Diagnostic utility of laser-Doppler vibrometry in conductive hearing loss with normal tympanic membrane

In Vivo Measurement of Ear Ossicle and Bony Wall Vibration by Sound Stimulation of Cartilage Conduction

The cartilage-conduction pathway was recently proposed as a third auditory pathway; however, middle-ear vibrations have not yet been investigated in vivo. We aimed to measure the ossicles and bone vibration upon cartilage-conduction stimulation with a non-contact laser Doppler vibrometer. We recruited adult patients with normal ear structures who underwent cochlear implant surgery at our hospital between April 2020 and December 2022. For sound input, a cartilage-conduction transducer, custom-made by RION Corporation (Tokyo, Japan), was fixed to the surface of the tragus and connected to an audiometer to regulate the output. A posterior tympanotomy was performed and a laser beam was directed through the cavity to measure the vibration of the ossicles, cochlear promontory, and posterior wall of the external auditory canal. Five participants (three men, mean age: 56.4 years) were included. The mean hearing loss on the operative side was 96.3 dB HL in one patient, and that of the other patients was off-scale. The vibrations were measured at a sound input of 1 kHz and 60 dB. We observed vibrations of all three structures, demonstrating the existence of cartilage-conduction pathways in vivo. These results may help uncover the mechanisms of the cartilage-conduction pathway in the future.

The Rise and Fall of Aural Acoustic Immittance Assessment Tools

Clinical assessment of middle ear function has undergone multiple transformations and developments since the first acoustic impedance measurements were made in human ears nearly a century ago. The decades following the development of the first acoustic impedance bridge by Metz in 1946 witnessed a series of technological advancements leading to the widespread use of single-frequency admittance tympanometry in the 1960s. In the 1970s, multi-frequency and multi-component tympanometry (MFT) emerged for clinical use, allowing for a better understanding of the middle ear acoustic-mechanical response at frequencies between 200 and 2,000 Hz. MFT has not gained widespread clinical adoption despite its advantages over single-frequency tympanometry. More recent technological developments enabled assessment for frequencies greater than 2,000 Hz, leading to the advent of wideband acoustic immittance measures with capabilities for comprehensive assessment of middle ear acoustic mechanics, and a great potential for use of acoustic immittance testing in various diagnostic practices. This article reviews important historical markers in the development and operation of middle ear assessment tools and analysis methods. Technical and clinical factors underlying the emergence and adoption of different acoustic immittance tests as a standard of clinical practice are described. In addition, we discuss the likelihood for widespread adoption of wideband acoustic immittance and wideband tympanometry in future clinical practice.

A Partial Ossicular Replacement Prosthesis With a Concentric Ball Joint in the Headplate

OBJECTIVE

In passive middle ear prosthetics, rigid implants have proven successful in reconstructing the ossicular chain. However, these cannot fully replicate the physiology of the ossicular chain. Pressure fluctuations cause high stresses in rigid passive prostheses, which can result in dislocation, protrusion, and pre-tension in the annular ligament resulting in unsatisfactory hearing results.

METHODS

In collaboration with MED-EL, we developed a new passive middle ear prosthesis that features a balanced, centered ball joint between the headplate and shaft of the prosthesis. We compared the sound transmission properties of this new prosthesis with those of a standard rigid prosthesis. Using Laser-Doppler-Vibrometry, we measured the sound-induced velocity of the stapes footplate relative to a given acoustic stimulus.

RESULTS

The new prosthesis showed equivalent sound transmission characteristics compared to the rigid prosthesis, whereas retaining the ability to compensate for pressure fluctuations due to its ball joint. This ensures good transmission properties even during displacements of the tympanic membrane.

CONCLUSION

This development is a further step toward a physiological reconstruction of the ossicular chain.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2022.

Evaluation of acoustic changes in and the healing outcomes of rat eardrums with pars tensa and pars flaccida perforations

Objectives

To systematically explore the differences in acoustic changes and healing outcomes of tympanic membranes (TMs) with pars flaccida perforation (PFP) and pars tensa perforation (PTP).

Methods

We created PFPs and PTPs of various sizes in Sprague–Dawley rats, and evaluated TM umbo velocity and hearing function using laser Doppler vibrometry and auditory brainstem response (ABR) measurement before and immediately after perforation. Two weeks later, hearing was reevaluated and TMs were investigated by immunohistochemical staining.

Results

Small PFPs and PTPs did not significantly affect umbo velocity and hearing function. Large PFPs increased umbo velocity loss at low frequency (1.5 kHz) and elevated ABR thresholds within 1–2 kHz. Large PTP caused significant velocity loss at low frequencies from 1.5 to 3.5 kHz and threshold elevations at full frequencies (1–2 kHz). Two weeks after the perforation, the hearing function of rats with healed PFPs recovered completely. However, high‐frequency hearing loss (16–32 kHz) persisted in rats with healed PTPs. Morphological staining revealed that no increase in the thickness and obvious increase in collagen I level of regenerated par flaccida; regenerated pars tensa exhibited obvious increase in thickness and increased collagen I, while the collagen II regeneration was limited with discontinuous and disordered structure in regenerated pars tensa.

Conclusion

The hearing loss caused by large PFP limits at low frequencies while large PTP can lead to hearing loss at wide range frequencies. PFP and PTP have different functional outcomes after spontaneous healing, which is determined by the discrepant structure reconstruction and collagen regeneration.

Vibration of Tympanic Membrane Influenced by Middle Ear Fluid

HYPOTHESIS

The amount and viscosity of middle ear fluid probably influences the vibration function of the tympanic membrane (TM).

BACKGROUND

There has been much research into the mechanisms of hearing loss resulting from middle ear fluid in the previous study. However, further study is required to understand how the middle ear fluid affects the vibration function of the TM.

METHODS

Tests on a TM in a fresh cadaveric human temporal bone specimen under different simulated conditions were carried out. Saline (1 cSt) and silicone oil (100 cSt, 1 000 cSt, 12 500 cSt) were used to simulate middle ear fluid. The fluid approximately contacted 50% or 100% of TM, which was proportional to the fluid amount. Induced by stimulus signal with frequency domain from 0.25 to 8 kHz, the vibration at 6 points of the TM was measured by laser Doppler vibrometer (LDV), respectively. Data acquisition and processing were accomplished by self-developed software.

RESULTS

With the increase of the fluid amount, the magnitude of velocity transfer function reduced across all frequencies. The effect of fluid viscosity on the TM vibration varied and reduced in a complicated way when the fluid viscosity changed.

CONCLUSION

Increasing fluid amount will significantly reduce the TM movement. The effect of fluid viscosity on the TM vibration was nonlinear and related to the fluid amount. The vibration at each point on the TM is frequency-dependent.

Optical measurements of eardrum vibrations and sound propagation in the ear canal for the fitting of active middle ear implants

BACKGROUND

Middle ear implants (MEI) are for the medical rehabilitation of the hearing function in case of sound conduction hearing losses as well as cochlear hearing losses and their combinations.

OBJECTIVES

An objective tool to reach the best fitting of the external worn sound processors is essential for patients who do not want or cannot participate in the fitting process.

