Biomedical subjects

H Witte

Publications and source records attributed to H Witte.

At least 73 records · Page 4Linked to original sources

PubMed1996

Analysis and classification of interictal spike discharges in benign partial epilepsy of childhood on the basis of the Hilbert transformation.

The spatial distribution of instantaneous power during the occurrence of rolandic spikes (computed via Hilbert transformation) can be utilized for classification of topographically different spike types. By visual analysis of the instantaneous power maps we found seven characteristic spike classes which correspond to the results of visual analysis of potential distribution. A neural network (NN) was trained with representatives of these classes. Single instantaneous power maps of 55/56 visually selected rolandic spikes, as well as map sequences of averaged spike segments (on-line) of 17 patients, were correctly classified by means of NN. The sensitivity of the NN for spikes from unknown patients was 98%. The classification scheme enables an objective classification of (multi-) regional spikes for selective averaging and for studies dealing with syndrome classification.

Child↗

PubMed1996

Dynamic coherence analysis of vasomotion and flow motion in skeletal muscle microcirculation.

The aim of our study was to determine the cause of fluctuations in microvascular blood flow measured by laser Doppler perfusion monitoring (LDPM) in microvessels of the hamster skin fold preparation. LDPM flow fluctuations (flow motion) were compared to simultaneous records of diameter changes obtained from arterioles and venules. Time-varying coherence analysis was used to quantify the frequency of flow and diameter changes in awake hamsters in control conditions and during sodium nitroprusside-induced vasodilation. Power spectrum analysis of LDPM signals of order 4 and 3 arterioles indicated frequencies of 0.06 +/- 0.01 and 0.08 +/- 0.02 Hz, respectively. Order 3 arterioles exhibited significant temporal coherence between flow motion and vasomotion signals at a frequency of the order of 0.1 Hz. There was lack of coherence when vasomotion was absent in arterioles. Order 4 arterioles had several coherent frequencies in addition to that around 0.1 Hz. In conclusion, time-variant coherence analysis indicated that spontaneous fluctuations in flow are caused by vasomotion of order 3 arterioles with frequency around 0.1 Hz that appears to coordinate local control processes in the microcirculation. Additional frequency components present in LDPM signals are unrelated to vasomotion.

Animals↗

PubMed1996

Use of adaptive Hilbert transformation for EEG segmentation and calculation of instantaneous respiration rate in neonates.

Broad, as well as narrow, band Hilbert transform filters (HTFs) were used as preprocessing units in the analysis of electroencephalogram (EEG) and respiratory movements in neonates. For these applications, new algorithms for the adaptation of the resonance frequency of a narrow-band-pass filter to the actual signal properties on the basis of an analytic filter design were developed. For the segmentation of the discontinuous EEG, the location of the resonance frequency was imbedded into the learning algorithm of a neural network (NN). In such automatic EEG pattern recognition, the detection of spike activity was taken into consideration. The spike detection scheme introduced uses broad-band HTFs as basis units. Additionally, the algorithm for the continuous control of the resonance frequency was applied to achieve the adaptation of the processing unit that performed the calculation of the instantaneous respiration rate, in this framework, a new on-line method for adaptive frequency estimation that is less sensitive to low signal-to-noise ratios (SNRs) was obtained. The new approaches introduced were tested in comparison with processing methods that have been established for the analysis of experimental and clinical data.

Algorithms↗

PubMed1996

Instantaneous frequency maps, dipole models and potential distributions of pattern reversal-evoked potential fields for correct recognition of stimulated hemiretinae.

