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 73 records · Page 4Linked to original sources
PubMed1988

Transmission acoustic microscopy of tissue sections (1 GHz). Histoacoustics and acoustic staining.

The acoustic microstructure of mouse small intestine has been studied with a transmission acoustic microscope working at 1 GHz and the influence of the histologic processing on the microacoustic pattern has been tested. Unstained thin sections provide pictures rich in details and highly contrasted. Gelatin has been used as hydrosoluble embedding medium and has been compared to paraffin. The former embedding procedure retained the viscoelastic properties of the specimen far more and provided the most detailed pictures. Osmiun tetroxide has been used to demonstrate acoustic staining.

Animals↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 1. Modelling the heart/thorax acoustic system.

A system model based on the simultaneous recording and analysis of the intracardiac and thoracic phonocardiograms to estimate the time-varying properties of the heart/thorax acoustic system of the dog is described. The presence of instrumental noise in the recording of intracardiac phonocardiograms is characterised, and it is demonstrated that its effect on the estimate of the transfer and coherence functions of the system can be quantified and corrected. Application of the model to study the spectral characteristics and the acoustic transmission properties of the mitral component M1 of the first heart sound and of the aortic component A2 of the second heart sound in the dog shows that the heart/thorax acoustic system acts like a bandpass filter having a higher attenuation for A2 than for M1. Between 20 and 100 Hz, the mean attenuation of M1 is 30 dB while that of A2 is 46 dB. Above 100 Hz, the attenuation slope is -12 dB per octave for M1 and -6 dB per octave for A2.

Animals↗
PubMed2001

Effect of nonadiabaticity of dust charge variation on dust acoustic waves: generation of dust acoustic shock waves.

The effect of nonadiabaticity of dust charge variation arising due to small nonzero values of tau(ch)/tau(d) has been studied where tau(ch) and tau(d) are the dust charging and dust hydrodynamical time scales on the nonlinear propagation of dust acoustic waves. Analytical investigation shows that the propagation of a small amplitude wave is governed by a Korteweg-de Vries (KdV) Burger equation. Notwithstanding the soliton decay, the "soliton mass" is conserved, but the dissipative term leads to the development of a noise tail. Nonadiabaticity generated dissipative effect causes the generation of a dust acoustic shock wave having oscillatory behavior on the downstream side. Numerical investigations reveal that the propagation of a large amplitude dust acoustic shock wave with dust density enhancement may occur only for Mach numbers lying between a minimum and a maximum value whose dependence on the dusty plasma parameters is presented.

Journal Article↗
PubMed2002

A method of determining acoustical physical constants for piezoelectric materials by line-focus-beam acoustic microscopy.

We developed a new method of determining acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of piezoelectric materials with high accuracy. This method acquires velocities of leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface, measured by line-focus-beam (LFB) acoustic microscopy, and bulk velocities of longitudinal and shear waves, measured with plane-wave transducers replacing the LFB device in the same system, together with the dielectric constants and density measured independently, for a small number of specimens. For LiNbO3 and LiTaO3 crystals, we demonstrated that we could accurately determine the constants by choosing proper propagation directions of LSAWs and bulk waves for three principal X-, Y-, and Z-cut specimens and one rotated Y-cut specimen [(104) plate for LiNbO3 and (012) plate for LiTaOa]. The accuracy is nearly the same as that for the constants determined only from the bulk wave velocities.

Journal Article↗
PubMed2001

Acoustic radiation of cylindrical elastic shells subjected to a point source: investigation in terms of helical acoustic rays.

The paper deals with the acoustic radiation of a cylindrical elastic shell with no internal loading surrounded by a fluid medium when its external surface is subjected to a point source. The problem is addressed via the use of the spatial Fourier transform. An expression is obtained for the radiated pressure that is evaluated for the far field using both the stationary phase method and the fast Fourier transform (FFT). The acoustic field calculated from the FFT is much more complicated than that obtained by using only the stationary phase method. In agreement with the geometrical theory of diffraction (GTD), alternative interpretations of the radiated field in terms of helical acoustic rays allows one to understand the reason for this result. The outstanding phenomenon underlined by the use of the FFT is the emergence of an infinite number of spatial dispersion curves associated with each leaky wave propagating in shells when excited by a point source.