METHODS

In addition to Laser-Doppler-Vibrometry (LDV) measurement, the sound pressure was measured distant to the eardrum to attain additional information for comparison. Three groups of patients with different middle ear characteristics were examined.

RESULTS

Because of the large spreading of measuring results even within a patient group with similar eardrum and middle ear conditions it is difficult to develop characteristic diagrams which represent the mean values of eardrum displacements with different sound processor adjustments being the base for normative data courses.

CONCLUSIONS AND SIGNIFICANCE

The LDV measurements can be used as a tool for fitting sound processors by finding individual maximum eardrum velocities in the frequency range 125 Hz to 8 kHz. In comparison to acoustical measurements the optical measurements have advantages concerning lower variations of measurement values, higher spectral resolution, and robustness against disturbing acoustic noise, especially at low frequencies.

Measurement of Incus and Stapes Velocity Following Sound Stimulus in the Setting of Incudostapedial Joint Separation and Reconstruction

OBJECTIVE

Understand the biophysical property changes of incudostapedial joint (ISJ) separation and ossicular hydroxyapatite application on middle ear function.

STUDY DESIGN

Basic science.

SETTING

Cadaveric temporal bone research laboratory.

SUBJECTS AND METHODS

A complete mastoidectomy was performed on five human temporal bones. A Laser Doppler Vibrometer was utilized to obtain velocity transfer function measurements of the incus and stapes across a range of frequencies in response to an acoustic stimulus. Under binocular microscopy the ISJ was separated and subsequently repaired with bone cement. Measurements were taken prior to ISJ separation, following joint separation, 30 to 60 min postrepair of the joint, and again 24 to 48 h postrepair of the joint.

RESULTS

The stapes measurements taken from the intact ossicular chain and from the chains repaired with bone cement demonstrated a similar distribution of measurements. The ISJ separation showed dramatically reduced velocity transfer function stapes measurements but increased incus velocity transfer function measurements. In the early and delayed repaired chains, the mean velocity of the incus and stapes velocity peaked between 1.5 and 2 kHz, matching intact maximal velocity. Pure tone average at 0.5, 1, 2, and 3 kHz demonstrated no change in reconstructed stapes velocity at 24 to 48 h.

CONCLUSIONS

Isolated ISJ separation in fresh frozen and thawed temporal bones produces stapes velocity transfer function changes that corresponds with the clinically experienced conductive hearing loss. Repair with bone cement produced similar velocity curves to the intact ISJ curve with excellent recovery across mid-frequencies. This model would be useful for future ossicular mechanical studies.

The impact of tympanic membrane perforations on middle ear transfer function

Purpose

Injury or inflammation of the middle ear often results in the persistent tympanic membrane (TM) perforations, leading to conductive hearing loss (HL). However, in some cases the magnitude of HL exceeds that attributable by the TM perforation alone. The aim of the study is to better understand the effects of location and size of TM perforations on the sound transmission properties of the middle ear.

Methods

The middle ear transfer functions (METF) of six human temporal bones (TB) were compared before and after perforating the TM at different locations (anterior or posterior lower quadrant) and to different degrees (1 mm, ¼ of the TM, ½ of the TM, and full ablation). The sound-induced velocity of the stapes footplate was measured using single-point laser-Doppler-vibrometry (LDV). The METF were correlated with a Finite Element (FE) model of the middle ear, in which similar alterations were simulated.

Results

The measured and calculated METF showed frequency and perforation size dependent losses at all perforation locations. Starting at low frequencies, the loss expanded to higher frequencies with increased perforation size. In direct comparison, posterior TM perforations affected the transmission properties to a larger degree than anterior perforations. The asymmetry of the TM causes the malleus-incus complex to rotate and results in larger deflections in the posterior TM quadrants than in the anterior TM quadrants. Simulations in the FE model with a sealed cavity show that small perforations lead to a decrease in TM rigidity and thus to an increase in oscillation amplitude of the TM mainly above 1 kHz.

Conclusion

Size and location of TM perforations have a characteristic influence on the METF. The correlation of the experimental LDV measurements with an FE model contributes to a better understanding of the pathologic mechanisms of middle-ear diseases. If small perforations with significant HL are observed in daily clinical practice, additional middle ear pathologies should be considered. Further investigations on the loss of TM pretension due to perforations may be informative.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-07078-9.

Handheld laser-fiber vibrometry probe for assessing auditory ossicles displacement

SIGNIFICANCE

Measurements of auditory ossicles displacement are commonly carried out by means of laser-Doppler vibrometry (LDV), which is considered to be a gold standard. The limitation of the LDV method, especially for in vivo measurements, is the necessity to expose an object in a straight line to a laser beam operating from a distance. An alternative to this approach is the use of a handheld laser-fiber vibrometry probe (HLFVP) with a curved tip.

AIM

We evaluate the feasibility of an HLFVP with a curved tip for measuring sound-induced displacement of the auditory ossicles.

APPROACH

A handheld vibrometer probe guiding the laser beam with a fiber-optic cable was used for displacement measurements of the incus body and the posterior crus of the stapes. Tonal stimuli at frequencies of 0.5, 1, 2, and 4 kHz were presented by means of an insert earphone positioned in the outer ear canal. The probe was fixed at the measurement site using a tripod or hand-held by one of the two surgeons.

RESULTS

The measurements were carried out on six fresh temporal bones. Multivariate analysis of variance showed statistically significant differences for stimulus frequency (F3,143  =  29.37, p  <  0.001, and η2  =  0.35), bone (F5,143  =  4.61, p  =  0.001, and η2  =  0.01), and measurement site (F1,143  =  4.74, p  =  0.03, and η2  =  0.02) in the absence of statistically significant differences for the probe fixation method (F2,143  =  0.15, p  =  0.862, and η2  =  0.001). Standard deviations of the means were 6.9, 2.6, 1.9, and 0.6  nm  /  Pa for frequency, bone, site, and fixation, respectively. Ear transfer functions were found to be consistent with literature data.

CONCLUSIONS

The feasibility of applying HLFVP to measure the displacement of auditory ossicles has been confirmed. HLFVP offers the possibility of carrying out measurements at various angles; however, this needs to be standardized taking into account anatomical limitations and surgical convenience.

Nitinol in Passive Ossicular Reconstruction-First Results From Temporal Bone Experiments

HYPOTHESIS

Nitinol is a suitable material for passive middle ear prosthesis.

BACKGROUND

In modern ear microsurgery, the restitution of hearing is tremendously important. In passive ossicular reconstruction, rigid alloplastic materials are widespread in use. However, rigid prostheses fail to adapt to atmospheric pressure changes. We describe the use of the super-elastic material nitinol in passive ossicular reconstruction to overcome this limitation.

METHODS

Together with an industrial partner, we developed a nitinol clip prosthesis equipped with a flexible prosthesis headplate. The new prosthesis was evaluated for flexibility and its sound transmission properties were compared with standard clip prostheses. For this purpose, the sound-induced acceleration of the stapes footplate was measured by laser-doppler vibrometry in temporal bones. Furthermore, the flexibility of the prosthesis plate was tested in a load-cell experiment.

