SATURATION DIVING WITH HELIOX TO 350 METERS - OBSERVATION ON HEARING THRESHOLD, BRAIN-STEM EVOKED-RESPONSE AND ACOUSTIC-IMPEDANCE

Four divers were compressed to 350 m to observe changes in hearing thr eshold, brainstem evoked response and acoustic impedance. The divers e xperienced no tinnitus, impairment of hearing, earache during compress ion. Examination showed Mat me threshold of lower frequency range of h earing was elevated because of the masking effect of Me noise in Me hy perbaric chamber. Changes in waveform and latency of brainstem evoked response were due to changes in sound wave transmission affected by th e chamber pressure and a poor ratio of signal to noise in the hyperbar ic environment with heliox. All these changes were transient. After le aving the chamber, the hearing threshold and brainstem evoked response returned to normal. Besides, there were no changes in tympanogram, ac oustic compliance and stapedius reflex before and after diving. This i ndicated the designed speed of compression and decompression in the ex periment caused no damage to the divers' acoustic system, and the func tions of their Eustachain tubes, middle and inner ears were normal dur ing the diving test.