Studies on the Function of the Eustachian Tube in A Series of Normal Individuals

Abstract

The method used in the present investigation has been previously described in detail in earlier papers by the writer (1955 a, 1955 b). In the following, only its fundamental features will therefore be mentioned. With regard to the impedance measurement and its relation to the middle ear pressure, only the following may be mentioned here: the acoustic impedance is the “resistance” of the tympanic membrane and the sound-conducting apparatus to a sound which reaches the ear. It is definitely determined by a calculation of the phase and the absorption from the readings taken from the calibrated acoustic measuring bridge introduced into clinical examination by Metz (1946). In the present study, however, only the absorption was calculated. A difference in pressures between auditory canal and middle ear will cause a fall in the absorption (a rise in the impedance).

A series based upon examination of 100 normal persons and dealt with statistically is reported.

The series was examined especially with a view to the following:

The threshold pressure, i.e. the lowest overpressure which it is necessary to apply in the rhinopharynx for the tube to open during deglutition, thus generally causing a rise in pressure in the middle ear and thereby a change in the acoustic impedance of the ear. Passage was obtained in 54 per cent of the cases with the lowest overpressure used, i.e. 3 cm of water. 83 per cent of the persons examined had threshold pressures of 10 cm of water or less. The highest pressure that had to be applied was 40 cm of water. It is shown that the threshold pressures measured must be supposed to represent the maximal negative pressure which may have been present in advance in the ear.

The pressure/absorption curve, i.e. the ratio between the overpressure established in the rhinopharynx and the absorption (one of the components of the acoustic impedance); the subject was asked to swallow at rising overpressure in the rhinopharynx after the threshold pressure had been reached. Four types of curve are stablished. It appears that in about half the cases the configuration of the curve was characterized by the fact that the tube was unable to keep back an overpressure in the middle ear which exceeded 15-30 cm of water.

The capacity of the tube to reduce by deglutition the overpressure produced in the middle ear. In 73 per cent of the cases the tube was able to equalize the overpressure completely. In 19 per cent, reduction only was obtained. In 8 per cent the overpressure in the middle ear remained unchanged in spite of repeated deglutitory movements. Complete equalization required from 1 to 3 deglutitory movements, the first resulting in the greatest reduction in pressure. A comparison between the results of the reduction experiments and the threshold pressure determinations showed that the threshold pressure was lowest in most cases at the tubes which could equalize the overpressure in the middle ear completely, and highest in the cases where no reduction took place.