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PubMed1987

Asymmetries in the acoustic reflexes of the cat stapedius muscle.

Electromyographic activity (EMG) was used to monitor contractions of the stapedius muscle evoked by both ipsilateral and contralateral sound in ketamine-anesthetized or decerebrate cats. After the onset of a continuing tone, stapedius EMG often had bursts of activity at regular intervals; similar bursts were also observed in the EMG from the tensor tympani muscle. Plots of the r.m.s. amplitude of stapedius-EMG versus sound level usually had a steep rising phase (small dynamic range) and a plateau at high sound levels. For sound stimulation at 1 kHz, the crossed stapedius reflex had a lower maximum amplitude (ave. amplitude ratio: 0.37) and a higher threshold (ave. 8 dB) than the uncrossed reflex. Since the uncrossed reflex evokes considerably more stapedius EMG than does the crossed reflex, it probably produces correspondingly greater changes in middle-ear sound transmission.

Acoustic Stimulation↗
PubMed2003

Influence of EEG monitoring on intraoperative stapedius reflex threshold values in cochlear implantation in children.

BACKGROUND: Cochlear implantation is a widely used means of treating deafness and severe hearing disorders. The surgical procedure includes inserting the cochlear implant electrode array into the cochlea and embedding the corresponding signal receiver in the mastoid bone behind the ear. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. For this purpose, electrically elicited stapedius reflex threshold values can be used. However, stapedius reflex threshold values measured intraoperatively are influenced by anaesthetics. The goal of this retrospective study was to find out whether electroencephalogram (EEG) control of anaesthesia produces more reliable reflex threshold values as a basis for the fitting of the speech processor. METHODS: Three groups of children, after surgery for cochlear implantation, were analysed with regard to the magnitude of intraoperative electrically elicited stapedius reflex threshold values and their deviations from postoperatively determined maximum comfortable levels (group 1: methohexital/remifentanil with EEG monitoring, n = 10; group 2: isoflurane/fentanyl with EEG monitoring, n = 9; group 3: isoflurane/fentanyl without EEG monitoring, n = 11). RESULTS: Children with EEG monitoring had significantly lower electrically elicited stapedius reflex threshold values and also significantly lower differences between intraoperative stapedius reflex threshold values and postoperatively determined maximum comfortable levels. CONCLUSIONS: Electroencephalogram monitoring in cochlear implantation is of considerable value in controlling anaesthesia and improving speech processor fitting based on more reliable intraoperative neurophysiological data.

Analysis of Variance↗
PubMed2003

Childhood otitis media and electrically elicited stapedius reflexes in adult cochlear implantees.

BACKGROUND: Electric stapedius reflex thresholds are helpful in programming cochlear implants, but only approximately two-thirds of patients have identifiable reflexes. HYPOTHESIS: Childhood otitis media correlates with absent stapedius reflexes or with high electric stimulation needed to elicit a reflex in cochlear implantees. STUDY POPULATION: Twenty-five adults with acquired hearing loss who underwent implantation with the MED-EL COMBI 40+ standard electrode array. STUDY PARAMETERS: The extent of temporal bone pneumatization, an indicator of childhood otitis media, was measured from preoperative computed tomographic images. Clinical units (in microamperes) needed to elicit a contralateral stapedius reflex, or maximum stimulation tried, were recorded. RESULTS: No definite association of pneumatization volume with intensity of stimulation was observed. The null hypothesis of no association cannot be rejected. CONCLUSION: Childhood otitis media does not seem to explain absent electric stapedius reflexes and the wide range of clinical units needed for maximum comfortable loudness level. Remaining potential explanations probably include the wide range of cochlear neurons that can be electrically stimulated, and that the maximum tolerable stimulation is too low to elicit a stapedius reflex.

Adult↗
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↗
PubMed1997

Effects of stapedius-muscle contractions on the masking of auditory-nerve responses.

