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Biomedical subjects

M Manfredi

Publications and source records attributed to M Manfredi.

At least 199 records · Page 11Linked to original sources
PubMed1987

Intracranial stimulation of the trigeminal nerve in man. III. Sensory potentials.

Percutaneous electrical stimulation of the trigeminal root was performed in 18 subjects undergoing surgery for idiopathic trigeminal neuralgia or implantation of electrodes into Meckel's cave for recording of limbic epileptic activity. All subjects had normal trigeminal reflexes and evoked potentials. Sensory action potentials were recorded antidromically from the supraorbital (V1), infraorbital (V2) and mental (V3) nerves. In the awake subject, sensory potentials were usually followed by myogenic artifacts due to direct activation of masticatory muscles or reflex activation of facial muscles. In the anaesthetised and curarised subject, sensory potentials from the three nerves showed 1.4-2.2 ms onset latency, 1.9-2.7 ms peak latency and 17-29 microV amplitude. Sensory conduction velocity was computed at the onset latency (maximum CV) and at the peak latency (peak CV). On average, maximum and peak CV were 52 and 39 m/s for V1, 54 and 42 m/s for V2 and 54 and 44 m/s for V3. There was no apparent difference in CV between subjects with trigeminal neuralgia and those with epilepsy. A significant inverse correlation was found between CV and age, the overall maximum CV declining from 59 m/s (16 years) to 49 m/s (73 years). This range of CV is compatible both with histometric data and previous electrophysiological findings on trigeminal nerve conduction. Intraoperative intracranial stimulation is also proposed as a method of monitoring trigeminal function under general anaesthesia.

Action Potentials↗
PubMed1987

Stimulation of motor tracts in motor neuron disease.

The muscle responses evoked by cortical and cervical stimulation in 11 patients with motor neuron disease were studied. The muscle potential in the abductor pollicis brevis, evoked by median nerve stimulation and the somatosensory potential evoked by wrist stimulation were also studied. In eight of 11 patients there was absence or increased central delay of the responses evoked by cortical stimulation. In four patients muscle responses on cervical stimulation and muscle action potentials on median nerve stimulation were also altered, indicating peripheral abnormalities. Somatosensory responses evoked by wrist stimulation were normal. Electrophysiological techniques are helpful in estimating the site of motor involvement in motor neuron disease.

Action Potentials↗
PubMed1987

Cortical and cervical stimulation after hemispheric infarction.

Cortical and cervical stimulation has been performed in 20 patients with hemiparesis or hemiplegia due to hemispheric infarction and in 20 control subjects. The motor action potentials (MAPs) were recorded from biceps and thenar muscles. MAPs evoked by stimulation of the undamaged hemisphere were normal in 18 out of 20 patients and in two there was a slight increase of central conduction time (CCT). The stimulation of the motor cortex of the damaged hemisphere did not evoke any response in 15 patients; in two the MAPs were absent in one muscle and in the remaining three were delayed in one or both muscles. Cervical MAPs were normal in 18 patients and delayed in the thenar muscle in two patients.

Action Potentials↗
PubMed1987

Neurophysiologic assessment of trigeminal function after surgery for trigeminal neuralgia.

To assess the function of the three trigeminal divisions, we studied corneal reflex, early and late blink reflexes, early and late masseter silent periods, and jaw jerk in normal subjects and in 35 patients submitted to surgery for trigeminal neuralgia. The corneal reflex was most sensitive to thermocoagulation and the jaw jerk to microcompression; the other reflexes showed an intermediate behavior, depending on afferent fiber size. Trigeminal function was less impaired after microcompression and recovered earlier than after thermocoagulation.

Adult↗
PubMed1986

Inhibition of jaw-closing muscles by electrical stimulation of the ophthalmic division in man.

High-intensity stimulation of the supraorbital region elicits, together with a blink reflex, a reflex inhibition of the jaw-closing muscles in normal man. The response differs from the well known inhibition obtained by intra- and perioral stimulation in two main features. Firstly, it consists of a single late silent period (SP), only occasionally preceded by a short and partial decrease of the background EMG activity; secondly, the inhibitory response appears at a rather high threshold, requiring a stimulus intensity which is 4-fold the sensory perception threshold and 3-fold that required to evoke the blink reflex. Electrical and mechanical stimulation of the cornea failed to evoke a significant inhibitory reflex. The silent period and the blink reflex were similarly affected by local anaesthetic infiltration of the supraorbital skin, suggesting that the afferents subserving the two reflexes belong to the same fibre group; the higher threshold of the supraorbital inhibitory response may be explained by the need for a larger spatial summation. The considerable latency gain and relatively rapid habituation shown by the supraorbital inhibitory response imply a multisynaptic circuit, similar to that responsible for the second silent period which occurs following 'oral' stimulation. A common interneuronal net for these two reflexes is suggested by the results of interaction experiments employing combined supra- and infraorbital stimulation.

Adult↗
PubMed1986

Excitability of the corneal reflex in man.

The corneal reflex evoked by electrical stimulation of the corneal mucosa and the blink reflex evoked by electrical stimulation of the supraorbital nerve were recorded in 8 normal subjects. Habituation to repetitive stimulation and the recovery cycle to double shock were studied. The corneal reflex habituated significantly to repetitive stimulations at a rate of 0.2-1 Hz but was more resistant than the late component of the blink reflex (R2). There was a clear dissociation between the recovery of the corneal reflex and that of R2; the corneal reflex was again less affected by the proceeding impulse. These results suggest that the corneal reflex is relayed through fewer intramedullary synapses than R2.

