Can infrasound protect the cochlea from a damaging level of noise?
Lee-SC; Bohne-BA; Harding-GW; Salt-AN
Abstr 26th Midwinter Res Meet 2003 Feb; 22:164
Infrasounds (ie, < 20 Hz for humans; < 100 Hz for chinchillas) are not audible, but they produce large movements of cochlear fluids (Salt & DeMott, 1999). It was speculated that infrasound might bias the basilar membrane & perhaps minimize noise-induced hearing loss (NIHL). Chinchillas were simultaneously exposed to a 30 Hz tone at 100 dB SPL & a 4-kHz OBN at either 108 dB SPL for 1.75 h or 86 dB SPL for 24 h. One tympanic membrane (TM) was perforated prior to exposure to attenuate infrasound transmission to that cochlea. Controls were exposed to infrasound or the 4-kHz OBN only. ABR threshold shifts (TS) & DPOAE level shifts (LS) were determined post-TM-puncture & immediately post-exposure, just before cochlear fixation. The cochleae were dehydrated, embedded in plastic, dissected as flat preparations & evaluated for hair-cell (HC) losses. For each animal, the magnitude & pattern of functional & HC losses were compared between their right & left cochleae. The infrasound exposure alone resulted in a 10-20 dB TS below 1 kHz, no LS & no HC damage/loss. Exposure to the 4-kHz OBN alone at 108 dB produced a 50-60 dB TS for 1-16 kHz, a 40-50 dB LS for 2-12 kHz & severe OHC loss in the middle of the first turn. When infrasound was added, the functional and HC losses extended much farther apically & basally than for the 4-kHz OBN alone. Exposure to the 4-kHz OBN alone at 86 dB produced a 40 dB TS for 3- 12 kHz & 30 dB LS for 3-8 kHz, but no HC loss in the middle of the first turn. When infrasound was added, no differences in the functional and HC losses were found compared to the 4-kHz OBN alone. We hypothesize that exposure to infrasound & an intense 4-kHz OBN increases cochlear damage because the large fluid movements from infrasound cause more intermixing of cochlear fluids through the damaged reticular lamina. Simultaneous infrasound & a moderate 4- kHz OBN did not increase cochlear damage because the reticular lamina rarely breaks down during this exposure.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals; Cell-damage; Cellular-reactions; Animal-studies
Abstracts of the 26th Midwinter Research Meeting
Washington University, St. Louis