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Biomedical subjects

R A Ruth

Publications and source records attributed to R A Ruth.

At least 37 records · Page 2Linked to original sources
PubMed1990

Use of the bone conduction ABR Wave I response in determination of cochlear reserve.

Interest in bone-conducted stimulus auditory brainstem response (BC-ABR) testing has centered around evaluation of cochlear integrity in neonates and in patients who are difficult to evaluate audiometrically. The present study was designed to evaluate the Wave I component of the BC-ABR and to determine the utility of this response in assessment of cochlear reserve. The source of Wave I has been shown to be the distal eighth nerve. It was postulated that the presence or absence of this component would provide ear specific information useful for determination of cochlear integrity. In order to test this hypothesis, patients with a documented unilateral hearing loss were studied. Stimulus presentation was via the Radioear B-70 bone vibrator used in conventional audiometric assessment. Evoked potential responses were recorded at four presentation levels. Subjects had either normal hearing bilaterally or normal hearing in one ear and a mild-to-profound sensorineural hearing loss in the opposite ear. Our data indicate that the Wave I response, when measured in this fashion, is ear specific. Ear specificity was shown to be aided by good waveform morphology, as typically observed in younger subjects, and by a relatively large discrepancy in hearing thresholds between the normal and hearing-impaired ears. This technique may be of value in determination of cochlear reserve in patients with problematic masking dilemmas.

Adult↗
PubMed1989

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 Meniere's 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 transtympanic 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.

Adult↗
PubMed1988

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.

Audiometry, Evoked Response↗
PubMed1988

Electrocochleography: methods and clinical applications.

The use of electrocochleography (ECoG) as a tool in the diagnosis, assessment, and monitoring of certain neuro-otologic disorders has attracted renewed attention in the United States. The use of ECoG among otologists and audiologists has increased in recent years, primarily due to the availability of relatively easily applied, noninvasive extratympanic electrodes. Information derived from ECoG recordings has been shown to be helpful in the objective identification and monitoring of Meniere's disease and endolymphatic hydrops. In addition, ECoG may be used to enhance our ability to observe the most peripheral component of the auditory brain stem response (Wave I) for routine clinical assessment or during intraoperative monitoring procedures in which certain structures of the ear are at risk for permanent damage. This article provides an overview of current techniques and clinical applications of ECoG.

Audiometry, Evoked Response↗
PubMed1988

Use of disposable ear canal electrodes in auditory brainstem response testing.

In this study a disposable ear canal electrode and stimulus delivery system (the Enhancer l) was evaluated for its clinical utility and the observed enhancement of the auditory brainstem response Wave I with its use. Data were collected from normally and abnormally hearing subjects, with both the conventional forehead-to-mastoid electrode array and the forehead-to-ear canal electrode arrangement provided by the Enhancer I ear canal electrode setup. For the normally hearing group, simultaneous acquisition of forehead-to-ipsilateral ear canal and forehead-to-ipsilateral mastoid electrode linkages was obtained. For the abnormally hearing subjects, a comparison was made between the Enhancer I system and the conventional forehead-to-mastoid electrode configuration used with a TDH-49 transducer for click delivery. Our findings indicate that Wave I was enhanced substantially when using the disposable ear canal electrode compared with the more conventional forehead-to-mastoid electrode configuration for both normally and abnormally hearing subjects. The Enhancer I electrode evaluated in this study proved to be painless for the subjects and extremely easy to use, requiring no more time in subject preparation than the more common surface recording electrode application.

Adult↗
PubMed1987

Meningitis and facial paresis. Implications for cochlear implantation.

Most postlingually deafened individuals receive auditory sensations with a cochlear implant. We describe a postmeningitic patient with bilateral facial paresis who failed to be stimulated with a multichannel device. In light of the facial dysfunction, primary auditory nerve damage by meningitis is postulated as the cause of implant failure. Preoperation electrical stimulation of the cochlea using an alternating current signal is recommended as a means of assessing cochlear implant candidacy.

Cochlear Implants↗
PubMed1985

Brain-stem auditory-evoked potentials during lidocaine infusion in humans.

Auditory brain-stem responses (ABR) were recorded in six healthy male volunteers during intravenous infusion of lidocaine that achieved systemic blood levels similar to those seen with conduction anesthesia and antiarrhythmic therapy. Following an initial loading dose of lidocaine (1 mg/kg), subjects noted prominent tinnitus, perioral numbness, and drowsiness. All of these symptoms except drowsiness abated during continued infusion as blood concentrations reached equilibrium. All subjects noted that the click stimuli used to elicit ABR varied markedly in intensity and character throughout the lidocaine infusion. Although waves I and III were unaffected by lidocaine, wave V exhibited significant decreases in amplitude and increases in latency. Therefore, the more central components of the auditory system seem to be the prominent site of lidocaine's central nervous system effects.

