Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ACOUSTICS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93Linked to original sources
PubMed1984

Detection of middle ear effusion by acoustic reflectometry.

Existing diagnostic methods for otitis media with effusion are inadequate. We designed, built, and tested an acoustic reflectometer to overcome such inadequacies. The probe is placed at the entrance to the external auditory canal, whereupon a swept tone (1800 to 7000 Hz) is generated. The device records sound amplitude representing the sum of incident and reflected sound. This sum reaches a nadir at a frequency for which the quarter wave length corresponds to the distance from the microphone to the tympanic membrane; at this frequency reflected sound is maximally out of phase with incident sound. We measured this nadir (in decibels) and correlated the decrease in sound level at the nadir with the presence or absence of middle ear effusion. With a diagnosis confirmed by acoustic admittance and pneumatic otoscopy (n = 290), and using a breakpoint of 4.0 dB, the sensitivity was 94.4% and the specificity was 79.2%. Acoustic reflectometry can be portable, results are virtually instantaneous, and the method is reliable independent of age, crying, cerumen, and lack of cooperation from the child.

Acoustic Impedance Tests↗
PubMed2003

The use of ultrasound-stimulated acoustic emission in the monitoring of modulus changes with temperature.

It has been previously shown that the amplitude of the ultrasound-stimulated acoustic emission (USAE) signal is sensitive to tissue temperature and, therefore, can help detect it. Its amplitude, however, is sensitive to both acoustical and mechanical parameters, that at most frequencies have opposite effects due to temperature. In this paper, we explore the feasibility of using a frequency shift of the resonant peaks of the USAE signal for monitoring the tissue stiffness variation with temperature. In a numerical simulation, the variation of the frequency shift at different temperatures is shown. Then, in a series of experiments involving a gel phantom and porcine muscle tissue, the frequency shift variation is shown to follow the known stiffness changes due to temperature. It is also shown that this shift indicates reversible changes as well as the onset of thermal coagulative necrosis. The necrosis is marked by a monotonically increasing positive frequency shift. It was thus shown that the USAE spectrum peaks undergo a negative shift (or, downshift) when the stiffness decreases and a positive shift (or, upshift) when the stiffness increases. The experimental frequency shifted around a peak at 22.1-22.5 kHz within a range of -250 to 80 Hz and -200 to 250 Hz for the gel and muscle tissue for the temperatures of 25-70 and 30-70 degrees C, respectively. Simulation and ex vivo experimental results indicate that the USAE frequency shift method can help decouple the mechanical from the acoustical parameter dependence as well as detect the onset of thermal coagulative necrosis.

Acoustics↗
PubMed2003

Hysteresis in response of nonlinear bistable interface to continuously varying acoustic loading.

In many experimental situations it is an equation of the forced relaxator and not of the forced oscillator that describes a variation in the acoustic field of the interface width (i.e. of a characteristic distance between the surfaces composing the interface). The developed theory predicts that some types of the nonlinear relaxators (depending on the structure of the nonlinear interaction force between the surfaces) exhibit hysteresis in their response to continuous acoustic loading of first increasing and then decreasing amplitude. Nonlinear (unharmonic) variation of the interface width starts at threshold amplitude of the incident sinusoidal acoustic wave, which is higher than threshold amplitude for returning to sinusoidal motion. This dynamic hysteresis (and accompanying it bistability) are possible, in particular, if the dependence of the effective interaction force on the interface width admits two quasi-equilibrium positions of the interface (bistable interface) or if the force itself is hysteretic (hysteretic interface). These theoretical predictions are relevant to some recent experimental observations on the interaction of powerful ultrasonic fields with cracks.

Acoustics↗
PubMed1981

Ultrastructure of capillaries in acoustic neurilemmoma.