RESULTS

On average, the pure tone transmission characteristics of the nitinol prosthesis is statistically not distinguishable from standard titanium clip prostheses. The tests in the load cell confirmed the flexibility of the prosthesis. Any measured prosthesis returns to its original state after deformation.

CONCLUSION

The newly developed nitinol clip prosthesis shows similar sound transmission properties in comparison to established prostheses with high flexibility indicating a step forward to a physiological ossicular chain reconstruction.

Functional assessment of moisture influenced cadaveric tympanic membrane using phase shift-resolved optical Doppler vibrography

An elevated relative moisture in the external ear canal and middle ear cavity may predispose to chronic otorrhea and related infections along with abnormal tympanic membrane (TM) vibration patterns. Therefore, phase shift-resolved optical Doppler vibrography (ODV) was used for vibration assessments of moisture influenced cadaveric TM. ODV was applied to generate time resolved cross-sectional and volumetric vibrographs of a cadaveric TM, driven acoustically at several frequencies. In order to analyze the effect of moisture on TM, homogenous moisture conditions were provided by soaking the cadaveric TM specimens in 1× phosphate buffer saline with a pH of 7.4. The TM specimen was exposed to a rapidly switchable frequency generator during the ODV image acquisition. The experiment was conducted for 3 hours and the cadaveric TM was exposed to each frequency with an interval of 30 minutes. Acquired phase shift-resolved ODV assessments revealed a depth dependent vibration tendency between the applied frequencies, along with a decline in the moisture level of the cadaveric TM specimen. Thus, the ODV method can aid our understanding of sound conduction in the middle ear, thus supporting the diagnosis of TM diseases.

Inner ear pressure evaluation using wideband tympanometry in children with Large Vestibular Aqueduct Syndrome (LVAS): A pilot study

OBJECTIVE

To investigate middle ear function in children with Large Vestibular Aqueduct Syndrome (LVAS) to explore the feasibility of measuring inner ear pressure using Wideband tympanometry (WBT).

METHODS

13 young children with LVAS were recruited. WBT and other audiological measurements i.e., Auditory Steady State Response (ASSR), Auditory Brain Stem Response (ABR), and Distorted Product Otoacoustic Emissions (DPOAE) were performed. Absorbance under ambient and peak pressure were compared with normative data, and analyzed using a one sample t-test.

RESULTS

Average absorbance in children with LVAS was significantly lower than normative data under ambient pressure at 1000, 1189, 1296, 2000 Hz and 4000 Hz. Absorbance under peak pressure was also significantly lower at 707, 794, 917, 1000, 1189, 1297, 1498 and 2000 Hz. However, absorbance was higher than standard values above 4000 Hz under ambient and peak pressure. It was also higher under ambient pressure at frequencies below 500 Hz.

CONCLUSION

The special characteristics of middle ear function found in children with Large Vestibular Aqueduct Syndrome (LVAS) indicate that WBT offers a sensitive and non-invasive method to evaluate inner ear pressure indirectly.

Finite element analysis of round-window stimulation of the cochlea in patients with stapedial otosclerosis

An active actuator coupled to the round window (RW) can transmit mechanical vibrations into the cochlea and has become a therapeutic option of hearing rehabilitation for patients with stapedial otosclerosis. A finite-element model of the human ear that includes sound transmission effects of the vestibular and cochlear aqueducts of the inner ear is adopted in this study for investigating the cochlear response to RW stimulation under stapes fixation. There are two effects due to otosclerosis of the stapes: the fixation of the stapedial annular ligament (SAL) and the increase of the stapes mass. The frequency responses of the middle ear and cochlea with normal and otosclerotic stapes are calculated under sound and RW stimulations. The results show that changes in the material property of the stapes have different effects on the cochlear responses under sound and RW stimulations. Because of the vestibuli aqueduct, the reduction in the low-frequency magnitude of the pressure difference across the cochlear partition due to SAL fixation is much smaller under RW stimulation than under sound stimulation. The results of this study help understand sound transmission during RW stimulation in patients with stapedial otosclerosis.

A study on the effect of ligament and tendon detachment on human middle ear sound transfer using mathematic model

The objective of this study is to investigate the effects of ligament and tendon detachment on human middle ear sound transfer. For this purpose, a geometric human middle ear model was reconstructed based on the computed tomography scanning data of the temporal bones from healthy adult volunteers. For the ear model, pars tensa was assumed to be fit for a 5-parameter Maxwell model and inverse method was used to obtain the necessary coefficients. Furthermore, frequency response method was implemented to investigate the vibration behaviors of tympanic membrane umbo and stapes footplate under an acoustic stimulus of 90 dB within 0.2-8 kHz. Meanwhile, nine patterns of fractured ligaments and tendons, whose effects on the middle ear sound transfer function were simulated by setting free the nodes of the ligaments and tendons of interest. The results indicate that the displacement of tympanic membrane umbo and stapes footplate as well as the velocity transfer function lies within the bounds of the published experimental data. The detachments of ligaments or tendons except for lateral mallear ligament may incur both gains as much as 15 dB and losses of -8 dB in the velocity of stapes footplate at low frequencies (f≤ 1 kHz), while no significant changes were observed at high frequencies (f > 1 kHz). However, detachment of the ligaments or tendons induces tiny changes in the displacement of stapes footplate at the frequencies of 0.2-8 kHz.

A lumped-element model of the chinchilla middle ear

An air-conduction circuit model was developed for the chinchilla middle ear and cochlea. The lumped-element model is based on the classic Zwislocki model of the same structures in human. Model parameters were fit to various measurements of chinchilla middle-ear transfer functions and impedances, using a combination of error-minimization-driven computer-automated and manual fitting methods. The measurements used to fit the model comprise a newer, more-extensive data set than previously used, and include measurements of stapes velocity and inner-ear sound pressure within the vestibule and the scala tympani near the round window. The model is in agreement with studies of the effects of middle-ear cavity holes in experiments that require access to the middle-ear air space. The structure of the model allows easy addition of other sources of auditory stimulation, e.g., the multiple sources of bone-conducted sound-the long-term goal for the model's development-and mechanical stimulation of the ossicles and round window.

Stapes hypermobility as a possible cause of hyperacusis

OBJECTIVE

Hyperacusis is a reduction of normal tolerances for everyday sounds. Although several publications have been produced demonstrating that minimally invasive surgical procedures may improve patient symptoms, the precise etiology of hyperacusis often remains elusive. This study describes 21 patients, 7 of whom stapes hypermobility is believed to be a mechanical genesis of their hyperacusis symptoms.

STUDY DESIGN

A prospective, repeated-measure single-arm design was used for this study.

SETTING

All patients were evaluated and treated at a tertiary level otologic referral center.

SUBJECTS AND METHODS

21 patients (Cohort A) with severe hyperacusis underwent oval and round window reinforcement. Seven patients (Cohort B) intraoperatively appeared to have subjective hypermobility of the stapes. Additional reinforcement of the stapes superstructure was performed in these patients.

