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PubMedDate not supplied

Ocular counterrolling in response to static and dynamic tilting: implications for human otolith function.

Nineteen subjects underwent rotation about the naso-occipital axis to examine ocular counterrolling (OCR) responses in both dynamic and static conditions. Dynamic rotation consisted of tilt to 90 degrees right and left at constant velocity of 3 degrees /s, with acceleration at 0.2 degrees /s(2). Static rotation (stepwise tilting) consisted of one minute at steps 30 degrees, 60 degrees, 90 degrees, 60 degrees, 30 degrees to each side. OCR amplitudes at each of the above head tilts in dynamic vs. static tilt showed highly significant differences, with dynamic tilt exceeding that of static. Although OCR disconjugacy was greater in static than dynamic in most subjects, that difference was not statistically significant. Possible explanations for the disparity in the responses to dynamic and static tilt in humans lie in vestibular experiments leading to the conclusion that the otolith membrane in cats moves not as a unit, but rather in patches (28). This is supported by work showing the otolith membrane in bullfrogs does not move en bloc (1). In addition, hair cell responses are found to be amplified during motion as compared to the responses during static positioning (20). Functionally, it is suggested that the otolith system may perform better in moving than in static conditions.

Adult↗
PubMed1992

A postural model of balance-correcting movement strategies.

The patterns of joint torques and movement strategies underlying human balance corrections were examined using a postural model. Two types of support-surface perturbation, dorsiflexion rotation (ROT) and rearward translation (TRANS), were employed. These two perturbations were adjusted to produce similar profiles of ankle dorsiflexion in order to obtain information on the role of lower leg proprioceptive inputs on triggering balance corrections. In addition, the dependence of balance control on head angular and linear accelerations was investigated by comparing the responses of normal and vestibularly deficient subjects under eyes-closed and eyes-open conditions. Differences in ROT and TRANS movement strategies were examined in three ways First, the amplitude and polarity of active joint torques were analysed. These were obtained by altering joint torques applied to a postural model until movements of the model accurately duplicated those of measured responses. Second, the pattern of body-segment angular movements depicted by stick figures moving in response to the computed joint torques was investigated. Third, the peak amplitude and patterns of crosscorrelations between joint torques were measured. Active ankle, knee, and hip joint torques computed for normal subjects rotated the body forward for ROT. In the case of TRANS, computed active torques in normals were of opposite polarity to those of ROT and reversed the forward motion of the body. Subjects with vestibular deficits had lower amplitude torques for ROT and failed to counter the platform rotation. Hip torques for TRANS in vestibular deficient subjects were of opposite polarity to those of normal subjects and resulted in excessive forward trunk rotation. Normally, neck torques acted to stabilize the head in space when trunk angular velocity peaked. Vestibular deficient subjects displayed head movements in response to ROT similar to those generated when neck torques were absent. For TRANS, these same subjects exhibited overcompensatory neck torques. Stick figures of normal responses indicated a stiffening of the body into a leg and a trunk-head link for ROT and a flexible multilink motion for TRANS. Likewise, normal response strategies, defined by using crosscorrelations of joint torques, differed for ROT and TRANS. All joint torque crosscorrelations were significant for TRANS. Neck torques led those of all other joint torques by 40 ms or more, and hip joint led ankle torques by 30 ms. Joint torque correlations for ROT were organised around hip and ankle torques without a major correlation to neck torques. Fundamental changes in all torque crosscorrelations occurred for vestibularly deficient subjects under both eyes-open and eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗
PubMed1992

Effect of positioning of the feet in posturography.

Static posturography has been developed from a basic research test to a widely used clinical tool for evaluating dizzy patients. Before any actual standardization can be achieved, however, several aspects of the test situations have to be evaluated, including the position of the feet. The quantitative significance of the standing position in posturographic measurements was evaluated with healthy volunteers studied under visual and nonvisual conditions, using 4 foot positions: heels together with the toes 30 degrees apart or at an angle of the volunteer's own choice, and the feet parallel and either 0 or 10 cm apart were studied separately. Each measurement was characterized in terms of 5 parameters (body sway velocity, vibration-induced shift of centre of force in anteroposterior and lateral directions, and maximum displacement of centre of force in the same directions). Body sway velocities were smallest when the feet were parallel and 10 cm apart. Although the position chosen by the subject was usually more stable than that with the toes 30 degrees apart, the difference was nonsignificant. According to our results, the standing position is not crucial in posturographic measurements provided that the distance between the heels is determined, and the subject can just as well choose the angle between the feet if the heels are kept together.

