Apparatus and method for determining the presence of vestibular perilymph fistulae and other abnormal coupling between the air-filled middle ear and the fluid-filled inner ear

A method for determining the presence of perilymph fistula or other abnormal coupling between a subject's middle ear and inner ear. The subject is placed on a support surface that is sway-stabilized about an axis that is co-linear with the subject's ankle joints. After the subject has assumed a position in equilibrium, a controlled changed in air pressure is introduced to the external canal of one of the subject's ears. It is then determined whether the controlled change in pressure produces a significant subject sway response. In an alternative embodiment, the sway response is monitored with the subject placed on a support surface that is sway-stabilized about an axis that is perpendicular to the axis that is co-linear with the subject's ankle joints.

TECHNICAL FIELD 
This invention relates generally to methods and devices for providing 
non-invasive, sensitive, and reliable tests for the presence of perilymph 
fistulae and other abnormal coupling between the middle ear and the inner 
ear. Such methods and devices are to be used as diagnostic tools for 
patients with symptoms of dysequilibrium, vertigo, and/or motion sickness. 
BACKGROUND ART 
A perilymph fistula is an abnormal connection, i.e., a small hole in the 
round or oval window, between the perilymph fluid of the inner ear and the 
middle ear air space. The first described cases of perilymph fistulas were 
a consequence of otic capsule bone erosion associated with middle ear and 
mastoid infections (Schuknecht, 1974). Fee (1968) was the first to report 
oval and round window fistulas caused by head trauma. Patients with both 
types of perilymph fistulas report episodes of dizziness, vertigo, 
dysequilibrium, tinitus, and hearing loss. Other abnormal couplings 
between the air-filled middle ear and the fluid-filled inner ear involve 
softening of the otic capsule, evulsion of the stapes footplate, 
deformation of the ossicular chain, and fractures of the ossicles or 
temporal bone. In some cases these problems are congenital rather than 
adventitious. 
A reliable and non-invasive clinical test for perilymph fistulas and other 
abnormal communication between the middle and inner ear is not possible 
with the devices and methods currently available to clinicians. Because 
the history and symptoms reported by the patient with a middle ear 
perilymph fistula often resemble those reported by patients with other 
forms of inner ear vestibular disorders, symptoms and history do not 
provide a reliable means to determine whether or not the patient has a 
perilymph fistula. According to a number of clinicians specializing in 
vestibular disorders, a definitive diagnosis of a post-traumatic middle 
ear perilymph fistula can be made only by direct inspection of the middle 
ear through surgical intervention, i.e., tympanotomy (Goodhill, 1980; 
Healy, 1974 & 1976; Simmons, 1982; Lehrer, 1984; Kohut, 1979; Nomura, 
1984; Singleton, 1978). Hence, a reliable non-invasive perilymph fistula 
test would eliminate the need for exploratory surgery in many cases. 
Several groups of individuals have attempted to develop non-invasive and 
yet reliable tests for the presence of middle ear perilymph fistulas. 
Daspit, et al., (1980) used an impedance bridge to introduce controlled 
changes in external ear canal pressure while recording the patient's eye 
movement responses using electronystagmography. These clinicians used air 
pressure stimuli ranging from -600 +300 millimeters of water. Supance 
(1983) and Healey, et al. (1979) used similar techniques. In all of these 
instances, however, the reliability of the test was found to be relatively 
low, ranging from a high of 75% to a low of 37%. Noting the high incidence 
of postural instability among fistula patients, Lehrer, et al. (1984) used 
the so called Quix test in which body sway responses to external ear canal 
pressure stimuli are measured with the subject standing freely. In the 
Quix test, however, the subject stands on a fixed surface and within a 
normally fixed visual surround. Hence, this method does not test the 
subject's postural response to external ear canal pressure at a time when 
the posture control system is maximally sensitive to vestibular inputs. 
