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Biomedical subjects

R A Ruth

Publications and source records attributed to R A Ruth.

At least 19 recordsLinked to original sources
PubMed1999

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. The cochlear aqueduct is the proposed route of infection from the meninges to the labyrinth (scala tympani). Endolymphatic hydrops was also noted throughout the cochlea. These experiments both establish a reproducible animal model of meningogenic hearing loss and support the hypothesis that this hearing loss is progressive rather than abrupt in onset and is related to the duration of untreated infection. CSF inflammatory cells appear to enter the cochlea through the cochlear aqueduct. This reliable animal model will enable future studies directed toward further understanding the pathogenesis and pathophysiology of this hearing loss.

Acute Disease↗
PubMed1997

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.

Acoustic Stimulation↗
PubMed1997

Recovery of useful hearing after posterior fossa surgery: the role of otoacoustic emissions: case report.

OBJECTIVE AND IMPORTANCE: Hearing preservation has become an important issue in surgical procedures involving the cerebellopontine angle (CPA). Although several prognostic factors for hearing preservation in patients with "useful" preoperative hearing have been described, it is difficult to predict which patients have the potential for hearing preservation or recovery. Otoacoustic emission measurement is a new technique that allows recording of sounds produced by the cochlear outer hair cells as a normal byproduct of the receptor process and can be used to assess cochlear involvement in patients with hearing loss. CLINICAL PRESENTATION: We present the case of a 53-year-old patient with a recurrent arachnoid cyst of the CPA. She had noticed progressive severe hearing loss ipsilateral to the cyst that was confirmed by preoperative audiogram. TECHNIQUE: Otoacoustic emissions were obtained and were within normal limits on the involved side, suggesting that the cochlear outer hair cells were still intact and that the patient had the potential for hearing recovery. The CPA was decompressed by marsupialization of the cyst. Postoperative audiogram demonstrated a dramatic recovery of hearing to a normal level. CONCLUSION: Otoacoustic emissions clearly provide valuable information about the potential for hearing preservation/recovery after CPA surgery and have significant implications for the current neurosurgical management of these lesions.

Arachnoid Cysts↗
PubMed1997

Evaluation of sensorineural hearing loss.

Advances in both the medical/surgical and nonmedical treatment of sensorineural hearing loss have drastically increased the need for more precise evaluation of inner ear disorders and their differentiation from retrocochlear sites of lesion. Consider, for example, the tremendous strides made in the application of cochlear implants to patients with severe to profound hearing loss who are unable to derive sufficient or adequate benefit from hearing aids. Equally impressive are the improvements made recently in the area of assistive listening technology. The newest hearing aid devices are smaller in addition to being capable of greater fidelity, and contain digital circuitry making them more flexible and responsive to a patient's auditory needs. A challenge for hearing healthcare professionals today is to successfully address the needs of the millions of hearing impaired individuals in the United States who are currently not adequately served, either medically or nonmedically, for their hearing problem.

Acoustic Impedance Tests↗
PubMed1996

Derived-band auditory brain-stem response estimates of traveling wave velocity in humans: II. Subjects with noise-induced hearing loss and Meniére's disease.

Estimates of cochlear traveling wave velocity (TWV) were computed from derived-band auditory brain-stem response (ABR) latencies in subjects with noise-induced hearing loss (NIHL) or Meniére's disease (MD). ABR wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's (1961) place-frequency function for humans. An exponential function of the form I = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the reciprocal of the derivative of the latency function with respect to distance [v = 1/(BCeCd)]. Expected values for subjects' TWV functions were compared to normative data from Donaldson and Ruth (1993) at five cochlear loci. NIHL subjects' TWV estimates fell within normal limits at all cochlear loci, and no relation between severity of high-frequency hearing loss and TWV could be discerned. MD subjects with good low-frequency hearing sensitivity generally yielded normal TWV estimates, whereas MD subjects with low-frequency hearing loss yielded either normal or elevated TWVs. MD subjects' data generally support the hypothesis that endolymphatic hydrops results in increased TWV or, alternatively, a basalward shift in the peak of the traveling wave, in cochleas with presumed normal basilar membrane elasticity.

Adult↗
PubMed1996

Effects of age, signal level, and signal rate on the auditory middle latency response.

The effects of age, signal rate, and signal level on the maturing auditory middle latency response (AMLR) were evaluated in 50 normal-hearing subjects ranging in age from 2 days to 35 years. Ipsilateral and contralateral AMLR waveforms were recorded in newborns (n = 10), children (n = 10), preteens (n = 10), teens (n = 10), and adults (n = 10). The AMLR Pa waveform was obtained in 70 to 100 percent of all subjects. The variables of age, signal level, and site of recording significantly affected Pa peak amplitude and absolute latency. However, stimulus rate did not significantly affect the response.

Adolescent↗
PubMed1995

The round window electromagnetic implantable hearing aid approach.

