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Biomedical subjects

M Panizza

Publications and source records attributed to M Panizza.

At least 19 recordsLinked to original sources
PubMed2001

Removal of organic pollutants from industrial wastewater by electrogenerated Fenton's reagent.

This study was performed to investigate the treatment of an industrial wastewater mainly containing naphthalene- and anthraquinone-sulphonic acids, by electrogenerated Fenton's reagent. The hydrogen peroxide was produced in situ by electrochemical reduction of oxygen on graphite-felt cathodes and the Fe2+ ions were also regenerated by cathodic reduction of Fe3+. The influence of cathode potential, Fe2+ concentration and electrode surface pre-treatment on chemical oxygen demand (COD) removal and colour fading were studied. Results indicated that the higher COD removal was obtained in the presence of 3 mM of ferrous ions working at a constant potential of -1 V vs. SCE. Moreover, it was shown that both chemical and electrochemical pre-treatments of the cathode surface resulted in a decrease of COD depletion.

Anthraquinones↗
PubMed1998

Differences between the time constant of sensory and motor peripheral nerve fibers: further studies and considerations.

Using a method of latent addition, we previously demonstrated that sensory fibers had time constants that were about three times longer than those of motor fibers. The aim of the present work was to confirm this difference by determining the time constants for single sensory axons by using microneurography and for single motor axons by recording single motor units with bipolar concentric needle electrodes. To determine the influence of the conditioning pulse on the neural time constant, we used both depolarizing and hyperpolarizing conditioning pulses. When hyperpolarizing conditioning pulses at comparable intensity were applied, the tendency was to find shorter time constants than when depolarizing pulses were applied, although still with the motor time constant being slightly shorter. Although the absolute values varied with the different methods, the sensory time constant was generally three times the motor time constant for depolarizing conditioning stimuli, whereas for hyperpolarizing conditioning stimuli the difference dropped to about one and a half. These characteristics improve understanding of the behavior of sensory and motor axons, and, in particular, explain the differential excitability. Determination of neural time constants might prove valuable for clinical use.

Adult↗
PubMed1998

Hypokalemic thyrotoxic paralysis: a rare cause of tetraparesis with acute onset in Europeans.

We describe a 21-year-old Italian male affected by hypokalemic tetraparesis with acute onset. In the emergency ward, the patient was agitated, with tachycardia (140/min) and systolic hypertension (180/70 mm Hg). He was not able to flex the lower extremities against a light resistance and furthermore, he was hypotonic and without tendon reflexes. One hour later he developed strength deficit of the upper extremities as well. Biochemical analyses revealed severe hypopotassemia (2.1 meg/l). After administration of 140 meq potassium phosphate, the patient began to improve, and 12 h after the onset he was able to walk normally. Successive investigations documented an undiagnosed case of Graves' disease. Thyrotoxic hypokalemic paralysis has been observed almost only in Asians, however, with this case and others reported, we believe that it should be considered as a cause of muscular paralysis also in Caucasians.

Acute Disease↗
PubMed1997

Computer-aided determination of the silent period.

Silence of electromyographic (EMG) activity after an evoked muscle twitch has been studied extensively. However, different criteria have been used to determine the level at which the silence of muscle activity ends, and the purpose of this work was to develop an objective method able to determine the silent period even when data were acquired using different EMG instruments. The silent period evoked by transcranial magnetic stimulation was determined bilaterally from abductor pollicis brevis (APB) muscles in 11 subjects, from trapezius muscles in 9 subjects, and from sternocleidomastoid muscles in 11 subjects. All subjects were healthy controls and gave their informed consent to participate in the study. Muscle activity was recorded via surface electrodes. Recordings from 10 stimuli were rectified, averaged, and plotted logarithmically by dividing the mean of the prestimulus EMG activity into the whole trace. Plotted in this way, the one-level represents the mean rectified EMG amplitude of the prestimulus activity. The end of the silent period was measured automatically as the moment at which Student's t test was no longer significantly different, when testing the window of mean prestimulus EMG activity with respect to a 4-ms window centered around the assumed end of the silent period (resolution 0.1 ms). The mean silent periods were 183.7 +/- 49.8 ms for APB, 194.2 +/- 28.8 ms for trapezius, and 194.8 +/- 73.6 ms for sternocleidomastoid muscles, measured from the M-response latency (mean latency: APB 19.7 +/- 1.9 ms, trapezius 7.8 +/- 0.6 ms, and sternocleidomastoid 6.7 +/- 0.8 ms). Computer-aided measurement proved to be a fast and objective tool able to standardize determination of the silent period.

Adult↗
PubMed1996

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.

Electric Stimulation↗
PubMed1996

A volume-conduction analysis of magnetic stimulation of peripheral nerves.

