Evaluation of the effects of Covid-19 on cochleovestibular system with audiovestibular tests

Purpose The purpose of the present study was to investigate the effects of COVID-19 on audiovestibular system with Transiently Evoked Distortion Otoacoustic Emissions (TOAE), Distortion Product Otoacoustic Emissions (DPOAE), video head impulse test (vHIT) and caloric test. Methods Audiovestibular findings of 24 patients with moderate/severe COVID-19 and 24 healthy controls were compared using pure tone audiometry, tympanometry, TOAE, DPOAE, caloric test, and vHIT. Results On audiometry, the pure tone averages of the COVID-19 patients were higher than the controls ( P = .038). The TEOAE amplitudes at 4000 and 5000 Hz ( P = .006 and P < .01), and DPOAE amplitudes at 3000, 6000, and 8000 Hz ( P < .001, P = .003 and P < .001) were significantly lower in COVID-19 patients compared to the controls. On vestibular tests, there was no significant difference between the caloric test results of the patients and the controls ( P > .05). On vHIT testing, amplitudes of right semicircular canal was found to be significantly lower in COVID-19 group compared to the control group ( P = .008). Conclusion COVID-19 may affect inner ear functions causing a subtle damage in the outer hair cells and lateral semicircular canals. It must be kept in mind that COVID-19 may cause cochleovestibular problems.

Assessment of Distortion Product Otoacoustic Emissions Input-Output Function in Individuals with and without Musical Abilities

Background and Aim: Musical training has shown to bring about superior performance in several auditory and non-auditory tasks compared to those without musical exposure. Distortion product otoacoustic emissions (DPOAE) input-output function can be an indicator of the non-linear functioning of the cochlea. The objective of this study was to evaluate and compare the differences in the slope of DPOAE input-output function in individuals with and without musical abilities. Methods: Twenty normal-hearing individuals were considered in the age range of 18–25 years. They were divided based on the scores obtained on the questionnaire of musical abilities, as individuals with and without musical abilities. DPOAE input-output function was done for each of the two groups. The slope of the DPOAE input-output function was compared at different frequencies between the groups. Results: The results of the Mann Whitney test revealed that the slope was significantly steeper at 2000, 3000, 4000 and 6000 Hz in individuals with musical abilities. There was no significant difference in slope at 1000 and 1500 Hz. Conclusion: The increased steepness of the slope indicates a relatively better functioning of the cochlea in individuals with musical abilities. The enhanced perception of music may induce changes in the cochlea resulting in a better appreciation of music.

Application of otoacoustic emissions and brainstem evoked response audiometry in newborn hearing screening

<p class="abstract"><strong>Background: </strong>Newborn hearing screening was conducted in a tertiary care hospital in a step by step manner using otoacoustic emissions (OAE) and brainstem evoked response audiometry (BERA) and details were recorded.</p><p class="abstract"><strong>Methods:</strong> A prospective institutional based study was conducted. All the newborns born in the hospital over a period of 18 months from December 2018 to May 2020 were considered in the study. Healthy newborns were screened bedside within 24 hours of delivery and NICU (Neonatal Intensive Care Unit) babies were screened in the NICU. Handheld OAE apparatus was used as the initial screening tool. A total of 3 OAEs were done for babies with a “refer” result in the OAEs, which were done 1 month apart. Babies with a “refer” in the third OAE were subjected for BERA.</p><p class="abstract"><strong>Results:</strong> A total of 14226 babies were screened at 24-48 hours of birth. Among them, 13,069 babies passed the first OAE screening in both ears. Remaining babies were referred for further follow-up. After subsequent follow-ups and successive testing, 11 babies were found to have hearing loss, which was diagnosed within 4-5 months of the child’s birth.</p><p class="abstract"><strong>Conclusions: </strong>Universal newborn hearing screening is the need of the day. OAE is an effective screening tool for newborn hearing loss. When complemented by BERA, majority of congenitally deaf babies can be diagnosed at a very early age. This helps in early intervention.</p>

Does gestational diabetes mellitus affect the hearing of the baby?

