Effect of mild hypothermia on the ischemic inner ear damage

DOI 18 References
  • Takeda Shoichiro
    Department of Otolaryngology, Ehime University School of Medicine
  • Hakuba Nobuhiro
    Department of Otolaryngology, Osaka Red Cross Hospital
  • Hyodo Jun
    Department of Otolaryngology, Ehime University School of Medicine
  • Hato Naohito
    Department of Otolaryngology, Ehime University School of Medicine
  • Gyo Kiyofumi
    Department of Otolaryngology, Ehime University School of Medicine

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Other Title
  • 低体温による虚血性内耳障害の防御: 低体温のタイミングと蝸牛内NOx濃度

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Abstract

Mild hypothermia is effective in preventing ischemic damage to the cochlea when applied during an ischemic insult; however, the effects of post-ischemic hypothermia remain unclear. This study addressed this issue by performing hypothermia at three different times in an animal model of transient cochlear ischemia. Furthermore, the effects of hypothermia on the concentrations of oxidative NO metabolites in the scala tympani were investigated.<BR>Adult male Mongolian gerbils were divided into three groups (each n=8) based on the timing of the start and end of hypothermia (32 °C) after reperfusion: 1-4, 3-6, and 6-9 hrs. Some animals were subjected to normothermia (n=8) or sham-operation plus hypothermia of 1-4 hrs. (n=4). Transient cochlear ischemia was induced by occluding both vertebral arteries at the neck for 15 min. Mild post- ischemic hypothermia was effective in attenuating the increase in the auditory brainstem response (ABR) threshold at 8 kHz and the loss of hair cells, when applied within 3 hrs. after reperfusion. The effects were more prominent with an earlier application of hypothermia. By contrast, no such attenuating effects were observed in the 6-9 hrs., normothermic group.<BR>Oxidative NO metabolites were measured by titrating the nitrite (NO2-) and nitrate (NO3-) concentrations in the perilymph on the day following ischemia using in vivo microdialysis and an on-line high-performance liquid chromatography (HPLC) system. In this study, the animals were allotted to no-treatment (n=2), normothermia (n=5), sham-operation plus hypothermia (n=2), and three hypothermia groups (each n=5): 1-4, 3-6, and 6-9 hrs. Significant increases in the perilymph NO2- and NO3- concentrations were found in the normothermia group, while hypothermia prevented the increase. The earlier the hypothermia was applied, the more the increase was attenuated.

Journal

  • Otology Japan

    Otology Japan 19 (2), 123-130, 2009

    Japan Otological Society

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