RESULTS

In Cohort A, loudness discomfort level (LDL) values improved on average from 72.7 dB to 81.9 dB. Hyperacusis questionnaire (HQ) scores improved from 30.1 to 14.7. Numeric Rating Scale scores (0-10) decreased from 8.5 to 4.0. In Cohort B, values similarly improved from an average of 72.4 dB to 88.2 dB. HQ scores improved from 35.8 to 18.9. Numeric Rating Scale scores fell from 10.0 to 3.7. Postoperatively there were no complaints of hearing loss. Sixteen out of 21(76%) reported improved quality of life and diminished symptoms of hyperacusis.

CONCLUSION

It is possible that patients suffering from hyperacusis may have a mechanical cause for their symptoms. Further research is necessary to clarify stapes mobility in patients with these symptoms. Excess temporalis tissue reinforcement of the stapes along with round window reinforcement shows promise as a minimally invasive surgical option for patients suffering from hyperacusis.

Human middle-ear muscles rarely contract in anticipation of acoustic impulses: Implications for hearing risk assessments

The current study addressed the existence of an anticipatory middle-ear muscle contraction (MEMC) as a protective mechanism found in recent damage-risk criteria for impulse noise exposure. Specifically, the experiments reported here tested instances when an exposed individual was aware of and could anticipate the arrival of an acoustic impulse. In order to detect MEMCs in human subjects, a laser-Doppler vibrometer (LDV) was used to measure tympanic membrane (TM) motion in response to a probe tone. Here we directly measured the time course and relative magnitude changes of TM velocity in response to an acoustic reflex-eliciting (i.e. MEMC eliciting) impulse in 59 subjects with clinically assessable MEMCs. After verifying the presence of the MEMC, we used a classical conditioning paradigm pairing reflex-eliciting acoustic impulses (unconditioned stimulus, UCS) with various preceding stimuli (conditioned stimulus, CS). Changes in the time-course of the MEMC following conditioning were considered evidence of MEMC conditioning, and any indication of an MEMC prior to the onset of the acoustic elicitor was considered an anticipatory response. Nine subjects did not produce a MEMC measurable via LDV. For those subjects with an observable MEMC (n = 50), 48 subjects (96%) did not show evidence of an anticipatory response after conditioning, whereas only 2 subjects (4%) did. These findings reveal that MEMCs are not readily conditioned in most individuals, suggesting that anticipatory MEMCs are not prevalent within the general population. The prevalence of anticipatory MEMCs does not appear to be sufficient to justify inclusion as a protective mechanism in auditory injury risk assessments.

[New clinical applications for laser Doppler vibrometry in otology]

BACKGROUND

An instrument to measure vibration in the middle ear needs to be sensitive enough to detect displacement on a nanometer scale, yet not affect the vibration itself. Numerous techniques have been described in the literature, but laser Doppler vibrometry (LDV) has nowadays become established as the standard method in hearing research.

OBJECTIVE

This article aims to present possible clinical applications of an LDV system in otology.

MATERIALS AND METHODS

A commercially available single-point vibrometer was used. Measurements were carried out both with the sensor head mounted on an operating microscope and as a handheld device with the sensor head manually inserted in the ear canal. For the latter, a custom-made unit containing an electrically tunable lens was attached to the sensor head. Middle ear vibrations were measured in a temporal bone model as well as in patients during and after implantation of a Vibrant Soundbridge (VSB; MED-EL Corp., Durham/NC, USA).

RESULTS

Different types of middle ear pathologies can be distinguished by the frequency response of the umbo. The LDV technique can be used for intraoperative quantification of the coupling quality of the VSB's Floating Mass Transducer (FMT; MED-EL) to the ossicle chain during VSB implantation. Postoperatively, the method serves as a follow-up testing tool if a deterioration in aided hearing threshold occurs. The measurement can reveal changes in the umbo transfer function, e. g., due to middle ear scarring or dislocation of the FMT.

CONCLUSION

Many clinical questions in otology can be addressed by LDV. However, due to the high acquisition costs of an LDV system, the relatively large instrumental setup, and the large inter-ear variability of middle-ear function, the technique has not (yet) become established in clinical routine.

Sequential motion of the ossicular chain measured by laser Doppler vibrometry

OBJECTIVE

In order to help a surgeon make the best decision, a more objective method of measuring ossicular motion is required.

METHODS

A laser Doppler vibrometer was mounted on a surgical microscope. To measure ossicular chain vibrations, eight patients with cochlear implants were investigated. To assess the motions of the ossicular chain, velocities at five points were measured with tonal stimuli of 1 and 3 kHz, which yielded reproducible results. The sequential amplitude change at each point was calculated with phase shifting from the tonal stimulus. Motion of the ossicular chain was visualized from the averaged results using the graphics application.

RESULTS

The head of the malleus and the body of the incus showed synchronized movement as one unit. In contrast, the stapes (incudostapedial joint and posterior crus) moved synchronously in opposite phase to the malleus and incus. The amplitudes at 1 kHz were almost twice those at 3 kHz.

CONCLUSIONS

Our results show that the malleus and incus unit and the stapes move with a phase difference.

Functional Outcomes of Heparin-Binding Epidermal Growth Factor-Like Growth Factor for Regeneration of Chronic Tympanic Membrane Perforations in Mice

We aim to demonstrate that regeneration of chronic tympanic perforations with heparin-binding epidermal growth factor-like growth factor (HB-EGF) delivered by an injectable hydrogel restored hearing to levels similar to that of nonperforated tympanic membranes. Chronic tympanic membrane perforation is currently managed as an outpatient surgery with tympanoplasty. Due to the costs of this procedure in the developed world and a lack of accessibility and resources in developing countries, there is a great need for a new treatment that does not require surgery. In this study, we show in a mouse model through measurement of auditory brainstem response and distortion product otoacoustic emissions that tympanic perforations lead to hearing loss and this can be predominantly recovered with HB-EGF treatment (5 μg/mL). Our animal model suggests a return to function between 2 and 6 months after treatment. Auditory brainstem response thresholds had returned to the control levels at 2 months, but the distortion product otoacoustic emissions returned between 2 and 6 months. We also show how the vibration characteristics of the regenerated tympanic membrane, as measured by laser Doppler vibrometry, can be similar to that of an unperforated tympanic membrane. Using the best available methods for preclinical evaluation in animal models, it is likely that HB-EGF-like growth factor treatment leads to regeneration of chronic tympanic membrane perforations and restoration of the tympanic membrane to normal function, suggesting a potential route for nonsurgical treatment.

Long-range, wide-field swept-source optical coherence tomography with GPU accelerated digital lock-in Doppler vibrography for real-time, in vivo middle ear diagnostics

We present the design, implementation and validation of a swept-source optical coherence tomography (OCT) system for real-time imaging of the human middle ear in live patients. Our system consists of a highly phase-stable Vernier-tuned distributed Bragg-reflector laser along with a real-time processing engine implemented on a graphics processing unit. We use the system to demonstrate, for the first time in live subjects, real-time Doppler measurements of middle ear vibration in response to sound, video rate 2D B-mode imaging of the middle ear and 3D volumetric B-mode imaging. All measurements were performed non-invasively through the intact tympanic membrane demonstrating that the technology is readily translatable to the clinic.

