Biomedical subjects

G R Long

Publications and source records attributed to G R Long.

At least 19 recordsLinked to original sources

PubMed2003

Low-frequency distortion product otoacoustic emissions in two species of kangaroo rats: implications for auditory sensitivity.

Low-frequency distortion-product otoacoustic emissions were measured in two species of kangaroo rats to test the prediction that a large footdrumming species (e.g., Dipodomys spectabilis) would have greater distortion-product otoacoustic emission amplitude than a small non-footdrumming species (e.g., Dipodomys merriami), indicating better hearing sensitivity at low frequencies. Equal-level (65 dB SPL) stimulus tones ( f(1), f(2)), presented over a ( f(1)) range of 200-1000 Hz, were used to evoke the 2 f(1)- f(2) distortion-product otoacoustic emission. Mean 2 f(1)- f(2) levels for D. merriami showed good correspondence to previously published audiograms for that species. Mean 2 f(1)- f(2) levels and 95% confidence intervals indicated species differences below 400 Hz, supporting the theory that low-frequency hearing sensitivity is better in large kangaroo rat species. These results suggest that the size-related divergence in footdrumming behavior may be related to differential auditory sensitivity.

Animals↗

PubMed2002

A comparative study of avian auditory brainstem responses: correlations with phylogeny and vocal complexity, and seasonal effects.

We conducted a comparative study of the peripheral auditory system in six avian species (downy woodpeckers, Carolina chickadees, tufted titmice, white-breasted nuthatches, house sparrows, and European starlings). These species differ in the complexity and frequency characteristics of their vocal repertoires. Physiological measures of hearing were collected on anesthetized birds using the auditory brainstem response to broadband click stimuli. If auditory brainstem response patterns are phylogenetically conserved, we predicted woodpeckers, sparrows, and starlings to be outliers relative to the other species, because woodpeckers are in a different Order (Piciformes) and, within the Order Passeriformes, sparrows and starlings are in different Superfamilies than the nuthatches, chickadees, and titmice. However, nuthatches and woodpeckers have the simplest vocal repertoires at the lowest frequencies of these six species. If auditory brainstem responses correlate with vocal complexity, therefore, we would predict nuthatches and woodpeckers to be outliers relative to the other four species. Our results indicate that auditory brainstem responses measures in the spring broadly correlated with both vocal complexity and, in some cases, phylogeny. However, these auditory brainstem response patterns shift from spring to winter due to species-specific seasonal changes. These seasonal changes suggest plasticity at the auditory periphery in adult birds.

Acoustic Stimulation↗

PubMed2000

Modeling the combined effects of basilar membrane nonlinearity and roughness on stimulus frequency otoacoustic emission fine structure.

A theoretical framework for describing the effects of nonlinear reflection on otoacoustic emission fine structure is presented. The following models of cochlear reflection are analyzed: weak nonlinearity, distributed roughness, and a combination of weak nonlinearity and distributed roughness. In particular, these models are examined in the context of stimulus frequency otoacoustic emissions (SFOAEs). In agreement with previous studies, it is concluded that only linear cochlear reflection can explain the underlying properties of cochlear fine structures. However, it is shown that nonlinearity can unexpectedly, in some cases, significantly modify the level and phase behaviors of the otoacoustic emission fine structure, and actually enhance the pattern of fine structures observed. The implications of these results on the stimulus level dependence of SFOAE fine structure are also explored.

Basilar Membrane↗

PubMed1999

Experimental confirmation of the two-source interference model for the fine structure of distortion product otoacoustic emissions.

High-resolution measurements of distortion product otoacoustic emissions (DPOAEs) from three different experimental paradigms are shown to be in agreement with the implications of a realistic "two-source" cochlear model of DPOAE fine structure. The measurements of DPOAE amplitude and phase imply an interference phenomenon involving one source in the region of strong nonlinear interaction of the primary waves (the strong "overlap" or generation region), and the other source region around the DPOAE tonotopic place. The component from the DPOAE place can be larger than the one from the generator region. These findings are supported by the analysis of the onset and offset of the DPOAE when the higher-frequency primary is pulsed on and off. The two-source hypothesis was further tested by adding a third tone closer in frequency to the DPOAE which modifies the amplitude of the component from the DPOAE place and leaves the one from the generator region unchanged. The results agree well with the model prediction that the variation with frequency, and implied latency, of the phase of the DPOAE tonotopic-place component are greater than the corresponding quantities for the component from the generation region.

