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D Farina

Publications and source records attributed to D Farina.

At least 55 records · Page 3Linked to original sources
PubMed2001

A novel approach for precise simulation of the EMG signal detected by surface electrodes.

We propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. The effects of electrode configuration, electrode size and inclination of the fibers with respect to the detection system are included in the transfer function of the filter. Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.

Action Potentials↗
PubMed2001

Concentric-ring electrode systems for noninvasive detection of single motor unit activity.

New recording techniques for detecting surface electromyographic (EMG) signals based on concentric-ring electrodes are proposed in this paper. A theoretical study of the two-dimensional (2-D) spatial transfer function of these recording systems is developed both in case of rings with a physical dimension and in case of line rings. Design criteria for the proposed systems are presented in relation to spatial selectivity. It is shown that, given the radii of the rings, the weights of the spatial filter can be selected in order to improve the rejection of low spatial frequencies, thus increasing spatial selectivity. The theoretical transfer functions of concentric systems are obtained and compared with those of other detection systems. Signals detected with the ring electrodes and with traditional one-dimensional and 2-D systems are compared. The concentric-ring systems show higher spatial selectivity with respect to the traditional detection systems and reduce the problem of electrode location since they are invariant to rotations. The results shown are very promising for the noninvasive detection of single motor unit (MU) activities and decomposition of the surface EMG signal into the constituent MU action potential trains.

Action Potentials↗
PubMed2001

Effect of electrode shape on spectral features of surface detected motor unit action potentials.

A method for simulating the effect of electrodes of any shape on surface detected motor unit action potentials (MUAPs) is described. The method is based on an approach we have recently proposed according to which the spatial integration of an electrode with physical dimensions is described as a two-dimensional spatial filtering of the electric potential over the skin. The effect of circular, square and bar electrodes on the frequency characteristics of surface detected MUAPs is investigated from the theoretical point of view. In particular the appearance of characteristic frequencies at which the power spectrum of the detected surface EMG signal is zero (spectral dips) is analyzed in relationship with electrode size and shape. It is shown that the physical dimensions of the electrodes may determine spectral dips in the surface EMG power spectrum but only for particular electrode shapes. Simulation results are shown to validate the theoretical considerations.

Action Potentials↗
PubMed2001

Motor unit recruitment during constant low force and long duration muscle contractions investigated with surface electromyography.

Surface EMG signals were detected from the biceps brachii muscle of five subjects using linear electrode arrays during isometric voluntary contractions at low force levels. A classification method based on neural networks has been used to identify the active motor units during the contraction. In addition, surface EMG global variables have been computed. It was found that at low contraction levels it is possible to reliably identify motor unit action potentials from the interference surface EMG signal and to classify them as belonging to different motor units. Progressive recruitment of new motor units during long duration contractions was observed in all the investigated cases from the first few minutes of contraction (3-4 minutes), indicating a change in the recruitment threshold of non-active motor units as a consequence of muscle fatigue. The recruitment of new motor units was more pronounced for higher force contraction levels than for the lower ones. This behaviour was confirmed in two out of five cases by changes of the global EMG variables.

Action Potentials↗
PubMed2000

Geometrical factors in surface EMG of the vastus medialis and lateralis muscles.

Surface EMG signals detected in dynamic conditions are affected by a number of artefacts. Among them geometrical factors play an important role. During movement the muscle slides with respect to the skin because of the variation of its length. Such a shift can considerably modify sEMG amplitude. The purpose of this work is to assess geometrical artefacts on sEMG during isometric contractions at different muscle lengths. The average rectified value (ARV) of 15 single differential signals was obtained by means of a linear array of 16 bar electrodes from the vastus medialis and lateralis muscles. The knee angle was changed from 75 degrees to 165 degrees in steps of 30 degrees and voluntary isometric contractions at a low, medium and high force level were performed for each angle. The ARV pattern was normalized with respect to the mean activity to compare signals from different joint angles. From the data collected it was possible to separate the geometrical changes from the changes due to different intensities of activation. In three out of five subjects, we found (within the resolution of our measures) a 1 cm shift for the vastus medialis muscle while no shift was observed for the other two subjects. For the vastus lateralis muscle a 1 cm shift was found in two out of four subjects. Such a shift produces the main contribution to geometrical artefacts. To avoid such artefacts the innervation zones should be located and the EMG electrodes should not be placed near them.

