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Biomedical subjects

G Pfurtscheller

Publications and source records attributed to G Pfurtscheller.

At least 127 records · Page 7Linked to original sources
PubMed1994

Event-related desynchronization (ERD) during visual processing.

Event-related desynchronization (ERD) is the short-lasting attenuation or blocking of rhythms within the alpha (beta) band. ERD is found during but also before visual stimulation. Two different types of ERD can be differentiated: one short-lasting, localized to occipital areas and involving upper alpha components; the other longer lasting, more widespread, most prominent over parietal areas and maximal for lower alpha components. The former most likely reflects primary visual processing and feature extraction, the latter is more related to cognitive processing and mechanisms of attention.

Alpha Rhythm↗
PubMed1994

Selection of electrode positions for an EEG-based brain computer interface (BCI).

One major question in designing an EEG-based Brain Computer Interface to bypass the normal motor pathways is the selection of proper electrode positions. This study investigates electrode selection with a Distinction Sensitive Learning Vector Quantizer (DSLVQ). DSLVQ is an extended Learning Vector Quantizer (LVQ) which employs a weighted distance function for dynamical scaling and feature selection. The data analysed and classified were 56-channel EEG recordings over sensorimotor areas during preparation for discrete left or right index finger flexions. Data from 3 subjects are reported. It was found by DSLVQ that the most important electrode positions for differentiation between planning of left and right finger movement overlie cortical finger/hand areas over both hemispheres.

Adult↗
PubMed1994

Analysis of cardiorespiratory signals--methodology and applications in infants.

Heart rate variability and thoracal respiratory movements were examined in two babies aged six months during eight hour polysomnographic recordings. Computer-assisted analysis in the time and frequency domain were performed to investigate the mechanisms underlying cardiorespiratory control. Coherence and phase relation between cardiac cycles and respiration were investigated in detail. Both methods demonstrated that during quiet sleep (stage 3/4), the cardiorespiratory coupling was significantly increased as compared to active sleep (REM sleep).

Brain Stem↗
PubMed1994

[A method for determining pulse wave transmission time].

Analysis of the transit time of a pulse wave is a possibility for the continuous observation of the changes in blood pressure activity. With invasive procedures, the interval between two notable events on pressure pulse waveforms, which is known as the pulse transit time, is often calculated. Using the second heart sound, the pre-ejection period and the left-ventricular ejection time (systolic time interval) are computed in order to be able to exclude the effect of haemodynamic parameters on aortic pressure increase. Since the use of noninvasive procedures excludes computation of the systolic time interval, and a phonocardiography is also often lacking, a method of relatively quickly determining the time interval between the R-wave of the ECG and the peripheral pulse was developed. The computed pulse transmission time is suitable for studying phasic events and their effects on the mean blood pressure.

Blood Pressure↗
PubMed1994

Computer-assisted neurovegetative monitoring in patients after heart transplantation.

The effects of orthotopic heart transplantation on spontaneous fluctuations of the respiration rate and heart rate were studied with a computer-assisted system for neurovegetative monitoring in 22 patients (mean age +/- SD: 48.7 +/- 9.4 years) 19.5 +/- 14.4 months after transplantation. The control group consisted of 12 healthy volunteers (mean age +/- SD: 38.7 +/- 6.6 years). The mean (+/- SE) respiratory rate was higher in the transplantation group than in the control group (17.7 +/- 0.8/min vs. 14.6 +/- 1.1 breaths/min, P < 0.2). The mean variability of the respiratory rate was smaller in the transplant patients than in the controls (3.7 +/- 0.3 vs. 2.8 +/- 0.4, P < 0.2). The heart rate variability coefficient in the patients after transplantation was lower than that in the controls (1.3 +/- 0.1% vs. 6.9 +/- 0.5%, P < 0.001). Spectral analysis of heart rate variability showed a smaller decrease of variability of respiration (P < 0.05) than of blood pressure regulation (P < 0.001) or of the angiotensin-renin system (P < 0.001). A separate group of 7 transplant patients (mean age 51.0 +/- 7.7 years) had activated cardiac pacemakers and thus no spontaneous physiologic heart rate oscillations. The variability of the respiratory rate in these patients was lower than in the other 22 transplant patients (1.8 +/- 0.2 vs. 3.7 +/- 0.3, P < 0.001). The data provided by multiparametric neurovegetative monitoring support the evaluation of complex regulatory mechanisms of respiratory and cardiovascular function and their adaptability after orthotopic heart transplantation.

Adult↗
PubMed1993

40-Hz oscillations during motor behavior in man.

40-Hz oscillations were measured during finger, toe and tongue movement using an electrode array of 56 electrodes over the pre and post central areas. Each movement was made 150 times in intervals of 12 s. The average power increase in narrow frequency bands between 8 and 40 Hz was then calculated and the topographical distribution studied. 40-Hz oscillations were only found contralateral over the hand area for finger movements, close to the vertex for toe movements and bilateral symmetrical for tongue movements. The maxima of the 40-Hz oscillations occurred before movement onset.

