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PubMedDate not supplied

[Distortion products in Menière's disease].

Distortion Product Otoacoustic Emissions (DPOAEs) are elicited by simultaneous application of two tones to the ear canal. These emissions are a result of nonlinear mechanical characteristics of the cochlea at a specific point and have a precise mathematical relation with the frequencies of the two eliciting primary tones f1 and f2. This frequency-selective property of DPOAEs suggests that they should be regarded as useful monitor of localized cochlear function at any predetermined frequency. The present study was designed to investigate DPOAEs in patients with Menière's disease. DPOAEs were recorded before and after glycerol administration to verify if the fluctuation of the hearing threshold induced by this hyperosmotic agent causes selective changes in the activity of the outer hair cells. DPOAEs were present in patients in which the mean duration of the disease was shorter compared to those patients without measurable DPOAEs. An improvement of DPOAEs after glycerol intatte was observed in a half of our cases. The improvement of DPOAEs does not appear to be brought about by modifications of the auditory threshold induced by glycerol.

Audiometry↗

PubMed1993

Frequency selectivity in noise-damaged cochleas.

Measures of auditory threshold and masked threshold were obtained at six audiometric test frequencies along with cochleograms on a total population of 363 noise-exposed chinchillas. Seventy animals were chosen from this sample and were separated into five relatively homogeneous groups based upon the amount of permanent threshold shift and sensory cell losses the animals incurred. Tuning curve (TC) metrics were compared to the mean preexposure TC metrics for each group and to the reference preexposure TC metrics obtained from the sample of 363 animals. These data show that in animals with relatively little hearing loss changes in TC metrics can provide evidence for noise-induced sensory cell losses and that the low frequency slope of the TC is a sensitive index of trauma.

Animals↗

PubMed2004

Acute endolymphatic hydrops generated by exposure of the ear to nontraumatic low-frequency tones.

Low-frequency sounds presented at high nontraumatizing levels induce temporary hyperacusis in humans and animals. One explanation of this finding is that the basilar membrane operating point may be disturbed by an endolymph volume change. This possibility was investigated using volume and flow markers iontophoresed into the endolymphatic space of guinea pigs. Marker concentrations were measured with ion-selective microelectrodes placed apically and basally to the iontophoresis site during exposure of the ear to low-frequency tones. Concentration changes were interpreted quantitatively using a finite-element model of the endolymphatic space that allowed changes of endolymph cross-sectional area and flow to be derived. Stimulation with a 200 Hz tone at 115 dB SPL for 3 min produced marker concentration changes consistent with the induction of transient endolymphatic hydrops and a basally directed displacement of endolymph. Endocochlear potentials were greater than normal after the exposure when hydrops was present. During identical tone exposures of animals without marker, we found that action potential (AP) threshold changes and endolymph potassium changes associated with the hydropic state were small. Marker concentration changes were compared with changes in endocochlear potential and AP thresholds for a range of exposure frequencies and levels. AP hypersensitivity occurred with 200 Hz exposure levels below those inducing endolymph volume disturbances. Endolymph volume changes are thought to be the result of, rather than the cause of, changes in operating point of the cochlear transducer. The observations that auditory threshold and endolymph potassium changes are minimal under conditions where substantial endolymphatic hydrops is present is relevant to our understanding of the hearing loss in patients with Meniere's disease.

Acute Disease↗

PubMed1995

Alterations in microvasculature are associated with atrophy of the stria vascularis in quiet-aged gerbils.

Age-related changes in the integrity of the stria vascularis and its microvasculature were assessed in whole mount preparations of the gerbil cochlear lateral wall. Small focal regions containing few or no capillaries were present at the extreme ends of the stria vascularis in most 5-9 month-old gerbils. A few ears in this age range also contained small regions devoid of capillaries at the extreme basal end of the stria. These degenerate foci expanded in a systematic fashion toward the middle turn of the cochlea with increasing age. Gerbils aged 33 months or older exhibited a normal strial vasculature pattern only in portions of the middle and upper basal turns. The remainder of the stria in these older gerbils contained degenerate regions which showed both loss of capillaries and atrophy of strial marginal cells. Quantification via computer-aided image analysis confirmed that the areas of strial atrophy correlated well with the loss of strial capillaries at all ages. However, regions containing capillaries with decreased diameter were not necessarily accompanied by atrophic changes in marginal cells. The results suggest that degeneration of the stria vascularis begins prior to onset of auditory threshold shift and is preceded and possibly initiated by changes in the strial microvasculature.

