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S A Counter

Publications and source records attributed to S A Counter.

At least 37 records · Page 2Linked to original sources
PubMed1993

Acoustic middle ear muscle reflex protection against magnetic coil impulse noise.

Electromagnetic stimulation (EMS) of the brain and the intracranial portion of the facial nerve has become a widely used clinical technique. The high intensity impulse noise acoustic artifact generated by some magnetic coils used in EMS has been shown to cause severe cochlear damage in experimental animals. This damage results in permanent threshold shifts throughout the auditory spectrum of the rabbit. As with other impulse and impact noise signals, the duration of the coil impulse noise is too short to be influenced by the normally protective acoustic middle ear muscle reflex. Artificially activating the acoustic reflex with a contralateral broad band noise during exposure to the intense coil artifact reduced the compound threshold shift (CTS) significantly, and the permanent threshold shifts (PTS) to near zero at each tone frequency and noise band tested. The results demonstrate the effectiveness of a suprathreshold sound in activating the acoustic middle ear muscle reflex and protecting against impulse noise-induced hearing loss caused by high frequency magnetic coil acoustic impulses.

Acoustic Impedance Tests↗
PubMed1993

Oto-traumatic effects of computer simulated magnetic coil impulse noise: analysis of mechanisms.

The brief impulse noise artifacts of 1.0 ms or less generated by some magnetic coils used in extracranial magnetic stimulation may induce acoustic trauma. We investigated the effects of these magnetic coil acoustic artifacts (MCAA) on the inner ear by exposing rabbits to computer stimulated impulse noise designed to mimic the impulse noise of the coil in spectrum and acoustic energy. The simulated impulse noise stimuli (50 impulses) were varied in maximum peak sound pressure (160, 157, and 155 dB re: 20 muPascal), rise-time (100 microseconds and 1,000 microseconds) and duration. The frequency spectrum of the simulated impulse noises were kept constant at 0.5 kHz to 7 kHz with peak energy in the 2-5 kHz range. The results indicated that the simulated magnetic coil impulse noise caused extensive cochlear damage and permanent threshold shifts largely equal to those induced by the MCAA. The MCAA created slightly greater PTS than the simulated impulse of the same peak sound pressure. Each of the 3 experimental stimuli induced similar PTS in the auditory range of 0.5 to 16 kHz, with the higher peak sound pressure stimuli (157 and 160 dB) causing greatest hearing loss. Increasing the rise-time of the simulated brief impulse noise from 100 microseconds to 1,000 microseconds did not reduce the level of PTS significantly. The results suggest that for brief acoustic signals of around 1 ms or less, the peak pressure and spectral content rather than the rise-time and duration were the important factors in the development of noise-induced hearing loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1993

Electromagnetic stimulation of the auditory system: effects and side-effects.

Extracranial electromagnetic stimulation (EMS) is a recently developed clinical technique which may be used in place of conventional transcutaneous electrical stimulation to activate the central and peripheral nervous systems. This technique is widely used in neurology and otolaryngology for non-invasive stimulation of the brain and facial nerve. EMS uses electromagnetic field pulses which pass unimpeded through the cranium and soft tissues to activate excitable membranes of volume conductors. In this series of studies, the effects and side-effects of electromagnetic stimulation on the auditory system of humans and experimental animals were investigated. In the first study, 18 profoundly hard-of-hearing and deaf patients who were candidates for cochlear implants were examined by non-invasive EMS in an effort to determine whether EMS could stimulate residual neurons in the cochlea, 8th nerve proper, or higher auditory brain centers, and evoke auditory sensations. The patients were stimulated with a magnetic coil positioned at the (1) auricle, (2) mastoid process, and (3) the temporal lobe area. EMS elicited auditory sensations in 26 ears (of 14 patients/subjects). The lowest threshold of auditory sensation (TAS) at each stimulus position was found to be at the 20% EMS level, with a range of 20-50% of the maximum level (2.0 Tesla), and with equal sensitivity in each coil position. There was no correlation between the EMS/TAS and the immediate postoperative psychoacoustic tests in ten patients receiving cochlear implants. A prominent side effect of EMS was found to be the high intensity, high frequency impulse noise generated by the coil which causes severe cochlear damage and permanent sensorineural hearing loss in experimental animals. Measurements of the sound pressure level (SPL) of the magnetic coil acoustic artifact (MCAA) at the tympanic membrane of the rabbit ear showed levels of up to 160 dB for maximum EMS. Measurements of the spectral content and SPL of the MCAA in the ear canal of life size models of the human cranium with the stimulating coil placed at standard clinical positions indicated that the major acoustic energy of the pulse is concentrated in the 2-5 kHz range, and that the SPL of the pulse at some positions may place persons at risk for hearing loss. Studies on computer simulated impulse noises showed that the peak sound pressure rather than the rise time (in the range 0.1-1.0 ms) determined the permanent threshold shift (PTS). The MCAA was more harmful than a 128 dB SPL continuous noise with 100 times more energy.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Analysis of the coil generated impulse noise in extracranial magnetic stimulation.

