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Biomedical subjects

N T Shepard

Publications and source records attributed to N T Shepard.

17 recordsLinked to original sources
PubMed1992

Effect of hearing loss of cochlear origin on the auditory brain stem response.

Auditory brain stem response (ABR) testing is widely used to detect lesions of the auditory neural pathways. The ABR waves depend not only on the integrity of the neural pathways, but also on the condition of the cochlea. To properly interpret the ABR response, it is necessary to understand the effects of cochlear hearing loss on the ABR wave latencies. We studied two populations of subjects with cochlear hearing loss: one with varying degrees of high-frequency hearing loss and the other with varying degrees of flat configuration hearing loss. The degree of cochlear hearing loss was quantified in several different ways and subjected to one linear and three nonlinear regression analyses to test for accuracy in predicting ABR wave latencies and interpeak intervals (waves I, III, V, I-V, I-III, and III-V) for three click intensities. Hearing loss levels from 2 to 6 kHz, in particular 4 kHz, were superior to other audiometric test frequencies as predictors of ABR wave latencies for the group with the high-frequency losses. No particular characterization was found to be superior for the flat hearing loss configurations. From these results, modeled predictions of wave latencies as a function of degree and configuration of hearing loss were made. The modeled predictions are then used to suggest guidelines for interpretations of ABR results where hearing impaired patients are involved.

Adult↗
PubMed1992

Rehabilitation therapy for patients with disequilibrium and balance disorders.

Vestibular rehabilitation is based on the use of adaptive and compensatory mechanisms already existing in the human brain. Research using animals provides a great deal of information on the neural mechanisms responsible for these functions and suggests strategies that should be helpful in rehabilitation of patients with disequilibrium and balance disorders. Research in animals and human beings suggests that rehabilitation should be specifically designed, depending on the patients' deficits. It also suggests that to be effective it needs to be started soon after impairment and that vestibulosuppressive medication may reduce recovery. Studies are now underway to evaluate the effectiveness of vestibular rehabilitation on several groups of patients and to answer some fundamental questions about the mechanisms and the effectiveness of these treatment methods. Current information suggests that vestibular rehabilitation is an effective method of therapy for many patients with disequilibrium and balance disorders and that for some patients it is the best therapy available.

Animals↗
PubMed1992

Platform pressure test in identification of perilymphatic fistula.

In an effort to better define the effectiveness of the use of posturography in the preoperative diagnosis of perilymphatic fistula (PLF), a prospective investigation of the use of platform pressure posturography was performed. Six different protocols used atmospheric pressure change applied to the external auditory canal. Postural sway, monitored as the output parameter, was evaluated relative to its sensitivity and specificity in five different patient groups. Two independent surgeon groups were used to establish the final diagnosis of perilymphatic fistula. Results within a given surgeon group demonstrate varying sensitivity from 53 to 100 percent and specificity from 56 to 89 percent. Results across the two surgeon groups show nonstatistically significant changes in sensitivity and specificity, yet statistically significant differences exist between the surgeon groups for rate of surgery performed given a suspected patient group, and for rate of positive identification of PLF during surgery. We conclude that although the platform pressure test (PPT) shows promise as a test to raise preoperative suspicion for PLF, actual test performance figures cannot be calculated until a more definitive, objective, test is available to confirm the final diagnosis. The variability of selection criteria and diagnosis by surgical observation is too great to draw clear conclusions relative to test performance. Additionally, the use of vestibular rehabilitation techniques is suggested as a presurgical management strategy for a selected group of suspect patients.

Atmospheric Pressure↗
PubMed1991

Bilateral vestibular paresis: diagnosis and treatment.

Patients with bilateral peripheral vestibular dysfunction present a substantial diagnostic and therapeutic challenge to the otologist. Caloric irrigations that suggest bilateral weakness may mislead the clinician when considerable peripheral function remains. Rotary chair testing at several frequencies is helpful in confirming the degree of residual function and may identify patients who have a better prognosis in rehabilitation. Forty-nine patients with bilateral vestibular paresis were evaluated. The diagnosis was based on caloric responses of less than 5 degrees/sec in both ears and reduced gain on rotary chair trials. Oscillopsia occurred in the minority of patients (35%) and was rare unless severe paresis was present. Episodic vertigo occurred in 43%. All patients had abnormal posturography results, with vestibular dysfunction and severe dysfunction patterns predominating. The treatment outcomes of 22 patients who underwent vestibular rehabilitation are discussed. Prevention of bilateral vestibular paresis remains a high priority.

Adult↗
PubMed1991

Physical therapy program for vestibular rehabilitation.

