[Saturation of middle ear reflexes in occupational hearing loss]

In the ENT department of the Factory Institute of National Health of the uranium industry in Príbram a group of 196 men (392 ears) was examined who worked exposed to the risk of noise in different occupations, mostly as miners in the uranium mines. The noise exposure was 17.5 +/- 6.5 years, age 60.2 +/- 11.7 years, the total percentage hearing loss (calculated according to Fowler) 54.7 +/- 21.1%. The group was formed by 144 men who were examined during a preventive follow-up examination, 52 men where hypacusia was evaluated as an occupational disease. The examination of all patients was supplemented by a record of middle-ear reflexes induced by contralateral stimulation at frequencies of 0.5 kHz, 1 kHz, 2 kHz and 4 kHz and by white noise (WN). The regression equation y = 50.54-0.044X (y = percentage hearing loss per ear, x = noise exposure in years) was calculated from data of the group subjected to the preventive follow up examination and made it possible to divide the group into sub-groups, sensitive and resistant to noise. The group of occupational hypacusia comprised only sensitive subjects. The authors tested the frequency and thresholds of middle ear reflexes at different frequencies and WN, the frequency and thresholds of saturation of reflexes separately in groups sensitive and resistant to noise. It was not possible to draw conclusions from the results which would permit a forecast of the individual development of occupational hypacusia as regards early evaluation of sensitivity or resistance to noise.