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At least 613 records · Page 34Linked to original sources
PubMed2004

Motor cortex inhibition induced by acoustic stimulation.

The influence of the brainstem motor system on cerebral motor areas may play an important role in motor control in health and disease. A new approach to investigate this interaction in man is combining acoustic stimulation activating the startle system with transcranial magnetic stimulation (TMS) over the motor cortex. However, it is unclear whether the inhibition of TMS responses following acoustic stimulation occurs at the level of the motor cortex through reticulo-cortical projections or subcortically, perhaps through reticulo-spinal projections. We compared the influence of acoustic stimulation on motor effects elicited by TMS over motor cortical areas to those evoked with subcortical electrical stimulation (SES) through depth electrodes in five patients treated with deep brain stimulation for Parkinson's disease. SES bypasses the motor cortex, demonstrating any interaction with acoustic stimuli at the subcortical level. EMG was recorded from the contralateral biceps brachii muscle. Acoustic stimulation was delivered binaurally through headphones and used as a conditioning stimulus at an interstimulus interval of 50 ms. When TMS was used as the test stimulus, the area and amplitude of the conditioned motor response was significantly inhibited (area: 57.5+/-12.9%, amplitude: 47.9+/-7.4%, as percentage of unconditioned response) whereas facilitation occurred with SES (area: 110.1+/-4.3%, amplitude: 116.9+/-6.9%). We conclude that a startle-evoked activation of reticulo-cortical projections transiently inhibits the motor cortex.

Acoustic Stimulation↗
PubMed2000

Pediatric acoustic schwannoma showing rapid regrowth with high proliferative activity.

Acoustic schwannoma is a slow-growing tumor and usually occurs in adult patients. We report a rare pediatric case of acoustic schwannoma with high proliferative potential. A 10-year-old boy was diagnosed as having a right cerebellopontine angle tumor. The tumor was subtotally resected. Histological examination revealed a typical acoustic schwannoma with a few mitotic figures. Chromosomal analysis showed no abnormality on the long arm of chromosome 22 associated with neurofibromatosis type 2. The lesion re-grew rapidly as an acoustic schwannoma, necessitating subtotal resection on three occasions and CyberKnife radiosurgery. The immunohistochemical MIB-1 staining indices of the specimens obtained at the first, second, and third operations were 2.3%, 4.6% and 14.7%, respectively. The immunohistochemical proliferative potential of acoustic schwannoma is discussed.

Biomarkers, Tumor↗
PubMed2001

Comparison of perceptional nasal obstruction with rhinomanometric and acoustic rhinometric assessment.

Perception of nasal stuffiness, together with rhinomanometric and acoustic rhinometric assessments were evaluated before and after nasal and/or sinus surgery in 50 Japanese adult patients. Nasal resistance on both expiration and inspiration correlated well with the patients' perceptions (P<0.05). Nasal volumes (0-4 cm and 0-7 cm) obtained from acoustic rhinometry measurements also correlated well with perception (P<0.05). No significant relationships were found between rhinomanometric and acoustic rhinometric results. Perceptional nasal obstruction, rhinomanometric and acoustic rhinometric results (except for the sectional areas at the I-notch) improved significantly after the operations. Rhinomanometry and acoustic rhinometry are valuable methods for assessing nasal stuffiness, but we must take account of the differences between the two methods.

Adult↗
PubMed2001

Combined intra-operative monitoring of hearing by means of auditory brainstem responses (ABR) and transtympanic electrocochleography (ECochG) during surgery of intra- and extrameatal acoustic neurinomas.

