Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
1999-01-15
2001-09-25
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
C600S559000, C073S585000, C073S587000, C073S589000
Reexamination Certificate
active
06295467
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for detecting a reflex of the human stapedius muscle in particular for a hearing test, by which the reflex is triggered by means of an acoustic test signal having a frequency of, for example 500 Hz or higher, and with a sound level of at least 65 dB HL; and the impedance prior to and the impedance after the reflex on the tympanic membrane is measured by means of at least one acoustic measuring signal with a frequency of, for example about 220 Hz and with a sound level of clearly below 65 dB HL, said measuring signal lasting longer, if need be, and being compared by forming a difference between the corresponding measuring signals or measuring signal ranges.
Furthermore, the invention relates to a device for detecting a reflex of the human stapedius muscle, with a signal transmitter for emitting acoustic signals or sounds, and with a signal receiver, preferably a microphone for carrying out said method.
2. The Prior Art
In stapedius reflex audiometry of the type concerned herein, a reflex or the human stapedius muscle is used, which can be triggered by an acoustic stimulus, whereby sound stimuli exceeding a level of 80 or 90 dB HL (hearing level) are conventionally offered.
The level threshold above which the reflex of the stapedius muscle can be observed is referred to as the acoustic reflex threshold.
The stapedius muscle is the smallest muscle in the human body. It is located in the middle car and connected with the stapes, one of the auditory ossicles. Tensioning of said muscle changes the mechanical properties of the chain of auditory ossicles and thereby also the acoustic impedance on the tympanic membrane. It can be said in a simplified way that the sound reflection properties of the tympanic membrane change depending on the tensioning of the stapedius muscle, which changes not only the intensity and thus also the amplitude of a reflected sound, but also its phase as compared to the phase of the reflected signal when the stapedius muscle is relaxed.
Said described behavior of the stapedius muscle and the impedance variation resulting therefrom are used in stapedius reflex audiometry for the measurement, for example within the framework of a hearing test or other scientific function tests of a human ear.
The following procedure is conventionally employed in this connection: A continuous measuring sound with a frequency of, for example 226 Hz is emitted, such sound having a relatively lower level not sufficient for triggering the muscle reflex, and a short signal is additionally generated and emitted during the duration of the measuring sound in order to trigger the stapedius reflex. Said signal frequently has a sound level far above 80 dB HL and another frequency, for example the audiogram frequencies 500 Hz, 1 KHz, 2 KHz, and 4 KHz. The test signal also may be wide-banded (e.g. noise) and it may be repeated at short intervals.
As soon as the stapedius reflex has been triggered by the signal, the sound curve received by a signal receiver, for example by a microphone—with the auditory canal closed in most cases—changes due to the changed impedance on the tympanic membrane. Measured is in this connection the change in amplitude of the measuring sound reflected on the tympanic membrane.
Said measuring method exhibits little sensitivity because of the very minor variations of the reflected measuring sound, so that a stapedius reflex is not always safely detectable.
However, a method as described above is known from U.S. Pat. No. 3,949,735, by which the differences between the level of the reaction to the measuring sound prior to and after the reflex are more exactly detected by difference formation. However, a rectifier is employed for this purpose, which makes any later effect of phase information impossible.
Furthermore, the level employed for the test sound in the state of the art frequently reaches the range of the discomfort threshold, which is graded by test persons as unpleasant or insufferable. Therefore, the conventional stapedius reflex audiometry method cannot be applied unlimited with some test persons, in particular not with patients who shortly before suffered a sudden drop in hearing ability.
SUMMARY OF THE INVENTION
The invention has the object of rendering the stapedius reflex audiometry method more precise and less stressing for the test person in practical application.
According to the invention this object is achieved in that with omission of any usual measuring signal, use is made of at least two chronologically successive or mutually overlapping acoustic test signals, the latter being as identical as possible with respect to their frequencies and sound levels; and that the information about any possible variation in impedance on the tympanic membrane is obtained by means of forming the difference between the sound curves produced and registered by the test signals.
Other than with the conventional method, no distinction is made between the measuring signal and the test signal. Use is made instead only of test signals which are as identical as possible and presented in a rapid sequence. This may be two short sound pulses of identical frequency, or also two identical segments in a periodic signal (for example a sound or sound complex or a wide-banded noise).
The time sequence of the signals employed exploits the fact that the stapedius reflex requires a certain reaction time for reacting to the first test signal. Therefore, the time space between the test signals is coordinated in such a way that the second test signal is emitted at just the point in time when it can be assumed that the stapedius muscle had adequate reaction time for reacting to the first test signal provided it is capable of such a reaction at all because of the conditions present in the respective ear or the sound level employed.
The signal components recorded by the signal receiver, for example a microphone, are stored in a first analytical step, for example with a digital recording device, and subtracted from each other. Coupling between the sound-emitting device and the sound-recording device must be assured in this connection. The difference of the recorded test signals contains only one noise component in a system equally reacting to the first and the second test signals. When the system is changed, for example by a stapedius reflex that has been triggered by the first test signal, the difference signal is greater than the aforementioned noise.
The advantage with said method as defined by the invention consists, for example in that a distinctly lower level can be employed as compared to conventional stapedius reflex audiometry. This means that a more distinct distance from the discomfort threshold is maintained with the level employed, so that the method as defined by the invention is more pleasant for the test persons and that the number of test persons who can be used is increased as well.
The method as defined by the invention in particular offers the advantage that it is not only possible in this way to register a possible change in amplitude as with the conventional method, but also a shift in phase that is caused by the change in tension of the tympanic membrane as well. Such phase shift effects under certain circumstances a much greater difference signal and thus one that can be registered in a superior way.
Preferably, the time space between the test signals is selected in the order of magnitude of about 100 ms, whereby it is possible also, if need be, to employ several test signals that are chronologically staggered one after the other for detecting the curve of the reflex. Two successive separate, independent measurements should be spaced from each other in terms of time to such an extent that a certain recovery phase is available for the stapedius reflex. The time space should subsequently amount to about at least half a second. On the other hand, it is entirely desirable to carry out several measurements as defined by the invention in order to obtain a more precise measuring result in
Kollmeier Birger
Neumann Joachim
Collard & Roe, PC.
Lateef Marvin M.
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