PubMed Health⌕ Search

Biomedical subjects

J D Durrant

Publications and source records attributed to J D Durrant.

At least 19 recordsLinked to original sources
PubMed1992

Correlations of neuroanatomical measures to auditory brain stem response latencies.

Magnetic resonance imaging (MRI) was used to obtain measures presumed to scale the dimensions of the lower auditory pathway in humans for the purpose of further defining the relationship between length of the auditory pathway and auditory brain stem response (ABR) latencies. Specifically, measurements of soft tissue structures, that is, the eighth nerve and brain stem, were made for comparison with skull dimensions and ABR latencies. It was hypothesized that the brain stem dimensions covary significantly with skull dimensions and that the ABR parameters covary with both skull and brain stem dimensions. In general, only weak correlations were obtained with coefficients failing to reach statistical significance for most comparisons. These findings suggest that variance in ABR latencies cannot be attributed completely to variance in brain stem dimensions and raise suspicion that skull dimensions do not directly reflect brain stem dimensions.

Acoustic Impedance Tests↗
PubMed1992

The frequency-following response and the onset response: evaluation of frequency specificity using a forward-masking paradigm.

The onset and frequency-following response (FFR) components of the auditory brain stem response were investigated using a tone on tone forward-masking paradigm, as an alternate strategy to simultaneous masking, in an effort to further clarify the issue of place specificity of these components when elicited by a low-frequency stimulus (500 Hz tone burst). The results of this preliminary investigation suggest that both the onset and FFR components yield frequency-specific information, that is, they reflect activity along a limited apicalward region of the cochlea, but both are biased somewhat basalward to the place of the probe frequency. Also, of the two, the FFR is the relatively more place-specific response.

Acoustic Impedance Tests↗
PubMed1991

Analog model of human click-elicited SP and effects of high-pass filtering.

Recent advances in electrode design have helped to rekindle clinical interests in noninvasive electrocochleography--to enhance auditory brain stem response (ABR) recordings (namely, wave I) and to screen Meniere's disease. The salient feature of the response in suspected cases of endolymphatic hydrops is an unusually large summating potential (SP). Since the SP is a DC potential, conventional wisdom suggests the use of relatively low cutoff frequencies (i.e., long-time constants) for recording, but this may degrade the recording due to the presence of excessive low-frequency noise. However, the click-elicited SP also is a transient of relatively short duration, considering the characteristics of the click. This may permit more liberal high-pass filtering with acceptable wave-form distortion. This is a report of findings obtained using an analog model for SP generation and recordings from normal subjects using an electrode placed directly on the tympanic membrane. Responses were obtained using various low-frequency cutoffs. Cutoffs up to 30 Hz caused little distortion. Even in the face of considerable distortion at the highest cutoffs (100 and 300 Hz), the SP remained detectable and the SP:AP essentially unchanged. Therefore, higher filter settings may be used in recording the SP than commonly assumed, although the decreased amplitudes of the component potentials may not be tolerable under all clinical test conditions.

Adult↗
PubMed1991

On the origin of wave II of the auditory brain stem evoked response.

The generators of the several components of the auditory brain stem evoked response (ABR) have yet to be completely identified. However, there is compelling evidence to suggest specific generators for waves I and II, namely the distal and proximal portions of the auditory nerve, respectively. Although there is no question concerning the origin of wave I, there remains some uncertainty as to whether or not wave II arises entirely from the auditory nerve. The purpose of this study was to examine the behavior of wave II, as recorded via vertical versus horizontal derivations, in an effort to determine if wave II in both derivations is equally affected by stimulus manipulations (i.e., as would be presumed from a single generator theory). ABR recordings were obtained from normal-hearing young adults using vertical (hairline-to-ipsilateral mastoid and hairline-to-contralateral mastoid) and horizontal (mastoid-to-mastoid) derivations of responses to clicks presented at a variety of stimulus levels (40-80 dB nHL) and rates (19.9-59.9/sec.). The results indicate a shorter latency for wave II recorded in the horizontal derivation (wave IIa), compared to the vertical derivation (wave IIb). Also, wave IIa was found to be more susceptible to increased stimulus rate and exhibited a different latency behavior than wave IIb. These findings seem difficult to reconcile on the basis of a single generator for waves IIa and IIb.

