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Biomedical subjects

P Gatev

Publications and source records attributed to P Gatev.

At least 19 recordsLinked to original sources
PubMed2001

Effects of maturity and training on bimanual ballistic isometric handgrip.

We studied maturity and training effects on maximal force and accuracy of force targeting during ballistic handgrips. Male right-handed nontrained adolescents (16-20 yrs.), trained adolescents (oarsmen--16-18 yrs.) and nontrained adults (21-44 yrs.) did right (R) unilateral (UL), left (L) UL handgrip and bilateral (BL) maximal ballistic handgrips. Next, they targeted 30% of maximal respective UL handgrip. We found peak force L:R ratios in adolescents significantly closer to 1 compared to nontrained adults suggesting less hemisphere dominance in adolescents, especially in trained ones. Nontrained adolescents showed smaller bilateral deficit for L hand than the other groups. Adolescents showed a significant underestimation of L hand during BL task (-4.6%), especially oarsmen (-8.7%), while adults showed neither overestimation, nor underestimation during all tasks. The disappearance of the asymmetry of bilateral deficit and L hand errors of force targeting suggest a diminution of neural cross-talk from dominant to non-dominant hand and its better estimate with maturity.

Adolescent↗
PubMed2001

Changes in plantar pressures during bipedal stance with different stance width.

We studied the influence of stance width and vision on the plantar pressures for the left and right foot during bipedal quiet standing on the pressure-sensitive insoles. The support widening shifted the left and right centers-of-foot-pressure (CFPs) laterally and forward (right foot), diminished SDs of: the left and right mean plantar pressures (MPPs), the anteroposterior and mediolateral displacements of left and right CFPs. It also decreased negative correlations between left and right MPPs and between mediolateral displacements of left and right CFP and increased positive correlation between anteroposterior displacements of left and right CFPs, more expressive with eyes-open. The later results suggested that support widening increased the weight of exploratory behaviour regarding anteroposterior equilibrium and decreased exploratory sway serving mediolateral equilibrium. Eyes' closure lead to a small left bias of the body-weight-bearing and forward shift of the left versus right CFP, thus suggesting that vision increased bilateral symmetry of stance.

Adult↗
PubMed1999

Feedforward ankle strategy of balance during quiet stance in adults.

1. We studied quiet stance investigating strategies for maintaining balance. Normal subjects stood with natural stance and with feet together, with eyes open or closed. Kinematic, kinetic and EMG data were evaluated and cross-correlated. 2. Cross-correlation analysis revealed a high, positive, zero-phased correlation between anteroposterior motions of the centre of gravity (COG) and centre of pressure (COP), head and COG, and between linear motions of the shoulder and knee in both sagittal and frontal planes. There was a moderate, negative, zero-phased correlation between the anteroposterior motion of COP and ankle angular motion. 3. Narrow stance width increased ankle angular motion, hip angular motion, mediolateral sway of the COG, and the correlation between linear motions of the shoulder and knee in the frontal plane. Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased. The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision. 4. Low, significant positive correlations with time lags of the maximum of cross-correlation of 250-300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance. Narrow stance width decreased both correlations whereas absence of vision increased the correlation with COP. 5. Ankle mechanisms dominate during normal stance especially in the sagittal plane. Narrow stance width decreased the role of the ankle and increased the role of hip mechanisms in the sagittal plane, while in the frontal plane both increased. 6. The modulation pattern of the lateral gastrocnemius muscle suggests a central program of control of the ankle joint stiffness working to predict the loading pattern.

Adult↗
PubMed1996

Mechanically evoked cerebral potentials to sudden ankle dorsiflexion in human subjects during standing.

Mechanically evoked cerebral potentials (MECP) were studied in humans standing on a movable platform with three different stance widths. A sudden platform tilt of 4 degrees produced ankle dorsiflexion and resulted in scalp potentials of five distinct components, the earliest being a positive deflection at 35/60 ms. Their latencies have shown fairly consistent values among the three stance widths, while the amplitudes underwent some significant changes under the wide stance condition as compared with tightly close feet. These findings were interpreted as purporting evidence of altered somaesthetic afferent input from lower limbs during standing with widely apart support surface.

Adult↗
PubMed1996

Effects of diminished and conflicting sensory information on balance in patients with cerebellar deficits.