A number of signal processing methods exist for determining whether or not 
a stimulus produces statistically significant changes in a measured 
variable. One such technique is termed "pulse triggered averaging". The 
stimulus in this technique consists of a train of discrete mono or 
biphasic pulses. The measured variable is divided into segments that are 
time locked to the onset of the stimulus pulses. The segments are then 
averaged. A significant change in the properties of the measured variable 
correlated with the onset of pulses indicates that the measured variable 
is influenced by the stimulus. A second technique uses continuously 
varying sinusoidal or step-like stimuli and "linear systems analysis" to 
determine whether or not temporal properties of the measured variable are 
significantly correlated with the stimulus (for example; Brown, et al., 
1982). 
DISCLOSURE OF INVENTION 
The present invention provides a method and apparatus for determining the 
presence of perilymph fistulas and other forms of abnormal coupling 
between the middle ear and the inner ear. Controlled air pressure stimuli 
are introduced to the external auditory canal of an erect standing subject 
while the subject's posture control system is maximally sensitive to 
inputs from the inner ear vestibular system. Maximum sensitivity to 
vestibular inputs is achieved by eliminating vision and then gradually 
disrupting somatosensory orientation inputs provided by contact between 
the feet and the support surface. 
In accordance with methods of the present invention, the subject assumes an 
erect standing position in equilibrium on a support surface. The support 
surface is rotatable about a horizontal axis approximately 2 inches above 
the surface. The subject's feet are placed such that the support surface 
and ankle joint rotation axes are approximately co-linear. To eliminate 
visual orientation inputs, the subject's eyes are closed. To eliminate 
accurate orientation inputs derived from the somatosensory senses in 
contact with the support surface, angular sway displacements of the 
subject's body from the assumed erect equilibrium position in the 
antero-posterior plane are measured and the support surface rotated in 
direct proportion to this measured quantity. In the previous Nashner 
application of which this application constitutes a continuation-in-part, 
this was called the "stabilized" support surface condition. Subsequent to 
this application, however, we have altered terminology and now refer to 
this as the "sway-referenced" support surface condition, because the 
orientation of the surface is referenced to the sway angle of the 
subject's center of gravity rather than fixed in relation to the gravity 
vertical. 
Some patients suspected of having perilymph fistulas are unable to maintain 
their balance under sway-referenced support surface conditions. Therefore, 
it is sometimes necessary to modify the extent to which somatosensory and 
visual orientation inputs are removed. Patient's requiring vision to 
maintain their balance are tested eyes open. To provide the individual 
patient with sufficient somatosensory orientation information to maintain 
standing equilibrium, the support surface is rotated in fractional 
relation to the measured sway orientation of the subject's center of body 
gravity. For example, when the subject's body sways forward 4 degrees, the 
support surface is rotated forward one-half as much or 2 degrees. We refer 
to this fractional relation between body sway and support surface rotation 
as the sway-reference "gain". 
Pressure within the middle ear space can be changed by introducing 
controlled changes in air pressure to the external canal of the ear. There 
are potentially at least two pathways to the vestibular system. The 
relative contribution of each of these pathways is, to a certain extent, 
dependent upon the integrity of the tympanic membrane and the middle-ear 
transmission system. 
Specifically, with a perforation of the tympanic membrane or with an intact 
tympanic membrane and complete interruption of the ossicular chain, the 
only mechanism for stimulating vestibular transducers is through changes 
in the middle ear pressure. In contrast, an intact tympanic membrane and a 
compliant middle-ear transmission system also permits us to move 
perilymphatic fluid through direct piston action of the stapes footplate. 
The interaction of these two coupling modes currently is not clear for 
subjects with normal hearing and for patients with various types of 
middle-ear and tympanic-membrane problems. If the subject has one or more 
abnormal connections between the inner ear perilymph fluid and the middle 
ear space (perilymph fistula), then the vestibular sense organs will be 
stimulated by the pressure change. With the subject's posture control 
system maximally sensitive to vestibular inputs, the presence of a 
perilymph fistula is highly probable if the subject has a postural 
reaction to the external ear canal pressure stimulus. 
The accuracy and reliability of this perilymph fistula test is 
significantly greater than that possible with currently available clinical 
methods. Furthermore, by altering what we call the sway-reference "gain" 
of the support surface motions, a threshold level for perilymph fistula 
sensitivity can be established. 
In a preferred embodiment of the present invention, the subject stands on a 
support surface, which rests on three or more vertical force transducers. 
