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Biomedical subjects

H Hinrichs

Publications and source records attributed to H Hinrichs.

15 recordsLinked to original sources
PubMed1992

Hemodynamic and electrophysiological evaluation following extracranial/intracranial bypass surgery.

We examined 50 patients with an extracranial/intracranial bypass using transcranial Doppler blood flow mapping, somatosensory evoked potentials, and computer-assisted EEG analysis. The investigation was supplemented by temporary compression of the extracranial supplying vessel. Transcranial Doppler sonography revealed in addition to 4 patients with nonpatent anastomoses, a bypass-mediated retrograde flow in the ipsilateral middle cerebral artery beyond a depth of 40 mm in the majority of patients. In 9 patients, retrograde flow could be demonstrated in the whole proximal (M1) MCA segment. The precommunicating segment of the anterior cerebral artery (A1) could be reliably insonated in all but 5 patients. Bypass-compression dependent alterations in the SSEP and in EEG analysis were only observed in a small number of patients. Transcranial Doppler sonography, with the aid of the flow mapping system, appears therefore, to be a reliable and repeatedly performable noninvasive technique for the assessment of intracranial hemodynamics following bypass surgery.

Adult↗
PubMed1992

Basic emotions reflected in EEG-coherences.

The differentiation of basic emotions by means of EEG power spectra has been discussed extensively by Machleidt et al. (1989). The present contribution concentrates on the interhemispheric coupling of different EEG-signals as depending on the modulation of these emotions. In the first part the estimation and interpretation of squared coherence spectra is outlined. Results from this technique are presented in the following section. Intention, Aggression and Joy are mainly characterized by an increase of alpha-coherence, whereas a decrease is seen for Anxiety and Sorrow. These effects showed a widespread distribution.

Adult↗
PubMed1992

[Computer-assisted analysis of the electromyogram for routine clinical use].

A computerized EMG analysis system implemented on an MS-DOS computer was developed explicitly for clinical routine usage. It incorporates analysis of interference pattern as well as of motor unit action potentials (MUAPs). Key features of MUAP analysis are the automatic segmentation and parameterization of the EMG signal and the automatic assignment of MUAPs to motor units. Determination of muscle activity is based on threshold detection of the signal's first derivative, leading to the definition of a MUAPs central component. Its parameters (length, amplitude, maximal steepness, area between curve and base-line, area between first derivative and base-line, number of turns etc.) are used when comparing MUAPs. The automatic assignment of MUAPs to motor units was implemented as an iterative procedure. MUAPs are compared to a reference MUAP and eventually assigned to it if their parameters are sufficiently similar. For such a group of MUAPs the most representative MUAP is determined which is then used as new reference MUAP in the next iteration step. Most important for clinical routine usage are simple handling, speed and the clearly arranged presentation of results. The system allows for interactive modification of MUAP assignment as well as start and end points of every MUAP. Analysis results may be displayed on the screen and printed, giving the user a quick impression of the muscle under study. Thus this method meets basic requirements for computer assisted decision making in differential diagnosis.

Action Potentials↗
PubMed1992

[Automatic (computer-assisted) EEG analysis in comparison with visual EEG analysis in patients following minor cranio-cerebral trauma (a follow-up study)].

The study was designed to examine the clinical applicability and use of computer-assisted EEG-analysis in comparison to visual EEG-analysis in patients with minor head injuries. For this in 31 patients the following examinations were performed within the first 24 hours, one, three and eight weeks after traumatization: EEG, neurological examination and standardized evaluation of subjective complaints. The EEG was analysed visually as well as computer-assisted. The results were compared to the neurological findings and subjective complaints. Reversible posttraumatic EEG-changes were observed in 50% of all patients. The results of computer-analysis and visual analysis were equivalent in respect to baseline-activity (as one of the main characteristic EEG-features). Furthermore, based on computer-assisted analysis a discriminant function is provided, which is of diagnostic and prognostic value in the single patient. We conclude that the computer-assisted EEG-analysis can be a useful alternative in EEG-routine diagnosis after minor head injuries.

Adolescent↗
PubMed1992

[Neurophysiologic monitoring in neurosurgical vascular operations: specific technical requirements and their conversion].

Several authors have presented evidence for a strict relation between regional cerebral blood flow and EEG. Therefore the EEG can serve as an adequate physiological parameter when monitoring cerebral function in the operating room. However, to exploit the inherent information as far as possible, both multichannel EEG and somatosensory evoked potentials should be recorded simultaneously. In the present article we describe a monitoring system which is capable to handle this task under the conditions of an operating room. In the first step some numerically simple algorithms are applied to detect gross artifacts. In the subsequent processing stage an analysis procedure is performed which is robust with respect to the remaining more subtile artifacts. In addition the raw signals are continually displayed on a monitor to allow for a visual evaluation of the EEG. The results of a trend analysis procedure are presented on the same graphical display by means of a compact topographical scheme. The system has been running under routine conditions for approximately two years now.

Artifacts↗
PubMed1991

EEG data compression with source coding techniques.

A data compression algorithm for the EEG, derived from the adaptive pulse code modulation scheme, is described where the consecutively computed differences are coded by passing them through a quantizer possessing only a few levels; the range of these levels is adapted to local signal statistics. Three different versions of the algorithm with data reduction up to 75% are presented. The system was validated using several multichannel-routine EEG recordings with both visual evaluation and computation of signal-to-noise ratios.

Algorithms↗
PubMed1990

Neurophysiological assessment of early hepatic encephalopathy.

The spontaneous EEG, pattern reversal VEPs, and the P300 wave were studied in patients with liver cirrhosis and early stages of hepatic encephalopathy (HE). The sensitivities of the different neurophysiological methods in the early stages of hepatic encephalopathy were compared with each other and with several neuropsychological tests. P300 latency was shown to be the most appropriate neurophysiological method for detection of early HE. The diagnostic sensitivity of the P300 latency resembled that of the number connection test (NCT). These results are discussed with regard to methodological considerations and the clinical use of both methods.

Adult↗
PubMed1987

EEG data acquisition.

This paper is a compressed version of a tutorial which was presented during the 1986 training course of the International Pharmaco-EEG Group, in Santa Margherita Ligure, Italy. The paper starts with a discussion of some basic features of the encephalograph, sketches the frequency modulation recording technique and presents some fundamental rules and concepts concerning digital data acquisition. Patient safety is a further aspect of the tutorial. Finally, two calibration procedures are outlined.

Analog-Digital Conversion↗