Abstract
Thirty patients undergoing open heart surgery under induced hypothermia had transient evoked otoacoustic emissions (TEOAE) recorded during cooling to 26.07°C (standard deviation (SD) 4.25°C) vesically measured temperature and 24.86°C (SD 4.7°C) nasopharyngeally measured temperature respectively. Subsequently the patients were rewarmed until normal body temperature was reached again. There was a clear influence of body temperature on the amplitudes and reproducibilities of the TEOAE. The relationship of temperature and amplitude or reproducibility during the cooling phase was significantly different from that during rewarming. No TEOAE were measurable during cooling at a mean temperature lower than 33.41°C (SD 2.04°C) vesical temperature and 30.16°C (SD 3.0°C) nasopharyngeal temperature respectively. During rewarming the echoes became recognizable again at a mean temperature of 28.75°C (SD 3.38°C) vesical temperature and 27.49°C (SD 2.99°C) nasopharyngeal temperature. These results suggest a hysteresis in the relationship between the amplitude of TEOAE and temperature, similar to the well-established relationship between evoked potentials and temperature.