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

Abstract

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 occurred 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.

Eustachian tube opening measured by sonotubometry is poorer in adults with a history of past middle ear disease

“…While the principal underlying the test methodology for sonotubometry is firmly grounded in theory 17 , in vivo mechanisms for the production of ear-canal sound envelopes during swallowing that may be similar to those predicted for an ET opening when a true opening does not occur have been suggested 17,22,24,27 . For example, some researchers have argued that variations in the nasopharyngeal “noise” level caused by the act of swallowing could be transmitted to the ear-canal by bone conduction and recommended the use of test sounds at frequencies higher than those typical for swallowing sounds 16,18,19,22 . However, this mechanism for the production of “false positive” test results presumes that the amplitude and duration of a bone-conducted swallowing sound signal are of similar magnitude and duration at the ear-canal as an ET conducted sound signal which is unlikely and unproven.…”

“…Usually, the envelope of the sound signal during a swallow is analyzed and the results are expressed as a dichotomous, yes/no assignment of ET opening based on a pre-defined threshold change in a signal amplitude and/or width, but no study has established the parameter(s) and their cutoffs that yield the highest specificity and sensitivity for assigning a tubal opening 20,25 . Alternatively, a few studies treated parametric measures of the shape of the sound envelope recorded during swallowing as continuous variables that capture quantitative information on ET opening efficiency 22-24,26 .…”

Reliability of Eustachian tube function measurements in a hypobaric and hyperbaric pressure chamber

“…could show a clearly lower ICC between 0.49 and 0.51 in 215 healthy participants compared with this study. A previously presented study by Di Martino et al . examined the reliability of sonotubometry concerning the evaluation of ET function.…”

A method to assess the accuracy of sonotubometry for detecting Eustachian tube openings

“…Suggestions to reduce the impact of these effects on test accuracy include: introducing large volume source speakers as components of the test system [16,26]; repeat testing while alternating nasal sides for sound presentation [16,26]; using a source sound with particular and/or unique characteristics (e.g. white noise [16,29,26], narrow band white noise [14,21,22], “perfect-sequence” sounds [23] [24], pure tones [18–20]) and selective frequency filtering of the signals outputted from the ear-canal microphones [16,14,23]. As yet, there is no accepted standard configuration for sonotubometric testing and the choice of a “best” (i.e.…”

“…However, investigators have continued to question the accuracy of sonotubometry for assigning ET openings/non-openings during a swallow or other maneuver based on theoretical considerations [4,16,11,17,18], and recommended various modifications to the core sonotubometry protocol intended to reduce false test results [16,18–20,14,21–25,11]. To date, there is no “accepted” protocol (configuration) for ET function testing using sonotubometry and no study has compared the accuracy of these different protocols for discriminating “true” ET openings.…”