Biomedical subjects

D Farina

Publications and source records attributed to D Farina.

At least 37 records · Page 2Linked to original sources

PubMed2004

Non-invasive assessment of single motor unit mechanomyographic response and twitch force by spike-triggered averaging.

A method for non-invasive assessment of single motor unit (MU) properties from electromyographic (EMG), mechanomyographic (MMG) and force signals is proposed. The method is based on the detection and classification of single MU action potentials from interference multichannel surface EMG signals and on the spike-triggered average of the MMG (detected by an accelerometer) and force signals. The first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles were investigated at contraction levels of 2% and 5% of the maximum voluntary contraction (MVC) force. A third contraction was performed by selective activation of a single MU with surface MU action potential visual feedback provided to the subject. At 5% MVC, the mean (+/-standard error) single MU MMG peak-to-peak value was 11.0+/-1.8 mm s(-2) (N= 17) and 32.3+/-6.5 mm s(-2) (N=20) for the FDI and ADM muscles, respectively. The peak of the twitch force was, at the same contraction level, 7.41+/-1.34 mN and 14.42+/-2.92 mN, for the FDI and ADM muscles, respectively. The peak-to-peak value of the MMG was significantly different for the same MU at different contraction levels, indicating a non-linear summation of the single MU contributions. For the FDI muscle, the MMG peak-to-peak value of individual MUs was 21.5+/-7.8 mm s(-2), when such MUs were activated with visual feedback provided to the subject, whereas, for the same MUs, it was 11.8+/-3.8 mm s(-2), when the subject maintained a constant force level of 2% MVC. The method proposed allows the non-invasive assessment of single MU membrane and contractile properties during voluntary contractions.

Action Potentials↗

PubMed2004

Comparison of spatial filter selectivity in surface myoelectric signal detection: influence of the volume conductor model.

Spatial filters are used for increasing selectivity in surface EMG signal detection. The study investigated the importance of the description of the volume conductor to the inference of conclusions on comparing filter selectivity from simulation analyses. A cylindrical multi-layer description of the volume conductor was used for the simulation analysis. Different anatomies were analysed with this model, and results on filter selectivity were compared. The longitudinal single (LSD), double (LDD) and normal double differential (Laplacian, NDD) filters were investigated. Largely different conclusions could be drawn when comparing filter selectivity resulting from simulations with different volume conductor models. A filter that performed best with a particular anatomy could be the poorest with another anatomy. With a bone-muscle model and superficial fibres, the ratio between peak-to-peak values of the propagating and non-propagating signal components was approximately 220% for LDD and LSD and lower than for NDD (approximately 290%). With a bone-muscle-fat-skin model, LSD performed significantly worse (150%) than both LDD and NDD, which showed similar performances (approximately 300%). Similarly, if the lateral distance of the recording was increased by 10 degrees, the signal amplitude was reduced to 2% with LSD and LDD and to 4% with NDD. With another anatomy, LSD and LDD reduced signal amplitude to 20-25%, and NDD reduced it to 4%. Similar considerations could be drawn for other selectivity indexes. Thus, modelling should be used carefully to infer conclusions on spatial selectivity and to indicate particular choices of spatial filters.

Action Potentials↗

PubMed2004

Effect of accelerometer location on mechanomyogram variables during voluntary, constant-force contractions in three human muscles.

To understand better the features of the mechanomyogram (MMG) with different force levels and muscle architectures, the MMG signals detected at many points along three muscles were analysed by the application of a linear array of MMG sensors (up to eight) over the skin. MMG signals were recorded from the biceps brachii, tibialis anterior and upper trapezius muscles of the dominant side of ten healthy male subjects. The accelerometers were aligned along the direction of the muscle fibres. One accelerometer was located over the distal muscle innervation zone, and the other six or seven accelerometers were placed over the muscle, forming an array of sensors with fixed distances between them. The array covered almost the entire muscle length in all cases. MMG signals detected from adjacent accelerometers had similar shapes, with correlation coefficients ranging from about 0.5 to about 0.9. MMG amplitude and characteristic spectral frequencies significantly depended on accelerometer location. The MMG amplitude was maximum at the muscle belly for the biceps brachii and the tibialis anterior. Higher MMG characteristic spectral frequencies were associated with higher amplitudes in the case of the biceps brachii, whereas the opposite was observed for the tibialis anterior muscle. In the upper trapezius, the relationship between characteristic spectral frequencies, MMG amplitude and contraction force depended on the accelerometer location. This suggested that MMG spectral features do not only reflect the mechanical properties of the recruited muscle fibres but depend on muscle architecture and motor unit territorial distribution. It was concluded that the location of the accelerometer can have an influence on both amplitude and spectral MMG features, and this dependence should be considered when MMG signals are used for muscle assessment.