Lateral hemifield pattern-reversal visual evoked potential (PVEP) field data were evaluated using potential distributions, dipole modelling and distributions of Hilbert transformation-based instantaneous frequency in order to determine the stimulated hemisphere. Twenty channel records were collected from 35 normal volunteers in two laboratories using similar stimulus conditions (11-20.5 degrees target, 60-75 min checks, 2/s reversal, 500 ms analysis epoch). P100 latency was determined in each average by the global field power maximum between 90 and 120 ms. Using the data from O1 and O2 at P100 latency, the stimulated hemisphere was identified by maximal potential or minimal instantaneous frequency on the stimulus-contralateral side, or, using the 20-electrodes data at P100 by the ipsilateral lateralization of the dipole model. Correct classification of the stimulated 70 hemiretinae was achieved by potential distribution in 44 cases, by dipole modelling in 54 cases and by instantaneous frequencies in 68 cases. Errors in the classification by potential distribution and dipole location were twice as frequent for decisions based on expected locations over the left than over the right hemisphere. This finding might be caused by the relatively larger size of the left occipital lobe. We conclude that a single value of instantaneous frequency which implies a massive data reduction can serve as a robust parameter for the characterization of the input conditions of hemifield PVEP (i.e. the stimulated hemiretina). It is more successful than potential distribution or dipole modelling, probably because instantaneous frequency incorporates considerably more information than the other two measures. It is suggested to explore instantaneous frequency as a parameter to recognize small retinal area stimuli in perimetry studies.

Adult↗

PubMed1996

Size influences on primate locomotion and body shape, with special emphasis on the locomotion of 'small mammals'.

The mechanical laws which make possible several characteristic and well-known modes of primate locomotion are reviewed. Biological requirements are fulfilled in small and in large primates by utilizing different mechanical principles. On the basis of the mechanics, special morphological traits can be identified which are advantageous for performing these locomotor modes, and which determine different life-styles. These morphological 'adaptations' consequently are different in larger and smaller primates. The divergence between large and small forms is clarified by the inclusion of non-primate mammals into the comparisons.

Animals↗

PubMed1995

Methods of dynamic spectral analysis by self-exciting autoregressive moving average models and their application to analysing biosignals.

Dynamic methods in the spectral domain are necessary to analyse biological signals because of the frequently nonstationary character of the signals. The paper presents an adaptive procedure of fitting time-dependent ARMA models to nonstationary signals, which is suitable for on-line calculations. The properties of the model parameter estimations are examined, and in the stationary case are compared with the results of convergent estimation methods. On this basis time-varying spectral parameters with high temporal and spectral resolution are calculated, and the possibility of their application is shown in EEG analysis and laser-Doppler-flowmetry.

Electroencephalography↗

PubMed1995

A new approach for detecting the position of retinal vessels and calculating their diameter on the basis of dynamic spectral analysis.

Fast adaptive algorithms were used for the detection of retinal vessels and for pre-processing the signals. By using different methods of dynamic spectral analysis, the local frequency of the vessels was determined. On this basis a method of calculating the diameters of the vessels was constructed; it is robust in relation to disturbances in the domain of the edges.

Algorithms↗

PubMed1995

Structure optimization of neural networks with A* -algorithm application in EEG pattern analysis.

The A* - Algorithm for heuristic search is applied to construct a Neural Network structure (NS) that optimally fits the structure of data to be learned. In this way, the user of Neural Networks (NN) is able to avoid the empirical testing of different structures. The method given here is applied to the recognition of different patterns derived from the EEG of an epileptic patient.

Algorithms↗

PubMed1995

Application of optimized pattern recognition units in EEG analysis: common optimization of preprocessing and weights of neural networks as well as structure optimization.

The main goal of this study is to demonstrate the possibility of training the Neural Network (multilayer perceptron) classifier and preprocessing units simultaneously, i.e., that properties of preprocessing are chosen automatically during the training phase. In the first realization step, adaptive recursive estimation of the power within a frequency band was used as a preprocessing unit. To improve the efficiency of special units, the power and momentary frequency estimation was replaced by methods that are based on adaptive Hilbert transformers. The strategy was developed to obtain optimized recognition units that can be efficiently integrated into strategies for monitoring the cerebral status of neonates. Therefore, applications (e.g., in neonatal EEG pattern recognition) will be shown. Additionally, a method of minimizing the error function was used, where this minimization is based on optimizing the network structure. The results of structure optimization in the field of EEG pattern recognition in epileptic patients can be demonstrated.

Algorithms↗

PubMed1993

Study of dietetic knowledge among members of the primary health care team.

