Vulnerability of the gerbil cochlea to sound exposure during reversible ischemia

Cochlear ischemia induces a sensorineural hearing loss, in part through a f ast functional impairment of outer hair cellls. Assuming that the cochlea i s rendered fragile during ischemia and reperfusion and that stimulation its elf can jeopardize its functional recovery, we used a model of reversible s elective cochlear ischemia in Mongolian gerbils to establish what type of s ound exposure call be deleterious during and immediately after reversible i schemia. Several groups of gerbils were used, with different ischemia durat ions and levels of sound exposure. Control groups were only exposed to tone s at 80 and 90 dB SPL during 30 min, while other groups underwent complete and fully reversible blockage of the labyrinthine artery, during 5.5 or 8 m in, and were exposed to 60 or SO dB SPL tones during 30 min. The amount of ischemia and reperfusion was measured by means of laser Doppler velocimetry , whereas outer hair cells' function was continuously monitored through dis tortion-product otoacoustic emissions (DPOAEs). The losses of DPOAE levels after 8 min transient ischemia and 60 dB SPL exposure were as large as thos e induced by 80 dB SPL exposures combined with 5.5 min ischemia, or 90 dB S PL exposures without ischemia, with a maximum loss around 25-30 dB, half an octave above the stimulus frequency. These results give evidence for an ex tremely high cochlear vulnerability to low-level sound exposure when associ ated with reversible ischemia. This vulnerability may have important clinic al consequences in patients with cochlear circulatory disturbances. (C) 199 9 Elsevier Science B.V. All rights reserved.