Intracochlear Pressure Changes due to Round Window Opening:
A Model Experiment
P. Mittmann, A. Ernst, and I. Todt
Department of Otolaryngology, Head and Neck Surgery, Unfallkrankenhaus Berlin, Warenerstraße 7, 12683 Berlin, Germany
Correspondence should be addressed to P. Mittmann; email@example.com
Received 17 March 2014; Accepted 29 April 2014; Published 22 May 2014
Academic Editor: Afshin Teymoortash
Copyright © 2014 P. Mittmann et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
To preserve residual hearing in cochlea implantation, the electrode design has been refined and an atraumatic insertion of the
cochlea electrode has become one aspect of cochlea implant research. The opening of the round window can be assumed to be a
contributing factor in an atraumatic concept. The aim of our study was to observe intracochlear pressure changes due to different
opening conditions of an artificial round window membrane. The experiments were performed in an artificial cochlea model. A
pressure changes. Openings of the artificial round window membrane were performed using different ways. Opening the artificial
round window mechanically showed a biphasic behaviour of pressure change. Laser openings showed a unidirectional pressure
change. The lowest pressure changes were observed when opening the artificial round window membrane using a diode laser. The
various intracochlear pressure changes.
and a loss of fluid. In our model experiments, we could prove that the opening of the artificial round window membrane causes
criteria for cochlea implantation evolved, the perioperative
surroundings, electrode design, and surgical technique have
developed as well. Common surgical sense is that a selective
scala tympani insertion should be achieved  and the
of discussion. The insertion trauma is assumed to depend on
to some degree: the way and degree of opening the cochlea,
insertion of the electrode array, additional medication (e.g.,
steroids and the form of application) , sealing of the
cochlea, and the electrode design. The two major surgical
techniques for access to the cochlea have been the round
window approach and the “soft surgery” cochleostomy .
Following the pathway of a pure round window insertion,
there are, to our knowledge, no studies that compare or
describe the opening of the round window membrane. The
anatomical conditions make it mandatory to drill away the
promontorial lip to overlook the round window membrane
, but the opening procedure itself has not been further
There are different ways to open the cochlea. Opening of
the round window membrane can be performed with blunt
or sharp tools or with a laser. The cochlea is a fluid dynamic
system. If the round window membrane is manipulated, the
pressure is directly transferred into the cochlea and damage
related to this force could occur. The aim of the present study
was to compare different opening techniques with regard to
pressure changes in a cochlea model.
2. Material and Methods
2.1. Pressure Sensor. The intracochlear pressure was mea-
sured using the microoptical pressure sensor developed by
Olsen . Details about design, fabrication, and capacity
can be found in the literature . Basically, the tip of the
pressure sensor is a hollow glass tube sealed on one end by
Hindawi Publishing Corporation
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Volume 2014, Article ID 341075, 7 pages
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Figure 1: Artificial cochlea model with polythene foil. The sensor is
placed in the helicotrema area.
a plastic thin film diaphragm coated with a reflective surface
with a small distance (50–100휇m) to the diaphragm tip. The
fibre, and isreflected by the gold-covered flexible diaphragm.
The reflected light is sensed by the photodiode. A small
pressure induces distance displacements of the diaphragm,
which modulate the intensity of the reflected light. Time
sensitivity of the sensor is 300 measurements per second.
The sensor is connected to a module, which is again linked
to a computer. Evolution software was used to record the
optical fibre is attached to a light-emitting diode (LED) light
2.2. Preparation of the Cochlea Model. The experiments were
performed in a synthetic transparent artificial cochlea model
(Figure 1). The round window was a circular opening with
a diameter of 1.5mm and impressed slightly greater in
comparison with other studies (1.23mm)  (Figure 2). In
the helicotrema area of the cochlea model, an extra channel
was drilled that was slightly larger (about 800휇m) than the
and the position of the sensor within the channel was fixed
and sealed with fibrin glue. The sensor was placed within
the channel in such a way that the tip had contact to the
edge of neither the channel nor the ground. The round
foil. Polythene foil was chosen because it is similar in its
lack of resistance and distension and in tear strength to the
natural round window membrane. Afterwards, the cochlea
was microscopically controlled to suspend any enclosed air
sensor tip to insert the pressure sensor. After the pressure
sensor was inserted, the cochlea was filled up with water
2.3. Measurements. The experimental setup was the same
in every measurement. To standardise the conditions, all
Figure 2: Top view on the cochlea model; the 々 marks the round
openings of the artificial round window membrane were
performed by the same surgeon. The sensor was calibrated
in the cochlea and the initial value was set to zero. A
measurement was considered to be useful if the measured
mmHg value after finalisation of the experiment was close
to zero. Under these conditions, five openings of the round
window membrane were performed. After every opening,
the membrane was replaced by a new foil and the cochlea
was refilled with water and checked microscopically for
any enclosed air bubbles. We performed different opening
When opening the round window membrane with a
needle, the needle was gently placed on the membrane and
was pulled sideways carefully to perforate the membrane.