The microvasculature of normal acoustic nerve tissue and small intracanalicular and large extracanalicular neurilemmomas was analyzed by electron microscopy. The capillaries of normal acoustic nerve were nonfenestrated, but the microvasculature in nerve-sheath neoplasms was fenestrated. Hypertrophy and hyperplasia of endothelial cells were observed only in the small lesions. The proliferated and enlarge endothelial cells often partially occluded the vascular lumen and formed multichannel vascular lumina. Many fenestrae of capillaries were found in small neoplasms, but these were rarely identified in the large extracanalicular lesions. The gap junctions of endothelium in small nerve-sheath neoplasms were long, wavy, and convoluted, had no openings, and differed from those of large lesions in which the tight junctions were short, straight, and occasionally patent. Additionally, heavy vascularization and erythrocytes within basement membranes were observed only in large neurilemmomas. These ultrastructural features may constitute a basis for differences between large and small acoustic neurilemmomas noted in cerebrospinal fluid findings.

Capillaries↗
PubMed2001

Reflections of depression in acoustic measures of the patient's speech.

BACKGROUND: The literature on acoustic measures of voice in depression is reviewed. Authors have separated results derived from studies of automatic speech, such as counting or reading, from free speech. Free speech requires cognitive activity such as word finding and discourse planning in addition to the motor activity of automatic speech. Also, results have been less ambiguous if homogeneous groups of agitated or retarded depressed patients were examined. METHODS: These distinctions are applied to the results of a 12-week double-blind treatment trial that compared response to nortriptyline (25-100 mg/day) with sertraline (50-150 mg/day). Twelve male and ten female elderly depressed patients and an age-matched normal control group (n=19) were studied. Patients were divided into retarded or agitated groups on the basis of ratings. Results from measures of fluency (speech productivity and pausing) and prosody (emphasis and inflection) are described. RESULTS: Depressed patients showed less prosody than the normal subjects. Improvement in the retarded group was reflected in briefer pauses but not longer utterances. There was a trend in the agitated group for improvement to be reflected in the utterance but not the pause measure. CONCLUSIONS: Clinical impressions are substantially related to acoustic parameters. Temporal changes associated with depression appear to reflect the depressed state whereas prosodic features seem to reflect a depressed trait. Acoustic measures of the patient's speech may provide objective procedures to aid in the evaluation of depression. Limitations of the study are discussed.

Aged↗
PubMed2002

Influence of restraint and acute isolation on the selectivity of the adult zebra finch zenk gene response to acoustic stimuli.

Zebra finches respond to certain auditory stimuli with the activation of the immediate early gene zenk. It has been shown that the amount of sound-mediated zenk gene expression varies in the zebra finch caudomedial neostriatum (NCM), apparently correlated with stimulus type (conspecific>heterospecific>noise>tones) and familiarity. Here we tested the impact of two additional factors-song-specific acoustical properties and testing conditions-on the specificity of the sound-mediated zenk response, as assessed by in situ hybridization. A variant of a normal conspecific song was first produced by randomizing the spectral content while retaining the amplitude envelope ('song-enveloped noise'). This stimulus and related controls were presented to birds which were either free in cages or restrained in a stereotaxic instrument, after isolation either overnight or for only 1 h prior to testing. We confirmed prior results that unrestrained birds show a greater zenk response to normal conspecific song than to other acoustic stimuli. However, under restraint, birds showed little or no selectivity for conspecific song compared to matched stimuli lacking a song organization. Thus the specificity of the zenk response to song is not determined simply by the acoustic structure and familiarity of the stimulus. We conclude that the intrinsic selectivity of sensory responses measured in the CNS may be influenced by factors associated with attention, arousal or vigilance, and may be significantly altered by experimental conditions that involve physical restraint.

Acoustic Stimulation↗
PubMed2002

Introversion and individual differences in middle ear acoustic reflex function.

A growing body of psychophysiological evidence points to the possibility that individual differences in early auditory processing may contribute to social withdrawal and introverted tendencies. The present study assessed the response characteristics of the acoustic reflex arc of introverted-withdrawn and extraverted-sociable individuals. Introverts displayed a greater incidence of abnormal middle ear acoustic reflexes and lower acoustic reflex amplitudes than extraverts. These findings were strongest for stimuli presented at a frequency of 2000 Hz. Results are discussed in light of the controversy concerning the anatomic loci (peripheral vs. central neuronal activity) of the individual differences between introverts and extraverts in early auditory processing.

Adolescent↗
PubMed2000

Objective auscultation for traditional chinese medical diagnosis using novel acoustic parameters.

