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PubMed2004

[Individual postoperative refraction after cataract surgery -- a comparison of optical and acoustical biometry].

BACKGROUND: Optical biometry with the IOL-Master is an innovative technique that claims to improve the refractive results of cataract surgery compared to acoustical biometry. METHODS: In 140 consecutive non-selected eyes prior to cataract surgery firstly an optical biometry (IOL-Master, Zeiss, V.2.02) and secondly an ultrasound biometry (Sonomed) were carried out. Cataract surgery was performed using either a PMMA-IOL (n = 56) or an acrylic IOL (n = 84). The PMMA-IOL's were implanted in the capsular bag via a scleral tunnel. The acrylic-IOL's were implanted via a clear cornea incision in the capsular bag. The length of the globe was analysed and the deviations between the postoperative refraction after 3 month and the preoperative planned refraction were compared. RESULTS: The mean axial length difference between optical biometry and acoustical biometry was 0.19 mm in the PMMA-lens group and 0.16 mm in the acrylic-lens group. The deviation of postoperative refraction (spherical mean) from the planned refraction was 0.46 +/- 0.88 D in the PMMA-IOL group and 0.25 +/- 0.77 D in the acrylic IOL group when biometry was performed by ultrasonography. When optical biometry was performed the respective values were 1.15 +/- 0.83 D in the PMMA-IOL group and 0.84 +/- 0.75 D in the acrylic IOL group. The differences in mean postoperative refraction of optical and acoustical biometry can be compensated by adaptation of the A constants. The standard deviation of the difference between the postoperative refraction and the preoperatively planned refraction - that means the individual deviations between postoperative refraction and preoperatively planned refraction - were almost identical in optical and acoustical biometry. CONCLUSION: Optical biometry represents a significant simplification in the course of investigation prior to cataract surgery. The claim of optical biometry, however, to gain a higher precision and thus a significantly better prediction of individual postoperative refraction after cataract surgery is not yet fulfilled.

Acrylates↗
PubMed1998

Tips for preventing cerebrospinal fluid rhinorrhea after acoustic neurinoma surgery: technical note.

CSF rhinorrhea is a common complication of acoustic neurinoma surgery via the suboccipital route. In this paper we present our incidence of CSF rhinorrhea and our surgical techniques for reducing the risk of this post-surgical complication. Following removal of the acoustic neurinoma, the drilled posterior wall of the internal auditory canal is covered with bonewax, muscle or fat pieces, and fibrin-glue, while the previously reflected dura is sutured in place keeping the packing material in position. Bone chips removed during the craniectomy are then mixed with fibric glue and are used for a cranioplasty. Although we routinely perform aggressive drilling of internal auditory canal to facilitate total removal of the acoustic neurinoma, only 1 out of 94 consecutive cases (1%) showed postoperative CSF rhinorrhea. Since previous reports mention the rate of this complication following acoustic neurinoma surgery varies between 4% and 27%, we believe that our methods may be useful in helping reduce the incidence of postoperative rhinorrhea.

Journal Article↗
PubMed1993

Acoustic schwannoma presenting as acute posterior fossa hematoma: case report and review of the literature.

Acoustic schwannomas usually present with gradually progressive unilateral sensorineural hearing loss. As the tumor enlarges, symptoms and signs develop when the adjacent cranial nerves, cerebelhim, and/or brainstem become compressed. Rarely, acoustic tumors present with acute subarachnoid or intratumoral hemorrhage. Of the 12 cases of acoustic schwannoma with tumoral hemorrhage presented in the literature of which we are aware, this is the third such case of a patient presenting with spontaneous pure intratumoral hemorrhage and the first such case presenting with sudden multiple cranial nerve palsies, The purpose of this report is to increase the awareness of this rare form of presentation of acoustic schwannoma in the hope of achieving better preservation of cranial nerves.