An intense impulse noise artifact is generated by the coil used in extracranial magnetic stimulation (EMS) of the brain and cranial nerves. In this study we measured and analyzed the sound pressure level (SPL), spectral content, wave form, and time course of the magnetic coil acoustic artifact (MCAA) impulse noise in the sound field and in the ear canal of life-size models of the human cranium. Two different clinical magnetic stimulators and coils were used. Sound field measurements from both coils showed the MCAA to be a transient impulse noise with a rapid rise-time, brief duration, broad acoustic spectrum, and high intensity. Measurements made on models of the human head with the magnetic coils positioned at selected standard clinical positions for EMS, particularly the peripheral facial nerve, auricle and mastoid areas, indicated that the MCAA may reach sound pressure levels that exceed noise damage-risk criteria limits for sensorineural hearing loss. The maximum peak energy in the acoustic spectrum of the MCAA measured in the ear canal of the model heads was from 2 to 5 kHz, the range of highest sensitivity in human ears. Ear protectors were found to attenuate the SPL of the MCAA, reaching the ear canal of the model heads by 15-22 dB SPL, and were recommended for use by patients and subjects exposed to EMS.

Brain↗
PubMed1992

Sound perception induced by extracranial magnetic stimulation in deaf patients.

Two profoundly hard-of-hearing and deaf patients were examined by non-invasive extracranial magnetic stimulation (EMS) in an effort to determine whether EMS could evoke auditory sensations. The patients were fitted with standard earplugs and were stimulated at the auricle, the mastoid and the temporal lobe area. The threshold of auditory sensation (TAS) was determined at each stimulus position and found to be approximately 20-40% of the maximum EMS level (2.0 Tesla). The TAS was generally lowest in mastoid stimulation, but was variable, and dependent on the angle and position of the stimulating coil relative to the skull. Middle-ear muscle reflex (MEMR) tests performed by EMS of the auricle, mastoid and temporal lobe area contralateral to the probe ear were negative. It was concluded that EMS of the auditory system, particularly the mastoid area, can evoke auditory sensations in cochlea-deaf ears, and that this technique deserves further study as a non-invasive procedure for evaluating potential cochlear implant patients in conjunction with electrostimulation.

Acoustic Impedance Tests↗
PubMed1991

Acoustic trauma in extracranial magnetic brain stimulation.

The effects of the magnetic coil acoustic artifact (MCAA) associated with extracranial magnetic field stimulation (EMFS) of the brain were studied in normal hearing rabbits. Spectral and intensity analyses showed that the MCAA is a high intensity transient signal with peak energy between 2 and 5 kHz, and peak amplitudes in the first 100-200 mu sec. At EMFS levels of 50-100% of maximum output (2.0 Tesla), the corresponding MCAA levels were 131-142 dB sound pressure level (peak hold) at the outer ear and amplified by the external meatus to reach 145-157 dB sound pressure level (SPL) at the position of the tympanic membrane in rabbits. Measurements of the acoustic middle ear muscle reflex (AMR) in non-anesthetized rabbits indicated that exposure to EMFS levels of 50-100% resulted in correspondingly increasing compound threshold shifts (CTS) and permanent threshold shifts (PTS) in the unprotected ears of the experimental animals. Auditory brain-stem responses (ABR) measures on the same and additional animals corroborated these findings. Morphological studies showed evidence of substantial cochlear trauma at EMFS levels as low as 50%, with increasing severity up to 100% EMFS. Morphological examination of inner ear structures following exposure to the MCAA in the acute preparation (fixed within hours after exposure) showed ruptures between pillar cells and a detached organ of Corti. Preparations examined 3 or more weeks after exposure showed damaged pillar cells, a widespread loss of outer hair cells, fused and fractured inner hair cell stereocilia, and kinocilium outgrowth on inner hair cells. Although this extremely short impulse contains approximately 2 orders of magnitude less acoustic energy than a continuous noise exposure of 131 dB for 15 min, it is substantially more injurious to the cochlea. The present findings suggest that the acoustic artifact produced by the EMFS coil in some clinical instruments may pose a potential risk for temporary and permanent hearing loss in patients and clinicians when held in close proximity to the unprotected ear. Initial studies suggest that the magnetic field alone did not appear to cause permanent hearing impairment. We recommend the use of ear protectors for the patient and clinician during EMFS as a precautionary measure to prevent possible hearing loss from the MCAA.