The goal of this work is to propose novel acoustic parameters of voice for the purpose of providing a quantitative analysis of auscultation in traditional Chinese medical diagnosis. There is rare amount of available literature related to this topic. Four novel acoustic parameters, the average number of zero-crossings, the variations in local peaks and valleys, the variations in first and second formant frequencies, and the spectral energy ratio, are presented to analyze and identify the characteristics among non-vacuity, qi-vacuity, and yin-vacuity subjects. Among these acoustic parameters, two temporal parameters, the average number of zero-crossings and the variations in local peaks and valleys, outperformed other parameters in classifying both non-vacuity and deficient subjects. The spectral energy ratio was adequate for the classification between qi-vacuity and yin-vacuity patients. This research is a first step in an ongoing effort to modernize the auscultation in traditional Chinese medical diagnosis.

Acoustics↗
PubMed1997

Expert opinion on the diagnosis of acoustic tumors.

Ideally, clinicians recommend diagnostic tests when the patient's risk of disease is sufficient to justify putting numerous similar patients through the morbidity required to diagnose disease in one patient. In the case of acoustic tumor diagnosis, there are few published data available to the clinician to help assess risk in an individual patient. The purpose of this study was to obtain information by an opinion poll of a group of experts. We used the Delphi method to poll clinicians trained at the House Ear Clinic. We asked these experts 20 questions related to acoustic tumor diagnosis. Some of the expert opinion presented herein is the only data related to acoustic tumor diagnosis available to clinicians. These data are a first step in elevation of decision-making for tumor diagnosis above the level of speculation. However, the experts' responses displayed a pattern of inaccuracy that limits the clinical application of their opinion. Exposing this pattern was instructive for identifying desirable features of protocols for diagnosing tumors. We recommend that protocols not depend on clinicians estimating probability of tumor. Instead, protocols may list specific findings, such as unilateral distortion on the telephone, to indicate, when present, that the risk of tumor is sufficient to order a diagnostic test.

Adult↗
PubMed1998

Auditory-nerve integrity after middle-fossa acoustic-tumor removal.

We sought to investigate the functional integrity of the auditory nerve in patients with postoperative hearing loss after middle cranial fossa acoustic-tumor removal in a case-series descriptive study. The study setting was a tertiary referral center, a private otologic practice. The study population comprised seven patients who underwent a middle-cranial-fossa approach for unilateral acoustic-tumor resection and sustained postoperative anacusis with an anatomically intact auditory nerve. Four were men and three women; they ranged in age from 30 to 60 years; all underwent surgery between 1990 and 1994 and agreed to return to the center to participate in the study during 1995. Diagnostic electrical promontory stimulation was used to determine the functional integrity of the auditory nerve. Our main outcome measures were the presence or absence of discrete tone perception, electrical threshold, maximum acceptable level and dynamic range, gap detection and temporal difference limen during electrical promontory stimulation. Three of the seven patients demonstrated positive responses to electrical promontory testing (e.g., discrete tone perception). All three were able to perform the gap-detection and temporal difference limen tests. None of the preoperative characteristics was related to performance on promontory stimulation testing. We conclude that the middle cranial fossa approach permits anatomic--and, in some cases, functional auditory-nerve preservation. These data suggest that auditory rehabilitation in some patients who sustain anacusis after the middle cranial fossa approach to acoustic tumors, as in neurofibromatosis 2, may be provided with cochlear implantation.

Adult↗
PubMed1998

Normative standards for nasal cross-sectional areas by race as measured by acoustic rhinometry.

Acoustic rhinometry evaluates the geometry of the nasal cavity with acoustic reflections and provides information about nasal cross-sectional area and nasal volume within a given distance. Variations in internal nasal diameters have attracted increased interest since the advent of endoscopic surgical techniques. Race is known to be one of the most important factors affecting the nasal structure. In this study, we evaluated 106 healthy adult volunteers with acoustic rhinometry to determine internal nasal diameters and volumes and obtained normative data for four racial/ethnic groups. The data were analyzed with regard to race, sex, height, and weight. All measurements were made before and after the application of a topical nasal decongestant so that the effects of the nasal cycle were eliminated by decongestion.