There has been little exploration of the mechanisms by which stapedius muscle contractions reduce the masking of responses to high-frequency sounds by low-frequency sounds. To fill this gap in knowledge, controlled stapedius contractions were elicited with direct shocks in anesthetized cats, and measurements were made of the effects of these contractions on the masking of single auditory-nerve fibers and on the attenuation of middle-ear transmission. The results show that the stapedius-induced reductions of masking can be much larger than the attenuations of low-frequency sound. With a 300-Hz band of masking noise centered at 500 Hz, and signal tones at 6 or 8 kHz, unmasking effects over 40 dB were observed for sounds 100 dB SPL or less. The data suggest that much larger unmasking might occur. The observed unmasking can be explained completely by a linear stapedius-induced attenuation of sound transmission through the middle ear and a nonlinear growth rate of masking for auditory-nerve fibers. No central effects are required. It is argued that the reduction of the upward spread of masking is probably one of the most important functions of the stapedius muscle.

Acoustic Stimulation↗
PubMedDate not supplied

Effects of isoproterenol on the orbicularis oculi and stapedius muscles.

The effect of the beta-adrenoceptor agonist, isoproterenol, on the orbicularis oculi and stapedius muscles was studied. Rats were injected with isoproterenol (5 mg/kg) every day. The animals were sacrificed after 1 and 2 weeks, and the orbicularis oculi muscle and stapedius muscle were removed. Muscle fibers were separated into single fibers, and cytochrome oxidase enzyme staining was applied with 1% MnCl2, DAB + H2O2. The density of cytochrome oxidase enzyme reaction products and the diameter of individual muscle fibers were analyzed by computer-assisted measurement. The administration of isoproterenol increased the activity of cytochrome oxidase as well as the diameter of muscle fibers in the orbicularis oculi muscle and stapedius muscle. It was suggested that these muscle fibers exhibited increases in functional activity after the administration. The results showed that the diameter and cytochrome oxidase enzyme activity of the orbicularis oculi and stapedius muscles increased. We conclude that isoproterenol induces hypertrophy of the orbicularis oculi and the stapedius muscle fibers, and promotes cytochrome oxidase enzyme activity.

Adrenergic beta-Agonists↗
PubMed1979

The noise protection effect of the stapedius reflex.

The purpose was to estimate the attenuation and protection effect of the acoustic stapedius reflex on the inner ear. The acoustic stapedius reflex was recorded by means of extratympanic manometry (ETM). This method was used, as it is able to differ between the stapedius and the tensor reflex. Patients with unilateral Bell's palsy were investigated during palsy time and after recovery. The amplitude of the contralateral acoustic stapedius reflex was used as a relative measure of the excitation of the cochlea on the affected side. The attenuation effect, 20 dB above the reflex threshold, was approximately 15 dB for all tested patients. After the ETM investigation a temporary threshold shift was shown on the affected side (average 34 dB). The hearing threshold on the healthy side was unchanged. Thus the attenuation effect of the acoustic stapedius reflex protects the inner ear from an acoustic damage. A protection effect of the tensor tympani was not demonstrated.

Audiometry↗
PubMed2000

[Degenerative changes in stapedius muscle morphology caused by aging].

Degenerative changes in the morphology of the stapedius muscle caused by aging using a collection of human temporal bones obtained by our department. The diameter of the muscle fibers, the variance in muscle fiber diameter, the ratios of intermuscular connective tissue and muscle to the area of the bone niche for the stapedius muscle, the number of muscle fibers around the tendon, and the adipose cell count were measured for each temporal bone. In total, 80 temporal bones were examined, excluding specimens with facial nerve degeneration, degenerative diseases, middle ear disease and leukemia. Between the ages of 38 fetal weeks and 9 years, the muscle fibers and thin and the variance in fiber diameter is small. The areas of intermuscular connective tissue, muscle and the number of muscle fibers around the tendon do not change between 38 fetal weeks and 60 years. All of the parameters measured showed no significant changes between the ages of 10 and 60 years. The variance in muscle fiber diameter began to increase in specimens aged 70 years or older because some of the muscle fibers had begun to atrophy. Adipose cells were sometimes observed in very old specimens. In contrast to the tensor tympani muscle, in which degenerative changes begin during childhood, atrophic degeneration of the stapedius muscle as a result of aging begins at a very late age. The difference in aging between the stapedius muscle and the tensor tympani muscle is probably related to evidence suggesting that the stapedius muscle contracts in response to acoustic stimulation.