Acceleration↗

PubMed2004

Decreased integrin gene expression in patients with MS responding to interferon-beta treatment.

Interferon-beta (IFN-beta) ameliorates disease course in a subset of patients with MS. The reasons for heterogeneity of clinical responses, however, are unclear. We assessed possible effects of IFN-beta on the gene expression of the leukocyte adhesion molecules VLA-4 and LFA-1 during the first year of treatment of 50 patients with relapsing-remitting MS who showed differential clinical responses. We observed a significant reduction of VLA-4 (P=0.002) and LFA-1 (P=0.03) mRNA expression compared to baseline in first-year clinical responders (n=22). In contrast, first-year IFN-beta non-responders (n=28) had unchanged levels of VLA-4 and LFA-1. In vitro treatment of PBMC with IFN-beta indicated a direct effect on transcription of the integrins' genes. Transcriptional downmodulation of adhesion molecules during IFN-beta treatment may contribute to its mode of action in MS.

Adjuvants, Immunologic↗

PubMed2004

Surface EMG crosstalk evaluated from experimental recordings and simulated signals. Reflections on crosstalk interpretation, quantification and reduction.

OBJECTIVES: Surface EMG crosstalk is the EMG signal detected over a non-active muscle and generated by a nearby muscle. The aim of this study was to analyze the sources of crosstalk signals in surface EMG recordings and to discuss methods proposed in the literature for crosstalk quantification and reduction. METHODS: The study is based on both simulated and experimental signals. The simulated signals are generated by a structure based surface EMG signal model. Signals were recorded with both intramuscular and surface electrodes and single motor unit surface potentials were extracted with the spike triggered averaging approach. Moreover, surface EMG signals were recorded from electrically stimulated muscles. RESULTS: From the simulation and experimental analysis it was clear that the main determinants of crosstalk are non-propagating signal components, generated by the extinction of the intracellular action potentials at the tendons. Thus, crosstalk signals have a different shape with respect to the signals detected over the active muscle and contain high frequency components. CONCLUSIONS: Since crosstalk has signal components different from those dominant in case of detection from near sources, commonly used methods to quantify and reduce crosstalk, such as the cross-correlation coefficient and high-pass temporal filtering, are not reliable. Selectivity of detection systems must be discussed separately as selectivity with respect to propagating and non-propagating signal components. The knowledge about the origin of crosstalk signal constitutes the basis for crosstalk interpretation, quantification, and reduction.

Action Potentials↗

PubMed2003

Single motor unit analysis from spatially filtered surface electromyogram signals. Part I: spatial selectivity.

The aim of the study was to compare experimentally, on the basis of single motor unit (MU) activities, the selectivity of different spatial filters commonly used to detect surface electromyogram (EMG) signals. Surface EMG signals were recorded from the biceps brachii and the upper trapezius muscle of five subjects using a two-dimensional (2D) electrode array consisting of 16 pin electrodes. The subjects performed isometric contractions at different elbow angles and shoulder abduction and flexion. The same monopolar surface EMG signals were filtered using longitudinal single and double differential, transverse single and double differential and normal double differential filters. From the single MU action potentials, extracted by automatic EMG decomposition, indexes of transverse (perpendicular with respect to the fibre direction) and longitudinal (along the fibre direction) selectivity were computed. The number of detected MUs was 46 for the upper trapezius, with the arms held in the sagittal plane, and 52 when the arms were held in the frontal plane; 85 MUs were identified from the biceps brachii contractions. The results showed that transverse selectivity was significantly higher for the 2D and transverse one-dimensional (1D) filters with respect to the 1D longitudinal filters, whereas longitudinal selectivity was higher (i.e. MU action potentials were shorter) for the 2D filter and the longitudinal double differential filter. In particular, the relative attenuation of potential amplitude moving 5 mm from the source was, on average (for the two muscles), 16.5% for the least selective filter in the transverse direction (longitudinal single differential) and 35.7% for the most selective one in the same direction (transverse double differential). The MU action potential duration was, on average, 13.8 ms for the most selective filter in the longitudinal direction (longitudinal double differential) and 18.7 ms for the least selective one (transverse double differential). The normal double differential filter resulted in spatial selectivity indexes that ware not statistically different in the two directions from those of the best filters in each direction.