Dizziness and balance disorders are among the most frustrating problems for many physicians to treat. Traditional interventions such as medication or surgical procedures offer limited improvement for many patients. Although generic habituation exercises have existed for years, the merits of vestibular rehabilitation are only beginning to be recognized. Current retrospective studies indicate that 85 percent of patients with chronic vestibular dysfunction gain at least partial relief of their symptoms after undergoing vestibular rehabilitation, with approximately 30 percent of patients being completely cured. This modality provides a valuable and rational complement to current established methods of treating the patient with dizziness. Many physicians and physical therapists may be unfamiliar with these new techniques and require clarification of the actual therapeutic approaches in use. This article describes the current evaluation and treatment approach utilized in the vestibular rehabilitation program at the University of Michigan Medical Center.

Adult↗
PubMed1990

Habituation therapy for chronic vestibular dysfunction: preliminary results.

Chronic vestibular dysfunction is often a frustrating problem for both patient and physician. A program of customized vestibular habituation therapy is introduced and its efficacy in a group of 65 patients is evaluated. Preliminary findings suggest that 59% of patients will have a dramatic improvement, after which their vestibular symptoms no longer cause any restriction in their lifestyles. An additional 23% of patients note considerable improvement, but have persistent symptoms that continue to restrict their activities. Vestibular habituation therapy is a rational, multidisciplinary approach to the treatment of chronic vestibular dysfunction that is a significant alternative to traditional pharmacologic management. Failure of vestibular compensation after involvement in a disciplined program of habituation therapy constitutes a much stronger indication for vestibular surgery in patients with unilateral peripheral lesions.

Adult↗
PubMed1990

Habituation and balance retraining therapy. A retrospective review.

The results presented indicate that rehabilitation therapy for balance disorders can be of significant benefit for a wide range of patients as a singular management tool or in combination with medical or surgical techniques. Although more investigative work is needed to adequately address the issue of customized versus generic programs, the present data begin to suggest some possible advantages to an approach individualized to each patient.

Adult↗
PubMed1989

The clinical use of dynamic posturography in the elderly.

We provide an overview of the clinical uses of dynamic posturography. Although the equipment described to perform this testing is expensive, the concepts, especially those for sensory organization, can be applied for +20.00. To apply the six sensory organization conditions, one merely needs some way to disrupt proprioceptive information by maintaining ankle angle and providing for visual conflict stimuli. We found that proprioceptive information can be disrupted easily by asking the patient to stand on a thick (4-inch) dense piece of foam rubber like that used in cushions for furniture. Visual stabilization conflict can be provided by having the patient wear a 19- to 20-inch Japanese lantern with a head-mounting system in the center so that the patient's movements do not reflect themselves in relative movements to the visual environment. With use of these two simple tools, the six sensory organization tests can be approximated in a clinical situation in a short time and can provide some relative information about a patient's postural control capabilities. With minor additional work, a quantitative measure of output that gives indications of the amount of anterior-posterior sway also can be provided. For elderly patients with a variety of problems ranging from general unsteadiness to frank vertigo, the risk of falling can be devastating, and it is important to provide a thorough investigation of the total balance system. The systematic investigation, qualitatively or quantitatively, of integration of sensory input and motor outputs provides a dimension that typically has been lacking in the routine "dizzy patient workup" for all ages but especially for elderly patients. Therefore, the application of the postural maintenance theory with the above-described procedures or variations in these procedures appears to have a great deal of clinical relevance in the evaluation of patients with gait and balance disorders. These types of evaluations represent an adjunct or addition to the evaluation of the vestibular system and the vestibulo-ocular reflexes and by no means should be considered a substitute for that traditional evaluation. It is the combination of information that can provide the clinician with a more global picture of the entire balance system and its functional capabilities.

Adult↗
PubMed1988

Neurophysiologic intraoperative monitoring: I. Auditory function.

As a result of advances in neuro-otology and neurosurgery, surgeons often operate in the vicinity of sensitive and delicate neural structures in an attempt to restore their function, remove tumor, or alleviate distressing and disabling symptoms. Concerns about preservation of neural function during these surgical procedures have provided the need and motivation for the development and adaptation of neurophysiologic techniques designed to provide feedback about impending trauma. The most common functions that are at risk in neuro-otologic surgery are related to the auditory nerve and centers and the facial nerve. This paper deals with principles and practices of intraoperative monitoring of auditory function. The following applications are illustrated and discussed: 1) intraoperative monitoring of auditory function during posterior fossa tumor resection, 2) auditory brain stem response and VIIIth nerve monitoring during retrolabyrinthine vestibular nerve section, 3) monitoring of auditory function during microvascular decompression of cranial nerve VII, VIII, or IX, and 4) special applications related to cochlear implant surgery.