Acoustics↗
PubMed2003

Acoustic assessment of the voice quality before and after medialization thyroplasty using the titanium vocal fold medialization implant (TVFMI).

OBJECTIVE: This study was designed to objectify the vocal outcome in patients with unilateral vocal fold paralysis. Acoustic parameters were evaluated and compared to perceptual voice sound assessments before and after medialization thyroplasty using the titanium vocal fold medialization implant (TVFMI). STUDY DESIGN AND SETTING: Twenty-eight patients underwent external medialization thyroplasty using TVFMI. Prior to and after surgery videostroboscopy, perceptual voice evaluation and acoustic analysis based on the computerized "hoarseness diagram" were performed. RESULTS: In videostroboscopy, most patients showed an almost complete glottal closure after thyroplasty. The statistical analysis revealed a significant improvement in the perceptual voice parameters (p<0.001). The acoustic measurements could objectify the positive impact on the voice after thyroplasty (p< or =0.001). CONCLUSION: The results confirm that the TVFMI is an excellent and individually adjustable device for medialization thyroplasty. The "hoarseness diagram" allows the vocal outcome after surgery to be documented and objectified in an easy and reliable manner.

Adult↗
PubMed2000

Recurrence of acoustic neuroma after incomplete resection.

OBJECTIVE: To determine the risk of recurrent tumor in patients after incomplete resection of acoustic neuroma. STUDY DESIGN: Retrospective case review. SETTING: A tertiary referral center. PATIENTS: Thirty-nine patients were identified who underwent incomplete resection of acoustic neuroma between January 1988 and December 1993, and had a minimum follow-up of 3.5 years, at a mean of 6.2 years (range 3.5-10.2 years). INTERVENTION: Regular follow-up. using either computed axial tomography or magnetic resonance imaging yearly. MAIN OUTCOME MEASURES: Growth of residual tumor as determined by the increase in its greatest dimension on follow-up imaging studies and the necessity for additional treatment. RESULTS: Tumor regrowth occurred in 17 patients (44%). Ten patients (26%) required additional treatment during the follow-up period. CONCLUSION: This study suggests that incomplete resection of acoustic neuroma is associated with a significant risk of recurrent tumor requiring subsequent intervention.

Adult↗
PubMed2000

Hearing preservation in acoustic neuroma surgery: middle fossa versus retrosigmoid approach.

OBJECTIVE: To compare the results of the middle fossa approach with those of the retrosigmoid approach in acoustic neuroma hearing preservation surgery. STUDY DESIGN: Retrospective review. SETTING: Tertiary care facility. PATIENTS: Patients of the otology service with acoustic neuromas and useful hearing. Fifteen intracanalicular tumors were removed via a middle fossa approach and matched with 15 intracanalicular tumors removed via the retrosigmoid approach. Four additional patients with larger tumors were operated on via the middle fossa approach and matched with patients having similar tumors removed via the retrosigmoid approach. MAIN OUTCOME MEASURES: The 1994 Committee on Hearing and Equilibrium guidelines for the evaluation of hearing preservation in acoustic neuroma were applied. Facial nerve results were graded according to the House-Brackmann grading scale 3 months postoperatively. RESULTS: In the group operated on by the middle fossa approach, the average preoperative pure-tone threshold average (PTA) was 23 dB with a word recognition score (WRS) of 79%, and the postoperative PTA averaged 49 dB with a mean WRS of 56%. In the group operated on by the retrosigmoid approach, the mean preoperative PTA was 16 dB with a WRS of 95% and a postoperative PTA value of 62 dB and WRS of 51% (hearing preservation rate of 47%). The middle fossa patients had an average change in PTA of 19 dB and an average change in WRS of 20% (hearing preservation rate of 57%). Overall, the retrosigmoid patients had an average change in PTA of 42 dB and an average change in WRS of 40%. The average change in PTA for larger tumors removed via the middle fossa approach was 32 dB, whereas all matched retrosigmoid patients lost all hearing. The rate of cerebrospinal fluid leak and facial nerve outcomes were similar between the two groups. The retrosigmoid group had a higher rate of postoperative headache. CONCLUSIONS: Compared with the retrosigmoid approach, the middle fossa approach for hearing preservation surgery yields better hearing results for intracanalicular tumors and also has a lower incidence of postoperative headache.

