Alterations in cochlear function after exposure to short term broad band noise assessed by otoacoustic emissions.

Identifying three otopathologies in humans

High sodium salicylate doses can cause reversible hearing loss and tinnitus, possibly due to reduced outer hair cell electromotility. Sodium salicylate is known to alter outer hair cell structure and function. This study determined the reversibility and cochlear recovery time after administration of an ototoxic sodium salicylate dose to guinea pigs with normal cochlear function. Prospective experimental investigation. All animals received a single 500 mg sodium salicylate dose, but with different durations of action. Function was evaluated before drug administration and immediately before sacrifice. Cochleae were processed and viewed using scanning electron microscopy. Changes in outer hair cell function were observed to be present 2 hours after drug administration, with recovery of normal anatomy beginning after 24 hours. Subsequently, derangement and distortion of cilia reduced, with effects predominantly in row three. At 168 hours, cilia were near-normal but with mild distortions which interfered with normal cochlear physiology. Ciliary changes persisted for up to 168 hours after ototoxic sodium salicylate administration.

Background: Dental professionals are routinely exposed to occupational noise from high-speed handpieces and ultrasonic scalers, with levels that can reach up to 90 dB(A). While such exposure is suspected to affect cochlear function, objective assessments in this population remain limited. This study investigated short-term changes in distortion product otoacoustic emissions (DPOAEs) as a biomarker of outer hair cell (OHC) function following routine clinical dental procedures. Methods: DPOAEs were recorded at frequencies from 1000 to 6000 Hz in young dental professionals with clinically normal hearing. Measurements were obtained at three time points: prior to dental procedures (baseline), immediately after exposure (3-5 min post-procedure), and at a 48-h (follow-up). Participants were stratified into two groups based on exposure profile: those exposed to occupational dental noise alone (Group 1) and those with concurrent use of personal listening devices (PLDs) in addition to occupational exposure (Group 2). Results: A significant reduction in DPOAE amplitudes was observed immediately following dental procedures in both groups, indicating an acute effect on OHC function. This reduction was more pronounced in Group 1 (PLD users) compared to Group 2 (occupational noise only). Amplitudes returned to baseline levels at the 48-h follow-up in both groups, confirming the transient nature of the effect. The absence of significant Frequency × Time interactions indicates that the observed amplitude reductions were broadly distributed across the tested frequency range rather than confined to a specific spectral region. Conclusions: Routine clinical dental procedures can induce transient, measurable changes in cochlear outer hair cell function, detectable by DPOAEs in young professionals with normal audiometric thresholds. Although these changes appear reversible within 48 h, the greater acute response observed in individuals with concurrent personal listening device use suggests that cumulative acoustic exposure may increase cochlear susceptibility. These findings support the integration of objective cochlear monitoring into occupational health surveillance for dental personnel.

Acute changes in cochlear potentials due to cisplatin

A View to Natural Killer Cells in Hepatitis C

The absence of thyroid hormone (TH) during late gestation and early infancy can cause irreparable deafness in both humans and rodents. A variety of rodent models have been utilized in an effort to identify the underlying molecular mechanism. Here, we characterize a mouse model of secondary hypothyroidism, pituitary transcription factor 1 (Pit1dw), which has profound, congenital deafness that is rescued by oral TH replacement. These mutants have tectorial membrane abnormalities, including a prominent Hensen's stripe, elevated β-tectorin composition, and disrupted striated-sheet matrix. They lack distortion product otoacoustic emissions and cochlear microphonic responses, and exhibit reduced endocochlear potentials, suggesting defects in outer hair cell function and potassium recycling. Auditory system and hair cell physiology, histology and anatomy studies reveal novel defects of hormone deficiency related to deafness: (1) permanently impaired expression of KCNJ10 in the stria vascularis of Pit1dw mice, which likely contributes to the reduced endocochlear potential, (2) significant outer hair cell loss in the mutants, which may result from cellular stress induced by the lower KCNQ4 expression and current levels in Pit1dw mutant outer hair cells and (3) sensory and strial cell deterioration, which may have implications for thyroid hormone dysregulation in age related hearing impairment. In summary, we suggest that these defects in outer hair cell and strial cell function are important contributors to the hearing impairment in Pit1dw mice.

