Ferdinando Grandori

Magnetic stimulation of the nervous system : Induced electric field in unbounded, semi-infinite, spherical, and cylindrical media

Knowledge of the electric field that is induced in the brain or the limbs is of importance in magnetic stimulation of the nervous system. Here, an analytical model based on the reciprocity theorem is used to compare the induced electric field in unbounded, semi-infinite, spherical, and cylinder-like volume conductors. Typical stimulation coil arrangements are considered, including the double coil and various orientations of the single coil. The results can be used to determine when the influence of the boundaries is negligible enough to allow the use of more simplified geometries.

Transverse-field activation mechanism in magnetic stimulation of peripheral nerves

The activating function of peripheral nerves in magnetic stimulation is thought to be the gradient of the induced electric field component parallel to the nerve. This implies that there are several orientations of the coil that should not excite nerves. We show that these orientations, however, often yield high-amplitude and even supramaximal muscle response, indicating that the model of the activating function has to be modified. We propose that the electric field component perpendicular to the nerve is responsible for these unexpected muscle responses. Our conclusion is based on practical experiments with different coils and on computer simulations of the induced electric field and its gradient.

Wavelet analysis of click-evoked otoacoustic emissions

Time-frequency distribution methods are being widely used for the analysis of a variety of biomedical signals. Recently, they have been applied also to study otoacoustic emissions (OAEs), the active acoustic response of the hearing end organ. Click-evoked otoacoustic emissions (CEOAEs) are time-varying signals with a clear frequency dispersion along with the time axis. Analysis of CEOAEs is of considerable interest due to their close relation with cochlear mechanisms. In this paper, several basic time-frequency distribution methods are considered and compared on the basis of both simulated signals and real CEOAEs. The particular structure of CEOAEs requires a method with both a satisfactory time and frequency resolution. Results from simulations and real CEOAEs revealed that the wavelet approach is highly suitable for the analysis of such signals. Some examples of the application of the wavelet transform to CEOAEs are provided here. Applications range from the extraction of normative data from adult and neonatal OAEs to the extraction of quantitative parameters for clinical purposes.

Theory of multichannel magnetic stimulation: toward functional neuromuscular rehabilitation

Human excitable cells can be stimulated noninvasively with externally applied time-varying electromagnetic fields. The stimulation can be achieved either by directly driving current into the tissue (electrical stimulation) or by means of electromagnetic induction (magnetic stimulation). While the electrical stimulation of the peripheral neuromuscular system has many beneficial applications, peripheral magnetic stimulation has so far only a few. This paper analyzes theoretically the use of multiple magnetic stimulation coils to better control the excitation and also to eventually mimic electrical stimulation. Multiple coils allow electronic spatial adjustment of the shape and location of the stimulus without moving the coils. The new properties may enable unforeseen uses for peripheral magnetic stimulation, e.g., in rehabilitation of patients with neuromuscular impairment.

‘Derived Nonlinear’ versus ‘Linear’ Click-evoked Otoacoustic Emissions

Recordings of emission evoked in response to transient stimuli (TEOAE) are partially contaminated by the initial stimulus artifact. For this reason, a nonlinear estimation method is widely used (derived nonlinear response, DNLR). The aims of this paper are: (1) to analyse some very basic properties of the derived nonlinear emissions such as the short-time input/output relationships; and (2) to show similarities and differences between the classical averaging (linear) and the derived nonlinear recording techniques, in the same ears, both in time and in the frequency domain. At latencies greater than about 6 ms, responses which are recorded using the derived nonlinear technique exhibit no additional features in comparison with linear recordings, at all stimulus levels. At latencies less than 6 ms, the derived nonlinear technique greatly reduces the linear content of the acoustic artifact, and the response may be considered as the initial part of the emission. However, the derived nonlinear responses tend to be considerably noisier than the linear emissions, thus reducing the effectiveness of the technique. The linear responses show a strikingly similar frequency content with respect to the derived nonlinear responses, at least at a high stimulus level and around the main peaks of the spectrum.

