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F Hlavacka

Publications and source records attributed to F Hlavacka.

36 records · Page 2Linked to original sources
PubMed1990

[Correlation of the evoked vestibulo-postural reaction and spontaneous body sway while standing].

The stability of upright posture was studied by the method of stabilometry in 16 healthy subjects. The efficacy of involving visual, vestibular and proprioceptive afferentation in maintaining posture was examined in four test situations. A direct correlation of stabilometric parameters was established at posture on soft surface and at galvanic stimulation of the vestibular analyzer. The recorded data indicate an indirect correlation between the sensitivity of the vestibular sensor and the sensitivity of that part of the central nervous system which processes vestibular information. The observed relationship results presumably from the action of central compensatory mechanisms in the function of the vestibulo-postural circuit.

Adult↗
PubMed1990

[Physiologic range of stabilometry values obtained in the upright posture using a computer].

The authors present physiological ranges of values of seven parameters of stabilometric examinations of the upright posture in man. In order to make the examination effective, the authors suggested and tested three situations which make it possible to characterize the activity of the visual, vestibular and proprioceptive feedback in the process of maintenance of the upright posture. For measuring the supporting forces during the upright posture the authors used a stabilometer with automatic compensation of the body weight. Amplitude analysis of the obtained stabilometric curves was made "on line" by means of a microcomputer PMD 85-2. The mentioned stabilometric parameters make it possible to evaluate objectively the ability of the subject to maintain an upright posture based on a) the median amplitude and velocity of deviations of the body in an anterioposterior and lateral direction, b) complex parameters of the length of the curve, the total area and root mean square deviation of the statokinezigram.

Adult↗
PubMed1986

Sinusoidal galvanic stimulation of the labyrinths and postural responses.

We studied the effect of sinusoidal stimulation of the labyrinths on postural reflexes in man, using a 0.3 Hz current of alternating polarity and +/- 1 mA intensity for stimulation. The test subjects were tested binaurally by the bipolar method (BB), with two electrodes on the mastoid processes, and binaurally by the monopolar method (BM), with electrodes localized bilaterally on the mastoid process and the hand. Stabilographic postural parameters were measured in 22 subjects in five experimental situations. Each situation lasted 60 s. Body sway, detected by astabilometer, was recorded on a Philips FM tape-recorder and then analysed off-line on a PDP-11/34 computer. On BB stimulation of the labyrinths, the variance of body sway in the left-right (LR) direction increased more than in the anteroposterior (AP) direction. In BM stimulation, only the variance of LR sway increased. Other posturographic parameters displayed a similar effect. From the aspect of body sway frequency, BB stimulation produced a peak in the course of the power spectral density of the lateral stabilogram at 0.3 Hz. In this experimental situation, a habituation effect was manifested, depending on the subject. It can be stated that binaural bipolar (BB) stimulation of the labyrinths selectively influences lateral body sway, while the increase in AP body sway in this situation is merely a concomitant phenomenon.

Adult↗
PubMed1986

Compensation effect of visual biofeedback in upright posture control.

The effectivity of the compensatory role of visual biofeedback in cases of decreased stability of upright posture has been analysed. The deterioration of stance was modelled by a subject standing on a soft surface and with additional weight load on the body. The influence of visual biofeedback was positive only for the compensation of decreased stability of upright posture caused by artificially increased body weight of the subject. The compensatory effectivity of visual biofeedback in stabilization of upright posture during stance on a soft surface was practically negligible. The results have shown that effective compensation of the destabilizing effect by visual biofeedback in human upright posture was possible only when the activity and efficiency of efferent-action part of the postural system remained unchanged.

Adult↗
PubMed1982

Electrophysiological characteristics of reticulospinal neurones in relation to the conduction velocity of their axons.

Activity was recorded intracellularly from the bodies of 87 reticulospinal neurones in the cat's gigantocellular nucleus, whose axons had a conduction velocity of 18-148 m.s-1. Slow-conducting neurones (18-45 m.s-1, 23%) were characterized by a wider action potential, higher input resistance (3.8-7.0 M omega) and a lower rheobase (1.0-1.7 nA). They were also very sensitive to changes in membrane polarity and generated regular rhythmic activity. Fast-conducting neurons (45-148 m.s-1) were characterized by a short action potential, low input resistance (0.7-2.9 M omega) and a higher rheobase (1.5-5.2 nA). When depolarizing current pulses were applied, they generated responses with action potentials with a high frequency, especially in the initial phase of depolarization, but their thresholds for the initiation of activity and steady firing were higher than in the case of slow neurones. Slow reticulospinal neurones always responded to stimulation of the spinal funiculi (mainly the dorsal funiculus) by a characteristic large postsynaptic potential on which large numbers of spike potentials were superimposed and which did not occur in fast neurones. The differences observed in membrane properties and in the character of generation of action potentials draw attention to the phasic character of fast, and the tonic character of slow, reticulospinal neurones.

Action Potentials↗
PubMedDate not supplied

Postural responses evoked by sinusoidal galvanic stimulation of the labyrinth. Influence of head position.

In 15 healthy subjects we studied body sway reactions to sinusoidal 0.3 Hz binaural bipolar galvanic current up to 2 mA under three conditions. With the head forward and eyes closed, there is only a periodic lateral displacement of the centre of gravity, following the stimulation with a phase lag. In two other conditions, the head turned to the left or to the right without trunk torsion, the direction of sway was modified in such a way that there were mainly anteroposterior movements. It is thought that this experiment shows the modulatory influence of neck afferents on the direction of vestibulospinal motor effects in man.

Adult↗