Effects of Altitude Hypoxia on Middle Latency Auditory Evoked Potentials in Humans

Background: This paper presents an investigation of auditory evoked responses in humans subjected to high altitude hypoxic conditions.

Methods: Middle latency (MLAEPs) as well as short latency (BAEPs) evoked potentials were recorded in 10 healthy subjects, first at sea level (N), then 24 h (H1) and 72 h (H3) after their arrival at an altitude of 4350 m. At the same time, arterial blood parameters (PaO2, PaCO2 and pH) were measured and the clinical status of the subjects was assessed.

Results: In altitude conditions, the amplitude of BAEP peak V decreased (-17%). The MLAEP waves showed variations in the shape of their latest waveforms. Their amplitudes, however, were not affected. The Pa-Nb interpeak latency significantly decreased (-2.2 ms) between N and H1, and remained stable during the stay at high altitude.

Conclusion: A correlation was found between the relative decrease of PaCO2 and the shortening of Nb wave latency, suggesting that the variations in MLAEPs could be preferentially related to the ventilatory response of the subjects in hypoxic conditions. However, no correlation was found between the clinical status of the subjects (Acute Mountain Sickness score) and the parameters of the waves.