Animals↗
PubMed1990

Stapedius reflex thresholds in relation to tails of auditory nerve fiber frequency tuning curves.

The acoustic stapedius reflex (ASR) threshold on non-anesthetized rabbits was compared to some measures of the single auditory nerve fiber activity of rabbits. The observations were made on normal-hearing animals, with some additional data from noise-exposed individuals. The results showed that the ASR threshold was reached at a sound level above saturation of discharge rate for individual neurons at their characteristic frequency (CF) in normal animals. It was found, on the other hand, that the ASR threshold measured across frequencies from 0.25 to 12.0 kHz were at a level similar to that of the tails of the frequency tuning curves (FTCs). Cochlear lesions-induced changes in FTC tail levels were paralleled by changes in ASR threshold levels. The raise of ASR threshold was, however, somewhat larger than the raise of the tails which might be explained by the significant relative decrease in the total number of units found in the frequency region corresponding to the lesion. There was also a decrease in the high spontaneous rate (SR) compared to the low and medium SR fibers for higher frequencies. It is concluded that the FTC tails can be a major eighth-nerve correlate to ASR activation.

Acoustic Stimulation↗
PubMed1990

Hearing loss from the acoustic artifact of the coil used in extracranial magnetic stimulation.

The stimulating coil used in extracranial magnetic field stimulation (EMFS) emits a high intensity impulse sound artifact that causes permanent threshold shifts in the unprotected ears of experimental animals. At magnetic stimulation levels of 50 to 100%, the magnetic coil acoustic artifact (MCAA) ranged from 145 to 157 dB peak sound pressure level at the eardrum. The magnetic field alone did not appear to cause hearing impairment since no threshold shifts were observed in ears that were plugged with ear protectors during exposure to the MCAA. These findings suggest that the acoustic artifact produced by EMFS in the clinic may pose some risk for hearing loss in patients and clinicians when held in close proximity to the unprotected ear. We recommend the use of ear protectors for the patient and clinician during EMFS as a precautionary measure to prevent hearing loss.

Animals↗
PubMed1990

Hypoacusis among the Polar Eskimos of northwest Greenland.

Audiological tests were conducted on 188 Polar Eskimos (75 males and 43 females) in small, remote, nonindustrialized settlements of Northwest Greenland. Most males of this small Eskimo tribe hunt regularly for food using rifles and shotguns. The means of the pure tone hearing thresholds indicated that 77% of the males in the population sample had a hearing loss (greater than 25 dB HL) in the high frequency range (above 2,000 Hz), in one or both ears. Also, 73% of the males had bilateral hearing losses (greater than 25 dB HL), and 73% had hearing thresholds greater than or equal to dB in one or both ears. A high frequency hearing loss was found in 46% of the males of the younger age groups (less than or equal to 40 years), mainly in the 3,000 to 8,000 Hz range, with the mean loss gradually extending to 2,000 and 1,000 Hz, and increasing in severity with age. The mean pure tone thresholds of 6- to 60-year-old female Polar Eskimos (who do not hunt with firearms) were generally within normal limits over the entire audiometric frequency range for the younger groups, and increased with age to the mild hearing loss range. Among the females, 35% had a hearing loss (less than 25dB HL) in the high frequency range (above 2,000 Hz) in one or both ears, and 21% had thresholds of greater than or equal to 50 dB in one or both ears. Conductive hearing losses in the low frequency range were not widespread among the males or females of this survey. The findings of this study suggest: (1) The high incidence of age-related hearing loss among the Polar Eskimo males is the result of frequent exposure to high intensity, impulse firearm noise, which is the major source of noise for this population, in an otherwise "noise-free" environment. (2) The primary noise-induced permanent threshold shift among Polar Eskimo hunters occurs in the age range of 10-40 years, and increases slowly thereafter, mainly as a result of continual noise exposure and presbyacusis. It is recommended that ear protectors and a comprehensive hearing conservation/rehabilitation program be provided for the Polar Eskimo population at once in order to prevent further hearing impairment and to rehabilitate those persons presently suffering from hearing loss.

