Roger A. Ruth

Electrical middle ear muscle reflex: Use in cochlear implant programming

Programming of multichannel cochlear implants (CIs) requires subjective responses to a series of sophisticated psychophysical percepts. It is often difficult for young prelinguistically deaf children to provide adequate responses for device fitting. This is especially true in setting levels of maximum comfortable loudness, whereby failure to indicate growth of loudness may result in elevation of stimulus levels to the threshold of pain. The acoustic or stapedial muscle reflex has been used previously to provide objective confirmation of acoustic stimulation, and there have been attempts to use the reflex in hearing aid fitting. It has also been suggested that electrically elicited middle ear muscle reflexes (eMEMR) may have applicability in confirming and quantifying electrical stimulation through a CI. To assess the relationship between eMEMR characteristics and levels of loudness perception with CIs, determine reliability of the response, and investigate potential use of eMEMR in CI programming, 25 postlinguistically deafened adult CI users were evaluated. Reflexes have also been attempted on 40 children, with responses present in 31 (71%). Comfort levels predicted by eMEMR were highly correlated with those obtained through subjective judgments in the adult subjects. The eMEMR provides an objective, accurate, and rapid method of estimating maximum comfortable loudness levels, which may be useful in the initial programming of young implant recipients.

Round window electromagnetic implantable hearing aid

An implantable hearing aid device including a vibrational element which is mounted to the round window of the cochlea and a transmitter which can be mounted externally of the ear or within the mastoid bone of the skull. The transmitter includes a microphone for picking up sound waves and converting the sound waves into electromagnetic signals which are imparted to the vibrational element fixed to the round window of the cochlea. The placement of the vibrational element on the round window provides significant advantages over conventional implantable hearing aids which transmit vibrational impulses to the oval window of the cochlea through a pathway which interferes with normal hearing. With the implantable hearing device of the present invention, the normal pathway used for receiving acoustically input sound waves is left unobstructed. With such an arrangement, two separate pathways are available for inputting vibrations to the cochlea, which allows constructive and destructive interference patterns to be set up between the acoustic wave vibrations and the magnetically induced vibrations. This allows the amplification of the signal components and canceling of the noise components.

Time course of hearing loss in an animal model of pneumococcal meningitis.

A leading cause of morbidity from bacterial meningitis is an irreversible, usually profound sensorineural hearing loss, with an incidence as high as 30% in some studies. Bacterial meningitis remains the most common cause of acquired postnatal sensorineural deafness. Although several clinical studies have examined the long-term outcome of hearing in meningitis, few studies have examined the time course of hearing loss during the acute course of the disease. We have developed an animal model of meningogenic hearing loss in the rat and have plotted the time course of that hearing loss. Serial auditory brain stem responses (ABRs) were measured in rats inoculated in the cisterna magna (subarachnoid space) with Streptococcus pneumoniae (10 5 to 10 7 colony-forming units). All rats injected developed meningitis as evidenced by increased cerebrospinal fluid (CSF) white cell counts and positive CSF cultures. Serial ABR measurements taken 6, 12, 15, 18, 21, and 24 hours after inoculation demonstrated significant threshold shifts and eventual loss of the ABR waveform as compared with measurements in control rats injected with sterile culture medium. Hearing loss began approximately 12 to 15 hours after inoculation and progressed to complete loss by 24 hours (17 of 18 animals). No correlation was found between the magnitude of hearing loss and CSF white cell count or bacterial titer. Temporal bone histology of rats with meningitis shows a dense inflammatory cell infiltrate throughout the subarachnoid space. Labyrinthine inflammatory cells were confined to the scala tympani.

Comparison of tympanic membrane to promontory electrode recordings of electrocochleographic responses in patients with Menière's disease.

The purpose of the present study was to evaluate ECoG recordings obtained simultaneously from a transtympanic electrode and a tympanic membrane electrode In 26 patients with unilateral Menieres disease. The ECoG recordings were examined quantitatively with regard to absolute amplitude of the summating potential and action potential. Recordings were examined qualitatively in terms of overall waveform quality and ease of component wave Identification. All patients demonstrated a clear response with both electrodes. Although the transtympanlc electrode resulted in the most robust responses in overall amplitude, the tympanic membrane electrode provided recordings equal to or, In most cases, superior to other noninvasive, extratympanic methods currently available. Furthermore, In our patient population, the likelihood of a positive (upward-going) summating potential was less for the tympanic membrane electrode recordings than for the TT electrode recordings. The major advantages of the TM electrode system are Its unique method of stimulus delivery and Its ease of application.

Simultaneous recording of noninvasive ECoG and ABR for use in intraoperative monitoring.