Acoustic Stimulation↗
PubMed1991

Evaluation of three strategies for fitting hearing aids binaurally.

Three strategies for evaluating optimum frequency shaping and noise reduction in binaural digital hearing aids were compared in a repeated-measures design, using a new preference-based prescriptive fitting method. These strategies consisted of using preferred frequency shaping and noise reduction values binaurally: (1) based on monaural testing; (2) based on separate evaluations of each ear; and (3) based on evaluation of a second ear while subjects wore an aid programmed with the preferred values in the first ear. Individually preferred characteristics were programmed for 17 hearing-impaired subjects, most of whom exhibited symmetrical sensorineural hearing loss. Each subject was administered intelligibility estimation and midplane localization measurements in the laboratory, as well as a questionnaire survey based on situational listening in the real world. No statistically significant differences in preferences for either frequency shaping or noise reduction were found for the three fitting strategies, suggesting that monaural testing is sufficient in symmetrical cases to provide information for binaural fitting. Related to this finding, differences across binaural conditions were minimal for both intelligibility estimation and localization results. A significant improvement in localization performance under binaural conditions over monaural listening, however, was documented by both the laboratory and the real world data. A strong overall preference for binaural over monaural amplification was also documented under real world conditions.

Adult↗
PubMed1990

Emergence of the brain-stem auditory evoked potential in the premature lamb.

Brain-stem auditory evoked potentials (BAEPs) were elicited by bone conducted stimuli in the very immature lamb following delivery, wherein liquid ventilation techniques were utilized to control cardiopulmonary and acid-base conditions, independent of umbilical-placenta support. Unlike previous studies of the in utero fetal lamb in which the BAEP could not be elicited by earphone delivered stimuli until 117 days gestation, our results demonstrate that the BAEP emerges at least as early as 106 days gestation in the lamb and consists of a full complement of readily discernible and reproducible wave forms. In addition, the results demonstrate substantial maturation of the BAEP from 106 to 122 days gestation during which time there is a significant decrease in absolute and interpeak latencies with an increase in developmental age. It is concluded that the ability to elicit the BAEP utilizing bone conduction at this early stage of gestation is related to improved stimuli delivery. Furthermore, this study demonstrates the feasibility and flexibility afforded by liquid ventilation and bone conduction BAEP techniques to study brain-stem function at particularly vulnerable stages of development.

Animals↗
PubMed1990

Gender, head size, and ABRs examined in large clinical sample.

Intergender differences in auditory brain stem response (ABR) latencies have been attributed to intergender differences in head size. We examined ABR data obtained clinically and head dimensions measured from mastoid to mastoid and mastoid to vertex to derive horizontal and vertical vectors which might scale lengths of horizontally and vertically oriented pathways, respectively. Correlations with ABR latencies were all somewhat weak, and slopes of regressions were found to be too small to fully account for intergender latency differences. Head-size matched male and female samples also demonstrated significant differences in wave V latency, and, even in cases with relatively large heads, the use of a head-size correction could not be justified. The coupling between head dimensions and the I-V interpeak interval appears to be small enough to be ignored for clinical purposes. Nevertheless, to the extent to which relationships exist between head dimensions and ABR latency measures, this nonpathologic variable may be completely neutralized through the use of interpeak latency ratios (e.g., wave V latency divided by wave I latency).

Adult↗
PubMed1990

Correlation study of two-channel recordings of the brain stem auditory evoked potential.

Two-channel recordings of the brain stem auditory evoked potential (BAEP), for example, forehead to ipsilateral mastoid and forehead to contralateral mastoid, presumably provide "views" of the generators from different, nearly orthogonal, directions. The two channels thus are expected to register somewhat different waveforms, as revealed by past research. Still, the absolute latencies of the peaks are expected to be strongly correlated between channels. To test this notion, correlation analyses were made of the latencies of positive and negative peaks of normal-appearing BAEPs. The results demonstrated the expected high correlations for brain stem components but less tight coupling between peaks of waves of more peripheral origins. The possible influence of residual noise also was considered. Implications of the findings for clinical and multichannel recording applications are discussed.