BACKGROUND: Although being established as a standard procedure in intra-operative monitoring in acoustic neurinoma surgery, auditory brainstem responses (ABR) represent a far-field technique bearing some technical limitations. This prospective study was designed to evaluate electrocochleography (ECochG) as a supplementary tool for hearing preservation. METHOD: 84 patients with unilateral intra-/extrameatal acoustic neurinomas (extrameatal diameter: 5-55 mm) preserving serviceable hearing, were operated on using a combined (neuro-/otosurgical) suboccipital approach. ECochG was recorded simultaneously to ABR following transtympanic insertion of a steel needle electrode into the promontory under otoscopic view. FINDINGS: Serviceable hearing (Class 1-3 according to Gardner/Robertson) was preserved in 43 out of 84 patients (51.2%), of whom 40 showed both ECochG and ABR being preserved. All 24 patients with loss of both modalities became deaf. Hearing preservation was observed in 4 out of 12 patients with preserved ECochG but loss of ABR (waves III-V). The reverse was observed in 2 cases with postoperative deafness. While both ECochG and ABR amplitudes were significantly correlated with pre- and postoperative hearing, latencies of ECochG summating (SP) and action potential (AP) proved to be more reliable indicators for preserved hearing than ABR (peak I/III/V) latencies. The predictive value of baseline ABR amplitudes for postoperative hearing, however, was superior to ECochG parameters. Only in large neurinomas (extrameatal diameter: >2 cm) tumour size was found to be a significant predictor for the preservation of hearing. Apart from three cases with postoperative otoliquorrhea and one further case presenting with local bleeding within the external acoustic meatus, no side effects were observed. CONCLUSIONS: In combination with ABR monitoring, ECochG proved to be a useful supplementary tool for hearing preservation in acoustic neurinoma surgery. It is particularly helpful during electrocautery and drilling, since no averaging is required. Special applications are: (1) small tumours with good serviceable hearing; (2) and/or a large intrameatal portion; (3) cases with lost or endangered contralateral hearing (e.g. bilateral acoustic neurinomas), when the preservation of poor or even non-functional hearing is desirable.

Adult↗
PubMed2000

Novel approach to acoustical voice analysis using artificial neural networks.

Perceptual rating scales are widely used for the assessment of voice quality. These ratings may be influenced by the individual experience of the listener. Thus, researchers have turned to acoustical measures which may eventually correlate with voice quality. In this study we tested whether multivariate statistics, combined with artificial neural networks, could identify patterns of acoustic voice parameters corresponding to a widely used perceptual rating scale. In a multicenter study with 31 raters, voice samples of 117 individuals with or without voice disorders were perceptually rated. The RBH index, consisting of a 4-point scale of roughness, breathiness, and hoarseness, was used. Voice samples were then analyzed with an acoustical feature extraction and classified using amultivariate regression tree analysis with the perceptual ratings as a priori information. Artificial neural networks were trained to selected acoustic parameters having high "relative importance" in the regression trees. Mean classification accuracies were around 30% with topographic feature maps (trained with Learning Vector Quantization algorithm) and 65-85% with feedforward networks (trained with RProp algorithm). Based on the best-fitting results with feedforward networks, a classification system (computer program) consisting of 50 simultaneous working networks was developed. Using this program, the classification matched 40% of the a prori values in both R and B domains. In 65% they matched at least in one domain. These accuracies are within the range reported by other authors using artificial neural networks in biology and clinical medicine. Thus, the results encourage further research of feedforward networks for acoustic voice analysis.

Humans↗
PubMed2004

Characterization of vibration and acoustic noise in a gradient-coil insert.

High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.

Acoustics↗
PubMed2006

An in-vitro test set-up for evaluation of a voice-producing element under physiologic acoustic conditions.

To improve the voice quality of laryngectomised patients, a voice-producing element has been developed. Prior to in vivo testing we constructed and validated an in-vitro test set-up, consisting of a physical model of the subglottal tract and three physical models of the vocal tract, for the vowels /a/, /i/ and /u/ to evaluate the voice-producing element under physiologic acoustic conditions. To meet acoustic conditions described in the literature, we determined the appropriate dimensions of these physical models, using a numerical model of the pressure perturbation in rigid tubes. The numerical model showed that an acoustic equivalent of the subglottal tract could be obtained with a three-tube system and an end impedance. Vocal tract models could be constructed using two- and four-resonator tubes. The physical models were built and successfully validated according to the human acoustic properties. The developed in-vitro set-up can now be applied to test voice-producing elements or vocal fold models under physiologic acoustic conditions.

Acoustics↗
PubMed1986

Fetal acoustic stimulation testing. II. A randomized clinical comparison with the nonstress test.