Action Potentials↗

PubMed2003

Single motor unit analysis from spatially filtered surface electromyogram signals. Part 2: conduction velocity estimation.

The aim of the study was to compare experimentally conduction velocity (CV) estimates obtained with different estimation methods based on surface electromyogram (EMG) signals detected using five spatial filters. The filters investigated were the longitudinal single and double differential, transverse single and double differential, and normal double differential. The same surface EMG signals detected as described in Part 1 were used in this work. CV was estimated with four commonly used delay estimation techniques, i.e. from the distance between the peak values of two waveforms (with and without polynomial interpolation around the peak), and by the maximum likelihood estimate (MLE) based on two or more surface EMG channels. The average standard deviation of CV estimation (for all the MUs and the two muscles together) was 0.61 m s(-1) and 0.79 m s(-1) for the peak method, with and without interpolation, respectively, and 0.50 m s(-1) and 0.31 m s(-1) for the MLE method, from two and more surface EMG channels, respectively. Moreover, the mean of CV estimates varied by as much as 1 m s(-1) depending on the spatial filter used and the method adopted for CV estimation. Considering the dependence on the spatial filter only, the average (over all estimation methods) CV estimates obtained with the five spatial filters were 4.32 m s(-1) (normal double differential), 4.23 m s(-1) (longitudinal double differential), 4.61 m s(-1) (transverse double differential), 4.64 m s(-1) (transverse single differential) and 4.03 m s(-1) (longitudinal single differential). It was concluded that the comparison of single MU CV values obtained in different studies is critical if different spatial filters and processing techniques are used for their estimation. Higher estimates of CV were attributed to a smaller reduction in non-travelling signal components and thus were assumed to be positively biased.

Action Potentials↗

PubMed2002

Lymphomononuclear cells from multiple sclerosis patients spontaneously produce high levels of oncostatin M, tumor necrosis factors alpha and beta, and interferon gamma.

Proinflammatory cytokines are deemed to play a pivotal role in the pathogenesis of multiple sderosis (MS). They provide signals for T-cell activation and inflammatory cell recruitment in the brain and might directly alter neuroglial and neuronal cell survival and function. We found that peripheral blood mononuclear cells (PBMCs) from MS patents spontaneously produce high levels of TNFalpha, TNFbeta, IFNgamma, and oncostatin M (oncM), a proinflammatory cytokine actng on cells of neural, vascular, hematopoietic, and lymphoid origin. Spontaneous production of these cytokines was significantly higher (p < 0.01) in PBMC short-term culture supernatants from MS patients than in blood donors (HC). On average, lectin-induced production of these cytokines by PBMC was higher in MS patents than in HC significantly so only for TNFalpha (p = 0.013). Determination of TNFalpha, TNFbeta IFNgamma, and oncM in corresponding sera showed that on average, oncM levels were higher in MS patients than in HC, though the results were not statistically significant whereas levels of TNFalpha, TNFbeta and IFNgamma were below the assay threshold in most patients. The finding that MS PBMCs are primed in vivo to produce and release high levels of proinflammatory cytokines suggests the presence of a basal activation of the immune system which, in turn, may play a role in the complex circuitry of molecular and cellular interactions responsible for neurologic damage in MS.

Adolescent↗

PubMed2001

Dark solitons in electron-positron plasmas.

We demonstrate that a dark soliton is a stable nonlinear coherent mode in electron-positron plasmas. The dark soliton comprises the minimum of the electromagnetic energy density and the minimum of the plasma density. Contrary to a bright soliton, the dark soliton can advect the trapped charged particles. The energy of trapped particles is well above the kinetic energy of the particles in the background plasma.

Journal Article↗

PubMed2001

Relativistic electromagnetic solitons in the electron-ion plasma.

We present the results of the investigation about the ion motion influence on relativistic soliton structure, and show that in the case of moving multinode solitons the effect of the ion dynamics results in the limiting of its amplitude. The constraint on the maximum amplitude corresponds to either the ion motion breaking in the low-node-number case, or to the electron trajectory self-intersection in the case of high-node-number solitons. The soliton breaking leads to the generation of fast ions, and provides a novel mechanism for the ion acceleration in the plasma irradiated by the high-intensity laser pulses.

Journal Article↗

PubMed2001

Hydrodynamic approach to the interaction of a relativistic ultrashort laser pulse with an underdense plasma.

