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Biomedical subjects

V Dietz

Publications and source records attributed to V Dietz.

At least 217 records · Page 12Linked to original sources
PubMed1981

Electrophysiological studies of gait in spasticity and rigidity. Evidence that altered mechanical properties of muscle contribute to hypertonia.

The surface electromyogram (EMG) of mm. tibialis anterior and triceps surae was recorded in 10 patients with spasticity, 10 patients with rigidity and 20 normal subjects and correlated with the changes in ankle joint angle during the different phases of the gait cycle. While the strength and timing of EMG activity recorded from triceps surae during the stance phase of gait did not differ from that of normal subjects, the EMG of tibialis anterior was significantly stronger during the swing phase in both groups of patients. Although the reciprocally organized innervation pattern of the leg muscles was preserved, spastic patients could hardly lift up the affected foot during the swing phase despite the enhanced activity of tibialis anterior. There was no coactivation of the calf muscles during the hyperactivity of tibialis anterior. Therefore, no electrophysiological explanation could be found for the increased muscle tone in either group of patients. The possibilities of reduced force development by the muscle fibres of tibialis anterior or of some mechanical obstruction in the ankle joint were largely excluded as alternative explanations underlying the impeded elevation of the foot. We suppose that in both diseases the muscle fibres undergo changes which are responsible for increased muscle tone in spasticity and rigidity. The pathophysiological mechanism of these changes remains unknown.

Adolescent↗
PubMed1981

Interaction between pre-activity and stretch reflex in human triceps brachii during landing from forward falls.

1. Electromyographic (e.m.g.) profiles of proximal arm muscles were studied in human subjects falling forward onto a platform. 2. The stretching of the triceps lasted 200-300 msec for deep falls, and immediately after impact angular velocities of the elbow joint up to 1000 degrees sec-1 were reached. 3. For angles of fall between 50 and 90 degrees, more than half of the subjects exhibited marked short-latency e.m.g. responses of the triceps brachii. Such responses began 20-30 msec after touchdown, arising from a more or less plateau-like activity which started about 130 msec before impact. In some cases distinct later responses were found, the second peak having a latency of 60-80 msec after touchdown. 4. The early e.m.g. response even appeared when the subject was blindfolded and when the depth of the fall was randomly varied. 5. It is concluded that both the pre-existing activity and the spinal stretch reflex contribute significantly to the over-all activity of the triceps during stretch after impact.

Adult↗
PubMed1980

Characteristics of postural instability induced by ischemic blocking of leg afferents.

After minimizing proprioceptive input from the legs by ischemia without degradation of muscle force and excluding visual stabilization by eye closure, a characteristic anterior-posterior postural sway around 1 Hz was observed in three normal subjects. This is similar to the instability seen in two tabes dorsalis patients. From the spectral analysis of head and hip movements, displacements of the center of force and of ankle angle as well as from EMG recordings of the anterior tibial and gastrocnemius muscle it is concluded that the oscillations around 1 Hz are due to the long latency and high threshold of vestibularly induced leg muscle discharges (200-300 ms) arriving in the counterbalancing phase of the trunk, which causes an overshoot in body sway.

Adult↗
PubMed1980

Cyclist's palsy: Neurological and EMG study in 4 cases with distal ulnar lesions .

Four cases of cyclist's palsy -- a distal compression syndrome of the ulnar nerve which can develop after long cycling tours -- are described. In two patients extensive neurological and electromyographic (EMG) studies were performed in order to document the degree and time course of recovery of the motor and sensory deficiencies. In contrast to either EMG-studies it could be demonstrated that not only the deep motor branch of the ulnar nerve is involved, but also that a severe lesion of the superficial branch supplying the skin of the 4th and 5th finger can occur, as indicated by a complete loss of the orthodromic sensory action potential recorded above the ulnar nerve in both cases. The results furthermore show that a functionally significant paresis of the hand muscles can persist for several months. The pathogenesis and some practical implications will be discussed.