Acoustic Stimulation↗
PubMed1983

Comparison of auditory brainstem response and behavioral audiometry in infants.

Sixty-three normal hearing infants, ranging from 1 to 12 months of age, were evaluated with Behavioral Observation Audiometry (BOA), Visual Reinforcement Audiometry (VRA), and Auditory Brainstem Response Audiometry (ABR). BOA thresholds decreased with increasing age for infants 0 to 6 months of age, while ABR threshold were essentially constant as a function of subject age. In general, VRA threshold were obtained only for infants over 4 months of age, and were relatively constant for the age range of 4 to 12 months. For neonates, BOA thresholds were significantly higher than ABR thresholds. BOA, VRA, and ABR thresholds tended to converge at a subject age of approximately 6 months, with VRA yielding the lowest and BOA the highest threshold. ABR provided the most consistent threshold for all subjects tested, regardless of age.

Acoustic Impedance Tests↗
PubMed1982

Stapedius reflex in curarized subjects: an index of neuromuscular weakness.

To examine the validity of the acoustical stapedial reflex (AR) as an index of neuromuscular weakness, the AR was measured along with other indices of muscle strength during administration of d-tubocurarine (dTc) to six healthy subjects. AR decreased immediately after each dTc dose and preceded changes in handgrip strength and respiratory muscle strength, but the peak effects of each dose similarly affected AR and other muscle strength. The findings with electrocutaneous stimulation and effects on growth function of the AR indicate that dTc affects primarily stapedius muscle contraction, the efferent portion of the reflex arc, and does not affect afferent or central portions of the reflex. We therefore conclude that the AR is a valid index of the integrity of neuromuscular transmission which promptly reflects early phase weakness. Unlike other measures of muscle strength, AR testing does not depend on subject cooperation, and involves no discomfort. The test therefore provides a useful means of assessing neuromuscular weakness.

Adult↗
PubMed1981

A comparison of stapedial reflex fatigue with repetitive stimulation and single-fiber EMG in myasthenia gravis.

The pattern of stapedial reflex fatigue in response to pulsed acoustic stimulation was measured and compared to results of repetitive nerve stimulation and single-fiber electromyography (EMG) in 89 patients with myasthenia gravis. Studies were also made on 22 patients with other neuromuscular disorders and 40 control subjects with no evidence of neuromuscular impairment. Stapedial reflex fatigue exceeded normal control values in 84% of the patients with myasthenia gravis. Repetitive stimulation and single-fiber EMG measurements were abnormal in 56% and 91% of this same population, respectively. Stapedial reflex abnormalities were most prevalent in patients with mild forms of myasthenia (predominantly ocular or oropharyngeal weakness). Of 22 nonmyasthenic patients with neuromuscular disease tested, 6 had abnormal stapedial reflex fatigue according to our normal values, indicating that this form of testing also detects other diseases of the motor unit. The measurement of stapedial reflex fatigue is painless, is easy to perform, and requires minimal patient cooperation. Due to the relatively high occurrence of abnormal stapedial reflex fatigue in patients with myasthenia gravis, this procedure appears to have considerable potential value in screening and monitoring patients for the presence of defects in neuromuscular transmission.

Acoustic Stimulation↗
PubMed1979

Audiometric evaluation of noise induced hearing loss.

Audiometric evaluation in conjunction with other components of the hearing conservation program serves to minimize the potential hazard of noise related hearing loss. Success of the industrial hearing conservation program rests in large measure with the implementation of competent audiometric testing procedures. Thus, consideration must be given to certain critical factors necessary for measurement of hearing sensitivity, such as the qualifications of the examiner, monitoring schedules, test environment, instrumentation, method of testing, recording of results, interpretation of test findings, and appropriate referral criteria.

Audiometry↗
PubMed1977

Prediction of hearing sensitivity from acoustic reflexes in mentally retarded persons.

The ability of the sensitivity prediction from acoustic reflex (SPAR) technique to estimate hearing loss in mentally retarded subjects was investigated by comparing measured pure-tone thresholds determined through tangible-reinforcement operant-conditioning audiometry with predicted sensitivity from the SPAR procedure. Measurements were completed on a total of 32 retarded individuals having hearing levels ranging from normal to profound hearing loss. With minor exception, absences of the acoustic reflex were always accompanied by clearly abnormal tympanometry findings in the probe ear; therefore, the problem of unexplained absences of the reflex appeared to be minimal. Hearing loss never was present in those subjects for which SPAR predicted normal hearing, and the SPAR procedure never failed to detect an existing sensorineural hearing loss. On the other hand, there was some tendency for hearing loss to be predicted in normal-hearing subjects and for extent of hearing loss to be overestimated in subjects having a hearing loss.

Adolescent↗
PubMedDate not supplied

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 +/- 120 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.

Acoustic Impedance Tests↗
PubMedDate not supplied

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.

Acoustic Stimulation↗