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Biomedical subjects

A Nardone

Publications and source records attributed to A Nardone.

At least 73 records · Page 4Linked to original sources
PubMed1991

Free and supported stance in Parkinson's disease. The effect of posture and 'postural set' on leg muscle responses to perturbation, and its relation to the severity of the disease.

Upright stance and its reflex control were studied in parkinsonian patients and in age-matched normal subjects. They stood unperturbed on a force-measuring surface (static conditions), or were displaced by movement of a supporting platform (dynamic conditions). During quiet stance the following variables were analysed, with eyes open or closed: position of the centre of foot pressure (CFP), average sway area, length of sway path, amplitude and distribution of tonic leg muscle EMG activity. Perturbations of stance were induced by toe-up or toe-down rotations, and by backward or forward translations of the platform. Amplitude of short, medium and long-latency EMG responses to displacement were measured in the tibialis anterior (TA) and in the three heads of the triceps surae (TS) muscle. The perturbations were produced during both free and supported stance (holding onto a stable structure), under which condition normal subjects suppress medium and long-latency responses. Under static conditions, the only significant finding in parkinsonians was represented by a shift in the position of the CFP. This was correlated with the severity of the disease (Webster scale), the less affected patients being shifted backwards and the more affected patients forwards, with respect to normals. Under dynamic conditions, the reflex responses to perturbations of free stance were similar in both groups. Only the medium-latency burst of gastrocnemius lateralis and the long-latency burst TA evoked by TS stretch were larger in parkinsonians. The amplitude of these responses, as well as of all the others, was not related to the Webster score. Within the patients' group, a relationship between position of CFP and area of EMG burst was found for both medium and long-latency TA responses evoked by forward translation and toe-up rotation, respectively. Under supported conditions, the capability to suppress all medium and long-latency muscle responses to any perturbation was lost or impaired in the parkinsonians. The degree of impairment was unrelated to the position of the CFP, but was significantly related to the severity of the disease. The suppression to 40% (supported/nonsupported), of TA response to toe-down rotation is proposed as the point of separation between normals and parkinsonians. The forward projection of the CFP, occurring in the severe stages of the disease, and the increase in amplitude of some responses to perturbations of free stance might be a compensatory adaptation to the anomalous upright posture.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Different activations of the soleus and gastrocnemii muscles in response to various types of stance perturbation in man.

The soleus (Sol) and medial and lateral gastrocnemii (GM and GL) behave differently during various movements, but no attempt has been made to disclose any distinct activation of these muscles during perturbations of upright stance. Therefore the pattern of activation of the three triceps surae (TS) muscles and of the tibialis anterior (TA) was studied in normal subjects following rotational and linear displacements of a movable platform. The effect of "postural set" on the responses was also studied while holding onto a frame. In free-standing subjects, TS stretches (upward tilt, UT and backward translation, BT) evoked a large short latency response (SLR) in Sol; smaller SLRs were sometimes induced in GM or GL. A medium latency response (MLR) was consistently present in both or only one gastrocnemii. On the average, the amplitude and the frequency of occurrence of the responses were distributed as follows: SLR, Sol greater than GL greater than GM; MLR, GM greater than GL greater than Sol. The type of perturbation did not affect the latency of all TS muscle responses, but the duration, amplitude and frequency of MLRs were larger during BT than UT. MLRs were followed by an antagonistic reaction (AR) in the TA, larger and more frequent during UT than BT. TA stretches (downward tilt, DT and forward translation, FT) induced a TA MLR, with duration and area larger in FT than DT. ARs occurred in one or more muscles of TS, being larger and more frequent in Sol. Under the conditions of stabilized stance, SLRs were not affected, but all the MLRs and ARs were much reduced in amplitude. The analogies between TS and TA MLRs (frequency of occurrence, latency and suppression under stabilized condition) suggest a common underlying mechanism and a similar postural role. On the other hand, all the TS responses are unequally distributed in the individual muscles and in the various subjects. This recommends caution in drawing conclusions in their absence or from their susceptibility to postural set in patients, when only one muscle of TS is being recorded.

Adult↗
PubMed1990

Responses of leg muscles in humans displaced while standing. Effects of types of perturbation and of postural set.