Controlled exploration of the effects of conductive hearing loss on wideband acoustic immittance in human cadaveric preparations

Current clinical practice cannot distinguish, with any degree of certainty, the multiple pathologies that produce conductive hearing loss in patients with an intact tympanic membrane and a well-aerated middle ear without exploratory surgery. The lack of an effective non-surgical diagnostic procedure leads to unnecessary surgery and limits the accuracy of information available during pre-surgical consultations with the patient. A non-invasive measurement to determine the pathology responsible for a conductive hearing loss prior to surgery would be of great value. This work investigates the utility of wideband acoustic immittance (WAI), a non-invasive measure of middle-ear mobility, in the differential diagnosis of pathologies responsible for conductive hearing loss. We focus on determining whether power reflectance (PR), a derivative of WAI, is a possible solution to this problem. PR is a measure of the fraction of sound power reflected from the middle ear when a sound stimulus is presented to the ear canal. PR and other metrics of middle-ear performance (such as ossicular motion via laser Doppler vibrometry) were measured in well-controlled human temporal bone preparations with simulated pathologies. We report measurements before and after simulation of stapes fixation (n = 8), malleus fixation (n = 10), ossicular disarticulation (n = 10), and superior canal dehiscence (n = 8). Our results are consistent with the small set of previously published reflectance measurements made in temporal bones and patients. In this present study, these temporal bone experiments with different middle- and inner-ear pathologies were compared to the initial normal state by analyzing both WAI and ossicular motion, demonstrating that WAI can be a valuable tool in the diagnosis of conductive hearing loss.

Methodology for Intraoperative Laser Doppler Vibrometry Measurements of Ossicular Chain Reconstruction

Objectives

Despite the increasing number of research concerning the applications of the Laser Doppler Vibrometry (LDV) in medicine, its usefulness is still under discussion. The aim of this study is to present a methodology developed in our Department for the LDV intraoperative assessment of ossicular chain reconstruction.

Methods

Ten patients who underwent “second look” tympanoplasty were involved in the study. The measurements of the acoustic conductivity of the middle ear were performed using the LDV system. Tone bursts with carrier frequencies of 500, 1,000, 2,000, and 4,000 Hz set in motion the ossicular chain. The study was divided into four experiments that examined the intra- and interindividual reproducibility, the utility of the posterior tympanotomy, the impact of changes in the laser beam angle, and the influence of reflective tape presence on measurements.

Results

There were no statistically significant differences between the two measurements performed in the same patient. However, interindividual differences were significant. In all cases, posterior tympanotomy proved to be useful for LDV measurements of the ossicular prosthesis vibrations. In most cases, changing the laser beam angle decreased signal amplitude about 1.5% (not significant change). The reflective tape was necessary to achieve adequate reflection of the laser beam.

Conclusion

LDV showed to be a valuable noncontact intraoperative tool for measurements of the middle ear conductive system mobility with a very good intraindividual repeatability. Neither a small change in the angle of the laser beam nor performing the measurements through posterior tympanotomy showed a significant influence on the results. Reflective tape was necessary to obtain good quality responses in LDV measurements.

Experimental and modeling study of human tympanic membrane motion in the presence of middle ear liquid

Vibration of the tympanic membrane (TM) has been measured at the umbo using laser Doppler vibrometry and analyzed with finite element (FE) models of the human ear. Recently, full-field TM surface motion has been reported using scanning laser Doppler vibrometry, holographic interferometry, and optical coherence tomography. Technologies for imaging human TM motion have the potential to lead to using a dedicated clinical diagnosis tool for identification of middle ear diseases. However, the effect of middle ear fluid (liquid) on TM surface motion is still not clear. In this study, a scanning laser Doppler vibrometer was used to measure the full-field surface motion of the TM from four human temporal bones. TM displacements were measured under normal and disease-mimicking conditions with different middle ear liquid levels over frequencies ranging from 0.2 to 8 kHz. An FE model of the human ear, including the ear canal, middle ear, and spiral cochlea was used to simulate the motion of the TM in normal and disease-mimicking conditions. The results from both experiments and FE model show that a simple deflection shape with one or two major displacement peak regions of the TM in normal ear was observed at low frequencies (1 kHz and below) while complicated ring-like pattern of the deflection shapes appeared at higher frequencies (4 kHz and above). The liquid in middle ear mainly affected TM deflection shapes at the frequencies higher than 1 kHz.

Effect of different stapes prostheses on the passive vibration of the basilar membrane

The effect of different stapes prostheses on the basilar membrane (BM) motion was determined. To that end, a three dimensional finite element (FE) model of the passive human cochlea was developed. Passive responses of the BM were found based on coupled fluid-structure interactions between the cochlear solid structures and the scala fluids. The passive BM vibrations in normal (healthy) cochlea were compared with vibrations in the cochlea in which a 0.4-mm piston or a proposed new type of prosthesis was implanted. The proposed chamber prosthesis was not experimentally implanted, but only numerically simulated. Design of the new chamber stapes prosthesis is presented for the first time in this paper. The simulation results showed 10-20 dB decrease in BM displacement amplitude in the case of the piston. In contrast, the BM responses in the cochlea with the new prosthesis are higher with respect to the healthy ear. The results obtained in this study are promising for further research to optimize the design of the new chamber stapes prosthesis.

Experimental measurement of tympanic membrane response for finite element model validation of a human middle ear

The middle ear consists of a tympanic membrane, ligaments, tendons, and three ossicles. An important function of the tympanic membrane is to deliver exterior sound stimulus to the ossicles and inner ear. In this study, the responses of the tympanic membrane in a human ear were measured and compared with those of a finite element model of the middle ear. A laser Doppler vibrometer (LDV) was used to measure the dynamic responses of the tympanic membrane, which had the measurement point on the cone of light of the tympanic membrane. The measured subjects were five Korean male adults and a cadaver. The tympanic membranes were stimulated using pure-tone sine waves at 18 center frequencies of one-third octave band over a frequency range of 200 Hz ~10 kHz with 60 and 80 dB sound pressure levels. The measured responses were converted into the umbo displacement transfer function (UDTF) with a linearity assumption. The measured UDTFs were compared with the calculated UDTFs using a finite element model for the Korean human middle ear. The finite element model of the middle ear consists of three ossicles, a tympanic membrane, ligaments, and tendons. In the finite element model, the umbo displacements were calculated under a unit sound pressure on the tympanic membrane. The UDTF of the finite element model exhibited good agreement with that of the experimental one in low frequency range, whereas in higher frequency band, the two response functions deviated from each other, which demonstrates that the finite element model should be updated with more accurate material properties and/or a frequency dependent material model.

