gms | German Medical Science

Introduction: In bone conduction hearing vibrations of the skull bone are transmitted to the cochlear fluid leading to sound perception. Bone conduction hearing aids use this phenomenon to provide hearing for patients with conductive or mixed hearing disorders. Determination of the mechanical properties of transcutaneous bone conduction implants is essential because of the limited physical access to implants and transducers after implantation. In this study, we investigated a new approach by measuring bone conducted sound in nostrils. This method can potentially be used intra- and postoperatively even in patients with atresia or malformation of the outer ear canal.

Method: Twenty normal hearing subjects were included in the study. The nasal sound pressure (NSP) was measured by a probe microphone in the nasal cavity when the stimulation was applied at the position approximately 50 mm posterior to the mastoid and at the mastoid bone 10 mm behind the auricle. The stimulation signal was a swept sine with frequencies between 100 Hz and 10 kHz. A bone vibrator with a steel spring headband was placed over the skin at the mentioned positions.

Results: The average amplitude NSP at 0.5, 1, 2, 4 kHz was 85.7 ± 6.8 dBSPL (Mean value ± standard deviation). A moving average method was applied to decrease the amplitude variation amongst individuals. The position closer to the ear canal provided higher NSP amplitude in average data.

Conclusion: The results show that NSP is measurable with sufficient signal-to-noise ratio (SNR>10 dB) at frequencies between 100 and 8000 Hz. The findings imply that the method can potentially be used as an alternative to outer ear canal sound pressure measurement in patients that have no ear canals.

Unterstützt durch: This work was supported by the DFG Cluster of Excellence EXC 1077/1 "Hearing4all".

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