Adolescent↗
PubMed1989

Acoustic middle ear reflexes in laboratory animals using clinical equipment: technical considerations.

Acoustic middle ear muscle reflexes (AMR) were examined in nonanesthetized rabbits using clinical oto-impedance devices to determine the feasibility of utilizing clinically available instruments in studies of laboratory animals, particularly with regard to parameters such as probe tone frequency and intensity. The Karolinska Sjukhuset clinical impedance instrument and the Madsen Electronics ZO174 standard clinical impedance meter were used. The results of this study show that reliable AMRs and tympanograms can be obtained from rabbits with both clinical instruments. Probe tone frequencies in the range of 800-1,200 Hz were most effective for eliciting tympanograms and the AMR in rabbits. The probe tone level was also found to be an important factor, with the most reliable sound pressure level being around 70 dB SPL, and below that of the reflex threshold. Both clinical instruments recorded AMR threshold elevations in animals with 7th-nerve and cochlear lesions. AMR decay was observed at 8 and 12 kHz, but no decay was seen in normal-hearing animals up to 4 kHz, suggesting that this frequency may be suitable for detecting and measuring pathological decay in the rabbit. The overall results suggest that standard oto-impedance instruments with a probe tone frequency of 1,000 Hz may be used effectively in experimental studies of several aspects of the AMR in laboratory animals, such as rabbits.

Acoustic Impedance Tests↗
PubMed1987

A histochemical characterization of muscle fiber types in the avian M. stapedius.

The muscle fiber types and sizes in the M. stapedius (middle ear muscle) of the domestic chicken, Gallus gallus were determined histochemically on the basis of their reactions to myofibrillar adenosine triphosphatase (mATPase), succinic dehydrogenase and NADH diaphorase. Only type II fibers were identified at pH 9.4 and 4.2. At pH 4.6 three levels of activity were seen: high, intermediate and low. With the staining techniques three subtypes of fibers for oxidative enzymes, Types II1 (highly glycolytic), II12 (intermediately glycolytic and lipolytic) and II123 (highly lipolytic) were identified. Fiber diameter was also measured for the different fiber types. The average fiber diameter was around 20 micron for each fiber type. Although similar in size, the fiber types were markedly different in their histochemical properties. These findings plus those of earlier physiological studies suggest that the M. stapedius of G. gallus is a fast twitch, muscle with fibers of similar diameter showing mainly fatigue resistance characteristics.

Adenosine Triphosphatases↗
PubMed1986

Audiological screening of Amerindians of the Suriname rainforest.

Audiological screening tests were conducted among a remote, relatively noise-free population of Amerindians in the deep rainforests of Surinam, South America. These preliminary tests, the initial step in a planned long-term study, were the first such examinations on these people, and were intended to examine the overall audiological health of the population as a function of age and sex. Audiological testing of this non-technological population was more challenging than conventional test situations in modern industrial societies because the tests were hampered by a variety of extraneous factors. The results from a sample of the population showed a range of hearing impairments similar to that seen in modern industrial societies, including conductive, mixed, and sensorineural hearing losses. Also, hearing sensitivity was found to deteriorate with age in both females and males, particularly at the higher frequencies (2, 4, and 8 kHz). This deterioration was slightly greater for males, who as hunter-gatherers regularly use shotguns for hunting. Impact noise from hunting guns is the only source of intense noise to which the Amerindian population is exposed with any regularity. The diet of the Amerindians includes as the main carbohydrate staple the manioc cassava, which has also been linked to sensorineural hearing loss in some populations.

Acoustic Impedance Tests↗
PubMed1985

Brain-stem evoked potentials and noise effects in seagulls.

Brain-stem auditory evoked potentials (BAEP) recorded from the seagull were large-amplitude, short-latency, vertex-positive deflections which originate in the eighth nerve and several brain-stem nuclei. BAEP waveforms were similar in latency and configurations to that reported for certain other lower vertebrates and some mammals. BAEP recorded at several pure tone frequencies throughout the seagull's auditory spectrum showed an area of heightened auditory sensitivity between 1 and 3 kHz. This range was also found to be the primary bandwidth of the vocalization output of young seagulls. Masking by white noise and pure tones had remarkable effects on several parameters of the BAEP. In general, the tone- and click-induced BAEP were either reduced or obliterated by both pure tone and white noise maskers of specific signal to noise ratios and high intensity levels. The masking effects observed in this study may be related to the manner in which seagulls respond to intense environmental noise. One possible conclusion is that intense environmental noise, such as aircraft engine noise, may severely alter the seagull's localization apparatus and induce sonogenic stress, both of which could cause collisions with low-flying aircraft.

