CAN THRESHOLD SHIFT MEASUREMENTS AT A SINGLE FREQUENCY RELIABLY CAPTURE THE MAIN PHYSIOLOGICAL RESPONSES OF THE HEARING TO OCCUPATIONAL NOISE EXPOSURES?

摘要

Temporary threshold shifts after noise exposures are typically measured at only one frequency within the highest sensitivity of the hearing. However, it is not clear, whether the main physiological responses of the hearing to occupational noise can be captured reliably at this single frequency. Therefore, in a cross-over test design, 10 subjects (Ss) were exposed to continuous noise (94 dB (A) for 1 h) and to two impulse noises (9000 energy-equivalent 5-ms impulses at a level of 113 dB and to an identical number of 2.5-ms impulses). For all Ss and exposures, substantially weaker responses were measured at the lower and upper neighboring frequencies than at the main frequency. On average, for the adjacent frequencies, the total physiological costs which the hearing must "pay" for the continuous noise were merely around 25 % of those at the main frequency. The impulse noise exposures caused physiological costs at the adjacent frequencies which amounted to less than 20 % or even 10 % (5-ms and 2.5-ms impulses). The results which reflect the specific excitation of the basilar membrane in the inner ear seem to prove that the main responses of the hearing to a large variety of sound exposures can be captured by a single frequency.