Brain Stem↗
PubMed1986

Compound action potential thresholds and tuning curves in the alligator lizard.

Compound action potential (AP) thresholds and tuning curves were measured in the alligator lizard using techniques similar to those used with the mammal. For tone burst stimuli, the AP was a major component of the gross response, the electrical response to sound recorded by a wire electrode near the cochlea. The AP thresholds agreed well with threshold estimates based on single-fiber data. A forward masking paradigm produced AP tuning curves which resemble single-fiber tuning curves. A simultaneous masking paradigm produced curves which match the boundaries of single-fiber two-tone rate suppression. The AP thresholds and tuning curves provide useful information about the peripheral physiology of the ear of the alligator lizard.

Acoustic Stimulation↗
PubMed1981

Characteristics of hearing-impaired children in the public schools: part I--demographic data.

Survey questionnaires eliciting incidence information about degree and type of hearing loss, educational placement, use of amplification, and other demographic data were completed by audiologists in 13 of the 15 Area Education Agencies in Iowa in an attempt to describe the characteristics of hearing-impaired children in public-school settings. The information revealed patterns of hearing loss related to age and sex, use of hearing aids, and classroom placement that may be useful in planning support services for this population.

Age Factors↗
PubMedDate not supplied

Newborn hearing screening using the Linco-Bennett auditory response cradle: a pilot study.

A modified mass newborn hearing screening program was piloted using a combination of a simplified high-risk register and a newly developed automated screening device, the Auditory Response Cradle. The program was designed to handle a total of 4000 babies per year. All children participating received both the high-risk register review and the automated screening test. The Auditory Response Cradle used a binaurally presented high-pass noise through a closed acoustic system at an intrameatally monitored level of 85 dB SPL (re 20 mu Pa) +/- 3 dB. Three independent motor and two respiratory response channels were monitored by the controlling microprocessor unit during a 5-sec prestimulus interval, and a 5-sec stimulus interval. Typical time for a complete test ranged from 5 to 10 min. The results of the present work indicate a false positive rate at or below 1.5%. The described program appears to be a cost-effective means of providing a mass neonatal hearing screening.

False Positive Reactions↗
PubMedDate not supplied

Clinical performance of audiological and related diagnostic tests.

This paper is the second in a series of three concerning audiological tests and test batteries designed to differentiate cochlear from retrocochlear site-of-lesion. The first paper discussed the application of clinical decision analysis to diagnostic tests, particularly audiological tests. This paper uses the techniques of clinical decision analysis to evaluate the clinical performance of audiological, vestibular, and radiological tests based on data derived from the last 15 years of the clinical literature. Using calculated measures of test performance, we compared and divided the test into four groups.

Audiometry↗
PubMedDate not supplied

Formulating and evaluating audiological test protocols.

This paper is the last in a series about audiological tests and test protocols (test batteries) designed to differentiate cochlear from retrocochlear site-of-lesion. While the first two papers dealt with individual tests, this paper is concerned with the audiological test protocol. A conceptual framework is presented for formulating a test protocol, and techniques are discussed for evaluating protocol performance. Using clinical data, we evaluate the performance of the traditional audiological test battery and make recommendations for the clinical use of audiological test protocols.

Audiometry, Pure-Tone↗
PubMedDate not supplied

Auditory-nerve potentials from ear canals of patients with otologic problems.

Summary--The feasibility of making rountine measurements of human auditory-nerve potentials in an office environment is demonstrated. Using a portable device for stimulus generating and response recording, auditory-nerve potentials are recorded from subjects with normal and abnormal hearing by means of an electrode placed on the skin of the ear canal. The results can be compared with those of others obtained under laboratory conditions. Preliminary results indicate that in many instances, the nature of the hearing deficit is related to the latency and size of the click-evoked auditory-nerve potentials. The precise relationships between nerve responses and specific disease conditions are still difficult to formulate.

Action Potentials↗
PubMedDate not supplied

Compound action-potential tuning curves in normal and acoustically traumatized cats.

Compound action-potential tuning curves, using a forward-masking paradigm, were developed on both a control group and a group of acoustically traumatized cats. Differences observed between the two populations included a decrease in the sharpness of the tip, in the sensitivity of the tip, and/or in the sensitivity of the tail region. Phase-contrast light microscopy was performed on all exposed ears using a celloidin-embedding technique with horizontal sectioning. Whenever an abnormality in an action-potential tuning curve was seen, histological evidence of damage to the organ of Corti in an appropriate region corresponding to the signal frequency was observed. However, several cases of damage to the cochlea were observed with normal tuning curves. Whenever the tip region of the tuning curve was elevated, evidence of damage to all three rows of outer hair cells and to the inner hair cells was seen.

Animals↗