Adolescent↗
PubMedDate not supplied

Objective intraoperative method to record averaged electromyographic stapedius muscle reflexes in cochlear implant patients.

We have developed a procedure to measure the averaged stapedius muscle reflex in response to electrical stimulation (AESR) with a cochlear implant. The AESR, as activated by ipsilateral stimulation with a cochlear implant, was investigated intra-operatively in a series of 12 children. After the cochlear implant was placed into the cochlea and secured by the surgeon, an electromyographic (EMG) needle electrode was gently placed into the stapedius muscle. During stimulation of the cochlear implant, the stapedius reflex was monitored visually (VESR) and as an averaged EMG response (AESR). Consistent AESRs were obtained in 7 of the 12 children. These measures provide a method to obtain stapedius muscle responses that may be helpful in the programming of young children with cochlear implants. Comparative post-operative measures were also obtained, including behavioral threshold levels, behavioral comfort levels, and the contralateral stapedius reflex threshold (ESR) on selected electrodes.

Auditory Threshold↗
PubMed1977

Normal values of the ipsilateral acoustic stapedius reflex threshold.

It is frequently taken for granted that the acoustically evoked stapedius reflex is bilaterally symmetrical. Contrary to this, Møller described an asymmetry of the acoustic stapedius reflex with an ipsilaterally 2--14 dB lower threshold. The determination of normal values of the ipsilateral acoustic stapedius reflex threshold with a large number of patients is difficult as the intensity of the stimulus depends considerably on the position of the probe in the acoustic meatus and is therefore not defined with sufficient accuracy. For this reason we determined the values of the ipsilateral threshold by applying a stimulus sound of high intensity to the deaf ear of unilaterally completely deaf patients with a normal headphone, which can be calibrated much more accurately. After subtraction of the individual cross hearing loss, the exact ipsilateral intensity was obtained. By this method a stapedius reflex could be evoked with 49 of the 62 patients. By mathematical consideration of the data of the positive cases, as well as the maximum available intensities with the negative cases, determination of the median value of the ipsilateral threshold was possible: at 0.5 kHz 59 dB; at 1kHz 62.5 dB; at 2 kHz 67 dB; at 4 kHz approx. 67 dB. The difference between ipsilateral and contralateral stapedius reflex threshold was in the range of 15 dB. A new definition of the normal value for the ipsilateral measured Metz recruitment appears necessary.

Auditory Threshold↗
PubMedDate not supplied

Eardrum displacement following stapedius muscle contraction.

Simultaneous monitoring in human subjects on the same ear of eardrum displacement by tympanomanometry, and impedance with the electroacoustic bridge, provided information concerning contraction of the stapedius muscle and its effect on eardrum displacement. Extensive control procedures were employed to elicit only the stapedius reflex; lower intensity auditory stimulation, electrocutaneous stimulation of the homolateral external ear canal, and anesthetization of nerves leading to the tensor tympani. Following these procedures the following results were obtained: (1) Extremely small biphasic and monophasic eardrum movements were seen in the stapedius--only ear to auditory and electrocutaneous stimulation; the form of the response was much less predictable to auditory stimulation. (2) At high sound intensities relatively large inward and biphasic movements of the eardrum occurred in the normal ear, unquestionably due to contraction of the tensor tympani. These results were further validated in a group of stapedectomized ears, without the stapedius but with normal tensor tympani. (3) Biphasic responses did not occur in the tensor tympani--only ear, only monophasic inward responses. (4) Upon air-jet stimulation to the orbit of the eye, these subjects had an accentuated tensor response in that large inward movements of the eardrum occurred as compared with those in normal ears, suggesting that there is an alteration of the tensor response by the presence of the stapedius muscle. Estimates of the actual eardrum displacement were calculated based on a model of the external ear canal and eardrum.

