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PubMed2000

Visual control of postural orientation and equilibrium in congenital nystagmus.

PURPOSE: To investigate how humans with congenital nystagmus (CN) use visual information to stabilize and orient their bodies in space. METHODS: Center of foot pressure (COP) and head displacements in the lateral plane were recorded using a sway platform and Schottky barrier photodetector, respectively. In experiment 1, a comparison was made of the oscillatory characteristics of body sway with eyes open compared with eyes closed. Experiment 2 studied the postural readjustments made in response to absolute or relative motion (motion parallax) of objects in the visual scene, generated by lateral displacement of background scenery. RESULTS: Experiment 1 revealed that subjects with CN were not able to use visual information to stabilize COP but were able to stabilize the head at frequencies lower than 1 Hz. Experiment 2 showed that in response to the displacement of a visual display, for both absolute motion and motion parallax, subjects with CN reoriented their body in space in a manner similar to control subjects. CONCLUSIONS: The results suggest that despite involuntary eye movements, subjects with CN use orientation cues to control their posture, but not dynamic cues useful to control the rapid oscillations that are particularly important at the level of COP. These findings suggest that in CN, visual control of posture is restricted by low-frequency sampling of the visual scene.

Adult↗
PubMed2000

[Factors contributing to falls in elderly subjects leading to acute-care hospitalization].

OBJECTIVE: Falls are a frequent reason for hospitalization in short-stay geriatric units. Paradoxically, the factors determining such hospitalization remain unknown. The objective of our study was to identify the explanatory factors of falls leading to acute-care hospitalization of elderly subjects. PATIENTS AND METHODS: We prospectively compared patients hospitalized for falls and those hospitalized for another reason in a short-stay geriatric unit. Data were collected over a 6-month period starting with a questionnaire and a physical examination. RESULTS: Patients admitted for falls were predominantly women (76.9%) living alone (76.9%). Falls depended mainly on intrinsic factors. The precipitating factor was a medical condition (84%) and acute (96%). The pattern of multiple disease conditions was not specific for patients who fell. Inversely, osteoarthritis and visual and auditory deficits with direct effects on motor functions were correlated with falls. The environment played a determining role, but was primarily a predisposing and not a precipitating factor as is was directly the cause of falls in only 4% of cases. The loss of self-sufficiency for daily activities was also significantly more frequent in patients who fell. DISCUSSION: The explanatory factors of falls as the reason for hospitalization of elderly subjects in short-stay geriatric units are intrinsic factors. They are associated with a precipitating factor which is usually an acute medical condition and a chronic multiple disease state having an effect on postural balance leading to the fall. These factors are combined in a context of social and environmental isolation.

Accidental Falls↗
PubMed2000

Turning difficulty characteristics of adults aged 65 years or older.

BACKGROUND AND PURPOSE: Falls that occur while walking have been associated with an increased risk of hip fracture in elderly people. This study's purpose was to describe movement characteristics in older adults that serve as indicators of difficulty in turning while walking. SUBJECTS: Three groups were assessed: young adults who had no difficulty in turning (age range=20-30 years, n=20) (YNDT group), elderly adults who had no difficulty in turning (age range=65-87 years, n=15) (ENDT group), and elderly adults who had difficulty in turning (age range=69-92 years, n=15) (EDT group). METHODS: All subjects were videotaped performing a self-paced 180-degree turn during the Timed "Up & Go" Test. Movement characteristics of each group were identified. Four characteristics were used to identify difficulty in turning: (1) the type of turn, (2) the number of steps taken during the turn, (3) the time taken to accomplish the turn, (4) and staggering during the turn. RESULTS: In general, the EDT group took more steps during the turn and more time to accomplish the turn than the YNDT and ENDT groups. Although the only turning strategy used by the YNDT group was a pivot type of turn, there was an almost total absence of a pivot type of turn in the EDT group. No differences were found among the groups on the staggering item, yet the EDT group was the only group in which staggering was present. We believe these changes observed in the 4 characteristics only in the EDT group are indicators of difficulty in turning while walking. CONCLUSION AND DISCUSSION: These indicators of difficulty may be useful for the early identification of individuals aged 65 years or older who are having difficulty in turning and may well serve as the basis for the development of a scale for difficulty in turning in older adults. Preliminary findings indicate the need for further study into the reliability, validity, and sensitivity of measurements obtained with such a scale.

Accidental Falls↗
PubMedDate not supplied

[Reproduction by means of a methematical model of the dynamic characteristics of human vertical posture maintenance].

Some peculiarities of invisible oscillations of man's body during his standing are reproduced using a mathematical model. The stability of the corresponding dynamic system with two delayed feedbacks and its behaviour in response to irregular and regular effects has been investigated. The results are compared with the experimental data. It is suggested that the mathematical model satisfactorily reflects principal peculiarities of the process of equilibrium support of man's body.

Biomechanical Phenomena↗
PubMed2000

[Falling in Parkinson disease: more often due to postural instability than to environmental factors].

