Abstract
286 persons with an equal representation of both sexes in the ages 10 to 80 years were submitted to impedance audiometry. The series was strictly selected so that only persons with normal eardrums, normal conventional audiograms, and no exogenous or endogenous factors that might cause impairment of hearing were accepted. Tympanometric curves were normal (type A). The absolute eardrum compliance values were measured and the stapedial reflex thresholds were determined at the frequencies 500, 1000, 2000 and 4000 Hz.
The absolute compliance in the individual person exhibited very small right-left difference, there was no dependency on sex or age but the standard deviations were very large. For the reflex thresholds too there were no significant right-left differences or dependency on sex. In the young (10–12 year old) group the reflex thresholds were significantly poorer for all frequencies than in the rest of the series. Thus thresholds in the magnitude of 100–110 dB HL were not rare in this particular group. Against this background it can be argued that high stapedial reflex thresholds occur as a physiological phenomenon in children.
Reflex thresholds for the frequencies 500, 1000 and 2000 Hz do not differ significantly from each other in different age and sex groups. This is in contrast to the findings for 4000 Hz, where the thresholds are poorer which might be a contributing factor for the well known vulnerability of hearing towards noise at this frequency.
Stapedial thresholds expressed in dB SL decrease systematically at a rate of 3,5 dB/age decade, while the reflexes when measured against a HL reference remain the same. There is nothing in this series that indicates the presence of progressive mechanical middle-ear disturbances as part of the aging process.