ROLE OF HYPERBARIC OXYGEN AND HIGH CONCENTRATION OXYGEN IN PREVENTION AND TREATMENT OF NOISE-INDUCED HEARING DAMAGE

Guinea pigs weighing 280-480 gm were randomly divided into four groups: 1. normal control, 2. noise-exposed （1/3 octave-band noise centered at 1000 Hz, 126 or 136 dB SPL, 1 hour duration）, 3. 2atm oxygen-treated （2 hours duration including 30 minutes compression and 30 minutes decompression） either before exposure （prophylactic group） or after exposure （treatment group） to a. 136 dB SPL noise, 4. latm oxygen-treated （ 2 hours duration） before exposure or/and after exposure to a 136 dB SPL noise. Experimental results were as follows:
1. A 25 dB average permanent click threshold shift in guinea pigs was found when measured 480 hours after exposure to a noise of 136 dB SPL. Pre-exposure （to the same noise level） inhalation of oxygen at 2atm, however, prevented this kind of permanent threshold shift.
2. One period of pre-exposure （to 136 dB SPL noise） inhalation of pure oxygen at 2atm had the same effect as 6 periods of postexposure inhalation in reducing hearing threshold shift. Hearing threshold shift measured 72 hours after exposure for animals exposed to 136 dB SPL noise and oxygen-treated by either one period of pre-expasure or 6 periods of postexposure inhalation of oxygen at 2atm equaled that for animals exposed to 126 dBSPL noise without oxygen treatment. Thus, the effect of breathing oxygen at 2 atm corresponded to reducing the noise level by 10 dB （i.e. from 136 to 126 dB）.
3. So far as the effect of reducing noise-induced hearing damage is concerned prevention and treatment inhalation of pure oxygen at 2atm is much better than at latm; pre-exposure inhalation is better than postexposure one if guinea pigs inhale pure oxygen at 2atm both before and after noise exposure, the effect will be even more noticeable.