Adult↗
PubMed1990

Extratympanic electrode support via vented earmold.

An adaptation of the Stypulkowski extratympanic electrode design is described. The electrode is supported by a stock earmold which has been vented with a large enough bore to just accommodate the tubing used in this electrode design. The electrode tubing and wire assembly is merely advanced through the vent and released upon contact with the tympanic membrane; further manipulation is not required to maintain contact. The earmold also serves to couple the second transducer to the ear canal. This approach offers ease of electrode placement and consistency of positioning and, thereby, simplifies the extratympanic method of (noninvasive) electrocochleography.

Audiometry, Evoked Response↗
PubMed1990

Vestibular recruitment in Meniere's disease.

The aim of this study was to search for vestibular recruitment in a sample of patients with Meniere's disease. Recruitment was defined as an abnormal growth of response with increasing stimulus intensity. Twenty-nine patients were tested with sinusoidal rotation of three different magnitudes at four different frequencies. We also searched for auditory recruitment in each patient via tests of auditory brain stem responses, acoustic reflexes, and loudness balance and discomfort level. Analysis of vestibular responses indicated, on average, a linear relationship between stimulus magnitude and response magnitude, ie, doubling the stimulus magnitude resulted in twice the response magnitude. Meniere's patients did not yield results significantly different (although they were more variable) from those of the normal subjects. The vestibular responses of patients with auditory recruitment did not differ systematically from those of patients without auditory recruitment. We conclude that vestibular recruitment, if it exists in patients with Meniere's disease, is not demonstrated by sinusoidal rotational testing.

Adult↗
PubMed1990

Hearing loss--risk factor for cisplatin ototoxicity? Observations.

Ototoxicity associated with cisplatin chemotherapy is well established, but opinion is split regarding the relative risk associated with preexisting hearing loss. The emerging consensus is that pretreatment loss does not increase the risk of cisplatin ototoxicity. Results from a preliminary study of a small sample from our patient population supports this consensus.

Audiometry↗
PubMed1989

Masking level difference at relatively high masker levels: preliminary report.

The binaural masking level difference (MLD) was measured at multiple masking levels (i.e. 500 Hz narrow band noise presented at 50-100 dB overall SPL) in normal hearing subjects and clinical subjects with varying types and degrees of hearing loss. MLD versus noise level (MLD-NL) functions then were derived for each subject. Some growth in the MLD-NL was seen in nearly all cases of hearing loss up to 70 dB in the poorer ear. These findings suggest that the MLD-NL function may provide the basis for extending the diagnostic usefulness of the MLD test in cases of substantive hearing loss.

Adolescent↗
PubMed1989

Development of an educational module for surgical training: a case study.

This paper describes the design of software that will be used as part of an interactive video programme for the training of otolaryngologists. Although the construction of the programme is still in progress, some insight is given into the process by which the ideas were first developed and the production and evaluation of the prototype software. The procedure chosen was stapedectomy.

Education, Medical, Continuing↗
PubMed1987

Pattern-reversal auditory evoked potential.

The late auditory evoked potential (AEP) was studied in response to an alternatingly frequency-modulated complex tone. This 'pattern-reversal' AEP was found to be a heartier response than the more conventional tone-burst evoked potential, albeit longer in latency.

Acoustic Stimulation↗
PubMed1987

Auditory-evoked potential to pattern-reversal stimulation.

The late auditory-evoked potential (AEP) was studied in response to a frequency-modulated complex synthesized from discrete tones, somewhat analogous to visual stimulation using reversals of alternating light and dark stripes. The "pattern-reversal' AEP was found to be a heartier response than the familiar transient-evoked AEP (e.g. tone-burst-elicited potential), but the latencies of the component potentials were longer. The apparent enhancement of the AEP is postulated to be due to response summation across critical bands, akin perhaps to loudness growth as stimulus bandwidth increases.

Acoustic Stimulation↗
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↗