Abstract
The cortical auditory evoked responses (AER), recorded at the skull vertex were studied in 56 experiments using 29 healthy subjects with normal breathing and during the following altered respiratory conditions: hyperventilation, hypoxia, asphyxia, and hypercapnia. All four conditions approached the limits of physiological tolerance. Since such conditions can occur in aircrew when exposed to malfunction of the aircraft oxygen regulation system or during other emergencies in flight, it was of interest to know, therefore, which of these conditions might impair hearing perception. Under the assumption that AER latency changes correlate with hearing impairment (or raise in auditory threshold), it can be concluded that only those respiratory changes, which include a raised end-tidal Pco2> are effective in this regard, for these conditions caused significant latency increase of all the auditory evoked response components (Px, N,, P2 and N2). These conditions involve asphyxia and hypercapnia. With hypercapnia, a positive significant correlation was found between the relative Pco2 increase and the relative latency increase. The possible implications of these findings to aircrew safety are apparent.
