AIR-CONDUCTION AND BONE-CONDUCTION REFERENCE THRESHOLD LEVELS: A MULTICENTER STUDY

Abstract

Objectives: Air-conduction (AC) and bone conduction (BC) thresholds were measured to evaluate standard reference threshold values and recommend revisions to the audiometer standards. Design: AC and BC thresholds were measured from listeners with normal hearing (NH) and sensorineural hearing loss (SNHL) at three sites with recently calibrated audiometers. Study Sample: NH participants (n = 53) were selected based on age (18 to 25 years), normal AC thresholds, tympanometry and otoscopy, and absence of otologic disease. SNHL participants (n = 49) were selected based on AC thresholds, tympanometry and otoscopy, and absence of otologic disease. Results: AC thresholds obtained from NH listeners with the Radioear DD450 earphone averaged 3.7 dB HL. Air bone gaps (ABGs) occurred in NH and SNHL listeners above 2000 Hz and SNHL listeners at 250 Hz. ABGs were larger in SNHL listeners than NH listeners. Conclusions: Small corrections to the standard circumaural earphone RETSPLs are recommended for use with the DD450 earphone. The causes of ABGs in listeners without conductive pathology are discussed. False ABGs place patients at risk for unnecessary medical and surgical intervention. Reference threshold levels are recommended that will achieve two objectives: 1) AC thresholds from young NH listeners should average 0 dB HL; 2) ABGs from listeners with normal middle-ear function should average 0 dB.