<p><strong>Background: </strong>Hearing screening results of babies born to mothers with and without gestational diabetes mellitus done within 24-48 hours of delivery using otoacoustic emissions was compared. Babies who failed the screening were recalled for further testing.<strong></strong></p><p><strong>Methods: </strong>A prospective institutional based study was conducted between December 2018 and May 2020. All the babies were screened for hearing impairment using handheld OAE apparatus within 24-48 hours of delivery. History of gestational diabetes mellitus in the mother was enquired. Any baby with a “refer” result in the OAE study was recalled for a repeat OAE testing after a month. This was repeated two more times if the baby failed the test every time. In case of failing the test for the third time, the baby was sent for brainstem evoked response audiometry for confirmation of hearing loss.<strong></strong></p><p><strong>Results: </strong>Screening was done for 14226 babies. Among them, 44 babies were born to mothers with gestational diabetes mellitus. The hearing screening results did not show a significant association between gestational diabetes mellitus and hearing impairment in the baby.<strong></strong></p><p><strong>Conclusions: </strong>Gestational diabetes is considered as one of the risk factors for deafness in the baby. This study could not establish such a relationship.<strong></strong></p>

Characterizing the Access of Cholinergic Antagonists to Efferent Synapses in the Inner Ear

Stimulation of cholinergic efferent neurons innervating the inner ear has profound, well-characterized effects on vestibular and auditory physiology, after activating distinct ACh receptors (AChRs) on afferents and hair cells in peripheral endorgans. Efferent-mediated fast and slow excitation of vestibular afferents are mediated by α4β2*-containing nicotinic AChRs (nAChRs) and muscarinic AChRs (mAChRs), respectively. On the auditory side, efferent-mediated suppression of distortion product otoacoustic emissions (DPOAEs) is mediated by α9α10nAChRs. Previous characterization of these synaptic mechanisms utilized cholinergic drugs, that when systemically administered, also reach the CNS, which may limit their utility in probing efferent function without also considering central effects. Use of peripherally-acting cholinergic drugs with local application strategies may be useful, but this approach has remained relatively unexplored. Using multiple administration routes, we performed a combination of vestibular afferent and DPOAE recordings during efferent stimulation in mouse and turtle to determine whether charged mAChR or α9α10nAChR antagonists, with little CNS entry, can still engage efferent synaptic targets in the inner ear. The charged mAChR antagonists glycopyrrolate and methscopolamine blocked efferent-mediated slow excitation of mouse vestibular afferents following intraperitoneal, middle ear, or direct perilymphatic administration. Both mAChR antagonists were effective when delivered to the middle ear, contralateral to the side of afferent recordings, suggesting they gain vascular access after first entering the perilymphatic compartment. In contrast, charged α9α10nAChR antagonists blocked efferent-mediated suppression of DPOAEs only upon direct perilymphatic application, but failed to reach efferent synapses when systemically administered. These data show that efferent mechanisms are viable targets for further characterizing drug access in the inner ear.

Modelling the Generation of the Cochlear Microphonic

<p>The human ear is a remarkable sensory organ. A normal healthy human ear is able to process sounds covering a wide range of frequencies and intensities, while distinguishing between different components of complex sounds such as a musical chord. In the last four decades, knowledge about the cochlea and the mechanisms involved in its operation has greatly increased, but many details about these mechanisms remain unresolved and disputed. The cochlea has a vulnerable structure. Consequently, measuring and monitoring its mechanical and electrical activities even with contemporary devices is very difficult. Modelling can be used to fill gaps between those measurements that are feasible and actual cochlear function. Modelling techniques can also help to simplify complex cochlear operation to a tractable and comprehensible level while still reproducing certain behaviours of interest. Modelling therefore can play an essential role in developing a better understanding of the cochlea. The Cochlear Microphonic (CM) is an electrical signal generated inside the cochlea in response to sound. This electrical signal reflects mechanical activity in the cochlea and the excitation processes involved in its generation. However, the difficulty of obtaining this signal and the simplicity of other methods such as otoacoustic emissions have discouraged the use of the cochlear microphonic as a tool for studying cochlear functions. In this thesis, amodel of the cochlea is presented which integrates bothmechanical and electrical aspects, enabling the interaction between them to be investigated. The resulting model is then used to observe the effect of the cochlear amplifier on the CM. The results indicate that while the cochlear amplifier significantly amplifies the basilar membrane displacement, the effect on the CM is less significant. Both of these indications agree with previous physiological findings. A novel modelling approach is used to investigate the tuning discrepancy between basilar membrane and CMtuning curves. The results suggest that this discrepancy is primarily due to transversal phase cancellation in the outer hair cell rather than longitudinal phase cancellation along the basilar membrane. In addition, the results of the model suggest that spontaneous cochlear microphonic should exist in the cochlea. The existence of this spontaneous electrical signal has not yet been reported.</p>