An analytical model to predict the electric field and excitation zones due to magnetic stimulation of peripheral nerves

The main unknown factor in understanding magnetic stimulation of peripheral nerves is the distribution of the induced electric field. The authors have applied the so-called reciprocity theorem and developed an analytical model to compute the electric field and its spatial derivatives inside pseudocylindrical structures. The results can be used to predict the site of excitation in magnetic stimulation of peripheral nerves.<<ETX>>

Interventions following hearing screening in adults: A systematic descriptive review

Abstract Objective: Adult hearing screening may be a solution to the under-diagnosis and under-treatment of hearing loss in adults. Limited use and satisfaction with hearing aids indicate that consideration of alternative interventions following hearing screening may be needed. The primary aim of this study is to provide an overview of all intervention types that have been offered to adult (≥ 18 years) screen-failures. Design: Systematic literature review. Articles were identified through systematic searches in PubMed, EMBASE, Cinahl, the Cochrane Library, private libraries, and through reference checking. Results: Of the initial 3027 papers obtained from the searches, a total of 37 were found to be eligible. The great majority of the screening programmes (i.e. 26) referred screen-failures to a hearing specialist without further rehabilitation being specified. Most of the others (i.e. seven) led to the provision of hearing aids. Four studies offered alternative interventions comprising communication programme elements (e.g. speechreading, hearing tactics) or advice on environmental aids. Conclusions: Interventions following hearing screening generally comprised referral to a hearing specialist or hearing aid rehabilitation. Some programmes offered alternative rehabilitation options. These may be valuable as an addition to or replacement of hearing aid rehabilitation. It is recommended that this be addressed in future research. Sumario Objetivo: El tamiz auditivo en adultos puede ser una solución al diagnóstico y tratamiento insuficiente de las alteraciones auditivas en adultos. El uso y satisfacción limitados con los auxiliares auditivos indica que pueden necesitarse intervenciones alternativas luego del tamiz auditivo. El propósito primario de este estudios es echar un vistazo a todos los tipos de intervención que han sido ofrecidas a adultos (≥ 18 años) que fallan dicho tamiz. Diseño: Revisión sistemática de la literatura. Se identificaron artículos a través de una búsqueda sistemática en PubMed, EMBASE, Cinahl, la Biblioteca Cochran, bibliotecas privadas y a través de revisión de referencias. Resultados: De los 3027 trabajos iniciales obtenidos de las búsquedas, se encontró un total de 37 que eran elegibles. La gran mayoría de los programas de tamiz auditivo (p.e., 26) refirieron los fallos del tamiz a un especialista en audición, sin especificar nada adicional sobre rehabilitación. La mayoría de los otros (p.e., 7) llevaron a la adaptación de auxiliares auditivos. Cuatro estudios ofrecieron intervenciones alternativas que involucraban programas de comunicación (p.e., lectura labio-facial, tácticas para escuchar) o consejo sobre ayudas ambientales. Conclusiones: Las intervenciones que siguez al tamiz auditivo involucraron referencia a especialistas en audición o rehabilitación con auxiliares auditivos. Algunos programas ofrecieron opciones alternativas de rehabilitación. Estos pueden ser valiosos como una adición o en reemplazo de la rehabilitación con auxiliares auditivos. Se recomienda que esto sea analizado en investigaciones futuras.