Antepartum fetal heart rate testing, specifically the nonstress test, is of accepted value in the antenatal surveillance of high-risk pregnancies. Fetal rest-activity cycles coupled with arbitrary test intervals appear to lead to falsely nonreactive tests. Methods to alter fetal behavioral states have not been uniformly successful. A retrospective analysis of the adjunctive use of acoustic stimulation at our institution demonstrated a 50% reduction in the number of nonreactive tests. Consequently a prospective randomized clinical trial was undertaken to compare the standard nonstress test with the fetal acoustic stimulation test. Those patients randomized to the fetal acoustic stimulation test underwent transabdominal acoustic stimulation with a Model 5C electronic artificial larynx. The incidence of nonreactive tests was 14% in the control group and 9% in the study group (chi 2 = 11.09, p = 0.004). A significant reduction in testing time was also observed. The fetal acoustic stimulation test offers advantages over the traditional nonstress test by lowering the incidence of nonreactive tests and reducing testing time.

Acoustic Stimulation↗
PubMed1990

Fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition.

Fetal acoustic stimulation has recently received much attention in the literature. This study evaluates fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition. The study group consisted of 201 patients, approximately 60% of whom had complicated pregnancies. All were in the latent phase of labor with singleton, vertex-presenting fetuses. Gestational age ranged from 37 to 43 weeks. Fourteen of the 201 fetuses (7%) showed a nonreactive response to fetal acoustic stimulation and those fetuses were at significantly greater risk of initial and subsequent abnormal fetal heart rate patterns, meconium staining, and cesarean delivery because of fetal distress and Apgar scores less than 7 at both 1 and 5 minutes. Transient fetal heart rate decelerations after a reactive response occurred in 25% of patients; however, fetal outcome was not worse in this group. A reactive response to fetal acoustic stimulation was associated with high specificity and negative predictive values. Therefore we conclude that fetal acoustic stimulation in the early intraprtum period may discriminate the compromised from the noncompromised fetus.

Acoustic Stimulation↗
PubMed1980

Acoustic priming and kanamycin-induced chochlear damage.

The cochleae from 3 lines of mice, selectively bred for differential susceptibility to priming-induced audiogenic seizures, were examined following acoustic priming and retest or kanamycin treatment, and the degree of cochlear damage was assessed. After 60 sec of acoustic priming, animals from the high and unselected lines which had subsequently developed audiogenic seizure susceptibility exhibited severe cochlear damage limited to the outer hair cells. Low line mice, which had been selected for resistance to acoustic priming-induced audiogenic seizures and were not seizure susceptible, exhibited no cochlear pathology following acoustic priming. Following kanamycin treatment, all 3 lines developed subsequent audiogenic seizure susceptibility. Histological examination of cochleae from mice so treated revealed a pattern of damage similar to that caused by acoustic priming, except that the cochleae of priming-induced audiogenic seizure resistant low line mice revealed a significant amount of outer hair cell damage. The results are discussed with respect to the physiological mechanism underlying a selectively bred behavioral phenotype in terms of a possible instance of damage/disuse-supersensitivity in the central nervous system.

Acoustic Stimulation↗
PubMed1993

NMDA and non-NMDA antagonists infused into the nucleus reticularis pontis caudalis depress the acoustic startle reflex.

The neural pathway that mediates the acoustic startle reflex has been proposed; however, the pharmacology underlying this reflex is less well known. The present study examined the role of excitatory amino acid receptors at the level of the nucleus reticularis pontis caudalis, a brainstem nucleus obligatory for the whole body startle reflex and implicated as the locus where extrinsic systems such as the amygdala may act to modulate acoustic startle. Twenty-nine rats, chronically implanted with bilateral cannulae aimed at the nucleus reticularis pontis caudalis, were tested to assess the effects of gamma-D-glutamylglycine (DGG), DL-2-amino-5-phosphonopentanoic acid (AP5), and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on the amplitude of the acoustic startle reflex. Local infusion of each of the 3 compounds significantly reduced startle amplitude by as much as 70-80%. AP5 and CNQX attenuated startle over a dose range which indicated that the reticularis pontis caudalis may be much more sensitive to these compounds than other nuclei along the primary startle pathway. These results suggest that, at the level of the nucleus reticularis pontis caudalis, an excitatory amino acid neurotransmitter may mediate acoustic startle, and that both NMDA and non-NMDA receptor subtypes may be important for the expression of the acoustic startle reflex.

2-Amino-5-phosphonovalerate↗
PubMed1993

Electrolytic and ibotenic acid lesions of the medial subnucleus of the medial geniculate prevent the acquisition of classically conditioned heart rate to a single acoustic stimulus in rabbits.