Acoustic Stimulation↗

PubMed2002

Perinatal exposure to Aroclor 1254 impairs distortion product otoacoustic emissions (DPOAEs) in rats.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that are a potential health hazard to human and wildlife populations. Low-frequency auditory impairments have previously been documented in Aroclor 1254 (A 1254)-exposed rats, including elevated behavioral auditory thresholds and decreased amplitude and prolonged latency auditory evoked brain stem responses (ABRs). Furthermore, outer hair-cell loss on the basilar membrane of the cochlea has been documented, demonstrating that the cochlea is a target organ for PCB ototoxicity. The current experiment assessed the effects of A1254 on cochlear function by measuring distortion product otoacoustic emissions (DPOAEs). ABRs were measured to determine the effects of A1254 on the central nervous system auditory pathways. Pregnant Long-Evans rats received either 0 or 6 mg/kg A1254 (po) in corn oil from gestation day 6 to lactational day 21. The auditory function of male and female offspring was assessed at approximately 18 months of age. The rats were anesthetized and a probe-unit, consisting of 2 insert earphones and a microphone, was positioned in the ear canal. DPOAE amplitudes were reduced and thresholds increased in the A1254-exposed rats. The deficits were most pronounced at the lowest frequencies tested (2.1-3.2 kHz), but deficits were also observed at higher frequencies (3.7-8.6 kHz). Males and females were equally affected at the lower frequencies, but females were more impaired at the higher frequencies. In contrast, ABR latencies and amplitudes were not altered by A1254 exposure. These findings provide the first functional evidence supporting a cochlear site of damage in PCB-induced hearing loss.

Animals↗

PubMed1989

The combined effect of cisplatin and furosemide on hearing function in guinea pigs.

The effect of the combined administration of cisplatin and furosemide on the electrophysiological hearing thresholds and endocochlear DC potential (EP) was studied in guinea pigs. A lack of interaction was found in animals given repeated intraperitoneal injections of a low dose of cisplatin with a pharmacological dose of furosemide. An ototoxic interaction occurred when a moderately high dose of cisplatin was administered intravenously at a time when the strial function was most affected by a very high dose of furosemide. The interaction was seen both as a decreased EP and a pronounced shift of auditory thresholds. It is concluded that the stria vascularis plays a role in the ototoxic mechanism of cisplatin.

Animals↗

PubMed1995

[A study on the reliability of evoked response audiometry in infants below one year of age; a long-term follow-up].

The reliability of brainstem evoked response audiometry (ERA) as an objective audiometric study was evaluated in long term follow-up infants with moderate to severe sensorineural hearing loss. None of the infants had either brain damage (cerebral palsy, mental retardation) or other severe complications (genetic diseases). The thresholds of ERA at 1 kHz and 4 kHz were measured in 234 infants below one year of age, from 1983 to 1990, in our hospital. These infants were followed-up to the age when conditioned oriented response audiometry (COR) and play audiometry could be conducted. Pure tone thresholds obtained by COR and play audiometry were compared with those of ERA. In addition, speech problems in these patients were evaluated. In all of those infants, hearing aids were fitted before one year of age to achieve early habilitation. As a results, ERA was found to be a reliable and efficacious test for determining auditory thresholds, and providing hearing aids for early habilitation in one-year old infants with moderate to severe sensorineural hearing loss.

Audiometry, Evoked Response↗

PubMed1981

[A practical method to differentiate the sensations of hearing and feeling (auditory and vibration threshold) in the low-frequency range (author's transl)].

An uncomplicated method to differentiate between an auditory and a vibration threshold. It is a well-known problem that it is very difficult or almost impossible to distinguish in a deaf person between the genuine auditory threshold, especially the bone conduction threshold, and a vibration threshold in the range of low frequencies up to 1000 cps. The studies conducted by the authors show that a frequency-modulated tone is extremely suitable for this purpose, because it is very easy to recognize a 5-6% frequency modulated tone of 5 dB (SL) by hearing, whereas it is almost impossible to detect it by feeling. The observations by Fastl (1978) regarding the large inter-individual variation of the frequency modulation threshold does not limit the study conducted by the authors, because the degree of modulation used is far above the threshold. It is not possible to use an amplitude-modulated tone for differentiation between the auditory and the vibration thresholds.