Toe-up or toe-down tilts of a platform on which a subject stands induce early EMG responses in the leg muscles initially stretched by the perturbation and late responses in the antagonist muscles. Early responses are thought to be connected with the stretch of the leg muscle in which they appear. Disagreement exists as to the origin of the late responses occurring in the antagonist muscle. The aims of this study were to assess (1) whether the late responses are induced by afferent volleys from the spindles of the muscle stretched by the initial perturbation, or (2) whether they are connected with the induced overall postural imbalance, and (3) whether the postural set may influence the occurrence of the late responses. Subjects standing on a platform underwent randomized perturbations stretching the soleus (Sol) muscle (upward tilts and backward translations) and tibialis anterior (TA) muscles (downward tilts and forward translations). The platform movement was regulated in order to yield changes in ankle angle of similar extent and velocity during both tilt and translation. Surface EMGs of Sol and TA were recorded bilaterally. An optoelectronic device detected the movements of markers fixed on the body. From these data, movements of the head, and changes in hip, knee and ankle angles, along with variations in the length of Sol, gastrocnemii (Gas) and TA were computed. Both tilts and translations, equally stretching Sol or TA, induced similar early responses in the stretched muscle. Consistent late responses in the antagonist muscle (antagonist reactions, ARs) were induced only by tilts. In spite of similar changes in ankle angles, the most striking differences in body movements between tilts and translations stretching the same leg muscle concerned changes in knee angles and Gas length. Slight differences were also seen in vertical head movements. Standing and holding onto a frame strongly decreased the amplitude and the frequency of occurrence of both early responses and ARs only in the TA muscle, while all Sol responses were not affected. This modulation of TA responses occurred in spite of changes in ankle angle and head movements similar to those occurring under the free-standing condition. It was concluded that early EMG responses are connected with the stretch of the muscle induced by the platform movement. The ARs, on the other hand, appear to be related to the type of overall postural imbalance. The absence of ARs during translations suggests a role in these responses of the afferences from the joint and muscles of the lower limb.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Patterns of activity of perioral facial muscles during mastication in man.

The activity of buccinator, orbicularis oris superior and inferior, quadratus and triangularis muscles was recorded by surface and needle electrodes during spontaneous unilateral mastication of small or large boluses. Their activity was compared with that of the masticatory muscles masseter and digastric, and with the vertical movement of the jaw. The facial muscles were active during mastication, displaying both tonic and phasic activity. Although the cyclic activity was broadly linked to lowering of the jaw, there was no strict time correspondence between the activity of the various facial muscles themselves, or between the activity of the facial muscles and the digastric. The timing and amplitude of facial muscle activity were affected by the duration of the masticatory cycle, the side on which chewing took place, the size of the bolus, and whether or not lip to lip contact was made.

Adult↗
PubMed1989

Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles.

1. We have investigated the possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast-twitch motor units, accompanied by derecruitment of slow-twitch motor units. 2. The behaviour of motor units in soleus, gastrocnemius lateralis and gastrocnemius medialis muscles was studied during (a) controlled isotonic plantar flexion against a constant load (shortening contraction, S), maintained plantar flexion, or dorsal flexion resisting the load and gradually yielding to it (lengthening contraction, L), (b) isometric increasing or decreasing plantar torque accomplished by graded contraction or relaxation of the triceps surae muscles, (c) isometric or isotonic ballistic contractions, and (d) periodic, quasi-sinusoidal isotonic contractions at different velocities. The above tasks were performed under visual control of foot position, without activation of antagonist muscles. The motor units discharging during foot rotation were grouped on the basis of the phase(s) during which they were active as S, S + L and L. The units were also characterized according to both the level of isometric ramp plantar torque at which they were first recruited and the amplitude of their action potential. 3. S units were never active during dorsal flexion; some of them were active during the sustained contraction between plantar and dorsal flexion. Most S + L units were active also during the maintenance phase and were slowly derecruited during lengthening; their behaviour during foot rotations was similar to that during isometric contractions or relaxations. L units were never active during either plantar or maintained flexion, but discharged during lengthening contraction in a given range of rotation velocities; the velocity of lengthening consistently influenced the firing frequency of these units. Such dependence on velocity was not observed in S + L units. 4. A correlation was found between the amplitude of the action potential and the threshold torque of recruitment among all the units. In addition, the amplitudes of both the action potential and the threshold torque were higher in the case of L units than in the case of S and S + L units. Most L units could be voluntarily recruited only in the case of ballistic isometric or isotonic contraction. 5. Occasionally, L units were directly activated by electrical stimulation of motor fibres and their conduction velocity was in the higher range for alpha-axons. In contrast, nerve stimulation could induce a reflex activation of S and S + L units.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Postural adjustments associated with voluntary contraction of leg muscles in standing man.