Journal Article↗
PubMed1989

Comments on "Effects of Noise on Speech Production: Acoustic and Perceptual Analyses" [J. Acoust. Soc. Am. 84, 917-928 (1988)].

The effect of background noise on speech production is an important issue, both from the practical standpoint of developing speech recognition algorithms and from the theoretical standpoint of understanding how speech is tuned to the environment in which it is spoken. Summers et al. [J. Acoust. Soc. Am. 84, 917-928 (1988]) address this issue by experimentally manipulating the level of noise delivered through headphones to two talkers and making several kinds of acoustic measurements on the resulting speech. They indicate that they have replicated effects on amplitude, duration, and pitch and have found effects on spectral tilt and first-formant frequency (F1). The authors regard these acoustic changes as effects in themselves rather than as consequences of a change in vocal effort, and thus treat equally the change in spectral tilt and the change in F1. In fact, the change in spectral tilt is a well-documented and understood consequence of the change in the glottal waveform, which is known to occur with increased effort. The situation with F1 is less clear and is made difficult by measurement problems. The bias in linear predictive coding (LPC) techniques related to two of the other changes-fundamental frequency and spectral tilt-is discussed.

Humans↗
PubMed1992

[Changes in otoacoustic emissions with simultaneous acoustic stimulation of the contralateral ear in normal probands and patients with unilateral acoustic neurinoma].

Contralateral white noise alters the amplitude of transitory evoked otoacoustic emissions (TEOAE). 27 students between 20 and 28 years of age with no history of ear disease or dizziness were tested for normal hearing by pure tone audiogram. OAE evoked by nonlinear stimuli were measured with and without contralateral stimulation by 40, 50 and 60 dB white noise. The contralateral stimulation resulted in a statistically significant diminution of the amplitude of the TEOAE under contralateral acoustic stimulation. This diminution is probably caused by the effect of the crossed bundle of the efferent innervation on the outer hair cells resulting in altered vibratory properties of the basilar membrane. In patients with unilateral acoustic neuroma and measurable TEOAE a diminution of the amplitude of the TEOAE under contralateral sound stimulation was not found. The testing can easily be performed with the routine measurement of TEOAE. It could be useful in the diagnostic of lesions of the cerebello pontine angle and the brain stem.

Acoustic Stimulation↗
PubMed1996

Acoustic reflexes, auditory brainstem response, and MRI in the evaluation of acoustic neuromas.

Patient records were reviewed to determine whether persons with absent acoustic reflexes have a higher incidence of abnormal auditory brainstem response (ABR) results in the absence of a cerebellopontine angle (CPA) tumor than those with normal acoustic reflexes. Results showed patients with absent reflexes to have borderline or abnormal ABR results in 45.2% of the cases. Patients with normal reflexes had borderline or abnormal ABR results in 14.2% of the cases. Results indicate that magnetic resonance imaging is a more appropriate test for patients with absent reflexes, since ABR was often nondiagnostic for a CPA tumor in this group.

Evoked Potentials, Auditory, Brain Stem↗
PubMed2003

Diagnostic potential of acoustic startle reflex, acoustic blink reflex, and electro-oculography in progressive supranuclear palsy: a prospective study.

We carried out a prospective study to analyze the diagnostic potential of acoustic startle reflex (ASR), acoustic blink reflex (ABR) and electro-oculography (EOG) in early stages of atypical parkinsonian syndrome. The study was carried out in a consecutive series of 41 patients clinically diagnosed as atypical parkinsonism (mean time from first symptoms of 38 months and follow-up of 26 months). The three procedures were carried out immediately after the first clinical evaluation. ASR and ABR were elicited by auditory stimuli while the patient was attending to a simple reaction time task. Outcome measures were: ASR (absence/presence, latency), ABR (absence/presence, latency) and EOG (suggestive/not suggestive of progressive supranuclear palsy [PSP]). Final clinical diagnosis was carried out by two neurologists blind to the neurophysiological results. A study of diagnostic sensitivity and odds ratio (OR) calculation for the PSP diagnosis was carried out. Neurophysiological examination showed the following sensitivity/specificity (%) for the diagnosis of PSP: ASR: 100/89; ABR 85/89; EOG 100/72. OR values were: ASR: 0.011; ABR: 0.037; EOG: 0.038. The three tests taken simultaneously showed a sensitivity of 100% and a specificity of 95%. The three neurophysiological tests investigated provided sensitive and specific measures with predictor value in early stages of atypical parkinsonian syndrome.

