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Biomedical subjects

H J Freund

Publications and source records attributed to H J Freund.

At least 163 records · Page 9Linked to original sources
PubMed1977

The comparison of small-size rectangle and checkerboard stimulation for the evaluation of delayed visual evoked responses in patients suspected of multiple sclerosis.

The use of foveal small-size rectangle stimulation to elicit visual evoked responses was compared with VERs elicited by the standard checkerboard pattern. Foveal stimulation achieved a significantly better discrimination of optic nerve lesions in the early diagnosis of multiple sclerosis. Sources of misdiagnosis due to different neurological disorders are discussed.

Adolescent↗
PubMed1976

[The selective examination of the neck arteries by directional Doppler sonography (author's transl)].

The Doppler examination of the neck arteries of 300 subjects showed, that the common, internal and external carotid arteries and the vertebral artery can reliably be distinguished on the basis of their different pulse-curve characteristics. In addition, the compression of branches of the external carotid artery can identify these vessels in particular in pathologic cases. The details of the normal flow profiles and their changes by the compression tests are described. Compression of the vessels leads to a rise in flow resistance. The effect of such a rise in resistance is demonstrated using the A. radialis as a model. The identification of the neck arteries provides the basis for diagnostic examination and localization of their stenoses and occlusions.

Arterial Occlusive Diseases↗
PubMed1976

[The diagnosis of stenoses and occlusions of the carotid arteries by means of directional Dopplersonography (author's transl)].

The Doppler examination of the carotid arteries in the neck was compared with the results of the examination of the supratrochlear artery and of the angiographic controls in 76 patients. The results of this study indicate that the insonation of the carotid arteries considerably improves the diagnostic possibilities offered by the examination of the supratrochlear artery alone. There are three main advantages: 1. The reliability of the Doppler examination is improved. The insonation of the carotid arteries of the 76 angiographically controlled patients including stenoses from 50% onward gave only one false-positive and one false-negative result. The percentage of correct diagnoses thereby attained was 97%. 2. The insonation of the carotid arteries permits reliable differentiation between stenoses and occlusions. This is not possible by the insonation of the supratrochlear artery alone. There was only one case in which the distinction was wrong. 3. The localization of the pathologic process was possible in all cases. These conclusions are only valid for the detection of occlusions and stenoses of more than 50%. Low degree stenoses cannot be detected by this method.

Arterial Occlusive Diseases↗
PubMed1976

[The diagnosis of obstructions of the vertebral and subclavian arteries by means of directional Doppler sonography (author's transl)].

The Doppler examination of the vertebral and subclavian arteries was compared with the angiographic findings in 40 cases. The vertebral flow was recorded at its atlas slope, the subclavian artery at the supraclavicular fossa. Twenty-seven normal Doppler results were confirmed by angiography in 26 cases. In one case there was a 70% stenosis at the origin of the vertebral artery. Occlusions, stenoses, and severe hypoplasia of the vertebral artery can be detected, but not distinguished from each other by the Doppler examination. Diagnostically relevant findings are either nondetectable flow above the vertebral artery or only minor pulsations with amplitudes less than 25% of the normal side. Eleven cases showed a flow reversal in a vertebral artery. Five of them were angiographically controlled and all showed a typical subclavian steal syndrome. Although the precision of the results of the examination of the vertebral artery is not as good as for the carotid arteries, it is a rough, suitable atraumatic screening method particularly for the subclavian steal syndrome.

Arterial Occlusive Diseases↗
PubMed1976

The relationship between the rate of rise of isometric tension and motor unit recruitment in a human forearm muscle.

The recruitment properties of single motor units from the human extensor indicis muscle were investigated during voluntary isometric contractions of different rate of rise but equal amplitude. Both the electrical and the contractile events associated with recruitment were analyzed. The threshold force of recruitment (measured as the total muscle force at firing onset) decreased with increasing rate of rise of isometric tension. This was consistently found for all units. Differences between low and high threshold units indicating a preferential tonic or phasic mode of activation were not observed. The contractile events associated with recruitment were analyzed analoguously to the electrical events. For this purpose, muscle force was measured at the time of the first twitch as it was measured at the time of the first spike. This separate measurement of the electrical and mechanical recruitment of a unit is necessary, because during a change of muscle force, force is different at firing onset and during the subsequent twitch contraction. Muscle tension at the time of the peak of the first twitch contraction was calculated from measurements of the twitch concentration time of the single motor units. In contrast to firing onset, the peak of the first twitch of a motor unit occurs at approximately the same muscle tension no matter how fast the contraction is performed. This is the consequence of the result that the average decrease of the threshold force of recruitment at successively faster contraction has the same value as the corresponding increase of total muscle force during the mean contraction time of the motor units. On the basis of this precise matching between these two changes, the mechanical recruitment of motor units occurs at approximately the same force level irrespective of the rate of rise of tension.

Electric Stimulation↗
PubMed1976

[Diagnosis of internal carotid artery obstructions (author's transl)].

The diagnostic value of directional ultrasound Doppler-sonography (UDS) of the supratrochlear (medial frontal) artery was evaluated by examination of 191 angiographically controlled cases in whom a carotid obstruction was suspected. A systematic compression of the facial and temporal arteries of both sides was performed. In 108 cases the UDS findings were normal, 6% of these were false negative and actually had a stenosis (n = 6) or occlusion (n = 2) of the internal carotid artery. In 88% of the pathological findings a stenosis (n = 39) or occlusion (n = 34) of the internal carotid artery was revealed by angiography. 79% of the stenoses were of severe degree (more than 50%). These results show that UDS is a useful diagnostic tool for the detection of severe stenoses or occlusions of the internal carotid artery. A distinction between stenosis and occlusion by UDS of the supratrochlear artery is, however, not possible, unless additional examination of the carotid arteries is performed. The method is not suitable for the detection of low grade stenoses.

Arterial Occlusive Diseases↗
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↗
PubMed1975

[Two-dimensional ultrasonic diagnosis of brain tumors and subdural hematomas by electronic sector scanning (author's transl)].

Electronic sector scanning (ESS) is a new two-dimensional ultrasonic technique which provides continuous and instantaneous cross-sections of intracranial structures through the intact skull, including the ventricles and large cerebral arteries, by means of a stationary probe. 2. The efficiency of the ESS in the diagnosis of brain tumors and extracerebral hematomas in 295 neuroradiologically controlled cases out of an unselected number of patients during 1972-1974 is described. 3. Supratentorial brain tumors can be detected directly with the ESS by abnoramal reflections of the tumors as well as indirectly by displacement of intracranial reference structures, mainly the ventricular borders. In 239 cases of suspected brain tumor, 126 were neurodiologically confirmed as supratentorial brain tumors. Among these 126 brain tumors the correct localization was determined by the ESS in 86.5%. 4. The highest reliability of the ESS proved to be the direct demonstration of frontal tumors (93%), whereas space-occupying lesions near the midline could be shown only in 79%. Up to now there have been difficulties in the diagnosis of tumors situated near bony structures, e.g., calvarian meningiomas. 5. Subdural hematomas (56 patients) could be lateralized correctly in 93%. Hwever, direct demonstration of the border of the hematomas could be achieved only in 48,2%. Chronic subdural hematomas in children are easier to recognize and the border could be demonstrated in 18 out of 19 cases. 6. The clinical applicability and diagnostic values of the ESS as a nontraumatic investigation procedure are discussed in comparison to cerebral angiography, pneumoencephalography, brain scintigraphy, and CAT scan. scintigraphy, and CAT scan.

Age Factors↗
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↗