It is commonly thought that as an acoustic neuroma grows it exerts pressure on the acoustic nerve resulting in alterations of the acoustic reflex and brain stem audiometry. This hypothesis has not been confirmed. In this study in an animal model, acute pressure was applied to the nerves of the internal auditory canal, and changes in the acoustic reflex were measured. Our results support the theory that pressure on the acoustic nerve causes an increase in the rate of adaptation and a decrease in the amplitude of the acoustic reflex. The contralateral reflex appears to be the most sensitive indicator of these effects. We feel that this animal model can be useful to investigate the effects of pressure on the acoustic nerve.

Acoustic Impedance Tests↗

PubMedDate not supplied

Hearing loss from acute carbon monoxide intoxication.

A case of fluctuating sensorineural hearing loss from acute carbon monoxide (CO) poisoning with presentation of a U-shaped audiogram is reported. Acute CO intoxication seems to involve vestibular function more frequently than auditory function. Hearing loss is uncommon, but when present, may often display a U-shaped audiometric curve. Decrease in hearing sensitivity probably results from hypoxia to the cochlea, VIII nerve and brain stem nuclei. Fluctuation in hearing sensitivity may be an early manifestation of acute CO exposure, and requires periodic audiometric examination until the hearing has stabilized.

Acute Disease↗

PubMedDate not supplied

Surgical evaluation of candidates for cochlear implants.

The customary presentation of surgical procedures to patients in the United States consists of discussions on alternative treatment methods, risks of the procedure(s) under consideration, and potential benefits for the patient. Because the contents of the normal speech signal have not been defined in a way that permits a surgeon systematically to provide alternative auditory signals to a deaf patient, the burden is placed on the surgeon to make an arbitrary selection of candidates and available devices for cochlear prosthetic implantation. In an attempt to obtain some information regarding the ability of a deaf patient to use electrical signals to detect and understand speech, the Good Samaritan Hospital and Neurological Sciences Institute cochlear implant team has routinely performed tympanotomies using local anesthesia and has positioned temporary electrodes onto the round windows of implant candidates. The purpose of this paper is to review our experience with this procedure and to provide some observations that may be useful in a comprehensive preoperative evaluation for totally deaf patients who are being considered for cochlear implantation.

Cochlear Implants↗

PubMedDate not supplied

Vestibulo-ocular and vestibulospinal function before and after cochlear implant surgery.

Vestibular function in cochlear implant candidates varies from normal to total absence of function. In patients with intact vestibular function preoperatively, invasion of the otic capsule places residual vestibular function at risk. Speech-processing strategies that result in large amplitude electrical transients or strategies that employ high amplitude broad frequency carrier signals have the potential for disrupting vestibular function. Five patients were tested with and without electrical stimulation via cochlear electrodes. Two patients experienced subjective vestibular effects that were quickly resolved. No long-term vestibular effects were noted for the two types of second generation cochlear implants evaluated. Histopathological findings from another patient, who had electrically generated vestibular reflex responses to intramodiolar electrodes, indicated that responses elicited were a function of several variables including electrode location, stimulus intensity, stimulus amplitude, and stimulus frequency. Differential auditory, vestibulocolic, and vestibulospinal reflexes were demonstrated from the same electrode as a function of stimulus amplitude, frequency, and duration.

Aged↗

PubMedDate not supplied

Multiple frequency, multiple component tympanometry: new approaches to an old diagnostic problem.

Tympanometry with low-frequency probe tones provides useful clinical information for patients with disorders of the tympanum, the tympanic membrane, and the Eustachian tube. Low-frequency, single component tympanometry, however, is relatively insensitive to many lesions that affect the ossicular chain. This review focuses upon a collection of four, interrelated acoustic measurement techniques that have been developed for identification and differential diagnosis of those middle ear disorders that do not always yield pathognomonic patterns with conventional tympanometry. Specifically, the initial hypotheses, the methods, normative data and representative clinical findings are summarized for: (1) a multiple frequency magnitude array; (2) a multiple frequency phase-angle array; (3) a three-dimensional array; and (4) a differential sound pressure level and phase plot.

Acoustic Impedance Tests↗