Action Potentials↗
PubMed1980

Balancing as a clinical test in the differential diagnosis of sensory-motor disorders.

During balancing on a seesaw normal individuals have a mean sway oscillation of 4.3 Hz, which is significantly lower (3.3 Hz) in patients with peroneal muscular atrophy. It is assumed that the oscillations in both cases are generated by spinal stretch reflexes and that the lower frequency in patients with peroneal muscular atrophy is due to their slower nerve conduction velocity. The balancing movements are altered when spinal stretch reflex activity is reduced by ischaemia but are normal in patients with a dorsal column lesion despite a similar sensory loss. The analysis of balancing movements can be a diagnostic tool in differentiating several sensory-motor disturbances.

Adolescent↗
PubMed1979

Neuronal mechanisms of human locomotion.

1. The surface electromyogram (EMG) of human leg muscles was recorded during running at different speeds; The EMG was compared with the simultaneously recorded vertical force exerted by the foot and with the angle of the ankle joint. 2. During running, the electrical activity of the gastrocnemius muscle increased sharply 35--45 ms after ground contact and reached its maximum at the end of muscle stretch; This activity was superimposed on a slowly increasing level of activation, which began 120--180 ms before ground contact. At the end of the stance phase, gastrocnemius became inactive and, simultaneously, there was a sudden increase in tibialis anterior activity. The assumption that the steep increase in the gastrocnemius EMG reflects the spinal stretch reflex of alpha-motoneurons is supported by the following findings. 3. The peak level of gastrocnemius EMG in the stance phase of fast running was 2--3 times higher than the activity during maximum voluntary contraction. 4. With stimulation of the tibial nerve at different rates, the maximum isometric force was about 30--40% higher than the maximum voluntary isometric contraction. 5. The increase in EMG at 35--45 ms after ground contact was markedly diminished during running, after partial blockage of Ia afferents by ischemia, at a time when the strength of voluntary contraction was shown to be uninfluenced by the ischemia. 6. The gastrocnemius activity during running was simulated by electrical stimulation of the tibial nerve. The rate of stimulation was varied so as to approximate to the EMG profile during running. This indicated that a spinal stretch reflex could become mechanically effective within the shortest stance phase measured in a fast sprint (ca. 120 ms).

Adult↗
PubMed1978

[Tremor. Mechanical effect of the discharge behavior of motor neurons].

From the accordance of the discharge and recruitment behaviour of motor units with the Fourier-analysis of the tremor ripples it is shown that the action tremor originates from any muscle innervation and is equivalent to the mechanical effect of the discharges of all motoneurones of a particular muscle. The power spectrum of tremor is mainly caused by the twitch contractions between recruitment (7--8/sec) and total fusion (25/sec) of the discharging motoneurones. The maximum of the frequency spectrum, which represents the dominant tremor rate, corresponds to the discharge frequency just after recruitment of each motoneurone. The twitch contractions of these newly recruited motor units are mechanically least fused. The power spectrum of the tremor in patients with motor disturbaces parallels the changes in the discharge and recruitment behaviour of motoneurones during voluntary contraction. The correlation between the discharges of two simultaneously recorded motor units shows a tendency to synchronization of all discharge rates the extent of which corresponds to the individual tremor intensity.

Fourier Analysis↗
PubMed1978

Peripheral nerve conduction in patients with a cervical rib and band.

In 14 patients with wasting of the hand due to a cervical rib and band, motor and sensory conduction studies on the peripheral parts of the median and ulnar nerves were helpful in establishing the correct diagnosis. The median nerve findings excluded carpal tunnel syndrome even when the clinical pattern of wasting in the hand suggested this diagnosis. Preservation of conduction velocity in the ulnar nerve excluded ulnar entrapment at the elbow; the reduced amplitude of the ulnar sensory action potentials (SAPs) indicated that the lesion was distal to the dorsal root ganglia. In 3 patients with ulnar SAP amplitudes that were low but not clearly abnormal, the level of the lesion was confirmed by a reduced response to intradermal injection of histamine on the inner side of the forearm.