The round window electromagnetic implantable hearing aid (RWEM) approach uses a magnet surgically implanted onto the round window membrane of the cochlea to impart vibrational energy to the inner ear when driven by a nearby electromagnetic coil. In this article, experimental methods used in animal ABR studies are described for this approach and evidence for the viability of this technique is demonstrated by the similarity of ABR waveforms obtained using RWEM and acoustically-evoked stimuli.

Animals↗
PubMed1995

Chronic otitis media and sensorineural hearing loss: is there a clinically significant relation?

Previous investigations into the possible relation between chronic otitis media (COM) and sensorineural hearing loss (SNHL) have resulted in differing results and conclusions. A retrospective study was conducted to examine the relation between COM and SNHL, using strict selection criteria for cases so as to eliminate co-variables. In addition, various COM parameters were studied to determine if a correlation with the severity of the SNHL existed. At the University of Virginia, charts of all patients undergoing chronic ear surgery from September 1983 to March 1993 were reviewed. Sixty-nine patients met the following criteria: unilateral COM and no history of head trauma, meningitis, post-traumatic tympanic membrane perforation, labyrinthine fistula, or coexisting otologic condition of either ear. From these charts, audiograms were then analyzed for evidence of SNHL, defined as the difference in preoperative bone conduction thresholds between diseased and control (normal contralateral) ears. Mean bone conduction differences were small: -0.5 dB at 500 Hz, 0.9 dB at 1,000 Hz, 4.4 dB at 2,000 Hz, and 3.6 dB at 4,000 Hz. There were nonsignificant bone conduction threshold differences that trended toward greater SNHL with diseased mucosa and cholesteatoma at 2,000 and 4,000 Hz. There was no consistent correlation between severity of SNHL and presence of otorrhea, degree of ossicular erosion, or duration of disease. The authors conclude that COM may cause SNHL, but in the vast majority of patients this loss is not clinically significant.

Adolescent↗
PubMed1995

Promontory stimulation following translabyrinthine excision of acoustic neuroma with preservation of the cochlear nerve.

Promontory stimulation is an accurate method of assessing the functional integrity of the cochlear nerve by electrical stimulation. This technique is widely used in screening prospective candidates for cochlear implants. Recent reports have confirmed the integrity of cochlear nerve responses to electrical stimulation following labyrinthectomy and unsuccessful hearing preservation attempt by the retrosigmoid approach. In this report, the authors present three patients with intracanalicular acoustic neuromas excised through a translabyrinthine approach in which the cochlear nerve was preserved. In each patient, promontory stimulation elicited repeatable behavioral responses. These responses were consistent over a 9-month period of observation.

Auditory Threshold↗
PubMed1994

Electric auditory brain-stem responses in nucleus multichannel cochlear implant users.

OBJECTIVE: The electrically elicited auditory brain-stem response (EABR) has been proposed as a tool for use in cochlear implant device setting. To systematically examine the relationships of psychophysical perceptions and EABRs, implant users underwent a series of comparative measurements. The characteristics of the EABR were assessed for their predictive value in determining the subjective measures needed to set the implant device. DESIGN: Characteristics of the EABR and various perceptual measures in a group of cochlear implant users served as compared variables in a correlational study. SETTING: The study was carried out in the audiology clinic of a university hospital. The audiology clinic maintained a fully equipped evoked potential laboratory, and was part of an otolaryngology department that supported a cochlear implant program. SUBJECTS: The subjects consisted of 10 consecutively selected postlinguistically deafened adult multichannel cochlear implant users. MAIN OUTCOME MEASURES: Morphology, latency, and amplitude measures of the EABR recordings were compared with behavioral perceptions of threshold, most comfortable and uncomfortable loudness levels. RESULTS: Perceptual measures of threshold were found to be significantly related to the threshold of the EABR across subjects and electrode position. Simple linear regression analysis was used to measure the degree of the relationship. An r value of 0.89 attests to a significant relationship. The EABR wave latencies and amplitudes were found to have no significant relationship to any of the perceptual measures examined. CONCLUSIONS: Although EABR cannot replace behavioral measurements for device setting, in difficult cases EABR thresholds may be used as a starting point from which to estimate settings for the device.

Adult↗
PubMed1993

Derived band auditory brain-stem response estimates of traveling wave velocity in humans. I: Normal-hearing subjects.