Acoustic Stimulation↗
PubMed1983

Stapedius reflex test, brainstem audiometry and opto-vestibular tests in diagnosis of acoustic neurinomas. A comparison of test sensitivity in patients with moderate hearing loss.

The stapedius reflex test, brainstem audiometry and the opto-vestibular tests for identifying acoustic neurinomas (AN) were evaluated and compared in a study of 21 patients with radiologically or surgically verified AN and a pure tone average not exceeding 60 dB HL. The stapedius reflex test results were interpreted according to the criteria developed at this clinic. The stimuli for the auditory brainstem response (ABR) were 2 kHz haversine waves and 4 kHz square waves. The vestibular examination consisted of a caloric test and the recording of eye-tracking and gaze nystagmus. In the cases studied the stapedius reflex test gave 1 false-negative result and ABR none. The ENG gave 3 false-negatives whereas the results of speech discrimination tests were misleading in no fewer than 1/3 of the cases. The results of the different tests were directly correlated but correlation coefficients did not exceed 0.65. Tumours larger than 15-20 mm showed a different test pattern than those below that size: stapedius reflex response, ABR and caloric response were eliminated and all of these patients had abnormal optomotor function. It is suggested that an optimal routine test procedure should consist of a pure tone audiogram, supplemented by ABR or the stapedius reflex test. Opto-vestibular tests may be of value in a preliminary estimation of tumour size.

Audiometry↗
PubMed1983

The locations of stapedius and tensor tympani motoneurons in the cat.

The numbers and locations of motoneurons to the stapedius and tensor tympani muscles were determined by retrograde transport of horseradish peroxidase. Stapedius motoneurons lay outside the traditionally recognized facial nucleus, in several distinct locations: (1) in the interface between the facial nucleus and the superior olive; (2) in a thin, scattered lamina of somewhat smaller cells spread dorsal to the facial nucleus; and (3) in a cluster located ventromedial to the rostral third of the facial nucleus. Some cells also lay dorsal to the superior olive or scattered in the reticular formation, just medial to the descending loop of the facial nerve. Tensor tympani motoneurons also lay outside the traditionally recognized trigeminal motor nucleus, in an area just ventral to it. Both motoneuron pools were large, producing innervation ratios that establish stapedius and tensor tympani among the most finely innervated muscles yet studied. The degree of intermingling of large and small cells in these pools may explain, in part, why it has been easier to identify slow muscle fibers physiologically in tensor tympani than in stapedius.

Animals↗
PubMed1985

Identification of stapedius muscle motoneurons in squirrel monkey and bush baby.

The location of brainstem neurons which mediate the stapedius reflex was identified by injecting horseradish peroxidase into the stapedius muscle of squirrel monkeys and bush babies. Retrogradely labeled neurons, arranged in a one- to three-cell column, were found medial to the main facial motor nucleus in squirrel monkeys and ventral to it in bush babies. Nissl, protargol, and acetylcholinesterase stains were subsequently used to identify and describe this unique column of cells. It was found that staining characteristics, as well as shape, size, and location, distinguish stapedius muscle motoneurons from closely associated cell groups. Furthermore, stapedius muscle motoneurons are morphologically similar to periolivary cells and morphologically dissimilar to cells within the facial motor nucleus.

Animals↗
PubMed1992

Stapedius reflexes to electrical stimulation in the rabbit for the assessment of hearing.

