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PubMedDate not supplied

Dynamic platform sway measurement in Menière's disease.

Fourteen patients in the latent phase of Menière's disease and 14 control subjects were tested on a moving platform apparatus as part of a protocol of investigations for Menière's disease. Subjects were tested under 3 different visual conditions (eyes open, eyes closed, sway feedback) and 2 proprioceptive conditions (fixed platform and ankle stabilization). There was a significant interaction between subject group and visual condition, Menière's patients had a larger RMS sway amplitude than controls with their eyes open and closed, but this difference was abolished by sway feedback. Loss of either visual or proprioceptive sensory information increased sway amplitude, indicating that both cues influence postural control, and in different ways, but patients were able to use these cues to maintain upright posture almost as effectively as controls. More patients than controls lost balance with ankles stabilized and eyes closed, but the difference was not statistically significant (P = 0.0516). There was no detectable relationship between clinical ratings of disease severity and sway scores. The dynamic platform tests described in this report are more suitable for tests involving comparisons between groups of subjects rather than for diagnostic testing of individuals.

Adult↗

PubMed1995

Body sway in diabetic neuropathy.

OBJECTIVE: To evaluate the influence of peripheral neuropathy on body sway assessed by posturography. RESEARCH DESIGN AND METHODS: The age-matched study subjects included 10 insulin-dependent diabetes mellitus (IDDM) patients with peripheral neuropathy (DN), 23 IDDM patients without peripheral neuropathy (D) according to the San Antonio Consensus Conference guidelines, and 21 control subjects (C). All subjects with symptoms and/or clinical signs of postural instability were excluded from the study. RESULTS: The trace surface was significantly larger in the DN than in the C and D groups (P < 0.05), and the trace length was longer in the DN than in the C and D groups (P < 0.01). Mean velocity was faster in the DN than in the other two groups (P < 0.001). A direct relationship was found between the parameters of posturography and some parameters of the nerve conduction velocity. CONCLUSIONS: Diabetic patients with peripheral neuropathy demonstrate a relative deficit in their ability to maintain posture. Posturography allows an early disclosure of the failure of postural control.

Adult↗

PubMed1989

Contribution of postural muscle tone to full expression of posture and locomotor movements: multi-faceted analyses of its setting brainstem-spinal cord mechanisms in the cat.

In this minireview, I have summarized and discussed our results concerning the neuronal mechanisms of postural suppression, and our thoughts about contribution of postural muscle tone to the full expression of locomotion. The identified brainstem-spinal cord system is schematically illustrated in Fig. 1 with its neuronal constituents (A). When cells of origin of this system (cells in the nucleus reticularis pontis oralis), or the pathway descending from these cells (DTF area) are tonically activated, cells in the nucleus reticularis gigantocellularis (gc cells) are also tonically activated, and with this process the system as a whole exerts generalized or non-reciprocal tonic inhibitory effects upon alpha-motoneurons innervating hindlimb extensor and flexor muscles. In consequence, postural muscle tone, especially that of the hindlimbs, is tonically suppressed and results in sustained suppression of postural support both in acute decerebrate cats (locomotor preparation) and in awake, freely moving cats, terminating locomotor movements. Since postural control and locomotor control are not separate phenomena, our results indicate that interaction of the above-described two control systems should be studied at each level of the brainstem and the spinal cord. In fact, contribution of brainstem neurons and of spinal interneurons has already been studied. It may also be interesting to elucidate supra-pontine structures which activate the identified brainstem-spinal cord inhibitory system. Such a study may elucidate the neuronal structures related not only to the termination of on going movements but also to the muscular atonia observed during active sleep. As demonstrated, even for the understanding of the brainstem-spinal cord system involved in postural suppression, multi-faceted and mutally related analytical approaches have been necessary as suggested by Brookhart, and these approaches allowed us to approach a much better understanding of the problem one faces. They were neuroanatomical analyses of plausible neuronal structures, electrophysiological analyses of their synaptic organizations, the neuropharmacological analyses of their putative neurotransmitters, and finally the most important, behavioral analyses. For a thorough understanding of the dynamics of postural and locomotor control systems, the problems we are now concerned with are to identify both the "hardware" and the "software" of these two systems. Understanding of the hardware requires an elucidation of the neuronal circuits including synaptic organizations, and that of the software an identification of the putative neurotransmitters that set the identified neuronal circuit to work, so that the systems as a whole exhibit a meaningful external manifestation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Nystagmus and postural instability after headshake in patients with vestibular dysfunction.

