Effects of acetylsalicylic acid on speech discrimination

Speech discrimination scores were obtained in quiet and against a background of competing noise for 5 persons both before and after they had ingested large doses of acetyl-salicylic acid (aspirin). The results indicate that for some persons, aspirin produces a substantial decrease in speech understanding in noise, even though there may not be a decrease in pure-tone sensitivity or speech discrimination in quiet.

Pure-tone and speech intelligibility disturbances in patients with ototoxic disorders

The prevalence and severity of hearing impairment caused by ototoxic drugs are surprisingly high. This emphasizes the importance of the questions arising from the treatment. In 33.7% of the cases, the hearing impairment caused by ototoxic antibiotics was of severe degree and in 25.4%, it was extremely severe. Parenteral, topical or oral administration of aminioglycoside antibiotics is dangerous. Because of the very poor speech intelligibility, most probably not only the spiral organ but the vestibulocochlear nerve and the higher auditory pathways are also affected by these antibiotics. In some cases, the severe distortion in sound perception cannot be compensated even by a hearing aid of the best quality, and lip-reading which was advised occasionally was without any result. To prevent these toxic effects, these drugs should be administered very parsimoniously and then under very strict conditions and close control.

[Physiopathology and clinical aspects of Menière's disease]

The most prominent changes in temporal bone histopathology of Menière's disease are hydrops-like extensions of the endolymphatic spaces. The endolymphatic hydrops seems to be the consequence of a diminished function or complete atrophy of the endolymphatic sac. The etiology or pathomechanism of perisaccular fibrosis or saccular degeneration is unknown. But as a consequence of experimental datas obtained by animal studies the pathogenesis of the endolymphatic hydrops can be explained by osmotic active forces which develope within the endolymphatic spaces after blockage of the endolymphatic aqueduct or sac: An increasing concentration of osmotic active endolymphatic components cause an influx of water from the perilymphatic (extracellular) environment so that the limiting membranes of the endolymphatic space have to extend (e.g. Reissner's membrane, saccular membrane). At any topographic location of the endolymphatic spaces these membranes can rupture followed by intermixing of potassium-rich endolymph with sodium rich perilymph. This leads to an acute or chronic intoxication of those sensory nerve elements which have close contact to perilymphatic fluid. The hypothesis of an osmotic induced accumulation of "water' during endolymphatic hydrops is supported by sometime striking results of the glycerol test. Nevertheless, the pathogenesis and etiology of Menière's disease remains obscure, as indicated by the diverging spectrum of the different conservative or surgical therapeutic methods in use.

The effects of pentobarbital upon auditory and visual thresholds in the baboon

Adult male baboons were trained to perform a reaction time procedure, which required holding a lever depressed for varying time intervals and releasing it during a 1.5 sec test stimulus to receive food. The test stimulus was a 16 kHz tone for auditory threshold testing, and a white light for visual threshold testing. Stimulus intensities were randomly varied to determine detection thresholds, and the latency of each correct lever release was recorded as a measure of reaction time. Acute, IM injections of pentobarbital (1.0 to 17.0 mg/kg) were given at the beginning of 2-hr experimental sessions. Pentobarbital elevated the absolute visual threshold and increased both auditory and visual reaction times in a dose-related manner. Two of three baboons showed reaction time and visual threshold decrements at pentobarbital doses which produced no change in absolute auditory thresholds.

The effects of alcohol on the acoustic Reflex Relaxation Index

Normal-hearing young adults (6 M, 5 F) ingested 1.5 ml alcohol per Kg body weight over 90 min (blood alcohol level then being 0.104 +/- 0.016%), then tested for contralateral acoustic reflex (AR) threshold using an otoadmittance meter, and given the acoustic Reflex Relaxation Index (RRI) test of Norris, Stelmachowicz and Taylor. Each stimulus for the RRI was a 4-sec train of pulses at a level 10 db above AR threshold at .5, 1, or 2 kc/s, with equivalent on-time of 166.7 msec and off-time of 200 msec. AR responses were displayed on an X-Y recorder. RRI was taken as the percentage of total relation of the AR during off-times. The AR relaxed relatively more during off-times, and the RRI consequently significantly increased, in the alcohol vs the control condition, mean differences in RRI score in percent being 5.0, 12,9, and 21.3% for .5, 1, and 2 kc/s, respectively. Group mean RRI at all 3 frequencies under alcohol was close to the cut-off score suggested as "normal" by the test originators, but in 6 of the 11 Ss RRI interpretation by that criterion changed from "normal" to "not normal" under alcohol at one or more frequencies. There are unresolved differences in the effect of specific temporal stimulus patterning on RRI. Caution is recommended in interpreting RRI in the clinic as suggestive of sensorineural hearing impairment if S is at the time under the influence of a CNS depressant.

