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At least 883 records · Page 49Linked to original sources
PubMed1994

Acoustic quantification: new diastolic indices of left ventricular function in hypertension correlation with Doppler echocardiography.

A study of left ventricular diastolic function in early hypertension was performed by the new method of acoustic quantification and Doppler echocardiography. A total of 23 untreated patients, five males and 18 females (mean age 53.52 +/- 9.10 years) with mild or moderate hypertension (160 +/- 13/98 +/- 10 mmHg) and 12 normal, age- and heart-rate-matched, control subjects were studied. All subjects showed normal left ventricular systolic function and wall thickness on two-dimensional echocardiography. The following indices were obtained. (1) Acoustic quantification (AQ): the time rate of area change in early diastole (dA/dt)E, in late diastole (dA/dt)A and their ratio (dA/dt)E/(dA/dt)A. (2) Doppler echocardiography: the early peak E, the late peak A flow velocities, their ratio E/A and deceleration E-F slope in early diastole. Measurements of left ventricular diastolic function by acoustic quantification showed, in the patient group, that the time rate of area change in early diastole (dA/dt)E was significantly lower (64.7 +/- 11.0 cm2/second versus 74.3 +/- 5.9 cm2/second; P < 0.01), the rate of area change in late diastole (dA/dt)A was not significantly higher (43.3 +/- 9.2 cm2/second versus 38.4 +/- 6.0 cm2/second; P > 0.05), and the ratio between the above indices (dA/dt)E/(dA/dt)A was significantly lower (1.55 +/- 0.42 versus 1.95 +/- 0.20; P < 0.01), compared with normal values. Doppler diastolic indices were all significantly abnormal in patients, in comparison with the values of the control group. Reduced left ventricular diastolic function was found in nine of 23 patients (39.1%) by the AQ method and eleven of 23 patients (47.8%) by Doppler echocardiography. Acoustic quantification was in agreement with Doppler echocardiography in identifying left ventricular diastolic dsyfunction in nine of 11 hypertensive patients with reduced Doppler diastolic values (82% sensitivity, 100% specificity). The correlation between the two methods showed that the time rate of area change in early diastole (dA/dt)E correlated well with the early peak E flow velocity (r = 0.59), the ratio between the time rates in early and late diastole (dA/dt)E/(dA/dt)A also correlated well with the Doppler E/A ratio (r = 0.89), while a poor correlation was found between the time rate of area change in late diastole (dA/dt)A and peak A flow velocity (r = 0.26). Thus abnormal diastolic filling of the left ventricle can be seen in the early stages of hypertension, even in the presence of normal systolic function and wall thickness, while acoustic quantification could be considered as a useful noninvasive modality for the early identification of left ventricular diastolic abnormalities.

Algorithms↗
PubMedDate not supplied

[A study of damaged acoustic biopotentials in guinea pigs following exposure to white noise].

62 guinea-pigs were treated twice exposed to white noise, 105 dB SPL, 20 to 20 000 cps for 40 minutes with a break of 24 hours in between. The cochlear microphonics (CM), the compound action potentials of the acoustic nerve (NAP) and the slow evoked potentials (SEP) were recorded. There were different degrees of damage to be seen in the acoustic biopotentials. The CM showed little damages only whereas the compound action potentials of the hearing nerve showed significant impairments in excitation and in adaptation. In the SEP excitation was decreased. From this, we may conclude that the CM must not be the only criterion for judging damages in the acoustic system after acoustic trauma. Furthermore we see that the central acoustic pathway is capable to compensate peripheric hearing damages within a short time. An additional exposure to noise does not necessarily add or cumulate the degrees of damage.

Action Potentials↗
PubMed1993

Attentional modulation of the phonetic significance of acoustic cues.

Four experiments addressing the role of attention in phonetic perception are reported. The first experiment shows that the relative importance of two cues to the voicing distinction changes when subjects must perform an arithmetic distractor task at the same time as identifying a speech stimulus. The contribution of voice onset time to phonetic labeling decreases when subjects are distracted, while that of FO onset frequency increases. The second experiment shows a similar pattern for two cues to the distinction between the vowels /i/ (as in "beat") and /I/ (as in "bit"). Under low attention conditions, formant pattern has a smaller effect on phonetic labeling while vowel duration has a larger effect. Together these experiments indicate that careful attention to speech perception is necessary for strong acoustic cues (voice-onset time and formant patterns) to achieve their full impact on phonetic labeling, while weaker acoustic cues (FO onset frequency and vowel duration) achieve their full impact on phonetic labeling without close attention. Experiment 3 shows that this pattern is obtained when the distractor task places little demand on verbal short-term memory. Experiment 4 provides a data set for testing formal models of the role of attention in speech perception. Attention is shown to influence the signal-to-noise ratio in the phonetic encoding of acoustic cues; the sustained phonetic contribution of weak cues without close attention stems from reduced competition from strong cues. This principle is instantiated in a network model in which the role of attention is to reduce noise in the phonetic encoding of acoustic cues. Implications of this work for understanding speech perception and general theories of the role of attention in perception are discussed.

