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.
Introduction
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.
(...)
Discussion
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.
