No Reduction in the 226-Hz Probe Tone Acoustic Reflex Amplitude Following Severe Inner Hair Cell Loss in Chinchillas.

The relationship between the middle ear acoustic reflex (AR) and inner hair cell (IHC) loss is currently unknown. Given that IHC are believed to convey nearly all acoustic information to the central auditory nervous system, it has been assumed that loss of IHC would significantly impact the AR. To evaluate this relationship, we assessed the presence and amplitude of the AR in chinchillas before and after treatment with carboplatin, an anticancer drug that reliably and selectively destroys IHC in this species. Baseline measures of hearing sensitivity, including auditory brainstem response (ABR) thresholds and distortion product otoacoustic emissions (DPOAE), were assessed and then re-evaluated following carboplatin treatment. Post-carboplatin ABR thresholds and DPOAE were found to be unchanged or slightly elevated; results were consistent with published reports. Our main hypothesis was that loss of IHC would abolish the reflex or significantly reduce its amplitude. Contrary to our hypothesis, the ipsilateral 226-Hz AR continued to be reliably elicited following carboplatin treatment. Post-mortem histological analysis confirmed significant IHC loss (65-85 %), but no measurable loss of outer hair cells (OHCs). Given that loss of IHC alone does not significantly reduce the 226-Hz AR, our results suggest that few IHC are needed to maintain the 226-Hz AR response. These results suggest additional studies are needed to better understand the role of IHC in the reflex arc, present opportunities to further study the reflex pathway, and could change how we use the clinical AR as a potential diagnostic tool for IHC dysfunction, including those related to IHC synaptopathy.

Effect of Selective Carboplatin-Induced Inner Hair Cell Loss on Temporal Integration in Chinchillas.

Integration of acoustic information over time is essential for processing complex stimuli, such as speech, due to its continuous variability along the time domain. In both humans and animals, perception of acoustic stimuli is a function of both stimulus intensity and duration. For brief acoustic stimuli, as duration increases, thresholds decrease by approximately 3 dB for every doubling in duration until stimulus duration reaches 500 ms, a phenomenon known as temporal integration. Although hearing loss and damage to outer hair cells (OHC) have been shown to alter temporal integration in some studies, the role of cochlear inner hair cells (IHC) on temporal integration is unknown. Because IHC transmit nearly all acoustic information to the central auditory system and are believed to code both intensity and timing information, these sensory cells likely play a critical role in temporal integration. To test the hypothesis that selective IHC loss degrades the temporal integration function, behaviorally trained chinchillas were treated with carboplatin, a drug known to selectively destroy IHC with little to no effect on OHC in this species. Pure-tone thresholds were assessed across frequencies (1, 2, 4, 8, 12 kHz) as a function of signal duration (500, 100, 50, 10, and 5 ms). Baseline testing showed a significant effect of duration on thresholds. Threshold decreased as a function of increasing duration, as expected. Carboplatin treatment (75 mg/kg) produced a moderate to severe loss of IHC (45-85%) with little-to-no loss of OHC. Contrary to our hypothesis, post-carboplatin temporal integration thresholds showed no significant differences from baseline regardless of stimulus duration or frequency. These data suggest that few IHC are necessary for temporal integration of simple stimuli. Temporal integration may be sensitive to loss of OHC and loss of cochlear non-linearities but does not appear to be sensitive to selective IHC loss.

The rat animal model for noise-induced hearing loss.

Rats make excellent models for the study of medical, biological, genetic, and behavioral phenomena given their adaptability, robustness, survivability, and intelligence. The rat's general anatomy and physiology of the auditory system is similar to that observed in humans, and this has led to their use for investigating the effect of noise overexposure on the mammalian auditory system. The current paper provides a review of the rat model for studying noise-induced hearing loss and highlights advancements that have been made using the rat, particularly as these pertain to noise dose and the hazardous effects of different experimental noise types. In addition to the traditional loss of auditory function following acoustic trauma, recent findings have indicated the rat as a useful model in observing alterations in neuronal processing within the central nervous system following noise injury. Furthermore, the rat provides a second animal model when investigating noise-induced cochlear synaptopathy, as studies examining this in the rat model resemble the general patterns observed in mice. Together, these findings demonstrate the relevance of this animal model for furthering the authors' understanding of the effects of noise on structural, anatomical, physiological, and perceptual aspects of hearing.

