230 Singh et al Indian J Physiol Pharmacol 2004; 48(2) Indian J Physiol Pharmacol 2004; 48 (2) : 230–234 EFFECT OF HIGH ALTITUDE ON HUMAN AUDITORY BRAINSTEM RESPONSES S. B. SINGH*, L. THAKUR, J. P. ANAND, DEEPAK YADAV, AMITABH, P. K. BANERJEE AND W. SELVAMURTHY Defence Institute of Physiology, And Allied Sciences (DIPAS), Lucknow Road, Timarpur, Delhi – 110 054 ( Received on June 17, 2003 Received on June 17, 2003 Received on June 17, 2003 Received on June 17, 2003 Received on June 17, 2003 ) Abstract : Abstract : Abstract : Abstract : Abstract : The effect of hypobaric hypoxia on Brain Stem Auditory evoked potentials (BAERs) were studied. BAERs were recorded in 30 volunteers at sea level (SL) and then at high altitude (HA) of 3200 m (HA I) and 4300 m (HA II) in Eastern Himalayas and on return to sea level (RSL). The BAERs were recorded using Nicolet Compact – 4 (USA) in response to monaural auditory stimuli consisting of clicks of 100 μs square pulse at a rate of 15/sec. The BAERs were recorded on day 4 of their stay at 3200 m and 4300 m respectively. Findings indicated an increase in absolute peak latencies of wave V at 3200 m, which was statistically significant. On further ascent to 4300 m there was an increase in absolute peak latencies of wave I and III indicating delay in sensory conduction at the medullo-pontine auditory pathways. Key words : Key words : Key words : Key words : Key words : auditory evoked potential high altitude absolute peak latency interpeak latency * Corresponding Author INTRODUCTION Earlier we have reported that high altitude stress causes delay in peak latencies of wave I of Brain Stem Auditory Evoked Responses (BAERs) recording during the first week of induction to HA which normalized during further stay at HA (1). In these studies the Brainstem Auditory Evoked Responses were recorded at 3500 m in the Western Himalayas where the subjects stayed for 3 weeks. In the present study, the subjects were inducted to high altitudes in Eastern Himalayas for a total duration of two weeks. The Brainstem auditory evoked potentials were recorded at two altitudes i.e. 3200 m and 4300 m in an ascending order to see the effect of increasing altitude on BAERs. METHODS The study was carried out on 30 healthy male volunteers, between the ages of 21–32 years. All subjects were informed about the nature of experiments. They had never been