[Circadian variation in the latency of auditory brainstem response]

The auditory brainstem response (ABR) has been found to reflect many pathological conditions within the auditory system and brainstem. And now, many neurosurgeons are using it to monitor the integrity of the auditory pathway during neurosurgical procedures. It is said that ABR shows little variation from person to person or laboratory to laboratory, nor is it easily affected by anesthesia, level of consciousness, fluctuation of blood pressure or hypoxemia. On the other hand, previous studies have shown that component waves of the ABR increase in latency and decrease in amplitude with lowered temperature. We reported here that naturally occurring circadian variations in body temperature were correlated with similar changes in the latency of the ABR. Tympanic temperature (Tty), deep forehead temperature (Thd) and ABR were recorded every 3 hours during a 24-hour period for a total of 8 recording sessions from each of 6 healthy persons (2 males and 4 females, mean age 24.3 years). The subjects were free to come and go during the day but slept overnight in the laboratory. All subjects had circadian variations in each temperature on the order of one degree. Thd had a tendency to fluctuate and its range of difference from Tty was -0.5-0.4 degree C. There was a more significant negative correlation between the latency of the ABR and Tty than that of Thd. It has become apparent that ABR latency is affected by small temperature changes such as circadian variation. The rate of a latency change in the ABR was 0.15msec per degree (C).(ABSTRACT TRUNCATED AT 250 WORDS)