Brain Mapping↗
PubMed1993

Alpha frequency, cognitive load and memory performance.

EEG-signals were recorded from subjects as they performed a modified version of Schneider's and Shiffrin's memory search paradigm. The hypothesis was tested whether individual (centre of gravity) alpha frequency, termed IAF, is related to memory performance and/or attentional demands. The results show that memory performance exerts the strongest effect on IAF. As compared to a resting period, the difference in IAF between age-matched good and bad memory performers reached a maximum when subjects were actually retrieving information from their memory. During retrieval, the IAF of good performers is 1.25 Hz higher than for bad performers. Attentional and task demands also tend to reduce IAF, but as compared to memory performance-to a much lesser degree. The results of amplitude analyses demonstrate further that during retrieval, alpha desynchronization is more pronounced for bad performers than for good performers. Taken together, the results indicate that a decrease in IAF is always related to a drop in performance.

Adult↗
PubMed1993

Visual evoked potentials and electroretinography in brain-dead patients.

Visual evoked potentials and electroretinograms were elicited by light-emitting diode stimulation and recorded simultaneously, with cephalic and noncephalic references, in 30 normal subjects and in 30 brain-dead patients. A characteristic pattern was found in the group of patients: when a cephalic reference was used for both visual evoked potentials and the electroretinogram, the a- and b-waves of the electroretinogram were recognized in all patients, and visual evoked responses consisted of waves with inverse polarity, similar morphologic characteristics, the same latency, and less amplitude than those of the electroretinogram. When a noncephalic derivation was chosen for the electroretinogram and visual evoked potentials, electroretinogram did not change in either morphologic features or latency, whereas the visual evoked potential channel showed no response. Only in two cases was it possible to record waves in the visual evoked potential lead with a noncephalic reference, showing a spread of the electroretinogram to the occipital area, with a considerably reduced amplitude. These results suggest that, although contamination of visual evoked potential records by the spread of the electroretinogram to the occipital area could occur, it is easy to confirm the absence of a true cortical visual response in brain-dead patients by means of a noncephalic reference. This pattern clearly confirms that in the visual pathways of brain-dead patients, electrical activity is confined to the retina.

Adolescent↗
PubMed1993

Neural network based classification of single-trial EEG data.

Standard Back Propagation (BP), Partially Recurrent (PR) and Cascade-Correlation (CC) neural networks were used to predict the side of finger movement on the basis of non-averaged single trial multi-channel EEG data recorded prior to movement. From these EEG data, power values were calculated and used as parameters for classification. The results obtained on three subjects show that the Cascade-Correlation neural network is an appropriate choice for neural network based classification of spatio-temporal single-trial EEG patterns. It is fast, stable and able to discover and recognize underlying dynamics of rhythmic activities within the alpha band which precede execution of hand movements.

Algorithms↗
PubMed1993

Regeneration of sympathetic activities in small bowel transplants.

In order to study the activity of noradrenergic nerve fibres along mesenteric arteries in small-intestinal grafts, the entire jejunoileum was transplanted heterotopically in an isogeneic rat model (group I, n = 12). To assess their influence on graft motility, 9 cm of jejunum were transplanted in an orthotopic position and three bipolar electrodes sutured to the seromuscular layer of the graft (group II, n = 10). Fasting motility was recorded up to postoperative day 42. Animals of group I were sacrificed from day 7 on at weekly intervals and mesenteries were analysed histochemically by fluorescence microscopy. After the 1st and 2nd week, grafts were found to be completely depleted of noradrenaline. At the end of the 3rd week, fluorescence became detectable along graft mesenteric arteries and showed normal intensity from the end of week 4. Migrating myoelectric complexes (MMCs) were present in all animals of group II. The variability of the MMC period (mean 12.6 min; SD 6.2 min) expressed as variation coefficient (median 36.5; 14.6-74) did not change during the observation period. From these findings it is concluded that there are no extrinsic noradrenergic activities in rat small-intestinal transplants for the first 3 postoperative weeks but they do recover there after. Their influence on graft function remains unclear: MMC periodicity, however, was no influenced.

Animals↗
PubMed1993

Computer-based analysis of continuous non-invasive blood pressure and heart rate variability-methodology and normal values during wakefulness and sleep.

Polysomnographic recordings were made in 10 healthy male adult subjects (mean age 25.1 +/- 2.8 years). Parameters were obtained from continuous non-invasive measurement of blood pressure and from heart rate spectra analysed both in the waking state and during sleep (stage 4). The total heart rate variability (mean +/- SE) was not significantly diminished (p < 0.2; paired t-test) during stage 4 sleep (6.2 +/- 0.5%) as compared with the waking state (7.1 +/- 0.5%). The relative heart rate variability coefficient within the frequency band HRV-II ((3-9)/min) was, however, significantly higher (p < 0.001) during slow-wave sleep (0.55 +/- 0.04) than during wakefulness (0.34 +/- 0.04). This fact is in accordance with results concerning an estimated value of the baroreflex sensitivity, which was also significantly higher (p < 0.001) during sleep stage 4 (7.0 +/- 0.8 ms/mmHg vs. 10.4 +/- 1.4 mmHg).

