The influence of hypothermia on outer hair cells of the cochlea and its efferents

Abstract

Transient evoked otoacoustic emissions (TEOAE) were recorded in 21 guinea-pigs undergoing hypothermia. The minimal average body temperature during cooling was 26 degrees C/24.9 degrees C measured orally or rectally, respectively. The animals were subsequently warmed to normal body temperature. A clear influence of body temperature on TEOAE could be documented. During cooling the amplitude and reproducibilities decreased, disappearing completely at a mean temperature below 28.5 degrees C (oral) and 27.3 degrees C (rectal). The emissions reappeared during rewarming at a mean temperature of 30.1 degrees C (oral) and 30.8 degrees C (rectal). Contralateral auditory stimulation (CAS) led to a decrease of the amplitudes of TEOAE during cooling down to a mean of 33 degrees C/32 degrees C (oral/rectal temperature). During rewarming, influences of the CAS could be recognized, again at an oral temperature above 35 degrees C. The changes to the TEOAE observed in these experiments suggest that hypothermia affects not only the outer hair cells (OHC) of the cochlea but also the efferent supply to the cochlea.

Estudo das emissões otoacústicas por produto de distorção durante a hipotermia em humanos

“…During anesthesia, they reported mild alterations mainly when nitrous oxide was being administered. Seifert et al 12 , however, did not find general anesthesia to have affected the recording of evoked transient OAEs. In our study there was no detected impact of general anesthesia without nitrous oxide on the recording of DPOAEs when comparing the PRE vs. ANESTHESIA data series.…”

“…Seifert et al 12 measured middle ear SPL during evoked transient OAE acquisition under hypothermia. Evoked transient OAEs disappeared at bodily temperatures of approximately 30ºC and middle ear SPL of -177 dPa.…”

“…Such impact, however, inhibits OHC contraction as activity in the olivocochlear pathway is increased in the CNS 12,16 . Thus, we do not believe that diminished CNS activity during hypothermia42 and reduced OHC inhibition by the medial olivocochlear system can account for DPOAE amplitude decrease.…”

“…According to Seifert et al 12 , the OHC contraction mechanism that leads to OAE does not energetically depend on adenosine triphosphate, but on the energy coming from the endocochlear potential. EP changes during hypothermia 44 may be responsible for their decrease.…”

“…Could DPOAE, as it mimics OHC, be utilized to monitor such risk? It has been established in the literature that hypothermia impacts cochlear potential, spontaneous OAE and evoked transients, both in animal and human models [6][7][8][9][10][11][12] . However, there are no reports on altered DPOAE test results during hypothermia in humans.…”