A digital computer samples signals from the force transducers and 
calculates the front-back and side to side positions of the center of 
force exerted by the subject's feet against the surface and the front-back 
angular position of the subject's body center of gravity in relation to 
the ankle joints. An electric servomotor positions the support surface 
about a rotational axis parallel and approximately 2 inches above the 
surface. The computer controls on a continuous basis the rotational 
position of the support surface, such that the surface rotates in relation 
to the calculated position of the center of vertical pressure, the angular 
orientation of the subject's center of body gravity, or a combination of 
the two variables. Air pressure changes to the external auditory canal of 
an ear are introduced through a tube. The tube is connected to a air 
pressure generating source which is also controlled on a continuous basis 
by the computer. 
In a preferred protocol based on the above preferred embodiment, the 
computer calculates the anteroposterior and lateral positions of the 
center of vertical force and the anteroposterior angular position of the 
subject's body center of gravity in relation to the ankle joints. The 
support surface is fixed in the horizontal position by setting the 
sway-reference gain to 0.0. The statistical properties of anteroposterior 
and lateral movements of the center of vertical force are calculated. 
Then, a series of brief controlled changes in ear canal pressure are 
introduced and the statistical properties of anteroposterior and lateral 
movements of the center of vertical force re-calculated by the computer. 
Significant increases in motions of either one or both of the 
anteroposterior and lateral center of vertical force positions following 
imposition of the pressure stimuli, as determined by standard statistical 
tests, indicates a high probability of perilymph fistula, and the protocol 
is terminated. 
If the imposition of pressure stimulation with the support surface fixed in 
the horizontal position does not produce a significant postural response, 
the above proceedure is repeated with the sway-reference gain increased to 
0.12. If a statistically significant postural response is again not 
demonstrated, the above proceedure is repeated with the sway-reference 
gain increased in subsequent trials to 0.25, 0.50, 0.75, and then 1.0. 
Statistically significant increases in motions of either one or both 
center of vertical force positions correlated with the pressure stimuli at 
one of these sway-reference gains indicates a high probability of 
perilymph fistula. The absence of pressure correlated increases in 
postural activity at any of the sway-refernce gains indicates that a 
perilymph fistula in the stimulated ear is highly unlikely. 
In an alternative embodiment of the invention, information about the 
patient's postural activity is enhanced by also measuring 
electromyographic (EMG) activity of a plurality of leg and lower trunk 
muscles supporting the body against gravity.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
In co-pending application Ser. No. 873,125, filed 6-11-86, a continuation 
of Ser. No. 408,184, filed Aug. 16, 1982, for an invention of Lewis M. 
Nashner, one of the inventors herein, a method and apparatus were 
described which force a subject to use vestibular orientation information 
while maintaining a position in equilibrium. Somatosensory (inputs from 
contact with the support surface) and visual orientation inputs to the 
subject are masked by: (1) placing the subject on a movable support 
surface, (2) having the subject stand eyes closed, (3) measuring the 
spontaneously occurring displacements of the subject away from the 
equilibrium position, and then (4) moving the support surface in 
functional relation to the displacement of the subject from equilibrium. 
In a preferred embodiment of the Nashner invention, the subject stands 
erect with his ankle joints co-linear with the rotational axes of support 
surface. According to a preferred protocol of the Nashner invention, the 
support surface rotates in direct proportion to the rotational 
displacements of the subject's center of body gravity in relation to the 
feet. This is called the "sway-referenced" support surface condition, 
because the orientation of the surface is referenced to the sway 
orientation of the subject rather than to gravity. This technique makes 
the orientation information derived from somatosensory inputs (inputs from 
contact with the support surface) inaccurate and therefore unreliable for 
controlling equilibrium. Under sway-referenced support surface conditions 
with eyes closed, a subject standing on the platform support surface is 
forced to rely on vestibular inputs to maintain his position in 
equilibrium. Under these conditions, therefore, the patient is maximally 
sensitive to vestibular stimuli. 
Utilizing the present invention, a relatively straightforward test protocol 
can determine whether or not a subject has a perilymph fistula in one or 
both ears or other abnormal coupling between the middle-ear and the 
inner-ear. 