Magnetic stimulation is a method to study several nervous disorders as well as the intact nervous system in humans. Interest in magnetic stimulation of peripheral nerves has grown rapidly, but difficulties in locating the site of excitation have prevented it from becoming a routine clinical tool. It has been reasoned that the activating function of long and straight nerves is the first spatial derivative of the electric field component parallel to the nerves. Therefore, to predict the site of activation, one has to compute this field feature. We describe here an analytical mathematical model and investigate the influence of volume-conductor shape on the induced field. Predictions of the site of activation are given for typical stimulation coil arrangements and these results are compared with experimental and literature data. Comparisons suggest that the activating function is not simply the spatial gradient of the induced electric field, but that other mechanisms are also involved. The model can be easily utilized in the search for more efficient coil constructions and improved placements with respect to the target nerves.

Computer Simulation↗
PubMed1994

The time constants of motor and sensory peripheral nerve fibers measured with the method of latent addition.

The time constants of motor and sensory fibers in the human ulnar, median and tibial nerves were determined using the method of latent addition. Two square-wave stimuli were applied: the first one was subthreshold and the second, at various delays relative to the first, was adjusted to achieve threshold activation. Strength-delay curves were obtained, from which the time constant was determined using a mathematical model. Sensory fibers had time constants that were about 3 times the time constant for motor fibers. The strength-delay curves gave similar time constants as those obtained from strength-duration curves.

Adolescent↗
PubMed1993

Principles of digital sampling of a physiologic signal.

The practice of clinical neurophysiology requires fast, reliable and accurate assessment of a variety of biologic signals. Appropriate filters and rates of analog-to-digital sampling must be used to avoid distorting the signal. Using principles of sampling theory and examples, we describe the frequency content of signals encountered in clinical neurophysiology laboratories, offer guidelines for band-limiting frequencies, and give rules for determining minimal sampling frequencies. Errors introduced by undersampling (aliasing) are illustrated. When sophisticated computational techniques, such as discrete Fourier transform, are used to reconstruct the original wave form, a sampling frequency just above the double of the highest frequency content of the signal is adequate. Sampling neurophysiologic wave forms for direct display, however, requires a sampling frequency at least 4 times as high as that of the upper frequency filter.

Electromyography↗
PubMed1992

Relevance of stimulus duration for activation of motor and sensory fibers: implications for the study of H-reflexes and magnetic stimulation.

Electric stimuli with durations of 0.5-1.0 msec are optimal for studies of H-reflexes. It is more difficult to obtain H-reflexes with shorter duration stimuli or with magnetic stimulation. In order to understand this behavior, we studied the excitation thresholds for motor and sensory fibers in the ulnar, median and tibial nerves using both electric and magnetic stimulation. For short duration electrical stimuli (0.1 msec) the threshold for motor fibers is lower than for sensory fibers. For longer duration electric stimuli (1.0 msec) the threshold for sensory fibers is lower. For magnetic stimulation the threshold for motor fibers is much lower than for sensory fibers. Thus, stimulus duration is a critical parameter for sensory fiber excitation, and current magnetic stimulators are not optimal.

Adult↗
PubMed1992

Determining the site of stimulation during magnetic stimulation of a peripheral nerve.

Magnetic stimulation has not been routinely used for studies of peripheral nerve conduction primarily because of uncertainty about the location of the stimulation site. We performed several experiments to locate the site of nerve stimulation. Uniform latency shifts, similar to those that can be obtained during electrical stimulation, were observed when a magnetic coil was moved along the median nerve in the region of the elbow, thereby ensuring that the properties of the nerve and surrounding volume conductor were uniform. By evoking muscle responses both electrically and magnetically and matching their latencies, amplitudes and shapes, the site of stimulation was determined to be 3.0 +/- 0.5 cm from the center of an 8-shaped coil toward the coil handle. When the polarity of the current was reversed by rotating the coil, the latency of the evoked response shifted by 0.65 +/- 0.05 msec, which implies that the site of stimulation was displaced 4.1 +/- 0.5 cm. Additional evidence of cathode- and anode-like behavior during magnetic stimulation comes from observations of preferential activation of motor responses over H-reflexes with stimulation of a distal site, and of preferential activation of H-reflexes over motor responses with stimulation of a proximal site. Analogous behavior is observed with electrical stimulation. These experiments were motivated by, and are qualitatively consistent with, a mathematical model of magnetic stimulation of an axon.

Adult↗
PubMed1992

Optimal focal transcranial magnetic activation of the human motor cortex: effects of coil orientation, shape of the induced current pulse, and stimulus intensity.

We studied the effects of coil orientation, stimulus intensity, and shape of the induced current pulse on the amplitudes of motor evoked potentials in the left abductor pollicis brevis of 10 normal adults who had transcranial magnetic stimulation. The optimal direction of currents induced in the brain is approximately perpendicular to the central sulcus, flowing diagonally from back to front. The most effective coil orientation depends on the shape of the induced current pulse and, when the first and second phases of the pulse are of similar size, also on the intensity of stimulation. Optimal mapping of the human motor cortex with magnetic stimulation requires knowledge of the influences of all these factors.

Adolescent↗
PubMed1991

Spinal cord inhibitory mechanisms in Parkinson's disease.

