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PubMed1978

Acoustic trauma effects from doubling the exposure time.

Guinea pigs were used to test acoustic trauma effects from doubling the exposure time. Previously, two frequencies (20 kHz and 4 kHz) were used in conjunction with each other (ie double exposure) to see whether a prior exposure of the cochlea to one frequency would alter the extent of damage caused by a secondary frequency, when compared with damage caused by either frequency alone. A reduced area of damage was attained after double exposures. To complete the series, the same two frequencies were used separately, but the exposure time was doubled. The results from the 20 kHz series surprisingly indicated that a reduced area of damage was obtained after doubling the exposure time. No significant differences were found in the 4 kHz series.

Acoustic Stimulation↗
PubMed1997

Effect of hyperbaric oxygen treatment on permanent threshold shift in acoustic trauma among rats.

Impulse noise from firearms is a common cause of acute acoustic trauma (AAT). Recently hyperbaric oxygen treatment has become available in many hospitals treating AAT. We exposed 39 Wistar rats to intense impulse noise of 60 shots from the assault rifle (162 dB SPL). After the exposure 15 animals were given hyperbaric oxygen treatment (HBO) by 10 treatment cycles of 90 minutes 100% oxygen in 0.25 MPa, one treatment cycle per day. Four weeks after the exposure the hearing thresholds were measured with auditory brainstem response audiometry at frequencies of 1.0, 2.0, 4.0, 6.0, 8.0 and 10.0 kHz. Characteristics for the resulting noise-induced hearing loss were large variations in its severity not only between animals, but also between the ears of a single animal. The largest permanent threshold shifts were found at 6.0, 8.0 and 10.0 kHz. Most of the HBO-treated animals showed less threshold shift than the non-treated animals. The difference between the HBO group and the control group was only slightly statistically significant (p = 0.067).

Animals↗
PubMed1987

Regeneration of hair cell stereociliary bundles in the chick cochlea following severe acoustic trauma.

Examination of pure-tone acoustic damage in the chick cochlea revealed a significant amount of hair cell recovery over a 10 day period following the exposure. The recovery included both a regeneration of stereociliary bundles to replace those that were lost and a reshuffling of the mosaic pattern of the hair cell surfaces that survived. Ten-day-old chicks were exposed to a 1500 Hz pure tone at 120 dB SPL for 48 h and their cochleae were processed for scanning, transmission and light microscopy at 0 h, 24 h, 48 h, 4 d, 6 d and 10 d after exposure. Immediately after exposure the damaged region exhibited two types of hair cell trauma. The first was a defined area of complete hair cell loss and the second was an area where the hair cells survived but exhibited varying amounts of stereocilia injury. After 48 h of recovery, new hair cells were identifiable in the region of hair cell loss and with time they underwent a progressive maturation of their stereociliary bundles. The surviving hair cells showed a dramatic rearrangement and expansion of their surfaces but exhibited no repair of the damaged stereociliary bundles. These results suggest that the chick cochlea is capable of a significant amount of recovery and regeneration following acoustic trauma.

Animals↗
PubMed1989

Sensorineural high-frequency hearing loss after drill-generated acoustic trauma in tympanoplasty.

Tympanoplasty can cause a sensorineural hearing loss by a mechanism of acoustic trauma. Although this lesion appears to be relatively infrequent in clinical practice, we believe that its low apparent incidence is caused when clinicians fail to assess the auditory frequencies above 8000 Hz. Twenty-four patients with normal bone-conduction audiometric thresholds scheduled for tympanoplasty were assessed with an electro-stimulation, bone-conduction high-frequency audiometer which can measure hearing frequencies up to 20 kHz before and after surgery. A measurable hearing loss was found in the upper limits of the audible frequencies in 9 patients (37.5%), and was considered important in 4 of them (16.7%). This hearing loss was recorded above the upper frequency limit of conventional audiometers. The findings in this study indicate that drilling of the temporal bone can impair the hearing level in the high frequencies in a significant number of patients. High-frequency audiometry is a very sensitive tool to assess any damage caused to the inner ear by surgical procedures carried out in the middle ear and temporal bone.

