86,595 research outputs found
Cochlear reflectivity and teoae transfer function
No full textCochlear reflectivity has been theoretically estimated for different otoacoustic emission generation mechanisms, using a standard perturbative approach based on the WKB approximation and the osculating parameters technique. The predictions of theoretical models have been compared with experimental measurements of the TEOAE transfer function at different stimulus levels, between 60 and 90 dB pSPL. The phase-gradient delay of the TEOAE response has also been compared to the estimates of the cochlear transmission delay obtained with time-frequency analysis of the same TEOAE waveforms. Place-fixed and wave-fixed OAE generation mechanisms are discussed in the light of the results
Input/output functions of different-latency components of transient-evoked and stimulus-frequency otoacoustic emissions
No full textThe input/output functions of the different-latency components of human transient-evoked and stimulus-frequency otoacoustic emissions are analyzed, with the goal of relating them to the underlying nonlinear dynamical properties of the basilar membrane response. Several cochlear models predict a cubic nonlinearity that would yield a correspondent compressive response. The otoacoustic response comes from different generation mechanisms, each characterized by a particular relation between local basilar membrane displacement and otoacoustic level. For the same mechanism (e.g., reflection from cochlear roughness), different generation places would imply differently compressive regimes of the local basilar membrane dynamics. Therefore, this kind of study requires disentangling these contributions, using suitable data acquisition and time-frequency analysis techniques. Fortunately, different generation mechanisms/places also imply different phase-gradient delays, knowledge of which can be used to perform this task. In this study, the different-latency otoacoustic components systematically show differently compressive response, consistent with two simple hypotheses: (1) all emissions come from the reflection mechanism and (2) the basilar membrane response is strongly compressive in the resonance region and closer to linear in more basal regions. It is not clear if such a compressive behavior also extends to arbitrarily low stimulus level
Intensimetric detection of distortion product otoacoustic emissions with ear canal calibration
No full textDistortion product otoacoustic emissions (DPOAEs) have been accurately measured with an intensimetric technique, involving simultaneous measure of pressure and velocity in the ear canal, which allows one to correctly calibrate both the input stimuli and the otoacoustic emission (OAE) level. Suitable combinations of standard intensimetric quantities, active intensity and power density [Stanzial, Shiffrer, and Sacchi, J. Acoust. Soc. Am. 131, 269-280 (2012)], are used to equalize the stimuli transmitted to the middle ear, and to estimate the DPOAE level emitted by the eardrum. The DPOAE intensimetric spectra are consistent with those recorded with a high-quality conventional otoacoustic probe with state-of-the-art calibration of both stimulus and OAE response [Charaziak and Shera, J. Acoust. Soc. Am. 141, 515-525 (2017)], demonstrating the applicability of the intensimetric method to OAE measurements
DPOAE generation dependence on primary frequencies ratio
No full textTwo different mechanisms are responsible for the DPOAE generation. The nonlinear distortion wave-fixed mechanism generates the DPOAE Zero-Latency (ZL) component, as a backward traveling wave from the "overlap" region. Linear reflection of the forward DP wave (IDP) generates the DPOAE Long-Latency (LL) component through a place-fixed mechanism. ZL and LL components add up vectorially to generate the DPOAE recorded in the ear canal. The 2f1-f2 and 2f2-f1 DPOAE intensity depends on the stimulus level and on the primary frequency ratio r = f2/f1, where f1 and f2 are the primary stimuli frequencies. Here we study the behavior of the ZL and LL DPOAE components as a function of r by both numerical and laboratory experiments, measuring DPAOEs with an equal primary levels (L1 = L2) paradigm in the range [35, 75] dB SPL, with r ranging in [1.1, 1.45]. Numerical simulations of a nonlocal nonlinear model have been performed without cochlear roughness, to suppress the linear reflection mechanism. In this way the model solution at the base represents the DPOAE ZL component, and the solution at the corresponding DPOAE tonotopic place corresponds to the IDP. This technique has been not effectual to study the 2f2-f1 DPOAE, as a consequence of its generation mechanism. While the 2f1-f2 generation place is known to be the tonotopic place x(f2), the 2f2-f1 DPOAE one has to be assumed basal to its corresponding reflection place. That is because ZL components generated in x(f2) cannot significantly pass through their resonant place. Moreover increasing the ratio r, 2f2-f1 ZL and LL generation place approach each other, because the overlap region of primary tones decreases. Consequently, the distinction between the two places becomes complicated. DPOAEs have been measured in six young normal-hearing subjects. DPOAE ZL and LL components have been separated by a time-frequency filtering method based on the wavelet transform 1. due to their different phase gradient delay. Amplitude/phase vs ratio and ratio-frequency maps have been analyzed both in numerical and laboratory data. As already observed in animal studies [4], the generation of 2f1-f2 DPOAE is around the f2 tonotopic place with a maximum around r = 1.2 for the ZL component, while the LL component shows a decreasing trend with r. Instead, 2f2-f1 DPOAEs show a decreasing trend with r for both ZL and LL components
Otoacoustic emissions as a promising diagnostic tool for the early detection of mild hearing impairment - Technical advances in acquisition, analysis and modeling
No full textIsolation and characterization of polyphenol oxidase from Sardinian poisonous and non-poisonous chemotypes of Ferula communis (L.)
