Effects of ear-canal pressurization on middle-ear bone- and air-conduction responses.
In extremely loud noise environments, it is important to not only protect one's hearing against noise transmitted through the air-conduction (AC) pathway, but also through the bone-conduction (BC) pathways. Much of the energy transmitted through the BC pathways is concentrated in the mid-frequency range around 1.5-2 kHz, which is likely due to the structural resonance of the middle ear. One potential approach for mitigating this mid-frequency BC noise transmission is to introduce a positive or negative static pressure in the ear canal, which is known to reduce BC as well as AC hearing sensitivity. In the present study, middle-ear ossicular velocities at the umbo and stapes were measured using human cadaver temporal bones in response to both BC and AC excitations, while static air pressures of +/-400 mm H(2)O were applied in the ear canal. For the maximum negative pressure of -400 mm H(2)O, mean BC stapes-velocity reductions of about 5-8 dB were observed in the frequency range from 0.8 to 2.5 kHz, with a peak reduction of 8.6(+/-4.7)dB at 1.6 kHz. Finite-element analysis indicates that the peak BC-response reduction tends to be in the mid-frequency range because the middle-ear BC resonance, which is typically around 1.5-2 kHz, is suppressed by the pressure-induced stiffening of the middle-ear structure. The measured data also show that the BC responses are reduced more for negative static pressures than for positive static pressures. This may be attributable to a difference in the distribution of the stiffening among the middle-ear components depending on the polarity of the static pressure. The characteristics of the BC-response reductions are found to be largely consistent with the available psychoacoustic data, and are therefore indicative of the relative importance of the middle-ear mechanism in BC hearing.
Homma
Kenji
K
Adaptive Technologies, Inc, 2020 Kraft Dr, Suite 3040, Blacksburg, VA 24060, USA. kenji@adaptivetechinc.com
Shimizu
Yoshitaka
Y
Kim
Namkeun
N
Du
Yu
Y
Puria
Sunil
S
D000161:Acoustic Stimulation; D000388:Air; D001844:Bone Conduction / Q000502:physiology*; D002102:Cadaver; D004424:Ear Canal / Q000502:physiology*; D004429:Ear Ossicles / Q000502:physiology; D004430:Ear Protective Devices; D004432:Ear, Middle / Q000502:physiology*; D020342:Finite Element Analysis; D006309:Hearing / Q000502:physiology*; D006317:Hearing Loss, Noise-Induced / Q000517:prevention & control; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D011312:Pressure; D011571:Psychoacoustics; D013701:Temporal Bone / Q000502:physiology