The postural adjustments associated with a voluntary contraction of the postural muscles themselves have been studied in the legs of normal standing men. We focussed on the following questions. Do postural adjustments precede the focal movement as in the case of movements of the upper limb? Which muscle(s) are involved in the task of stabilizing posture? Can the same postural muscle be activated in postural stabilization and in voluntary movement at the same time, in spite of the opposite changes in activity possibly required by these conditions? Six subjects standing on a dynamometric platform were asked to rise onto the tips their toes by contracting their soleus muscles, or to rock on their heels by contracting their tibialis anterior muscles. The tasks were made in a reaction time (RT) situation or in a self-paced mode, standing either freely or holding onto a stable structure. Surface EMGs of leg and thigh muscles, and the foot-floor reaction forces were recorded. The following results were obtained in the RT mode, standing freely. 1. Rising onto toe tips: a striking silent period in soleus preceded its voluntary activation; during this silent period, a tibialis anterior burst could be observed in three subjects; these anticipatory activities induced a forward sway, as monitored by a change in the force exerted along the x axis of the platform. 2. Rocking on heels: an enhancement in tonic EMG of soleus was observed before tibialis anterior voluntary burst, at a mean latency from the go-signal similar to that of the silent period; this anticipatory activity induced a backward body sway. 3. Choice RT conditions showed that the above anticipatory patterns in muscle activity were pre-programmed, specific for the intended tasks, and closely associated with the focal movement. When both tasks were performed in a self-paced mode, all the above EMG and mechanical features were more pronounced and unfolded in time. If the subjects held onto the frame, the early features in the soleus or tibialis anterior EMG were absent, and the corresponding changes in the foot-floor reaction forces were lacking. The anticipatory phenomena observed are considered postural adjustments because they appear only in the free-standing situation, and induce a body sway in the appropriate direction to counteract the destabilizing thrust due to the voluntary contraction of soleus or tibialis anterior. The central organization and descending control of posture and movements are briefly discussed in the light of the short latency of the anticipatory phenomena and of their close association with the focal movement.

Adult↗
PubMed1988

Shift of activity from slow to fast muscle during voluntary lengthening contractions of the triceps surae muscles in humans.

1. Raw or rectified and integrated electromyograms (integrated EMGs) of the leg muscles were recorded during (a) isotonic ramp shortening or lengthening contractions consisting of foot plantar flexions against a constant load, or dorsal flexions accomplished by braking the load and yielding to it, respectively, and (b) isometric increasing or decreasing plantar torques accomplished by graded contractions or relaxations of the triceps muscles. 2. During plantar flexions or increasing torques, the EMG of soleus, gastrocnemius lateralis, medialis, and peroneus increased in parallel. During decreasing torques, motor unit derecruitment took place gradually and simultaneously. The tibialis anterior was silent. During dorsal flexions, one of two characteristic patterns was observed in different subjects: (a) soleus was abruptly derecruited at the beginning of the task, while gastrocnemius lateralis (or medialis) exhibited a large recruitment lasting throughout the lengthening contraction; (b) soleus remained active during the task, showing large motor unit potentials, while the gastrocnemius lateralis recruitment was of a lesser extent than in (a). Peroneus derecruitment was gradual and tibialis anterior activity was absent in both cases. 3. The EMG patterns observed during plantar flexions or in increasing and decreasing torques, and the two patterns observed during shortening or lengthening contractions, were closely reproduced during sinusoidal oscillations of the foot or in isometric contractions and relaxations. 4. When recruitment of the gastrocnemius lateralis was present during dorsal flexion, the slope of its integrated EMG envelope was steeper, the higher the velocity of lengthening contraction. The most rapid and the slowest tasks, however, did not require its activation. Gastrocnemius lateralis integrated EMGs of an amplitude similar to those occurring during lengthening contractions were observed only during ballistic plantar flexions. 5. The two patterns of triceps activation occurring during lengthening contraction could be traced to different mechanical characteristics of the soleus muscles, the gastrocnemius lateralis being activated preferentially in subjects with long soleus half-relaxation times, and the soleus in subjects with short soleus half-relaxation times. 6. The soleus and gastrocnemius lateralis H reflexes were tested during shortening and lengthening contractions.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1986