No full textFerula communis (L.), a plant belonging to Apiaceae, is widely present in Sardinia, Italy. Currently, interest in F. communis focuses on the presence of two chemotypes in the wild. One chemotype is poisonous to animals, whereas the other chemotype is non-poisonous. Polyphenol oxidase (PPO) has been extracted and partially purified from the two chemotypes of F. communis. The biochemical characterization of the enzymes showed significant differences. In particular, while the two PPOs were not able to use 6- and 7-hydroxycoumarin as substrates, they showed distinct specificity for 6,7- and 7,8-dihydroxycoumarin. Significant differences in the enzyme behavior towards common PPO inhibitors were also observed. In addition, activation energy and activation energy for denaturation were determined, showing significant differences between FP-PPO and FNP-PPO, particularly for denaturation kinetics. The possible roles of the two PPOs in determining differences in composition and toxicity of the two F. communis chemotypes are also discusse
Irreversible affinity immobilization of lentil seedling amine oxidase with activity retention
No full textAn aliphatic-amine-bearing chromatographic support, based on commercial silica, was prepared and tested as potential matrix for affinity immobilization of a copper/topaquinone-containing amine oxidase from lentil seedlings. The support proved to be noticeably effective in immobilizing the enzyme with concomitant purification and activity retention. The immobilization yields and some properties of this preparation were also determined and compared with those of the soluble enzyme. High activity retention, good operational stability and low preparative costs are best combined in this promising immobilized amine oxidase
Evaluation of antioxidant capacity of antioxidant-declared beverages marketed in Italy
No full textClinical literature suggests a negative correlation between fruit juice consumption and the occurrence of various diseases. Consequently, many commercially available beverages are based on fruit juices or green tea extracts with specific additives that increase their antioxidant power. In order to fully estimate their potential antioxidant capacity, several products marketed in Italy were analyzed for total phenolics and flavonoids, DPPH scavenging activity, TEAC, FRAP and ORAC-PYR. On average, fruit-based samples had more antioxidants than green teas, but specific additives significantly improved total antioxidant power. Differences between these samples and plain fruit juices were also evaluated. Total antioxidant supply remained almost constant during the entire shelf life of the products
Distortion product otoacoustic emission generation mechanisms and their dependence on stimulus level and primary frequency ratio
No full textIn this study, a systematic analysis of the dependence on stimulus level and primary frequency ratio r of the different components of human distortion product otoacoustic emissions has been performed, to check the validity of theoretical models of their generation, as regards the localization of the sources and the relative weight of distortion and reflection generation mechanisms. 2f1 - f2 and 2f2 - f1 distortion product otoacoustic emissions of 12 normal hearing ears from six human subjects have been measured at four different levels, in the range [35, 65] dB sound pressure level, at eight different ratios, in the range [1.1, 1.45]. Time-frequency filtering was used to separate distortion and reflection components. Numerical simulations have also been performed using an active nonlinear cochlear model. Both in the experiment and in the simulations, the behavior of the 2f1 - f2 distortion and reflection components was in agreement with previous measurements and with the predictions of the two-source model. The 2f2 - f1 response showed a rotating-phase component only, whose behavior was in general agreement with that predicted for a component generated and reflected within a region basal to the characteristic place of frequency 2f2 - f1, although alternative interpretations, which are also discussed, cannot be ruled out
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