There is growing emphasis on health promotion in primary care. The success of this endeavour depends in part on the ability of members of the primary health care team to provide appropriate and practical advice and support, relating to lifestyle. A study of 58 primary health care professionals was carried out in the Grampian region of Scotland to assess their nutritional knowledge and their ability to provide practical dietary advice, particularly in relation to the prevention of coronary heart disease. Overall, the primary health care workers had a broad understanding of recommendations for healthy eating, but there was some confusion over specific aspects of these recommendations. Health professionals also found it difficult to translate knowledge into practical dietary advice tailored to an individual case. If health promotion in primary care is to work effectively, the infrastructure necessary for effective training and continuing education has to be addressed.

Coronary Disease↗

PubMed1992

Primary structure of a gene-sized DNA encoding calmodulin from the hypotrichous ciliate Stylonychia lemnae.

We have isolated and characterized a gene-sized DNA encoding calmodulin (Clm) from macronuclear (MA) DNA of the hypotrichous ciliate, Stylonychia lemnae. The gene has 3500 copies per macronucleus. The length of the gene was deduced by agarose-gel electrophoresis of MA DNA and Southern blot analysis using a Clm cDNA probe from chicken. We then isolated the gene from a MA library. The overall length of the gene is 821 bp with a 450-bp intronless coding region. The deduced amino acid (aa) sequence of ciliate Clm has 149 aa and an M(r) of 16,819. Both ends of the cloned gene have the hypotrichous telomeric C4A4 repeat. The coding region is flanked by a 158-bp 5'-leader sequence and a 3'-trailer sequence of 213 bp. S1 analysis was used to locate the transcription start point (tsp) 49 bp upstream from the start codon. No common eukaryotic transcription signals were found upstream from the tsp. A second gene-sized DNA, detected by its cross-hybridization with the Clm DNA, predicts the existence of a second Ca(2+)-binding protein with only one Ca(2+)-binding site. It's function and biological significance is yet unknown.

Amino Acid Sequence↗

PubMed1992

[Application of Fourier transformation as the basic algorithm for processing cardiorespiratory data of newborn infants].

The multiple possibilities for the application of Fast Fourier Transformation (FFT) in the cardiorespirography of neonates are shown as a summary of our own results. The basis is the power spectral analysis of instantaneous heart rate and respiratory movements, which can be complemented by a coherence analysis of both parameters. A model-aided method for quantification of respiratory sinus arrhythmia (RSA) as an additional application for power spectral and coherence analysis is discussed. The realization of Hilbert transformation by FFT makes possible the interval-related calculation of respiration rate. The necessity of this supplementation, as well as the resulting strategies of additional processing steps are emphasized. The results is a concept of signal processing which increases the efficiency of previously employed methods in computer-aided cardiorespirography.

Algorithms↗

PubMed1991

Use of discrete Hilbert transformation for automatic spike mapping: a methodological investigation.

On the basis of discrete Hilbert transform (DHT) realised by fast Fourier transform (FFT), a new strategy for automatic spike mapping is introduced. The further computation of the EEG time series after DHT results in the time series of the momentary power and the momentary frequency. Both are used for the solution of the main requirements of automatic spike mapping. The spike-mapping concept introduced meets the requirements of efficient automatic spike detection and also has an insensitivity with regard to EMG interference and transient signal components, a frequent cause of false positive detections. Additionally, there are advantages if the momentary power of the spike is mapped instead of the spike potential. The use of momentary power makes a combination of power spectral mapping and spike-mapping strategies possible.

Algorithms↗

PubMed1991

Using discrete Hilbert transformation for interval-related calculation of the respiration rate in neonates.

From the basis of the fast Fourier transformation (FFT), the discrete Hilbert transformation (DHT) is used to compute the instantaneous respiration rate in neonates. This interval-related computation of respiration rate must be combined with a concept of adaptive filtration of the respiratory movements. This strategy is performed by adaptive recursive estimations of mean values with different adaptation constants. Additionally, a frequency band limitation is carried out on the basis of the peak characteristic of the power spectrum (respiratory movements). By means of the adaptive estimation of the variance of respiratory movements, an amplitude-time window is calculated to choose between epochs with breaths and apnoea.

Algorithms↗

PubMed1991

Experimental and clinical studies of neonatal eeg mapping--methodical prerequisites and data interpretation.