Adult↗
PubMed1986

Fast complex arm movements in Parkinson's disease.

Fast arm movements involving the shoulder and elbow joints have been analysed in normal controls and in patients with Parkinson's disease. The subjects were requested to draw on a graphic tablet triangles and squares of different size and shape. The patients produced a larger number of EMG burst compared with controls. The movements were accurate, and each segment of the geometric figures was performed with a roughly straight trajectory, but the time necessary to trace the geometric figures and the pauses at the vertices were prolonged. We conclude that in Parkinson's disease the disability in generating two joint ballistic movements depends on a difficulty in running motor programmes for complex trajectories.

Adult↗
PubMed1986

[Nursing education in Latin America].

The article identifies health trends that must be taken into account in nursing and nursing education in Latin America if the goal of health for all by the year 2000 is to be achieved: population growth, the aging of the population, the rise of chronic diseases in groups at risk, the emergence of new pathological entities, the higher awareness of users of health services, and changes in the composition of the family and in the urban-rural composition of the population. The influence of these tendencies on nursing practice and training is examined. In the examination of practice, critical areas stand out: the numbers, distribution and use of nursing personnel; the quality of practice; the definition of functions for personnel categories; participation in decision-making; and preparation to assume new functions. On the education side, the article examines the situation, envisages the needed activities, and outlines a model study plan guided by the following principles: a comprehensive view of man in society; an epidemiologic and "dialectic" conception of the health/disease process; adherence to the scientific method; attention to priority health problems; a scientific understanding of the object of study; integration of theory and practice; and a multisector and multiprofession approach to nursing.

Education, Nursing↗
PubMed1985

The corneal reflex and the R2 component of the blink reflex.

A reflex contraction of the human orbicularis oculi muscles can be evoked by stimulation of either the supraorbital region ("blink reflex") or the cornea ("corneal reflex"). We found that the latency of the corneal reflex was longer, and the duration was longer than the R2 component of the blink reflex. The absolute refractory period of the R2 component of the blink reflex was longer after supraorbital than after corneal conditioning stimulation. When the R2 component of the blink reflex was habituated by repetitive stimuli, stimulation of the cornea still evoked a reflex, but supraorbital stimulation produced only a depressed R2 response. These findings suggest that the two reflexes do not have identical neural connections.

Adult↗
PubMed1985

[Corneal reflex in normal and pathological subjects].

The orbicularis oculi response can be evoked both by mechanical stimulation of the cornea (corneal reflex) and by electrical stimulation of the skin overlying the supraorbital nerve (blink reflex). Mechanical stimuli to the cornea activate A delta and C free nerve endings of the corneal mucosa. Electrical stimuli to the supraorbital nerve activate A beta, A delta and C fibers of the nerve trunk. Both reflexes present a bilateral late response, but the blink reflex shows in addition an early ipsilateral component (R1), which has never been observed with the corneal stimulation in man. We have developed a simple technique of electrical stimulation of the cornea which provides stable responses and allows precise measurements of threshold and latency of the reflex. In normal subjects, the threshold ranged from 50 to 350 microA, and the maximal stimulus that the subject could bear (tolerance level) ranged from 1000 to 2500 microA. The minimal latency to tolerance level stimuli was 39 +/- 3 msec. The latency difference between the direct responses evoked from the two opposite corneas never exceeded 8 msec and the difference between the direct and consensual responses elicited from the same cornea never exceeded 5 msec. An early ipsilateral component similar to the R1 response of the blink reflex was not observed, even with supramaximal stimulation. The electrically evoked corneal reflex was normal in 10 cases of essential trigeminal neuralgia, while the responses showed significant abnormalities in 18 subjects submitted to thermocoagulation of the Gasserian ganglion as a treatment of neuralgic pain, as well as in 2 cases of symptomatic neuralgia.(ABSTRACT TRUNCATED AT 250 WORDS)

Blinking↗
PubMed1984

Recovery cycle of the masseter inhibitory reflex in man.

The masseter inhibitory reflex from stimulation of the mental nerve has been recorded electromyographically in 10 healthy subjects. The recovery cycle of the two silent periods interrupting the tonic contraction of the masseter muscles have been studied with the paired shock technique. There was a clear dissociation between the recovery of early and late inhibition, the latter being far more affected by a preceding impulse. It is concluded that the two silent periods are mediated by separate neural nets. The differences with the recovery curves of the two components of the blink reflex are discussed.

Adult↗
PubMed1984

Two joints ballistic arm movements.

Fast planar arm movements involving two joints have been analyzed in humans. The EMG activity associated with the drawing of straight lines or geometric figures was characterized by sequences of bursts in the agonist and antagonist muscles of constant duration and different amplitude. The shape of each trajectory is defined by a particular sequence of burst activity in the four muscles studied. A pattern of one burst in the agonist and one in the antagonist is the basic building block for different kinds of ballistic trajectories. The time of execution increased linearly with the number of sides of the geometric figures by steps of about 210 ms and did not increase linearly with their size.

Adult↗