Biomedical subjects

Frantisek Hlavacka

Publications and source records attributed to Frantisek Hlavacka.

3 recordsLinked to original sources

PubMed2006

Modification of human postural responses to soleus muscle vibration by rotation of visual scene.

Sensory interaction in posture control in 20 healthy subjects was investigated by postural responses to differently timed proprioceptive and visual stimulation. As proprioceptive stimulation was used both soleus muscles vibration. Visual stimulation was rotating disc moving in forward and backward direction. Centre of foot pressure (CoP) and trunk tilts in antero-posterior (AP) direction were measured during stance by two accelerometers on the upper and the lower trunk level. Subjects performed four series of eight trials lasted 20s: vibration with eyes open and closed, visual scene motion forward or backward, vibration together with scene motion forward or backward, scene motion forward or backward 3s before vibration. The results showed that early velocities and final angles of body tilt induced by soleus muscle vibration were modified by motion of visual scene. Early part of postural responses was changed slightly if sensory stimulation starts together. When visual stimulation started 3s before muscle vibration, the induced early CoP and trunk tilt records of postural response to vibration occurred with the faster slope similar for both directions of scene motion and for condition of vibration alone with eyes closed. Significantly different final CoP shifts and trunk angles were measured between condition with visual scene motion forward and backward. The effect of visual input on posture control was two times enhanced in paired sensory stimulation. The results indicated an important influence of unstable visual field on posture response to somatosensory stimulation where the early part of postural reaction indicated absence of visual influence.

Adult↗

PubMed2006

Effects of linear versus sigmoid coding of visual or audio biofeedback for the control of upright stance.

Although both visual and audio biofeedback (BF) systems for postural control can reduce sway during stance, a direct comparison between the two systems has never been done. Further, comparing different coding designs of audio and visual BF may help in elucidating how BF information is integrated in the control of posture, and may improve knowledge for the design of innovative BF systems for postural control. The purpose of this paper is to compare the effects of linear versus sigmoid coding of trunk acceleration for audio and visual BF on postural sway in a group of eight, healthy subjects while standing on a foam surface. Results showed that sigmoid-coded audio BF reduced sway acceleration more than did a linear-coded audio BF, whereas a linear-coded visual BF reduced sway acceleration more than a sigmoid-coded visual BF. In addition, audio BF had larger effects on reducing center of pressure (COP) displacement whereas visual BF had larger effects on reducing trunk sway. These results suggest that audio and visual BF for postural control benefit from different types of sensory coding and each type of BF may encourage a different type of postural sway strategy.

Auditory Perception↗

PubMed2002

Vestibular stimulation affects medium latency postural muscle responses.

This study explores whether galvanic vestibular stimulation can alter automatic postural muscle responses triggered 100 ms after surface translations. Our previous study concluded that a step of bipolar, galvanic vestibular stimulation delivered 500 ms prior to a platform translation tilted the internal representation of vertical because subjects' final center of foot pressure and center of mass equilibrium position shifted toward the anode and this tilt was larger than the sum of effects for platform translations and galvanic alone. In the current study, we show that 0.2-0.4 mA of galvanic vestibular stimulation produced significant changes in the tilt of the trunk in space that was realized by changes in the magnitude of the medium latency postural muscle responses at the ankle. The galvanic-induced changes in latency and magnitude of the first 50 ms of gastrocnemius muscle burst in response to the backward surface translation were consistent with changes in background muscle tone induced by the direct vestibulospinal effects of the galvanic current. However, the galvanic-induced changes in the second 50 ms of the gastrocnemius response were in the opposite direction and consistent with the forward- or backward-tilted, final postural equilibrium goal. Kinematic analysis showed that galvanic-induced tilt was first initiated in the trunk and that the shank and thigh segment angles were not altered by galvanic stimulation prior to platform translation such that changes in gastrocnemius and soleus postural responses to translations were not due to an effect of galvanic stimulation on initial ankle angle. More proximal muscles and antagonist muscles involved in the postural response were not altered by the galvanic stimulation. These results suggest that galvanic vestibulospinal stimulation can alter medium latency, automatic postural responses in prime movers by changing the postural equilibrium goal.

Adult↗