Acoustic Stimulation↗

PubMed1998

Volume recruitment and oxygenation in pulmonary edema: a comparison between HFOV and CMV.

PURPOSE: In acute lung injury, edema floods alveoli decreasing mean lung volume (MLV) and increasing pulmonary venous admixture (Ova/Qt). We reasoned that a ventilatory strategy that uses large tidal volumes (VT) might recruit volume differently than a strategy that uses very small VT (high-frequency oscillatory ventilation, HFOV) which may require an inflation maneuver to total lung capacity (TLC) for full recruitment. MATERIALS AND METHODS: We studied six dogs with pulmonary edema induced by oleic acid injury and compared HFOV with conventional mechanical ventilation (CMV). Increasing mean airway opening pressure (Pao) from 6 to 14 cm H2O raised MLV from 932+/-162 to 1,550+/-210 mL and from 872+/-145 to 1,242+/-192 mL during CMV and HFOV, respectively, whereas Qva/Qt decreased from 24.1+/-8.5 to 9.3+/-4.3% and from 42.2+/-6.8 to 30.4+/-9.3%. We repeated our measurements at a Pao of 14 cm H2O after an inflation maneuver to TLC. RESULTS: Intlation to TLC recruited additional lung volume and decreased Qva/Qt further only during HFOV. After an inflation to TLC, we observed a rapid isobaric volume loss from the deflation limb of the pressure-volume curve during both CMV and HFOV. CONCLUSIONS: We conclude that after oleic acid injury in dogs pressure-volume hysteresis has two components: a recruitable portion associated with gas exchange improvement and a nonrecruitable portion. At the level of PEEP used in this study (8.5 cm H2O), full lung recruitment during HFOV required inflation to TLC, whereas during CMV it was accomplished by the relatively large VT.

Animals↗

PubMed1998

The dependence of the distortion product 2f1-f2 on primary levels in non-impaired human ears.

The optimal intensity relation between the two primaries used to generate Distortion Product Otoacoustic Emissions (DPOAEs) in unimpaired human ears, over a clinically relevant intensity range, was evaluated using a commercially available clinical device. The ILO92 was used to determine the level of the DPOAE at 2f1-f2 for 16 combinations of primary levels in the range of 40 to 80 dB SPL from 40 unimpaired, young adult ears. Data were collected between 1 and 6 kHz at 1, 1.5, 2, 3, 4, 5, and 6 kHz. The commonly used procedure of dropping data points less than 3 dB above the noise floor was compared to a power subtraction procedure. A multivariate ANOVA was performed to determine main effects of gender, ear, stimulus levels, frequencies, and interactions between stimulus levels and frequencies. An overall increase of DPOAE amplitude with increase in primary level was observed, along with a decrease of the optimal difference in primary levels as L2 was increased. Although the power subtraction and 3-dB drop paradigms yielded similar results at high stimulus levels, the power subtraction paradigm provided a more realistic indicator of DPOAE level when low level primaries were used. Possible mechanisms responsible for the level dependence of the optimal relationship between primaries and implications for clinical choice of primary levels are discussed.

Acoustic Stimulation↗

PubMed1998

Modeling otoacoustic emission and hearing threshold fine structures.

