Surgery – Diagnostic testing – Ear or testing by auditory stimulus
Patent
1998-06-26
2000-06-06
Hindenburg, Max
Surgery
Diagnostic testing
Ear or testing by auditory stimulus
A61B 512
Patent
active
060712465
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to the field of the objective, i.e. independent of the patient's participation, determination of the hearing acuity using acoustically evoked potentials (AEPs) or otoacoustic emissions (OAEs).
BACKGROUND OF THE INVENTION
Processes developed for the application of AEPs are used particularly with newborns and infants for whom the usual subjective audiometry (sounds of different frequencies are applied through headphones--the patient is to indicate whether he/she hears the applied sound) is not suitable. In this case the auditory brainstem responses (ABRs) are preferably used.
Generated by a single acoustic stimulus an ABR has a very small amplitude. It cannot be detected in the spontaneous EEG on the usual lead from the scalp through electrodes as the signal-to-noise ratio is very bad. In order to enhance the signal-to-noise ratio the so-called averaging method is employed. In this method a large number of stimuli is applied in a short period of time and the post-stimulus segments of the spontaneous EEG (sweeps) are summed (averaged).
Provided the interfering spontaneous EEG has a random character its proportion in the result of the averaging becomes smaller and smaller with progressing summing.
Averaging must be continued until an AEP is present that can be evaluated reliably. The decision whether a response potential is present or not, is made by the examining person. The ostensibly objective audiometry is thus only objective concerning the recording of the data, but the evaluation is of a subjective nature.
This is the main problem of the objective determination of the hearing threshold by AEPs: On approaching to the hearing threshold the AEPs are becoming continuously smaller, the signal-to-noise ratio is hence becoming worse and worse. As a consequence, the evaluation is becoming problematic. Making the evaluation still more difficult is the fact that the spontaneous EEG, as a rule, is not an ideal stochastic process as it has been taken for granted. For that reason, the averaging result of the near-to-threshold AEP is superimposed by a substantial residual noise. The evaluation requires therefore a great deal of experience. Often all experience is no help because a random waviness in the AEP time range cannot be differed in the averaging result from an actual AEP or a low-amplitude response is completely covered by residual noise.
An effective support in decision-making can only be expected from suitable statistical methods that are not applied to the averaging result but to the sample of sweeps. The statistical method may be applied either to the time functions of the sweeps or to binomial features derived from the time functions or, after a spectral transformation having been made, to the spectra of the sweeps.
The development of a suitable process using a statistical (automatic) AEP detection makes the "objective audiometry" into a really completely objective determination of the hearing threshold.
A number of authors have published on that approach but the problem has not yet been solved satisfactorily.
The only practical result known so far is the U.S. Pat. No. 4,275,744 by Thornton and Obenour and the device ALGO-1 Plus from the company NATUS, which operates according to this method.
The method described in that patent relates to the middle latency responses (MLRs) whereas the ALGO-1 Plus device employs the ABRs that are more suitable for the hearing test of babies both methods using, in principle, the same process: The basis is a model ABR, the so-called template, as it is expected of normally hearing infants as the average response to the acoustic click stimulus used. The template is here the average of the ABRs of 35 normally hearing babies to a stimulus of 35 dB HL. Based on this template 9 data points were determined which are particularly stable. Only the sweep values at these points are then evaluated with different weights using a binomial statistics. At the selected times the template is positive or negative respectively after the stimulat
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Kopp et al. "Messplatz zur Ableitung akustisch evozierter Hirnstammopotentiale mit dem Elektroenzephalograph BST 1", Medizintechnik, Mar. 27, 1987, International Search Report from corresponding PCT Application No. PCT/DE96/02453.
Baag Matthias
Cebulla Mario
Sturzebecher Ekkehard
Thie Rainer
Hindenburg Max
Pilot Blankenfelde Medizinisch-Electronische Gerate GmbH
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