Adult↗
PubMed2000

Comparison of algorithms for estimation of EMG variables during voluntary isometric contractions.

Many algorithms have been described in the literature for estimating amplitude, frequency variables and conduction velocity of the surface EMG signal detected during voluntary contractions. They have been used in different application areas for the non invasive assessment of muscle functions. Although many studies have focused on the comparison of different methods for information extraction from surface EMG signals, they have been carried out under different conditions and a complete comparison is not available. It is the purpose of this paper to briefly review the most frequently used algorithms for EMG variable estimation, compare them using computer generated as well as real signals and outline the advantages and drawbacks of each. In particular the paper focuses on the issue of EMG amplitude estimation with and without pre-whitening of the signal, mean and median frequency estimation with periodogram and autoregressive based algorithms both in stationary and non-stationary conditions, delay estimation for the calculation of muscle fiber conduction velocity.

Algorithms↗
PubMed2000

Relativistic solitons in magnetized plasmas

The results of analytical and numerical investigations on the properties of one-dimensional (nondrifting) solitons of relativistic amplitude, in the presence of an externally imposed uniform magnetic field B0, are presented and compared with those of the unmagnetized plasma theory (Esirkepov et al., Pis'ma Zh. Eksp. Teor. Fiz. 68, 33 (1998) [JETP Lett. 68, 36 (1998)]). The presence of a uniform longitudinal magnetic field, the intensity of which corresponds to an electron cyclotron frequency Omega(e)=eB(0)/m(e)c that is a non-negligible fraction of the laser frequency omega(0), has important consequences on the properties of relativistically intense solitons. The region of the parameter space (omega(0),Omega(e)) where magnetized solitons exist is determined analytically, and new conditions of breaking due to the total density depletion are given. It is shown that stable high energy magnetized solitons can be produced.

Journal Article↗
PubMed2000

Noninvasive estimation of motor unit conduction velocity distribution using linear electrode arrays.

Determining the conduction velocity of motor unit action potentials is one of the most important problems in surface electromyography. The estimate of one average conduction velocity value depends on a variety of uncontrollable factors. More meaningful information is obtained from the estimation of the distribution of the different delays in the myoelectric signals. A solution to the problem is the separation and characterization of the individual components propagating at different velocities. A technique, based on surface electrode array recording, is proposed to estimate motor unit conduction velocity distribution. The method consists in the identification of the single action potentials in the time scale domain (with the continuous wavelet transform) and in the estimation of their conduction velocities based on the beamforming algorithm. The performances of the technique have been evaluated using simulated and real myoelectric signals. The results demonstrate that the technique is accurate and reliable. The method may be useful for the diagnosis of neuromuscular disorders, for the monitoring of muscle fatigue and for noninvasive investigation of individual motor units.

Action Potentials↗
PubMed1999

Efavirenz plus zidovudine and lamivudine, efavirenz plus indinavir, and indinavir plus zidovudine and lamivudine in the treatment of HIV-1 infection in adults. Study 006 Team.

BACKGROUND: Efavirenz is a nonnucleoside reverse-transcriptase inhibitor of human immunodeficiency virus type 1 (HIV-1). We compared two regimens containing efavirenz, one with a protease inhibitor and the other with two nucleoside reverse-transcriptase inhibitors, with a standard three-drug regimen. METHODS: The study subjects were 450 patients who had not previously been treated with lamivudine or any nonnucleoside reverse-transcriptase inhibitor or protease inhibitor. In this open-label study, patients were randomly assigned to one of three regimens: efavirenz (600 mg daily) plus zidovudine (300 mg twice daily) and lamivudine (150 mg twice daily); the protease inhibitor indinavir (800 mg every eight hours) plus zidovudine and lamivudine; or efavirenz plus indinavir (1000 mg every eight hours). RESULTS: Suppression of plasma HIV-1 RNA to undetectable levels was achieved in more patients in the group given efavirenz plus nucleoside reverse-transcriptase inhibitors than in the group given indinavir plus nucleoside reverse-transcriptase inhibitors (70 percent vs. 48 percent, P<0.001). The efficacy of the regimen of efavirenz plus indinavir was similar (53 percent) to that of the regimen of indinavir, zidovudine, and lamivudine. CD4 cell counts increased significantly with all combinations (range of increases, 180 to 201 cells per cubic millimeter). More patients discontinued treatment because of adverse events in the group given indinavir and two nucleoside reverse-transcriptase inhibitors than in the group given efavirenz and two nucleoside reverse-transcriptase inhibitors (43 percent vs. 27 percent, P=0.005). CONCLUSIONS: As antiretroviral therapy in HIV-1-infected adults, the combination of efavirenz, zidovudine, and lamivudine has greater antiviral activity and is better tolerated than the combination of indinavir, zidovudine, and lamivudine.