Estimates of cochlear traveling wave velocity (TWV) were computed from derived band auditory brain-stem response (ABR) latencies in 24 normal-hearing subjects. Wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's [J. Acoust. Soc. Am. 33, 1344-1356 (1961)] place-frequency function for humans. Two procedures were used to estimate TWV. In one procedure, an exponential function of the form l = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the inverse derivative of the latency function with respect to time. In the second procedure, average TWVs between adjacent derived bands were computed directly from subjects' ipsilateral wave V latencies. Values obtained with the two procedures were similar for middle and apical cochlear loci; however, TWV functions produced lower estimates of TWV at the most basal of five cochlear sites. TWVs based on ipsilateral wave V latencies ranged from 5.6 to 78.0 m/s (geometric mean 11.2 m/s) in the cochlear base (7.53 mm from the stapes) and from 1.2 to 3.4 m/s (geometric mean 1.96 m/s) in the cochlear apex (24.1 mm from the stapes). Intersubject variability was large at the most basal point of TWV estimation but was progressively smaller at more apical sites. Mean TWV estimates were lower than those reported by several previous investigators. The range of values obtained in various studies may stem from differences in the procedures used to estimate TWV.

Acoustic Stimulation↗
PubMed1992

Promontory electrical stimulation in postoperative acoustic tumor patients.

Complete deafness can follow acoustic tumor surgery and results from labyrinthine injury, auditory nerve trauma, and/or vascular compromise. A central auditory prosthesis is one potential rehabilitative strategy in such patients. Anatomical studies suggest that some spiral ganglion cells may survive after vascular occlusion, and we have demonstrated responses to electrical stimulation in patients after labyrinthectomy. It was thus hypothesized that patients deafened after a hearing conservation attempt, but maintaining an intact auditory nerve, could utilize an intracochlear implant. To investigate this possibility, promontory electrical stimulation was performed on three patients who had tumors less than 2 cm and who had serviceable preoperative hearing, but no responses postoperatively. Behavioral responses and electrically evoked auditory brainstem and middle latency responses were obtained from two patients, one of whom was 6 years postsurgery. These data indicate that a cochlear implant may be possible after acoustic tumor surgery.

Adult↗
PubMed1991

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 4-year-old child deafened by meningitis at age 20 months had bilateral cochlear ossification by computed tomography. At surgery, a canal wall-down mastoidectomy and closure of the ear canal were performed. A trough around the modiolus was drilled, and the electrode array was placed in it. Post-operatively, the patient gave aversive or no responses to electrode stimulation. To assess electrode function, auditory brainstem responses to individual electrode activation were obtained under general anesthesia. Functioning electrodes could thus be selected for mapping. The patient now responds well to sound.

Child, Preschool↗
PubMed1991

Auditory evoked potentials.

Auditory evoked potentials (AEPs) have become an integral part of the current otologic/audiologic test battery. With these techniques, synchronous neural activity can be examined from the peripheral end organ of hearing up to the cortical structures responsible for audition. The clinical applications of AEPs range from their use as an indicator of auditory sensitivity in patients who either cannot or will not respond in a conventional behavioral test situation to their use in the diagnosis and monitoring of various otologic and neurologic disorders. As such, measurement of AEPs allows the clinician a unique glimpse of the auditory system.

Audiometry, Evoked Response↗
PubMed1990

Promontory electrical stimulation in labyrinthectomized ears.

Bilateral deafness can occur in patients with Menière's disease who have undergone a labyrinthectomy in one ear. To investigate the feasibility of a cochlear implant in the labyrinthectomized ear, promontory electrical testing by transtympanic needle was performed in six patients who had undergone a unilateral transmastoid labyrinthectomy 6 weeks to 5 years previously. All patients had a behavioral response to the stimulus, and each described a different pitch percept with the four frequencies used. Five of the patients demonstrated an electrically evoked middle latency response. These data are comparable with behavioral and electrophysiologic responses from ears deafened by other causes and now successfully implanted. The results suggest that peripheral neural elements and central auditory pathways remain at least partially functional many years after a labyrinthectomy. Thus, a labyrinthectomy should not be withheld as a surgical option if otherwise indicated.

Adult↗
PubMed1990

Trends in rehabilitation after cochlear implantation.

Although postimplant rehabilitation is generally considered to be an important aspect of a cochlear implant program, the literature reports widely varying practices in the implementation of such programs. The National Institutes of Health consensus statement on cochlear implantation (May 1988), while recognizing that aural rehabilitation facilitates maximal use of the implant, offers no specific guidelines or recommendations. A questionnaire survey was made of over 200 otolaryngologists to determine current practices in a variety of aspects of their cochlear implant programs. Results were obtained from a total of more than 1400 patients, including adults, adolescents, and children. Rehabilitation is an integral part of the cochlear implant program in the vast majority of active programs surveyed. General aspects of cochlear implant programs, as well as those of rehabilitation programs in particular, are discussed.

Adolescent↗
PubMed1990

Trends in electrocochleography.

Currently there appears to be a resurgence of interest in the measurement of the peripheral-most electrical potentials of the auditory system. These measurements, known collectively as electrocochleography, may be used (1) to assess and monitor patients with Meniere's disease or endolymphatic hydrops, (2) to enhance wave I of the surface recorded ABR, and (3) as a means of monitoring the peripheral auditory structures during surgery. Various recording techniques and electrode types are reviewed and suggestions are provided for response interpretation in several patient populations.

Acoustic Stimulation↗