Characterizing the ear canal acoustic impedance and reflectance by pole-zero fitting

This study characterizes middle ear complex acoustic reflectance (CAR) and impedance by fitting poles and zeros to real-ear measurements. The goal of this work is to establish a quantitative connection between pole-zero locations and the underlying physical properties of CAR data. Most previous studies have analyzed CAR magnitude; while the magnitude accounts for reflected power, it does not encode latency information. Thus, an analysis that studies the real and imaginary parts of the data together, being more general, should be more powerful. Pole-zero fitting of CAR data is examined using data compiled from various studies, dating back to Voss and Allen (1994). Recent CAR measurements were taken using the Mimosa Acoustics HearID system, which makes complex acoustic impedance and reflectance measurements in the ear canal over a 0.2-6.0 [kHz] frequency range. Pole-zero fits to measurements over this range are achieved with an average RMS relative error of less than 3% with 12 poles. Factoring the reflectance fit into its all-pass and minimum-phase components estimates the effect of the residual ear canal, allowing for comparison of the eardrum impedance and admittance across measurements. It was found that individual CAR magnitude variations for normal middle ears in the 1-4 [kHz] range often give rise to closely-placed pole-zero pairs, and that the locations of the poles and zeros in the s-plane may systematically differ between normal and pathological middle ears. This study establishes a methodology for examining the physical and mathematical properties of CAR using a concise parametric model. Pole-zero modeling accurately parameterizes CAR data, providing a foundation for detection and identification of middle ear pathologies. This article is part of a special issue entitled "MEMRO 2012".

Feasibility of Laser Doppler Vibrometry as potential diagnostic tool for patients with abdominal aortic aneurysms

The application of laser measurements in medical applications makes it possible to measure even very small vibrations without contacting the skin surface. In the present work we investigate the use of a scanning vibrometer to measure the mechanical wave of the abdominal wall caused by the heart beat and blood pressure pulse. A Laser Doppler Vibrometer, triggered by cardiac signals, is used to scan points on a grid positioned on the abdomen of human subjects. The proposed procedure is intended for detecting anomalies in the abdominal cavity such as aortic aneurysms. Here, we outline the technical setup used in our preliminary in vivo experiments and present some preliminary results. This feasibility study shows that the proposed measurement procedure allows for measuring the skin motion, that the skin motion measured is related to the heart activity, and that there are indication that the presence of an abdominal aortic aneurysm significantly modifies the relation between blood pressure pulsations and skin motion on the abdomen.

A three-dimensional finite element model of round window membrane vibration before and after stapedotomy surgery

Piston stapes prostheses are implanted in patients with refractory conductive or mixed hearing loss due to stapes otosclerosis to stimulate the perilymph with varying degrees of success. The overclosure effect described by the majority of researchers affects mainly low and medium frequencies, and a large number of patients report a lack of satisfactory results for frequencies above 2 kHz. The mechanics of perilymph stimulation with the piston have not been studied in a systematic manner. The objective of this study was to assess the influence of stapedotomy surgery on round window membrane vibration and to estimate the postoperative outcomes using the finite element (FE) method. The study hypothesis is that the three-dimensional FE model developed of the human inner ear, which simulates the round window (RW) membrane vibration, can be used to assess the influence of stapedotomy on auditory outcomes achieved after the surgical procedure. An additional objective of the study was to enable the simulation of RW membrane vibration after stapedotomy using a new type of stapes prosthesis currently under investigation at Warsaw University of Technology. A three-dimensional finite element (FE) model of the human inner ear was developed and validated using experimental data. The model was then used to simulate the round window membrane vibration before and after stapedotomy surgery. Functional alterations of the RW membrane vibration were derived from the model and compared with the results of experimental measurements from temporal bones of a human cadaver. Piston stapes prosthesis implantation causes an approximately fivefold (14 dB) lower amplitude of the RW membrane vibrations compared with normal anatomical conditions. A satisfactory agreement between the FE model and the experimental data was found. The new prosthesis caused an increase of 20–30 dB in the RW displacement amplitude compared with the 0.4-mm piston prosthesis. In all frequencies, the FE model predicted a RW displacement curve that was above the experimental curves for the normal ear. The stapedotomy can be well simulated by the FE model to predict the auditory outcomes achieved following this otosurgery procedure. The 3D FE model developed in this study may be used to optimize the geometry of a new type of stapes prosthesis in order to achieve a similar sound transmission through the inner ear as for a normal middle ear. This should provide better auditory outcomes for patients with stapedial otosclerosis.

Laser Doppler vibrometry measurements of human cadaveric tympanic membrane vibration

OBJECTIVE

To determine the feasibility of measuring tympanic membrane (TM) vibrations at multiple locations on the TM to differentiate normal eardrums from those with associated ossicular pathologies.

DESIGN

Cadaveric human temporal bone study.

SETTING

Basic science laboratory.

METHODS

A mastoidectomy and facial recess approach was performed on four cadaveric temporal bones to obtain access to the ossicles without disrupting the TM. Ossicles were palpated to ensure normal mobility and an intact ossicular chain. Laser Doppler Vibrometry (LDV) measurements were then taken on all four TMs. LDV measurements were repeated on each TM following stapes footplate fixation, incudo-stapedial joint dislocation, and malleus head fixation.

MAIN OUTCOME MEASURES

LDV measurements of TM vibration at the umbo, the lateral process of the malleus, and in each of the four quadrants of the TM.

RESULTS

The best signal-to-noise ratios were found between 2 and 4 kHz, at the umbo, the anterior superior quadrant, the anterior inferior quadrant, and the posterior inferior quadrant. Since our goal was to assess the ossicular chain, we selected the TM locations closest to the ossicular chain (the umbo and lateral process of the malleus) for further analysis. Differences could be seen between normals and the simulated ossicular pathologies, but values were not statistically significant.

CONCLUSIONS

LDV measurements are technically challenging and require optimization to obtain consistent measurements. This study demonstrates the potential of LDV to differentiate ossicular pathologies behind an intact tympanic membrane. Future studies will further characterize the clinical role of this diagnostic modality.

Assessing eardrum deformation by digital holography

A novel system measures the structure, shape, and acoustically induced changes to the membrane of the human middle ear, to help diagnose and treat hearing disorders.

Comparison of ear-canal reflectance and umbo velocity in patients with conductive hearing loss: a preliminary study

OBJECTIVE

The goal of the present study was to investigate the clinical utility of measurements of ear-canal reflectance (ECR) in a population of patients with conductive hearing loss in the presence of an intact, healthy tympanic membrane and an aerated middle ear. We also sought to compare the diagnostic accuracy of umbo velocity (VU) measurements and measurements of ECR in the same group of patients.

DESIGN

This prospective study comprised 31 adult patients with conductive hearing loss, of which 14 had surgically confirmed stapes fixation due to otosclerosis, 6 had surgically confirmed ossicular discontinuity, and 11 had computed tomography and vestibular evoked myogenic potential confirmed superior semicircular canal dehiscence (SCD). Measurements on all 31 ears included pure-tone audiometry for 0.25 to 8 kHz, ECR for 0.2 to 6 kHz using the Mimosa Acoustics HearID system, and VU for 0.3 to 6 kHz using the HLV-1000 laser Doppler vibrometer (Polytec Inc, Waldbronn, Germany). We analyzed power reflectance |ECR| as well as the absorbance level = 10 × log10(1 - |ECR|). All measurements were made before any surgical intervention. The VU and ECR data were plotted against normative data obtained in a companion study of 58 strictly defined normal ears ().