The present study examined the role of the medial subnucleus of the medial geniculate (mMG) in classical heart rate (HR) conditioning to a single acoustic conditioned stimulus (CS) in rabbits. Previous electrophysiological and neuroanatomical studies have implicated the mMG as a potential site of plasticity in forming the HR conditioned response (CR) to acoustic stimuli. In addition, several studies have found that bilateral lesions of the rabbit mMG prevent differential conditioning to acoustic stimuli, however animals still exhibit a significant bradycardiac response to the tones. In order to determine if the residual bradycardia seen in differential conditioning studies was due to learned responses or non-associative effects, rabbits with either bilateral electrolytic or ibotenic acid lesions of mMG, and animals with lesions outside of mMG (lesion control), were subjected to one session of single tone Pavlovian conditioning. In this paradigm, an acoustic CS was paired with an aversive unconditioned stimulus (US) in the conditioning groups, and in a pseudoconditioning group the CS and US were unpaired. The results suggest that bilateral lesions of mMG prevent the acquisition of the HR CR relative to control lesioned animals. The results also suggest that cells intrinsic to mMG are involved in conditioned bradycardia to a single tone, as well as in the discrimination between two tones, as reported previously. The lesion effects upon CRs are discussed with respect to other areas in the acoustic thalamus.

Acoustic Stimulation↗
PubMed1982

Changes in the blink responses to combined trigeminal, acoustic and visual repetitive stimulation, studied in the human subject.

Habituation of blink reflexes as measured by amplitude decrement in the orbicularis oculi EMG was examined in 9 human subjects using combinations of repetitive electric stimuli to the bridge of the nose (trigeminal stim.), short clicks (acoustic stim.), and flashes (visual stim.). With trains of paired stimuli, both homogeneous and mixed, habituation was increased when the two stimuli were separated by 250 msec but was decreased when the interval was 30 (50) msec, as compared to single stimulus trains of identical repetition rate. Following acoustic or visual prehabituation the habituation to trigeminal stimuli was enhanced. This "transfer of habituation' was also obtained with acoustic before visual stimuli and vice versa. Regarding dishabituation, interposition of single extrastimuli, for example visual or acoustic within repeated trigeminal stimulation, was more effective than a simple pause by omitting one electric pulse. The results suggest the existence of a pool of interneurones that is that the common final relay for the blink relfex afferents from the trigeminal, acoustic and visual input.

Acoustic Stimulation↗
PubMed1989

Spinal vs. supraspinal sites of action of the alpha 2-adrenergic agonists clonidine and ST-91 on the acoustic startle reflex.

Previous work has shown that stimulation of alpha 2-adrenergic receptors depresses the startle responses in rats. The present study suggests that this depressant effect involves supraspinal rather than spinal alpha 2-adrenergic receptors because intraventricular but not intrathecal infusion of the hydrophilic alpha 2-adrenergic agonist ST-91 depressed the acoustic startle reflex. To determine the point in the acoustic startle pathway where alpha 2-adrenergic receptor activation might ultimately alter neural transmission, startle responses were elicited electrically from different points along the acoustic startle pathway after systemic administration of clonidine. Clonidine depressed acoustically-elicited startle and startle elicited by electrical stimulation of the ventral cochlear nucleus to a comparable magnitude and over a similar time course. It also partially depressed startle elicited by electrical stimulation of the nucleus reticularis pontis caudalis (RPC). Taken together, these data suggest that alpha 2-adrenergic stimulation depresses startle by acting on supraspinal receptors, but that this effect is ultimately expressed, at least in part, by actions at both spinal and brainstem levels of the acoustic startle response pathway. The results are compared to other drugs known to affect the startle reflex.

Acoustic Stimulation↗
PubMed1995

Modulation of electrically elicited blink reflex components by visual and acoustic prestimuli in man.

