Maturation of skull properties with implications for the fitting and verification of the soft band bone-anchored hearing system for infants and young children

• Main Author: Mackey, Allison Ruth
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/44058

Soft band bone-anchored hearing systems (BAHS) are optimal for individuals with conductive or mixed hearing losses. Although it is understood that bone-conduction hearing is different between infants and adults, few studies have attempted to explain why these differences exist or how they affect the fitting of a soft band BAHS. The main objectives in this study were: (i) to better understand how properties of the developing skull contribute to the maturation of bone-conduction attenuation and sensitivity, and (ii) to determine how future BAHS fitting and verification protocols should be adjusted for infants and young children. The transcranial attenuation of pure-tone bone-conduction stimuli was measured on infants and young children (age 1 month to 7 years) and adults using sound pressure in the ear canal when the transducer was placed on different positions across the skull. In addition, the mechanical impedance magnitude for the forehead and temporal bone was collected for contact forces of 2, 4, and 5.4 N using an impedance head, a BAHS transducer, and a specially-designed holding device. This study was the first to measure mechanical impedance of the skull, which is an essential component to bone-conduction hearing, on young children and infants. Transcranial attenuation was greatest for young infants, and decreased throughout maturation. Attenuation was also greater from the forehead compared to the contralateral temporal bone for infants and children over 10 months of age. In addition, mechanical impedance was lowest for the youngest infants and increased throughout maturation for low frequencies, but for high frequencies, these infants had the highest impedance on the temporal bone only. The effect of contact force was significant for low frequencies, and the effect of placement was significant for high frequencies. These results suggest that the properties of the developing skull relate to infant-adult differences in transcranial attenuation, and the mechanical impedance of the skin and subcutaneous tissue may explain the infant-adult differences in bone-conduction sensitivity. The results also provide important implications for fitting and verifying output from the BAHS for infants and young children.