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Biomedical subjects

V Dietz

Publications and source records attributed to V Dietz.

229 records · Page 13Linked to original sources
PubMed1975

[Delayed initiation of voluntary movements after pyramidal lesions in man (author's transl)].

The reaction times for rapid movements in muscles of arm and leg were measured in 20 patients with unilateral lesions of the motor cortex and the internal capsule. Rapid unilateral and bilateral movements after an acoustic signal (click) on the pyramidally paretic side were compared with the normal side. In these patients and in 10 normal subjects, electromyographic and mechanical recordings from symmetrical muscles of both sides were compared. 2. All patients with pyramidal lesions showed in the case of unilateral movements a marked prolongation of motor latency in the affected muscles: compared to the normal side, the movement started 30-160 msec later in muscles contralateral to the lesion of the motor cortex. In contrast, normal subjects showed equal latencies on both sides with maximal differences of 10-20 msec. 3. When movements were executed bilaterally the latency prolongation in the pyramidally paretic muscles was markedly diminished or disappeared in later stages. In most patients the bilateral movements started simultaneously in the normal and the paretic muscles, except in 5 recent lesions of the contralateral motor cortex. 4. The significance of the findings is discussed in terms of the function of the human motor cortex in starting and controlling voluntary movements. It is assumed that the disappearance of latency prolongation when movements are executed bilaterally in patients with unilateral pyramidal lesions can be best explained by homolateral projections of uncrossed pyramidal fibres to the motoneurones. 5. These results, and other observations, suggest that the motor cortex starts and controls voluntary movements via rapidly conducting pyramidal fibres to the motoneurones. This occurs after a preprogramming and a readiness posture is established by other cerebral structures. The prolongation of motor latencies after motor cortex lesions is probably due to a disturbance in the rapidly conducting cortico-spinal projections to spinal motoneurones and interneurones.

Adult↗
PubMed1975

[Alcoholic polyneuropathy. Electrophysiological and clinical findings in 85 patients (author's transl)].

Maximum motor and sensory nerve conduction velocities, amplitudes of muscle action potentials (surface electrodes) and of sensory nerve action potentials, and needle electromyograms were studied in 80 patients with alcoholic neuropathy and in 5 chronic alcoholics without clinical signs of neuropathy. The electrophysiological results were compared to the clinical findings. Neurographic criteria compatible with the diagnosis "alcoholic neuropathy" were defined. Neurographic findings contrary to a diagnosis of alcoholic etiology were demonstrated in 3 patients. Only in a smaller group of patients could a reduction of conduction velocity be found, especially in regions of peripheral nerve entrapment. A decrease in conduction velocity outside of the entrapment sites can be explained in some cases by segmental demyelination in chronic hepatitis or cirrhosis of the liver.

Action Potentials↗
PubMed1975

Activity of single motor units from human forearm muscles during voluntary isometric contractions.

1. Microelectrode recordings from single motor units of the first dorsal interosseus and the extensor indicis muscles of normal human subjects were studied during voluntary, isometric contractions. The conduction velocity of the nerve fiber innervating the muscle unit was used as an estimator of the size of the motoneuron. 2. During slowly increasing contractions, the units were recruited at force levels which were closely correlated to conduction velocity. The units associated with low conduction velocity were recruited first, those with high conduction velocity, last. 3. If small, stepwise force increments were used instead of slowly, continuously increasing contractions, the units were first activated during the steps and became inactive during the subsequent plateaus. If higher steady-force levels were reached, the activity was maintained also during the plateaus. This steady force, where a unit remained continuously active independent of the rate of rise of tension, represents its tonic threshold. 4. The tonic threshold is positively correlated with conduction velocity, as is the threshold force of recruitment. As a consequence, high-threshold units have a large force range below tonic threshold where they can only be transiently activated, whereas low-threshold units have a large physiological force range above tonic threshold where they operate tonically. The phasic or tonic appearance of discharge pattern reflects quantitative differences in tonic threshold between units of different size. All units examined could be activated phasically (below) and tonically (above tonic threshold). No evidence was found indicating the existence of two qualitatively different classes of units corresponding to a tonic and phasic type, although both muscles investigated consist of about equal numbers of type I and type II muscle fibers. 5. The change in firing rate per unit force was inversely related to conduction velocity: the slower conducting units showed larger changes in firing rate per unit force than faster conducting units. This corresponds to the larger excitability of the smaller units indicated by their earlier recruitment. 6. The data of this study are consistent with the hypothesis that the functional characteristics of human motoneurons are determined by the graded excitability of motoneurons according to size.

Adult↗
PubMed1974

Correlation between tremor, voluntary contraction, and firing pattern of motor units in Parkinson's disease.