Ménière's disease and the summating potential. III. Effect of glycerol administration

We investigated the effect of administering hypertonic glycerol on cochlear and auditory nerve responses to rectangular-pulse clicks and on pure-tone behavioral thresholds. Eleven ears with Ménière's disease, and 20 ears without the disease were studied. Among the ears with Ménière's disease summating potential (SP) amplitudes decreased and 250 to 1,000-Hz thresholds improved after glycerol administration. Action potential amplitudes from the ears with Ménière's disease also decreased after glycerol ingestion, but to a lesser degree. In contrast, among the ears without Ménieère's disease, 250- to 1,000-Hz behavioral thresholds did not change significantly after glycerol nor did any of the electrophysiologic responses. Analogous group differences were found when the ears were regrouped according to the presence of absence of pathologic SP enlargement. These results demonstrate a tendency for three variables-(1) clinical diagnosis of Ménière's disease, (2) enlarged SP, and (3) positive glycerol test result-to cluster together in the same population of ears.

[Influence of hydrocortisone 17-butyrate 21-propionate on the visual and the auditory organs (author's transl)]

The visual toxicity and the ototoxicity of hydrocortisone 17-butyrate 21-propionate (HBP), a newly synthesized anti-inflammatory steroid, was investigated using rats and dogs. (1) Electroretinogram (ERG) and visually evoked potential (VEP) in rats were not changed when HBP was administered intravenously and intraperitoneally, even at the semilethal doses. Consequently, it was suggested that HBP had no effect on the visual nervous system. (2) Similar to other corticosteroids, the intra ocular pressure rose in the dogs received HBP. Nevertheless, these dogs showed neither the remarkable changes in ERG, in the fundus of the eye, in the histological examination, nor the turbidity of the cornea and the lens. Based on these facts, it was reasonable to think that the the rise in the intra ocular pressure caused by HBP was not so severe that induce the secondary influence to other visual functions. (3) The rats received HBP did not show any changes in the auditory function by the audiometry. As the result, HBP was thought to be one of the rather safety corticosteroids concerning the visual toxicity and the ototoxicity.

Auditory intensity discrimination after selective loss of cochlear outer hair cells

The contributions of the inner and outer hair cells of the mammalian cochlea to auditory intensity discrimination were evaluated in a combined behavioral-anatomical study of the guinea pig. Intensity difference thresholds were unchanged from baseline values after selective destruction of outer hair cells, suggesting that those cells are unnecessary for normal intensity discrimination.

[Study of the mechanism of auditory adaptation by simultaneous recording of cortical auditory evoked potentials and cochlear microphonic potentials]

Auditory adaptation, apart from the effect of the neurotropic drugs, galanthamine, GABA and nanophyn on this adaptation, was examined in 35 rabbits exposed to white noise (90 dB, re 2.10(-5) Pa, 10 min) by concurrent recording of evoked potentials of the brain and microphonic potentials of the cochlea. The results suggest that the mechanism of auditory adaptation is determined by the processes that occur in the synapses of the auditory system central parts and is monitored by the sympathetic nervous system.

