Detection of Early Noise-Induced Hearing Impairment in Pilots

Objective To detect early signs of noise-induced hearing loss(NIHL) in military pilots without hearing complaints. Methods Pure tone audiometry and acoustic reflex thresholds were tested in 36 military pilots (72 ears) with noise exposure history but no complaints of hearing loss. Conventional test frequencies (0.25-8 kHz) and extended high frequencies (EHF, 10 and 12.5 kHz) were included in audiometry. White noise and pure tones at 0.5, 1, 2, and 4 kHz were used for acoustic reflex tests. Twenty normal hearing subjects(40 ears) with no exposure to occupational noise were used as controls. Results Pure tone thresholds at all conventional frequencies and at EHFs were elevated in the pilots, with the maximum shift at 4 kHz, compared with controls (p < 0.01). The pilots also showed elevated ART to white noise and decreased differentials between white noise and pure tone ARTs (p< 0.01). Conclusion Early signs of NIHL are present in some symptom-free military pilots. High frequency hearing threshold shift, elevated white noise ART and decreased differential between white noise and pure tone ARTs may be objective indicators of early NIHL.