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Biomedical subjects

J D Durrant

Publications and source records attributed to J D Durrant.

At least 55 records · Page 3Linked to original sources
PubMed1980

Computer identification of waves in the auditory brain stem evoked potentials.

The high reliability with which the waves I through V can be identified in auditory brain stem potential (BAEP) recordings suggests the possibility of using the computer to identify the peaks. This paper examines the application of a smoothing algorithm in which detection of zero crossings in the derivative array of the averaged potentials is used to identify waves I--V in clinical BAEP recordings. A comparison of computer wave identification with human evaluation is presented. The results suggest that computer evaluation cannot entirely replace 'manual' evaluation of the waves, but can expedite analysis and alert the clinician to potentially abnormal responses.

Acoustic Stimulation↗
PubMed1979

Comments on the effects of overstimulation on microphonic sensitivity.

Utilizing the differential recording technique, microphonic isopotential measurements were carried out before and after overstimulation. Recordings were made in the first and third turns of guinea pig cochleas. The exposure stimuli were pure tones of frequencies near the best frequency of the recording site. The results were suggestive of differences in the effects of overstimulation in different turns of the cochlea, at least as they are manifested electrophysiologically.

Acoustic Stimulation↗
PubMed1972

Cochlear inner and outer hair cells: functional differences.

The cochlear microphonic response was measured with differential electrodes from the first and third cochlear turns of normal guinea pigs and those treated with the ototoxic drug kanamycin. Histological controls showed that the outer hair cells in treated animals were missing over the basal half of the damaged cochleas, while the inner hair cells were intact. Measurements are consistent with the hypothesis that the potentials produced by inner hair cells are proportional to the velocity of the basilar membrane, whereas potentials generated by outer hair cells (which dominate the response of normal cochleas) are proportional displacement of the basilar membrane.

Animals↗
PubMedDate not supplied

Long-latency rotational evoked potentials in subjects with and without bilateral vestibular loss.

Human subjects with and without profound bilateral vestibular loss were evaluated using repetitive rotational stimulation about an earth-vertical axis and signal averaging of vertex-recorded potentials. The stimulus events to which averaging was synchronized were acceleration/deceleration pulses produced by abrupt reversals in direction of angular velocity. In control subjects the long-latency rotational evoked potentials elicited via this paradigm were robust and reproducible. The responses of subjects with vestibular loss did not differ remarkably from those of the control subjects. We conclude that the long-latency rotational evoked potential elicited using a conventional rotary chair is not primarily of vestibular origin.

Adolescent↗
PubMedDate not supplied

Changes in BAEP under hypoglycemia: temperature-related?

Latencies of the brain-stem auditory evoked potentials were observed to increase in subjects whose plasma glucose levels were reduced. These changes appeared to be attributable to reduced body temperature, rather than direct effects of hypoglycemia on the auditory nerve or the brain-stem. The results suggest the need for caution in interpreting evoked potential measurements under hypoglycemia.

Acoustic Stimulation↗
PubMedDate not supplied

Eighth nerve signs in a case of multiple sclerosis.

We evaluated a 25-year-old woman with multiple sclerosis who presented with the acute onset of a profound unilateral high-frequency, sensorineural hearing loss that resolved clinically within 10 days. Click-elicited brain stem-evoked responses were abnormal at the time of presentation and demonstrated only limited recovery over a follow-up period of 11 months. Magnetic resonance imaging disclosed a lesion in the eighth nerve root-entry zone and the cochlear nucleus. Our findings in this case support the hypothesis of eighth nerve root-entry zone involvement in sudden hearing loss in multiple sclerosis and reinforce the notion that click-elicited brain stem-evoked responses are useful primarily to evaluate the high-frequency regions of the auditory system.

Adult↗
PubMedDate not supplied

Surface dependence: a balance control strategy in panic disorder with agoraphobia.