Aged↗
PubMed2002

A critical review on the participation of inferior colliculus in acoustic-motor and acoustic-limbic networks involved in the expression of acute and kindled audiogenic seizures.

The main goal of this article is to review the key role that the inferior colliculus plays in the expression of acoustic-motor and acoustic-limbic integration involved, respectively, in acute and chronic audiogenic seizures. In order to put this in context, we will review the behavioral characterization of acute and chronic audiogenic seizures, neuroanatomical substrates, neurochemistry, neuropharmacology, electrophysiology, as well as the cellular and molecular mechanisms involved in their expression. Secondly, we will also correlate our results, collected from audiogenic seizures susceptible rats, before and after the genetic selection of our own audiogenic susceptible strain, and from those sensitized by lesions or drug microinjections, with those pertinent from the international literature. In brief, genetic or sensitized animals express acute audiogenic seizures as a wild running behavior preceding the onset of tonic-clonic seizures. The latter can have several presentations including opistotonus and fore- and hindlimb tonic hyperextensions, followed by clonic convulsions of fore- and hindlimbs. Chronic (kindled) audiogenic seizures change this behavioral expression, with similar patterns such as those present in temporal lobe epileptic seizures, intermingled with the original audiogenic seizure pattern, which is known to be dependent on brainstem networks.

Acoustic Stimulation↗
PubMed1989

Comments on "Acoustic Transfer Characteristics in Human Middle Ears Studied by a SQUID Magnetometer Method" [J. Acoust. Soc. Am. 82, 1646-1654 (1987)].

The study by Brenkman et al. [J. Acoust. Soc. Am. 82, 1646-1654 (1987)] of malleus umbo and anterior crus of stapes displacement in 14 human temporal bones shows a mean -7.3-dB/oct slope above 1.0 kHz for stapes displacement in response to a 80-dB SPL input at the eardrum. The slope they obtained for midfrequency (1.0-4.0 kHz) stapes displacement is significantly flatter than what was found previously [Gyo et al., Acta Otolaryngol. 103, 87-95 (1987); Gundersen, Prostheses in the Ossicular Chain (University Park, Baltimore, MD, 1971); Kringlebotn and Gundersen, J. Acoust. Soc. Am. 77, 159-164 (1985); Vlaming and Feenstra, Clin. Otolaryngol. 11, 353-363 (1986a)]; in these studies, stapes displacement rolled off at -12.0 to -14.9 dB/oct above 1.0 kHz. It appears that their mean midfrequency stapes displacement slope has been flattened by some unusual results in a small number of ears. Possible reasons for these results are discussed.

Acoustic Stimulation↗
PubMed1991

Acoustic microcavitation: its active and passive acoustic detection.

In this work acoustic microcavitation in water is studied primarily at 0.75 MHz and 1% duty cycle. To detect cavitation, two kinds of acoustic detectors are used. The first one is an unfocused, untuned 1-MHz receiver transducer that serves as a passive detector. The other one is a focused 30-MHz transducer that is used in pulse-echo mode and is called the active detector. Cavitation itself is brought about by a focused PZT-8 crystal driven in pulse mode. The active detector is arranged confocally with respect to the cavitation transducer. Both the interrogating pulse and the cavitation pulse arrive simultaneously at the common focus, which is the region of cavitation. With the test chamber filled with clean water, no cavitation is observed, even when the cavitation transducer is driven to give its peak output of 22 bar peak negative. Cavitation is, however, observed when polystyrene microparticles are added to the host water. Our view of how these smooth, spherical, monodispersed microparticles give rise to cavitation is described with some estimates. An attempt has been made to understand whether the presence of "streaming" affects the thresholds, and it has been found that the active detector field affects the cavitation process.

Acoustics↗
PubMed1992

The feasibility of using oto-acoustic emissions to monitor cochlear function during acoustic neuroma surgery.

The feasibility of using evoked oto-acoustic emission (EOAE) measurement for intra-operative monitoring of cochlear function was assessed during removal of an acoustic neuroma in a 53-year-old woman with normal hearing on the operated side prior to surgery. The high level of noise in the operating theatre was the only material problem encountered and this was not sufficient to prevent recording of identifiable waveforms. During manipulation of the brainstem, damage to the cochlea was indicated by an increase in EOAE latency and its eventual disappearance. A total hearing loss in the operated ear was revealed after surgery. Monitoring cochlear function with EOAEs is probably best considered at present as an adjunct to auditory brainstem response monitoring of the composite cochlea and eighth nerve, thus providing differential information.