The Milan Project: A newborn hearing screening programme: Newborn hearing screening programme

Aim: Since 1997 a newborn hearing screening programme has been implemented by the U.O. Neurologia‐Neurofisiopatologia and Dipartimento di Neonatologia of the Istituti Clinici di Perfezionamento ICP in Milan for both babies with no risk and those at risk of hearing impairment. This programme was named the Milan Project. Methods: The protocol for no‐risk babies consisted of three stages: in the first two stages, newborns were tested with transient click‐evoked otoacoustic emissions (TEOAE), in the third one with conventional auditory brainstem responses (ABR). The first TEOAE test was performed by 36 h of age, before discharge, the second one after 15–30 d in case of referral, and the third one, by ABR, for those babies who failed the second TEOAE stage. Newborns at audiological risk were submitted to conventional ABR before the third month of corrected age. Some of this latter population was also submitted to the TEOAE test. The entire tested population (no‐risk babies and newborns at audiological risk) consisted of 19 777 babies: 19 290 without risk (“no risk”) and 487 at risk (“at risk”). Results: During the course of the Milan Project, hearing impairment (ABR threshold equal to or greater than 40 dB nHL) was identified in 63 newborns (19 from the no‐risk and 44 from the at‐risk population), with a prevalence of 0.32%. Bilateral hearing impairment (BHI) was found in 33 newborns (10 from the no‐risk and 23 from the at‐risk population), corresponding to 0.17%. Among infants with bilateral hearing impairment, 30.3% had no risk factors. The prevalence of hearing impairment was determined on days 15–30 after birth.

Universal newborn hearing screening programs in Italy: survey of year 2006

Conclusion.Our results suggest a rapid diffusion of newborn hearing screening programs in Italy and indicate that three conditions seem to play a crucial role in the implementation of Universal Newborn Hearing Screening (UNHS) programs: the size (>800 births/year) and location (metropolitan urban areas) of the hospital, and the presence of an audiologist in the UNHS coordinating team Objectives. The aim of this paper is to provide data on the degree of implementation and coverage of UNHS programs in Italy Materials and methods. Data were collected through a Screening Survey Questionnaire that was sent to all birthing hospitals active in Italy in 2006 and was filled in by the chief of the hospital or by the UNHS program coordinator Results. In Italy UNHS coverage had undergone a steep increase from 29.3% in 2003 (156 048 newborns screened) to 48.4% in 2006 (262 103 screened). The majority of UNHS programs were implemented in the two most economically developed areas, i.e. in the north-west area (79.5%, 108 200 of 136 109 births), and in the north-east area (57.2%, 52 727 of 92 133 births), while a limited diffusion still remains in some areas, typically in the islands (11.3%, 7158 of 63 460 births).

Comparison of two methods of TEOAE recording in newborn hearing screening.

This paper summarizes the results of trials performed in two hospitals, comparing the scoring of transient evoked otoacoustic emissions (TEOAEs) on the same neonates and within the same test session, recorded by the fully automatic device EchoScreen (Madsen Electronics/Fischer-Zoth GmbH) and ILO Otodynamics Ltd system. These trials form part of a larger project (Project Sentinel), whose primary aim is to stimulate the creation of new neonatal hearing screening programmes. Four thousand two hundred and forty-eight neonates were tested with both devices (8494 ears), in randomized order. The response scores obtained with the two devices are in full agreement in 98.72% of the tested ears. Considering the recording time, the fully automatic Echo Screen was, on average, about 3.6 times faster than the ILO88, bearing in mind, however, that when using ILO88, the end of the recording is decided by the operator on the basis of some mandatory decision rules.This paper summarizes the results of trials performed in two hospitals, comparing the scoring of transient evoked otoacoustic emissions (TEOAEs) on the same neonates and within the same test session, recorded by the fully automatic device EchoScreen (Madsen Electronics/Fischer-Zoth GmbH) and ILO Otodynamics Ltd system. These trials form part of a larger project (Project Sentinel), whose primary aim is to stimulate the creation of new neonatal hearing screening programmes. Four thousand two hundred and forty-eight neonates were tested with both devices (8494 ears), in randomized order. The response scores obtained with the two devices are in full agreement in 98.72% of the tested ears. Considering the recording time, the fully automatic Echo Screen was, on average, about 3.6 times faster than the ILO88, bearing in mind, however, that when using ILO88, the end of the recording is decided by the operator on the basis of some mandatory decision rules.