A cannula was used to incise the membrane and then
pulled sideways carefully to open the artificial membrane
horizontally. With the diode laser, the tip was placed in the
round window membrane was seen under the microscope.
Measurements were performed with different intensities
using 4, 6, and 10W. The opening of the round window
membrane with the CO2laser was performed with a Zeiss
centre of the round window membrane and several impulses
were emitted until the membrane was perforated.
Since internationally different pressure sizes are used,
a conversion table is attached: 1mm/Hg = 133 pascal =
0.019psi = 1.35cmH2O.
S5, OPMI TwinER (20W). The finder sight was aimed at the
An opening of the artificial round window membrane was
an insertion of a CI electrode. With every tool, five openings
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Table 1: Maximum intracochlear pressure in mmHg while opening the round window membrane (five measurements).
Table 2: Pressure gain velocity in mmHg/msec (five measurements).
When opening the round window membrane with a
needle, the maximum intracochlear pressure ranged from
1.59 to 4.59mmHg, with a median of 3.28mmHg (standard
deviation(SD) ±1.28). Thecourse of thepressure change was
varied from 0.002mmHg/msec to 0.05mmHg/msec, with a
to 5.06mmHg, with a median of 3.84mmHg (SD ± 1.45).
maximum pressure gain (푃 > 0.05) or for the pressure gain
Opening of the round window membrane using a diode
laser showed lower maximum pressure levels. Measurements
Withan intensity of 4W, the maximum pressure level ranged
recorded and depicted in real time in a graph. Furthermore,
the velocity of the pressure gain was calculated (Table 2). For
The pressure gain velocity varied from 0.003mmHg/msec
to 0.04mmHg/msec, with a median of 0.0666mmHg/msec
cannula showed a maximum pressure gain from 1.51mmHg
(SD ± 0.98). Comparison of the two groups using the 푡-test
showed no statistically significant difference either for the
velocity(푃 > 0.05).Bothgroupsshowedabiphasicpatternof
pressure change related to opening (Figures 3(a) and 3(b)).
(SD ± 0.22). Slightly higher values were measured using
with a median of 1.08mmHg (SD ± 0.31). The observed
the diode laser at 6W. Values for the maximum pressure
ranged from 0.15mmHg to 0.88mmHg, with a median of
0.29mmHg (SD ± 0.27). Using 10W, the maximum pressure
pattern was a unidirectional pressure change (Figures 3(c)–
values were higher, ranging from 0.39mmHg to 2.18mmHg,
The paired 푡-test for the maximum pressure of the
opening using a needle in comparison with a diode laser
showed statistically significant differences. For all levels of
a statistically significant difference (푃 < 0.05) was observed.
Usage of a cannula in comparison with a diode laser also
showed a statistically significant difference (푃 < 0.05) for
the diode laser showed no statistically significant difference
every level of intensity (4W, 6W, and 10W). Comparison of
(푡-test, 푃 > 0.05) for the intensity level of 4W versus
6W. However, comparing the rather low maximum pressure
results for 4W and 6W with the intensity level of 10W, a
statistically significant difference (푡-test, 푃 = 0.044) was
was found at 4W. Using 4W, the pressure gain velocity
ranged from 0.001mmHg/msec to 0.0005mmHg/msec, with
Regarding the pressure gain velocity, the lowest gain
a median of 0.0003mmHg/sec (SD ± 0.00015). Values using
ranging from 0.00008mmHg/msec to 0.003mmHg/msec,
0.0007mmHg/msec, with a median of 0.0004mmHg/msec
difference for the pressure gain velocity. The paired 푡-test
every level of intensity (4W, 6W, and 10W). The difference
between the higher pressure gain velocity of the cannula in
comparison with the lower diode laser pressure gain velocity
sure gain velocity values ranged from 0.0001mmHg/msec to
(SD ± 0.00026).
showed a statistically significant difference (푃 < 0.05) for
(at 4W, 6W, and 10W) was statistically significant (푡-test,
the pressure gain velocity of the needle and the diode laser at
푃 < 0.05). Within the different groups of the diode laser,
above, opening of the round window membrane using a
CO2laser showed a negative and high amplitude pressure
no statistically significant difference was seen between the
different intensity levels (푡-test, 푃 > 0.05).
from −0.24mmHg to −50.16mmHg, with a median of
direction (Figure 3(f)). The intracochlear pressure decreased
−20.1mmHg (SD ± 19.81). However, the pressure gain
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0 0.340.67 1 1.341.67 2 2.342.67 3 3.34
0.33 0.671 1.33 1.672
0.396 0.796 1.1961.596 1.996
0 0.2 0.4 0.6 0.8
1.2 1.4 1.6 1.8
0 0.3960.796 1.196
Figure 3: (a) Biphasic pressure change related to opening of the round window membrane with a needle. (b) Biphasic pressure change
membrane with a diode laser (4W). (d) Unidirectional pressure change through opening of the round window membrane with a diode laser
(6W). (e) Unidirectional pressure change through opening of the round window membrane with a diode laser (10W). (f) Unidirectional
pressure change through opening of the round window membrane with a CO2laser (20W).