Adolescent↗
PubMed2001

Prognosis of acute acoustic trauma: a retrospective study using multiple logistic regression analysis.

OBJECTIVE: The prognosis for acute acoustic trauma (AAT) is difficult to predict. Multiple logistic regression analysis was used in this study to determine which factors were most strongly related to outcome for patients with AAT. METHODS: The study group was comprised of 52 patients (52 ears). Separate analyses were performed on the no change and partial recovery groups, and on the no change and full recovery groups. The following eight factors were examined as explanatory variables, age; number of days before the start of treatment; use of earplugs; drug therapy (adrenocortical hormones, low molecular weight dextrans, and vitamin B12), mean hearing levels at 0.5, 1, and 2 kHz (pure tone average, PTA), and mean hearing levels at 4 and 8 kHz (high tone average, HTA). RESULTS: Factors determined to be most strongly related to outcome were the number of days before the start of treatment, PTA, and HTA. No significant relation to outcome was determined for the five following factors, age; use of earplugs; and drug therapy (adrenocortical hormones, low molecular weight dextrans, and vitamin B12). CONCLUSION: Our results will increase the ability to prognosticate the outcome for AAT.

Acute Disease↗
PubMed2000

Cochlear de-efferentation and impulse noise-induced acoustic trauma in the chinchilla.

The olivocochlear bundle (OCB) has been shown to protect the ear from acoustic trauma induced by continuous noise or tones. The present study examines the OCB's role in the ear's response to impulse noise (150 dB pSPL, 100 impulses, 50 s total exposure duration). Successful section of the OCB was achieved through a posterior parafloccular fossa approach for the right ears of six out of 15 adult chinchillas. The left ears from the same animals served as efferent-innervated controls. Measurements of inferior colliculus evoked potentials (ICPs) showed that the de-efferented ears incurred similar temporary and permanent threshold shifts as the control ears. Twenty days after noise exposure, depressed ICP amplitudes had virtually recovered to pre-values in the control ears whereas those in the de-efferented ears remained significantly depressed. Greater loss of inner hair cells was seen in the de-efferented ears than in the control ears. Both control and de-efferented ears incurred large loss of outer hair cells, with no statistically significant differences between groups. The current data are intriguing, yielding tentative evidence to suggest that inner hair cells of de-efferented ears are more susceptible to impulse noise than those in efferented control ears. In contrast, outer hair cell vulnerability to impulse noise appears to be unaffected by de-efferentation.

Acoustic Stimulation↗
PubMed1992

Acoustic trauma in a telephone operator.

This case report describes an incident where a telephone operator suffered acoustic trauma from a subscriber blowing a whistle down a telephone mouthpiece, the sound being transmitted into the ear of the operator. Evidence of hearing loss persisted for several months before complete recovery was achieved. Comparison is made with hearing loss associated with the use of cordless telephones.

Adult↗
PubMed1997

Impulse noise and acute acoustic trauma in Finnish conscripts. Number of shots fired and safe distances.

This prospective study of acute acoustic trauma (AAT) from exposure to impulse noise during compulsory military service focused on three issues the number of shot or explosion impulses that the conscript was exposed to at the time of AAT, distance of injured ear from causal firearm, and the circumstances under which AAT occurred protected ears. The series includes 449 consecutive, verified cases of AAT seen at the Central Military Hospital in Helsinki, Finland, in the period 1989-1993. AAT usually occurred during combat training (87%) as a result of exposure to impulses from small arms (83%). In 41%. AAT was caused by a single shot or detonation impulse. As many as 92% of all AATs occurred within 2 m of the causal firearm. Fourteen percent were wearing hearing protectors when the accident took place, but every third had badly fitting protectors or had neglected safety regulations and used insufficient protection. Of all AATs caused by one noise impulse in protected ears. 83% were attributable to heavy arms and only 14% to small arms. The results of the study suggest that combined use of earmuffs and earplugs in association with a safe distance of over 5 m from the noise source gives adequate protection against AAT. However, for conscripts using certain heavy arms e.g. hazooka. more effective hearing protection should be developed.

