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Biomedical subjects

S Radovanović

Publications and source records attributed to S Radovanović.

17 recordsLinked to original sources
PubMed1998

Changes in fusimotor activity during repetitive lengthening muscle contractions in decerebrate cats.

Responses of fusimotor neurons to lengthening vs isometric contractions have been studied in decerebrate cats. Spike discharges of fusimotor neurons to the medial gastrocnemius muscle were recorded from this muscle nerve filament during sequences of contractions and/or stretches of the lateral gastrocnemius and soleus muscles. The sequences lasted for 250-450s (duty cycle 4:2 s). Isometric contractions were elicited by electrical stimulation (40 Hz, 1.3 times motor threshold) of the muscle nerves. Lengthening contractions were elicited in the same way while the muscles were stretched by 4 mm at a velocity of 1 mm/s. Of 25 fusimotor neurons studied, 23 responded to muscle contractions with an increase in firing rate, subsiding towards the end of the sequence. The increase was either modulated with each subsequent contraction or smooth throughout the sequence. Approximately 64% of fusimotor neurons, responding to muscle contractions, responded in a similar way to the sequences of muscle stretches, applied alone. Responses to sequences of the lengthening contractions were significantly larger, on average, than those to the isometric ones, but smaller than the sum of the responses to the contractions and stretches applied separately. On the other hand, they were also larger in fusimotor units, showing no overt responses to muscle stretches alone.

Animals↗
PubMed1998

The effects of prior antagonist muscle vibration on performance of rapid movements.

The effects of prior vibration of the antagonist triceps muscle on the performance of rapid discrete elbow flexion movements were studied in healthy volunteers. The subjects performed 520 movements over five experimental sessions. The application of prior vibration resulted in a shift of the initial position, an undershoot of the final position in untrained subjects, and also in trained subjects if not applied during practice. On the contrary, no undershoot occurred in trained subjects when prior vibration was applied during practice. Improvement in movement performance, as judged by a decrease in variability of the final position, was less successful when vibration was applied during practice. It is supposed that the undershoots were due to prior vibration-induced alterations in proprioceptive messages and a consequent erroneous sense of the arm position. These effects seem to be overcome by practice, but also seem to interfere with learning-based movement improvement.

Acceleration↗
PubMed1997

A comparison of the effects of agonist and antagonist muscle fatigue on performance of rapid movements.

The aim of this study was to investigate the effects of agonist and antagonist muscle fatigue on the performance of rapid, self-terminating movements. Six subjects performed rapid, consecutive elbow flexion and extension movements between two targets prior to and after fatiguing either the elbow flexor or elbow extensor muscles. The experiments demonstrated consistent results. Agonist muscle fatigue was associated with a decrease in peak velocity and peak deceleration, while a decrease in peak acceleration was particularly prominent. Antagonist muscle fatigue, however, was associated with a decrease in peak deceleration, while a decrease in both the peak velocity and peak acceleration was modest and, in some tests, non-significant. The relative acceleration time (i.e. acceleration time as a proportion of the total movement time) increased when agonists were fatigued, but decreased when antagonists were fatigued. Taken together, these results emphasize the mechanical roles of the agonist and antagonist muscles; namely, the fatigue of each muscle group particularly affected the movement phase in which that group accelerated a limb, while changes of the movement kinematics pattern provided more time for action of the fatigued muscles. In addition, the results presented suggest that agonist muscle fatigue affects movement velocity more than antagonist muscle fatigue, even in movements that demonstrate prominently both mechanical and myoelectric activity of the antagonist muscles, such as rapid, self-terminating movements.

Adult↗
PubMed1997

Effects of cutaneous afferent input on fatigue-induced changes in fusimotor activity of decerebrate cats.

Interaction of cutaneous and small-diameter, primarily fatigue-induced, muscle afferent inputs on fusimotor neurons has been studied in decerebrate cats. Spike discharges of fusimotor neurons to medial gastrocnemius were recorded from filaments dissected free from this muscle nerve. Non-noxious mechanical stimuli (10 Hz, 2 mm vibration) were applied to the skin area on the lateral side of the heel, innervated by sural nerve, during long-lasting (250 s) fatiguing contraction of lateral gastrocnemius and soleus muscles, elicited by electrical stimulation (40 Hz, 1.3 x motor threshold) of the muscle nerves. In 15 units (58%) the pattern of responses to muscle contraction and/or fatigue (initial transient, and late long-lasting increase in firing rate, respectively) was preserved in the presence of skin vibration which, by itself, provoked either a slight increase or no changes in fusimotor discharge rate. Pattern of the response to skin vibration prevailed in the presence of muscle contraction and fatigue only if the vibration by itself induced marked increase in fusimotor discharge rate (three units). In the remaining eight units the responses to both stimuli applied simultaneously were dissimilar in pattern to the response to either stimulus applied alone: the initial, tension-related, increase in firing rate was prolonged, while the late, fatigue-induced one was attenuated and its post-contraction part almost abolished. Possible mechanisms and functional role of interaction between cutaneous and muscle afferent inflows are discussed.

