Abstract: Auditory functions were studied in ten subjects before, during, and after a 90-day stay in a closed environment and exposure to the following factors:noise, 85-109 dBA (working area) and 70 dBA (living area), temperature, 27-33C (working area) and 25C (living area), relative humidity 55-60%, confinement, mental strain and trace of some atmospheric components (CO₂,CO, NO₂ etc.). Pure tone audiograms (both AC and BC), threshold of frequency modulation detection, poststimulation fatigue, threshold of intelligibility, and maximum discrimination score were measured to assess the functional state of the auditory system.
TTS of the subjects reached their maximum stationary levels in the early period of exposure (15-30 days). Complete recovery of hearing thresholds occurred on the 15th day after exposure.
The AC curves were close to the BC curves in all conditions. Maximum TTS (20-40 dB) appeared in the frequency range from 1000 to 4000 Hz, which was also the dominant frequency range in the spectrum of the environmental noise. The maximum discrimination score was reduced by 10% and the threshold of intelligibility was increased by 7 dB at the end of the 90-day exposure. Post-stimulation fatigue test showed that auditory fatigue lasted for more than 15 days after termination of experimental exposure, although recovery of hearing threshold had been completed earlier. The threshold of frequency modulation detection rose statistically significantly during the period of 60-90 days, indicating that fatigue in the central nervous system developed and accmulated during the later period of exposure. The relationship between the auditory functions and the enviromental factors, including noise, was also discussed in this paper.