A class of cochlear models which account for much of the characteristic variation with frequency of human otoacoustic emissions and hearing threshold microstructure is presented. The models are based upon wave reflections via distributed spatial cochlear inhomogeneities and tall and broad cochlear activity patterns, as suggested by Zweig and Shera [J. Acoust. Soc. Am. 98, 2018-2047 (1995)]. They successfully describe in particular the following features: (1) the characteristic quasiperiodic frequency variations (fine structures) of the hearing threshold, synchronous and click-evoked emissions, distortion-product emissions, and spontaneous emissions; (2) the relationships between these fine structures; and (3) the distortion product emission filter shape. All of the characteristic frequency spacings are approximately the same (0.4 bark) and are mainly determined by the phase behavior of the apical reflection function. The frequency spacings for spontaneous emissions and threshold microstructure are predicted to be the same, but some deviations from these values are predicted for synchronous and click-evoked and distortion-product emissions. The analysis of models is aided considerably by the use of the solutions of apical, and basal, moving solutions (basis functions) of the cochlear wave equation in the absence of inhomogeneities.

Acoustic Stimulation↗

PubMed1997

Spontaneous otoacoustic emission frequency is modulated by heartbeat.

Detailed analysis of spontaneous otoacoustic emissions (SOAEs) in human subjects revealed that all stable SOAEs sufficiently above the noise floor to permit appropriate analysis have sidebands at multiples of approximately 1 Hz. This is consistent with the hypothesis that SOAEs are modulated by heartbeat. Simultaneous measurement of the rate of blood flow to the thumb and the separation of the spectral sidebands demonstrated that they covary (r = 0.982, p < 5 x 10(-10)). An adaptive least-squares fit (LSF) paradigm was developed to facilitate the measurement of the instantaneous frequency and amplitude of the signals. A combination of traditional spectral analyses and new LSF analyses showed that the sideband generation stems from frequency modulation of the emissions. If there is any amplitude modulation correlated with the blood flow, it is below the noise floor of the analysis. The frequency of the emission was at a minimum when the blood flow was maximal. Examination of alternative mechanisms using computer simulations suggests that these changes stem from changes of 10-100 ppm in the mass of the basilar membrane.

Cochlea↗

PubMed1996

Temperature dependence of spontaneous otoacoustic emissions in the edible frog (Rana esculenta).

The change in frequency of individual emissions in the European edible frog (Rana esculenta) when the temperature of the frog is modified, is part of a complex pattern of interaction between spontaneous otoacoustic emissions. At high temperatures (above 24 degrees C) two emissions are always detected (e.g., one near 800 Hz and one near 1200 Hz). The higher-frequency emission is lower in level and has a wider bandwidth than the lower-frequency emission. It is also often asymmetric and sometimes breaks into two emissions when an external suppressor tone is applied. When the temperature is decreased, these emissions are reduced in frequency at a rate of 0.04 octave/degree C. The higher-frequency emission becomes narrower and taller, and the lower-frequency emissions becomes broader and less intense. At approximately 18 degrees C the lowest of these emissions (now between 600 and 700 Hz) disappears and is replaced by a new emission approximately 100 Hz lower in frequency. When the temperature is carefully controlled the two emissions can exist simultaneously. The lowest-frequency emission changes 0.015 degree C/octave suggesting that the mechanisms controlling the frequency of this emission may be different than those determining the frequencies of the other emissions. All but the lowest-frequency emissions are maximal in level and have minimal bandwidth when the frequency is close to 700 Hz, which is interpreted as evidence that these emissions are filtered by a temperature-independent process.

Acoustic Stimulation↗

PubMed1996

Relaxation dynamics of spontaneous otoacoustic emissions perturbed by external tones. III. Response to a single tone at multiple suppression levels.

The relaxation dynamics of spontaneous otoacoustic emissions (SOAEs) interacting with an external tone have been successfully described using a van der Pol limit cycle oscillator model [Murphy et al., J. Acoust. Soc. Am. 97, 3702-3710 (1995) and Murphy et al., J. Acoust. Soc. Am. 97, 3711-3720 (1995)]. Data were collected for an SOAE interacting with a single-frequency ipsilateral suppressor. Transitions between different suppressed states were achieved by adding or removing signal at the suppressor frequency. The relaxation dynamics of the van der Pol model provided a good fit to the data.

Humans↗

PubMed1995

Relaxation dynamics of spontaneous otoacoustic emissions perturbed by external tones. I. Response to pulsed single-tone suppressors.