Nystagmus after rapid head-shaking (post-headshake nystagmus) is often seen in patients with vestibulopathy. Post-headshake nystagmus is transient and is frequently associated with symptoms of dizziness, dysequilibrium, or vertigo. The phenomenon presumably reflects headshake-induced asymmetry in vestibulo-ocular reflex pathways, which persists after head-shaking stops. We postulated that the same vestibular imbalance that underlies post-headshake nystagmus might produce an equivalent in postural instability. To test this hypothesis, we investigated the effect of headshake on postural control and eye movements in patients who exhibited post-headshake nystagmus, vestibulopathy, or both. Postural instability was quantified with a dynamic platform device, whereas eye movements were recorded with electrooculography. Ten normal controls and 21 patients with a history of post-headshake nystagmus or unilateral vestibulopathy were evaluated. Subjects were tested for 20 seconds before and immediately after passive horizontal headshake (+/- 30-degree amplitude) at 2 Hz for 20 seconds. Postural stability was assessed while subjects stood with eyes closed, and the floor was modulated proportionally with sway. The difference in normalized peak-to-peak sway (equilibrium score) before and after headshake was assessed in all subjects and compared between groups. Post-headshake nystagmus was documented by electro-oculography recorded during posturography. Results for normal controls and vestibulopathic subjects without post-headshake nystagmus showed only a small transient decline in postural stability after headshake. Those with post-headshake nystagmus (regardless of caloric asymmetry) showed a robust decline in postural stability.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2004

Trunk position influences vestibular responses of fastigial nucleus neurons in the alert monkey.

Vestibulospinal reflexes play an important role for body stabilization during locomotion and for postural control. For an appropriate distribution of vestibular signals to spinal motoneurons, the orientation of the body relative to the head needs to be taken into account. For different trunk positions, identical vestibular stimuli must activate different sets of muscles to ensure body stabilization. Because the cerebellar vermis and the underlying fastigial nucleus (FN) might be involved in this task, vestibular neurons in the rostral FN of alert rhesus monkeys were recorded during sinusoidal vestibular stimulation (0.1-1.0 Hz) in the roll and pitch planes at different trunk-re-head positions (center and +/-45 degrees ). From the sensitivity and phase values measured in these planes, the response properties in the intermediate planes and the stimulus orientation eliciting the optimal response [response vector orientation (RVO)] were calculated. In most neurons, the RVOs rotated systematically with respect to the head, when trunk-re-head position was altered, so that they tended to maintain their orientation with respect to the trunk. Sensitivity and phase at the RVO were not affected. This pattern was the same for neurons in the right and left FN and independent of stimulus frequency. The average sensitivity of this partially compensatory RVO shift in response to trunk-re-head displacements, evaluated by linear regression analyses, was 0.59 degrees / degrees (n = 73 neurons). These data show that FN neurons may encode vestibular information in a coordinate system that is closer to a trunk-centered than to a head-centered reference frame. They indicate an important role of this nucleus in motor programs related to posture and gait control.

Animals↗

PubMed1995

Effect of galvanic vestibular stimulation on human postural responses during support surface translations.

1. We investigated the role of the vestibular system in postural control by combining galvanic vestibular stimulation (0.2-0.5 mA) with platform translations in standing subjects. Vestibular stimulation delivered 500 ms before and continuously during the platform translation produced little change in the earliest center of pressure (COP) and center of mass (COM) movements in response to platform translations, but resulted in large changes during the execution of the postural movement and in the final equilibrium position. 2. Vestibular stimulation produced anterior or posterior shifts in the position of COP and COM, depending on the polarity of the galvanic current. These shifts were larger during platform translations than during quiet stance. The peak of these shifts in COP and COM occurred at 1.5-2.5 s after the onset of platform translation, and increased in magnitude with increasing platform velocity. The final equilibrium positions of COP and COM were also shifted, but these shifts were smaller and not dependent on platform velocity. 3. These results imply that a tonic step of galvanic current to the vestibular system can change the final equilibrium position for an automatic postural response. Furthermore, these results indicate that the vestibular system may play a larger role in interpreting sensory reafference during postural movements, and especially during fast postural movements, than in controlling quiet stance. Finally, these results indicate that the vestibular system does not play a critical role in triggering the earliest postural responses, but it may be critical in establishing an internal reference for verticality.

Adult↗

PubMed2006

Postural sway and joint kinematics during quiet standing are affected by lumbar extensor fatigue.