Adult↗
PubMed1992

Behavioural and neural correlates of vestibular compensation.

Sudden complete loss of input from one labyrinth results in a massive change in behaviour. A vigorous horizontal ocular nystagmus occurs together with postural changes. These dramatic changes are short-lived and within about a week they have almost disappeared. This very rapid recovery has been the basis for the postulation that vestibular compensation is a textbook model for the study of neural plasticity in the central nervous system. Whilst the behavioural recovery is dramatic, quantitative testing reveals the loss and the permanent asymmetry of the system (Table 1). Recordings from single neurones show that many neurones in the ipsilesional VN are silenced by the unilateral loss, but as they start to fire again, so the spontaneous nystagmus declines. The major question which is still unanswered is the cause of the return of the firing of neurones in the ipsilesional VN. The answer may be found by studies of the neurochemistry of the VN using brain slice preparations. This review shows some of the errors which have been made by attempting to infer purely vestibular function from measurements of eye movements when other sources of ocular motor control may operate.

Animals↗
PubMed2000

Effect of microgravitation on the human equilibrium.

The 38-year period of human space exploration has gained for us a lot of experience in the problem of space motion sickness. The authors collected some causes of space sickness from the literature and from their research results. We collaborated with the Soviet-Russian space researchers and elaborated those vestibular research methods that were carried out by human space missions in the Soviet-Russian space station, on Earth, and after flight: spontaneous eye movement, foveal and peripheral optokinetic nystagmus, and vestibular stimulation. Using an earthly model of the effect of microgravitation on the human body, we tried to provide explanations of the origin of space motion sickness.

Adult↗
PubMedDate not supplied

A comparison of the latencies of visually induced postural change and self-motion perception.

This study compared the latencies of visually induced postural change and self-motion perception under identical visual conditions. The results showed that a visual roll stimulus elicits postural tilt in the direction of scene motion and an increase in postural instability several seconds before the subject begins to perceive illusory self-motion (vection) in the opposite direction. Postural and vection latencies correlate highly with one another, but bear little relationship with the magnitude of either sway or vection.

Adolescent↗
PubMed1991

[Sanitary and hygienic conditions and characteristics of work of female electric coil winders].

The article contains a hygienic assessment of the working conditions of female coil winders engaged in high-powered electric engines' assembling. Relationships were established between the unfavourable labour conditions, anthropometric inadequacy of the equipment used and the female workers' labour capacity, their functional states and morbidity. Corresponding preventive measures were proposed to lower the labour intensity of female electric coil winders.

Adult↗
PubMedDate not supplied

[Vascular reactivity related to postural changes in diabetics].

Resting skin flow (RF) and the venoarteriolar response (VAR) were studied in 40 patients with diabetic microangiopathy and neuropathy, in 40 diabetes with microangiopathy and in 30 normal subjects using laser-Doppler flowmetry. In patients with microangiopathy and neuropathy RF was increased and the VAR was impaired to a greater extent than in patients without neuropathy. We evaluated the microangiopathy index (VAR/RF) that was lower in diabetics without neuropathy and even lower in those with neuropathy than in normals We also evaluated the VAR with different postural changes.

Adult↗
PubMed1991

Human postural dynamics.