Journal Article↗
PubMed2001

The vestibular evoked response to linear, alternating, acceleration pulses without acoustic masking as a parameter of vestibular function.

In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n = 400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs.

Animals↗
PubMed1985

The systematic use of semantic and acoustic processing by younger and older adults.

To examine age differences in semantic and acoustic processing, 80 older and 80 younger adults participated in an incidental learning study. The study compared free recall and semantic and acoustic cued recall performance after five orienting conditions. The younger adults performed better than the older adults, especially after acoustic orienting. Encoding specificity effects occurred at both age levels. The results indicated that both age groups performed better with semantic processing than acoustic processing, but that older adults relied on the semantic information far more than the younger adults.

Adult↗
PubMed2006

The influence of acoustic transmit parameters on the destruction of contrast microbubbles in vitro.

In this study, the destruction of the contrast agent Sonazoid (GE Healthcare, Oslo, Norway) was measured in vitro as a function of centre frequency (2-3 MHz), acoustic amplitude (0.66-1.6 MPa), pulse length (2-16 cycles) and PRF (0.5-8.0 kHz). Up to 82% of microbubbles were destroyed after exposure to a single 1.6 MPa acoustic pulse (16 cycles, 2.5 MHz and PRF of 1.0 kHz), while at a low amplitude of 0.66 MPa, fractional destruction increased gradually from 0 to 40% after exposure to 9 (identical) pulses. Fractional destruction increased from approximately 8 to 66% as pulse length was changed from 2 to 16 cycles following exposure to a single 2.5 MHz, 1.3 MPa pulse. As the PRF was increased from 0.5 to 8.0 kHz, shorter exposure time intervals (from 4.8 to 1.2 ms) were needed to achieve the same fractional destruction of 80%. Conversely, as the transmit frequency was increased from 2 to 3 MHz the fractional destruction decreased (by more than half within the first 3 pulses). The influence of changes in acoustic pressure and duty cycle on the destruction of Sonazoid microbubbles was highly statistically significant (p < or = 0.01) with a threshold around 0.67 MPa for a duty cycle of 0.0064. In conclusion, the fractional destruction increases with the duty cycle and the acoustic pressure amplitude and decreases with ultrasonic transmit frequency. Better understanding of the influence of the ultrasound transmit parameters on the destruction of contrast microbubbles should help improve existing contrast-assisted imaging modalities and may help develop new techniques for better use of contrast agents.

Contrast Media↗
PubMed2004

The percentage of the population exposed to harmful acoustic pollution levels resulting from vehicular traffic in the Hospital' area of Turin.

This paper presents the methodology and the main results of a study that has as its principal aim, the experimental identification the application and the quantification of the sustainable indicator 'Percentage of the population exposed to acoustic pollution levels' in the 'Hospital' area of Turin. The investigation of this indicator was prompted by the province of Turin's previous categorisation as 'Lead City' in the project 'Towards a support description at local the level--European Community Indicators'. Alongside, the process of experimenting, applying and quantifying the sustainable indicator--and as a logical fit with what was foreseen by the Italian normative regulation on protection against environmental acoustic pollution--the study supplies the base elements to analyse the environmental acoustic climate conditions in an important area of the city and defines the interaction tools that are the environmental indicators for the town council's future Acoustic Restoration Plan (PRA).

Automobiles↗
PubMed1989

Meningioma, meningeal hemangiopericytoma (angioblastic meningioma), peripheral hemangiopericytoma, and acoustic schwannoma. A comparative immunohistochemical study.