The purpose of this study was to investigate changes in postural sway and strategy elicited by lumbar extensor muscle fatigue. Specifically, changes in center of mass (COM), center of pressure (COP), and joint kinematics during quiet standing were determined, as well as selected cross correlations between these variables that are indicative of movement strategy. Twelve healthy male participants stood quietly both before and after exercises that fatigued the lumbar extensors. Whole-body movement and ground reaction force data were recorded and used to calculate mean body posture and variability of COM, COP, and joint kinematics during quiet standing. Three main findings emerged. First, participants adopted a slight forward lean post-fatigue as evidenced by an anterior shift of the COM and COP. Second, post-fatigue increases in joint angle variability were observed at multiple joints including joints distal to the fatigued musculature. Despite these increases, anterior-posterior (AP) ankle angle correlated well with AP COM position, suggesting the body still behaved similar to an inverted pendulum. Third, global measures of sway based on COM and COP were not necessarily indicative of changes in individual joint kinematics. Thus, in trying to advance our understanding of how localized fatigue affects movement patterns and the postural control system, it appears that joint kinematics and/or multivariate measures of postural sway are necessary.

Adult↗

PubMed2006

Changes in step variability of new walkers with typical development and with Down syndrome.

Models of human gait are based on adult locomotion. C. E. Bauby and A. D. Kuo (2000) proposed that adults rely on passive mechanisms at the spinal level to control motion in the anteroposterior direction and rely on direct monitoring of postural control in the lateral direction. The authors' purpose in this study was to determine if that model applies to control at the onset of walking in typically developing toddlers (n = 9) and in toddlers with Down syndrome (n = 6). Their longitudinal data suggested that toddlers control gait in a distinctly different manner than adults do. An adult pattern of control emerges with experience. In addition, the effect of experience on the emergence of that pattern is magnified by task-specific early intervention. The present data support the emergence and discovery of efficient patterns of control in this fundamental human behavior.

Down Syndrome↗

PubMed2001

Control of steering in the presence of unexpected head yaw movements. Influence on sequencing of subtasks.

Control of the head during locomotion has been suggested as a means of facilitating overall postural control of the body. The control of online steering is challenging, as it requires the central nervous system (CNS) to simultaneously control body reorientation in a new direction while modifying the ongoing step cycle. Stable body posture during steering is maintained via appropriately organized postural responses to error signals detected by the visual, vestibular, and/or proprioceptive systems. Modifications to the gait cycle include step-width regulation and movement of body center of mass (COM) in the direction of travel, and may be preceded by independent control of head orientation to see where one is going. The purpose of this investigation was to examine how the ability to successfully steer is influenced by unexpected head perturbations and how various body segments are coordinated and controlled to successfully steer along different pathways. Body kinematics were monitored as participants changed their direction of travel by varying amounts when visually cued one stride before the turn. Perturbations to the head were applied to either assist or oppose the change in direction one step prior to initiation of the turn. Analyses focused on the timing of the changes in head yaw, trunk yaw, and COM trajectories in the mediolateral plane. Results indicate that the order of control over the body segments was head and trunk reorientation in the direction of travel and finally movement of the COM in the intended direction. Thus gaze, inferred from head movement, preceded changes in COM trajectory. This suggests that looking where you are going is critical for steering. When steering is potentially compromised by unexpected head movements, the CNS delays committing movement of the COM until it has a chance to look at the new travel path.

Adult↗

PubMed1998

Agreement between a frequency-weighted filter for continuous biomechanical measurements of repetitive wrist flexion against a load and published psychophysical data.

A previous pilot study demonstrated that a force and frequency-weighted filter network could be developed for processing continuous biomechanical measures of repetitive wrist motions and exertions. The current study achieves the objective by modelling subjective discomfort for repetitive wrist flexion using controlled posture, pace and force. A three-level fractional factorial experiment was conducted involving repetitive wrist flexion (2 s/motion, 6 s/motion, 10 s/motion) from a neutral posture to a given angle (10 degrees, 28 degrees, 45 degrees) against a controlled resistance (5 N, 25 N, 50 N) using a Box Behnken design. Ten subjects participated. Discomfort was reported on a 10 cm visual analogue scale. Results of response surface regression analysis revealed that main effects of force, wrist flexion angle, and repetition were all significant (p < 0.05) and that no second-order effects were observed. Linear regression analysis on these factors established a discomfort model on which the filter characteristics were based. The pure error test model revealed no significant lack of fit (p > 0.05). The continuous model was compared and agreed with discrete psychophysical data from other published studies. The model was used for generating parameters for a force and frequency-weighted digital filter that weighs continuous wrist postural signals with corresponding force in proportion to the equal discomfort function as a function of frequency of repetition. These filters will enable integration of large quantities of biomechanical data in field studies.

Adult↗

PubMed2001

[A forward leaning posture affects more the amplitudes of the centre of pressure displacements than those of the centre of gravity].