Background: Recreational noise exposure, including personal music device use (PMD), has become a growing public health concern, as it may potentially result in the development of hearing difficulties.Objectives: The aim of the study was to determine the differential impact and short-term effects of simultaneous cardiovascular workout and PMD use on the outer hair cell (OHC) function of young adults.Method: A quantitative research approach was followed. In this study a pre-test post-test approach was used and twelve subjects participated in three 1 h testing conditions with altered variables including: (i) exposure to PMD use in isolation, (ii) exposure to cardiovascular workout in isolation, and (iii) simultaneous exposure to the latter mentioned. Distortion product otoacoustic emissions (DPOAEs) were conducted pree and post exposure for each testing condition as primary indicator of cochlear responses. The process consisted of a cycling procedure through the preset stimulus frequency sequence, measuring the 2f₁—f₂ (75—70 dBSPL) and constructing a plot of DPOAE levels as a function offrequency.Results: Individual testing conditions did not result in statistically significant changes of the DPOAE response, however a significantly different profile in the DPOAE response level increase/decrease for the higher frequencies (6—8 kHz) was obtained when comparing the different sessions. Exposure to cardiovascular workout condition in isolation indicated a clear trend of an increased DPOAE response level between the pre-exposure and post exposuretesting from 2 kHz to 8 kHz with a maximum increase at 6 kHz. Both the music-only condition and the combined condition resulted in a clear trend of decreased DPOAE response amplitudes between the pre-exposure and post-exposure testing for the higher frequencies.Conclusion: Findings support the notion of a clear effect of cardiovascular workout with and without music exposure on the OHC function at higher test frequencies, as measured by DPOAEs. Decreased DPOAE amplitudes between 2 kHz and 8 kHz were observed with music exposure and the opposite effect was observed for cardiovascular workout in isolation.

Introduction: Schroeder-phase masking has been proven to be more sensitive than pure tone audiometry in detecting changes in cochlear function. Schroeder harmonic complexes with different phases have been observed to excite basilar membranes differently and give different masking abilities (‘phase effect’) when used as maskers. Previous theory suggested that phase effect was contributed by cochlear non-linearity of outer hair cells (OHC); however the theory was derived from behavioral observation alone. Therefore, this study aims to further investigate the cochlear non-linearity involvement in phase effect mechanism by measuring the Schroeder phase effect together with another electrophysiological test that measures the cochlear non-linearity function, i.e. Distortion Product Otoacoustic Emission (DPOAE). Methods: Twelve normal hearing and four sensorineural hearing loss subjects were recruited. Schroeder phase masking test was conducted and phase effect (using 75 dB A masker) at 1kHz and 2 kHz was measured. DPOAE was recorded at multiple intensities (45-75 dB SPL) for 1 kHz and 2 kHz, and slope of DPOAE input output function was measured. Correlation analysis was performed to find correlation between phase effect and slope of DPOAE input output function. Results: Result showed no significant correlation (p > 0.05) between phase effect and slope of DPOAE input output function. Conclusions: This findings suggest that Schroeder-phase effect may not be/ may not only be contributed by OHC’s cochlear non-linearity. This finding opens the possibility of other auditory functions’ involvement in phase effect mechanism, and contribute to better understanding towards auditory perceptions.

Introduction: Hyperbilirubinemia in newborns has been hypothesized to cause damage to inner ear, thus leading to sensorineural hearing loss. Phototherapy is treatment protocol in most of the hospitals for newborns with high bilirubin levels. The present study aimed to determine the effects of phototherapy on outer hair cell (OHC) function of cochlea. Methods: Twenty-two neonates with hyperbilirubinemia undergoing phototherapy and 22 neonates without any high-risk registers were included in the study. Distortion product otoacoustic emission (DPOAE) was administered before and after phototherapy. Auditory brainstem response (ABR) evaluation was done during the postphototherapy recording. Results: Results showed that DP amplitude and signal-to-noise ratio improved significantly after phototherapy. ABR evaluation revealed; 19 neonates had significantly prolonged wave V latency compared to normal, whereas no peaks were identified among three neonates. Most of the infantile hyperbilirubinemia are found to be harmless until and unless treatment is not initiated at the earliest, but still it is found that short-term increase in bilirubin level can induce temporary changes in OAEs and ABR measures. ABR needs to be repeated over a period of time for these three neonates to rule out auditory dyssynchrony (AD). Conclusion: The results indicate that phototherapy has temporary effects on OHC function and can improve as the bilirubin levels reduce. Follow-up testing over a period of time helps in discriminating the sensory pathology and AD.

Short-term effects of simultaneous cardiovascular workout and personal music device use on the outer hair cell function of young adults

This study measured distortion product otoacoustic emissions (DPOAEs) and DPOAE input/output (I/O) curves to assess the effects of smoking on cochlear function. Twenty-four healthy adults, 12 smokers and 12 nonsmokers in the 20-30 years age range were selected based on self-reported histories of five to eight years of smoking or no smoking, respectively. All subjects received tympanometric screening to rule out middle ear pathology. Conventional (0.25-8 kHz) and ultra high frequency (UHF; 10-20 kHz) audiometry showed normal or age-appropriate thresholds across both groups. DPOAE results showed small, but significant, decline in DPOAE levels without concomitant changes in noise floors in smokers as compared to nonsmokers. I/O detection thresholds were also significantly elevated at high frequencies in smokers as compared to their nonsmoking counterparts. These findings indicate that smokers are at greater risk for cochlear damage than nonsmokers, and that DPOAE amplitudes and I/O detection thresholds may identify early changes in cochlear function in smokers.