The interaction of an ultrashort, high peak power laser pulse with an underdense plasma is investigated within a physical model based on the three-dimensional cold hydrodynamic approach, which allows one to study the dynamics of the laser pulse and of the generated wakefields self-consistently, in the fully relativistic, strongly nonlinear regime. Our model is developed with the aim of describing very short laser pulses (with l(0)<lambdap and l(0)<<l perpendicular, where l(0),l perpendicular, lambdap are the pulse length, its transverse scale, and the plasma wavelength, respectively) down to single cycle radiation wave packets, which have become available with the recent progress in laser technology. The space-time structure and the evolution of large quasistatic electric and magnetic fields are studied, together with the pulse dynamics, by the direct numerical integration of the relativistic fluid and field equations, within the extended paraxial approximation.

Journal Article↗

PubMed2001

Estimation of single motor unit conduction velocity from surface electromyogram signals detected with linear electrode arrays.

This work addresses the problem of estimating the conduction velocity (CV) of single motor unit (MU) action potentials from surface EMG signals detected with linear electrode arrays during voluntary muscle contractions. In ideal conditions, that is without shape or scale changes of the propagating signals and with additive white Gaussian noise, the maximum likelihood (ML) is the optimum estimator of delay. Nevertheless, other methods with computational advantages can be proposed; among them, a modified version of the beamforming algorithm is presented and compared with the ML estimator. In real cases, the resolution in delay estimation in the time domain is limited because of the sampling process. Transformation to the frequency domain allows a continuous estimation. A fast, high-resolution implementation of the presented multichannel techniques in the frequency domain is proposed. This approach is affected by a negligible decrease in performance with respect to ideal interpolation. Application of the ML estimator, based on two-channel information, to ten firings of each of three MUs provides a CV estimate affected by a standard deviation of 0.5 m s(-1); the modified beamforming and ML estimators based on five channels provide a CV standard deviation of less than 0.1 m s(-1) and allow the detection of statistically significant differences between the CVs of the three MUs. CV can therefore be used for MU classification.

Action Potentials↗

PubMed2001

BOLD contrast fMRI of whole rodent tumour during air or carbogen breathing using echo-planar imaging at 1.5 T.

The aim of this study was to evaluate the feasibility of functional MR imaging (fMRI) at 1.5 T, exploiting blood oxygenation level-dependent (BOLD) contrast, for detecting changes in whole-tumour oxygenation induced by carbogen (5% CO2+95% O2) inhalation of the host. Adult WAG/Rij rats with rhabdomyosarcomas growing subcutaneously in the lower flank were imaged when tumours reached sizes between 1 and 11 cm3 (n=12). Air and carbogen were alternatively supplied at 2 l/min using a snout mask. Imaging was done on a 1.5-T MR scanner using a T2*-weighted gradient-echo, echo-planar imaging (GE-EPI) sequence. Analysis of the whole-tumour EPI images was based on statistical parametric maps. Voxels with and without signal intensity changes (SIC) were recorded. Significance thresholds were set at p<0.05, corrected for multiple comparisons. In continuous air breathing condition, 3 of 12 tumours showed significant negative SIC and 1 tumour had a clear-cut positive SIC. The remaining tumours showed very little or no change. When switching to carbogen breathing, the SIC were significantly positive in 10 of 12 tumours. Negative SIC were present in 4 tumours, of which three were simultaneously characterised by positive SIC. The overall analysis indicated that 6 of the 12 tumours could be considered as strong positive responders to carbogen. Our research demonstrates the applicability of fMRI GE-EPI at 1.5 T to study whole-tumour oxygenation non-invasively. The observed negative SIC during air condition may reflect the presence of transient hypoxia during these measurements. Selection of tumours on the basis of their individual response to carbogen is possible, indicating a role of such non-invasive measurements for using tailor-made treatments.

Animals↗

PubMed2001

Low-dose oral methotrexate treatment in chronic progressive multiple sclerosis.

