Estimating Noise-Induced Permanent Threshold Shift from Audiometric Shape: The ISO-1999 Model

In Brief Objective: To describe the relation between audiometric shape and noise-induced permanent threshold shift averaged across the speech frequencies (N5123). Design: Using an international standard (ISO-1999), 270 audiograms were created, representing both sexes and a variety of ages, exposure levels, and percentiles. Bulge depth (BD) was defined as the difference between pure-tone average for 2, 3, and 4 kHz and PTA for 1 and 6 kHz. Results: N5123 was well-predicted by quadratic functions of BD, which accounted for 72 to 95% of the variance in N5123. Conclusions: Estimates of N5123, based on BD, can be helpful in medical-legal diagnosis and allocation of hearing loss. In middle age, the classic 4 kHz notch of noise-induced hearing loss may be effaced by the addition of agerelated threshold shifts. Often, the notch is replaced by a “bulge,” the depth of which might provide a clue for diagnosis as well as an estimate of the magnitude of the contribution of noise to the individual's hearing loss. The objective of this study was to describe the relationship between audiometric shape and noise-induced permanent threshold shift averaged across the speech frequencies (N5123). Using an international standard (ISO-1999), 270 audiograms were created, representing both sexes and a variety of ages, exposure levels, and percentiles. Bulge depth (BD) was defined as the difference between pure tone average (PTA) for 2, 3, and 4 kHz and PTA for 1 and 6 kHz. N5123 was well-predicted by quadratic functions of BD, which accounted for 72 - 95% of the variance in N5123. Estimates of N5123 based on BD can be helpful in medical-legal diagnosis and allocation of hearing loss.