Biomedical subjects

J W Schwegler

Publications and source records attributed to J W Schwegler.

6 recordsLinked to original sources

PubMed1995

The origin of the human auditory brain-stem response wave II.

Auditory brain-stem responses (ABRs) were recorded from human subjects undergoing neurosurgical procedures which exposed the auditory nerve. Scalp recordings indicated that the latency of the negativity between waves I and II (In) and the latency of positive peak II (IIp) were shorter when the nerve was suspended in air than when the nerve was submerged in cerebrospinal fluid or saline, while earlier and later waves remained unaffected. These results could not be attributed to changes in stimulus or recording parameters or conduction velocity. Computational and somatosensory experimental evidence of stationary potentials generated by physical properties of the volume conductor, including changes in conductivity or geometry, are presented to develop a model of wave IIp generation. The results of this study suggest that wave IIp (and probably In) are manifestations of current flux asymmetries across conductivity boundaries created by the temporal bone-cerebrospinal fluid intradural space-brain-stem interfaces. The current flux asymmetries are generated as the propagating auditory nerve action potential crosses the conductivity boundaries. These results also indicate that the physical characteristics of the volume conductor and neural pathways must be considered when interpreting surface recorded evoked potentials.

Action Potentials↗

PubMed1994

New techniques of hearing assessment.

This article reviews current literature in the areas of otoacoustic emissions and auditory brain stem responses (ABRs) and their application to the evaluation of peripheral auditory function in infants and children. The different types of otoacoustic emissions are described along with their incidence, development, clinical applications, and interpretation in the pediatric group. The development of the auditory system, reflected by ABRs, is presented in detail with previously unpublished results from three-channel Lissajous' trajectory studies performed in infants. Clinical application of frequency-specific ABRs, both air and bone conducted, are presented. Finally, a discussion of the need to develop objective estimators of signal quality and threshold detection for otoacoustic emissions and ABRs in infants and children is presented, which includes previously unpublished results evaluating a new technique.

Auditory Perception↗

PubMed1993

Salicylate-induced changes in cat auditory nerve activity.

The purpose of this study was to measure, in the cat, spontaneous auditory nerve (AN) activity before and after injection with sodium salicylate. Ten cats were anesthetized, and the AN and round window (RW) were surgically exposed. Electrodes were applied to allow recording from three channels, including bipolar electrodes and monopolar electrodes located directly on the auditory nerve, in addition to an RW electrode. Spectral averaging of the spontaneous activity was performed before and during salicylate treatment. An increase in spectral activity near 200 Hz was noted in all cats by 3 hours after salicylate injection. This activity was present in bipolar, monopolar, and RW records, and was temporarily diminished or eliminated by injection of lidocaine. No such spectral changes were found in saline-injected control animals. These results show promise of developing a noninvasive, objective, quantitative measure of tinnitus for studies in animals and in man.

Animals↗

PubMed1993

Bipolar cochlear nerve recording technique: a preliminary report.

To preserve hearing during vestibular neurectomy and acoustic neuroma removal, the cochlear nerve must be identified. Present techniques, including monitoring eighth nerve action potentials, help the surgeon identify those maneuvers that increase the risk of nerve injury but do not help in the anatomic identification of the cochlear nerve or the cochlear-vestibular cleavage plane. The purpose of this study was to demonstrate an electrophysiologic method of identifying the cochlear portion of the eighth cranial nerve. A flush-tipped, bipolar electrode recording probe was used to directly record responses to monaural click stimuli from the cochlear nerve but not from surrounding tissue. It was also used to delineate the cochlear-vestibular cleavage plane. Stimulus intensity levels over 25 dB sensation level tended to reduce the accuracy of nerve identification, and lower levels prolonged recording time. This technique and its application to posterior fossa surgery is discussed.

Adolescent↗

PubMed1992

Contralateral effects of cerebello-pontine angle exposure on human auditory brain-stem evoked potentials.

Auditory brain-stem evoked potentials (ABEPs) were recorded during surgical procedures which exposed the cerebello-pontine angle (CPA) in humans. Recordings made with the CPA contralateral to stimulus exposed were compared with those obtained with the skin sutured at the end of surgery. Single-channel as well as 3-channel Lissajous' trajectory (3-CLT) analyses were used to evaluate the effect of the surgical exposure on ABEP. The results suggest that exposure of the CPA contralateral to the stimulated ear did not affect dipole equivalent orientation nor magnitude, but did affect timing of the recorded activity being more pronounced for segments 'd'-'e' (corresponding to waves IV-V) than for 'a'-'b' (waves I-II). The results imply that the effects of disrupting the volume conductor may have been overwhelmed by other effects, such as local temperature changes. These changes, although not associated with clinical sequella, should be accounted for when analyzing subtle quantitative changes involving surgical exposures.

Acoustic Stimulation↗

PubMedDate not supplied

Temporal correspondence of intracranial, cochlear and scalp-recorded human auditory nerve action potentials.

Conventional, vertex-ipsilateral ear records ('A'), as well as 3-channel Lissajous' trajectories (3-CLTs) of auditory brain-stem evoked potentials (ABEPs) were recorded from the scalp simultaneously with tympanic membrane electrocochleograms ('TME') and auditory nerve compound action potentials ('8-AP') recorded intracranially using a wick electrode on the auditory nerve between the internal auditory meatus and the brain-stem. The recordings were made during surgical procedures exposing the auditory nerve. The peak latency recorded from 'TME' corresponded to trajectory amplitude peak 'a' of 3-CLT and to peak 'I' of the 'A' channel ABEP. Peak latency of '8-AP' was slightly longer than the latency of peak 'II' of 'A' when '8-AP' was recorded from the root entry zone and the same or shorter when recorded from the nerve trunk. '8-AP' peak latency was shorter than trajectory amplitude peak 'b' of 3-CLT regardless of where the wick electrode was along the nerve. Peak latencies from all recording sites clustered into two distinct groups--those that included N1 from 'TME,' peak 'I' of the 'A' record and trajectory amplitude peak 'a' of 3-CLT, and those that included the negative peak of '8-AP' and trajectory amplitude peak 'b' of 3-CLT, as well as peak 'II' of the 'A' record, when present. In one case, the latency of peak 'II' and trajectory amplitude peak 'b' was manipulated by changing the conductive properties of the medium surrounding the auditory nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