OBJECTIVE: An ordinary and practical method to assess the postural control mechanisms is to measure, through a force platform, the point of application of the resultant reaction forces. The recorded signal, the centre of pressure CP, is used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference CP-CG(v). The former is considered in this postural task as the controlled variable whereas the latter is thought to express the ankle resultant stiffness. Interestingly, the CG(v) motions can be extracted from the CP trajectory through a simple mathematical model. MATERIALS AND METHODS: The relationship between CP and the elementary motions CP-CG(v) and CG(v) has been tested in the present study by comparing the postural effects induced by a leaning forward position to a normal one consisting to stand still. RESULTS: A large increase is noticed for the amplitudes of the CP-CG(v) motions for both medio-lateral ML and antero-posterior AP directions. On the other hand, a similar effect appears for the CG(v) motions but only on the ML direction. Nevertheless, the frequency analysis indicates that the constancy of the CG(v) motions on the AP direction is accompanied by a change in the frequency distribution, as assessed by the MPF parameters. DISCUSSION-CONCLUSION: These features highlight the necessity, to interpret rigorously the postural performance, to take into account in separate ways each of the elementary CP-CG(v) and CG(v) motions which, combined, constitute the CP displacements.

Adult↗

PubMed1994

Development of manipulation in capuchin monkeys during the first 6 months.

This study describes the orderly changes in manipulation over the first 6 months in capuchin monkeys (Cebus apella). By 6 months of age, all the basic forms of manipulation seen in adults have appeared. Actions that occur frequently in the first 8 weeks are gentle and involve sustained visual orientation and aimed reaching. Later actions are more vigorous, and involve grasping. Large increases in the rate of activity are evident over the period of development studied. The increase from the first 8 weeks to the second may be due to (a) an increase in the amount of time spent alert and active, (b) a decrease in the amount of time spent in a ventral position, (c) improvements in postural control and stamina and (d) the onset of independent locomotion. Changes in form can be attributed primarily to postural factors and to neuromuscular development (precisely aimed and controlled movements appearing in the 5th and 6th months).

Aging↗

PubMed1990

Postural stability during long-term treatment of cancer patients with epidural opioids.

Ten cancer patients treated with stable doses of epidural opioids were tested for postural stability. The postural stability was measured using a quantitative Romberg's test, performed on a computerized force-plate system. Sway tendencies in the sagittal and the transverse directions were recorded. The postural stability of the patients was compared with values obtained from healthy controls. Comparing the cancer patients with the controls, postural stability in eight out of ten patients was intact. The study suggests that long-term epidural opioid treatment has little influence on the patient's ability to stand safely.

Adult↗

PubMed2003

Importance of body sway velocity information in controlling ankle extensor activities during quiet stance.

In literature, it has been suggested that the CNS anticipates spontaneous change in body position during quiet stance and continuously modulates ankle extensor muscle activity to compensate for the change. The purpose of this study was to investigate whether velocity feedback contributes by modulating ankle extensor activities in an anticipatory fashion, facilitating effective control of quiet stance. Both theoretical analysis and experiments were carried out to investigate to what extent velocity feedback contributes to controlling quiet stance. The experiments were carried out with 16 healthy subjects who were asked to stand quietly with their eyes open or closed. During the experiments, the center of pressure (COP) displacement (COPdis), the center of mass (COM) displacement (COMdis), and COM velocity (COMvel) in the anteroposterior direction were measured. Rectified electromyograms (EMGs) were used to measure muscle activity in the right soleus muscle, the medial gastrocnemius muscle, and the lateral gastrocnemius muscle. The simulations were performed using an inverted pendulum model that described the anteroposterior kinematics and dynamics of quiet stance. In the simulations, an assumption was made that the COMdis of the body would be regulated using a proportional-derivative (PD) controller. Two different PD controllers were evaluated in these simulations: 1) a controller with the high-derivative/velocity gain (HDG) and 2) a controller with the low-derivative/velocity gain (LDG). Cross-correlation analysis was applied to investigate the relationships between time series obtained in experiments 1) COMdis and EMGs and 2) COMvel and EMGs. Identical cross-correlation analysis was applied to investigate the relationships between time series obtained in simulations 3) COMdis and ankle torque and 4) COMvel and ankle torque. The results of these analyses showed that the COMdis was positively correlated with all three EMGs and that the EMGs temporally preceded the COMdis. These findings agree with the previously published studies in which it was shown that the lateral gastrocnemius muscle is actively modulated in anticipation of the body's COM position change. The COMvel and all three EMGs were also correlated and the cross-correlation function (CCF) had two peaks: one that was positive and another that was negative. The positive peaks were statistically significant, unlike the negative ones; they were larger than the negative peaks; and their time shifts were much shorter compared with the time shifts of the negative peaks. When these results were compared with the CCF results obtained for simulated time series, it was discovered that the cross-correlation results for the HDG controller closely matched cross-correlation results for the experimental time series. On the other hand, the simulation result obtained for LDG controller did not match the experimental results. These findings suggest that the actual postural control system during quiet stance adopts a control strategy that relies notably on velocity information and that such a controller can modulate muscle activity in anticipatory manner without using a feed-forward mechanism.