The relationship between meningeal hemangiopericytoma (angioblastic meningioma), meningiomas of meningothelial derivation, and peripheral hemangiopericytoma is controversial; and immunohistochemical studies have yielded conflicting results. Likewise, immunohistochemistry has been touted as a reliable means of differentiating fibrous meningioma from acoustic schwannoma. By the immunoperoxidase method, we studied 40 meningiomas (11 meningotheliomatous, four transitional, 11 fibrous, three secretory, four metaplastic, one xanthomatous, one papillary, four atypical, one malignant), five arachnoid granulations, 13 angioblastic meningiomas, nine peripheral hemangiopericytomas, and seven acoustic schwannomas. Antisera to vimentin, epithelial membrane antigen (EMA), keratin, S-100 protein, carcinoembryonic antigen (CEA), desmin, factor VIII, Ulex europeaus, and glial fibrillary acidic protein (GFAP) were utilized. All meningiomas and arachnoid granulations stained for vimentin and EMA; 15% and 12% of meningiomas were S-100 and keratin positive, respectively. The latter was noted primarily in areas of secretory (pseudopsammomatous) differentiation. In contrast, all angioblastic meningiomas stained for only vimentin. This profile of immunoreactivity was also seen in the peripheral hemangiopericytomas, with the exception of single cases that stained focally for EMA and S-100 protein, respectively. Acoustic schwannomas all stained positively for S-100 protein, vimentin, and were variably reactive for EMA, a pattern not distinct from meningioma. We conclude that (a) meningiomas express both epithelial and mesenchymal markers as do arachnoid granulations, (b) that angioblastic meningiomas demonstrate only mesenchymal markers, (c) that angioblastic meningiomas express identical markers to peripheral hemangiopericytoma and should thus be considered a variant thereof, (d) among meningiomas, CEA and keratin appear to be relatively specific markers for the "secretory" variant, and (e) because of overlap in S-100 and EMA reactivity, these markers are unreliable in differentiating meningioma from acoustic schwannoma.

Antibodies, Neoplasm↗
PubMedDate not supplied

Quantification of the relationship between crossed and uncrossed acoustic reflex amplitudes.

Acoustic reflex amplitude data were obtained for 92 subjects. Uncrossed (ipsilateral) and crossed (contralateral) acoustic reflex activity was measured simultaneously and computer averaged with specially constructed apparatus. For all subjects, amplitude was greater for uncrossed than crossed acoustic reflexes. The ratio of maximum uncrossed versus crossed reflex amplitude for young normal-hearing subjects ranged from 1.06 to 2.38, with an average of 1.50. This relationship was not significantly influenced by subject age, sensorineural hearing impairment, or mild abnormalities in acoustic immittance. Clinical investigation of the diagnostic application of the uncrossed versus crossed reflex amplitude ratio in central auditory nervous system pathology is suggested.

Adult↗
PubMedDate not supplied

Cortical activation response to acoustic echo planar scanner noise.

PURPOSE: Our goal was to determine the distribution of auditory and language cortex activation in response to acoustic echo planar scanner noise with functional MRI (fMRI). METHOD: Acoustic scanner noise and spoken text, reproduced on high output cassette tape, were separately delivered at equivalent intensities to six normal hearing adult volunteers through earphones during fMRI data acquisition. In nine other subjects, taped scanner noise was delivered in five successive iterations of the task to assess the consistency of cortical activation to the noise stimulus. Gyri of the auditory and language system were divided into 10 different subregions for analysis of cortical activation. The number of activated pixels and proportion of volunteers activating each cortical subregion were determined using a cross-correlation analysis. RESULTS: Cortical activation to taped acoustic scanner noise was present within the transverse temporal gyrus (primary auditory cortex) in all subjects, but activation was highly variable between subjects in auditory association and language relevant cortex. Auditory association cortex activation was seen in the planum polari, planum temporali, and middle temporal gyrus/superior temporal sulcus regions in one-half to two-thirds of the volunteers. There was no significant difference in the distribution of cortical activation within individual subjects across five successive iterations of the scanner noise task. Listening to spoken text consistently activated primary and association auditory cortex bilaterally as well as language relevant cortex in some cases. The mean number of activated pixels was significantly greater for text listening than acoustic scanner noise in auditory association and language relevant cortical subregions (p < 0.01), although the distribution of activity was similar between the two tasks. CONCLUSION: This preliminary investigation suggests that the complex sounds produced by the echo planar pulse sequence can activate relatively large regions of auditory and language cortex bilaterally, with the extent of activation outside the primary auditory cortex being variable between subjects. However, the distribution of activation within individual subjects was relatively constant across several iterations of the scanner noise stimulus.