Inhibition of jaw-closing muscle activity by tactile air-jet stimulation of peri- and intra-oral sites in man.

There were two distinct periods of suppression in electromyograms of masseter and temporalis muscles in 8 subjects after light tactile stimulation (a puff of air) of the peri-oral zone; the latencies were 16 and 60 ms, respectively. These effects were similar to those induced by painful electrical stimulation. A single period of suppression with a latency of 50 ms, was evoked by tactile stimulation of the mucosa of the hard palate or of the tongue. Threshold for suppression was lower in mucosa than skin. Low-threshold and fast-adapting receptors are likely to be involved in this reflex inhibition.

Adult↗
PubMed1986

Modulation of the Hoffmann reflex by rapid muscle contraction or release.

The inhibition of the H-reflex of the Soleus (Sol) muscle that takes place during and after voluntary release of Sol muscle has been attributed to presynaptic inhibition of autogenetic spindle afferences. In the present study, the time-relationship between onset of H-reflex depression and termination of Sol contraction was investigated to ascertain whether the reflex inhibition is linked to the command to release, or whether it is an accompanying phenomenon connected to changes in the neural outflow from the periphery. A parallel investigation was carried out on the temporal characteristics of the facilitation of the H-reflex that precedes onset of Sol contraction, in an attempt to point at the different functional organization of the two motor tasks. Voluntary releases from a bilateral isometric plantar torque, or bilateral plantar flexions, were performed in response to an acoustic stimulus, in a reaction time (RT) situation. The intervals from the starting signal to complete termination, or to beginning, of the Sol EMG were measured. The H-reflex was evoked at random during the tasks in one leg and its amplitude was referred in time to the end, or to the onset, of the EMG recorded from the contralateral Sol muscle. The RTs of the termination of Sol EMG had an average duration of about 100 ms, being some 20 ms shorter than those of the onset of EMG. In the release-task, the H-reflex amplitude was higher than that of the controls during the holding phase, and started to decrease about 20 ms before the cessation of the EMG.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Voluntary muscle release is not accompanied by H-reflex inhibition in patients with upper moto neuron lesions.

Changes in excitability of the soleus (Sol) monosynaptic reflex arc were investigated in spastic subjects, affected by amyotrophic lateral sclerosis (ALS), upon voluntary relaxation of tonic contraction of triceps surae muscle. Force and electromyograms (EMG) were recorded during triceps release, performed in response to an acoustic signal, in a reaction-time (RT) situation. Sol H-reflex was evoked at random during the task, and its amplitude was referred in time to the end of Sol EMG. At variance with the results for the same task in normal subjects, it was found that in ALS patients the RTs of the termination of EMG were longer than those of the beginning of the EMG, the decrease in force was prolonged and perturbed owing to intercurrent clonus-like EMG activity, and the H-reflex did not undergo the expected profound inhibition. It is suggested that the absence of the activation of presynaptic inhibitory mechanisms by the descending command to release brings about major disorders in voluntary muscle relaxation.

Amyotrophic Lateral Sclerosis↗
PubMed1984

Interhemispheric transfer of voluntary motor commands in man.

