11-5. Effects of ear-canal pressurization on middle-ear responses for bone and air conduction*
Kenji Homma(1), Yoshitaka Shimizu(3,4), Namkeun Kim(2), Yu Du(1), Sunil Puria(2,3,4)
Affiliation: 1) Adaptive Technologies, Inc. 2020 Kraft Dr., Suite 3040, Blacksburg, VA 24060 ; 2) Department of Mechanical Engineering, Stanford University, Stanford CA 94305; 3) Department of Otolaryngology-HNS, Stanford University, CA 94305; 4) Palo Alto Veterans Administration, Palo Alto, CA 94305
Background: In extremely loud noise environments, it is important to protect one’s hearing against noise transmitted not only through air conduction (AC) but also through bone conduction (BC) pathways. The main peak of BC noise transmission spectrum is around 1.5 - 2 kHz, which is believed to be associated with the middle ear. One potential approach in mitigating this is to use ear-canal pressurization, which is known to reduce BC as well as AC hearing sensitivity. Materials and Methods: Umbo and stapes velocities were measured using human cadaver temporal bones in response to both shaker excitation (BC) as well as ear-canal acoustic pressure (AC) at multiple levels of ear-canal static pressure ranging between ±400 mmH2O. A finite element (FE) model of a human middle ear was also used to analyze the measured data. Results: Measurement shows up to 7-8 dB of mean BC response suppression for both umbo and stapes velocities mainly around 1-2 kHz for 400 mmH2O of static pressure. Results indicate that this is caused by the shifting of the middle-ear resonances, which are nominally in 1-2 kHz, into high frequencies. The BC responses appear to be suppressed more in negative pressure than in positive pressure. The FE analysis suggests that this may be attributable to a difference in the distribution of stiffening among the middle-ear components depending on the direction of pressurization. Conclusion: Middle-ear BC responses in the critical mid-frequency range of 1-2 kHz are significantly reduced by the ear-canal pressurization, mainly through the suppression of the middle-ear resonance effect. The present temporal bone measurement data are largely consistent with the psycho-acoustical data from the literature. Funding Source: Air Force Office of Scientific Research (AFOSR) under a STTR funding (contract No: FA9550-07-C-0088).
Total time: 20 minutes
Comments
11-5
Dear Dr. Homma,
the phenomenon of loudness decrease of b.c. sound with a change of ear canal pressure has been known since many decades and it is still used clinically by some otologists as the "Gellé-test" for diagnosis of a stapedial ankylosis.