Учебники / Middle Ear Mechanics in Research and Otology Huber 2006

noise, the pitch ranging from 82 to 134 Hz. When the ear canal was occluded by inserting the index finger, loudness of the induced sound was 17.2±4.5dB. When the ear canal was filled with water, it was 9.4±2.2dB. In contrast, such sound was not heard when wearing an AC receiver.

3. E ect of Wearing an Air Conduction Receiver on Tinnitus Matching Test

3.1 Materials and methods

This study was undergone by 25 patients su ering from unilateral tinnitus. Original diseases were chronic otitis media in 12 cases, unknown sensorineural hearing loss in 10 cases, tinnitus without hearing loss in 2 cases and sudden deafness in 1 case. Pitch and loudness matching were done by presenting a comparative sound to the uninvolved ear, with or without wearing an AC receiver on the involved ear. Comparative sounds were adjusted by 1/2 octave step in pitch matching, and by 5 dB step in loudness balancing.

3.2 Results

Pitch of the tinnitus was di erently perceived when wearing a receiver in 9 of 25 patients (36%), while that of loudness in 15 patients (60%). As shown inFig.1,loudnessoftinnitusmaybeoverestimatedwhentestedbywearing an AC receiver on the involved ear.

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Fig. 1 E ects of wearing an air conduction (AC) receiver on tinnitus matching test. By wearing an AC receiver, loudness of tinnitus became louder in 12 of 25 ears, while pitch remained unchanged in many cases.

4. Loudness of a Sound in the Ear Canal Radiated by Bone Conduction Sound

4.1 Materials and methods

Twenty-twoearsof11normalvolunteerswerethesubjectsofthisstudy.An electret type microphone (Rion AD-02) was placed deep in the ear canal. It was hooked up to a B&K type 2113 amplifier. Test sound was applied via a bone conduction receiver placed on the forehead. The receiver was activated by Rion AA-70 audiometer. Stimulus sound was set to be maximum at each test frequency in order to improve S/N of the emitted sound.

4.2 Results

Fig. 2 shows a sound pressure recorded in the ear canal with and without wearing an AC receiver, when a BC receiver is activated at the maximum output level. Fig. 3 summarizes the changes in sound pressure by wearing an AC receiver. Ear canal sound became larger by wearing an AC receiver by 17.9±4.9dB at 0.8 kHz, although it decreased at 2–4 kHz.

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Fig. 2 Sound pressures recorded in the ear canal during bone conduction (BC) test withand withoutwearingACreceiver.Stimulussoundwassetto be maximumateach test frequency in order to improve S/N of the emitted sound. BC sound pressures are shown in brackets.

Fig. 3 Increment of the ear canal sound pressure by wearing an AC receiver. The increment was calculated by subtracting the data without the stimuli from those with the stimuli. Ear canal sound became larger by wearing an air-conduction receiver at 0.8 kHz, although it decreased at 2–4 kHz.

5. Discussion

Low tone sound induced by occlusion of the ear canal is supposed to be a mixture of various vital sounds such as vascular pulsation, bruit, respiratory noise, vibration of the mucosal villi, etc. (Fig 4). As shown in the present study,natureofthesoundwasclosetoaroaringtinnitusresembling125Hz band pass noise. This may indicate that a spontaneous oto-acoustic emission(OAE)doesnotcontributetothisphenomenon,sincethepitchofOAE ranges between 1 and 2 kHz [3]. Occlusion-induced sound is rather similar to a tinnitus noticed in a sound-proof room which is normally heard in

very quiet circumstances. According to Asakuma et al. [4], such tinnitus is 91 originated from a vital sound in the middle ear, since it is not blocked by intravenous administration of lidocaine that should reduce tinnitus of the inner ear origin.

Fig. 4 Origin of a sound induced by occlusion of the ear canal.

Wearing an AC receiver did not induce any sound in all the subjects, probably due to insu cient occlusion of the ear canal. As the sound in the ear canal increased at most 10 dB below 125 Hz by wearing the receiver, we are not aware of such a small change of sound. This phenomenon may modify the results of audiological testing. In the present tinnitus test, loudness was estimated larger by wearing an AC receiver in almost half of the cases. This is probably due to the fact that an AC receiver not only blocked an environmental noise coming into the ear but also enhanced an intrinsic sound by a resonant e ect of the ear canal, thus interfering with the loudness of tinnitus.

Occlusion of the ear canal a ects variously on audiological testing.

92Therefore, careful attention should be paid in evaluating the results when measurement is undergone while wearing an AC receiver.

