Biomedical subjects
Publications and source records attributed to G Pfurtscheller.
Simultaneous continuous recording and processing of evoked potentials, various cardiovascular, and respiratory signals was realized with the aid of a PC-controlled monitoring system. The system is at present used for monitoring patients in intensive care units, during neurosurgical interventions and for sleep investigations in infants.
The influence of planning of self-paced voluntary finger movements on alpha band components was studied in 6 volunteers. Brain potentials from 29 electrodes, referred to the right ear, were recorded 4 sec before and 2 sec after movement onset. These data were transformed to obtain the laplacian operator, which was done by computing the local average reference. The event-related desynchronization (ERD) of upper alpha components was then calculated in each record at intervals of 250 msec and topographically displayed in the form of serial ERD maps. A first significant ERD (P less than 0.01, sign test) was found 1.75 sec +/- 0.61 before the movement, most prominent over the contralateral sensorimotor area and over midfrontal areas (the latter can probably be interpreted as an activation of the supplementary motor area). From these data we can conclude that the side of movement is predetermined more than 1 sec before movement onset.
Event-related desynchronization (ERD) of alpha components was studied in four subjects during self-paced voluntary movements and somatosensory stimulation. EEG was recorded from 29 electrodes with a common right ear reference; local average reference derivations were calculated and used for computing ERD maps at 250-ms intervals. It was found that upper alpha components were desynchronized close to electrodes C3 and C4 overlying the primary sensorimotor cortex during voluntary movements and somatosensory stimulation. ERD started contralaterally more than 2 s before the movement and some hundreds of milliseconds before the stimulation. During the performance of unilateral movement and unilateral stimulation, ERD was bilaterally symmetric. Desynchronization of lower alpha components was found over the superior parietal cortex, clearly starting some hundreds of milliseconds after the desynchronization of upper frequency components. Therefore, the desynchronization of lower and upper alpha components reflects activation of different neuronal structures.
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Event-related desynchronization (ERD) is a term describing alpha band amplitude changes in response to an event (stimulus presentation, self-paced movement, etc.). ERD mapping is a brain-imaging technique used to display the topographical pattern and time course of alpha power changes. Multi-lead EEG data referred to one ear were recorded during voluntary finger movements. From these data, transverse bipolar, source and common average reference derivations and the laplacian operator were calculated, and ERD maps are computed. The ERD is enhanced and best localized with the laplacian operator method, or with source derivations. ERD maps with ear reference required cautious interpretation.
The hemispheric asymmetry model of lateral eye movements (LEM), hypothesizing a relation between a predominance of lateral gazes to one side with a predominance of activity in the hemisphere contralateral to the preferred direction of gaze, was tested in male, right-handed subjects. During presentation of cognitive tasks (verbal synonym tasks and spatial orienting tasks) the decrease in alpha-power from a reference period to each of four activation periods (anticipation, task-presentation, first LEM, answer) for 6 derivations from each hemisphere was calculated using the method of 'Event-related desynchronisation'. Evidence for the hypothesis was found only during the EEG-epoch one second before the answer. Discrimination between subjects with a predominance of left vs right eye movements (left- vs right-movers) was best at temporal (T3, T4) and central (C3, C4) sites. These results were significant for the entire alpha-band (8-12 Hz) and--even more pronounced--for the alpha-2-band (10-12 Hz). The alpha-1-band (8-10 Hz) did not produce significant differences. Comparing the two types of tasks, synonym tasks yielded results which were more congruent with the hypothesis. The results suggest that lateral eye movements indicate individual differences in hemispheric EEG-asymmetries under certain experimental conditions (task, segment of EEG-analysis, site, frequency band).
Ten measurements of intracranial pressure (ICP) (ventricular n = 5, epidural n = 3) in 8 patients (3 after aneurysm surgery, 5 with head trauma) were performed before and after application of conventional headphones for stimulating brainstem auditory evoked potentials (BAEP). The effects of miniature earphones and sound tubes on ICP were also studied. In 7 of 10 measurements after application of headphones a reversible increase of ICP (mean 26 +/- 19% in patients with ICP greater than 10 mmHg was recorded; in 3 patients (ICP less than or equal to 10 mgHg) no changes of ICP were seen. Using miniature earphones and sound tubes no increase of ICP was noted in any patient, and hence these can be recommended for stimulating BAEP in case of increased ICP.