The effects of a prestimulus on the electrically elicited blink reflex components were investigated in 20 healthy subjects. In the first group of 10 subjects (warned group), electric shocks were delivered in isolation or preceded, at an interstimulus interval (ISI) of 0.1 s, 1 s, or 10 s, by a visual or acoustic warning stimulus. In the second group of 10 subjects (unwarned group), the electric shocks were delivered either in isolation or preceded, at the same ISI, by visual or acoustic stimuli having no warning value. The modulation of the three blink reflex components was then analysed. Compared to the baseline condition, the R1 oligosynaptic component was enhanced at 0.1 s and 1 s ISI, in the warned group with the visual prestimulus, but only at 0.1 s after a visual and acoustic prestimulus in the unwarned group. On the contrary, the polysynaptic responses showed a different course: R2 was significantly reduced at the 0.1 s interval in the warned group with both the prestimuli, and only with the visual prestimulus in the unwarned group. The R3 was inhibited at all three intervals with the visual prestimulus, and at the 0.1 s and 1 s with the acoustic one in the warned group, and only at 0.1 s in the unwarned group, both after visual and acoustic prestimuli. The decrement in R2 and R3 observed with the shortest interval was probably related to the prepulse inhibition of startle reflex. Furthermore, only R3 was still inhibited at longer intervals, when the sustained processes of attention may have influenced this component. Perhaps this combination of events represents, in the warned group, the best preparation for voluntary reflex reaction.

Acoustic Stimulation↗
PubMed1986

Acoustic emission as a measure of exposure of suspended cells in vitro.

Cell viability, survival, and growth of C1300 mouse neuroblastoma cells were assayed by trypan blue dye exclusion, clonogenesis, and culturing, respectively, after exposure in suspension to therapeutic levels of ultrasound (1 MHz; continuous wave; spatial peak intensity 0.9, 1.7, and 2.6 W/cm2; 5 min at 37 degrees C). Acoustic emission from the cavitating cell suspensions was recorded as the rms value of the half-harmonic and noise components combined. Cell viability and survival appeared better correlated with acoustic emission than with spatial peak intensity, implying that acoustic emission may provide a more direct measure of insult to the cells in a cavitating field than the incident intensity. Biological assay results of growth were well correlated with spatial peak intensity but not with acoustic emission levels, which seems to imply that for this end point incident intensity is a more directly interacting parameter than cavitational activity, provided however that the latter is present. Further refinement of the technique for measuring acoustic emission from cell suspensions should permit separate measurements of the half-harmonic and noise components. When thus refined, it may provide the means to demonstrate cavitational action without resorting to additional experiments to suppress cavitation.

Acoustics↗
PubMed1991

Prediction of in situ exposure to ultrasound: an acoustical attenuation method.

The prediction of the acoustic levels occurring in a patient during ultrasound examination is important for the assessment of equipment safety. While considerable effort has been devoted to theoretical methods of predicting exposure levels, there is a need to develop simple experimental methods which are universally applicable to the wide range of ultrasonic fields generated by medical ultrasonic equipment. This article outlines a number of methods that have been proposed and explores in detail a new experimental method based on the use of acoustical attenuators, made of low-density polyethylene, which are placed in the ultrasound beam between the transducer and the measuring hydrophone. Measurements of important acoustical quantities have been made using a measurement system based on a multielement hydrophone and comparisons made between this new method and other methods such as electrical attenuation and linear derating theory. The acoustical attenuation technique has been systematically studied, and results are compared with reference levels obtained using tissue-mimicking material. A procedure involving making measurements with the attenuator placed first at the face of the transducer and then at the hydrophone has been developed. By taking the mean value of these two measurements, it has been shown that this new method can simulate within +/- 10% the acoustic levels obtained using the reference. It is concluded that it could be the basis of a universally applicable method.

Absorption↗
PubMed1995

A survey of the acoustic outputs of diagnostic ultrasound equipment in current clinical use.

Surveys published up to 1991 have highlighted a steady increase in the acoustic outputs from diagnostic ultrasound equipment. Since 1991 we have made measurements of the maximum peak negative pressure (p-) and spatial peak temporal average intensity (ISPTA) produced by 223 probes from 82 scanning systems in current clinical use in the Northern Region in the UK. Measurements have also been made of the maximum total acoustic power generated by 45 probes from 17 scanners. The results from these measurements are presented in this article and compared to the results of a similar survey of equipment from both the Northern and Wessex Regions in the UK and published in 1991. The comparison shows that measured ISPTA values have increased approximately sixfold in B mode and approximately threefold in colour Doppler mode. Also, measured total acoustic power values have doubled in pulsed Doppler mode. The present survey also draws attention to some particularly high ISPTA values obtained from a number of probes and scanning systems. This survey has shown that measurements of acoustic outputs from diagnostic ultrasound scanners in current clinical use are substantially higher than reported in earlier surveys and, for certain scanners, the acoustic outputs from scanned beam modes of operation can reach levels hitherto only found in pulsed Doppler mode.

Acoustics↗