References

1.Gyo K., Nishihara S., Takeda K., Tinnitus induced by closure of the external ear canal. Practica Otologica 83 (1990) pp. 1009–1013

2.GyoK.,HirataY.,KobayashiT.,E ectsofwearingairconductionreceiveronsound pressure transmitted to external ear canal. Practica Otologica 85 (1992) pp. 1545– 1549

3.Zurek P.M., Spontaneous narrowband acoustic signals emitted by human ears. J Acoust Soc Am 69 (1981) pp. 514–523

4.Asakuma S., Hirashima K., Okada S., The mechanism of tinnitus in the normally hearing person. Otologia Fukuoka 31 (1985) pp. 1–6

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ESTIMATION OF STAPES PISTON MOTION WITH UNI-DIRECTIONAL MEASUREMENTS IS PRONE

TO ERROR

W.F. Decraemer, S.M. Khanna, O. de La Rochefoucauld, W. Dong, J.J.J. Dirckx, E.S. Olson

Univ. of Antwerp, Biomed. Physics, 177 Groenenborgerlaan, B 2020, Antwerp, Belgium; Columbia Univ., Dept. of OTO / HNS, 630 West 168th St., New York, NY 10032, USA

Keywords: stapes, 3-D motion, piston axis component, uniaxial interferometer

In most experiments, access for direct measurement of stapes motion in line with the piston axis is not available and piston motion is estimated from single component interferometric measurements done under observation directions that make angles up to 60° with the piston axis. We measured the vibration velocity of the stapes in human and gerbil from di erent observation angles and calculated the complete set of 3-D motioncomponents.Weexpressedthecomponentsinanintrinsicreferencesystemand could foretell the motion component to be recorded with a single axis interferometer at an angle with the piston axis. A cosine factor provides a good correction for the axis o set only for low frequencies (f<1.5kHz) in human; at higher frequencies and for gerbil at all frequencies the piston component cannot be accurately estimated from a single o -axis observation and a cosine correction.

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1. Introduction

The vibration of the footplate produces the pressure wave in the cochlea that stimulates the sensory cells. We have shown that the vibration of the stapes in human, cat and gerbil exhibits all 3-D components of translation and rotation [1] and that mode changes occur with frequency. It is the piston component – we have good evidence that non-piston components do notcontributetothesignaltransmissionpath[2]–thatisusedinnearlyall studies to specify the input to the inner ear.

In most experiments access for measurement of stapes motion in-line with the piston axis is not available, and piston motion is estimated from

Wemeasuredthe vibrationvelocity[11,12]ofthestapesforpuretone from di erent observation angles with a heterodyne microscope/interferometer [13] and calculated the 3-D rigid body global translation and rotation for a frequency range covering the entire frequency range of the species under study.

Based on a micro CT scan of the experimental ear, a 3-D model of the stapes was made and registered in its experimental position (Fig. 1).

We determined a coordinate transform to bring the model in an intrinsic frame and used it to express the motion components in the same frame (Fig. 2): piston motion is translation along the y-axis, while tilting about the short and long axis of the footplate are rotation about the x and z axis, respectively.

b Y

1obs

O

X

Z

Fig.2aModelofagerbilstapesbroughtinanintrinsicreferencesystem.Pistonmotion is now along the y-axis.

Fig. 2b Angles specifying the observation direction for a stapes in an intrinsic frame.

The displacement vector of any point can readily be calculated (displace- 96 ments are so small we may treat them as di erentials)

WhenthemotionofthepointPi isobservedwithauniaxialmeasuringsystem with observation direction along 1obs, one records the following component

We specify the observation direction by angles α (between x-axis and the

projection of 1obs in the x,z plane) and β (between the y-axis and 1obs ) as seen on Fig. 2b.

3. Results with Discussion and Conclusions

3.1 Displacement path for 3 points on the human stapes

For the human temporal bone we determined the 3-D rigid body velocities normalized for ear canal pressure, dst(t) and Θ(t), and using Eq. (1) we calculated the displacement during a cycle for points on the posterior crus,anteriorcrusandfootplatecenterforafrequencyof190Hz.Thepaths are elliptical and shown, magnified by a factor of 18000, in front, top and sideways views (Fig. 3a). A thick dot marks the displacement at t=0, the smallerdotatt=T/4whichshowssenseofthepath.All3pointshavealarge piston component accompanied by some rocking about the long axis of the footplate.

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Fig. 3a Three orthogonal views of the displacement at three points of the human temporal bone Y83 at 190 Hz; displacements scaled up by 18000.