Cochlea↗
PubMed1994

Facial and acoustic nerve preservation during excision of extracanalicular acoustic neuromas using the suboccipital approach.

The results are presented from a consecutive operative series of 62 acoustic neuromas in 60 patients following the introduction of improved neurophysiological monitoring techniques. Twenty-two patients had usable preoperative hearing. Thirty tumours were less than 2.5 cm diameter and 32 greater in size. Operation was via a 3-4-cm diameter retromastoid craniectomy. The internal auditory meatus was opened by an ENT surgeon (RM) using a drill and the facial nerve identified by stimulation. The tumour was then centrally evacuated by a neurosurgeon (MT/HC) using an ultrasonic aspirator, and the thin exterior part of the tumour carefully dissected off the nerves in or around the capsule with constant stimulation and monitoring of facial EMG, BSAEP and electrocochleography. A new type of stimulation probe has been designed and coupled to a stimulator/integrator/tone burst generator (SB) so that continuous immediate direct feedback to the surgeon is possible. A variable amplitude discriminator rejects baseline EMG (> 50 microV) and a gating circuit prevents stimulus artefact (during monopolar stimulation) from causing interference. By these means the VII nerve could be identified even when translucent and undefinable as a nerve bundle. Anatomical preservation was possible in 98% of VII nerves. Full facial function was present in 20 cases immediately postoperatively. Full delayed recovery occurred in 23 cases giving an eventual total in House Grade I of 69%. Seven other cases recovered to House Grade II. There was therefore 81% satisfactory facial nerve function. This percentage is exactly the same for larger and for smaller tumours. Anatomical preservation of the VIII nerve was achieved in 24/62 (39%) of the whole series and 11/16 (69%) of those with a hearing loss of < 50 dB. Functional preservation of hearing described as usable by the patient (< 65 dB) was achieved in 7/22 cases (32%), 3/13 (23%) in tumours < 2.5 cm and 4/9 (44%) in those > 2.5 cm diameter. Hearing preservation of < 50 dB in patients with preoperative hearing threshold < 50 dB and tumours of < 2.5 cm was 3/11 (27%). Monitoring by BSAEP and ECochG was technically unsatisfactory because the responses were affected by drilling and stimulation. Acoustic nerve preservation should be attempted in all cases with measurable hearing, regardless of tumour size.

Ear Neoplasms↗
PubMed2003

[Acoustic rhinometry--examination technique and discussion of the recommendation of the Committee for Standardisation of Acoustic Rhinometry, European Rhinologic Association ].

Acoustic rhinometry (AR) is a technique of nasal patency assessment, ever more frequently used in clinical practice. As yet, no generally accepted recommendations has been developed concerning the method of examination performing. In the paper the technique of examination is presented and the recommendations of the Committee for Standardisation of Acoustic Rhinometry, European Rhinologic Association are discussed.

Airway Resistance↗
PubMed1989

[What should be expected of oto-acoustic emissions? A critical analysis of clinical applications of oto-acoustic emissions].

The aim of this article is to carry out a critical analysis of the clinical applications of acoustic oto-emissions based on analysis of more than 1,000 adult and pediatric audiometric records. The principal technical and clinical properties of acoustic oto-emissions are described. The clinical value would seem to be very limited in adult audiology, whereas this examination would appear to be a reliable and non invasive method for screening in children at risk of cochlear deafness. In this respect, the investigation is principally limited by middle ear pathology and involvement of the central auditory pathways.

Acoustic Stimulation↗
PubMedDate not supplied

[Time factors in the acoustic reflex of intra-aural muscles and brain stem acoustic evoked potentials in workers with occupational hearing loss and normal and delayed speech discrimination].

Time characteristics of brain stem acoustic evoked potentials and acoustic reflex of the intra-aural muscles were measured in workers with occupational hypoacusis having normal and delayed capacity for speech discrimination. The findings provided evidence for inhibition of speech information analysis at the level of the brain stem and dissociation of interaction between the brain stem nuclei.

Audiometry↗