In a series of 13 patients with cerebrovascular occlusive disease regional cerebral blood flow (rCBF) measurements (two-dimensional intravenous 133Xe clearance method) and quantitative EEG analysis (sensorimotor rhythms) as well as electronic measurement of handforce were performed before and during intravenous infusion of 1 microgram kg/min of one of the lipophilic dihydropyridine calcium channel blocker nimodipine (Nimotop). The aim of the study was to test the hypothesis of the existence of hypoperfusion (ischaemic penumbra) in the surroundings of chronic cerebral infarcts. All 3 parameters improved in one patient. Sensorimotor rhythms increased in 5 patients, rCBF in 3. EEG and rCBF improved in 2 patients. In 3 instances, a redistribution of rCBF in favour of the peri-infarct zone was noted (significant increase of rCBF from 35 +/- 2 SEM to 53 +/- 4 ml/100 g/min (p less than 0.01), whereas rCBF fell from 61 +/- 5 to 46 +/- 2 ml/100 g/min on a collimator remote from the infarct but in the infarcted hemisphere. The parallel improvement of rCBF and EEG in brain regions surrounding chronic infarcts in 3 patients was interpreted as functional improvement as a consequence of nimodipine-induced normalization of peri-infarct hypoperfusion, i.e. reversal of flow-dependent neuronal silence and/or dysfunction.
Visual evoked potentials (VEPs) were examined as an integrated parameter in a multimodal EP study of brain bioelectrical activity in 33 comatose patients (Glasgow Coma Score 3-6) after craniocerebral trauma. Recordings were performed not only from the occipital (01-02) but also from the central (Cz-C3, Cz-A1, Cz-C4) and frontal (F3-F4) areas. The results show an attenuation of the vertex VEP (SNR 3.2 +/- 1.7) and an increase in the occipital VEP (SNR 4.8 +/- 2.3) as compared to the control group (SNR vertex 7.0 +/- 3.0/SNR occipital 3.9 +/- 2.0). In addition, 16 of the comatose patients showed a very considerable loss of the normally polyphasic character of the occipital VEP in favour of a potential that looked almost monophasic; this was either left or right dominant, and was recorded as a negative or positive potential, respectively, in bipolar recording (01-02). Comparison of the electrophysiological and computer tomography findings showed a laterally correlated change in the occipital VEP: contralateral to the injured hemisphere, the VEP was dominant, ipsilateral it was reduced or extinguished.
Individual monitoring of EEG and evoked potentials is gradually becoming standard in neurosurgery: compressed power spectra during carotid endarterectomy, brainstem auditory evoked potentials (BAEP) during posterior fossa surgery, and somatosensory evoked potentials (SEP) mainly during spinal cord surgery. In this paper, a new technique is described in which EEG, BAEP, and SEP are recorded and evaluated simultaneously and continuously. This allows a better survey of different neuronal structures and systems in the brain and brainstem. First results from intraoperative and intensive care patient monitoring are reported.
Multimodal EPs and heart rate variability-measurements in comatose patients have been performed for few years at the university hospitals of Graz and Erlangen. The following data and parameters are analysed and discussed: brainstem auditory evoked potentials, mechanical evoked long-latency SEP, VEP recorded over the central and occipital region and heart rate variability (HRV). The method of data acquisition and processing is described and normative data are introduced. For the long-latency EP-components a signal-to-noise-ratio (SNR) is calculated. SNR is defined as ratio of the largest EP peak-to-peak amplitude and the mean amplitude (standard deviation) of a period prior to the stimulation. An unmeasurable or questionable EP is defined when SNR less than 2.6. For the vertex-SEP the following mean +/- standard deviation was obtained: SNR = 10.6 +/- 4.6; the vertex VEP was calculated with SNR = 7.0 +/- 3.0. The SNR of the bipolar recorded occipitally VEP was 3.9 +/- 2.0. Heart rate variability measurements in normal persons revealed the following mean +/- standard deviation at a heart rate of 67.8/min +/- 10.8/min: HRV = 7.8% +/- 2.5%.
