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With the aim of investigating the capability of otoacoustic emission (OAE) in the detection of low levels of noise-induced hearing loss, audiometric and otoacoustic data of young workers (age: 18-35) exposed to different levels of industrial noise have been recorded. These subjects are participating in a long-term longitudinal study, in which audiometric, exposure (both professional and extra-professional), and OAE data (transient evoked and distortion product) will be collected for a period of several years. All measurements have been performed, during routine occupational health surveillance, with a standard clinical apparatus and acquisition procedure, which can be easily used in the occupational safety practice. The first study was focused on the correlation between transient evoked OAE signal-to-noise ratio and distortion product (DPOAE) OAE level and the audiometric threshold, investigating the causes of the rather large intersubject variability of the OAE levels. The data analysis has shown that, if both OAE data and audiometric data are averaged over a sufficiently large bandwidth, the correlation between DPOAE levels and audiometric hearing threshold is sufficient to design OAE-based diagnostic tests with good sensitivity and specificity also in a very mild hearing loss range, between 10 and 20 dB.

Objectives: To assess the amplification and distortion of noise in incubators by measuring noise levels from various sources under various conditions. Study Design: We recorded sound pressure levels (SPL) of background noise, baby crying, alarms and porthole closing with the incubator hood open or closed. Then we tried to reduce the sound level in the incubator by applying a sound absorbing panel to the ceiling of the hood. Results: The sound sources analysed produced very high SPL. In free field baby crying and porthole noise were, respectively, 81–83 dB and 70–71 dB, closing the hood they raised to 84–87 and 73–74 dB: this means that the noise perceived by a baby in the incubator had twice the SPL of the same noise emitted in a free field; alarm noise was 56–57 dB inside incubators. Sound emitted inside the hood was also distorted, i.e. it had different features from the same source in a free field. The insulating panel prevented amplification and distortion due to the hood and reduced the SPL of alarms. Only background noise did not decrease with the panel. Sound absorbing panel reduced baby’s crying, porthole noise and alarm noise SPL to 82–85, 70–71 and 50–51 dB, respectively. Conclusions: Incubators are reverberating environments, which amplify the baby’s cry and other noises produced inside the hood. The frequency components of noises are altered by the hood. The sound absorbing panel reduced this phenomenon.

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