Acute Disease↗
PubMed1995

The effect of the sympathetic nervous system upon susceptibility to acoustic trauma.

This study was designed to determine whether the sympathetic nervous system exerts a protective or enhancing effect in acoustic overstimulation. The compound action potential of the cochlea (CAP) was recorded in guinea pigs while the cervical sympathetic nervous system (SNS) was electrically stimulated or after it was surgically eliminated. The stimulation or the elimination of the cervical SNS has no effect on the threshold of CAP. The threshold shift in CAP after acoustic overstimulation (110, 115, or 130 dB SPL for 10 min) was measured in the cervical SNS stimulation group, in the cervical SNS elimination group, and in the control group. When the animal was under insufficient sedation, there was no difference among these three groups. However, the CAP threshold shift was significantly smaller in the cervical SNS stimulation group than in the other two groups when the animals were sufficiently sedated. The cervical SNS stimulation had some protective effect on the susceptibility to acoustic trauma when the systemic SNS activity was suppressed.

Acoustic Stimulation↗
PubMedDate not supplied

Cordless telephones and acoustic trauma: a case study.

Cordless telephones have been reported to cause irreversible damage to the ear due to acoustic trauma. The present case study reports an unusual audiometric configuration associated with direct exposure to the ring from a cordless phone. Although pure-tone sensitivity was only moderately affected, speech understanding was severely compromised.

Adult↗
PubMed1987

Audiometric configurations in acute acoustic trauma caused by firearms.

We have analysed pure-tone audiometry curve of 361 Finnish conscripts who suffered acute acoustic trauma during their military service. In more than 75% of the ears the hearing loss was found in the high-frequency region (above 2 kHz). In the remaining 25% the speech frequency range was also affected. The main threshold shift started at 1 kHz in 8%, at 2 kHz in 49%, at 4 kHz in 19% and at 6 kHz in 6% of the ears. Impulse noise from large-calibre weapons and explosions appeared to cause low-tone hearing loss slightly more often than small arms fire. No etiological differences were apparent between the ears with dip-type hearing loss and ears with more abrupt-like hearing loss.

Adult↗
PubMed1980

[Therapeutic results in acute acoustic trauma (author's transl)].

The prime aim of this study is to investigate the influence of therapeutic measures in acute acoustic trauma (AAT). In a controlled clinical trial 209 patients (Table 1) was observed, starting within 2 days after the traumatic event. Various chemical agents, considered to have some influence on microciculation and metabolism of the inner ear, were administered as shown in Table 2. The control group was treated with NaCl infusions and glucose tablets. Statistical analysis of the audiometric data was performed in two different ways (Fig. 2). First, variations of absolute pure tone thresholds were studied in a regression analysis, revealing a close dependency of absolute hearing gains upon pretherapeutic hearing losses. Significant differences of permanent threshold shifts between test and control group could not be observed. Secondly, distribution curves of relative hearing gains (Figs. 1 and 2) were compared using the Kruskal Wallis test. The hypothesis of all of these curves being part of the same sample could not be rejected (P = 0.01). Thus, it was concluded that the four different forms of polypragmatic therapy used in this trial do not exert an effect on AAT exceeding that of NaCl infusions and glucose tablets. Under the assumption of a placebo effect of NaCl infusions and glucose tablets, either the supply with oxygen and neurotrop vitamins is no limiting factor in the regeneration process of the organ of Corti after an AAT, or the administered drugs fail to influence this supply. The effect of hospitalization with consequent reduction of noise and emotional stress was not studied in this paper.

Acute Disease↗
PubMed1997

Discharge properties of pigeon single auditory nerve fibers after recovery from severe acoustic trauma.