Hearing Screening in the Community.

BACKGROUND: Adults typically wait 7-10 yr after noticing hearing problems before seeking help, possibly because they are unaware of the extent of their impairment. Hearing screenings, frequently conducted at health fairs, community events, and retirement centers can increase this awareness. To our knowledge, there are no published studies in which testing conditions and outcomes have been examined for multiple "typical screening events." PURPOSE: The purpose of this article is to report hearing screening outcomes for pure tones and self-report screening tests and to examine their relationship with ambient noise levels in various screening environments. STUDY SAMPLE: One thousand nine hundred fifty-four individuals who completed a hearing screening at one of 191 community-based screening events that took place in the Portland, OR, and Tampa, FL, metro areas. DATA COLLECTION AND ANALYSIS: The data were collected during the recruitment phase of a large multisite study. All participants received a hearing screening that consisted of otoscopy, pure-tone screening, and completion of the Hearing Handicap Inventory-Screening Version (HHI-S). In addition, ambient sound pressure levels were measured just before pure-tone testing. RESULTS: Many more individuals failed the pure-tone screening (n = 1,238) and then failed the HHI-S (n = 796). The percentage of individuals who failed the pure-tone screening increased linearly with age from <20% for ages <45 yr to almost 100% for individuals aged ≥85 yr. On the other hand, the percentage of individuals who failed the HHI-S remained unchanged at approximately 40% for individuals aged ≥55 yr. Ambient noise levels varied considerably across the hearing screening locations. They impacted the pure-tone screen failure rate but not the HHI-S failure rate. CONCLUSIONS: It is important to select screening locations with a quiet space for pure-tone screening, use headphones with good passive attenuation, measure sound levels regularly during hearing screening events, halt testing if ambient noise levels are high, and/or alert individuals to the possibility of a false-positive screening failure. The data substantiate prior findings that the relationship between pure-tone sensitivity and reported hearing loss changes with age. Although it might be possible to develop age-specific HHI-S failure criteria to adjust for this, such an endeavor is not recommended because perceived difficulties are the best predictor of hearing health behaviors. Instead, it is proposed that a public health focus on education about hearing and hearing loss would be more effective.

Recruiting ENT and Audiology patients into pharmaceutical trials: evaluating the multi-centre experience in the UK and USA.

OBJECTIVE: Recruiting into clinical trials on time and on target is a major challenge and yet often goes unreported. This study evaluated the adjustment to procedures, recruitment and screening methods in two multi-centre pharmaceutical randomised controlled trials (RCTs) for hearing-related problems in adults. DESIGN: Recruitment monitoring and subsequent adjustment of various study procedures (e.g. eligibility criteria, increasing recruiting sites and recruitment methods) are reported. Participants were recruited through eight overarching methods: trial registration, posters/flyers, print publications, Internet, social media, radio, databases and referrals. The efficiency of the recruitment was measured by determining the number of people: (1) eligible for screening as a percentage of those who underwent telephone pre-screening and (2) randomised as a percentage of those screened. STUDY SAMPLE: A total of 584 participants completed the pre-screening steps, 491 screened and 169 participants were randomised. RESULTS: Both RCTs completed adjustments to the participant eligibility, added new study sites and additional recruitment methods. No single recruitment method was efficient enough to serve as the only route to enrolment. CONCLUSION: A diverse portfolio of methods, continuous monitoring, mitigation strategy and adequate resourcing were essential for achieving our recruitment goals.