Relationship between transducer type and low-frequency hearing loss for patients with ventilation tubes

To determine the relationship between the type of transducer used to perform pure-tone audiometry and the appearance of low-frequency hearing loss at 250Hz and 500Hz for patients with ventilation tubes.

Air conduction thresholds at 250Hz and 500Hz were measured using Telephonics TDH-49 supra-aural headphones and EARTONE 3-A insert earphones for patients with normal ears (N=16) and patients with ventilation tubes (N=114). Tympanometry was performed on each patient prior to audiometric testing. Audiometric test results obtained in normal ears were compared to results for patients with ventilation tubes. For analysis, the ventilation tube patients were separated into two groups, representative of ventilation tube type.

Audiometric results obtained using the two transducer types at 250Hz and 500Hz revealed significant differences in threshold for patients with ventilation tubes. Thresholds obtained using insert earphones were generally worse than thresholds obtained using supra-aural headphones for this group. On average, difference in threshold was 14.15dB worse with insert earphones at 250Hz and 9.75dB worse with insert earphones at 500Hz for patients with Sheehy tubes. Average difference in threshold for patients with Donaldson tubes was 13.93dB worse with insert earphones at 250Hz and 8.93dB worse with insert earphones at 500Hz. In addition, thresholds were more variable for patients with ventilation tubes than normal ears at 500Hz. There were no significant differences in threshold for normal ears using both transducers.

When performing pure-tone audiometry, choice of transducer can influence the accurate identification of a low-frequency hearing loss in patients with ventilation tubes. Low-frequency thresholds were generally worse using insert-style earphones to test subjects with tubes, resulting in the apparent identification of a hearing loss. However, with supra-aural headphones, no low-frequency hearing loss existed. There were no significant differences in threshold values using either transducer in normal ears.