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Biomedical subjects

M R Dimitrijevic

Publications and source records attributed to M R Dimitrijevic.

At least 73 records · Page 4Linked to original sources
PubMed1981

Underlying mechanisms of the effects of spinal cord stimulation in motor disorders. A review of the discussion.

Possible underlying neurophysiological mechanisms of spinal cord stimulation in the modification of motor disorders were discussed by scientists working in research on motor control mechanisms. Changes of motor unit properties in upper motoneuron lesions were reviewed, the role of proprioceptive input and long-loop reflexes in motor control was discussed, analysis of ramp and ballistic movements in motor control was presented, and some aspects of neural control of locomotion were reviewed. Some physiological considerations of the influence of electrical stimulation on various neural functions were given and the conclusion was reached that, at present, no definitive models of the action of spinal cord stimulation are available.

Animals↗
PubMed1981

Neural control of gait: clinical neurophysiological aspects.

From the three essential mechanisms in locomotion, the antigravity, equilibrium and stepping mechanisms, only the latter is specific for gait. The spinal cord is considered to be a central pattern generator in experimental animals and is under the influence of different afferent sources and descending impulses. In clinical practice locomotor mechanisms can be modified at peripheral levels, as with functional electrical stimulation of peripheral nerves, and at the spinal cord, as in spinal cord stimulation, and theoretically also at midbrain and subthalamic locomotor areas. The importance of the spinal cord pattern generator in spinal cord injured patients is discussed. The role of postural mechanisms in locomotion is emphasized.

Animals↗
PubMed1980

Scoliosis in neuromuscular disorders.

Hundred-seventy patients with the 4 commonest degenerative neuro-muscular disorders (limbgirdle and Duchenne muscular dystrphy, Kugelberg-Welander's spinal muscular atrophy and peroneal muscular atrophy) were screened for scoliosis, which was found in 56%. Of 76 patients in the early stages of their respective disorders (stages 1-6 of Gardner-Medwin and Walton), scoliosis was found in 72%. The incidence of scoliosis was not related to the duration or degree of clinical weakness. Morphologically, scoliosis in these disorders was not found to differ from idiopathic scoliosis. Neither side nor site of the scoliosis were related to the distribution of muscle weakness as determined by manual testing.

Humans↗
PubMed1980

Reflex responses of paraspinal muscles to tapping.

ERECTOR SPINAE REFLEX STUDIES IN HEALTHY SUBJECTS REVEALED TWO RESPONSES: a 12·0±1·6 ms latency, oligosynaptic response, and a 30 to 50 ms latency response with polysynaptic reflex characteristics. There was a silent period after the first and second responses. The effect of limb position, trunk, neck, postural changes, Jendrassik manoeuvre and vibration on both responses were also evaluated.

Adult↗
PubMed1980

Clonus: the role of central mechanisms.

The peripheral and central components in sustained clonus were investigated. The excitability of the motoneurons responding to maintained stretch by clonus was examined by tendon taps, trains of vibratory stimuli and by H-reflex afferent volleys. Every burst of clonic discharge of the motoneurons was shown to be followed by a refractory period, which was followed by a shorter excitatory period. It was concluded that the motoneurons responding clonically to a continuous stretch cannot respond until their excitability has been regained after the refractory period. Attempts to change the rate of clonus in various ways failed to do so. Whether motoneurons of clonic muscles tend to respond maximally to other Ia volleys at the rate of clonus was examined by applying repeated taps to the tendon at rates from 1 to 15 Hz. There was a maximal response at the rate of clonus. Inputs other than those induced by stretch cause clonus; examples of cutaneous inputs causing it are given.

Afferent Pathways↗
PubMed1980

Characteristics of spinal cord-evoked responses in man.

The averaged electrical potentials evoked by the stimulation of the peripheral nerves were recorded with surface electrodes over the lumbosacral, lower thoracic and cervical spine and with epidurally placed electrodes in the cervical area. The waveforms of the lumbosacral and cervical spinal cord potentials show similar complexity reflecting peripheral and central generators. The larger negative wave with at least two components is followed by a slower positive deflection. Evoked potentials recorded over the cervical segments of the spinal cord with epidural electrodes are of much higher amplitude and more complex waveform than those recorded with surface electrodes.

