mise à jour du
22 octobre 2006
Eur Arch Otorhinolaryngol
La trompe d'Eustache
Evaluation of Eustachian tube function
by sonotubometry: results and
reliability of 8 kHz signals in normal subjects
Di Martino EF, Thaden R, Antweiler C, Reineke T,
Westhofen M, Beckschebe J, Vorlander M, Vary P.
ENT Department, DIAKO Ev. Krankenhaus, Bremen, Germany,


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.
The Eustachian tube (ET) plays a role in ventilation, pressure equilibration and drainage of the middle ear and the mastoid. Since physiology and the impact of ET alterations on the pathogenesis of middle ear diseases are not fully understood, numerous methods such as tympanometric, manometric, radiologic, endoscopic and sonometric approaches have been developed for the evaluation of the ET function.
Most methods used in clinical routine study pressure variations in the middle ear. One major drawback of many methods is that they cannot be applied in both patients with an intact and patients with a perforated eardrum. Furthermore, most of these approaches do not resemble physiologic conditions.
Sonotubometry is a method that allows the examinationof the ET under physiological conditions. In this approach a sound is applied via a probe in the nose. At the same time, the changes of sound intensity during tube opening are recorded in the external ear canal.
Various approaches are reported. Pure-tone as well as broadband stimuli were used as signals. Some authors demonstrated that frequencies above 6 kHz are most favourable for clinical application since most noise pollution caused by pharyngeal activity occurs up to 5 kHz. Clinical studies with this method showed uniequivocal results for the diagnostic and predictive value of this method in preoperative assessment.
Although the sonotubometric approach has many potential advantages, it was not able to dominate the diagnostics for Eustachian tube (dys)function. Instead tympanometry became a widespread method despite some drawbacks.
Employing modern audiologic technology, the aim of this study was to evaluate the diagnostic reliability and to find normal values for tubal opening for the application of an 8 kHz pure-tone signal in sonotobometric studies. (...)
Eustachian tube activity can be detected by the application of an acoustic signals. A real-time monitoring of the dynamic of ET tube function under physiological conditions is possible with the method applied. A number of characteristically shaped sonotubograms can be found. It can be assumed that the different patterns reflect at least in part the highly differentiated muscular activity of the tubal muscles.
Direct monitoring of this activity is only possible by EMO, which is an invasive procedure. Magnetic resonance imaging is able to visualize muscular function but is costly and not always tolerated by the patient. Although sonotubograms reflect muscular activity only indirectly the results show an intra- and interindividual variability in the muscular activation that was also described with alternative methods by other groups. There was little variability in the duration of the tubal opening during dry and liquid swallowing. This may be explained by the fact that swallowing is a reflex that cannot be stopped once triggered. The fact that spike-shaped sonotubograms were mostly found suggests that a similar muscle activation pattern occurs in this manoeuvre.
The variability of tubal opening was much higher in forced manoeuvres such as yawning (2.8 ms-5.O s). The onset and duration of this kind of opening can be actively influenced by the proband. This is also true in part for Valsalva, the least physiologic manoeuvre investigated. The occurrence of two different types sonograms in the same manoeuvre reflects the forced nature of these manoeuvres. Opening and the duration of the pressure increase can be easily controlled. Since closure of the tube requires a passive decompression of the middie ear this part of tubal motility cannot be influenced. In Valsalva manoeuvre we saw most of the descending sonotubogram types. This may reflect an impaired relaxation, an individually increased rigidity or a clinically not apparent stenosis. Yet, further studies are necessary.
Sonotubometry with a 8 kHz pure-tone signal failed to demonstrate tubal opening in only 2.5% normal patients but in 45% manoeuvres. Not all manoeuvres triggered a detectable tube opening. This shows that the application of an acoustic signal is useful for ET diagnostic. Yet it also clearly demonstrates the limited sensitivity of the signal used in this study. First experiences with a new generation of acoustic signals, so-called perfect sequences, shows that other signals significantly enhance the use of sonotubometry for clinical application.
Little more than half of the measurements (55.2%) were assessable for evaluation, but there was a learning curve in the application of this method. Factors such as nasal fluid and cerumen were systematically eliminated during the course of the study. The compression of the nostrils that caused most problems during Valsalva is hard to be controlled. The dislocation of the nasal tube or the ear probe that may lead to false-negative result cannot always be avoided. Noise pollution during pharyngeal activity could not be totally eliminated by the described setting.
Since ET function is known to be influenced by various factors such as physical activity, age, body position and blood flow, a long-term registration like a Holter ECU recording would be desirable.
Although sonotubometry offers a number of desirable advantages when compared to other methods, the results of this study demonstrate clearly that in practice the reliability of applying an 8 kHz pure-tone signal is too limited for both a short-term and a long-term registration. Further technical refinements are necessary to increase the use of this method for clinical application.
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