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Biomedical subjects

A C Coats

Publications and source records attributed to A C Coats.

At least 19 recordsLinked to original sources
PubMed1989

Acoustic distortion products in humans: systematic changes in amplitudes as a function of f2/f1 ratio.

The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1-f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01-1.41 (4 kHz), 1.01-1.59 (2.5 kHz), or 1.01-1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus-parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.

Adult↗
PubMed1988

Spontaneous otoacoustic emissions in a nonhuman primate. I. Basic features and relations to other emissions.

Otoacoustic emissions in both ears of a rhesus monkey exhibiting stable spontaneous emissions (SOEs) were monitored over a 1-year period. The amplitudes and frequencies of both SOEs and stimulus-frequency emissions (SFEs) were routinely recorded, while transiently evoked (EOE) and distortion-product emissions (DPEs), at the frequency 2f1-f2, were occasionally examined. Between evaluation sessions, both the frequencies and amplitudes of SFEs remained relatively stable in both ears, while the frequencies and amplitudes of SOEs were less constant. Isosuppression contours for SOEs, plotted as a function of frequency and level of tonal maskers, revealed sharp tuning consistent with normal frequency selectivity. Detailed analyses of long-term measurements showed that SOEs occurred most frequently at the peaks of the SFE response. A regular frequency spacing between neighboring amplitude maxima and minima of the SFEs was consistent with the notion that this particular emitted response may result from a periodic disruption of the orderly pattern of sensory cells along the organ of Corti. Intramuscular administration of aspirin abolished SOE and SFE responses, while DPEs remained relatively unchanged suggesting the involvement of separate mechanisms in the generation of different emissions.

Acoustic Stimulation↗
PubMed1988

Spontaneous otoacoustic emissions in a nonhuman primate. II. Cochlear anatomy.

Both cochleas of a rhesus monkey exhibiting stable spontaneous and stimulus-frequency emissions were evaluated histologically using surface-preparation methods to determine if certain features of these emissions could be related to structural properties of the organ of Corti (OC). The comprehensive assessment included preparation of routine cytocochleograms and a detailed study of the arrangement of cochlear sensory cells, best revealed by the precise positional relationships between stereocilia bundles, in selected areas representing low-, medium-, and high-frequencies. Several additional measurements were made in an area extending from about 25-60% distance from the apex, which was estimated to encompass the cochlear region where emissions were generated. These quantifications included measures, in both micrometers and Hertz, of the distances between irregularities in the lateral border of the OC due to a sporadically occurring fourth row of outer hair cells (OHCs). Measures, in micrometers, of the changes in the radial extent of the corresponding OC in the presence or absence of this extra fourth row of OHCs were also made. A final measure within low-, medium-, and high-frequency OC regions consisted of describing the angles that the tips of the stereocilia bundles were displaced from an axis parallel to the tunnel of Corti. For comparative purposes, similar plots were made in comparable regions of the OC in the normal and experimental cochleas of three additional rhesus monkeys in which one ear had been systematically exposed to noise. In the emitting-monkey cochlea, there was a mild loss of sensory cells scattered throughout the OC which was generally greater for the OHCs. No evidence of small circumscribed lesions, defined as a loss of more than four adjacent hair cells, was found. The most striking observation which varied in degree across the three other monkeys was a generalized irregularity in the cellular organization of the OHC region which was most pronounced in the low- and midfrequency regions of the OC. The notable cellular disorganization specific to the apical half of the cochlea was reflected by an increased variance in the distribution of deviation angles measured for corresponding stereocilia bundles. Outer hair cells in the remaining basal region of the OC were arranged in three regular rows with the usual stereocilia orientation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustics↗
PubMed1987

Acoustic distortion products in rabbit ear canal. I. Basic features and physiological vulnerability.