Acoustic Stimulation↗
PubMed1982

Analysis of the avian middle ear muscle contraction by strain gauge and volume and impedance change measures.

1. Aves, unlike mammals, possess only one middle ear muscle, the stapedius. This muscle, which is innervated by a branch of the facial nerve, is exceptional in the respect that it alone exerts its effects on an entire physiological system, viz. the middle ear. 2. Measurements of the physiological effects of this muscle in situ revealed both fast and slow components: the fast component results from the active contractile machinery of the muscle while the slow component derives from certain passive, visco-elastic attachments. 3. The use of middle ear volume and impedance change measures in situ revealed a broader range of the muscle's physiological actions than was predictable by conventional strain gauge recording and/or histochemical studies.

Acoustic Impedance Tests↗
PubMed1981

Basic contraction properties of the avian stapedius muscle.

The basic contraction properties of the solitary avian middle ear muscle, the M. stapedius, was investigated in chicken, Gallus gallus, by a sensitive tension transducer. Previous experimental studies on the in situ muscle preparation revealed both fast and slow components in the muscle's physiological responses. In the present study, brief electrical stimulus pulses delivered to the "isolated" M. stapedius elicited rapid twitch contractions with average tension levels of 46 mN for maximal stimulation. The contraction time was 15 ms, the half relaxation time was 15 ms and the total twitch time was 54 ms. Repetitive stimulation (2.5-200 Hz) revealed maximum summation of responses at 10-20 Hz and apparent complete fusion at 160 Hz. Peak tension at 160 Hz ranged from 150 mN to 200 mN. The twitch tetanus ratio was found to be 0.25. In earlier experiments with an in situ preparation, a slow component was observed in the physiological responses. However, this slow component was not seen in the single twitch responses or the responses or the response to repetitive stimulation in the present study. The M. stapedius of Gallus gallus was found to be a "fast" muscle by conventional terminology. Its contraction time is slightly shorter than the contraction times of the M. stapedius in mammals such as the cat (21 ms) and the rabbit (22 ms). These findings are consistent with earlier morphological studies which show the M. stapedius of Gallus gallus to have the features of a fast twitch muscle.

Animals↗
PubMed1979

Physiological activation of the stapedius muscle in Gallus gallus.

The function of the avian middle ear muscle was investigated in the chicken, Gallus gallus (domesticus). The avian species offers excellent conditions for study of middle ear muscle function since it possesses a single middle ear muscle, the stapedius, which is located extracranially. Electromyograms (EMG), measurements of impedance change, and volume change in the middle ear cavity were used to assess the muscle's activity. The results showed that the middle ear muscle of Gallus does not exhibit an acoustic reflex. However, the stapedius is regularly activated during the animal's own vocalization. Measurements of the EMG and volume change showed the stapedial activity to increase systematically with increases in the vocal sound level. The use of volume change as a measure of stapedius function was found to be highly suitable in the present experiments in that it allows for measurements of the magnitude of the stapedius contraction without altering the intact physiological state of the middle ear, and is insensitive to the ambient noise and vocal sounds, that hamper the impedance technique.

Acoustic Impedance Tests↗
PubMed1979

Contraction properties and functional morphology of the avian stapedius muscle.

The influence of the stapedius muscle contraction on middle ear volume and acoustic impedance was investigated in the chicken, Gallus gallus. The time course of twitch responses to electrical stimulation (measured as volume and impedance changes) was found to be largely independent of the stimulus voltage, having a contraction time of 22 ms and a half-relaxation time of 22 ms. The stapedius muscle was therefore characterized as a fast twitch muscle. Slow contraction properties were also revealed: A summation of responses to repetitive stimulation beginning at 2.5 Hz and a slow decline to baseline were seen in volume and impedance change recordings. The morphological characteristics were consonant with that of a homogeneously fast muscle: Only fibres with high ATPase activity were identified and no fibres with "en grappe" or multiple innervation were observed. The slow characteristics were suggested to be due to visco-elastic elements in the middle ear. The chicken stapedius muscle is suggested to be analogous to both the stapedius and the tensor tympani of mammals.

Acoustic Impedance Tests↗