Adult↗
PubMed1993

Towards automated sleep classification in infants using symbolic and subsymbolic approaches.

The paper addresses the problem of automatic sleep classification. A special effort is made to find a method of extracting reasonable descriptions of the individual sleep stages from sample measurements of EGG, EMG, EOG, etc., and from a classification of these measurements provided by an expert. The method should satisfy three requirements: classification accuracy, interpretability of the results, and the ability to select the relevant and discard the irrelevant variables. The solution suggested in this paper consists of a combination of the subsymbolic algorithm LVQ with the symbolic decision tree generator ID3. Results demonstrating the feasibility and utility of our approach are also presented.

Algorithms↗
PubMed1993

[Computer controlled brain death documentation in the intensive care unit].

An interactive, knowledge-based computer system for brain death documentation is presented. The specific exponents BRAINDEX R and G were realised by the software tool Personal Consultant Plus and the programming language Clipper, respectively. The strategies of conclusion were forward chaining for approximate evaluation of coma stages and backward chaining for analysing the brain death syndrome. BRAINDEX was developed for use with an IBM personal computer or compatible equipment. Systemic analyses were compared retrospectively with the data from clinical brain death protocols (n = 132) of 128 comatose patients (mean age 35.1 +/- 15.8 years) with a Glasgow Coma Score of 3. Identical classifications (system vs physician) were found in all patients without diagnosis of brain death (n = 35). Differences related to the findings of the physician were evaluated in lower numbers of the systemic positive diagnosis of brain death (82 vs 89) and higher numbers of impossibility of systemic evaluation (11 vs 2). These results were obtained by conclusions of the computer system drawn by restrictive systemic mechanisms to avoid false-negative diagnoses. The system therefore seems to be useful for documentation, consultation, and as a teaching instrument and data bank in brain death.

Adult↗
PubMed1992

[Model of electromyographic study of small intestinal transplants in the rat].

Adequate motility of a small bowel transplant is a prerequisite for its resorptive function as well as its self-purging capacity. The literature contains some reports on changes in motility following denervation or transplantation, but none on the impact of acute rejection on motility of small bowel grafts. Therefore an experimental model was established to meet the following criteria: orthotopic position of graft, adequate nutritional status even when graft is functionally impaired, chronically implantable electrodes attached to graft and corresponding segment of native bowel, isogeneic or allogeneic set-up. 10 cm of proximal jejunum were transplanted from Lewis donors to five Lewis recipients in an orthotopic position just distal of the ligament of Treitz without resection of native small bowel. Three bipolar electrodes were sutured to the graft and the same number to the subsequent recipient bowel. Serial myoelectric measurements were taken until the end of week 3. From day 5 on, migratory myoelectric complexes independent of myoelectric activities of native bowel were recorded. Pacemaker frequency of the graft was found to be the same as that of the transsected native small bowel. This early reappearance of myoelectric activities makes this model suitable for comparative studies of small bowel transplant motility and in particular its changes during rejection, since even in strongly allogeneic combinations Lewis small bowel does not show histological signs of rejection before day 6.

Animals↗
PubMed1992

Brain death: timing of apnea testing in primary brain stem lesion.

In a 73-year-old patient complete areflexia of the cerebral and peripheral nerves following the rupture of an aneurysm of the basilar artery was diagnosed. During apnea testing the spectral analysis of electroencephalography (EEG) revealed an irreversible shift of peak from 6 to 3 Hz within the low-frequency bands. These findings suggest that apnea testing in patients with primary lesion of the brain stem should be carried out only after an isoelectric EEG.

Aged↗
PubMed1992

Prediction of the side of hand movements from single-trial multi-channel EEG data using neural networks.

Thirty channels of EEG data were recorded prior to voluntary right or left hand movements. Event-related desynchronization (ERD) was quantified in the 8-10 Hz and 10-12 Hz bands in single-trial data and used as training input for a neural network comprised of a learning vector quantizer (LVQ). After a training period, the network was able to predict the side of hand movement from single-trial EEG data recorded prior to movement onset.

Brain↗
PubMed1992

Event-related synchronization (ERS): an electrophysiological correlate of cortical areas at rest.

Oscillations in the alpha and beta bands can display either an event-related blocking response or an event-related amplitude enhancement. The former is named event-related desynchronization (ERD) and the latter event-related synchronization (ERS). Examples of ERS are localized alpha enhancements in the awake state as well as sigma spindles in sleep and alpha or beta bursts in the comatose state. It was found that alpha band activity can be enhanced over the visual region during a motor task, or during a visual task over the sensorimotor region. This means ERD and ERS can be observed at nearly the same time; both form a spatiotemporal pattern, in which the localization of ERD characterizes cortical areas involved in task-relevant processing, and ERS marks cortical areas at rest or in an idling state.

Adult↗