In contrast to evoked otoacoustic emissions, acoustic distortion products (DPs) recorded from the ear canal are present at predictable frequencies with respect to their primary tones, f1 and f2. Such specificity may provide detailed frequency-place information concerning the functional state of limited regions of the organ of Corti following experimental intervention. However, to date, it is not clear whether emitted DPs solely reflect activity at the basilar-membrane regions of primary tones or if the remote DP site makes a significant contribution to the emitted signal measured in the ear canal. We have investigated a number of the general features of acoustic-DP generation in the rabbit so that, in later experiments, the contributions of specific basilar-membrane regions involved in generating these DPs can be identified using techniques designed to manipulate their normal properties. The first report describes the outcome of systematic manipulations of a number of stimulus conditions and alterations to the physiological state of the cochlea by exposure to fatiguing sound or anoxia. Experimental findings for the 2f1-f2 DP showed that, in general, the relations of the levels and frequency of the primary tones to DP magnitude were consistent with previously published data from other mammalian species. Additional observations for other odd-order intermodulation DPs at the 3f1-2f2 and 2f2-f1 frequencies suggested that the basic attributes of the acoustic DPs were similarly affected by systematic manipulation of the basic parameters of the primary tones and the general metabolic state of the cochlea. General anesthesia, however, did not affect DP amplitude. A companion paper describes the results of a series of subsequent experiments using response-suppression, interfering-tone, and temporary threshold shift techniques which address more directly the issue of which basilar-membrane sites contribute to the generation of different acoustic DPs.

Anesthesia, General↗
PubMed1987

Acoustic distortion products in rabbit ear canal. II. Sites of origin revealed by suppression contours and pure-tone exposures.

Previous work on acoustic distortion products (DPs) recorded from the ear canal has not established unequivocally whether emitted DPs principally reflect basilar-membrane nonlinearities at the frequency sites of the primary tones, f1 and f2, or if the DP-frequency place itself makes a significant contribution to the emitted response. Results from some studies on acoustic emissions attribute generation of the emitted DP almost exclusively to the regions of maximum primary-tone interaction, while the findings of other investigations implicate reemission of the response from the DP locus as a significant contributor to response magnitude. Using suppression, interfering tones, and temporary threshold shift (TTS) procedures, the work reported here was designed to establish more definitively the precise contributions of the basilar-membrane regions involved in generating acoustic DPs in rabbits. Suppression tuning curves and interfering-tone experiments indicated that for the DP at 2f1-f2, regions near the f1 or f2 frequencies were the major contributors to the emitted response. However, for the higher-frequency DP at 2f2-f1, the basilar-membrane region just basal to the DP site was implicated as the generator. Following brief episodes of TTS at frequencies related to either the DP or the primary tones, the locus of the exposure stimulus that most effectively reduced the magnitude of the 2f1-f2 response also implicated the region of maximal primary-tone interaction in the generation of the acoustic DP. In contrast, for the DP at 2f2-f1, basilar-membrane sites nearer the DP were identified as the primary contributors to the emitted response. Both sets of results imply that different DPs recorded from the ear canal may originate from unique regions of primary-tone interaction along the basilar membrane.

Acoustic Stimulation↗
PubMed1986

The normal summating potential recorded from external ear canal.

With a "plastic leaf" electrode, cochlear summating potential (SP) and auditory nerve action potential (AP) responses to rectangular-pulse clicks were recorded from the ear canal skin surface of 96 normal-hearing ears of 48 subjects. The main goals of this investigation were to develop a more precise characterization of the relationship between SP and AP amplitudes across normal ears and to determine the confidence limits of this relationship so that a more accurate "normal limit" could be established for clinical testing. The results suggest that the across-subjects SP-AP amplitude relationship is linear. Also, SP scatter increases as AP amplitude increases, but the scatter is equalized by log transforming the data. The distance of the SP from the log-transformed SP-AP estimating line in SE ("AP-normalized SP amplitude") was found to be superior to the SP/AP amplitude ratio as a method of adjusting SP to AP amplitude, because the SP/AP ratio varied significantly with AP amplitude both across subjects and with different ear canal electrode positions.

Action Potentials↗
PubMed1986

Spontaneous, click-, and toneburst-evoked otoacoustic emissions from normal ears.