Action Potentials↗
PubMed1978

Analysis of the electrical muscle activity during maximal contraction and the influence of ischaemia.

(1) The mechanism underlying muscle fatigue has been studied in maintained isometric maximal contraction of the wrist flexor muscles under normal and ischaemic conditions. Automatic EMG analysis has been used to show the level of motor unit firing rates in fatiguing contractions. (2) Under non-ischaemic conditions the decay of force, turns and amplitude is about the same, whereas during ischaemia force and to a lesser extent amplitude pulses, decline steeply towards zero, while turns, representing the number of impulses, remain in the non-ischaemic range. (3) Depending on the duration of the ischaemia applied before contraction, force and amplitude are initially reduced but turns are nearly unchanged compared with the non-ischaemic values. It is suggested, that this is due to nerve blocking of high threshold motor units. (4) The results show that transmission failure at the neuromuscular junction is a minor factor in muscle fatigue and that this structure is not greatly affected by ischaemia. (5) It is believed that in the first phase of muscle fatigue the force decline is connnected with a slowing of discharge rates. This change of firing frequencies with time must be considered optimal in respect to the force produced because higher as well as lower discharge rates would reduce the force development. In the later phase it is possible that contractile element fatigue, connected with a reduction of action potential amplitudes of single muscle fibres, predominates, especially when the blood supply is obstructed.

Action Potentials↗
PubMed1978

Neuronal mechanisms underlying physiological tremor.

1. Tremor force was recorded during stationary isometric contractions of intrinsic hand muscles of normal subjects. Subjects maintained a steady force level between their thumb and forefinger for 30 s. The force level varied from weak (0.2 kg) to strong contractions (7 kg). These experimental conditions were the same as those in two preceding studies, where single motor-unit activity (14) and the correlation between the discharges of two simultaneously recorded motor units and physiological tremor (11) have been investigated. 2. Two alterations of the power spectra were observed at successively stronger contractions: increase of tremor amplitude and changes in the shape of the power spectrum. At all force levels, the power spectra of tremor force show the well-known decay of tremor amplitude from the lower to the higher frequencies with a local peak at 6--10 Hz. This peak does not show a significant change with respect to frequency when the force level is varied. It is shifted toward lower frequencies in a pathological condition (Parkinsonism) where the recruitment firing rates of the motor units are significantly lower than in the normal. 3. Higher frequencies (greater than 20 Hz) are barely present in the power spectrum during the very weak contractions. They become significant as the contractions become stronger. 4. The steep decay of the power spectrum toward higher frequencies has a similar slope (--43 dB/decade) as the reduction in amplitude of the unfused part of the muscle contractions with increasing stimulus rates (--38 dB/decade). The cutoff of the power spectrum above 25 Hz parallels the achievement of total fusion of muscle twitches above this rate. 5. The results are consistent with the hypothesis that the power spectrum over the range of 6--25 Hz is mainly caused by the unfused parts of the twitch contractions of motor units firing between recruitment (6--8/s) and total fusion of the twitches (25--30/s). The decline of the power spectrum toward higher frequencies can be explained by mechanical damping, which results from increasing fusion of the twitch contractions. The low-frequency part of the power spectrum is assumed to be the result of the slow force deviations produced by changes in the net output of the motoneuron pool. 6. These assumptions were supported by additional animal experiments where the number and rate of force-producing elements could be controlled. Bundles of ventral root filaments innervating cat soleus and gastrocnemius muscles were stimulated synchronously and asynchronously at a number of different rates. The force output of the strain gauge was recorded, filtered, and analyzed in the same way as the human force records. 7. Stimualtion of one nerve bundle at one fixed frequency led to a sharp peak in the power spectrum at that frequency plus peaks of decreasing height representing the harmonics of the stimulation frequency. The height of the peaks decreased at --37 dB/decade. 8...