Acoustic Stimulation↗
PubMed1986

Objective diagnosis of otitis media in early infancy by tympanometry and ipsilateral acoustic reflex thresholds.

Otitis media in early infancy carries a high risk of recurrent otitis media and prolonged middle ear effusion. To fulfill the need for objective diagnostic methods in this age group, we investigated susceptance tympanograms and ipsilateral acoustic reflex thresholds in infants younger than 5 months of age. Tympanometry and acoustic reflex thresholds were performed with an otoadmittance meter using a 660 Hz probe tone. Tympanograms were interpreted using quantitative measures. These findings were compared with independent otoscopic diagnoses in 67 ears with middle ear effusion and 69 ears that were effusion free. Diagnoses were confirmed by tympanocentesis when clinically indicated. There was excellent agreement among otoscopy, peak tympanogram susceptance, and ipsilateral acoustic reflex thresholds (kappa 0.82 to 0.86, agreement 91% to 93%). We conclude that susceptance tympanograms and ipsilateral acoustic reflex thresholds are accurate diagnostic tests for otitis media in infants younger than 5 months of age.

Acoustic Impedance Tests↗
PubMedDate not supplied

Preoperative speech and pure-tone audiometry in four types of patients with acoustic neuroma.

PURPOSE: The goal of this study was to compare pure-tone and speech audiometry in 4 groups of patients with confirmed unilateral acoustic neuroma in which auditory brainstem responses and transient-evoked otoacoustic emissions were either both normal, abnormal, or one of the tests was abnormal. MATERIAL AND METHODS: This study was realized during a preoperative assessment of 65 patients (29 men, 36 women) from 25 to 78 years of age suffering from unilateral acoustic neuroma. The assessment, preceded by tympanometry, included recordings of auditory brainstem responses, transient-evoked otoacoustic emissions, pure-tone audiometry, speech recognition thresholds, and speech discrimination. RESULTS: Some discrepancies between objective and behavioral test results were noticed. Subjects with no otoacoustic emissions but present auditory brainstem responses did not show any significant difference in their speech scores as compared with subjects with both auditory brainstem responses and otoacoustic emissions. CONCLUSIONS: In summary, this study showed that comparable audiometric findings in acoustic neuroma patients can be found regardless of the presence of transient otoacoustic emissions (TEOAEs). TEOAEs are a good screening tool and have been used, like auditory brainstem-evoked responses, as a predictive measure before hearing preservation procedures but cannot predict the audiogram or give information about speech perception. The findings confirm that even if auditory brainstem responses are an extremely useful diagnostic tool for identifying acoustic neuroma, this test provides only giving pieces of information regarding auditory abilities. Also, the pure-tone audiogram gives useful information but has to be used in conjunction with speech audiometry to get an accurate picture of the patient's true auditory abilities.

Acoustic Stimulation↗
PubMed1997

Frequency summation observed in the human acoustic reflex.

It is known that the threshold of an acoustically induced middle-ear-muscle (MEM) reflex can be lowered by the simultaneous presentation of a second tone (facilitator), which is presented to the ipsilateral or contralateral ear at a level below the acoustic reflex threshold (ART) of the facilitator itself (Sesterhenn and Breuninger, 1976; Blood and Greenberg, 1981). In the present study, a primary elicitor and a facilitator were presented to the ear contralateral to that used for measurement of the acoustic reflex (AR), and the effects of changing frequencies and sound levels of the facilitator were investigated in human subjects with normal ears. The sound levels of facilitators, which caused a significant reduction of ART for the primary elicitors (facilitation thresholds), showed an asymmetrical pattern as a function of frequency of the facilitators. The facilitation thresholds tended to be lower when a facilitator with a frequency lower than the frequency of the elicitor (1 kHz) was used. In addition, effects of the elicitor on the masked thresholds of the facilitator were examined to observe the possible interaction between elicitor and facilitator from the viewpoint of 'spread of excitation'. The underlying mechanism of summation effects of two tones are discussed based on the possible input mechanism involved in the acoustically induced MEM reflex are.