OBJECTIVE: Previous studies have reported vestibular dysfunction and impaired balance in patients with agoraphobia. Vestibular dysfunction may lead to an information processing strategy focusing on spatial stimuli from two nonvestibular sensory channels, vision and proprioception. This nonvestibular balance control strategy may in turn lead to discomfort in situations involving inadequate visual or proprioceptive spatial cues (space and motion discomfort). The objective of this study was to examine sensory integration of spatial information in agoraphobia. Because of previous findings that space and motion discomfort and vestibular dysfunction are common in agoraphobia, we hypothesized that agoraphobics would use a nonvestibular balance control strategy. METHOD: Using computerized dynamic posturography, we examined balance performance in patients with panic disorder with agoraphobia, uncomplicated panic disorder, nonpanic anxiety disorders, and depression without anxiety, as well as healthy subjects for comparison. The posturography procedure included six sensory conditions in which visual and proprioceptive balance information was manipulated experimentally by permutations of sway-referencing the support surface or the visual surround or by having patients close their eyes. RESULTS: The agoraphobics had impaired balance when proprioceptive balance information was minimized by sway-referencing the support surface (p < 0.02). This pattern, called surface dependence, tended to be more pronounced in agoraphobics who reported space and motion discomfort, including fear of heights or boats. CONCLUSION: Agoraphobics rely on proprioceptive cues for maintenance of upright balance. This strategy may lead to intolerance of situations characterized by unstable support.

Adult↗
PubMedDate not supplied

Remote extracochlear versus intracochlear recordings in the guinea pig.

A comparison was made of the whole-nerve action potential recorded from a wire electrode placed on the tympanic membrane (TM) (remote extracochlear recording) and than recorded from intracochlear electrodes in the first and third turn scala tympani of the guinea pig. Cochlear microphonics and summating potentials were also studied. The expected decreased sensitivity at the TM site was observed in all responses, although the microphonic (CM) was diminished more that the action potential (AP) as compared to the responses monitored via the ST1 electrode. Nevertheless, the TM-recorded cochlear potentials largely mimicked the ST1-recorded potentials in a qualitative manner, i.e., similar configurations of the CM pseudo-threshold functions. It was consistently observed that the N2 of the AP is proportionally larger (relative to N1) in the TM recording than in the ST1 recording. These phenomena were attributed to the complex spread of the bioelectrical potentials in the nonhomogeneous volume conductor formed by the tissues of the temporal bone. It was suggested that the observed change in the N1/N2 ratio at the different sites of recording is due to the different contributions of second-order neuronal discharges to the compound AP. In effect, the TM electrode "sees" proportionally more activity from second-order fibers than does the ST1 electrode, and the ST3 electrode, less.

Action Potentials↗
PubMedDate not supplied

Biasing of the summating potentials.

Summating potentials (SP) were recorded in the guinea pig cochlea, utilizing the differential-electrode technique. The effects of biasing the cochlear partition of the SP were observed under three different conditions: 1. electrical biasing--direct current polarization: 2. stimulus biasing--mechanical bias induced by low frequency sound stimulation, 3. COCB biasing--electrical stimulation of the crossed olivo-cochlear bundle. All three forms of biasing were found to have similar ellects on the SP which can be described in terms of the "absolute direction of change" in the potential. Under negative current (scala vestibuli negative; scala tympani positive), the negative phase of the stimulus bias (deflection of the cochlear partition towards scala vestibuli), or stimulation of the COCB, the SP is made more positive or less negative, as the case may be. In other words, the negative component of the differentially recorded SP is depressed, wheras the positive component is enhanced. The dominant influence os all three forms of biasing appears to be on mechanoelectric distortion arising in the hair-cell transduction process.

Acoustic Stimulation↗
PubMedDate not supplied

Relative effective frequency response of bone versus air conduction stimulation examined via masking.

An adaptation of the sensorineural acuity level procedure was employed to obtain thresholds under bone- (BC) vs. air-conducted (AC) white noise masking. For the BC masking condition, a Radioear B71 was placed on one mastoid. An Etymotic ER3 with a foam tip placed in the ear on the same side was used to deliver the pure-tone probe stimulus. This transducer was chosen to approximate the Telephonics TDH-39 earphone response characteristic while reducing occlusion effect. For the AC masking condition, the masker and probe were mixed electrically and delivered to the earphone. Masked threshold data, transformed into frequency response curves, demonstrated greater variance of BC vs. AC response across frequency but less high-frequency roll-off than expected from coupler measurements obtained using an artificial mastoid and 6-cm3 cavity, respectively.

Acoustic Stimulation↗