The dynamic aspects of the suppression of spontaneous otoacoustic emissions by external tones are evaluated. A Van der Pol oscillator driven by an external tone is used as an interpretive model for data on the pulsed suppression of spontaneous emissions obtained from six female subjects. Typical results for both the onset of, and recovery from suppression yield 1/r1 (where -r1 is the negative linear component of the damping function) in the range of 2-25 ms. In accordance with the predictions of the model, (a) the relaxation time for the onset of suppression increases with the amount of suppression induced by the external tone, (b) the values of r1 and the amplitudes of the unsuppressed emissions exhibit an inverse correlation, (c) the values inferred for r1 are not significantly dependent on the frequency of the pulsed suppressor tone, and (d) the inferred r1 values are not significantly dependent upon the amount of suppression.

Adult↗

PubMed1995

Relaxation dynamics of spontaneous otoacoustic emissions perturbed by external tones. II. Suppression of interacting emissions.

The level of a spontaneous otoacoustic emission (SOAE) during recovery from suppression by an external tone sometimes exhibits a prominent overshoot before reaching its normal level. At the onset of suppression, a less prominent undershoot is sometimes observed before the emission level stabilizes. The overshoot and undershoot are described in terms of the variable amount suppression produced by a neighboring higher-frequency SOAE which is responding more slowly to the modulation of the external tone. The variation of the SOAE amplitude during pulsed suppression is modeled by a pair of Van der Pol limit-cycle oscillators with the primary oscillator linearly coupled to the displacement of the secondary high-frequency one. We have found relaxation time constants for the onset of suppression of the order of 4.5 and 7.4 ms for the primary and secondary SOAEs, respectively, and for the recovery from suppression 4.8 and 10.48 ms for the primary and secondary SOAEs, respectively. The same model is also successful in describing the release from suppression of the primary SOAE by the secondary SOAE when the latter is partially suppressed by the external tone. Aspirin administration reduces the magnitude of the overshoot by reducing the level of the higher-frequency SOAE and thereby eliminating the suppression of the lower-frequency one.

Acoustic Stimulation↗

PubMed1994

Correlation between amplitude and frequency fluctuations of spontaneous otoacoustic emissions.

The normalized cross-correlation function between the amplitude and frequency fluctuations of 11 spontaneous otoacoustic emissions was measured. A significant correlation was found in seven subjects. The correlation coefficient ranged from -0.37 to +0.65 across subjects. In four subjects, the amplitude fluctuation lagged the frequency fluctuation. The time lag was between 1.6 and 5.5 ms. The results were interpreted using a noise-perturbed limit-cycle oscillator with nonlinear (Duffing) stiffness as a model for a spontaneous emission. The data show that the relative increase of the nonlinear stiffness in this model was between -0.010 and +0.015. This indicates that an even-order nonlinear stiffness plays a minor role in the emission generator.

Acoustic Stimulation↗

PubMed1993

New off-line method for detecting spontaneous otoacoustic emissions in human subjects.

Spontaneous otoacoustic emissions were evaluated in 36 female and 40 male subjects. In agreement with the results of previous surveys, emissions were found to be more prevalent in female subjects and there was a tendency for the male subjects to have fewer emissions in their left ears. The digitization of five minute samples of ear canal signals, combined with sophisticated data analysis, produced a substantial reduction in the emission detection threshold. 588 emissions were detected in 72% of the subjects and 56% of the ears. Of the observed emissions, 18 could be identified with cubic distortion products of other emissions, and 11 could be identified as harmonic products (i.e., integral frequency multiples of other emissions). The large number of emissions detected (one subject had 32 in her right ear and 25 in her left) permitted evaluation of the pattern of separation of emissions. The average effective separation along the basilar membrane (according to the Greenwood frequency map) for adjacent emissions of all ears was 0.427 mm with interquartile values of 0.387 mm and 0.473 mm. The relationship between emission power, frequency, and full width at half maximum appears to be in agreement with the implications of a noise perturbed Van der Pol oscillator model of spontaneous emissions.