We studied the effects of altered sensory information on standing balance in 25 patients with cortical cerebellar atrophy (CCA), nine patients with olivoponto-cerebellar atrophy (OPCA), and 10 normal subjects. The total sway path and its components, the anteroposterior (AP) sway path and the lateral sway path, were measured under six conditions: (1) standing on a fixed platform with the eyes open and visual surroundings fixed, (2) standing on a fixed platform with the eyes closed, (3) standing on a fixed platform with the eyes open and visual surroundings AP sway referenced, (4) standing on an AP sway-referenced platform with the eyes open and visual surroundings fixed, (5) standing on an AP sway-referenced platform with the eyes closed, and (6) standing on an AP sway-referenced platform with the eyes open and visual surroundings AP sway referenced. Patients swayed more than normal subjects during normal stance (condition 1), when the visual information was absent (condition 2) or distorted (condition 3), and when the proprioceptive information from the ankles was distorted (condition 4). Patients swayed much more than normal, and most fell, when two sensory modalities were affected under condition 5 (proprioceptive information distorted and visual information absent) and condition 6 (both proprioceptive information and visual information distorted). When the patients' sway was normalized to that of the first condition, however, only their lateral sway was greater than the sway in normal subjects. Unlike in normal subjects, the patients' lateral sway varied with the AP sway to approximately the same degree in each condition for conditions 1-5. Clinical ratings of gait and balance were highly correlated with the sway measures. Quantitative testing of standing balance with altered sensory information has better sensitivity than normal stance testing.

Adult↗
PubMed1995

Use of buspirone for treatment of cerebellar ataxia. An open-label study.

OBJECTIVE: To evaluate the efficacy of buspirone hydrochloride, a serotonin (5-hydroxytryptamine1A) agonist, in treating patients with cerebellar ataxia. DESIGN: Open-label study in which 20 patients (14 with cerebellar cortical atrophy and six with olivopontocerebellar atrophy) received buspirone hydrochloride, up to 60 mg/d, for 8 weeks. SETTING: Research hospital. MAIN OUTCOME MEASURES: Clinical, physiological, and psychological assessment. RESULTS: Nine patients with mild or moderate cerebellar dysfunction who completed the study showed significant improvement in clinical and self-assessment ratings, but not in a motor performance test, posturography (data were incomplete), State-Trait Anxiety Inventory, and Beck Depression Inventory. Seven patients with severe cerebellar dysfunction who completed the study had no improvement on any measure. CONCLUSIONS: Buspirone may be effective in treating mild to moderate cerebellar ataxia. A double-blind study of the efficacy of buspirone in cerebellar ataxia is warranted.

Adult↗
PubMed1993

Visual control of human stance on a narrow and soft support surface.

The influence of additional visual feedback (VF) on stance control was studied under conditions of changed afferent information from the foot sole and ankle joint due to different support surfaces. The changes of body sway amplitudes were analyzed and their frequency spectrum was established. The effect of visual feedback on the amplitude and frequency characteristics of human stance was manifested as: a) a decrease of the mean amplitude of body sway during visual feedback, corresponding to the decrease of power spectrum density (PSD) of stabilograms in the frequency range below 0.05 Hz, b) an increase of mean velocity of body sway corresponding to the increase of PSD of stabilograms in the frequency range of 0.4-1.5 Hz. The results showed that the improvement of the upright stance by additional visual feedback is mainly mediated through activation of postural muscles at the ankle level, or ankle strategy. The stabilization effect of VF on stance control is slight or negligible if the performance part in ankle joint (narrow support) was reduced.

Adult↗
PubMed1991

Postural adjustments upon arm movement during sinusoidal induced body oscillations.

Postural adjustments due to the fast forward right arm elevation, performed during sinusoidal induced body oscillations in the phase of platform-induced dorsal, as well as plantar flexion of the foot were studied. Start times of the changes in the cyclic way of the center-of-gravity position (SG) and right ankle goniogram (GG) as well as the EMG onsets of the right soleus (S), anterior tibial (AT) and femoral biceps (FB) muscles relative to the ipsilateral anterior deltoid muscle (AD) EMG onset were measured. The EMG onset of FB muscle was found to occur significantly before the EMG onset of the AD muscle during plantar flexion series, wherever during dorsal flexion series the EMG onset of the AT muscle was significantly before the AD muscle EMG onset. Only the FB muscle changed significantly its EMG onset with the change of platform direction and started later in the dorsal flexion series. The results showed that two different strategies of postural adjustments might be distinguished depending on the direction of the platform movement.

Adult↗
PubMed1991

Somatosensory evoked potentials during standing posture on different support surface.

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during standing on stable ground or on unstable support surface (seesaw) or on support surface short in relation to foot length. During standing on the seesaw and on the short support surface a decrease in the amplitude of the early component (N32-P39) was observed. The amplitude of N49-P58 decreased during standing on the short support surface. The amplitude of the later components (N49-P58; P58-N76; N76-P117) decreased during standing on the seesaw in comparison to that during standing on the stable ground and on the short support surface. Thus, the attenuation of the cerebral potential during standing depend on the conditions for maintenance of posture.

Adult↗
PubMed1991

M-response latencies changes as a tool for studying neuromuscular conduction during cyclic maximal voluntary contractions.