OBJECTIVE: To document the circumstances surrounding falls in patients with Parkinson's disease. DESIGN: Prospective. METHOD: Parkinson patients with a check-up appointment in the period 1 May 1998-31 May 1999 at the Neurology Outpatient's Department of Leiden University Hospital, used standardized forms to record the circumstances surrounding all incidents of falling during the subsequent 6 months. For control purposes, a partner or acquaintance with comparable living conditions was asked to do the same. The researchers judged whether falls were related to physical impairment (personal, intrinsic factors) or environmental factors (extrinsic factors). RESULTS: 59 patients with Parkinson's disease (21 women (36%); mean age: 60.8 years; mean Hoehn and Yahr score: 2.3) and 55 controls (37 women (67%); mean age: 59.6 years) were studied. Patients reported 205 falls and controls 10 falls. Recurrent (> or = 2) falls occurred in 15 patients (25%) and two controls (4%) (relative risk (RR): 9.0: 95% confidence interval (95% CI): 2.0-41.7). Recurrent falls were more common among persons using benzodiazepines (RR: 5.0: 95% CI: 1.6-15.5). Reliable information was obtained for 160 falls in patients. Most falls (79%) had an intrinsic cause, like turning around, standing up, bending and stumbling. Abrupt movements were a particularly frequent cause of falls. Simultaneous performance of multiple tasks contributed to almost 50% of falls in patients. CONCLUSION: Falls are common among Parkinson patients. Most falls are related to intrinsic factors. Prevention of these intrinsic falls requires treatment of the underlying postural instability. Use of benzodiazepines must be avoided whenever possible. Interventions aimed at extrinsic factors, such as reduction of domestic hazards, are possibly less effective.

Accidental Falls↗
PubMed2001

[Gait disorders in Parkinson disease. Clinical description, analysis of posture, initiation of stabilized gait].

A WELL INFORMED DESCRIPTION: The parkinsonian posture is generally described as a stooped one. At the beginning of the disease, the gait troubles remain moderate; gradually the gait is composed of small steps without a wide base; the patient tends to run after his centre of gravity by accelerating the step (festination phenomenon). Difficulties occurs for starting up (delay of gait initiation), for about-turn or for clearing obstacles. Kinetic jammings and standing around (freezing) can last several seconds and be responsible for falls. POSTURAL INSTABILITY, A MAJOR SYMPTOM IN PARKINSON'S DISEASE: This symptom is little improved by therapies and is responsible for serious disability. Postural instability induces a disequilibrium and is partially due to a simultaneous antagonist muscles contraction and to the impossibility of modifying postural responses to changing support conditions. The passive viscoelastic properties of muscles and tendons constitute a first line of defence against the disequilibrium and contribute to postural stability in the case of medium disturbances. Automatic and voluntary postural responses which come into play in the case of major disturbances can also be impaired (delay or defect of the responses). GAIT INITIATION FAILURE ARE FREQUENT: They result from an increase of the postural phase and a decrease of the propulsion forces, depending on a deficit of the postural anticipation mechanisms and also the sequential organization and the integration of two different motor programs, postural and locomotor. They can be controlled partially with sensory stimuli, notably visual inputs. DATA CONCERNING STABILIZED WALKING AND ITS PATHOPHYSIOLOGY REMAINS TO BE CLARIFIED: Spatial and temporal parameters are impaired: speed, step length and swing phase are reduced, while cadence increases to compensate these troubles. These modifications are the consequence of an incapacity to produce internal marks to generate regular steps. When the parkinsonian patient is supplied with external marks, these parameters can be normalized. From a pathophysiological point of view, gait disorders could result from defective central integration of proprioceptive information during movement within the basal ganglia, associated with a visual perceptive deficit linked with a retinal dopaminergic cells dysfunction and finally from an impairment of the proprioceptive feedback of the load receptors in the leg extensor muscles.

Antiparkinson Agents↗
PubMed2001

Muscular contractions and their effect on the vertical ground reaction force during quiet stance--Part I: Hypothesis and experimental investigation.

There is no consensus as to the origins of the oscillations of the vertical ground reaction force during quiet stance. The concept of a cardiovascular origin is supported by many ballistocardiographic studies, but its exclusivity has never been proven. A new hypothesis was formulated to explain their genesis: there is a neuromuscular postural control system, possibly different from the well-investigated mechanisms controlling the macroscopic sway, responsible for compensating the small endogenous forces perturbing the posture by causing some muscles to contract proportionately to the magnitude of perturbation. These contractions contribute to the ground reaction force oscillations. To verify this hypothesis, a series of experiments simultaneously recording the electrocardiogram, the electromyogram of several muscles, and the ground reaction forces were conducted on ten informed and consenting human subjects. The experimental results confirmed that the hypothesized muscular activity in response to the perturbation induced by the cardiac contraction and subsequent blood movement does in fact exist. The signal detected by electromyography is not a cardioelectric artifact, but an actual myoelectrical activity. Several interesting patterns of muscular activity emerged in this investigation. These results provide the needed background and justification for investigating the use of the vertical ground reaction force, not only in the study of posture, but also in the study of clinical conditions affecting the neuromuscular control and the musculature of the trunk.