We studied two spinal cord inhibitory mechanisms, recurrent (Renshaw) inhibition and reciprocal inhibition, in seven patients with asymmetric Parkinson's disease in order to determine their contribution to the pathogenesis of rigidity. Recurrent inhibition, studied in the leg, did not differ from that found in normal subjects. All three periods of reciprocal inhibition, studied in the forearm, were present but reduced in magnitude compared with those observed in normal subjects. The arms, whether more symptomatic or less symptomatic, gave similar results. The diminution of all three periods of reciprocal inhibition is similar to the findings in patients with dystonia and is apparently indicative of an abnormal supraspinal influence on spinal mechanisms in these two disorders of basal ganglia function.

Adult↗
PubMed1990

Effects of coil design on delivery of focal magnetic stimulation. Technical considerations.

The localization of effects from magnetic coil stimulation is not immediately obvious. We measured the magnetic fields produced by several different coils and compared the results with theoretical calculations. Magnetic stimuli were delivered from a Cadwell MES-10 magnetic stimulator using 3 circular coils (one 9 cm in diameter; two with an angulated extension, 5 and 9 cm in diameter) and twin oval coils arranged in a butterfly shape (each coil approximately 4 cm in diameter) and from a Novametrix Magstim 200 using two circular flat-spiral coils (6.7 and 14 cm in diameter). Peak-induced strength of the magnetic field was recorded with a measuring loop (1 cm in diameter) at different distances from the center of the coil. When the measuring loop was moved in the same plane laterally from the center of the coil, for all coils except the butterfly-shaped coil, the field was highest in the center and fell off near the circumference of the coil. The field dropped progressively when measurements were made more distant from the plane of the coils. The electric field induced from the magnetic coil could be calculated from the coil geometry. For all coils except the butterfly-shaped coil, the largest electric field was at the circumference of the coils. The 6.7 cm flat-spiral coil induced currents similar to those induced by the larger coils but more focally. The butterfly-shaped coil induced the largest currents under its center, where the circumferences of the two component coils come together. The component of the electric field parallel to the wire in the center of this coil was the largest and most localized.

Electric Stimulation↗
PubMed1990

H-reflex recovery curve and reciprocal inhibition of H-reflex in different kinds of dystonia.

We studied the H-reflex recovery curve and reciprocal inhibition of the H-reflex bilaterally in the upper limb of 5 patients with generalized dystonia, 5 patients with blepharospasm, 10 patients with spasmodic torticollis, and 14 patients with writer's cramp. We compared the results with those obtained from a group of healthy volunteers. The recovery curve of the H-reflex was normal in patients with writer's cramp or blepharospasm, but showed an increase of the physiologic recovery at a 200 msec delay in patients with spasmodic torticollis or generalized dystonia. Reciprocal inhibition of the H-reflex showed a decrease in the amount of inhibition in all the patient groups and a facilitation of the H-reflex during the 3rd period of inhibition in the patients with spasmodic torticollis or generalized dystonia.

Adult↗
PubMed1990

[Diagnosis and treatment of myasthenia gravis: study of an inpatient population].

Between 1974 and 1987 we have examined 50 patients with the diagnosis of myasthenia gravis. Female preponderance (2.5: 1) was found. Also, it was observed that most of the patients were aged between 20 and 49 years. Beside the clinical examination, the following tests were performed: (1) edrofonium test, (2) supramaximal repetitive nerve stimulation, (3) serum acetylcholine antibodies titers and (4) intraperitoneal passive transference of patient's sera to mice and recording of meepp's amplitude in the phrenic-diaphragm preparation in vitro. These four tests gave positive values for myasthenia in 90 to 100% of the cases. Thymus radiological examination was carried out by pneumomediastinography, which proved to correlate with the histological picture of the gland, and computed tomography, which disclosed some discrepances with the histology. Treatment was based on anticholinesterase drugs, corticosteroids and thymectomy, being the corticosteroids the most valuable therapeutical tool. Nine patients treated with steroids disclosed transitory worsening of their signs and symptoms at very early stages after onset of corticosteroid therapy, 6 of them had a disfavorable course in their follow-up. This observation seem to have value in the early prognosis of the disease.

Adolescent↗
PubMed1989

Optimal stimulus duration for the H reflex.

Authorities advocate different stimulus durations to produce an H reflex. In order to find the optimal stimulus duration for recording H reflexes, the recruitment curves for H reflexes and M responses were studied in 10 healthy subjects. The H reflex was recorded in the upper and lower extremities, and the durations of the electrical stimulus used ranged from 0.1 to 3 msec. The amplitude of the H reflex and the relation between the H reflex and M response changed with stimulus duration. H reflexes are brought out to advantage using a stimulus duration between 0.5 and 1 msec.

Adult↗
PubMed1989

Changes in tetrodotoxin-resistant action potentials after passive transfer of myasthenia gravis patient sera.

Muscle electrical activity has been studied in mice after intraperitoneal injection of sera from myasthenia gravis (MG) patients. Myasthenic serum did not modify the electrical properties of innervated muscle fibres. The resting membrane potential and the action potential parameters remained unchanged. However, tetrodotoxin (TTX)-resistant action potentials of denervated muscles were reduced by myasthenic serum, possibly in association with receptor endocytosis induced by the immunoglobulin. However, a direct effect of MG serum on TTX-resistant sodium channels cannot be ruled out.

Action Potentials↗