Békésy audiometry
The Békésy audiometry is a measurement method for the hearing in the Otorhinolaryngology . An automatic tone audiometer is used here, in which the test person controls the audiometer himself by pressing a push button and thus records the hearing threshold himself. However, Békésy audiometry was used less for determining hearing thresholds than for the differential diagnosis of sound sensation disorders . Due to the development of other examination methods, Békésy audiometry lost its importance. The automatic audiometer was introduced by Georg von Békésy in 1947 .
Investigation process
Georg von Békésy: “An audiometer is described in which the intensity of the tone increases continuously as long as a signal button is held down, and automatically drops again when the button is released. The person who operates the button can therefore let the intensity of the tone fluctuate between just above the hearing threshold and just below it. The amplitude of these oscillations is a measure of the intensity difference threshold, which is automatically recorded together with the hearing threshold. "
The device changes the frequency of the test tone continuously within 5 minutes from 125 Hz to 8000 Hz (originally from 100 Hz to 10,000 Hz) and the intensity by 2.5 dB per second (5 dB per second in the "fast" position). The result of the test is a zigzag line recorded by the device that corresponds to the hearing threshold.
If, in the Hörschwellenprüfung with the Békésy audiometer instead of a continuous tone a pulse tone (interrupted tone), so resulting in sensorineural hearing impaired to some extent better hearing thresholds than when using continuous tones. In such cases one speaks of a separation of the continuous tone curve from the impulse tone curve. This phenomenon must be viewed as an expression of a disturbed adaptation ( adaptation ) of the inner ear to the continuous tone. The position of the continuous tone curve in comparison to the pulse tone curve provides information about the functional disorder of the ear; the pulse tone curve serves as an independent comparison value, so to speak. Instead of the frequency- sliding method with continuous change in the test frequency , it was therefore advisable to examine the behavior of the continuous tone curve compared to the impulse tone curve in a single frequency over time ( constant frequency method ).
Examination result
The possibility of determining the hearing threshold with the Békésy audiometer took a back seat with regard to the differential diagnostic value of the assessment of the spike size and, above all, the separation.
During audiometry with the Békésy audiometer, the normal hearing person creates a jagged line with a height of 10 to 15 dB. Significantly smaller spikes are an indication of the presence of a disturbed loudness sensation ( recruitment ). This is considered evidence of cochlear hearing loss (hair cell damage).
The separation of the continuous tone curve from the impulse tone curve can reach very different dimensions. It can be maintained to a certain extent (limited separation) or it can become larger and larger (unlimited separation). The constant-frequency method is better suited to assessing the separation than the frequency-sliding method. The assessment is mostly based on the types proposed by Jerger (1960).
- Type I: Impulse tone curve and continuous tone curve overlap. This finding can be found in people with normal hearing, conductive hearing loss and occasionally in sensorial hearing loss of an unclear cause.
- Type II: The continuous tone curve separates from the pulse tone curve up to a maximum of 20 dB and then maintains this distance (limited separation). This picture can be found in cochlear hearing loss (hair cell damage).
- Type III: The continuous tone curve falls dramatically further and further below the impulse tone curve. The separation is 40 to 50 dB or more (unlimited separation). This finding suggests a retrocochlear hearing impairment (nerve hearing loss).
- Type IV: Limited separation, but stronger than type II. Uncertain classification, cochlear or retrocochlear hearing loss.
During simulation and aggravation , the test person writes the continuous tone curve over the impulse tone curve (i.e. at a lower volume), a finding that is otherwise not possible.
swell
- ^ Georg von Békésy: A New Audiometer . In: Acta Oto-laryngologica . tape 35 , 1947, ISSN 0001-6489 , pp. 411-422 , doi : 10.3109 / 00016484709123756 .
- ↑ Bruno Welleschik : Experience with Békésy audiometry . In: Laryngology, Rhinology, Otology . tape 55 , 1976, ISSN 0340-1588 , pp. 343 .
- ^ JF Jerger: Recruitment and allied phenomena in differential diagnosis . In: Proc. Soc. Int. Audiol. tape 5 , 1960, pp. 197 .