Acoustic Stimulation↗
PubMed1979

A systematic investigation of measurement parameters of acoustic-reflex adaptation.

Acoustic-reflex adaptation was assessed in 49 normal ears. Acoustic reflexes were elicited by the use of contralateral stimulation at four frequencies and five sensation levels. The results displayed the effects of stimulus frequency and sensation level on the amount of acoustic-reflex adaptation. Suggestions are presented for clinical procedures for obtaining contralateral acoustic reflex adaptation measures.

Acoustic Stimulation↗
PubMed2004

Combining acoustic and electrical speech processing: Iowa/Nucleus hybrid implant.

OBJECTIVES: In this paper we test the concept of combining electrical stimulation for high-frequency sound with acoustic hearing for low-frequency information in the same ear. In addition, we test whether residual hearing can be preserved when an electrode is placed up to 10 mm into the inner ear, and whether the site of electrical stimulation influences speech perception. MATERIAL AND METHODS: Nine post-lingual adults with severe high-frequency hearing impairment were recruited to participate in the study. A single-subject clinical trial design was employed. A unique six-channel cochlear implant was designed for this clinical trial. The intracochlear electrodes were either 6 or 10 mm in length based on a Nucleus CI-24 multichannel implant. Monosyllabic word understanding and consonant identification in a recorded sound-only condition were used to assess changes in speech perception. Follow-up was > 12 months. RESULTS: Acoustic hearing was preserved in all nine subjects. Preoperative monosyllabic word and sentence scores were unchanged in all subjects following implantation. A 30-40% improvement in consonant recognition occurred with the 10-mm electrode. The 10-mm electrode subjects were able to understand 83-90% of the monosyllabic words using the implant plus binaural hearing aids. Scores were more than doubled when compared to preoperative scores achieved with hearing aids only. CONCLUSIONS: The human ear has the capability to integrate both acoustic and high-frequency electrically processed speech information. Placement of a short 10-mm electrode does not appear to damage residual low-frequency inner ear hair cell function, interfere with the micro-mechanics of normal cochlear vibration or decrease residual speech perception. The improvement in speech recognition was due primarily to the increased perception of higher-frequency consonantal speech cues. Such a device can provide a substantial benefit in terms of speech understanding to those with severe high-frequency hearing loss, while still maintaining the benefits of the residual lower-frequency acoustic hearing. The position of the electrode and the site of frequency information within the cochlea are shown to be important factors in the success of such a device.

Acoustic Stimulation↗
PubMed1994

Identification of middle ear effusion by aural acoustic admittance and otoscopy.

The ability of aural acoustic immittance measures and validated pneumatic otoscopy to identify middle ear effusion (MEE) was determined for a group of children with chronic or recurrent otitis media. The measures were made immediately prior to surgery for placement of tympanostomy tubes, with the validating diagnosis of MEE made by the surgeons. Aural acoustic admittance measures were made by a certified and licensed clinical audiologist using an instrument that meets current standards and otoscopic examinations were made by a nurse practitioner validated for use of otoscopy in the identification of MEE. Logistic regression analyses were done to determine the ability of admittance variables, otoscopy, and their combination to discriminate between ears with and ears without MEE. Of the individual admittance variables, tympanometric width had the best performance. Otoscopy alone had good sensitivity but only fair specificity. Combining acoustic admittance data with the otoscopist's findings did not improve sensitivity greatly, but improved the specificity relative to that of the otoscopist. The criterion tympanometric width > 150 daPa or Ytm < 0.2, a criterion commonly used based on interim norms published in an appendix of ASHA guidelines for screening, had good sensitivity but very poor specificity in the group of children scheduled for surgery. Also, a comparison was made for tympanometric width measures from the children undergoing surgery with those from a group of children more representative of the general population. Three distributions were found; one for ears with MEE, one for ears with no MEE of children scheduled for otologic surgery and one for ears with no MEE from the group of children from the general population. The data illustrate the importance of the population characteristics on the test measure used and have implications for choosing test criteria. In addition, group estimates of performance of acoustic admittance variables were approximately the same when otoscopy was used as the gold standard for identification of MEE as when findings at surgery were used. However, when comparing the two diagnostic methods on a case-by-case basis, it was determined that the otoscopist's diagnosis disagreed with the diagnosis of the surgeons in over 21% of the ears.