Hearing loss as assessed by pure-tone audiometry (PTA) is significantly correlated with the intelligibility of synthetic speech. However, PTA is a subjective audiological measure that assesses the entire auditory pathway and does not discriminate between the different afferent and efferent contributions. In this paper, we focus on one particular aspect of hearing that has been shown to correlate with hearing loss: outer hair cell (OHC) function. One role of OHCs is to increase sensitivity and frequency selectivity. This function of OHCs can be assessed quickly and objectively through otoacoustic emissions (OAE) testing, which is little known outside the field of audiology. We find that OHC function affects the perception of human speech, but not that of synthetic speech. This has important implications not just for audiological and electrophysiological research, but also for adapting speech synthesis to ageing ears.

PurposeThe main objectives of this study were to assess the early changes in pulmonary function and intrarenal haemodynamics and to determine the correlation between pulmonary function and intrarenal haemodynamics in patients with type 2 diabetes mellitus (T2DM).Methods96 patients with T2DM (diabetes group) without diabetes kidney disease (DKD) and 33 healthy subjects (control group) were enrolled in studies intended to assess the early changes in pulmonary function and intrarenal haemodynamics associated with diabetes, as well as to determine the correlation between pulmonary function and intrarenal haemodynamics.ResultsPulmonary functional parameters were negatively correlated with HbA1c levels and diabetes duration (P< 0.05). Moreover, renal functional parameters were positively correlated with HbA1c levels and diabetes duration (P<0.05). Additionally, pulmonary functional parameters were negatively correlated with renal functional parameters (P<0.05). Multiple linear regression analysis of the relationship between pulmonary functional parameters and the bilateral kidney arterial resistivity index (RI) showed that all the pulmonary functional parameters were significantly correlated with the arterial RI (P< 0.05).ConclusionsPatients displayed changes in pulmonary function and intrarenal haemodynamics during the preclinical stages of DKD. Regulating glycaemia may improve intrarenal haemodynamics in the bilateral interlobular renal arteries. Moreover, during the preclinical stages of DKD, the right kidney RI is a effective predictor of early changes in pulmonary function in adult T2DM patients.Trial registrationClinicalTrials.gov (NCT02798198); registered 8 June 2016.

It is widely accepted that even a single acute noise exposure at moderate intensity that induces temporary threshold shift (TTS) can result in permanent loss of ribbon synapses between inner hair cells and afferents. However, effects of repeated or chronic noise exposures on the cochlear synapses especially medial olivocochlear (MOC) efferent synapses remain elusive. Based on a weeklong repeated exposure model of bandwidth noise over 2-20 kHz for 2 hours at seven intensities (88 to 106 dB SPL with 3 dB increment per gradient) on C57BL/6J mice, we attempted to explore the dose-response mechanism of prolonged noise-induced audiological dysfunction and cochlear synaptic degeneration. In our results, mice repeatedly exposed to relatively low-intensity noise (88, 91, and 94 dB SPL) showed few changes on auditory brainstem response (ABR), ribbon synapses, or MOC efferent synapses. Notably, repeated moderate-intensity noise exposures (97 and 100 dB SPL) not only caused hearing threshold shifts and the inner hair cell ribbon synaptopathy but also impaired MOC efferent synapses, which might contribute to complex patterns of damages on cochlear function and morphology. However, repeated high-intensity (103 and 106 dB SPL) noise exposures induced PTSs mainly accompanied by damages on cochlear amplifier function of outer hair cells and the inner hair cell ribbon synaptopathy, rather than the MOC efferent synaptic degeneration. Moreover, we observed a frequency-dependent vulnerability of the repeated acoustic trauma-induced cochlear synaptic degeneration. This study provides a sight into the hypothesis that noise-induced cochlear synaptic degeneration involves both afferent (ribbon synapses) and efferent (MOC terminals) pathology. The pattern of dose-dependent pathological changes induced by repeated noise exposure at various intensities provides a possible explanation for the complicated cochlear synaptic degeneration in humans. The underlying mechanisms remain to be studied in the future.

Calcitonin-gene-related peptide (CGRP) is a lateral olivocochlear (LOC) efferent neurotransmitter. Depression of sound-driven auditory brainstem response amplitude in CGRP-null mice suggests the potential for endogenous CGRP release to upregulate spontaneous and/or sound-driven auditory nerve (AN) activity. We chronically infused CGRP into the guinea pig cochlea and evaluated changes in AN activity as well as outer hair cell (OHC) function. The amplitude of both round window noise (a measure of ensemble spontaneous activity) and the synchronous whole-nerve response to sound (compound action potential, CAP) were enhanced. Lack of change in both onset adaptation and steady state amplitude of sound-evoked distortion product otoacoustic emission (DPOAE) responses indicated CGRP had no effect on OHCs, suggesting the origin of the observed changes was neural. Combined with results from the CGRP-null mice, these results appear to confirm that endogenous CGRP enhances auditory nerve activity when released by the LOC neurons. However, infusion of the CGRP receptor antagonist CGRP (8–37) did not reliably influence spontaneous or sound-driven AN activity, or OHC function, results that contrast with the decreased ABR amplitude measured in CGRP-null mice.