Evoked and spontaneous otoacoustic emissions were recorded bilaterally in a group of normal subjects (n = 14) using clicks and tonebursts at four frequencies (0.5, 1, 1.5, and 3 kHz). All ears (n = 28) demonstrated evoked emissions, but not to every stimulus type. The 0.5-kHz toneburst evoked emissions in only 10 (36%) ears, the 1.5-kHz toneburst in all ears, and the remaining stimuli in at least 80% of ears. Two distinct patterns of evoked emissions were identified. Five (18%) ears showed short, broadband click-evoked emissions lasting less than 20 ms after stimulus onset. In these ears, toneburst-evoked emissions were often more prominent than click-evoked emissions and no spontaneous emissions were detected. Twenty-three (82%) ears showed click-evoked emissions lasting longer than 20 ms poststimulus onset. Spectral analysis of these emissions demonstrated several (2-10) narrow frequency peaks. Highly similar peaks were present in the spectra of toneburst-evoked emissions within the range of toneburst spectra. Spontaneous emissions were recorded in 12 of the 23 ears. In these ears, at the frequencies of spontaneous emissions, prominent peaks in both click- and toneburst-evoked emission spectra were always present. Otoacoustic emission characteristics correlated significantly between the ears of individual subjects inferring that a symmetrical cochlear mechanism generates otoacoustic emissions.

Acoustic Stimulation↗
PubMed1985

Spontaneous otoacoustic emissions in the nonhuman primate: a survey.

A number of reports have described a relatively high incidence of spontaneous otoacoustic emissions (SOAEs) in recordings made from the sealed human ear canal. Our attempt to detect similar emissions in 122 presumably normal-hearing ears from 61 monkeys revealed SOAEs in 5% of the primates and 2.5% of the ears tested.

Animals↗
PubMed1979

Voluntary nystagmus masquerading as Tullio's Phenomenon.

Nystagmoid eye movements elicited by humming loudly was initially misdiagnosed as Tullio's phenomenon (abnormal acoustical stimulation of the vestibular apparatus owing to labyrinthine fistula). Further workup lead to a final diagnosis of a form of voluntary nystagmus characterized in some reports as "hysterical mystagmus". Some of the characteristics of this example of voluntary nystagmus differed from generally accepted descriptions.

Adult↗
PubMed1979

Normal short-latency electrophysiological filtered click responses recorded from vertex and external auditory meatus.

We recorded normal electrophysiological responses to third-octave filtered clicks from external auditory meatus (EAM) and vertex electrodes referred to coupled earlobe electrodes (forehead ground). From both vertex and EAM, polarity-sensitive responses predominated at low frequencies and exhibited characteristics of both phase-locked neural responses (frequency-following response or FFR) and cochlear microphonics (CM). The FFR-like response predominated at the vertex site and the CM-like response predominated at EAM. At high frequencies, polarity-insensitive responses closely resembled rectangular-pulse click action potentials and brainstem evoked potentials, with clearly defined N1 and V peaks recorded from EAM and vertex, respectively. As frequency was lowered, the N1 and V peak latencies increased, the peaks broadened, and the latency-intensity curves steepened with greater prolongation occurring at lower click intensities. Lowering click frequency also shortened the N1-V interval and caused the plot of N1-V interval versus click intensity to become steeper. Plots of polarity-insensitive response amplitudes and thresholds against frequency revealed a high frequency bias for both N1 and V, but the V "frequency response" was flatter. A possible explanation of the shortened N1-V interval at low click frequencies based on this flatter V "Frequency response" is presented.

Acoustic Impedance Tests↗
PubMed1978

Human auditory nerve action potentials and brain stem evoked responses.

Latency-intensity (L-i) functions for (1) the auditory nerve action potential (AP) N1 peak, (2) the brain stem evoked response (BER) V peak, and (3) the N1-V interval were related to hearing level and lesion location. The AP L-l curves tended to steepen with increasing 4 to 8 kHz hearing level. This relationship was identical for cochlear and retrocochlear ears, except for a few retrocochlear ears with "inappropriate AP perservation." Both high-frequency cochlear loss and retrocochlear abnormality prolonged peak V latency, but retrocochlear abnormality generally prolonged it more. Among cochlear-loss ears, as 4 to 8 kHz hearing levels increased, N1-V intervals decreased and L-i curve slopes increased. In contrast, retrocochlear abnormality greatly prolonged N1-V intervals. As a retrocochlear sign, N1-V prolongation was slightly more reliable than V prolongation.