Ototoxicity of intracisternal gentamicin in cats

The intrathecal administration of gentamicin has been used to treat bacterial meningitis. However, the influence of this route of administration on the well-known ototoxic activity of gentamicin is unknown. This route of administration should facilitate access to the inner ear and should increase the ototoxic liability. The possible ototoxic and neurotoxic effects of intrathecally administered gentamicin (0.5, 1, 2, 4, 6, 10 mg/day) in cats were evaluated. Hearing thresholds were obtained by a noninvasive technique prior to and on the 7th and 21st days after the initiation of a seven-day dosage regimen. Histological examination of the organ of Corti was routinely done. Additionally, the vestibular organs of one animal on the 4 mg/day regimen were examined. The concentrations of gentamicin in the cerebrospinal fluid were also determined. The data indicate that the 2 mg/day dose may be very close to the threshold dose for ototoxicity when gentamicin is given by intracisternal administration.

Threshold sensitivity of the auditory pathway: effects of worsening signal-to-noise ratio in the auditory nerve

Perfusions of scala tympani with high potassium solutions increase spontaneous activity of auditory nerve fibres without affecting their threshold sensitivity. In these circumstances, however, the signal-to-noise ratio of the auditory nerve response to a given stimuli is worsened. Recordings from cochlear nucleus neurones during such perfusions indicate that this worsening is critical for threshold sensitivity at higher levels in the auditory pathway.

Comparative ototoxicity of chloramphenicol and kanamycin with ethacrynic acid

Chloramphenicol is not ototoxic if administered for systemic effect, but topical applications of it to the middle ear produce severe cochlear toxic effects. Ethacrynic acid potentiates the ototoxicity of aminoglycosides. Guinea pigs were administered chloramphenicol or kanamycin sulfate with ethacrynic acid to compare the ototoxicity of chloramphenicol and ethacrynic acid with the ototoxicity of kanamycin and ethacrynic acid. Preyer's reflex audiometry and measurement of the endocochlear dc potential, the cochlear microphonics, and the negative potential of the organ of Corti indicate that ethacrynic acid does not potentiate the ototoxicity of chloramphenicol. There is not even indirect evidence that the blood-cochlear barrier for chloramphenicol is altered by ethacrynic acid. Assuming that the ototoxicity of chloramphenicol and ethacrynic acid are similar for man and guinea pig, the combination of the administration of chloramphenicol and ethacrynic acid of systemic effect in dosages commonly used clinically should not produce greater ototoxicity than either agent administered alone.

[Application of a shuttle avoidance schedule in rats to evaluate a drug-induced auditory impairment (author's transl)]

In attempts to study drug-induced auditory impairment we measured the auditory threshold in rats, using the shuttle box method. The auditory threshold with physical impairment of ears was also measured. The sensitivity of the rats to the auditory response was decreased to about 15dB in cotton-stuffed ears and to about 20dB in pierced eardrums. In this experiment, we used drugs known to be ototoxic; dihydrostreptomycin sulfate, kanamycin sulfate, neomycin sulfate and ethacrynic acid. With successive administration of each drug, the auditory sensitivity in rats decreased. This shuttle box method is easily facilitated and the auditory threshold of many rats can be measured over a short period. This approach may be a useful method for screening ototoxic drugs.

Extra-auditory responses to long-term intermittent noise stimulation in humans

Respiration, heart rate, cutaneous blood flow, and electroencephalogram (EEG) reactions to long-term intermittent noise exposure were recorded from 13 volunteers (20-29 yr) with normal hearing and vegetative reactivity. They received daily within 1 h 12 noise stimuli (16 s 100 dB (A) white noise) for 10 or 21 days, respectively. Most subjects reported partial subjective adaptation to the noise. Heart rate adapted within a session but did not change considerably during successive days. Vascular responses did not change during one session but diminished mainly during the first 10 days. Noise responses in the EEG remained constant, but a decrease in vigilance occurred during the whole experimental series. Respiration responses were unpredictable and showed no trend within the sessions. It was concluded that certain physiological responses adapt to loud noise but that the time course of adaptation is different. Therefore a general statement about physiological noise adaptation is not possible.