The lack of callosal fibres between homotopic areas of the hand in the sensorimotor cortex in man and its possible functional correlates were investigated in normal adult subjects by comparing simple reaction times (RTs) of voluntary movements triggered by a somaesthetic stimulus to the same or opposite side of the body. An air jet was delivered to the skin of distal (index finger) or proximal (shoulder) ipsi- or contralateral zones, and triggered voluntary extension of the index finger or flexion of the forearm. The RT was measured from the arrival of the stimulus to the skin to the onset of the surface EMG of the muscle extensor indicis proprius or biceps brachii. The RTs of the contralateral finger movements triggered by either proximal or distal skin stimuli were significantly longer than the RTs of the corresponding ipsilateral movements (mean difference 11.72 and 15.10 msec respectively). When the task was flexion of the forearm, the differences in RTs between contra- and ipsilateral movements were instead compatible with a transcallosal transfer (mean difference about 2 msec in both cases). It is concluded that transcallosal connections between hand sensorimotor areas are conceivably absent also in man. Furthermore, the delay in contralateral distal performance appears to be due to a lack of transfer of the command through the motor areas, rather than to a lack of transfer of the triggering cutaneous afferent information to the performing hemisphere.

Adult↗
PubMedDate not supplied

Influences of transcutaneous electrical stimulation of cutaneous and mixed nerves on subcortical and cortical somatosensory evoked potentials.

Aim of this study was to assess whether transcutaneous electrical nerve stimulation (TENS) 'gates' somatosensory evoked potentials (EPs) peripherally or centrally, and which afferent fibres and sensory nuclei mediate this effect. The following waves were recorded after stimulation of the median nerve at the wrist or of the digital nerves of the index finger: N9, the cervical N11 and N13, the parietal P9, P11, P14, N18, N20, P22, P27, P40. When both median or digital nerve EPs were conditioned by TENS delivered to the median nerve, reduction in amplitude of N9, P14, N18 and later generated cortical waves was observed. To measure the central contribution to this decrease, unconditioned 'reference' EPs were evoked by stimulating with a current strength yielding an N9 potential of an amplitude equal to that obtained during TENS. In this case, the amplitude of P14, N18 and later cortical waves was significantly greater than during TENS. When both median or digital nerve EPs were conditioned by TENS delivered to the digital nerves, waves were only slightly affected. No effects were seen on the EPs elicited from the median or index finger digital nerves when TENS was administered to the contralateral median or digital nerves or to the ipsilateral middle finger. It is concluded that TENS gates the somatosensory volley, both at a peripheral level through a 'busy line-effect' on large afferent fibres, and centrally at the level of the cuneatus nucleus.

Adult↗
PubMedDate not supplied

The effects of injectable sodium selenite on immune function and milk production in Sardinian sheep receiving adequate dietary selenium.

The aim of this preliminary study was to determine the effects of selenium (Se) injection on Se status, cell-mediated immunity (CMI), milk yield and milk somatic cell count (MSCC) of ewes fed adequate amounts of Se, and on Se status, passive immunization and CMI of their offspring. Thirty days before lambing, 36 Sardinian ewes were assigned to one of three groups. One group (NT) was not treated; a second group (BL) was given 5 mg of Se on day 30 before lambing; a third group (BLL) was given 2.5 mg of Se on day 30 before lambing and at lambing. Selenium was given intramuscularly as sodium selenite. Selenium status was assessed by measuring glutathione peroxidase activity of erythrocytes (GSHpx-E). The CMI was measured by determining the increases in double skinfold thickness after intradermal injection of phytohaemagglutinin (PHA). Compared to their NT counterparts, ewes belonging to BL and BLL groups and their offspring had significantly higher GSHpx-E (P < 0.01). The GSHpx-E values of lambs were positively related to those of their mothers (P < 0.0005). Ewes of group BL had a greater (P < 0.01) response to PHA 6 h after injection than ewes of the NT group. Lambs born to BL and BLL ewes had a greater (P < 0.0001) response to PHA 24 h after injection. Responses of ewes and lambs to PHA 24 h after injection were positively related (P < 0.05). Serum immunoglobulin at 10 days of age did not differ significantly among the three groups of lambs. Compared to the NT group, milk yield on day 70 of lactation was significantly higher in BL ewes (P < 0.05). The MSCC was not affected significantly by Se injection. Immunoresponsiveness and milk yield might represent additional and appropriate criteria to consider when re-evaluating Se requirements of dairy sheep.

Animals↗