PATIENTS WITH TREMOR OF PARKINSONISM SHOW THREE CHARACTERISTICS OF MOTOR UNIT ACTIVITY: rhythmic spontaneous resting discharge, abnormally low firing rates during voluntary contraction, and consistent differences in firing pattern between small and large motor units. Smaller units discharge once per tremor beat at weak contractions but change into bursts of two or three spikes per beat at stronger forces. Large units are later recruited and fire preferentially once per beat. The large tremor amplitudes can be partly explained by synchronization of unfused twitches of low frequency units which summate more powerfully than the partially fused contractions during physiological tremor, which is about twice as rapid. Tremor is strongly influenced by the force of voluntary contraction. It is strongest at rest or during weak muscular effort and with increasing force becomes continuously of higher frequency and smaller amplitude. Both changes are the consequence of increasing discharge rates of motoneurones at stronger contractions.

Electromyography↗
PubMedDate not supplied

Gait acts as a gate for reflexes from the foot.

During human gait, electrical stimulation of the foot elicits facilitatory P2 (medium latency) responses in TA (tibialis anterior) at the onset of the swing phase, while the same stimuli cause suppressive responses at the end of swing phase, along with facilitatory responses in antagonists. This phenomenon is called phase-dependent reflex reversal. The suppressive responses can be evoked from a variety of skin sites in the leg and from stimulation of some muscles such as rectus femoris (RF). This paper reviews the data on reflex reversal and adds new data on this topic, using a split-belt paradigm. So far, the reflex reversal in TA could only be studied for the onset and end phases of the step cycle, simply because suppression can only be demonstrated when there is background activity. Normally there are only 2 TA bursts in the step cycle, whereas TA is normally silent during most of the stance phase. To know what happens in the stance phase, one needs to have a means to evoke some background activity during the stance phase. For this purpose, new experiments were carried out in which subjects were asked to walk on a treadmill with a split-belt. When the subject was walking with unequal leg speeds, the walking pattern was adapted to a gait pattern resembling limping. The TA then remained active throughout most of the stance phase of the slow-moving leg, which was used as the primary support. This activity was a result of coactivation of agonistic and antagonistic leg muscles in the supporting leg, and represented one of the ways to stabilize the body. Electrical stimulation was given to a cutaneous nerve (sural) at the ankle at twice the perception threshold. Nine of the 12 subjects showed increased TA activity during stance phase while walking on split-belts, and 5 of them showed pronounced suppressions during the first part of stance when stimuli were given on the slow side. It was concluded that a TA suppressive pathway remains open throughout most of the stance phase in the majority of subjects. The suggestion was made that the TA suppression increases loading of the ankle plantar flexors during the loading phase of stance.

Electric Stimulation↗
PubMedDate not supplied

Body sway stabilization in human posture.

Electromyographic (emg) responses and joint movements of the leg were analysed in subjects standing with eyes closed on a sinusoidally moving treadmill (0.16 Hz or 0.33 Hz, amplitude 33 cm). Activity in antagonistic leg muscles was reciprocally modulated, with a predominant gastrocnemius activation during deceleration of forward movement and tibialis anterior activation during deceleration of backward movement of the treadmill. In these phases, it was necessary to compensate for sway induced by body inertia. The match between treadmill movement and emg activity was better for the gastrocnemius than for the tibialis anterior muscle. The characteristic pattern of leg muscle emg activity is suggested to be modulated predominantly by vestibulo-spinal reflexes partly because treadmill movements did not evoke muscle strength, and partly because patients with loss of vestibular function showed basic alterations in the emg pattern and could only compensate for the slow sinus while standing unsupported.

Adult↗
PubMedDate not supplied

Food-related illness and death in the United States.

To better quantify the impact of foodborne diseases on health in the United States, we compiled and analyzed information from multiple surveillance systems and other sources. We estimate that foodborne diseases cause approximately 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths in the United States each year. Known pathogens account for an estimated 14 million illnesses, 60, 000 hospitalizations, and 1,800 deaths. Three pathogens, Salmonella, Listeria, and Toxoplasma, are responsible for 1,500 deaths each year, more than 75% of those caused by known pathogens, while unknown agents account for the remaining 62 million illnesses, 265,000 hospitalizations, and 3,200 deaths. Overall, foodborne diseases appear to cause more illnesses but fewer deaths than previously estimated.

Acute Disease↗
PubMedDate not supplied

Treadmill training of paraplegic patients using a robotic orthosis.

Recent studies have confirmed that regular treadmill training can improve walking capabilities in incomplete spinal cord-injured subjects. At the beginning of this training the leg movements of the patients have to be assisted by physiotherapists during gait on the moving treadmill. The physical capabilities and the individual experience of the therapists usually limit this training. A driven gait orthosis (DGO) has been developed that can move the legs of a patient in a physiological way on the moving treadmill. The orthosis is adjustable in size so different patients can use it. Actuators at the knee and hip joints are controlled by a position controller. With the DGO the legs of patients with different degrees of paresis and spasticity could be trained for more than half an hour, and physiological gait patterns were obtained.

Exercise Therapy↗