The time course of recovery of compound action potential (CAP) thresholds was observed in individual adult pigeons after severe acoustic trauma. Each bird had electrodes implanted on the round window of both ears. One ear was exposed to a tone of 0.7 kHz at 136-142 dB SPL for 1 hr under general anesthesia. Recovery of CAP audiograms was monitored twice a week after trauma. Single unit recordings from auditory nerve fibers were made after 3 weeks and after 4 or more months of the exposure. The CAP was abolished immediately after overstimulation in all animals. Based on the temporal patterns of functional recovery of the CAP three groups of animals were identified. The first group was characterized by fast functional recovery starting immediately after trauma followed by a return to pre-exposure values within 3 weeks. In the second group, slow functional recovery of threshold started 1-2 weeks after trauma followed by a return to pre-exposure values by 4-5 weeks. A mean residual hearing loss of 26.3 dB at 2 kHz remained. The third group consisted of animals that did not recover after trauma. Three weeks after the exposure, tuning curves of single auditory nerve fibers were very broad and sometimes irregular in shape. Their thresholds hovered around 120 dB SPL. Spontaneous firing rate and driven rate were much reduced. Four or more months after exposure, the thresholds and sharpness of tuning of many single units were almost completely recovered. Spontaneous firing rate and driven rate were comparable to those of control animals. In the slow recovery group neuronal tuning properties showed less recovery, especially at frequencies above the exposure frequency. Thresholds and sharpness of tuning were normal at frequencies below the exposure frequency, but were much poorer at frequencies above the exposure. Spontaneous firing rate was much reduced in fibers with high characteristic frequencies. In fast recovering animals, the papilla was repopulated with hair cells after 4 months. In slow recovering animals, short (abneural) hair cells were still missing over large parts of the papilla after 4 months of recovery. Residual short (abneural) hair cell loss was largest at two areas, one more basal and the other more apical to the characteristic place of the traumatizing frequency. The results show that, in adult birds, functional recovery from severe damage to both short (abneural) and tall (neural) hair cells occurs. However, the onset of recovery is delayed and the time course is slower than after destruction of short (abneural) hair cells alone. Also, recovery is incomplete, both functionally and morphologically. There is residual permanent hearing loss, and regeneration of short (abneural) hair cells is incomplete.

Action Potentials↗
PubMed1986

[Efficacy of naftidrofurylhydrogenoxalate (Dusodril) as adjunctive therapy of patients with acute acoustic trauma. A controlled double-blind study].

A study was carried out on 60 patients who had suffered an acute acoustic trauma. The aim of the study was to examine the effect of using naphtidrofurylhydrogen oxalate (Dusodril Pi. i.v. or Dusodril ret.) as an adjunctive measure alongside dextran-40 infusions (Thomaedex 40). After spontaneous remissions had been largely excluded, the patients were randomly assigned to two therapy groups. Very similar results were obtained in the naphtidrofurylhydrogen oxalate group and in the control group (30 patients each), showing that the use of this drug as an adjunctive therapeutic measure in the treatment of high-frequency hearing loss or alleviated tinnitus does not produce a significant improvement of results.

Adult↗
PubMed2004

Characteristics of acute acoustical trauma in the Finnish Defence Forces.

In spite of strict safety regulations concerning firearm shooting, several hundred conscripts still suffer acute acoustical trauma (AAT) in the Finnish Defence Forces (FDF) every year, resulting in symptoms such as tinnitus and/or hearing impairment. The causes leading to AAT, causative weapons and mode and level of hearing protection were analysed to find out why so many AATs still occur in the FDF. The material consisted of 119 patients of the total 163 AAT patients treated at the Central Military Hospital during the year 2000. In 87.5% of cases, the AATs occurred in unprotected ears. The most common causative weapon was the assault rifle. Most of the AATs occurred during combat training in the field. Immediately after the AAT. 46.7% of conscripts had hearing impairment and 94.2% tinnitus. Hearing loss, tinnitus or both were experienced by 45% of conscripts at the last follow-up. Careful planning of training exercises could probably prevent some but not all AATs.

Adult↗