Magnitude and phase of three-dimensional (3D) velocity vector: Application to measurement of cochlear promontory motion during bone conduction sound transmission
&NA; Recent measurements of vibrational motion to assess sound transmission through ear structures and skull contents have included three‐dimensional (3D) behavior. The 3D motion of a point has been described with the three orthogonal components in the 3D space. In this article, a method to represent the 3D velocity with the magnitude and phase of the resultant velocity is introduced. This method was applied to the measurement of cochlear promontory motion as an indication of bone conduction (BC) sound transmission. The promontory motions were measured on the ipsilateral and contralateral sides, and the transcranial attenuation and phase delay of the contralateral side relative to the ipsilateral side were calculated. The transcranial attenuation and phase delay calculated with the maximum magnitudes and corresponding phases of the resultant were a better fit to the interaural threshold difference and transcranial time interval between the ipsilateral and contralateral sides as reported in the literature, than the attenuation and phase delay calculated with any individual Cartesian motion component. HighlightsA method to calculate the magnitude and phase of the 3D velocity vector is described.The 3D velocity of a point can be represented by the magnitude and phase of the resultant instead of the magnitudes and phases of the three orthogonal components.The method was applied to the measurement of cochlear promontory motion as an indication of bone conduction (BC) sound transmission.The maximum velocity vector of the cochlear promontory motion is a better descriptor of BC hearing than individual Cartesian components.
Influence of stimulation position on the sensitivity for bone conduction hearing aids without skin penetration
Abstract Objective: This study explores the influence of stimulation position on bone conduction (BC) hearing sensitivity with a BC transducer attached using a headband. Design: (1) The cochlear promontory motion was measured in cadaver heads using laser Doppler vibrometry while seven different positions around the pinna were stimulated using a bone anchored hearing aid transducer attached using a headband. (2) The BC hearing thresholds were measured in human subjects, with the bone vibrator Radioear B71 attached to the same seven stimulation positions. Study sample: Three cadaver heads and twenty participants. Results: Stimulation on a position superior-anterior to the pinna generated the largest promontory motion and the lowest BC thresholds. Stimulations on the positions superior to the pinna, the mastoid, and posterior-inferior to the pinna showed similar magnitudes of promontory motion and similar levels of BC thresholds. Conclusion: Stimulations on the regions superior to the pinna, the mastoid, and posterior-inferior to the pinna provide stable BC transmission, and are insensitive to small changes of the stimulation position. Therefore it is reliable to use the mastoid to determine BC thresholds in clinical audiometry. However, stimulation on a position superior-anterior to the pinna provides more efficient BC transmission than stimulation on the mastoid.
In-vitro results of rapid maxillary expansion on adults compared with finite element simulations.
This study was mainly performed to investigate the effects of high maxillary expansion forces on the skull with fresh and thiel-fixed human skulls. The maxillary suture was not weakened except in one experiment. This study compares the strain measured on the zygomatic process of the skull with the results of a finite element model generated for this purpose. An increasing transversal force was applied on the alveolar process (teeth) until rupture. Strain on the zygomatic process, maxilla displacement and the expanding forces were registered. The results of this study show linear material behaviour of the skull before rupture. The highest stress during the experiments and FE simulation was observed on the alveolar process. Conclusions of this study are the necessity of the existence of appropriate models and that female specimens seem to rupture at a lower force than male ones. Both male and female specimens show a similar linear behaviour in the force/strain curve within each gender group. The probability of maxillary suture opening in adults during ultra-rapid maxillary expansion with tooth anchorage is very low. Complications and unwanted rupture could occur.