Acoustic Impedance Tests↗
PubMed1989

Phenomenologic aspects of the acoustic reflex following noise exposure.

Thirty-seven normal hearing subjects were exposed to broadband noise for 2 hours at 90 dB (Lp). Measures of behavioral thresholds and acoustic reflex activity were completed prior to and following the noise exposure. As expected, temporary threshold shift was obtained at several different frequencies (1.0-6.0 kHz). In addition, reflex threshold shift occurred for all pure-tone elicitors under evaluation (0.5 to 4.0 kHz). The observed shift in acoustic reflex threshold at 0.5 kHz without a concomitant change in behavioral sensitivity reveals the limitation of utilizing behavioral threshold testing as the sole measure of cochlear disruption. Changes in acoustic reflex onset latency and magnitude were not observed after compensating for shifts in acoustic reflex threshold.

Acoustic Stimulation↗
PubMed2006

Dynamic mechanical response of elastic spherical inclusions to impulsive acoustic radiation force excitation.

Acoustic radiation force impulse imaging has been used clinically to study the dynamic response of lesions relative to their background material to focused, impulsive acoustic radiation force excitations through the generation of dynamic displacement field images. Dynamic displacement data are typically displayed as a set of parametric images, including displacement immediately after excitation, maximum displacement, time to peak displacement, and recovery time from peak displacement. To date, however, no definitive trends have been established between these parametric images and the tissues' mechanical properties. This work demonstrates that displacement magnitude, time to peak displacement, and recovery time are all inversely related to the Young's modulus in homogeneous elastic media. Experimentally, pulse repetition frequency during displacement tracking limits stiffness resolution using the time to peak displacement parameter. The excitation pulse duration also impacts the time to peak parameter, with longer pulses reducing the inertial effects present during impulsive excitations. Material density affects tissue dynamics, but is not expected to play a significant role in biological tissues. The presence of an elastic spherical inclusion in the imaged medium significantly alters the tissue dynamics in response to impulsive, focused acoustic radiation force excitations. Times to peak displacement for excitations within and outside an elastic inclusion are still indicative of local material stiffness; however, recovery times are altered due to the reflection and transmission of shear waves at the inclusion boundaries. These shear wave interactions cause stiffer inclusions to appear to be displaced longer than the more compliant background material. The magnitude of shear waves reflected at elastic lesion boundaries is dependent on the stiffness contrast between the inclusion and the background material, and the stiffness and size of the inclusion dictate when shear wave reflections within the lesion will interfere with one another. Jitter and bias associated with the ultrasonic displacement tracking also impact the estimation of a tissue's dynamic response to acoustic radiation force excitation.

Acoustics↗
PubMed1978

Threshold and growth of the acoustic reflex.

Measurements of the threshold and growth function of the acoustic reflex in man were made utilizing a signal-averaging technique. Pure tones (250, 500, 1000, 2000, and 4000 Hz) and broadband noise served as the contralateral stimuli delivered at intensity levels from the reflex threshold to 116 dB SPL. The acoustic conductance and susceptance components of admittance, at 220 and 660 Hz, were used to measure the reflex activity. The results are reported as changes in conductance, susceptance, and admittance in cgs mmho. The acoustic reflex thresholds were similar to those reported in other studies, with the 220-Hz probe yielding thresholds that averaged 3.5 dB higher than those obtained with the 660-Hz probe. Broadband noise and 1000-Hz stimuli produced the largest reflex magnitudes, while the smallest were observed with 250- and 4000-Hz signals. The dynamic ranges of the restricted growth functions were frequency dependent for pure tones and ranged from greater than 16 dB with 250 Hz to greater than 28 dB with 1000 Hz, while that for noise was greater than 50 dB. The first derivative of the best-fit third-degree polynomial was used to describe the slope characteristics of the growth functions, in which frequency and intensity effects were found. Relationships between the acoustic reflex and tympanometry were observed and are also discussed.

Acoustic Impedance Tests↗
PubMedDate not supplied

Acoustic reflex as a predictor of middle ear effusion.