Ninety patients were subjected to brain-stem auditory evoked potential (BAEP) measurements in the intensive care unit. The data are analyzed and discussed with respect to their quality, reliability, and reproducibility. BAEPs of a quality satisfactory for diagnosis were found in 90% of the patients. About 10% of the measurements were distorted by artifacts and could not be used for diagnostic purposes. Reasons for these artifacts and problems of interpretation are discussed. Examples of single BAEPs and on-line monitoring of BAEPs in the form of "compressed BAEPs" are shown.
Twenty patients with severe head injury and a Glasgow Coma Scale of 4-6 were subjects of a multimodality EP study. After EEG recording during rest (control 1) 60 mechanical vibration stimuli and 60 visual stimuli (interstimulus interval 10 sec) were applied. Thereafter a second EEG (control 2) was measured. To quantify a long-lasting stimulated EEG alteration, control 2 was compared with control 1 on the basis of the spectral theta/beta ratio calculated from central derivations. In 50% of the patients the theta/beta ratio was changed in control 2 and therefore a long lasting stimulation effect can be assumed. Stimulus-induced cardiac alterations were also found.
Twenty-four infants aged between 6 days and 7 months and 2 infants (16 m and 3 y) were subjects of combined brain-stem auditory evoked potential and heart rate variability measurements. Ten infants had a sleep apnea syndrome and one a Near miss sudden infant death syndrome; thirteen infants formed the control group. Seventeen of the twenty-six infants had normal, age-depended brain stem potentials. All infants of the apnea syndrome-group, which had no therapy, had increased I to V interpeak latencies outside of the one-sigma level, the six infants treated with aminophylline were within the normal range. Heart rate variability measurements revealed the following mean +/- standard deviation of the control group: 4.5% +/- 1.5%; of the apnea syndrome-group without therapy: 5.4% +/- 2.0%.
The spatial pattern and time course of cortical activation can be studied when the event-related desynchronization in 30 EEG recordings is being quantified, averaged over about 60 events and displayed in form of maps with integration times of 125 ms (8 maps/s). This method was named dynamic mapping and used for investigating cortical activation pattern during the following tasks: Planning and execution of voluntary self-paced thumb movements, tactile stimulation of the foot sole and recognition of words, displayed shortly on a computer terminal. All these experiments resulted in localized activation pattern.
BAEP can be recorded under anesthesiologic intensive care conditions. The method does not depend on the patient's state of consciousness and is noninvasive. Observations of the course and topodiagnosis are also possible, as is an assessment of the depth of coma. The sensitivity to centrally active drugs and metabolic influences is comparatively low. For recording and evaluation of signals the specific conditions in an intensive care unit have to be taken into account, with regard to both the patients as well as the technical equipment. Continuous monitoring with so-called "compressed" BAEP broadens the scope of acute diagnosis of brain stem lesions.
The effect of mechanical vibration and light stimulation on the ongoing and evoked bioelectrical activity was studied in two cases with clinically defined brain death and two other patients with severe head injury, one of them with an isoelectric EEG. The importance of such stimulation sequences for the definition of brain death is discussed, with particular emphasis on mechanical vibration.
Follow-up measurements of long-latency visual (VEP) and somatosensory (SEP) evoked potentials were performed on 30 comatose patients. Twenty-seven of the patients had severe head injury, 2 had encephalitis and 1 was in a posthypoxic state. For the SEP study a mechanical vibration stimulus was used, applied 60 times at intervals of 10 sec. The same rate was used for visual stimulation. The late EP components were classified by a signal-to-noise ratio (SNR), whereby an SNR of less than 2.6 is characteristic of a questionable or unmeasurable EP and an SNR greater than 2.6 is evidence of a clearly existing EP; the clinical state was scored using the Glasgow Coma Scale (GCS); the patient outcome was assessed 6 months after the injury using the Glasgow Outcome Scale. The highest correlation (r = 0.72) was found between the clinical state, represented by the GCS, and the SEP. A similar correlation (r = 0.66) was obtained between the GCS and the vertex VEP. The occipital VEP showed no correlation. Emergence from coma and recovery was accompanied by an increase of the SEP and an increasing spread of the VEP over the whole scalp. Most patients with a clear long-latency SEP in coma had a favourable outcome; a missing or a questionable SEP indicated a poor outcome.