Afferent Pathways↗
PubMed1996

Central changes in muscle fatigue during sustained submaximal isometric voluntary contraction as revealed by transcranial magnetic stimulation.

Changes in responses to transcranial magnetic stimulation (TMS) during submaximal isometric voluntary contraction (60% of maximal voluntary contraction (MVC) of the adductor pollicis muscle and the subsequent recovery period have been studied in healthy volunteers. TMS at twice the motor threshold was applied during the sustained contraction, as well as at rest and during short-lasting (2 s) 60% MVCs before and immediately after the sustained contraction, and at 5 min intervals during the recovery period. Both motor evoked potential (MEP) magnitude (peak and area) and silent period (SP) duration in electromyographic activity (EMG) of the adductor pollicis muscle showed a gradual decrease up to the endurance point and an increase thereafter. MEPs elicited at rest immediately after the fatiguing contraction were larger, whereas those elicited later on during the recovery period did not differ significantly from the controls. It is suggested that the changes in responses to TMS, divergent from those in ongoing voluntary EMG during the sustained 60% MVC, indicate complex processes at levels preceding the motor cortex output cells in an attempt to maintain a submaximal contraction of the fatigued muscle. The increase in MEP magnitude after the sustained 60% MVC may indicate residual changes in cortical activity after fatiguing contraction.

Adult↗
PubMed1995

Fusimotor outflow to pretibial flexors during fatiguing contractions of the triceps surae in decerebrate cats.

Changes in discharge rate of fusimotor neurones to pretibial flexor muscles were recorded during and after long-lasting fatiguing isometric and/or isotonic contractions of triceps surae in decerebrate cats. The contractions were elicited by electrical stimulation of the nerves to triceps. Fusimotor spikes were recorded from nerve filaments dissected free from the peroneal nerve. Responses of the fusimotor neurones were diverse. In isometric regime, 22 out of 40 units recorded exhibited an initial increase at the onset of muscle contraction, different in amplitude and duration among the units. In seven of these units an additional brisk burst of spike discharges, of different duration, occurred at the end of the contraction. In 15 fusimotor neurones (14 units with the initial response and an additional unit without it) a slow increase in discharge rate developed, starting during the contraction and outlasting it. In another eleven units the initial response was a decrease in discharge rate, lasting in six of them throughout the contraction. Another six units exhibited a sustained increase in discharge rate throughout the contraction, as well as, at a lower level, but still above the spontaneous one, thereafter. Similar patterns of changes in discharge rate, recorded in 31 of the units, were encountered during isotonic triceps contractions. It should be mentioned that many (about 20) additional silent neurones, responding to manipulating the skin and paw and/or stroking the fur, but not to triceps contractions were encountered. The majority of changes in discharge rate of fusimotor neurones to pretibial flexors differed markedly from those found previously in fusimotor neurones to triceps and hamstring muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMedDate not supplied

[The effect of bronchodilators in aerosol form on pulmonary function in patients with pulmonary emphysema].

The effects of inhaling 400 micrograms of fenoterol were investigated in patients with clinical and radiological evidence of pulmonary emphysema. Pulmonary function tests were consistent with emphysema in all patients. There was a small rise in the forced expiratory volume in one second (FEV1), but there was a much greater increase in forced vital capacity (FVC). There was not consistent change in the FEV1/FVC ratio after fenoterol administration and this ratio is misleading as an indicator of bronchodilator responsiveness in patients with emphysema. Symptomatic improvement after fenoterol is thus a valuable addition to treatment in patients with pulmonary emphysema and the response to treatment is best judged by measuring the improvement in FVC.

Adult↗
PubMedDate not supplied

[The importance of the transfer factor test in the diagnosis of pulmonary emphysema].

Physical examination, X-ray and lung function studies were performed in a group of 29 patients with chronic obstructive lung diseases. According to the diffusing capacity, patients were divided into two subgroups: one with normal and the other with decreased lung transfer-factor. Comparing the parameters of pulmonary function significantly more severe obstructive ventilatory insufficiency and greater lung hyperinflation were found in the subgroup of patients with decreased diffusing capacity. In this subgroup the collapsing type of flow-volume loop and X-ray signs of emphysema were present more frequently than in patients with normal lung diffusing capacity.

Bronchitis↗