Monitoring auditory evoked potentials, especially surface recorded responses (ABR), during neuro-otologic surgery is being widely used. Recording of the most peripheral components of the ABR with surface electrodes can be difficult, however, in patients with hearing loss. To enhance wave I, a newly designed canal electrode for noninvasive electrocochleography (ECoG) has been used. A small reticulated foam plug is inserted in the ear canal and serves as the electrode. The signal is transduced through a center polyethylene tube. The advantages of this system for ECoG are several: (1) simplified signal presentation, obviating the need for custom ear mold or button transducer; (2) large electrode surface area that lowers impedance and improves signal to noise ratio; and (3) stability of the electrode during manipulations within the surgical field. There are several advantages to supplementing ABR with simultaneous ECoG. First, there is a significant enhancement in wave I amplitude, an important factor when monitoring from hearing impaired patients in an operating room environment. Ability to clearly define wave I permits use of the I-V interwave interval, which can be a more sensitive parameter than wave V latency alone. Secondly, more rapid feedback on changes in cochlear function is available since, compared to surface recordings alone, fewer responses need to be averaged.

Stapedius Muscle Function Tests in the Diagnosis of Neuromuscular Disorders

Muscle weakness and different patterns of fatigability are frequently seen in neuromuscular disorders. The value of a battery of stapedial muscle function tests in the diagnosis and management of these disorders has been evaluated. Each test of stapedial muscle function is described, and case examples of these tests in various neuromuscular disorders including myasthenia gravis and idiopathic facial nerve paralysis are reported.

Multichannel cochlear implant and electrically evoked auditory brainstem responses in a child with labyrinthitis ossificans

Ossification of the cochlea following meningitis presents a surgical challenge. Electrode mapping, especially in the young child, is difficult given the uncertainty of electrode contact with viable neural elements. This paper reviews surgical technique and the use of auditory brainstem responses to map the electrodes.

A Study of Methods Used to Enhance Wave I in the Auditory Brain Stem Response

Auditory brain stem responses (ABR) were recorded in 15 audiometrically and neurologically normal adult subjects. The purpose of the study was to investigate various aspects of stimulus composition (intensity, click rate, and polarity) and response measurement parameters (band-pass filtering and electrode linkage) that might serve to enhance detectability of wave I in the ABR. Amplitude of wave I was significantly enhanced by an increase in intensity, a decrease in click rate, and use of a negative (rarefaction) polarity click. Amplitude of wave I was not significantly influenced by bandwidth of the response filter or by a horizontal (mastoid-to-mastoid) electrode linkage. Use of simultaneous response acquisition from an ipsilateral and contralateral reference electrode array did aid in the detection or visualization of wave I, particularly for lower stimulus intensity levels or faster click rates.

High-frequency sensitization of the acoustic reflex.

High-frequency sensitization of the acoustic reflex was studied in 10 normal-hearing subjects. The procedure involved pairing a subreflex 6000 Hz sensitizing tone with activating frequencies of 500.1000, and 2000 Hz. Both threshold and growth of amplitude of the acoustic reflex were examined. Acoustic reflex threshold was reduced by an average of 10 to 12 dB in the presence of a 6000 Hz sensitizing tone, an amount significantly less than previously reported in similar investigations. Variations in the method used to adjust the presentation level of the high-frequency sensitizing tone probably account for these differences. Growth of acoustic reflex amplitude was also found to be influenced by sensitizing stimulation, with the greatest effect occurring near acoustic reflex threshold.

Effects of ear canal pressure on threshold and growth of the acoustic reflex.

Acoustic reflex (AR) threshold and growth were measured in one ear for each of 20 normal-hearing individuals as pressure in the ear canal was varied between k120 mm of H2O. These same parameters were studied in 10 of the subjects after disruption of the probe seal. Activating stimuli for AR threshold measures were 500, 1000, 2000, and 4000 Hz tones and broadband noise. The AR growth function was generated by a 500 Hz tone. As ear canal pressure was increased or decreased relative to the point of maximal compliance, systematic increases in AR threshold were observed for all activating stimuli. These mean pressure effects were relatively small (4 to 8 dB) and were essentially independent of stimulus composition. The ear canal pressure variations had no effect on the relative difference between tone and broadband noise AR thresholds. Absence of an airtight seal had a negligible effect on AR threshold. Growth of the AR was significantly altered by application of a relatively mild positive or negative canal pressure. Absence of a probe seal which had no effect on AR threshold was found to significantly reduce magnitude of the AR. These findings indicate that caution should be exercised during the measurement of AR growth to ensure both proper maintenance of desired canal pressure and canal-probe coupling.