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velocity was rather low. It ranged from 0.0003mmHg/msec
to 0.011mmHg/msec, with a median of 0.005mmHg/sec (SD
a CO2laser was rather difficult as it took obviously longer to
This long opening period was reflected in the low pressure
± 0.00553). Opening of the round window membrane using
perforate the membrane in comparison with the other tools.
The criteria for cochlea implantation have changed over
the past years. The preservation of residual hearing has
become one of the goals in modern cochlea implantation
[2, 5, 9, 13, 14]. Preservation of residual acoustic hearing is
closely connected with an atraumatic CI electrode insertion.
Access to the cochlea via the round window is a widely used
access for an atraumatic CI electrode insertion [4, 6, 15].
The opening procedure of the round window membrane
itself is less frequently described in the literature. Briggs et
al.  used a hypodermic needle in their temporal bone
study to open the round window membrane after using a
1mm diamond burr for a full exposure of the round window
In our study, we compared the opening of the round
window membrane using different tools with regard to the
intracochlear pressure change. In every experiment, it was
the sensor tip was completely sealed to the cochlea model.
Mechanical opening of the round window membrane using
a needle or sharp cannula showed no significant difference
either in the maximum pressure value or in the pressure
gain velocity (Figures 4 and 5). Whilst mechanical opening
was attended by a rather fast pressure gain and rather high
significant lower maximum pressure values and a lower
pressure gain velocity (Figures 4 and 5). A less traumatic
opening with the diode laser in vivo can be assumed. In
contrast to the needle, cannula, and the diode laser, opening
of the round window membrane with a CO2laser caused
After opening the round window membrane with a CO2
bubbles were observed just underneath the round window
membrane. As fluid loss was not observed, it can be assumed
that the fluid had evaporated.
We could prove that even opening of the round win-
dow membrane leads to intracochlear pressure variation.
For the surgeon, one of the main goals is to minimise
intracochlear trauma. The influence of the intracochlear
pressure variation on intracochlear trauma remains unclear.
It should be presumed that less intracochlear pressure leads
to less intracochlear trauma. Regarding the probability of
slow fluid pressure changes have to be separated from fast
sound pressure-related fluid pressure changes. The literature
negative pressure, with high negative pressure maximum
laser, the fluidity within the cochlea was reduced and air
window membrane with standard deviation.
Mean pressure gain velocity (mmHg/ms)
Figure 5: Mean pressure gain velocity for opening of the round
described in the literature. In a gerbils model a maximum
of 10Pa was measured in scala vestibuli with a stimulus
of 90dBSPL at 15kHz in the ear channel . In scala
tympani, 3.5mm from the stapes with an input of 80dBSPL
at the stapes, the pressure varies up to 90dBSPL (0.63Pa)
near the basilar membrane . Our data from mechan-
ical round window membrane openings show hydrostatic
pressure changes up to 5.06mmHg (675Pa) and laser diode
data up to 2.18mmHg (291Pa). In contrast to sound induced
intracochlear pressure changes, manipulation to the cochlea
seems to cause multiple greater pressure shifts. How hydro-
static pressure changes are conferrable and comparable to
6 The Scientific World Journal
sound induced pressure changes needs to be investigated
The approach taken in our study has some limitations
regarding the applicability to the human cochlea. It has to
be considered that the intracochlear hydrostatic pressure
changes in vivo and in temporal bone measurements due to
natural drain systems. The cochlea model was sealed with
system with only one channel of fluid drain, the assumed
round window. The human cochlea and the vestibule are a
functional unit. Fluid pressure transfer between the differ-
ent labyrinthine compartments is widely described [21–23].
Therefore, a direct transfer to the saccus endolymphaticus as
a pressure equalisation unit could be speculated. However,
this must be assumed to be limited in vivo. A similar
limited quantity of fluid pressure transfer can be assumed
for the aqueductus cochlea in a regular cochlea . Surgical
experience in a normal cochlea has shown that there is no or
surface tension pressure, since we have observed no or only a
during CI surgery .
Regular intracranial pressure is known to be age-
dependent and ranges from 5mmHg in young patients to
15mmHg in old patients . Because of a lack of regular
human data, we have to compare the observed values with
animal data or the clinical experience we have gained from
cochlea implantation in anomalous cochlea with so-called
gushers of intense endolymphatic outflow .
ing, the valve capacity of the borderline structures between
cochlea and intracranial pressures remains unclear and a
transfer of the measured model values into in vivo behaviour
is problematic. The estimation of pattern and principles
of fluid pressure changes related to manual or mechanic
handlings in terms cochlea implantation is essential for the
establishment of a reproducible atraumatic cochlea implan-
tation. The observed differences in opening the cochlea
underline the importanceof this specific substep of electrode
We provide the first results of fluid pressure changes due to
the opening of an artificial round window membrane. To
transfer the results to the human cochlea temporal bone,
moreexperiments are needed. But the differences in the used
model underline the possible importance of how to open the
round window for an atraumatic cochlea implant procedure.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
This study was supported by Advanced Bionics, St¨ afa,
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