Effect of Short-Term Hypothermia on Cochlear Responses

Abstract

Hypothermia from 38°C to 20°C was induced in anesthetized guinea pigs. Cochlear microphonics (CM) and action potentials (N₁ and N₂) were recorded from first turn of the cochlea with differential electrodes. The latency of CM remained constant throughout the temperature drop of 18°C. This finding suggested that the mechanism which precedes the generation of CM is insensitive to impaired metabolism. The latency of action potentials, measured from beginning of CM to the negative peaks of N₁ and N₂, increased by 1.3 and 2.3 msec respectively. Both action potentials also showed changes in amplitude and shape which were comparable with those described for peripheral nerves. Threshold and amplitude of CM varied together. Losses of about 12 db and 8 db were observed consistently. These results were discussed on the basis of recent advances in the physiology of hearing. Reversibility of all these parameters lagged during warming, which suggested that cooling probably induced some transient alteration in the cell metabolism, so that the resetting of generators of cochlear potentials was slowed. Resistance of cochlear microphonics and neural components to asphyxia increased as temperature dropped. This observation indicated that the oxygen reserve in tissue and circulating blood was sufficient to prolong the survival of the generators of cochlear microphonics and neural components when their metabolic rate was reduced.