Adult↗
PubMed1999

Two methods for the measurement of voluntary contraction torque in the biceps brachii muscle.

Appropriate measurement of maximal voluntary contraction force of a single limb muscle or of a muscle group is important in clinical and research situations. To measure muscle force, one segment of an isometric measuring brace is fixed to a support and force is applied to the other. The output of this arrangement is affected by additional contributions such as pushing or pulling with the whole body. This paper quantifies the differences between measurements of torque produced by the biceps brachii with the brace fixed versus those produced when the elbow joint was isolated by suspending the brace from cables. No statistically significant differences were found between MVC values observed with the two methods within subjects. However, a statistically significant difference in EMG fatigue indices was observed and attributed to a different sharing of force production among different muscles in the two conditions. We conclude that different brace arrangements may lead to the same maximal force but to different rates of myoelectric manifestations of muscle fatigue since the effort may be shared differently among the muscles of synergic or stabilizing groups.

Adult↗
PubMed1999

[Trisomy 6 with choanal atresia. The first Italian case].

The authors report the first Italian case (second in the world) of partial trisomy syndrome of chromosome 6. All the essential signs were present, in addition to choanal atresia, reported only once before in Italy. The phenomenological picture of this extremely rare anomaly is in the process of being completed by successive reports.

Choanal Atresia↗
PubMed1999

Poland syndrome: a case with a combination of syndromes.

The case of Poland syndrome reported incorporates a number of previously unrecorded features: hypoplasia of the left lung and agenesia of the epiglottis in addition to the standard symptoms. The case also presents certain features typical of the Moebius Syndrome.

Adult↗
PubMed1999

Imaging of the parapharyngeal space.

The parapharyngeal space is a deep space of the neck, always well visible on CT and MR imaging of the head and neck; in normal circumstances, this space should look symmetrical. The parapharyngeal space is often subdivided in compartments; such subdivision is helpful when considering the site of origin of a parapharyngeal space mass. Several concepts of compartmentalization of this space exist, sometimes leading to confusion; not the names but the anatomy is important to know. This manuscript reviews shortly the anatomy of the parapharyngeal space, the use of modern cross-sectional imaging methods in the evaluation of this region, and focuses somewhat more on imaging of primary parapharyngeal lesions.

Adipose Tissue↗
PubMed1999

Tumours of the oropharynx and oral cavity: perineural spread and bone invasion.

Clinical examination of the oral cavity and oropharynx provides essential information in the assessment of neoplastic lesions. A precise evaluation of their deep spread along the most common growth pathways can be achieved by imaging, ranging from the basic, but nowadays incomplete, information of conventional X-ray, to the sophisticated details obtained by MR. Three oncological questions must be faced: the three dimensional evaluation of primary tumour spread; the assessment of nodal involvement; the post-treatment survey with the early detection of local recurrences, during the follow up. Either CT or MR accurately assesses the deep extension of neoplasms, nevertheless, the most cost-effective protocol is provided by a combination of CT and ultrasound (staging respectively T and N). MR is the technique of first choice when an infiltration of the base of the tongue or perineural spread is suspected, because of its superior ability to detect muscular invasion and segmental abnormalities of cranial nerves. Bone involvement can be adequately showed by MR not only because focal erosions of the cortical rim are well demonstrated, but also by means of the early demonstration of bone marrow abnormalities. Moreover, MR plays an essential role during the follow up, as it is the only morphological imaging technique permitting to differentiate recurrent tumour and necrosis from scar tissue.

Cicatrix↗
PubMed1997

CT appearance of the larynx after conservative and radical surgery for carcinomas.

