In this paper the following items were studied and discussed.
1. Mechanism of Stapedius Reflex (SR) decay.
It has been claimed that SR decay could not be attributed only to the stapedius muscle fatigue.
In this experiment, second stimuli of lower tone were added to an ipsilateral ear and SR of the contralateral ear was recorded in the adult cat, while SR decay was observed by continuous 4kHz stimuli. The response magnitude of obtained SR induced by second tone stimuli was dependent on the difference of the frequency of second stimulus tone, in that second stimuli of lower tone (eg. 1kHz) elicited bigger SR magnitude than higher tone (eg. 2kHz).
From the above results, it was concluded that SR decay was not only caused by the stapedius muscle fatigue, but also by the acoustic fatigue.
2. Influence of anestheticus on the SR decay.
The magnitude of SR induced by 1kHz pure tone stimuli was compared among slightly anesthetized and well-anesthetized cats with pentobarbital-Na by intra-peritoneal administrationand the cat anesthetized with Ketalar which has only slight influence on the brain stem. The following results were obtained.
In the well-anesthetized cat marked SR decay was recorded by continuous 1kHz pure tone stimuli, while in the slightly anesthetized cat and the cat anesthetized by intra-muscular administration of Ketalar no change in the magnitude of SR was observed. From these results it was concluded that the shift of acoustic threshold in well-anesthetized cat was due to SR decay.
3. SR test for the evaluation of prognosis of peripheral facial nerve palsy.
In 107 cases of Bell's palsy, 86 cases showed almost complete recovery of facial movement in which SR was first recorded within 40 days from the onset, while 21 cases showed incomplete recovery whose SR was first recorded after 40 days. In the cases with Ramsay Hunt syndrome the relation was the same as was observed in Bell's palsy.
From this fact it was concluded that SR test was useful for the evaluation of prognosis of peripheral facial nerve palsy.
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