

EEG frequency and phase coupling during human information processing.

Neuronal activity during information processing is represented by oscillations within local or widespread neuronal networks. These oscillations may be recorded by the EEG (electroencephalogram). The oscillatory interaction between neuronal ensembles may be at one single frequency or at different frequencies due to non-linear coupling. The investigation of momentary coherence and phase enables the examination of synchronized oscillatory network activity during fast-changing cognitive processes. On this basis information transfer from occipital areas towards frontal areas could be described during processing of visual presented words. Non-linear phase coupling between oscillations with different frequencies during memory processing was detected by means of cross-bicoherence.

Adult↗

PubMed2000

[What retropatellar changes result by implantation of a superficial knee joint prosthesis?].

The aim of this study was to evaluate the retropatellar pressure, force, and contact area in cases of knee arthroplasty compared to knees without arthroplasty. We examined six leg specimens before and after knee arthroplasty. The modified Thiel fixation was used, and arthroplasty was the Genesis I without patellar implant (Fa. Smith & Nephew, Schenefeld). Contact measurements were performed with pressure-sensitive film (Fuji Prescale type "super low") in 45 degrees, 60 degrees, 90 degrees, and 120 degrees knee flexion. The results were evaluated with special software, "Pressure Imaging and Analyzing System FPD-901 Series". The leg was exarticulated in the hip joint and the knee joint was opened from a suprapatellar approach. The film was placed at a defined area between the facies patellaris of the femur and facies articularis of the patella. Instantaneous pressure was measured during a time of 5-s pressure increase and a further 5 s. A force of 280 N was applied to the quadriceps muscle. Before knee arthroplasty, the contact area measured 154.3 mm2, the average pressure was 1.14 MPa, the force 182.13 N. After knee arthroplasty, the contact area was 119.94 mm2, the average pressure 1.522 MPa, the force 180.98 N. Following knee arthroplasty the contact area decreased significantly (P = 0.015), and the average (P = 0.0001) and maximum pressure (P = 0.0003) increased significantly. The force did not change significantly (P = 0.7642). The choice of the knee arthroplasty implant and approach to the knee joint should be considered in order to achieve an increased retropatellar contact area thus preventing smaller contact areas than before knee arthroplasty. The increased contact area could also prevent increasing retropatellar pressures after knee arthroplasty and further complications.

Aged↗

PubMed2000

Retropatellar contact characteristics in total knee arthroplasty with and without patellar resurfacing.

Total knee replacement with and without patellar resurfacing was performed in 6 cadaver specimens. The contact pressure and contact area between femur and patella was measured at 60 degrees of flexion. In comparison to specimens without resurfacing the specimens with small size resurfacing showed a significant decrease in contact area, whereas average and maximum pressure were unchanged. In specimens with medium size resurfacing, contact area and average pressure increased slightly, whereas maximum pressure increased significantly. Patellar resurfacing did not change the retropatellar pressure, but was associated with reduced contact area.

Aged↗

PubMed2000

Investigation of nonlinear ECoG changes during spontaneous sleep state changes and cortical arousal in fetal sheep.

We examined the processes of cortical activation and deactivation of the fetal brain during spontaneous sleep state transitions and during central nervous processing of vibroacoustic stimulations (VASs) using nonlinear analysis of the electrocorticogram (ECoG). Tests of nonlinearity and a random shuffling routine revealed deterministic and nonlinear portions in the fetal ECoG. As common nonlinear measures are not applicable to nonstationary time series, we developed an algorithm to estimate the predictability of the ECoG in its time course by means of a point prediction error (PPE). The ECoG was recorded before and during VAS from the maternal abdominal surface in seven chronically instrumented fetal sheep at 0.8 of gestation. The PPE during REM sleep was significantly higher than during NREM sleep. VAS in NREM sleep resulted in an abrupt increase of the PPE not reaching the level of REM sleep. The steep increase of the PPE at onset and its slow decrease after cessation of the stimulus were very similar to the dynamics of spontaneous sleep state transitions, suggesting the involvement of the same cortical activating mechanisms. In conclusion, the stage and the time course of fetal brain activation and deactivation patterns can be clearly shown by PPE techniques. The PPE is a useful complement to spectral analysis. Both techniques describe different properties of the ECoG.

Alpha Rhythm↗

PubMed2000

Method developments for iodine speciation by reversed-phase liquid chromatography-ICP-mass spectrometry.

Method developments are described for a iodine speciation method. This method is based on a reversed-phase liquid chromatography separation combined with inductively coupled plasma-mass spectrometry detection. Investigations are performed concerning the methanol tolerance/stability of inductively coupled plasma, postcolumn oxidation/volatilization of iodine from species, influences of buffer pH, and column temperature on separation efficiency. The experiments focused on six iodine species, namely iodine, monoiodothyrosine, di-iodothyrosine, tri-iodothyronine, reversed tri-iodothyronine, and thyroxin. Detection limits were determined between 0.08 and 1.5 microg/L (iodine related), dependent on species. Appplications on a urine sample were performed, showing iodide as the predominant iodine species.

Buffers↗