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Biomedical subjects

G K Martin

Publications and source records attributed to G K Martin.

At least 55 records · Page 3Linked to original sources
PubMed1991

A review of otoacoustic emissions.

Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool.

Animals↗
PubMed1991

Evidence for the influence of aging on distortion-product otoacoustic emissions in humans.

Previous measures of distortion-product otoacoustic emissions (DPOAEs) in young adults suggested that these responses were capable of detecting the functional effects of auditory aging. The primary goal of the present study was to provide more detailed evidence for the influence of aging processes on the ability of healthy, older ears to generate DPOAEs. Toward this end, DPOAEs were examined in a series of human subjects, with clinically normal hearing, ranging in age from 31 to 60 years. Acoustic-distortion products were measured in two basic forms consisting of "audiograms" and response/growth or input/output functions. Distortion-product "audiograms" depicted the detailed frequency pattern of DPOAE amplitudes in response to constant-level stimuli, whereas the growth functions described the detection "threshold" and suprathreshold aspects of DPOAE activity, at specific frequencies, in response to primary tones that were systematically increased in level. The principal finding was that, when compared to emissions in young ears, DPOAEs accurately tracked the systematic deterioration of high-frequency hearing in aging individuals.

Adult↗
PubMed1991

Acoustic-distortion products: separation of sensory from neural dysfunction in sensorineural hearing loss in human beings and rabbits.

Because distortion-product otoacoustic emissions (DPOAEs) provide a noninvasive measure of outer hair-cell (OHC) activity, they should provide a unique and sensitive indicator of the effects of agents that damage hearing. Using DPOAE methods, the present study was designed to assess the relative contributions of the cochlea's outer hair cells to some common sensorineural diseases, including Meniere's disease, acoustic neuroma, and noise-induced, hereditary, and sudden idiopathic sensorineural hearing loss. Parallel evaluations of DPOAEs were performed under essentially identical conditions in rabbit models of several of the human disorders, including noise-induced hearing loss, endolymphatic hydrops, and cochlear neurectomy. Animal studies were performed to assess the proficiency of DPOAEs to track a developing sensorineural deficit as well as to compare patterns of DPOAE dysfunction between clinical and experimental forms of peripheral hearing loss. Detailed measures of DPOAEs were collected in the stimulus-frequency and intensity domains as "audiograms" and response/growth or input/output functions, respectively. The outcome of analyses of both human beings and animals supported the notion that DPOAE testing is sensitive to sensory-cell disease. Thus, in combination with conventional audiometry, DPOAE measures permit a distinction between the relative contribution sensory and neural components of the cochlea make to hearing deficits.

Acoustic Stimulation↗
PubMed1990

Postnatal development of 2f1-f2 otoacoustic emissions in pigmented rat.

Distortion-product emissions at 2f1-f2 were measured in developing, pigmented rats to determine the characteristics of the functional onset and maturation of these emitted responses. Distortion-product testing was conducted on postnatal days 12, 14, 18, 21, 24, 28, and 51. The geometric-mean frequencies of the primaries were tested at one-half octave intervals, between 4 and 11.3 kHz. No emissions were detected on postnatal day 12; however, by day 14, emissions were measured at geometric-mean frequencies between 5.7 and 11.3 kHz, but not at 4 kHz. By the 18th postnatal day, all animals had measurable emissions at 4, 5, 7, 8, and 11.3 kHz. Both the functional onset and maturation of high- to midfrequency emissions developed before those elicited by lower-frequency primaries. Response/growth or input/output functions for the higher frequencies exhibited 'adult-like' properties that included an increase in maximum amplitude and 'saturation' at high levels of stimulation by the third to fourth postnatal week. Maturation of the lower-frequency responses progressed at a slower rate. These results differ somewhat from those reported previously for the neonatal albino rat. However, the present findings were based upon a wider frequency range of primary tones, lower levels of acoustic stimulation, and a measuring system with a significantly lower noise floor. These results are consistent with documented periods of the anatomical maturation of the rat outer hair-cell system and establish a functional 'baseline' for future studies utilizing agents that damage the developing cochlea.

Acoustic Stimulation↗
PubMed1990

Otoacoustic emissions in human ears: normative findings.

Otoacoustic emissions can be separated into two interrelated classes according to the type of eliciting stimulus. On the basis of this categorization, four discrete subtypes can be recognized that include spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. Methods of recording and findings in the ears of normally hearing humans are reviewed for each emission type.

Cochlea↗
PubMed1990

The clinical utility of distortion-product otoacoustic emissions.

