Current Research

Temporal Bone Research

Bone Conduction

Xiying Guan

The ears are the primary way to perceive sound, but the skull provides another pathway for sound to be interpreted by the sensory organ in the ear. Bone conduction has been used as a diagnostic tool and treatment for hearing loss since the 17th century. Recently there has been a growing popularity of bone conduction devices, such as Google glass and speaking pillow, which allows for audio communication without blocking sound entering through the ear.  With the innovative miniature pressure sensors, we are able to study the mechanisms of bone conduction. We also have an interest in understanding effects of diseases, such as otosclerosis and semicircular canal dehiscence, on bone conduction hearing.

bone conduction

Bone Conduction Setup with BAHA device

Round Window Stimulation Device

Darcy Frear

Instead of introducing sound to the inner ear by mechanically stimulating the oval window (as in normal air conduction - AC), the cochlea can be driven in “reverse” by mechanically stimulating the round window (RW), which is a pressure release system of the cochlea. The Nakajima lab is creating a device that helps those with outer and/or middle ear problems by stimulating the RW membrane. We focus on increasing the coupling of the device to any RW membrane despite variations in ear anatomy. We are currently testing new designs and have a patent pending. 

 

Modeling the Middle and Inner Ear

Darcy Frear

air conduction model

Air Conduction Stimulation Block Diagram

Our lab specializes in intracochlear pressure sensor measurements and we've accumulated enough data from many ears to create an impedance model of the middle and inner ear. Analyses of intracochlear pressures in the scala vestibuli (SV) and scala tympani (ST), as well as velocities of the middle ear, enables us to quantify the frequency-dependent impedances in the middle ear and cochlear system. Our analyses also further the understanding of air conduction (AC, pictured) and RW stimulation by quantifying the volume velocities of various paths of sound during different stimulation modes.

 

Human basilar membrane mechanics

Stefan Raufer

Human hearing spans a frequency range from 20 Hz to 20 kHz. Current models assume that the best frequency scales with the square-root of stiffness, requiring a stiffness gradient of six orders of magnitude from base to apex. Not only is the large stiffness gradient doubted, there is no consensus about the value of the stiffness at any given place in the human cochlea. We determine the acoustic impedance and stiffness of the human basilar membrane by measuring acoustic pressures in scala vestibuli and the velocity of the BM from scala tympani. Beside our method to determine the acoustic impedance of the basilar membrane, we consult other measurement techniques for making these measurements. We use a micro force probe developed by our collaborator Aleks Zosuls at Boston University to determine the mechanical impedance of biological tissue. facial recess

 

Low-frequency hearing and infrasound propagation through the middle and inner ear

Stefan Raufer

 

infrasound

It is widely believed that the hearing range of humans is between 20 Hz to 20 kHz (as described above). However, there is compelling evidence that infrasound (frequencies below 20 Hz) does enter the ear and even alter sound processing in the cochlea. Especially in industrialized nations, people are frequently exposed to high-energy, low-frequency sounds radiated by heavy machinery, making exposure to infrasound a possible public health concern. Yet the transmission of infrasound to and within the inner ear is not well described.

We measured the motion of middle ear bones and the round window membrane (part of the inner ear) for frequencies between 1 Hz and 2000 Hz and show that the middle ear considerably limits the sound energy transmitted to the inner ear at such low frequencies. However, inner ear pathologies such as semicircular canal dehiscence (SCD) decreases the velocity of the round window membrane in a predictable, frequency-dependent manner, demonstrating that acoustic energy is shunted through and exciting the vestibular system. Our findings suggest that mechanical perturbations of the inner ear could lead to vestibular hypersensitivity to infrasound.

 

 

Clinical Research

Superior Canal Dehiscence

Raphaelle Chemtob and Salwa Masud

First described by Minor and colleagues in 1998, superior canal dehiscence (SCD) is a disorder characterized by a defect in the bony covering of the superior semicircular canal in the inner ear. Patients with SCD experience a range of auditory and/or vestibular complaints. Although believed to be rare, knowledge and awareness of SCD among physicians has increased over the past decade. However, the diagnosis is difficult to establish as the presentation of SCD often mimics symptoms of other common ear pathologies. As a consequence, patients may wait years before getting their diagnosis and have often receive incorrect treatment for other pathologies.  

Our lab is interested in understanding the underlying mechanics of the inner and middle ear in patients with SCD and to develop methods to establish the diagnosis of SCD in patients. We perform wideband acoustic immittance and laser Doppler vibrometry in patients diagnosed with SCD at our institution. Furthermore, we compare measurements before and after surgery to assess the mechanical effect of surgery on SCD. In our temporal bone lab, we model the SCD in fresh human temporal bone specimens. The basic science work seeks to improve our understanding of the mechanisms behind SCD and to quantitatively study the effects of different surgical approaches to improve SCD treatment.

 

 

SCD

 

Development of computational models to diagnose mechanical lesions of the ear

Salwa Masud

Current clinical test reveal the cause of conductive hearing loss (CHL) in majority of patients, but there is a subset of patients with CHL in the aerated middle ear and intact tympanic membrane who present a diagnostic dilemma. The differential diagnosis in this setting include ossicular fixation or discontinuity, and third window disorders such as superior canal dehiscence. We have demonstrated the potential of Ear Canal Reflectance (ECR) and Laser-Doppler vibrometry (LDV) measurements in this subset of patients as a non-invasive diagnostic tool, which is valuable for patient counselling, surgical planning and may even spare patients from unneccesary diagnostic middle ear exploratory surgery. This project seeks to evaluate non-invasive diagnostic measurements such as wideband acoustic immittance and laser Doppler vibrometry for their efficacy in 1) detecting various macro-mechanical pathologies of the ear with computational models, and 2) monitoring the mechanical changes of the ear following surgical repair.

LDV                                        LDV

 

             Ear Canal Reflectance (ECR)                                                                                         Laser-Doppler vibrometry (LDV)