Adult↗
PubMed1980

Spasticity: medical and surgical treatment.

Electromyographic (EMG) recordings from multiple muscle groups with surface electrodes during systematic evaluation of phasic and tonic stretch reflexes, cutaneomuscular reflexes, long loop reflexes, postural reflexes, and volitional activation have been used to provide a neurophysiologic basis for selection of the appropriate treatment for spasticity, and to gain further insights into the general mechanisms of spasticity. Pharmacologic methods are useful as a temporary measure. Hypertonia of a single muscle can be effectively treated with 40% alcohol injections to the motor points and hypertonia of a muscle group with partial denervation through 6% phenol in water injected into the nerve trunk. Hypertonia of several muscle groups can be treated by chemical or surgical rhizotomy or myelotomy. Generalized hypertonia involving limb and trunk muscles can be modified through chronic epidural stimulation of the spinal cord. Modification of reciprocal antagonistic muscle activity may be achieved through electrical stimulation of the involved nerve trunks.

Ambulatory Care↗
PubMed1980

Biomedical engineering specifications for epidural spinal cord stimulation to augment motor performance.

Stimulating electrodes were placed in the posterior portion of the epidural space in the upper thoracic spinal region in 28 patients with upper motor neuron disorders. Parameters of stimulation commonly used for chronic stimulation were a 200 microsecond pulse width, 22 Hz repetition rate, and 5 ma amplitude. Using a 16 gauge Touhy needle, platinum electrodes were passed between the posterior vertebral processes into and up the spinal epidural space to upper thoracic locations. Passive implanted receivers, powered and controlled by external RF transmitter/pulse-generator devices, were employed to provide the stimulus current to the electrodes. A description of available systems, problems and diagnosis of problems, and future directions is presented. This is based on studies in patients with stimulation systems implanted for more than six months.

Biomedical Engineering↗
PubMed1980

Study of sensation and muscle twitch responses to spinal cord stimulation.

Electrically induced sensation and muscle twitches were studied in a group of 43 patients in whom epidural electrodes were percutaneously placed for the evaluation of the effect of spinal cord stimulation on modification of their impaired motor control. Mean stimulus strength for sensory threshold was 5.25 +/- 2.75 mA and the tolerance level was at the stimulus strength of 10.8 +/- 4.4 mA. Muscle twitches with short latencies were recorded in limb and trunk muscles within the segments at the stimulating cathode. Exceptionally, higher stimuli elicited muscle twitches of distant segments.

Adolescent↗
PubMed1980

Neurophysiological evaluation of chronic spinal cord stimulation in patients with upper motor neuron disorders.

Spinal cord stimulation was found to be an effective method for improving motor performance in patients with upper motor neuron disorders. Electromyographic analysis of segmental and suprasegmental activity was performed in 11 patients who had used spinal cord stimulation for more than 12 months. Neurophysiological analysis of electromyographic findings revealed improvement of volitional motor control and a reduction of spasticity in the examined muscles of the lower limbs in all patients.

Adult↗
PubMed1977

Reflex effects of vibration in patients with spinal cord lesions.

The vibration reflex was studied in 49 patients with traumatic spinal cord lesions. It was elicited in all patients, even after presumably complete division of the cord. The vibration relfex consisted of a short-latency, brief outburst of phasic activity of motor units, followed by rapidly decreasing phasic component and a later slowly declining tonic component. When periods of vibration were repeated at short intervals of 2 to 10 seconds, the responses showed an approximately exponential decline, although the beginning of each subsequent response was always larger than the end of the preceding response. A large part of this decline can be characterized as a habituation of the vibration reflex. In comparison with the vibration reflex in normal subjects, the phasic component was increased and the tonic one reduced. The tonic component was especially susceptible to potentiation and dishabituation by voluntary effort to contract the vibrated muscle, even in some patients with no other evidence that the lesion was incomplete. We suggest that the tonic component of the human vibration reflex depends, at least in part, on segmental interneurons and their descending spinal pathways, while the phasic component depends mainly on the excitability level of spinal motoneurons.

Evoked Potentials↗