The effect of oxygen inhalation on temporary threshold shift in humans

To examine the effects of an increased oxygen supply on the establishment of noise-induced TTS in humans, 20 Ss were exposed for 10 min to a narrow band of noise centered at 3 kc/s at 100 db SPL, while inhaling either a 60% or a 90% oxygen-air mixture. In a control condition, these Ss inhaled air only while being subjected to the same noise. In the 10 Ss who had inhaled the 90% mixture, TTS was less than when they had inhaled air (delta TTS - 2.06 db, p less than 0.25). Delta TTS (0.07 db) for the 10 Ss who inhaled the 60% mixture was not significant. A further 5 Ss inhaled the 90% mixture for 10 min with no noise exposure; there was no effect on the hearing threshold levels. It was concluded that inhalation of at least 90% oxygen-air for 10 min does not affect HTLs but does reduce TTS. A re-examination was suggested of the possibility that there is a relationship between auditory fatigue and supply of oxygen to cochlear structures.

Effects of prestimulatory carbogen inhalation on noise-induced temporary threshold shifts in humans and chinchilla

Human subjects and chinchilla breathed either Carbogen or compressed air prior to high level sound stimulation. Following stimulation, threshold shifts and recovery to prestimulation thresholds were monitored. Behavioral audiometry was used for human subjects and electrocochleography was utilized to measure noise-induced threshold shifts in the animals. Results were similar for both human and animal subjects in that preinhalation of Carbogen (05 percent 02 and 5 percent CO2) was seen to decrease the amount of temporary threshold shift (TTS) and to increase recovery rate. Further, histologic study of a limited sample of the experimental animals suggested a notable reduction in the amount of sensory cell damage in subjects that breathed Carbogen before sound stimulation. To follow up on this encouraging indication, an additional experiment was conducted to investigate any differences between Carbogen-treated and non-Carbogen-treated animals with respect to histologically observable high level noise exposure damage. The follow-up experiment resulted in strong evidence that Carbogen inhalation prior to intense sound stimulation decreases the susceptibility to hair cell damage. Carbogen-treated chinchilla sustained cochlear sensory cell damage ranging between 1.1 percent and 1.5 percent, whereas non-Carbogen-treated, noise-exposed chinchilla were found to have between 1.6 percent and 4.6 percent sensory cell damage. The use of Carbogen in prophylactic treatment for unavoidable or accidental noise exposure is discussed.

Supra-normal sensitivity to ototoxic antibiotic of the developing rat cochlea

A period of increased sensitivity to the ototoxic antibiotic amikacin was found in the cochlea of the developing rat. Starting either at birth, 10 or 30 days of age, rat were injected i.p. daily with 200 mg/kg of amikacine for 10 days. Only in the group injected with drug from 10 to 20 days of age was there evidence of a substantial (40-100 dB) permanent threshold shift (PTS). To characterize the period of supra-normal sensitivity more precisely, independent groups of pups were injected with 50 mg/kg of amikacin from 10 to 20, 15 to 25, 20 to 30, and 30 to 40 days of age. Only those pups injeced from 10 to 20 or 15 to 25 days of age showed PTS (30-60 dB). These data, taken together with those on rat cochlear maturation indicate that the sensitive period to ototoxicity starts at the age of onset of cochlear function (around day 10) and ends few days after the cochlea shows adult-like characteristics (3rd postnatal week).

[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.

Single-cell responses in normal and ototoxic drug-treated gerbils

Single cell data were obtained from the inferior colliculus of normal gerbils and from those treated with ethacrynic acid. Response changes found for the drug-treated animals are as follows: Fewer cells responded to auditory stimulation. Recruitment-like functions were found which were characterized by high threshold and precipitous increase in discharge rate with intensity. Some units showed abnormally low discharge rate over an extended intensity range, which could be the underlying change in responsiveness in human patients with reduced loudness range. One half as many collicular units were responsive to auditory phase differences. The most severly affected ears showed abnormal dependency upon phase relations. This would affect auditory space perception.

Ototoxicity of kanamycin in developing rats: relationship with the onset of the auditory function

In order to test the relationship between the ototoxicity of kanamycin and the onset of the auditory function, two groups of developing rats were intoxicated with kanamycin before and after the period of onset of cochlear potentials (8th postnatal day). Kanamycin was shown to have a weak ototoxic effect before the 8th postnatal day and a strong ototoxic effect after this period. These results indicate a critical period of sensitivity to ototoxic antibiotics during auditory development.