FIG. 1 shows a schematic block diagram of the principal components of a 
possible embodiment of an apparatus according to the present invention. In 
this embodiment, the subject 11 stands erect in a position of equilibrium 
on a support surface 12, which is rotatable about an axis 13 co-linear 
with the ankle joints. The support surface rests on vertical force 
transducers 14, the signals from which are transmitted to the computer 15 
for calculating anteroposterior and lateral positions of the center of 
vertical force and angular displacements of the subject's center of body 
gravity from the equilibrium position. The computer generates signals 
which rotate the support surface 16 in proportion to the computed angular 
displacement of the subject's center of body gravity. Finally, the 
computer activates a device which generates controlled changes in air 
pressure 17 to one of the subject's ears 18, and then computes whether or 
not pressure changes produce correlated and significant increases in one 
or more of the measured variables of postural activity. 
FIG. 4 shows one means for controlling the rotational position of the 
support surface 12, using a system comprising an electric motor 41, lead 
screw 42, and a ball nut 43. Rotations of the motor and lead screw move 
the ball nut back and forth and thus rotate the support surface. 
FIG. 5 shows one means for generating controlled changes in air pressure 
within the external ear canal using a pneumatic tube. A system comprising 
an electric stepper motor 51, lead screw 52, and ball nut 53, moves a 
piston within a pneumatic cylinder 54. The movements of the piston changes 
the volume of the tube, thus compressing the air and changing the 
pressure. The means for measuring air pressure within a volume and for 
accurately maintaining a given level of pressure using pressure feedback 
control are well-known in the art. 
In a preferred embodiment of the perilymph fistula test, the standing 
subject is positioned on the rotatable support surface 12 with eyes closed 
and ankle joint axis co-linear with the support surface rotation axis 13 
as shown in FIG. 1. 
The pneumatic tube is placed the one of the subject's ears 18. The angular 
orientation of the subject's center of body gravity in relation to the 
ankles in the antero-posterior plane of motion is calculated from the 
forceplate 14 measurements. The angular measure is multiplied by the 
sway-refernce gain factor. Then, the support surface 12 is rotated in 
direct proportion to the calculated angular measure. 
FIG. 3 illustrates the sequence of events measured during a perilymph 
fistula test conducted according to a possible embodiment of the present 
invention. Three measures of the subject's displacements from equlibrium 
are recorded by the computer for an interval of time sufficient to 
establish baseline levels of postural activity. After the three activity 
baselines are established, one or a series of brief pressure changes are 
introduced to the ear, while recording of the three measures of postural 
activity continues. Finally, mean levels of activitiy in each of the three 
measures of stability are computed during a 500 millisecond interval 
following each pressure stimulus. 
In part A of FIG. 3, the support surface is sway-referenced with a gain of 
0.25, i.e., it rotates one-fourth as much as the angular changes in 
orientation of the subject's center of body gravity in relation to the 
ankles. Changes in the anteroposterior position of center of vertical 
force (i.e., ankle torque) 32 and the angular displacement of the 
subject's center of body gravity with respect to the ankles 31 move 
randomly as the subject stands erect. EMG traces from four ankle and thigh 
muscles 33 typically show little activity under this quiescent condition. 
After the subject has stood for a period of time, a brief increase in air 
pressure 34 is introduced to the normal left ear. Following the pressure 
stimulus, there is no significant increase in the subject's displacement 
from equilibrium. The above described procedures are then repeated on the 
other ear. 
In part B of FIG. 3, the rotational position of the support surface is 
horizontally fixed by setting the sway-reference gain to 0.0. Now, after a 
period of quiescent standing, the pressure stimulus 34' is introduced to 
the abnormal right ear. With the surface fixed, however, no postural 
activity changes correlated with the pressure stimulus are observed in any 
of the three measurements 31', 32', and 33'. 
In part C, the rotational orientation of the support surface is again 
sway-referenced to the angular orientation of the subject's center of 
vertical force with a gain of 0.25. Now introduction of the controlled 
change in external ear canal pressure produces a large postural reaction 
consisting of rapid and significant changes in the center of vertical 
force position 31", the angular orientation of the center of body gravity 
32", and the leg muscle EMG signals 33". 