Otoacoustic emissions permit, for the first time, an unbiased means of examining the preneural elements of the peripheral auditory pathway that make the initial contribution to the perception of acoustic stimuli. Distortion-product otoacoustic emissions (DPOAEs) represent one type of evoked emission that has significant potential for becoming an important test in the audiometric evaluation of hearing capacity. In the present review, selected examples of several forms of sensorineural hearing loss demonstrate that DPOAEs have the ability to act as objective indicators of the frequency/level configuration of the conventional audiogram in cases in which hearing impairment results primarily from damage to the outer hair cells. In contrast, normal DPOAE functioning, in the presence of a significant hearing loss, indicates a locus of damage central to the region of the outer hair cells. Like the other emitted responses, DPOAEs can be measured noninvasively, are highly repeatable, under test-retest conditions, and are simple and rapid to detect using microcomputer-based instrumentation. Further, DPOAEs test both the "threshold" and suprathreshold levels of outer hair-cell activity in the form of response/growth functions, over a 30- to 40-dB stimulus range. In combination, these attributes indicate that DPOAEs can provide an objective and comprehensive assessment of the cochlear reserve of a given ear.

Audiometry, Evoked Response↗
PubMed1990

The clinical application of acoustic distortion products.

Otoacoustic emissions provide an objective measure of hair-cell function that is independent of retrocochlear activity. Because of their frequency specificity, distortion-product emissions have great potential for clinical use. The present report describes the results of initial studies in patients with known cochlear or retrocochlear disease, diagnosed with standard otologic and audiologic tests. The cochlear group consisted of those diagnosed with noise-induced hearing loss, Meniere's disease, or hereditary hearing loss, whereas patients with acoustic neuroma comprised a retrocochlear group. A final group consisted of patients with sudden sensorineural hearing loss of unknown origin. Detailed distortion-product emission testing included the computer-controlled acquisition of "audiograms" and response/growth functions. The outcomes of these studies demonstrated that distortion-product emissions provide a noninvasive, frequency-specific test of sensory-cell function that objectively depicts the boundary between normal and abnormal hearing. These emissions were also able to effectively track dynamic changes in progressive disease processes. Finally, as a screening tool, acoustic distortion products provide an objective means of assessing cochlear status in infants and young children and in adults at risk for hearing loss. Because acoustic distortion products accurately measure the sensory component of a sensorineural hearing loss, distortion-product testing may play an important role in the diagnosis and treatment of cochlear dysfunction.

Adolescent↗
PubMed1990

Distortion product emissions in humans. II. Relations to acoustic immittance and stimulus frequency and spontaneous otoacoustic emissions in normally hearing subjects.

Multifrequency and multicomponent evaluations of aural acoustic immittance, including tympanometry and acoustic reflex testing, were performed on 44 normal ears to examine the influence of middle ear functioning on the generation and detection of distortion product otoacoustic emissions (DPEs). In the same ears, the prevalence and parametric features of spontaneous and stimulus frequency emissions were also assessed so that their relationship to the detection "thresholds" and amplitudes of corresponding DPEs could be determined. The general outcome was that none of the examined features of acoustic immittance provided an explanation for the discrete, low-amplitude DPE regions observed in about one third of normal ears. Moreover, the presence of typical spontaneous and stimulus frequency emissions in these same "irregular" ears indicated that emission generation and reverse cochlear transmission were also operating normally within these regions of reduced DPEs. Consequently, other, as yet undetermined influences appear to contribute to the DPE variability noted in some ears. Finally, the simultaneous presence of stimulus frequency emissions, but not spontaneous emissions, appeared to reduce the detection "thresholds" and increase the amplitudes of low-frequency DPEs.

Acoustic Impedance Tests↗
PubMed1990

Distortion product emissions in humans. I. Basic properties in normally hearing subjects.

Distortion product otoacoustic emissions (DPEs) at the 2f1-f2 frequency were recorded from 44 normal ears in response to equilevel primary tones. Detailed testing included the recording of DPE "audiograms" in 100-Hz steps from 1 to 8 kHz at three primary-tone levels (65, 75, and 85 dB sound pressure level [SPL]). In addition, response-growth or input-output (I/O) functions depicting the relationship of the amplitudes of DPEs to primary-tone levels, ranging from 25 to 85 dB SPL in 5-dB steps, were also tested for 11 frequencies distributed at quarter-octave intervals over the identical frequency range. The average DPE "audiogram" illustrating the frequency response of these emissions demonstrated a bilobed contour having a low-frequency maximum at approximately 1.5 kHz and a high-frequency peak that plateaued at about 5.5 kHz. The two maximum regions were separated by a minimum around 2.5 kHz. Depending on the frequency region, the average I/O functions exhibited detection "thresholds" at 3 dB above the noise floor at primary levels between 35 and 45 dB sound pressure level. The dynamic range of the emitted response between detection "threshold" and maximum amplitude varied over a 40-dB extent of the stimulus-level dimension. Approximately one third of the ears exhibited irregular DPE "audiograms" in which emitted responses were significantly reduced in restricted regions tested by low, medium, or high frequencies. When the 44 ears were separated into two groups representing more-normal and less-normal responses, the irregular "normal" ears demonstrated increased variability, especially in high-frequency regions. Mean age did not explain the differences noted between the two types of normally hearing subjects. However, across ears, DPE amplitudes and "thresholds" for the highest frequencies tested were correlated significantly with age in that the oldest individuals showed higher "thresholds" and lower amplitudes.