RESULTS

Small increases in |ECR| at low-to-mid frequencies (400-1000 Hz) were observed in cases with stapes fixation, while narrowband decreases were seen for both SCD and ossicular discontinuity. The SCD and ossicular discontinuity differed in that the SCD had smaller decreases at mid-frequency (∼1000 Hz), whereas ossicular discontinuity had larger decreases at lower frequencies (500-800 Hz). SCD tended to have less air-bone gap at high frequencies (1-4 kHz) compared with stapes fixation and ossicular discontinuity. The |ECR| measurements, in conjunction with audiometry, could successfully separate 28 of the 31 cases into the three pathologies. By comparison, VU measurements, in conjunction with audiometry, could successfully separate various pathologies in 29 of 31 cases.

CONCLUSIONS

The combination of |ECR| with audiometry showed clinical utility in the differential diagnosis of conductive hearing loss in the presence of an intact tympanic membrane and an aerated middle ear and seems to be of similar sensitivity and specificity to measurements of VU plus audiometry. Additional research is needed to expand upon these promising preliminary results.

Ear-canal reflectance, umbo velocity, and tympanometry in normal-hearing adults

OBJECTIVE

This study compares measurements of ear-canal reflectance (ECR) to other objective measurements of middle ear function including audiometry, umbo velocity (VU), and tympanometry in a population of strictly defined normal-hearing ears.

DESIGN

Data were prospectively gathered from 58 ears of 29 normal-hearing subjects, 16 females and 13 males, aged 22 to 64 yr. Subjects met all of the following criteria to be considered as having normal hearing: (1) no history of significant middle ear disease; (2) no history of otologic surgery; (3) normal tympanic membrane on otoscopy; (4) pure-tone audiometric thresholds of 20 dB HL or better for 0.25 to 8 kHz; (5) air-bone gaps no greater than 15 dB at 0.25 kHz and 10 dB for 0.5 to 4 kHz; (6) normal, type-A peaked tympanograms; and (7) all subjects had two "normal" ears (as defined by these criteria). Measurements included pure-tone audiometry for 0.25 to 8 kHz, standard 226 Hz tympanometry, ECR for 0.2 to 6 kHz at 60 dB SPL using the Mimosa Acoustics HearID system, and umbo velocity (VU) for 0.3 to 6 kHz at 70 to 90 dB SPL using the HLV-1000 laser Doppler vibrometer (Polytec Inc).

RESULTS

Mean power reflectance (|ECR|) was near 1.0 at 0.2 to 0.3 kHz, decreased to a broad minimum of 0.3 to 0.4 between 1 and 4 kHz, and then sharply increased to almost 0.8 by 6 kHz. The mean pressure reflectance phase angle (∠ECR) plotted on a linear frequency scale showed a group delay of approximately 0.1 msec for 0.2 to 6 kHz. Small significant differences were observed in |ECR| at the lowest frequencies between right and left ears and between males and females at 4 kHz. |ECR| decreased with age but reached significance only at 1 kHz. Our ECR measurements were generally similar to previous published reports. Highly significant negative correlations were found between |ECR| and VU for frequencies below 1 kHz. Significant correlations were also found between the tympanometrically determined peak total compliance and |ECR| and VU at frequencies below 1 kHz. The results suggest that middle ear compliance contributes significantly to the measured power reflectance and umbo velocity at frequencies below 1 kHz but not at higher frequencies.

CONCLUSIONS

This study has established a database of objective measurements of middle ear function (ECR, umbo velocity, tympanometry) in a population of strictly defined normal-hearing ears. These data will promote our understanding of normal middle ear function and will serve as a control for comparison to similar measurements made in pathological ears.

Forward and reverse transfer functions of the middle ear based on pressure and velocity DPOAEs with implications for differential hearing diagnosis

Recently it was shown that distortion product otoacoustic emissions (DPOAEs) can be measured as vibration of the human tympanic membrane in vivo, and proposed to use these vibration DPOAEs to support a differential diagnosis of middle-ear and cochlear pathologies. Here, we investigate how the reverse transfer function (r-TF), defined as the ratio of DPOAE-velocity of the umbo to DPOAE-pressure in the ear canal, can be used to diagnose the state of the middle ear. Anaesthetized guinea pigs served as the experimental animal. Sound was delivered free-field and the vibration of the umbo measured with a laser Doppler vibrometer (LDV). Sound pressure was measured 2-3 mm from the tympanic membrane with a probe-tube microphone. The forward transfer function (f-TF) of umbo velocity relative to ear-canal pressure was obtained by stimulating with multi-tone pressure. The r-TF was assembled from DPOAE components generated in response to acoustic stimulation with two stimulus tones of frequencies f(1) and f(2); f(2)/f(1) was constant at 1.2. The r-TF was plotted as function of DPOAE frequencies; they ranged from 1.7 kHz to 23 kHz. The r-TF showed a characteristic shape with an anti-resonance around 8 kHz as its most salient feature. The data were interpreted with the aid of a middle-ear transmission-line model taken from the literature for the cat and adapted to the guinea pig. Parameters were estimated with a three-step fitting algorithm. Importantly, the r-TF is governed by only half of the 15 independent, free parameters of the model. The parameters estimated from the r-TF were used to estimate the other half of the parameters from the f-TF. The use of r-TF data - in addition to f-TF data - allowed robust estimates of the middle-ear parameters to be obtained. The results highlight the potential of using vibration DPOAEs for ascertaining the functionality of the middle ear and, therefore, for supporting a differential diagnosis of middle-ear and cochlear pathologies.

New aspects in the clinical diagnosis of otosclerosis using laser Doppler vibrometry

HYPOTHESIS

Laser Doppler vibrometry (LDV) applied to umbo motion measurement in healthy and otosclerotic ears shows statistically tested differences.

BACKGROUND

The LDV is a research tool that measures middle ear function by registering sound-induced tympanic membrane velocity. Its possible application in the diagnosis of different middle ear disorders, especially otosclerosis, is currently being evaluated. Established diagnosis can identify various ossicular chain pathologies in most cases but is still sometimes contradicted by the findings of surgical middle ear exploration.

METHODS

We used a fractionally modified LDV setting as previously reported to evaluate 150 normal-hearing ears and 49 ears with conductive hearing loss. In a first step, the impact of age variation on the umbo transfer function was investigated by dividing the normal-hearing population into 3 age groups. In a second step, the control group was compared with patients with conductive hearing loss; certain patterns in the umbo transfer function were especially investigated by discriminant analysis.

RESULTS

Mean magnitude of the oldest group was found to be significantly higher than the other 2 groups, but it was not possible to diagnostically classify the 3 groups. Discriminant analysis revealed the linear term of a cubic polynom to significantly best describe the umbo transfer function in normal ears (p < 0.0005; partial eta = 0.866) and in otosclerotic ears (p < 0.0005; partial eta = 0.799). Separating otosclerotic ear from normal-hearing ear evidence suggests a sensitivity of 82% and specificity of 92%.

CONCLUSION

Evaluation of LDV magnitude curve patterns gives helpful information in the diagnosis of otosclerosis but does not suffice as a single diagnostic tool.

Findings at exploratory tympanotomy for conductive hearing loss

Introduction:

Despite advances in imaging and other diagnostic tests, it is often impossible to establish with confidence a pre-operative diagnosis in a patient with a conductive hearing loss.