If a significant postural reaction to pressure stimulation occurs in one or 
more of the stability measures, then there is a high probability of one or 
more perilymph fistula and other abnormal coupling between the middle ear 
and the inner ear in the stimulated ear. The ear is highly unlikely to 
have a perilymph fistula or other abnormal coupling between the middle ear 
and the inner ear if there are no significant postural reactions to 
pressure stimulation under the any of the sway-referenced support surface 
conditions. 
The procedure can also be performed as the subject stands with the 
rotational axis of the ankles perpendicular to the rotational axes of the 
support surface. With this standing configuration, the sway-reference 
conditions are created by rotating the support surface in proportion to 
the left to right lateral displacements of the subject's center of body 
gravity in relation to the ankle joints. And, the proceedure can be 
performed with the subject standing on a support surface with 2 rotational 
axes, one colinear and one perpendicular to the ankles. With this system, 
sway-referenced conditions are created by rotating the colinear axis in 
proportion to the antero-posterior sway rotations of the subject's center 
of body gravity and the perpendicular axis in proportion to the left to 
right lateral sway displacements of the subject. 
With the support surface held fixed, the three measures of the subject's 
stability described in FIG. 3 are recorded by the computer for an interval 
of time sufficient to establish baseline levels of postural activity. 
After the three activity baselines are established, one or a series of 
brief pressure change stimuli are introduced to the external canal of one 
ear, while recording of the three measures of postural activity continues. 
Then, mean levels of activity in each of the three measures of stability 
are computed during a fixed time interval following each pressure 
stimulus. 
If a significant reaction to stimulation occurs in one or more of the three 
measures of stability, then testing of that ear is terminated. If no 
significant reactions are observed while the subject is standing on the 
fixed support surface, the above test procedure is repeated with the 
support surface rotating in proportion to changes in angular orientation 
of the subject's center of body gravity, i.e., the sway-referenced 
conditions. First, the support surface is rotated 0.12 times the angular 
rotation of the subject's center of body gravity, i.e., the 0.12 gain 
sway-referenced condition, and new baseline levels for the three measures 
of postural activity are calculated. Then, one or a sequence of brief 
external canal pressure stimuli are re-introduced to the ear. The methods 
described above are used again to determine whether or not statistically 
significant reactions occur in one or all of the measures of postural 
activity. If reactions are significant, the test is terminated. If no 
significant reactions occur, the procedure is repeated with the 
sway-reference gain increased to 0.25, then 0.50, 0.75, and then 1.0. 
To perform the perilymph fistula test, the waveform, amplitude, and 
frequency properties of the pressure stimulus can be varied. The maximum 
positive and negative pressure amplitudes are limited by patient comfort 
and safety. The stimulus waveform, however, determines the statistical 
methods used to identify the presence of postural responses. With discrete 
pulse stimuli, similar to those shown in FIG. 3, the presence of a 
postural response can be determined by pulse triggered averaging according 
to methods well-known in the prior art. With continuously varying pressure 
stimuli, stimulus-response correlations can be computed also according to 
means well-known in the prior art. 
In the perilymph fistula test, a support surface in which motions are 
actively controlled by a motor can be replaced with a support surface with 
viscoelastic compliant properties which moves passively in relation to the 
displacements of the subject from the maintained equilibrium position. 
FIG. 6 shows such simpler means for providing a support surface which 
rotates in functional relation to a quantity related to the subject's 
displacement from equilibrium. The support surface 12 is made compliant 
about the axis of rotation 13 by restrasining the rotational motion of the 
surface with a compliant element 61. The compliant element can have purely 
elastic properties, such as a linear spring, or it can have a combination 
of elastic and viscous properties, such as with a spring and fluid damper. 
In addition, variables for determining the subject's postural activity 
other than those described in the preferred embodiments can be used. For 
example, either one or both of the anteroposterior and side to side 
lateral changes in orientation of the body can be measured with a 
potentiometer linked to the body with a belt and flexible coupling. 
Postural activity can also be determined by measuing the electromyographic 
activity of one or more muscles providing postural support, using surface 
electrodes and high gain differential amplification.