Adult↗
PubMed1996

A review of the sharpened Romberg test in diving medicine.

The use of the sharpened Romberg test (SRT) was evaluated in injured divers. Over a 12 month period, thirty five divers presenting with decompression illness (DCI) to the Naval Base in Auckland were assessed before hyperbaric treatment and at discharge. Their scores were compared with those of an age and sex matched control group (n=60). Abnormal SRTs were seen in 49% of divers (n=17) before treatment. These results were significantly improved at discharge (p<0.001). The results in injured divers were significantly lower than controls at presentation (p<0.001), but not at discharge. The SRT is consequently considered to be a valuable examination in divers who suffer DCI. It is proposed that the SRT be conducted in a standardised manner and be scored as the best attempt of four.

Adolescent↗
PubMed1997

Effects of 20 days horizontal bed rest on maintaining upright standing posture in young persons.

The effects of 20 days horizontal bed rest (BR) on postural reflex were studied by measuring fluctuation of center of gravity in the body during two legs or one leg upright standing in 10 young volunteers. The fluctuation was decided as total moving distance of the center recorded during 60sec standing on a force plate. The stability was measured by the moved area. After BR, the moving distance increased during two legs standing with open eyes (p<0.05), but statistically unchanged with closed eyes. The moving area decreased during right one-leg standing with closed eyes (p<0.05), but unchanged during left one-leg standing. Despite with open eyes the increased distance suggested that postural reflexes to maintain upright position were probably decreased by increased unsuitable feedback informations from the visual receptor deconditioning during BR. The decreased area during right one-leg standing with closed eyes also suggested that the declined standing posture reflex was probably related to more rapidly lowered functions for maintaining standing position in the dominating leg than in the other.

Adult↗
PubMed2001

Human postural responses to different frequency vibrations of lower leg muscles.

We analyzed human postural responses to muscle vibration applied at four different frequencies to lower leg muscles, the lateral gastrocnemius (GA) or tibialis anterior (TA) muscles. The muscle vibrations induced changes in postural orientation characterized by the center of pressure (CoP) on the force platform surface on which the subjects were standing. Unilateral vibratory stimulation of TA induced body leaning forward and in the direction of the stimulated leg. Unilateral vibration of GA muscles induced body tilting backwards and in the opposite direction of the stimulated leg. The time course of postural responses was similar and started within 1 s after the onset of vibration by a gradual body tilt. When a new slope of the body position was reached, oscillations of body alignment occurred. When the vibrations were discontinued, this was followed by rapid recovery of the initial body position. The relationship between the magnitude of the postural response and frequency of vibration differed between TA and GA. While the magnitude of postural responses to TA vibration increased approximately linearly in the 60-100 Hz range of vibration frequency, the magnitude of response to GA vibration increased linearly only at lower frequencies of 40-60 Hz. The direction of body tilt induced by muscle vibration did not depend on the vibration frequency.

Adult↗
PubMed2001

[Effects of 7 d -6 degrees bed-rest on postural equilibrium].

OBJECTIVE: To quantitatively assess the effects of 7 d -6 degrees head-down bed-rest (HDBR) on postural equilibrium and to investigate the contributions of vestibular, somatosensory and visual informations to postural equilibrium. METHOD: Eight healthy males, aged 33 - 42 years, were exposed to -6 degrees head-down tilt bed rest for 7 d. Sensory Organization Test (SOT) and Motor Coordination Test (MCT) were measured before and after HDBR, and day 4 of recovery. RESULT: Equilibrium scores of SOT in condition 1 (eyes opened, platform and visual scence environment fixed), 5 (eyes closed visual scence environment fixed, platform movable) were significantly lower as compared with pre-HDBR value, and recovered to pre-HDBR level on day 4 of recovery. Postural strategy scores of SOT in condition 1, 2 (eyes closed, platform and visual scence environment fixed) and 3 (eyes opened, platform fixed, visual scence environment movable) were significantly lower as compared with pre-HDBR value, and recovered to pre-HDBR level on day 4 of recovery. The dependence of somatosensory and visual information (ratio pair codition 2/condition 1, condition 3/condition 1 in sensory analysis) was significantly higher as compared with pre-HDBR value, and recovered on day 4 of recovery. Mean SOT alignment scores in conditions 1, 4 (eyes opened, visual scence environment fixed, platform movable) and 6 (eyes opened, platform and visual scence environment movable) were significantly higher as compared with pre-HDBR value, and only the scores of conditions 1, 6 were recovered on day 4 of recovery, but that of condition 4 did not. Mean postural-evoked response latencies of MCT were not significantly different as compared with pre-HDBR value. CONCLUSION: 7 d -6 degrees head-down tilt bed-rest has significant effects on postural equilibrium. The contributions of somatosensory and visual informations to postural equilibrium are increased.

Adult↗
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↗