The study of posture dynamics is important not only to understand disorders of impaired equilibrium and protective reactions to unexpected displacements of the human body, but also to the design of prosthesis and functional neuromuscular stimulation as aids to patients with impaired postural stability and locomotion. Coordinated control of the body segments is a complex aspect of motor behavior, owing to the multiple degrees of freedom of the controlled system. Several interacting subsystems are involved in the dynamics of human posture and locomotion, including the skeletal, neuromuscular, and sensory systems. Human posture control is maintained by somatosensory, vestibular, and visual feedback, integrated within the locomotor and central nervous systems. Studies of posture dynamics and stability therefore entail the study of mechanical aspects of the human body, its sensory systems, and the principles governing coordination in motion control. In this paper is reviewed some of the research done in the field of human posture dynamics, including such topics as biomechanics, equilibrium, stability, motion coordination, neural feedback, neural control systems modeling, motion strategies, optimality of motion, and adaptation. We consider experimental approaches and theoretical models, as well as the gap between them. Principles for the experimental investigation of control systems are considered.

Animals↗
PubMed1991

[The relation between one-sided occipital flattening and laterality of rolling-over].

The rolling-over of the body is one of the developmental mile-stones. Several infants have the laterality of rolling-over in early state and the dominant side in later state. The abilateral occipital flattening is thought to be caused by head positioning in the neonatal period and early infancy. Asymmetrical development of rolling-over was studied in relation with head positioning, relating skull occipital flattening. We examined 2919 infants aged 7 months with the questionnaire about the side of skull occipital flattening and the initial turning side of rolling-over. 1975 infants had the dominant side of rolling-over; the left side 45.4%, and the right side 47.7%. 761 infants had one-sided occipital flattening; left-side 41.3%, and right-side 54.8%, 520 infants had dominant-sided rolling-over accompanied with one-sided occipital flattening. The positive relationship between the side of rolling-over and the side of occipital flattening could not be proved by chi-square statistical analysis. These findings suggest that laterality of rolling-over, one of asymmetrical motor developments is not related to the head positioning in early infancy.

Dominance, Cerebral↗
PubMedDate not supplied

[Posturography in unilateral peripheral vestibular deficiency].

A thorough study of vestibular function cannot be limited to the evaluation of VOR alone; it must also include the study of VSR which serves to control erect stance under both static and dynamic conditions. In unilateral peripheral vestibular lesions (UVL) computerized stabilometry makes it possible to perform a more accurate evaluation of the VSR complex through the quantification of "postural sway". Furthermore, the diagnostic potential of stabilometry can be further fine-tuned by introducing a sensitization test, in particular the head retroflexion (OCR) and head shaking (OC-HST) tests. In the present study 61 patients with UVL of various etiology (viral, toxic, vascular, idiopathic) were studied. Besides electrooculography, stabilometry was performed under base conditions (eyes open and closed) and with sensitizing tests (OCR, OC-HST). L and S were used as statokinesigram parameters while frequency and oscillation amplitude on the sagittal and transverse planes were used as stabilogram parameters. Of the 61 UVL patients, 47.5% showed VOR compensation while static postural alterations were found in 31.1%; this raised to 50.8% when the sensitization test was introduced. Apparently the compensation phenomena became manifest more quickly for VOR than for VSR. The introduction of the sensitization test, however, markedly reduced this variance. The two sensitization, maneuvers used provided quantitatively equivalent results although in the absence of reciprocal agreement. Agreement was not even recorded between stabilometric HST and the head shaking test. This confirms the presence of two different routes for VOR and VSR. Nonetheless, the introduction of the sensitization test made it possible to identify those "false negative" VSR cases which were really pathological, thus making it possible to properly identify the patients' condition and arrange for adequate treatment.

Adolescent↗
PubMedDate not supplied

Electroencephalographic and electrocardiographic features of vasovagal syncope induced by head-up tilt.

Two hundred and seventy-nine consecutive patients referred for transient loss of consciousness, compatible with syncope, underwent head-up tilt to 70 degrees during polygraphic (EEG, ECG, pneumographic) and blood pressure monitorings. Vasovagal syncopes occurred in 28 patients with the following EEG changes: progressive slowing until the appearance of middle or high amplitude delta waves generalized and synchronous in 9 patients; delta waves suddenly followed by transient flattening of EEG activity in 16 patients. In 2 patients EEG could not be interpreted because of muscle and/or movement artifacts. Fifteen out of 28 patients exhibited a marked cardioinhibition, expressed by long-lasting cardiac pauses; a relationship between duration of EEG flat and duration of asystole was not found.

Adolescent↗
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↗