Adult↗
PubMedDate not supplied

Acoustic neuroma presenting as sudden hearing loss.

Sudden hearing loss occurs as the initial symptom in 1 to 9 per cent of all acoustic neuromas. A case of an acoustic neuroma presenting with sudden hearing loss is described. In this case, the hearing thresholds returned to normal. To the authors' knowledge, this is the first case in which an acoustic neuroma presenting with sudden hearing loss exhibited a return to normal thresholds. This suggests that such tumors may have an initial reversible effect on hearing thresholds.

Acute Disease↗
PubMed2000

Predicting the acoustic response of a microbubble population for contrast imaging in medical ultrasound.

Although the behavior of a bubble in an acoustic field has been studied extensively, few theoretical treatments to date have been applied to simulate the acoustic response of a real population of variably sized microbubbles in a finite-width sound beam. In this paper, we present a modified Trilling equation for single bubble dynamics that has been solved numerically for different conditions. Radiated waveforms from a large number of such bubbles are combined, reflecting their size distribution and location and the shape of a real acoustic beam. The resulting time-domain pressure waveforms can be compared with those obtained experimentally. The dependence of second-harmonic radiation on incident focal amplitude at different frequencies is presented. This model is particularly suited to the study of interaction between a medical ultrasound beam and microbubble contrast agents in aqueous media.

Acoustics↗
PubMed2003

Bioeffects caused by changes in acoustic cavitation bubble density and cell concentration: a unified explanation based on cell-to-bubble ratio and blast radius.

Acoustic cavitation has been shown to load drugs, proteins and DNA into viable cells as a complex function of acoustic and nonacoustic parameters. To better understand and quantify this functionality, DU145 prostate cancer cell suspensions at different cell concentrations (2.5 x 10(5) to 4.0 x 10(7) cells/mL) were exposed to 500 kHz ultrasound (US) over a range of acoustic energy exposures (2 to 817 J/cm(2); peak negative pressures of 0.64 to 2.96 MPa; exposure times of 120 to 2000 ms) in the presence of different initial concentrations of Optison contrast agent bubbles (3.6 x 10(4) to 9.3 x 10(7) bubbles/mL). As determined by flow cytometry, molecular uptake of calcein and cell viability both increased with increasing cell density; viability decreased and uptake was unaffected by increasing initial contrast agent concentration. When normalized relative to the initial contrast agent concentration (e.g., cells killed per bubble), bioeffects increased with increasing cell density and decreased with increasing bubble concentration. These varying effects of contrast agent concentration and cell density were unified through an overall correlation with cell-to-bubble ratio. Additional analysis led to estimation of "blast radii" over which bubbles killed or permeabilized cells; these radii were as much as 3 to 90 times the bubble radius. Combined, these results suggest that extensive molecular uptake into cells at high viability occurs for low-energy exposure US applied at a high cell-to-bubble ratio.

Acoustics↗
PubMed2003

Polyacrylamide gel as an acoustic coupling medium for focused ultrasound therapy.

A hydrogel acoustic coupling medium was investigated as a practical alternative to water for clinical applications of focused ultrasound (US) therapy. Material characterization and functional testing of polyacrylamide gel couplers were performed. Acoustic, bulk and thermal properties were measured. Conical couplers were designed and fabricated to fit a 3.5-MHz, spherically concave transducer for functional tests, including Schlieren imaging, power efficiency measurements and in vivo hemostasis experiments. Polyacrylamide was shown to have favorable acoustic properties that varied linearly with acrylamide concentration from 10% to 20% weight in volume. Attenuation coefficient, sound speed and impedance ranged from 0.08 to 0.14 dB/cm at 1 MHz, 1546 to 1595 m/s and 1.58 to 1.68 Mrayl, respectively. An intraoperative in vivo hemostasis experiment in a sheep model demonstrated that the gel-coupled transducer was capable of inducing hemostasis in actively bleeding splenic and hepatic incisions. The results of this study show that polyacrylamide may be a promising coupling material for focused US therapy.

Acoustics↗