The possibility of using electrically induced stapedius reflexes as a means of objective hearing evaluation was investigated in the rabbit as an animal model. The contralateral stapedius reflex to acoustic and electrical stimulation was measured in anesthetized rabbits. For electrical stimulation, the middle ear was opened surgically and stimulation was applied by a monopolar electrode placed at or into the round window. Contraction of the middle ear muscle was monitored by digital sampling and averaging of the impedance changes in the contralateral ear. Acoustically evoked reflexes were recorded within expected limits despite anesthesia. The level of the electrical stimulus was raised until mass reflexes of the neck muscles were observed. A contralateral stapedius reflex to electrical stimulation could not be demonstrated. In our experiment, monopolar electrical stimulation at the round window could not elicit contralateral stapedius reflexes.

Acoustic Stimulation↗
PubMed1980

Stapedius reflexometry. A diagnostic test of myasthenia gravis.

Contraction of the stapedius muscle can be measured by electroacoustic impedance bridge. Muscle weakness and easy fatiguability which are cardinal features of myasthenia gravis (MG) are manifested by increased threshold and early decay of the stapedius reflex. This can be used as an objective test in the diagnosis of myasthenia gravis. Stapedius reflex was measured using Madsen Zo72 electroacoustic impedance bridge in 10 patients with myasthenia gravis and in an equal number of controls. The test was done before and 30 min after intramuscular injection of neostigmin. All patients with myasthenia gravis showed an elevated reflex threshold and 5 patients showed reflex decay. These findings reverted to normal after neostigmin injection. Stapedius reflexometry is a simple objective test for the diagnosis of myasthenia gravis.

Acoustic Impedance Tests↗
PubMed2003

A look at neural integration in the human auditory system through the stapedius muscle reflex.

Ipsilateral and contralateral stapedius muscle contractions were studied as functions of the sound pressure level (SPL) and duration of 2-kHz tone bursts. The study complemented a preceding study in which temporal summation of stapedius muscle contractions produced by pairs of short tone bursts was determined and analyzed. The muscle contractions were determined indirectly by measuring changes in the acoustic impedance they produced at the tympanic membrane. The data for the stapedius muscle contraction as a function of tone-burst duration were derived from another study and analyzed in part with the help of the SPL functions obtained in the present study. According to the experimental results, the stapedius muscle contraction produced by contralateral stimulation follows a compressive power function paralleling both the cochlear output and loudness functions. The ipsilateral contraction follows an expansive power function. Mathematical analysis showed that the muscle tension due to contralateral stimulation increases with tone duration approximately according to the characteristic of a linear integrator having an exponentially decaying memory with a time constant that increases with SPL from approximately 200 to 370 msec. The simple relationship appears to be possible because of mutual cancellation of neural-processing characteristics preceding and following the temporal integration.

Acoustic Stimulation↗
PubMed2002

Re-examination of the role of the human acoustic stapedius reflex.

The "rollover" seen in the word recognition performance scores of patients with Bell's palsy (facial nerve paralysis) has historically been taken as an indicator of the role of the stapedius reflex in the protection from upward spread of masking. Bell's palsy, however, may be a polyneuropathy, so it is not clear that the poor word recognition performance at high levels is necessarily attributable specifically to impaired facial nerve function. The present article reports two new experiments that probe whether an isolated impairment of the stapedius reflex can produce rollover in word recognition performance-intensity functions. In experiment 1, performance-intensity functions for monosyllabic speech materials were obtained from ten normal listeners under two listening conditions: normal and low-frequency augmented to offset the effects of the stapedius reflex on the transmission of low-frequency vibrations to the cochlea. There was no effect of the spectral augmentation on word recognition for stimulus levels up to 107 dB SPL. In experiment 2, six patients who had undergone stapedectomy were tested for rollover using performance-intensity functions. None of the patients showed rollover in their performance-intensity functions, even at stimulus levels in excess of 100 dB HL. These data suggest that if the stapedius reflex has a role in protection from upward spread of masking, then this role is inconsequential for word recognition in quiet.

Adult↗