TEST FOR PRESSURE CONTROL CAPACITY OF THE EUSTACHIAN-TUBE

Because the Eustachian tube controls middle ear pressure to maintain t he best hearing level, we tested the equilibration capacity of the Eus tachian tube by measuring hearing levels in a soundproof pressure cham ber. The number of swallows to recover normal hearing after the chambe r pressure reached -200 mm H2O (an index of equilibration capacity for the static pressure differences across the eardrum) was less than 9 i n normal subjects. The worst level of hearing and the time required to recover normal hearing from the beginning of alteration in the chambe r pressure to -700 mm H2O (indexes of equilibration capacity for dynam ic pressure differences across the eardrum) were 0-17 dB and within 12 0 a in normal subjects. It was difficult to determine definitive norma l ranges of the equilibrium capacity of the Eustachian tube when posit ive pressure was applied.