Adult↗
PubMed2001

Acoustic divergence in two cryptic Hipposideros species: a role for social selection?

We present evidence that a relatively widespread and common bat from South East Asia comprises two morphologically cryptic but acoustically divergent species. A population of the bicoloured leaf-nosed bat (Hipposideros bicolor) from Peninsular Malaysia exhibits a bimodal distribution of echolocation call frequencies, with peaks in the frequency of maximum energy at ca. 131 and 142 kHz. The two phonic types are genetically distinct, with a cytochrome b sequence divergence of just under 7%. We consider the mechanisms by which acoustic divergence in these species might arise. Differences in call frequency are not likely to effect resource partitioning by detectable prey size or functional range. However, ecological segregation may be achieved by differences in microhabitat use; the 131kHz H. bicolor is characterized by significantly longer forearms, lower wing loading, a lower aspect ratio and a more rounded wingtip, features that are associated with greater manoeuvrability in flight that may enable it to forage in more cluttered environments relative to the 142 kHz phonic type. We suggest that acoustic divergence in these species is a consequence of social selection for a clear communication channel, which is mediated by the close link between the acoustic signal and receptor systems imposed by the highly specialized nature of the hipposiderid and rhinolophid echolocation system.

Animals↗
PubMed2002

Functional coupling of acoustic and chemical signals in the courtship behaviour of the male Drosophila melanogaster.

During courtship, the male Drosophila melanogaster sends signals to the female through two major sensory channels: chemical and acoustic. These signals are involved in the stimulation of the female to accept copulation. In order to determine the respective importance in the courtship of these signals, their production was controlled using genetical and surgical techniques. Males deprived of the ability to emit both signals are unable to mate, demonstrating that other (e.g. visual or tactile) signals are not sufficient to stimulate the female. If either acoustic or chemical signals are lacking, the courtship success is strongly reduced, the lack of the former having significantly more drastic effects. However, the accelerated matings of males observed with males bearing wild-type hydrocarbons compared with defective ones, whichever the modality of acoustic performance (wing vibration or playback), strongly support the role of cuticular compounds to stimulate females. We can conclude that among the possible factors involved in communication during courtship, acoustic and chemical signals may act in a synergistic way and not separately in D. melanogaster.

Animal Communication↗
PubMed2000

Acoustic wave propagation in structurally helical media.

A theoretical analysis is given of the acoustic wave propagation in periodically nonhomogeneous media made of a solid material whose stiffness tensor is uniformly rotating along a given axis. In the last years, such media have been studied theoretically as well as experimentally, in particular for what concerns sample preparation and possible applications. A detailed analysis of their acoustical properties is given here, based on fully analytic and simple propagation equations. For axial propagation: (i) the dispersion curves of media where the transversal field components and the longitudinal ones are not coupled show only one forbidden band, that gives selective Bragg diffraction; in the opposite case they show at least a second forbidden band, that involves the quasilongitudinal and one of the quasitransversal eigenmodes; (ii) in the first case (absence of coupling), the medium gives pure acoustical rotation for p< >lambda; (iii) in the presence of the coupling, regions of mode exchange between the longitudinal component and a transversal one are generally present. The cases of lossy media and of quasiaxial propagation are also considered, and the analogies between optical and acoustical properties discussed.

Journal Article↗
PubMed2002

Collisionless damping of nonlinear dust ion acoustic wave due to dust charge fluctuation.