Audiometry↗

PubMed2003

Tanshinone (Salviae miltiorrhizae extract) preparations attenuate aminoglycoside-induced free radical formation in vitro and ototoxicity in vivo.

Antioxidant therapy protects against aminoglycoside-induced ototoxicity in animal models. A clinically suitable antioxidant must not affect the therapeutic efficacy of aminoglycosides or exhibit any side effects of its own. In addition, the treatment should be inexpensive and convenient in order to be implemented in developing countries where the use of aminoglycosides is most common. Standardized Salviae miltiorrhizae extracts (Danshen) are used clinically in China and contain diterpene quinones and phenolic acids with antioxidant properties. We combined in vitro and in vivo approaches to investigate the effect of a clinically approved injectable Danshen solution on aminoglycoside-induced free radical generation and ototoxicity. In vitro, Danshen inhibited gentamicin-dependent lipid peroxidation (formation of conjugated dienes from arachidonic acid), as well as the gentamicin-catalyzed formation of superoxide (in a lucigenin-based chemiluminescence assay) and hydroxyl radicals (oxidation of N,N-dimethyl-p-nitrosoaniline). Danshen extracts were then administered to adult CBA mice receiving concurrent treatment with kanamycin (700 mg/kg of body weight twice daily for 15 days). Auditory threshold shifts induced by kanamycin (approximately 50 dB) were significantly attenuated. Danshen did not reduce the levels in serum or antibacterial efficacy of kanamycin. These results suggest that herbal medications may be a significantly underexplored source of antidotes for aminoglycoside ototoxicity. Such traditional medicines are widely used in many developing countries and could become an easily accepted and inexpensive protective therapy.

Abietanes↗

PubMedDate not supplied

Neurophysiological correlate of the auditory after-image ('Zwicker tone').

The 'Zwicker tone' (ZT) is an auditory after-image that can be evoked most effectively when a band-suppressed noise (relative width of gap 1/3 octave) presented for a certain period of time has been switched off. The sensation of this purely monaural phenomenon is that of a pure tone with a frequency corresponding to the center frequency of the gap and an equivalent level of 10-15 dB above auditory threshold. The sensation decays gradually; it may last as long as 10 s depending on how long the evoking noise was presented. The search for a physiological correlate has been futile so far, probably because the search was confined to more peripheral levels of the auditory system (inferior colliculus). A neuromagnetic study was performed in normal-hearing subjects in order to look for a neurophysiological correlate of the ZT in the auditory cortex. With a stimulation paradigm especially designed for this study, we have been able to isolate poststimulus activity which appears to be related to the ZT and which originates in the supratemporal auditory cortex. It is a sustained neuromagnetic activity that shows a clear-cut dipolar field distribution, and it appears that this activity has certain similarities with the tone-evoked auditory sustained response. The hypothesis is put forward that during the sensation of the ZT a process takes place in the auditory cortex which is similar to that underlying the sustained response, and which gives rise to the sensation of the ZT. In contrast to the sustained response, however, which is due to neural activity evoked by an external acoustic stimulus, the sustained activity associated with the ZT is due to a temporary absolute or relative reduction of neural activity originating from those regions in which the ZT exciting stimulus caused an adaptation. These differences in neural activity cannot be distinguished by the auditory system from a corresponding external acoustic signal. Preliminary studies in patients suffering from tonal tinnitus yielded results which exhibit a certain similarity with those obtained in the ZT experiment.

Acoustic Stimulation↗

PubMed1997

Transient changes in cochlear potentials and DPOAEs after low-frequency tones: the 'two-minute bounce' revisited.

After exposure to a loud, non-traumatic low-frequency tone, auditory thresholds are elevated. Thresholds recover to normal in a non-monotonic manner, decreasing rapidly at first before increasing again, until they finally decrease monotonically towards normal. Although the transient elevation of thresholds after the initial improvement was originally called a 'bounce' by Hirsh and Ward (1952), Kemp (1986) suggests that the initial rapid recovery is the oddity: under some conditions a low-frequency tone can produce hypersensitivity in otoacoustic emissions, psychophysical thresholds, and perceived loudness (Kemp's 'bounce') without a later elevation of threshold (Hirsh and Ward's 'bounce'). Kemp also suggested that the transient hypersensitivity was caused by changes in the sensitivity of the active process within the cochlea. We have investigated the origin of this transient hypersensitivity (Kemp's bounce) in guinea pigs, recording cochlear potentials (CM, CAP, SP and EP) and otoacoustic emissions (DPOAEs at f2-f1, 2f1-f2, 2f2-2f1 and 3f1-2f2). Our results indicate that the bounce does not require neural activity, but is probably produced by non-neural cochlear mechanisms, possibly a transient decrease in the permeability of the organ of Corti which produces a small but significant change in standing current through outer hair cells. At least part of these changes, which are reduced as the stimulation frequency increases, and absent above 2 kHz, seem due to a small and transient movement of the cochlear partition towards scala tympani, probably due to a transient osmotic imbalance.

