Background and Objectives: It is well known that hearing loss can occur by the decreased cochlear blood flow. Because lactate is known to accumulate when there is ischemia in the tissue, we designed this study to analyze the effect of lactate delivered to the inner ear on the hearing threshold measured by the auditory brainstem response(ABR).
Materials and Method: We used 22 guinea pigs (GPs) with normal Preyer’s reflex, and used 6 GPs (12 ears) to investigate the effect of lactate concentration on the change of hearing threshold and used 6 GPs (12 ears) to investigate the effect of osmolarity on the change of hearing threshold. We determined the concentration of lactate to exclude the effect of osmolarity on the change of hearing threshold. Ten GPs were divided into a control group(n=5, 10 ears) and a study group (n=5, 10 ears). The mastoid cavity was opened to expose the round, and then HBSS buffer (300 mOsm) was applied on the round window. Hearing threshold was measured by ABR after application of 10mM lactate and buffer solution as control.
Results: In the control group, the initial hearing threshold was 29.5 dB±3.6 dB (mean±SD) and changed to 33.5 dB±4.7 dB when buffer was applied to the round window. It changed to 33.0 dB±4.2 dB 1 hour after applying the buffer, and 37.5dB±3.5 dB 4 hour later. In the study group, the initial hearing threshold was 27.0 dB±5.8 dB. The thresholds right after the buffer was applied to the round window, one hour and four hour later were 32.5 dB±4.8 dB, 48.0 dB±4.2 dB, and 54.5dB±5.9dB, respectively. There were significant statistical differences between the two groups with regard to the threshold after 1 hour and 4 hours (p<0.05).
Conclusion: We could observe the elevation of hearing threshold after applying lactate on the round window of guinea pigs. Through these findings, we can draw the conclusion that lactate may be one of the factors raising the hearing threshold by tissue ischemia.
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