A dissipation mechanism for the damping of the nonlinear dust ion acoustic wave in a collisionless dusty plasma consisting of nonthermal electrons, ions, and variable charge dust grains has been investigated. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust ion acoustic wave propagation to be described by the damped Korteweg-de Vries equation. Due to the presence of nonthermal electrons, the dust ion acoustic wave admits both positive and negative potential and it suffers less damping than the dust acoustic wave, which admits only negative potential.

Journal Article↗
PubMed2002

Oscillation mode conversion and energy confinement of acoustically agitated bubbles.

The acoustically agitated bubble oscillation in liquids that is considered to be related to the half-subharmonic acoustic bubble oscillations is discussed in terms of parametric decay instability. At the frequency of about 40 kHz, the half-subharmonic bubble oscillation mode should be a surface bubble oscillation that does not easily emit acoustic waves into water and confines acoustic energy from longitudinal waves. The half-subharmonic bubble oscillation is the dominant mode that leads to parametric decay instability of bubble oscillations.

Journal Article↗
PubMed2003

Anomalous acoustic reflection on a sliding interface or a shear band.

We study the reflection of an acoustic plane wave from a steadily sliding planar interface with velocity-strengthening friction or a shear band in a confined granular medium. The corresponding acoustic impedance is utterly different from that of the static interface. In particular, the system being open, the energy of an in-plane polarized wave is no longer conserved, the work of the external pulling force being partitioned between frictional dissipation and gain (of either sign) of coherent acoustic energy. Large values of the friction coefficient favor energy gain, while velocity strengthening tends to suppress it. An interface with infinite elastic contrast (one rigid medium) and v-independent (Coulomb) friction exhibits spontaneous acoustic emission, as already shown by Nosonovsky and Adams [Int. J. Eng. Sci. 39, 1257 (2001)]. But this pathology is cured by a moderately large V strengthening of friction, or, for systems with not too large friction coefficients, by any finite elastic contrast. We show that (i) positive gain should be observable for rough-on-flat multicontact interfaces and (ii) a sliding shear band in a granular medium should give rise to sizable reflection, which opens a promising possibility for the detection of shear localization.

Journal Article↗
PubMed2004

Dynamics of acoustically levitated disk samples.

The acoustic levitation force on disk samples and the dynamics of large water drops in a planar standing wave are studied by solving the acoustic scattering problem through incorporating the boundary element method. The dependence of levitation force amplitude on the equivalent radius R of disks deviates seriously from the R3 law predicted by King's theory, and a larger force can be obtained for thin disks. When the disk aspect ratio gamma is larger than a critical value gamma(*) ( approximately 1.9 ) and the disk radius a is smaller than the critical value a(*) (gamma) , the levitation force per unit volume of the sample will increase with the enlargement of the disk. The acoustic levitation force on thin-disk samples ( gamma</= gamma(*) ) can be formulated by the shape factor f(gamma,a) when a</= a(*) (gamma) . It is found experimentally that a necessary condition of the acoustic field for stable levitation of a large water drop is to adjust the reflector-emitter interval H slightly above the resonant interval H(n) . The simulation shows that the drop is flattened and the central parts of its top and bottom surface become concave with the increase of sound pressure level, which agrees with the experimental observation. The main frequencies of the shape oscillation under different sound pressures are slightly larger than the Rayleigh frequency because of the large shape deformation. The simulated translational frequencies of the vertical vibration under normal gravity condition agree with the theoretical analysis.

Journal Article↗
PubMed2004

Double-negative acoustic metamaterial.

We show here the existence of acoustic metamaterial, in which both the effective density and bulk modulus are simultaneously negative, in the true and strict sense of an effective medium. Our double-negative acoustic system is an acoustic analogue of Veselago's medium in electromagnetism, and shares many unique consequences, such as negative refractive index. The double negativity in acoustics is derived from low-frequency resonances, as in the case of electromagnetism, but the negative density and modulus are derived from a single resonance structure as distinct from electromagnetism in which the negative permeability and negative permittivity originates from different resonance mechanisms.

Journal Article↗