Modelling the Generation of the Cochlear Microphonic

<p>The human ear is a remarkable sensory organ. A normal healthy human ear is able to process sounds covering a wide range of frequencies and intensities, while distinguishing between different components of complex sounds such as a musical chord. In the last four decades, knowledge about the cochlea and the mechanisms involved in its operation has greatly increased, but many details about these mechanisms remain unresolved and disputed. The cochlea has a vulnerable structure. Consequently, measuring and monitoring its mechanical and electrical activities even with contemporary devices is very difficult. Modelling can be used to fill gaps between those measurements that are feasible and actual cochlear function. Modelling techniques can also help to simplify complex cochlear operation to a tractable and comprehensible level while still reproducing certain behaviours of interest. Modelling therefore can play an essential role in developing a better understanding of the cochlea. The Cochlear Microphonic (CM) is an electrical signal generated inside the cochlea in response to sound. This electrical signal reflects mechanical activity in the cochlea and the excitation processes involved in its generation. However, the difficulty of obtaining this signal and the simplicity of other methods such as otoacoustic emissions have discouraged the use of the cochlear microphonic as a tool for studying cochlear functions. In this thesis, amodel of the cochlea is presented which integrates bothmechanical and electrical aspects, enabling the interaction between them to be investigated. The resulting model is then used to observe the effect of the cochlear amplifier on the CM. The results indicate that while the cochlear amplifier significantly amplifies the basilar membrane displacement, the effect on the CM is less significant. Both of these indications agree with previous physiological findings. A novel modelling approach is used to investigate the tuning discrepancy between basilar membrane and CMtuning curves. The results suggest that this discrepancy is primarily due to transversal phase cancellation in the outer hair cell rather than longitudinal phase cancellation along the basilar membrane. In addition, the results of the model suggest that spontaneous cochlear microphonic should exist in the cochlea. The existence of this spontaneous electrical signal has not yet been reported.</p>

A Time-Course-Based Estimation of the Human Medial Olivocochlear Reflex Function Using Clicks

The auditory efferent system, especially the medial olivocochlear reflex (MOCR), is implicated in both typical auditory processing and in auditory disorders in animal models. Despite the significant strides in both basic and translational research on the MOCR, its clinical applicability remains under-utilized in humans due to the lack of a recommended clinical method. Conventional tests employ broadband noise in one ear while monitoring change in otoacoustic emissions (OAEs) in the other ear to index efferent activity. These methods, (1) can only assay the contralateral MOCR pathway and (2) are unable to extract the kinetics of the reflexes. We have developed a method that re-purposes the same OAE-evoking click-train to also concurrently elicit bilateral MOCR activity. Data from click-train presentations at 80 dB peSPL at 62.5 Hz in 13 young normal-hearing adults demonstrate the feasibility of our method. Mean MOCR magnitude (1.7 dB) and activation time-constant (0.2 s) are consistent with prior MOCR reports. The data also suggest several advantages of this method including, (1) the ability to monitor MEMR, (2) obtain both magnitude and kinetics (time constants) of the MOCR, (3) visual and statistical confirmation of MOCR activation.