Maturation of Mechanical Impedance of the Skin-Covered Skull: Implications for Soft Band Bone-Anchored Hearing Systems Fitted in Infants and Young Children

Abstract

Our findings show that mechanical impedance properties change systematically up to 7 years old. The significant age-related differences in mechanical impedance suggest that infant-adult differences in bone conduction thresholds may be related, at least in part, to properties of the immature skull and overlying skin and tissues. These results have important implications for fitting the soft band BAHS on infants and young children. For example, verification of output force form a BAHS on a coupler designed with adult values may not be appropriate for infants. This may also hold true for transducer calibration when assessing bone conduction hearing thresholds in infants for different skull locations. The results have two additional clinical implications for fitting soft band BAHSs. First, parents should be counseled to maintain sufficient and consistent tightness so that the output from the BAHS does not change as the child moves around during everyday activities. Second, placement of a BAHS on the forehead versus the temporal bone results in changes in mechanical impedance which may contribute to a decrease in signal level at the cochlea as it has been previously demonstrated that bone conduction thresholds are poorer at the forehead compared with a temporal placement.

Hearing Through Bone Conduction Headsets

“…However, their impedances are around 5 dB lower overall at 1 kHz compared to the current results. The current results at the mastoid are within 2 dB from the impedances of the mastoid with 2 N static force of adults in Mackey et al (2016). Moreover, Mackey et al (2016) showed that the mastoid mechanical impedance with 5.4 N static force was 3 to 5 dB higher than with 2 N static force in adults.…”

“…The current results at the mastoid are within 2 dB from the impedances of the mastoid with 2 N static force of adults in Mackey et al (2016). Moreover, Mackey et al (2016) showed that the mastoid mechanical impedance with 5.4 N static force was 3 to 5 dB higher than with 2 N static force in adults. Consequently, the slightly lower impedances for the mastoid reported here compared to Flottorp and Solberg (1976) and Håkansson et al (1986) is likely an effect of the lower static force used in the current study.…”

An objective bone conduction verification tool using a piezoelectric thin-film force transducer

“…The output properties of BCDs are affected by the mechanical impedance of the load ( Weece and Allen, 2010 ). Several researchers have thoroughly investigated the impedance of the mastoid, and the results showed that the mastoid impedance was influenced by age ( Flottorp and Solberg, 1976 ; Zhang, 1994 ; Mackey et al, 2016 ; Nie et al, 2022 )), and that differences in mastoid impedance will lead to differences in the output force of the BC transducer. In addition, there are some differences in mastoid impedance between Chinese subjects and B&K 4930 artificial mastoid ( Nie et al, 2022 ).…”

Assessment of Interaural Attenuation in Infants and Young Children Using Bone-Conducted Auditory Brainstem Response

“…The physical properties that may explain the different IAA across frequencies were elucidated in the fundamental study by Mackey et al (2016). The authors measured the magnitude of mechanical impedance to vibratile force transduced by a bone conduction hearing device placed on the mastoid or forehead of infants, children, and adults across frequencies of 100 to 10,000 Hz.…”

“…The resonance frequency is characterized by the point of lowest impedance across the frequencies and a zero-phase delay. Mackey et al (2016) showed that infants had significantly lower impedance in the lower frequencies when compared with adults. In the higher frequencies, infants had higher impedance when compared with adults.…”