抄録
The loudness recruitment phenomenon is valuable to differentiate the cochlear deafness from the conductive and retrocochlear lesions. There are many recruitment tests, i.e. balance test, DL test, SISI test, etc., which are performed routinely in many clinics. However, some cases cannot be tested satisfactrily, because these tests require trained subjective judgement of examinee to the complex sound stimuli. From this standpoint, a new objective test for recruitment phenomenon by the evoked response to DL and SISI stimuli has been contrived.
Forty-one cases were tested. Their ages were from 16 to 66 year-old. They were of 20 normal hearing, 3 conductive deafness and 18 perceptive deafness among which 3 retrocochlear deafness were included. Tone stimuli were DL or SISI, the increment of which was 0.2 to 5.0dB at 10dBSL and 30dBSL. The tone frequency was either 1000 or 2000Hz. The increments had a rise-fall time of 50msec and a duration of 1sec in DL or 200msec in SISI. Sixty increments were presented in every test run. The minimal size of DL was determined by the evoked response at the two hearing levels.
There was no difference between DL and SISI stimuli in the threshold of evoked response. The sizes of DL were as follows; 3.8-5.0dB (mean. 4.5dB) at 10dBSL and 1.8-4.0dB (2.8dB) at 30dBSL in normal hearing, 3.8-4.0dB (3.9dB) at 10dBSL and 2.8-3.2dB (2.9dB) at 30dBSL in conductive deafness and 1.0-4.0dB (2.4dB) at 10dBSL and 0.8-2.8dB (1.9dB) at 30dBSL in cochlear deafness. Three cases, suspected the retrocochlear lesions showed nearly the same DL sizes as those of normal hearing. From those observations, the following criteria of the objective test of recruitment were considered: (1); When the size of DL at 10dBSL is smaller than 3.0dB and the difference of the size between the two hearing levels than 0.6dB, recruitment is positive. (2); When the size is between 3.2 to 3.8dB at 10dBSL and is smaller than 1.0dB in the difference, recruitment is questionable. (3); The others are negative. In fact, 85% of cochlear deafness were decided as positive case. Meanwhile, the subjective recruitment tests showed 64% as positive.
According to these results, the newly developed method is considered as usefull for an objective test for the recruitment phenomenon.
