Abstract
Purpose
It is assumed that preoperative use of a bone-anchored hearing aid (BAHA) test-band will give a patient lower gain compared to real post-operative gain because of the reduction of energy through the scalp when using a test-band. Hearing gains using a BAHA test-band were analyzed in patients with unilateral hearing loss.
Materials and Methods
Nineteen patients with unilateral sensorineural hearing loss were enrolled. A test-band, which was connected to BAHA Intenso with full-on gain, was put on the mastoid. Conventional air-conduction (AC) pure-tone averages (PTAs) and sound-field PTAs and speech reception thresholds (SRTs) were obtained in conditions A (the better ear naked), B (the better ear plugged), and C (the better ear plugged with a test-band on the poorer mastoid).
Results
Air-conduction PTAs of the poorer and better ears were 91 ± 19 and 18 ± 8 dB HL. Sound-field PTAs in condition B were higher than those in condition A (54 vs. 26 dB HL), which means that earplugs can block the sound grossly up to 54 dB HL through the better ears. The aided PTAs (24 ± 6 dB HL) in condition C were similar to those of the better ears in condition A (26 ± 9 dB HL), though condition C showed higher thresholds at 500 Hz and lower thresholds at 1 and 2 kHz when compared to condition A. The hearing thresholds using a test-band were similar to the published results of BAHA users with the volume to most comfortable level (MCL).
Conclusion
Our findings showed that a BAHA test-band on the poorer ear could transmit sound to the cochlea as much as the better ears can hear. The increased functional gain at 1 and 2 kHz reflects the technical characteristics of BAHA processor. The reduction of energy through the scalp when using a test-band seems to be offset by the difference of output by setting the volume to full-on gain and using a high-powered speech processor. Preoperative hearing gains using a test-band with full-on gain seems to be similar to the post-operative gains of BAHA users with the volume to MCL.
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Introduction
Bone-anchored hearing aids (BAHAs) have been used to treat conductive or mixed hearing loss and single-sided deafness (SSD) by inducing the trans-cranial contralateral routing of signal . The implanted titanium screw allows the acoustic energy to be transmitted into the inner ears without any reduction of energy through the scalp. Thus, it is assumed that the functional gain achieved by a test-band on the mastoid will be lower than the post-operative gain that can be obtained by direct stimulation of the skull. Indeed, it has been reported that the transmission to the cranium is dampened by the underlying scalp by 10–20 dB . However, this numerical value is not useful in helping patients to obtain a realistic expectation of the hearing they will gain after surgery. Therefore, we wanted to know how much gain the patients with single-sided deafness can get by using a BAHA test-band and compare the results with the published post-operative gains of BAHA users. To test this, the hearing gains by using a BAHA test-band were estimated in patients with SSD.
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