M-response changes during cyclic maximal isometric voluntary forearm flexions were studied using a new method based on the following: 1) Monopolar stimulation of terminal motor point of the brachial biceps muscle by large surface electrodes; 2) Monopolar leading-off by a surface electrode placed on the middle between motor endplates and muscle fibers end; 3) Arm and forearm immobilization; 4) Averaging of M-response triggered by the stimulus during contraction; and 5) Latencies to the peak of negative (L1) and of final positive phase (L2) and peak-to-peak amplitude (PTPA) were measured, and peak-to-peak time (PTPT), which reflected muscle conduction velocity and leading-off electrode-to-end of fibers distance was calculated. Four cycles of 30-s contraction and 5-min rest were performed. Eight M-responses were evoked with a 1 Hz frequency starting from 5th s of the cycle. No significant changes of PTPA and L1 were found. Nevertheless, L2 significantly decreased in the third cycle by 6.4% and in the fourth-cycle by 7.6% of the first cycle value. PTPT decreased in the fourth cycle reaching 87.6% of the initial value. The advantage of the method and the possible causes of changes were discussed.

Adult↗
PubMed1990

Effect of body and foot positions on the somatosensory evoked potentials.

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during sitting and standing with variable foot positions. During standing a decrease in the amplitude of the early positive component was observed. The deviation of the foot from a horizontal position was associated with an increase in the amplitude of the early negative component. The combined influence of body and foot positions showed a decrease in the amplitude of both early and late components. The standing position induced changes in more components than the varied foot positions. This suggests that maintenance of the standing posture is a more complex task than the maintenance of the foot position itself.

Adult↗
PubMed1987

Postural adjustments associated with a fast voluntary arm movement at various foot positions.

The aim of the study was to further investigate postural adjustments associated with a fast voluntary arm elevation at various foot positions. The subjects stood upright on a force platform and participated in 3 sessions according to foot position: horizontal position, dorsal and plantar flexion of 6 degrees. EMG activity of anterior deltoid muscle (DA) and of ipsilateral and contralateral soleus (SD, SS), biceps femoris (BFd, BFs) and ipsilateral anterior tibial (TAd) muscles, initial acceleration (Acc) and stabilogram change (Sg) were recorded. The results showed that postural preadjustment was provided by a co-contraction of SOLd and TAd, preceding 31-37 ms the time onset of DA, observed in all foot positions. Time onset of EMG activity in BFd and BFs followed 105-134 ms after EMG onset of DA, showing some dependence on foot position. The co-contraction of SD and TAd presumably has postural function with the role to maintain stability of the body against the increased postural requirements associated with a very fast arm movement. The preceding activity of BFd and BFs and their participation in postural preadjustments is probably not necessary, since the co-contraction of SD and TAd has ensured fixation of the ankle joint.

Adult↗
PubMed1986

Motor unit activity during different functional states of the neuromuscular system.

The study showed that the mean interspike interval (ISI) and the variability of ISIs increased with fatigue for both low and high threshold motor units (MUs). The recruitment threshold tension decreased for both the low and high threshold MUs while the recruitment threshold in % of maximal voluntary contraction changed selectively because of decrease of muscle force. During ischaemia after an initial decrease of mean ISI and ISIs' variability there was an essential increase of variability of ISIs at almost the same mean ISI followed by a considerable final increase of both parameters. MUs' recruitment thresholds lowered with ischaemia more rapidly in the beginning and especially in the final stage of ischaemia.

Action Potentials↗
PubMed1981

Effect of ischaemia on the potentials of human single muscle fibres.

The changes in the parameters of the extracellular potentials of single muscle fibres are studied during ischaemia. These changes have two phases, preceded in part of the cases by a transient phase. The decrease in the propagation velocity (V) of the excitation predominates in the first phase, therefore, the length of the depolarized area (b) is shortened. The shortening of b, directly demonstrated by VEMG, conditions an increase in the peak-to-peak amplitude of the potentials (Ap) and of its components: the amplitude of the initial positive phase (A1) and the amplitude of the negative phase (Ad). During the second phase there is predominance of the lengthening of the time for depolarization (TD), as well as the time for fast repolarization (TR). This is manifested in elongation of the times for increase and decrease of the negative phase, accompanied by an increase in the times for increase and for decrease of the initial positive phase. The increase in b, proved directly by the changes in VEMG, results from the longer TDR. The increase in b leads to a decrease in the amplitudes Ap, AI and Ad. The changes during ischaemia are analogous to a certain extent to the changes in continuous activity of the muscle fibre, but the former occur more rapidly. They are accompanied by changes in the AI/Ad ratio which suggests changes in the intracellular potentials, most probably changes in the after-potentials. During ischaemia the influence of hypoxy is summated probably with the influence of long-lasting discharge and lowered temperature of the muscle.

Action Potentials↗