Acoustic Stimulation↗

PubMed2001

Aminoglycoside ototoxicity in adult CBA, C57BL and BALB mice and the Sprague-Dawley rat.

The availability of genetic information, transgenic and knock-out animals make the mouse a primary model in biomedical research. Aminoglycoside ototoxicity, however, has rarely been studied in mature mice because they are considered highly resistant to the drugs. This study presents models for kanamycin ototoxicity in adult CBA/J, C57BL/6 and BALB/c mouse strains and a comparison to Sprague-Dawley rats. Five-week-old mice were injected subcutaneously twice daily with 400-900 mg kanamycin base/kg body weight for 15 days. Kanamycin induced dose-dependent auditory threshold shifts of up to 70 dB at 24 kHz as measured by auditory brain stem-evoked responses. Vestibular function was also affected in all strains. The functional deficits were accompanied by hair cell loss in both cochlear and vestibular neurosensory epithelia. Concomitant administration of the antioxidant 2,3-dihydroxybenzoate significantly attenuated the kanamycin-induced threshold shifts. In adult male Sprague-Dawley rats, doses of 1 x 500 mg or 2 x 300 mg kanamycin base/kg body weight/day x 14 days induced threshold shifts of approximately 50 dB at 20 kHz. These were accompanied by loss of outer hair cells. The order of susceptibility, BALB>CBA>C57, was not due to differences in the pharmacokinetics of kanamycin. It also did not correlate with the presence of Ahl/Ahl2 genes which predispose C57 and BALB strains, respectively, to accelerated age-related hearing loss. Pigmentation, however, paralleled this rank order suggesting an influence of melanin on cochlear antioxidant status.

Aminoglycosides↗

PubMed1996

Otoacoustic emission amplification after inner hair cell damage.

Otoacoustic emissions (OAEs) are considered to originate from active cochlear processes involving the outer hair cells (OHC). These emissions are suppressed by activity in the efferent olivocochlear bundle (OCB) and following OHC damage caused by noise exposure or ototoxic drugs. Temporary enhancement of OAEs may occur following noise exposure, and permanent enhancement of emissions has been associated with primary afferent dysfunction in the auditory system. This suggests that there are active adaptation processes in the cochlea exist that could potentially compensate for loss of afferent input. We have used the anti-cancer drug carboplatin to induce selective inner hair cell (IHC) lesions in the cochleae of chinchilla and measured the elevation of auditory thresholds that occurred using brainstem responses (ABR). Following carboplatin treatment click evoked otoacoustic emissions (CEOAEs) were amplified from cochlear frequency regions, which demonstrated extensive IHC damage but apparently normal OHCs. These results support the theory that OHCs cells are involved in the production of these cochlear emissions but also provides further evidence that active adaptation processes exist in the cochlea. It is postulated that loss of afferent input reduces the activity in the medial efferent OCB resulting in de-suppression of OHC contractility. Enhanced OHC contractility could then produce amplification of CEOAEs.

Acoustic Stimulation↗

PubMed1977

Clinical acoustic reflex threshold measurements in infants.

Acoustic reflex thresholds elicited using clinical acoustic impedance techniques were obtained on normal infants between one month and one year of age. Reflex activating signals of 500, 1000, 2000 Hz, low-pass, high-pass, and white noise were used. Less intensity was required to elicit the acoustic reflex to the noise than to the pure tones, with the 500-Hz tone requiring the greatest intensity. Inference of auditory thresholds from the acoustic reflex indicated the presence of normal hearing in the infant group.

Acoustic Impedance Tests↗

PubMed1984

[Nonorganic (functional) hearing disorders in childhood].

