title: Distortion product of otoacoustic emissions as a sensitive indicator of hearing loss in pilots.
abstract: BACKGROUND
  When the ear is presented with two simultaneous pure tones, the cochlea produces intermodulation products called distortion product otoacoustic emissions (DP-OAEs). When cochlear function is affected by noise or ototoxic drugs, DP-OAEs decrease in amplitude or disappear. The aim of this study was to investigate whether DP-OAEs are a sensitive indicator of hearing loss in pilots, for whom flying time presumably correlates with exposure to steady noise.
  
  
  METHODS
  Subjects were 105 pilots, ages 25-44 yr, with flying times of 500-3500 hours. Pilots were divided into three groups according to their flying time and age-matched against control subjects (non-pilots) with normal hearing with no history of occupational exposure to noise. All subjects were tested by pure-tone audiometry, tympanometry, and measurement of DP-OAEs.
  
  
  RESULTS
  DP-OAEs were significantly different among the three pilot groups, decreasing gradually at 8 frequencies with flight time. For high frequency tones (F2 7966 and 5623 Hz), age and noise were cofactors. However, 11% of the pilots in this study showed resistance to noise-induced hearing loss.
  
  
  CONCLUSIONS
  DP-OAEs are a sensitive measure for monitoring early noise-induced hearing loss in pilots. Accumulating flight hours, presumed to involve steady noise exposure, initially affected high-frequency hearing, then progressed to affect middle and low frequency hearing with increased flight time. There is individual variability in susceptibility and resistance to noise-induced hearing loss in humans.
authors.affiliation: Audiology & Noise Laboratory, Institute of Aviation Medicine AF, Beijing, China. yange_zhang@hotmail.com
authors.forename: Yange
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xia
authors.initials: X
authors.lastname: Zhang
authors.forename: Wenfeng
authors.initials: W
authors.lastname: Zhu
authors.forename: Xuewen
authors.initials: X
authors.lastname: Zheng
authors.forename: Xiuping
authors.initials: X
authors.lastname: Deng
mesh_terms: D000158:Acoustic Impedance Tests; D000328:Adult; D001301:Audiometry, Pure-Tone; D001359:Aviation; D003051:Cochlea; D003937:Diagnosis, Differential; D004784:Environmental Monitoring / Q000379:methods*; D006317:Hearing Loss, Noise-Induced / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D008297:Male; D009784:Occupational Diseases; D017084:Otoacoustic Emissions, Spontaneous; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires; D000078329:Workforce