Observing the hearing disturbance from the tympanic membrane retraction and the state of the Eustachian tube catheterisation. The A type considered as normal hearing curve showed good insufflating condition and most cases did not showed the tympanic membrane retraction. The bad hearing curve, often observed as the employed years increased, showed the worse insufflating state in the group of 11-20 years employment and it was worse in the group of more than 21 years employmemt.
It is to be noted, however, the D type of more than 21 years employment showed bad insufflating state and the cases of not having tympanic membrane retraction increased compared with the group of 11-20 years. Generally speaking, the increased years of employment brought the state of bad insufflation and increased the tympanic memsbrane retraction.
