Evaluation of Eustachian tube function by sonotubometry:: results and reliability of 8 kHz signals in normal subjects

Sonotubometry allows an assessment of the Eustachian tube (ET) function under physiological conditions. The reliability of the application of an 8 kHz pure-tone signal was investigated. In 40 normal subjects (80 ears) sonotubometric studies were performed with a custom-made device. ET opening was provoked by swallowing, yawning and Valsalva manoeuvre. An opening was detected in all patients but not in all manoeuvres. Four characteristic sonotubogram types were found. Most common was the spike-type (60%). The double-peak and the plateau-shaped curves occured in 17% each. The finding of an descendant curve was rare (5%). Of 623 measurements, only in 55% manouvres a positive sonotubometric result was found despite the fact that the patients reported an opening in all cases. The median opening time in dry swallowing, liquid swallowing, yawning and Valsalva was found to be 486, 355, 1,263 and 1,250 ms. A median sound increase of 16.0, 13.8, 15.0 and 15.0 dB was recorded for these manoeuvres. There was a statistic significant difference (P < 0.02) between the increase in sound intensity of liquid and dry swallowing. There was also a statistic significant difference found for the duration of the forced manoeuvres Valsalva and yawning as compared to dry and liquid swallowing (P < 0.0001). The use of an 8 kHz pure-tone signal showed a limited sensitivity for the detection of ET openings. This is mainly due to noise pollution, but also because of an altered positioning and/or dislocation of the probes and compression of the nostrils. The application of an 8 kHz signal is therefore not reliable enough for the use in practice. Further technical refinements and the use of alternative signals are necessary for a broader clinical application.