We aimed to further assess the safety and efficacy of low-dose oral methotrexate (LDOM) treatment for chronic progressive MS (CPMS). We studied 20 CPMS patients, including 16 with secondary progressive MS who had shown disease progression in the previous year. The mean follow-up was 23 months. The mean EDSS score was 6.3+/-1.1 before treatment and 6.4+/-1.1 after one year of treatment. At one year, 15 of 20 patients were still being treated, and 10 were stable. Twelve patients have completed 18 months of treatment, and eight are stable. Two patients stopped treatment because of side effects, two more because they did not perceive benefit, and one was lost to follow-up. Six patients had mild, transient increases in liver enzymes not requiring treatment interruption, and two had localized herpes zoster. Magnetic resonance imaging (MRI) performed before treatment and at one year remained unchanged in responders. We confirm that LDOM is safe in carefully selected and monitored CPMS patients. MTX is inexpensive and, given its anti-inflammatory and immunomodulatory properties, may be used as add-on therapy in non-responders to interferon beta, although hepatic toxicity may be a problem in long-term treatment.

Adult↗

PubMed2001

Computed tomography and magnetic resonance imaging of pathologic conditions of the middle ear.

Computed tomography (CT) is an excellent technique for demonstrating even small abnormalities of the thin and complex bony structures of the middle ear. For this reason, it is the modality of choice in the study of conductive hearing loss (CHL). However, not every patient complaining of CHL requires a CT study. In fact, established indications encompass complex conditions, such as the complications of acute and chronic otomastoiditis, the postoperative ear in chronic otomastoiditis or in the localization of prosthetic devices, and the assessment of congenital or vascular anomalies. Particularly, the precise extent of bone erosion associated with cholesteatoma is correctly demonstrated by high resolution CT. Conversely, although fistulization through the tegmen tympani or the posterior wall of temporal bone is usually detectable by CT, the actual involvement of meninges and veins are better assessed by magnetic resonance (MR). MR is also indicated when complicated inflammatory lesions are suspected to extend into the inner ear or towards the sigmoid sinus or jugular vein. Neoplasms arising from or extending into the middle ear require the use of both techniques as their combined data provide essential information. Most important data for surgical planning concern the destruction of thin bony structures and the relationships of the lesion with the dura and surrounding vessels. DSA and interventional vascular techniques maintain an essential role in the presurgical work-up and embolization of paragangliomas extended into the middle ear.

Cholesteatoma↗

PubMed2001

Evaluation of intra-muscular EMG signal decomposition algorithms.

We propose and test a tool to evaluate and compare EMG signal decomposition algorithms. A model for the generation of synthetic intra-muscular EMG signals, previously described, has been used to obtain reference decomposition results. In order to evaluate the performance of decomposition algorithms it is necessary to define indexes which give a compact but complete indication about the quality of the decomposition. The indexes given by traditional detection theory are in this paper adapted to the multi-class EMG problem. Moreover, indexes related to model parameters are also introduced. It is possible in this way to compare the sensitivity of an algorithm to different signal features. An example application of the technique is presented by comparing the results obtained from a set of synthetic signals decomposed by expert operators having no information about the signal features using two different algorithms. The technique seems to be appropriate for evaluating decomposition performance and constitutes a useful tool for EMG signal researchers to identify the algorithm most appropriate for their needs.

Action Potentials↗

PubMed2001

Surface electromyography for noninvasive characterization of muscle.

Surface electromyography for noninvasive characterization of muscle. Exerc. Sport Sci. Rev., Vol. 29, No. 1, pp 20-25, 2001. Linear electrode arrays are used for noninvasive muscle characterization to study individual motor unit properties and the myoelectric manifestations of muscle fatigue during sustained contractions. The location of an electrode pair with respect to the innervation zone(s), the deterministic rather than stochastic nature of the signal, and the possibility of noninvasive fiber typing are discussed.

Electrodes↗

PubMed2001

A model for the generation of synthetic intramuscular EMG signals to test decomposition algorithms.

As more and more intramuscular electromyogram (EMG) decomposition programs are being developed, there is a growing need for evaluating and comparing their performances. One way to achieve this goal is to generate synthetic EMG signals having known features. Features of interest are: the number of channels acquired (number of detection surfaces), the number of detected motor unit action potential (MUAP) trains, their time-varying firing rates, the degree of shape similarity among MUAPs belonging to the same motor unit (MU) or to different MUs, the degree of MUAP superposition, the MU activation intervals, the amount and type of additive noise. A model is proposed to generate one or more channels of intramuscular EMG starting from a library of real MUAPs represented in a 16-dimensional space using their Associated Hermite expansion. The MUAP shapes, regularity of repetition rate, degree of superposition, activation intervals, etc. may be time variable and are described quantitatively by a number of parameters which define a stochastic process (the model) with known statistical features. The desired amount of noise may be added to the synthetic signal which may then be processed by the decomposition algorithm under test to evaluate its capability of recovering the signal features.

Action Potentials↗