Objective: To investigate the relationship between the morphological patency of the eustachian tube (ET) and sound transmission via the ET.
Study design: Retrospective chart review and model experiment.
Setting: Tertiary referral center.
Subjects: A total of 56 ears of 28 patients (9 men and 19 women, aged from 12 to 82 yr, mean 40.4 ± 21.5 yr) who underwent sonotubometric measurement using postural change as well as computed tomography (CT) of the ET in the sitting position, including 26 ears with definite patulous ET, 9 ears with possible patulous ET, and 21 ears without patulous ET.
Method: Commercial equipment for sonotubometry (JK-05A; RION Co., Ltd., Kokubunji, Tokyo, Japan) was used in the following two investigations. Retrospective survey: sound patency of 7 kHz band noise via the ET was assessed by comparison of acoustic transfer function via the ET in the sitting and forward-bending positions. Sound patency via the ET was compared with morphological patency of the ET (cross-sectional area in the narrowest portion) assessed by three-dimensional CT of the ET in the sitting position. Model experiment: effect of the ET caliber on the acoustic transfer function was examined using a simple model constructed with two truncated syringes with silicone barrels and a narrow connecting tube.
Results: Sound patency assessed by sonotubometry was well correlated with the cross-sectional area at the narrowest portion of the ET in the sitting position (r = 0.786, p < 0.001). Correlation between the sound patency via the narrow tube and the caliber of the tube was also confirmed by the model experiment.
Conclusions: Sound patency assessed by sonotubometry using 7 kHz band noise could be useful to predict the morphological severity of patulous ET.