Adult↗

PubMed2001

Profiling beds versus standard hospital beds: effects on pressure ulcer incidence outcomes.

Most standard hospital beds are flat based with a pull-out backrest, resulting in a tendency for the patient to slide down the bed. This study aimed to compare the outcome for patients at high risk of developing pressure ulcers nursed on either this type of bed or an electrically operated, multi-sectioned profiling bed. A total of 100 patients were randomly assigned either to the profiling bed with a pressure-reducing foam mattress (experimental group) or a flat-based bed with an appropriate pressure-redistributing mattress (control group) for a maximum of 10 days. Risk status and pressure damage were assessed daily. Both a patient and a nurse questionnaire were completed. Data from 70 patients who participated in the study for five days or more were included in the analysis. Pressure ulcer incidence was 0% in both groups. All patients (35) in the experimental group were able to maintain a sitting position compared with only 12/35 in the control group (p = 0.0001). While the questionnaire results suggest there were significant differences in postural control and ease of transfer between patients in the two groups, it was not possible to map this to pressure ulcer formation. Poor recruitment into the study was due to the 'blocking' of electric beds by heavily dependent patients who did not meet the inclusion criteria, precluding a significant result in terms of pressure ulcer outcomes. This nurse-led use of the profiling beds was examined alongside the main study to investigate why they were allocated in this way.

Adult↗

PubMed2004

Intra-abdominal pressure response to multidirectional support-surface translation.

A complex response of the trunk muscles occurs to restore equilibrium in response to movement of the support surface. Intra-abdominal pressure (IAP) is considered to contribute to control of the trunk. This study investigated the contribution of IAP to the postural response to multidirection support-surface translation. IAP was recorded with a thin-film pressure transducer inserted via the nose into the stomach and trunk motion was recorded with an optoelectronic system with markers over the spinous process of L1. A pattern of trunk movement was recorded in response to the support-surface translations that was consistent with a 'hip' strategy of postural control. The trunk moved in a manner appropriate to move the centre of gravity over the new base of support. IAP was increased with movement in each direction, but varied in timing and amplitude between translation directions. In general, the IAP was greater with translations in the sagittal plane compared to the frontal plane and was initiated earlier for translations in the backward direction. These data indicate that IAP contributes to the postural response associated with support-surface translation and suggest that this is consistent with stiffening the spine.

Abdominal Muscles↗

PubMed1984

Feedback control system for walking in man.

A computer control stimulation system is described which has been successfully tested by allowing a paraplegic subject to stand and walk through closed loop control. This system is a Z80 microprocessor system with eight channels of analog to digital and 16 channels of digital to analog control. Programming is written in CPM and works quite successfully for maintaining lower body postural control in paraplegics. Further expansion of this system would enable a feedback control system for multidirectional walking in man.

Adult↗

PubMedDate not supplied

Lack of effect of multiple doses of cimetidine on estimated hepatic blood flow.

Conflicting data exists regarding the effect of the H2-receptor blocking agent cimetidine on hepatic blood flow (HBF). The variance in the results of these studies may be due in part to differences in the duration of cimetidine administration, the posture of the volunteers during their course of study, and the method used to estimate HBF. To assess the effects of chronic cimetidine (300 mg q.i.d. X 4 days) on estimated HBF while controlling posture (supine and standing), a double-blind, placebo-controlled, repeated measures study was performed in 9 healthy males. Indocyanine green (ICG) plasma clearance after an i.v. dose of 0.5 mg kg-1 was used to calculate HBF. ICG plasma concentrations were measured by HPLC. Compared to placebo treatment, cimetidine had no effect on mean (SD) estimated HBF (ml min-1 m-2) in either the supine (497 (64) vs 494 (80] or the standing (443 (117) vs 404 (89] posture. These data had a power greater than 0.8 to detect a treatment effect of 20 per cent. Standing produced a significant decrease in estimated HBF (496 (70) vs 424 (102); p less than 0.01). In contrast to previous reports, chronic cimetidine treatment had no apparent effect on hepatic blood flow.

Adult↗