Acoustic Impedance Tests↗
PubMed1990

Distortion product emissions in humans. III. Influence of sensorineural hearing loss.

The realization that otoacoustic emissions are sensitive to cochlear disorders has resulted in the speculation that they may have considerable clinical potential as objective measures of hearing. To assess the clinical utility of one type of emission, the distortion product emission (DPE), a study was undertaken in individuals with hearing impairments representing a number of common otologic disorders. The results of this investigation provided evidence that tests of DPEs promise to satisfy a number of requirements important to clinical testing, including objectivity of measurement procedures, test-retest reliability, simple subject preparation, readily available instrumentation, and relatively brief examination periods. The fine resolution of DPEs within the stimulus frequency and level domains also permits an accurate confirmation of the pattern of hearing loss. For example, tests of DPEs detected a 20-dB hearing level impairment at a single frequency in an ear exhibiting early signs of noise-induced hearing loss, and a 10-dB improvement in sensitivity following ingestion of the hyperosmotic agent glycerol in an ear displaying a mild to moderate hearing loss due to Meniere's disease. Finally, the application of DPEs to the objective testing of otologic disorders suggests that the ability of these responses to assess the sensory component of a sensorineural disorder may contribute to the eventual understanding of the complicated pathogenesis of many cochlear diseases. When all the positive features of DPE testing are realized, the potential contribution that these measures can make in a clinical setting becomes apparent.

Adult↗
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↗
PubMed1989

Ultrastructural evidence of repair and neuronal survival after labyrinthectomy in the squirrel monkey.

Although the vestibular and cochlear branches of the VIIIth cranial nerve originate embryologically from the same primordia, results of the present investigation confirm previous findings indicating that the vestibular branch may be more plastic with respect to recovery after surgical insult than the cochlear division. In this report we show ultrastructural details of changes undergone by the vestibular nerve after surgery. Dendrites peripheral to the vestibular nerve ganglion (VNG) were severed by surgically removing the vestibular end organs; the squirrel monkeys were then allowed to recuperate, and tested for their vestibulospinal and vestibulo-oculomotor functions behaviorally. However, behavior deficits resulting from the injury are reported separately. The vestibular nerves excised from the internal acoustic meatus and the temporal bones were examined histologically for changes of VNG and fibers from day 1 to 1,247 days after labyrinthectomy. Light- and electron-microscopic examinations indicated that some perikarya and some fibers of the VNG remained in the ganglionic matrix for up to 1,247 days, the longest period studied, after the operation. Fibers extended toward the remodeled inner ear space in the absence of appropriate sensory cell targets. The surviving neurons and fibers exhibited various degrees of wallerian-like degeneration at first, but many of them retained ultracellular organelles and integrity even after 1,247 days. Since vestibular perikarya are bipolar, the unsevered fibers that project to the brainstem could retain functional synaptic connections, a possibility that is now under investigation. Schwann cells in the ganglionic matrix may also have contributed to vestibular neuron survival by providing the proper nourishment. Morphometric measurements determined that neurons remaining in the ganglion had significantly smaller cross-sectional areas than normal neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Incidence of spontaneous otoacoustic emissions in macaque monkeys: a replication.

An earlier survey of spontaneous otoacoustic emissions (SOEs) in Old- and New-World monkeys identified three of 61 animals (5%) as emitters. Since all three emitting monkeys belonged to the macaque genus, the present study was conducted in a group of 102 pigtail monkeys in an attempt to corroborate the incidence of SOEs in a readily available macaque species. This examination revealed nine primates (9%) with SOEs with three demonstrating bilateral emissions. These results demonstrate that the macaque monkey offers a unique nonhuman primate model for the study of SOE phenomena.

Animals↗
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↗
PubMed1988

The effect of cochleostomy on the development of endolymphatic hydrops--morphologic changes in the rabbit cochlea.

The present study was designed to examine the effects of cochleostomy on the development of endolymphatic hydrops in the rabbit. Fistulization of the cochlear partition and simultaneous obstruction of the endolymphatic duct was performed in one group of animals (n = 13). Rabbits in two other groups underwent either cochleostomy (n = 6) or endolymphatic duct obstruction (n = 6) alone. Animals were terminated at 1-, 4-, and 6-week intervals and the cochleas were examined with the light microscope to document the presence or absence of hydrops, or were evaluated with the scanning electron microscope to assess sensory-cell damage. Hydrops was observed in 67% of the animals in the combined duct-obstruction/cochleostomy group, in 100% of the duct-obstruction alone group, and in 0% of the cochleostomy alone group. Widespread sensory-cell degeneration was observed with the scanning electron microscope in the combined and the cochleostomy alone groups.

Animals↗
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↗