Adolescent↗

PubMed1991

Modeling synchronization and suppression of spontaneous otoacoustic emissions using Van der Pol oscillators: effects of aspirin administration.

Many of the aspects of the interaction of spontaneous otoacoustic emissions with external tones (suppression and synchronization) can be qualitatively simulated by the behavior of a single driven Van der Pol oscillator. Analytical and numerical investigations of a model of spontaneous otoacoustic emissions based on such an oscillator (with appropriate parametric changes in the nonlinear and negative damping components) lead to predictions of the nature of the changes in suppression and synchronization (frequency-locking) tuning curves when the levels of spontaneous otoacoustic emissions are modified. Observations of the suppression and synchronization of spontaneous otoacoustic emissions by external tones of different frequencies and levels were obtained while the levels of spontaneous emissions were altered by aspirin administration. Modeling an emission as a single Van der Pol oscillator qualitatively accounts for: (1) the reduction of the level of an external tone required to suppress the emission by a decibel amount equivalent to the level reduction induced by aspirin administration; (2) the broadening of the frequency-locking tuning curve of an emission whose level is reduced; and (3) the pulling of the emission frequency by an external tone. It does not account for: (1) the observed asymmetry in the slopes of the external-tone suppression curves (more gradual for frequencies of the suppressor tone higher, rather than lower, than that of the emission); and (2) the frequency pushing of the emission by an external tone.

Acoustic Stimulation↗

PubMed1991

Are spontaneous otoacoustic emissions generated by self-sustained cochlear oscillators?

Theoretical analyses supporting the assumption that spontaneous otoacoustic emissions (SOAEs) can be described as self-sustained oscillations (requiring a power source) are reviewed and extended. Spectral and statistical properties of spontaneous otoacoustic emissions are examined and shown to be consistent with this assumption. Several alternative models of spontaneous emissions (noise-driven saturating memoryless nonlinearity, noise-driven nonlinear-stiffness oscillator) are examined. Although some of these models are able to produce the types of statistical distributions of amplitude and displacement similar to those observed in the experimental data, this similarity is destroyed upon narrow-band filtering.

Animals↗

PubMed1989

Effects of ultrasonic flea collars on Ctenocephalides felis on cats.

Ultrasonic flea collars marketed by 2 companies were evaluated for their ability to reduce flea numbers on cats with experimentally induced flea (Ctenocephalides felis) infestations. The sound output of the collars was evaluated both before and after use to ensure that the collars were functional. Each brand was evaluated on 5 cats for a 7-day period. Collars generated peak frequencies of 40 kHz and 80 to 92 dB sound pressure level at 10 cm. An average of 98.6 and 97.4% of the fleas were still on the cats after treatment and control periods, respectively. The ultrasonic flea collars were ineffective in reducing flea numbers on these cats.

Animals↗

PubMed1989

Ventilatory response to sustained hypoxia: effect of methysergide and verapamil.

The biphasic nature of the ventilatory response to sustained (30 min) hypoxia may be explained by the central accumulation of a neurochemical with net inhibitory effect or, alternatively, peripheral chemoreceptor adaptation. To determine the role of serotonin (a putative central neuroinhibitor) and calcium ions (a putative peripheral neurotransmitter) in this response we measured VI and breathing pattern during 30 min of sustained isocapnic hypoxia in 11 normal adults 1 h after the double blind administration of either 2 mg methysergide (serotonin antagonist), 80 mg verapamil (calcium channel blocker), or placebo. Each subject was studied once a day for three days. After placebo the mean VI peaked at 12.5 +/- 3.4 L/min (176% of resting room air VI). VI then declined to a mean of 9.8 +/- 2.3 L/min (138% of room air VI) during 25 min of constant hypoxia. VI during hypoxia was always greater than VI during room air breathing (p less than 0.01), and peak VI during hypoxia was greater than final VI during hypoxia (p less than 0.05). The hypoxic response was not significantly affected by either pharmaceutical. At their maximal safe dosage in humans, methysergide and verapamil suggest no role for serotonin and calcium ions. Not excluded is the possibility that drug levels were inadequate to effect meaningful blockade.

Adult↗