Animals↗
PubMed1976

[Training and dominance in human voluntary movements. Right-left-comparisons of putting and throwing programs (author's transl)].

1. Muscle action potentials and efficiency were measured during shot putting and ball throwing in right and left handed normals. The dominant and the nondominant side were compared in trained and untrained persons in order to investigate motor learning effects. 2. Trained shot putters show a coordinated sequence of activation of trunk, leg and arm muscles of both sides which precedes the final arm extension. After turning the body from an initially inclined and twisted position the final arm extension transfers the force of the accelerated body mass to the shot. 3. When shot putting or throwing is performed by the nondominant arm in subjects trained for the dominant arm the coordination of the contralateral dominant arm is lacking, in contrast to the performance by the trained arm. 4. In untrained persons the shot putting is effected mainly by arm extension on either side. The preceding trunk and leg action is very incomplete and without coordination of the contralateral arm, whereas the shot putting arm shows stronger triceps brachii innervation. The distances achieved by untrained shot putters reach only one-fifth or one-third of those of highly trained persons. 5. In ball throwing the throwing arm shows final coactivation of the biceps and triceps muscles coordinated with trunk and contralateral arm movements. The distances reached by throwing with the untrained arm are about half of those of the trained dominant arm. 6. Trained sportsmen put the shot with the untrained nondominant arm to 73% of the distance achieved by the trained arm. Untrained persons, however, show an approximately equal, smaller range of shot with the dominant and nondominant arm (8% side difference). 7. A biomechanical factor causing different performances of trained and untrained persons in shot putting is the different force of the energy transferring mass: the untrained person thrusts mainly with the arm which has barely 1/20 of the mass of the whole body, used by the trained shot putter. 8. That bilateral training and not hemispheric dominance is the decisive factor producing the improved efficiency is demonstrated by three observations: a) the maximal efficiency and bilateral coordination of shot putting in trained persons, b) the lack of contralateral activation of the dominant arm in shot putting and throwing by the nondominant arm, and c) the minimal left and right side differences in performance of untrained persons.

Action Potentials↗
PubMed1976

Correlation between the dischanges of two simultaneously recorded motor units and physiological tremor.

Simultaneous recording was performed from pairs of motor units either in a small intrinsic hand muscle (first dorsal interosseus, 6 subjects, 37 records) or in two synergistic calf muscles (gastrocnemius and soleus, 6 subjects, 50 records). The two motor units were recorded by means of two electrodes inserted into the muscle during stationary isometric contractions of different strengths. Cross-correlograms were calculated in two ways: (1) between spike trains of two motor units; (2) between either spike train and the peaks of the tremor record. The cross-correlation between pairs of motor units showed a consistent tendency to synchronization in the hand as well as in the calf muscles. This synchronization was higher than could be expected from the random activity of asynchronously firing motor units. The amount of synchronization was correlated with the amplitude of physiological tremor: the stronger the tremor, the higher the synchronization coefficient. The cross-correlation between a spike train and the peaks of the tremor records showed a higher probability of unit firing 30-60 msec prior to the tremor beats. It is concluded that the tremor force produced by one muscle or a pair of synergistic muscles is the result of the synchronized activity of motor units. This hypothesis is supported by some characteristic changes in the amplitudes and rates of tremor in Parkinson's disease and myopathies. In these diseases the pathological changes in tremor rates simply reflect underlying changes of the motoneuronal firing rates.

Action Potentials↗
PubMed1976

Correction of class II malocclusion by combined sagittal ramus and subapical body osteotomy.

The complete mandibular subapical osteotomy has been presented as a method for correction of Class II malocclusions. At this point, it holds some promise as a solution to the skeletal relapse seen in the surgical correction of Class II malocclusions with use of other techniques. The procedure is a straight-forward combination of the sagittal osteotomy as described by Obwegeser and the subapical osteotomy as described by Köle. Further investigation into the versatility of this procedure is recommended.

Adult↗