The comparative efficacy of tympanometry and the acoustic reflex (threshold and supraliminal amplitude) in predicting the presence of fluid in the middle ear was studied just before myringotomy in 50 children (99 ears) prior to adenoidectomy. Impedance audiometry was carried out under a general anesthetic (ketamine and nitrous oxide) in 60%, and without anesthesia in 40% of the cases. The comparative efficacy of this test was assessed using objective criteria which were independent of the cut-off point between normal and abnormal groups. The prediction efficacy of acoustic reflex threshold and amplitude (Youden's index = 0.58) was superior to that of tympanometry peak amplitude and pressure (Youden's indexes = 0.29 and 0.36). The efficacy of the gradient was 0.41. Modifications due to anesthesia were not statistically significant for the whole group, but temporary abolition of the acoustic reflex at the start of anesthesia is probably related to the high percentage of false positives noted when the acoustic reflex is used alone in patients given a general anesthetic.

Acoustic Impedance Tests↗
PubMed1981

Diagnosis of acoustic neuroma.

The acquisition and application of new techniques in diagnostic screening have changed the approach to patients with suspected acoustic neuroma. In this paper, we review the extensive recent literature on acoustic tumors and present a critical analysis of the various diagnostic investigations. The older tests for cerebrospinal fluid protein, vestibular testing, and arteriography have been supplanted by modern audiometry with acoustic reflex testing, brain stem evoked responses, and computed tomography (CT). The various types of plain radiography are confirmed as an extremely useful screening modality. CT is insufficiently sensitive to serve as a primary screening procedure, but is a valuable confirmatory test. We propose a logical method of screening patients suspected of having an acoustic neuroma that can be applied by any practitioner in any clinical situation.

Adult↗
PubMed1980

The negative acoustic reflex in retrocochlear disorders.

The most frequent impedance abnormality of an acoustic tumor is an absent reflex. However, this finding also occurs with middle ear disorders and is therefore nonspecific. This study recorded the contralateral acoustic reflex of human subjects suspected of having an acoustic tumor. Many tumor subjects, by visual inspection of the impedance bridge balance meter, appeared to have an absent reflex. Most of these subjects, in fact, had small amplitude negative reflexes by offline analysis on an averaging computer. Recognition of these negative reflexes increases the specificity and sensitivity of the reflex test for acoustic tumors. We recommend reflex testing with averaging computer monitoring to ensure their recognition.

Acoustic Impedance Tests↗
PubMedDate not supplied

Comments on the acoustic-reflex response for bone-conducted signals.

Previous studies which have measured acoustic-reflex responses to bone-conducted signals have not effectively differentiated reflex responses from artifacts. A convenient method for identifying such artifacts was developed and employed on some acoustic-reflex measures for bone-conducted signals. The findings indicated that artifacts result when a frequently-used acoustic admittance meter (Grason-Stadler 1720B) and a conventional bone vibrator were used to measure reflex responses for tonal and noise-activating signals. It was suggested that the method be employed in future studies which investigate the acoustic reflex in response to bone-conducted signals.

Acoustic Impedance Tests↗
PubMed1982

Acoustic reflex amplitude. II. Effect of age-related auditory dysfunction.

Crossed and uncrossed acoustic reflex amplitude was measured in 99 adult subjects. Minor middle ear dysfunction profoundly influenced acoustic reflex amplitude. Reflex amplitude in subjects with minor impedance abnormality was, on the average, decreased by 68% in comparison to a matched control group. There was a complex relationship among age, sensorineural hearing loss, signal bandwidth and acoustic reflex amplitude. Sensorineural hearing loss differentially influenced acoustic reflex amplitude for young versus older subjects.

Acoustic Impedance Tests↗
PubMedDate not supplied

The effects on transient evoked otoacoustic emissions following changes in external auditory canal acoustic impedance.

The form of the transient evoked otoacoustic emission (TEOAE) generated by an acoustic impulse and recorded in the external auditory canal is dependent on many factors. Of these, the acoustic impedance of the external canal is possibly the most important. The effect of a change of acoustic impedance on the TEOAEs, induced by filling the external canal with helium or sulphur hexafluoride gas, is measured in a group of normal hearing subjects. The fundamental frequency of the TEOAEs is found to depend upon the density of the gas in the external canal. Compared to that of air (density 1.29 g/l) the frequency increased with helium (density 0.178 g/l) and decreased with sulphur hexafluoride (density 6.6 g/l). The amplitude of the TEOAEs was also found to depend upon the density of the gas in the canal, decreasing with helium and increasing with sulphur hexafluoride. These results suggest that the TEOAEs observed in the group of subjects tested arose within the external auditory canal. This does not imply that cochlear emissions are not generated in response to transient acoustic impulses, rather it implies that this study failed to show the presence of a cochlear-mediated emission.

Acoustic Impedance Tests↗