Action Potentials↗
PubMed1977

Human auditory nerve action potentials and brain stem evoked responses: effects of audiogram shape and lesion location.

Simultaneously recorded auditory nerve action potentials (APs) and brain stem auditory-evoked responses (BSERs) were correlated with audiogram shape and with location of patholgoic condition. High frequency (4 to 8 kHz) hearing loss (1) prolongs AP and BSER latency, (2) shortens the interval between the first AP peak (N1) and the fifth BSER peak (V), and (3) creates relatively large latency differences between condensation and rarefaction responses (thus bringing into question the common practice of combining condensation and rarefaction responses). Ears with retrocochlear deficits in the subjects in the study were detected reliably by prolonged N1 to V interval and increased BSER peak V latency. The reliability of these retrocochlear signs was further increased by allowing for the effects of audiogram shape. Another retrocochlear sign, termed "inappropriate AP preservation," was positive in 40% to 50% of the retrocochlear ears.

Action Potentials↗
PubMed1977

Voluntary nystagmus.

Voluntary nystagmus is a pendular, rapid, conjugate, primarily horizontal, benign nystagmus initiated and maintained by voluntary effort. The amplitude is variable, but always low. The rate is constant and rapid. Convergence is variable--apparently essential in some, nonessential in others, but related in all of our cases. This condition appears to have a familial component and is more common than originally thought. Voluntary nystagmus should be considered when dealing with any patient exhibiting nystagmus in order to minimize the possibility of misdiagnosis as occurred in one of our cases.

Adolescent↗
PubMed1976

The air caloric test. A parametric study.

We studied the normal air caloric response's intensity and variability. Intensities of "preliminary standard" (47 C, 25 C, 60 seconds, 10 liters/min) air and standard bithermal water responses were the same, but the air responses were more variable. Control experiments suggested that the tendency of the air stream to equilibrate toward ambient may account for much of air's relatively high variability. Increasing the air irrigation's duration, flow rate, and separation from body temperature increased response intensity. Air's test-retest variability decreased when flow rate and duration increased and when temperature approached ambient. Therefore, we suggested that irrigating temperatures be chosen as close to ambient as possible and duration and flow rate be made as large as possible. From a table equating air and standard bithermal water responses, we selected tentative clinical air irrigation parameters of 27.5 C, 45.5 C, 100 seconds, and 13 liters/min.

Adolescent↗
PubMed1975

Superior vestibular nerve sectioning. Experimental studies in squirrel monkeys.

Spontaneous, positional, and paroxysmal positional nystagmus were studied before and after sectioning the superior division of the vestibular nerve and the anterior vestibular artery in squirrel monkeys. Histopathologic study of the temporal bones confirmed the degeneration of the macula utriculi with release of statoconia, but failed to identify the released utricular statoconia within the vestibular endolymphatic space in any animal. Postoperatively the animals consistently demonstrated direction-fixed spontaneous nystagmus until the end of the experiment (five months). Positional tests and Dix-Hallpike maneuver occasionally changed the intensity of the spontaneous nystagmus, but never elicited paroxysmal positional nystagmus. Possible reasons for not demonstrating paroxysmal positional nystagmus in the squirrel monkey are as follows: a resorption of statoconia; slight morphological alteration of the sensory epithelia of the posterior cristae; interference of the posterior crista function due to partial collapse of the membranous ampulla; the existence of interspecies difference; or possibly a faulty hypothesis regarding the etiologic mechanism of benign paroxysmal positional vertigo.

Animals↗
PubMed1975

Temporal bone findings in cryptococcal meningitis.

A 19-year-old woman with cryptococcal meningitis died as a result of her disease, in spite of both intravenous and intraventricular administration of amphotericin B. Gross and microscopic examinations revealed multiple cysts containing Cryptococcus neoformans within the central nervous system. Studies of the temporal bones revealed both neural and end organ destruction with the presence of Cryptococcus when stained by Gomori methenamine silver nitrate method. We present the results of audiometric and vestibular examinations. The case history depicts a progressive neurological involvement by Cryptococcus.

Adult↗