To investigate whether the sampling theorem was fulfilled up to now in experimental and clinical EEG-mapping of neonates and to determine the "smearing effect" of EEG transmission by the leading media up to the skin, EEG-maps from 5 slightly anaesthetized term newborn piglets and 8 healthy human newborns were calculated. A spatial sampling rate of 1-2 cycles per cm is necessary for a sufficient reproduction of surface EEG topology in newborn piglets showing activity maxima within motor projection zones. In human neonates, 8-channel mapping gave insufficient results, whereas state and EEG pattern related 16-channel maps provided sufficiently constant, but not complete pattern. Simultaneous maps from epidural and epiossal, and epiossal, and surface recordings in newborn piglets showed only small "smearing" effects. We conclude, the more topical interpretation chances exist, like in neonates with smaller "smearing" effects of transmission media, the more complete uptake of original data for mapping is necessary. Up to now, it is done seldomly.

Animals↗

PubMed1991

[Quantification of artefacts in surface EMG by validating the lower frequency limit in clinico-physiologic studies].

The surface-EMG becomes more and more important because computer assisted analysing systems can be applied. The occurrence of artefacts makes it very difficult to compare several recorded EMG channels with each other. In this study a frequency related quantification of movement artefacts and ECG-related influences on the EMG is carried out to select a suitable lower cut-off frequency for surface-EMG investigations. In 764 monopolar surface-EMG-recordings of the neck and back muscles the solely artefact-caused part of EMG-segments was analysed and quantified by means of modelling methods.

Adult↗

PubMed1991

Human body proportions explained on the basis of biomechanical principles.

On the basis of theoretical biomechanics and of experiments, we investigated the mechanical requirements to which the body of a bipedally walking primate is subject, and the possibilities to meet these requirements with a minimum amount of energy. The least energy-consuming adaptation is clearly a body shape favourable for the preferred locomotion. Some characteristics of human body shape, in particular its proportions, could be identified as advantageous for fulfilling obvious biological roles or mechanical necessities. The characteristic length and the extended position of human hindlimbs make walking faster without additional input of energy. Mass distribution on the hindlimbs reduces the energy necessary for accelerating the swing limb after liftoff and for decelerating the swing limb before the heelstrike. Length and mass distribution in the forelimb gives it a pendulum length comparable to that of the hindlimb, so that both extremities swing at the same frequency. This swinging of the forelimbs counters in part the movements exerted by the moved hindlimbs on the trunk. The elongate and slim shape of the trunk provides great mass moments of inertia and that means stability against being flexed ventrally and dorsally by the forward and rearward movements of the heavy and long hindlimbs. Shoulder breadth in combination with the shallow shape of the thorax yield higher mass moments of inertia against the rotation of the trunk about a vertical axis than a cylindrical trunk shape. Further elongation of the hindlimbs is limited by the energy necessary for acceleration and deceleration, as well as for lifting them during the swing phase. In addition, the reaction forces exerted by the hindlimbs would expose the trunk to undue excursions if the proportions trunk length/limb length or trunk mass/limb mass would decrease. The above-noted kinetic requirements are partly in line, partly in conflict with the requirements of statics.

Arm↗

PubMed1991

[Methodologic studies in dynamic EMG mapping based on the Hilbert transformation].

On the basis of Discrete Hilbert Transformation spectral parameters for dynamic EMG analysis can be introduced. Within analysis intervals which are used in the same manner as in spectral analysis, the momentary power of EMG frequency bands can be computed as time series of the same interval duration. A close connection exists between momentary power and the current phenomenology of power spectral analysis because the momentary power of a defined frequency band can be seen as the exact dynamic equivalent of the corresponding mean power value deduced from the power spectrum. A multichannel EMG recording (greater than or equal to 16 channels) makes the representation of the topographical distribution of the spectral parameter by a coloured map possible. Additionally, the momentary power can be used to calculate map sequences. In this way, changes of EMG activity can be quantified by map sequences of an arbitrary time resolution. By calculation of momentary frequency via DHT an artefact detection scheme for ECG interference can be suggested. A completion of this methodology can be carried out by applications of adaptive filtration procedures. Using this concept of EMG processing, a new and common methodical basis of EMG power spectral analysis can be introduced.

Brain Mapping↗