Within a period of two years, we were able to observe five cases in which non-organic (functional) hearing defects occurred during infancy. The careful assessment of the case history and close observation, but also a differential-diagnostic audiological procedure in case of unstable hearing defects of unknown origin may disclose non-organic auditory communication disturbances. Based on our experience, the easily appreciated clinical picture is described. A pointer is supplied by the unstable auditory threshold in the tone audiogram. Integration of impedance audiometry and of acoustically evoked potentials (brain stem audiometry) into the individual audiometric experimental pattern is indispensable. In differential diagnosis it is essential to take into account fluctuating diseases of the internal ear, as well as high-grade auditory inattention as an expression of a partial conduction impairment.

Audiometry, Pure-Tone↗

PubMed1999

Relationship between hypertension and hearing disorders in the elderly.

OBJECTIVE: To investigate the relationship between hypertension and hearing disorders of the elderly. DESIGN: Prospective case-control study. SETTING: Lin Yi People's Hospital, Shandong Province, the People's Republic of China, from October 1995 to June 1997. PARTICIPANTS: Fifty five hypertensive patients and fifty five normal elderly subjects (control group) between the ages of fifty five and eighty nine years old were enrolled in the study. All patients were male and were divided into three groups according to age as follows: Group A: 55-64; Group B: 65-74; Group C: 75-89. INTERVENTIONS AND MAIN OUTCOME MEASURES: SIMENS DA-64 audiometer and MEDSON 2250 auditory brainstem response audiometry (ABR) were utilised to determine the degree of hearing disorders. Serum triglycerides and cholesterol were also tested in our central laboratory. RESULTS: Auditory thresholds collected during audiometric tests increased gradually in proportion with age, especially in the hypertensive group (p < 0.05). The results of the ABR demonstrated that the latencies of wave V, I-VIPL and III-VIPL were also prolonged compared with normal elderly subjects. The patient's duration of illness and the complications of hypertension had an influence on hearing disorders in relation to the ageing process. CONCLUSION: Hypertension, with a high level of blood triglycerides and cholesterol, worsens the hearing of the elderly. The hearing disorder in elderly people is a result of long duration of illness and the complications of the hypertension.

Age Distribution↗

PubMed1994

Heat-induced pain diminishes vibrotactile perception: a touch gate.

The gate control theory of pain (Melzack and Wall, 1965) suggests that tactile stimuli can decrease the perception of pain. We have found the reverse effect: Heat at levels that induce pain can substantially suppress tactile sensitivity, independently of shifts in attention or arousal. Ten human observers were stimulated by a tonic, pain-producing heat stimulus and vibrotactile stimuli (1, 10, and 100 Hz) coincidentally presented to the right thenar eminence. Vibrotactile thresholds were assessed with the skin at a normative temperature of 31 degrees C and at higher temperatures producing pain. Increases in vibrotactile thresholds (mean change = 7.3 dB) occurred at skin temperatures just below and above those that induced pain. Furthermore, absolute-magnitude estimates of suprathreshold vibrotactile stimuli determined during the same experiments showed decreased sensitivity and psychophysical recruitment. The changes are not attributable to attentional or arousal shifts, since they were not associated with changes in auditory thresholds. Furthermore, the changes occurred just below the subjects' pain thresholds (where nociceptors are presumably activated). This over-twofold diminution of vibrotactile sensitivity suggests that heat stimuli capable of inducing pain can significantly diminish taction, perhaps through a "touch gate" in a manner similar to the gate control theory proposed for pain.

Adult↗

PubMed1976

Dffects of imipramine on auditory sensitivity in the rat in relation to initial sensitivity.

Rats were divided into 2 groups according to their absolute auditory thresholds, as measured by a psychophysical method of limits using an operant conditioning technique. The procedure required a water-deprived rat to bar press repeatedly until a 3 s pure tone (3 kHz) came on. VR-15 schedule was used to determined the frequency of occurrence of the tone. Only within 4 s after the tone onset could the rat get water reinforcement by sticking its nose into the dipper area. The descending method was used with tone intensities ranging from 120 to 40 dB, in 2 dB steps. Imipramine was then administered 3 times at 24-h intervals (40, 80 and 160 mg/kg, p.o., respectively), and each rat was tested at 4, 8, and 12 h after each administration. Rats with high initial thresholds showed a decrease in thresholds with the lower dose of imipramine, and those with low initial thresholds an increase with the higher dose. An analysis of variance of these data showed significant effects of the type of subject (in terms of the level of initial thresholds), dose and interval conditions, and their interaction. It was demonstrated that the lower the initial sensitivity the greater the increase in sensitivity by imipramine.

Animals↗