Methods:

We studied a series of 340 exploratory tympanotomies for conductive hearing loss carried out by a single surgeon.

Results:

The most common operative diagnosis was otosclerosis (n = 164, 48.2 per cent). Ossicular discontinuity was found more commonly than previously reported (n = 103, 30.3 per cent). A small but significant number of patients were found to have cholesteatoma (n = 7.2 per cent).

Conclusions:

This information is of value when discussing potential findings at surgery for conductive hearing loss. While otosclerosis is the commonest finding in such cases, a significant number of patients have defects of the ossicular chain.

Preliminary Analyses of Tympanic-Membrane Motion from Holographic Measurements

Computer-aided, personal computer (PC) based, optoelectronic holography (OEH) was used to obtain preliminary measurements of the sound-induced displacement of the tympanic membrane (TM) of cadaver cats and chinchillas. Real-time time-averaged holograms, processed at video rates, were used to characterise the frequency dependence of TM displacements as tone frequency was swept from 400 Hz to 20 kHz. Stroboscopic holography was used at selected frequencies to measure, in full-field-of-view, displacements of the TM surface with nanometer resolution. These measurements enable the determination and the characterisation of inward and outward displacements of the TM. The time-averaged holographic data suggest standing wave patterns on the cat's TM surface, which move from simple uni-modal or bi-modal patterns at low frequencies, through complicated multimodal patterns above 3 kHz, to highly ordered arrangements of displacement waves with tone frequencies above 15 kHz. The frequency boundaries of the different wave patterns are lower in chinchilla (simple patterns below 600 Hz, ordered patterns above 4 kHz) than cat. The stroboscopic holography measurements indicate wave-like motion patterns on the TM surface, where the number of wavelengths captured along sections of the TM increased with stimulus frequency with as many as 11 wavelengths visible on the chinchilla TM at 16 kHz. Counts of the visible number of wavelengths on TM sections with different sound stimulus frequency provided estimates of wave velocity along the TM surface that ranged from 5 m s(-1) at frequencies below 8 kHz and increased to 25 m s(-1) by 20 kHz.

Optoelectronic holographic otoscope for measurement of nano-displacements in tympanic membranes

Current methodologies for characterizing tympanic membrane (TM) motion are usually limited to either average acoustic estimates (admittance or reflectance) or single-point mobility measurements, neither of which suffices to characterize the detailed mechanical response of the TM to sound. Furthermore, while acoustic and single-point measurements may aid in diagnosing some middle-ear disorders, they are not always useful. Measurements of the motion of the entire TM surface can provide more information than these other techniques and may be superior for diagnosing pathology. We present advances in our development of a new compact optoelectronic holographic otoscope (OEHO) system for full field-of-view characterization of nanometer-scale sound-induced displacements of the TM surface at video rates. The OEHO system consists of a fiber optic subsystem, a compact otoscope head, and a high-speed image processing computer with advanced software for recording and processing holographic images coupled to a computer-controlled sound-stimulation and recording system. A prototype OEHO system is in use in a medical research environment to address basic science questions regarding TM function. The prototype provides real-time observation of sound-induced TM displacement patterns over a broad frequency range. Representative time-averaged and stroboscopic holographic interferometry results in animals and human cadaver samples are shown, and their potential utility is discussed.

Doppler imaging using spectrally-encoded endoscopy

The capability to image tissue motion such as blood flow through an endoscope could have many applications in medicine. Spectrally encoded endoscopy (SEE) is a recently introduced technique that utilizes a single optical fiber and miniature diffractive optics to obtain endoscopic images through small diameter probes. Using spectral-domain interferometry, SEE is furthermore capable of three-dimensional volume imaging at video rates. Here we show that by measuring relative spectral phases, this technology can additionally measure Doppler shifts. Doppler SEE is demonstrated in flowing Intralipid phantoms and vibrating middle ear ossicles.

Clinical utility of laser-Doppler vibrometer measurements in live normal and pathologic human ears

The laser-Doppler vibrometer (LDV) is a research tool that can be used to quickly measure the sound-induced velocity of the tympanic membrane near the umbo (the inferior tip of the malleus) in live human subjects and patients. In this manuscript we demonstrate the LDV to be a sensitive and selective tool for the diagnosis and differentiation of various ossicular disorders in patients with intact tympanic membranes and aerated middle ears. Patients with partial or total ossicular interruption or malleus fixation are readily separated from normal-hearing subjects with the LDV. The combination of LDV measurements and air-bone gap can distinguish patients with fixed stapes from those with normal ears. LDV measurements can also help differentiate air-bone gaps produced by ossicular pathologies from those associated with pathologies of inner-ear sound conduction such as a superior semicircular canal dehiscence.

[Laser Doppler vibrometric measurements of DPOAE in humans. Eardrum vibrations reflect middle- and inner-ear characteristics]

BACKGROUND

Up to now, laser interferometric vibration measurements of the human eardrum have not provided any information about cochlear function, because the measurement devices have not been sufficiently sensitive.

METHODS

After designing a new type of laser Doppler vibrometer (LDV) that allows detection of displacement amplitudes down to about 1 pm, we used this device in 20 subjects to measure growth functions of the distortion products of otoacoustic emissions (DPOAE) as vibrations of the umbo. For comparison, DPOAE growth functions were also measured conventionally with an acoustic probe in the closed external auditory meatus. Hearing thresholds were estimated from both sets of measurements and compared with Békésy thresholds.

RESULTS

The standard deviation of the threshold estimate obtained from the vibration DPOAEs was 8.6 dB, which is significantly smaller than that of the threshold estimate (16.7 dB) obtained from the acoustic DPOAEs. We attribute the smaller standard deviation for the LDV data to the fact that these measurements are made in an open sound field and are therefore less susceptible to pressure calibration errors.

CONCLUSIONS

Being relatively free of sound-field measurement artefacts, the LDV method allows precise estimation of the hearing threshold. Vibration measurements of the umbo have, therefore, considerable potential for the differential diagnosis of mechanical dysfunction of the middle and inner ear.

Isolated fracture of the manubrium of the malleus

OBJECTIVE

To describe a series of five patients with isolated fracture of the manubrium of the malleus.

DESIGN

Retrospective case series.

SUBJECTS

Five patients aged 44-64 years with isolated fracture of the manubrium who presented to our institution over a five-year period (2000-2005).

RESULTS

All patients presented with a history of digitally manipulating the external auditory canal, leading to the manubrial fracture, which we presume was due to a suction-type mechanism. Otomicroscopy often revealed a break in the smooth contour of the manubrium. All patients had air-bone gaps on audiometry, especially at higher frequencies. Tympanometry showed hypermobility of the tympanic membrane in four patients who were tested. Laser-Doppler vibrometry revealed increased umbo velocity in four out of five patients. Four patients were treated conservatively. One patient underwent exploratory tympanotomy with successful ossiculoplasty.

CONCLUSIONS

Isolated fracture of the manubrium is a rare condition which may present as sudden-onset hearing loss after digital manipulation of the external auditory canal. The diagnosis can be made on the basis of otomicroscopy, audiometry, tympanometry and laser-Doppler vibrometry. Conservative treatment is often successful.