Characteristics of Distortion‐Product Otoacoustic Emissions Level Decrease at High Altitude

Abstract

Objective: 1) Understand the characteristics of Distortion-Product Otoacoustic Emissions (DPOAE) level decrease during ascent to high altitudes. 2) Learn whether DPOAE might provide information about the state of acclimatization and the risk of acute mountain sickness (AMS). Method: From March 12, 2006, until April 23, 2006, DPOAE (f2 = 1, 1.5, 2, 3, and 4kHz), blood oxygen saturation (SaO2), and the Lake Louise score (LLS) to assess AMS were measured in 187 trekking tourists on the Mt Everest trek in Nepal at 2610 m and 5170 m. Results: Mean DPOAE level decrease at 5170 m compared with 2610 m was -5.1dB (1kHz), -3.7dB (1.5kHz), -4.0dB (2kHz), -4.6dB (3kHz) and -3.7dB (4kHz). Mean SaO2 was 94.8% at 2610 m and 79.0% at 5170 m. The LLS indicates AMS when >2. While at 2610 m none of the study subjects had AMS (mean LLS 0.04), and at 5170 m 82 (43.9%) had AMS (mean LLS 2.8). Low SaO2 correlated with high LLS. Conclusion: DPOAE levels decrease during ascent to high altitudes across all frequencies. This phenomenon might be due to cochlear hypoxia. While low SaO2 seems to indicate an increased risk of AMS, a decrease of DPOAE levels is not correlated with AMS.