The purpose of this study was to evaluate the normal CT appearance of the larynx after conservative and radical surgery. Postoperative (conservative surgery n = 52, radical surgery n = 21) CT examinations of 73 patients suspected of local/regional recurrence (n = 53) or asymptomatic (n = 20) were retrospectively analysed. The CT findings of 45 patients negative at biopsy were utilised to assess the normal appearance after surgery. Changes in the laryngeal framework represented constant landmarks, whereas the variety of soft tissues resection often resulted in a more unpredictable appearance of the neolarynx. Considerable thickening of the mucosa covering the arytenoid cartilage(s) has been detected after horizontal supraglottic laryngectomy (40 %) or supracricoid laryngectomies (SL; 100 %). A "pseudocord" due to scar tissue appeared to be a constant finding following vertical haemilaryngectomy, frequently after SL. Dilation of a lateral recess of the hypopharynx was observed after SL. This "pharyngeal pouch" had considerable size and air or liquid content. The most frequent CT findings among 28 tumours recurrent after conservative or total surgery were a mass larger than 10 mm spreading beyond the larynx (63.1 %), thickening of anterior commissure (57.9 %), erosion of residual cartilages (16.9 %). Although CT detected one subclinical recurrence, its employment is justified only to assess the submucosal extent of the lesion. This requires a thorough knowledge of normal postoperative findings.

Humans↗
PubMed1997

MR of malignant nasosinusal neoplasms. Frequently asked questions.

This paper focuses on the role of MR imaging of malignant neoplasms through a particular layout that emphasizes: (a) the rationale for the application of imaging; (b) the factors influencing the selection of sequences, planes and their proper arrangement; (c) the correlation between MR findings, imaging staging and clinical decision making. Since in most cases surgery is the treatment of choice, the precise assessment of the local extent and spread of tumour plays a key role in planning the surgical approach and influences either the therapy and the prognosis. However, the degree of spatial/anatomical detail required in treatment planning significantly differs between surgery and radiotherapy. Planning of the examination technique focuses on: (a) assembling sequences and planes in the shortest time possible; (b) the solution of specific problems: distinction between neoplasm and retained secretions within nasosinusal cavities; staging of submucosal spread toward the anterior cranial fossa, the orbit, the pterygo-palatine and superior orbital fissures. Since the most effective barrier to spread of neoplasms beyond sinusal walls does not depend on the mineral content of bone, but on the periosteum, assessment of the integrity of periorbita or dura mater is an essential information. Although MR cannot detect focal erosions of the thin sinusal walls, it reliably demonstrates both residual barriers (periorbita and dura), even though the bone has been completely destroyed. However, the final decision concerning orbital exenteration is made according to intraoperative staging. MR imaging can accurately precise the degree of anterior cranial fossa involvement. Furthermore, since either MR and CT accurately indicate the need to perform an anterior craniofacial resection and adequately exclude neoplastic invasion requiring orbital exenteration, more comparative studies are required to demonstrate that MR preoperative staging of nasosinusal malignancies is cost-effective.

Adenocarcinoma↗
PubMed1997

No increase of serum autoantibodies during therapy with recombinant human interferon-beta1a in relapsing-remitting multiple sclerosis.

OBJECTIVES: The present investigation was aimed at establishing whether interferon (IFN)-beta would induce the synthesis of autoantibodies in patients affected by multiple sclerosis (MS). MATERIALS AND METHODS: The titres of different autoantibodies were measured in a group of 68 relapsing-remitting MS patients before and during treatment with human recombinant IFN-beta1a (3 MIU or 9 MIU subcutaneously 3x a week). ANA, anti-thyroid, anticardiolipin serum autoantibodies were assayed in all cases: when patients were found positive to ANA > 1 : 40, they were also tested for anti-DNA and anti-ENA antibodies. RESULTS: No increase was found in autoantibodies synthesis during 6 months of r-hIFNbeta1a therapy, either at low or high dosages. The percentage of patients positive to different types of autoantibodies varied between 0 and 29%, which are values similar to those already reported in untreated MS patients. CONCLUSION: Our data indicate that the short-term use of IFN-beta1a in MS is safe in terms of the induction of humoral autoimmune responses: however, further follow-up is needed to confirm these findings during long-term treatments.

Adjuvants, Immunologic↗