Significance of pressor input from the human feet in anterior-posterior postural control. The effect of hypothermia on vibration-induced body-sway

The importance to postural control of the mechanoreceptors of the soles was investigated in thirteen healthy subjects. Body-sway velocity was evaluated before and after exposing the subject's feet to hypothermia, and when calf muscles were exposed to vibration at frequencies between 20 and 100 Hz. Subjects were tested both with eyes open and closed. Body-sway velocity was found to increase significantly during hypothermia of the feet. The difference in body-sway between hypothermal and normothermal conditions was less prominent when the subject's eyes were open though the difference was significant in both cases. The present results indicate the importance of the mechanoreceptors of the soles to postural control and elucidate their interaction with compensatory visual input in maintaining postural control. These findings also suggest, that factors affecting pressor input should be taken into consideration when assessing patients with complaints of dysequilibrium.     

Postural adaptation in elderly patients with instability and risk of falling after balance training using a virtual-reality system

Our aim in this study was to assess postural control adaptation quantitatively in unsteady elderly patients at risk of falls in open spaces and given balance training with a virtual-reality system reproducing environmental stimulation. Using a balance rehabilitation unit based on a virtual-reality system that changes sensory information (visual, vestibular, and somatosensory), we treated 26 elderly, unsteady patients who were prone to falling (age range, 73-82 years) and who were enrolled in a customized vestibular rehabilitation program. We assessed postural responses by posturography before and after 6 weeks in the vestibular rehabilitation program under two conditions: (1) standing, eyes open, static visual field, and (2) standing, eyes open, dynamic visual field through virtual-reality goggles, generating horizontal optokinetic stimulation (70 degrees per second angular velocity). We recorded postural responses with a platform measuring the confidential ellipse of the center-of-pressure distribution area and sway velocity with a scalogram analyzing postural behavior by wavelets. After 6 weeks of treatment, postural response confidential ellipse and sway velocity values were lower, evincing decreased amplitudes and sway frequency contents in the scalogram by wavelet under both stimulation paradigm conditions. These findings suggest postural adaptation under the two perceptual conditions when patients had static and dynamic visual fields. The possibility of treating elderly fallers with balance disorders using a virtual-reality environmental stimulation reproduction system is discussed.     

Effects of lifetime ethanol consumption on postural control: a computerized dynamic posturography study

The relationship between lifetime alcohol consumption and postural control was investigated in 35 subjects with no clinically-detectable neurologic abnormalities, using computerized dynamic posturography (CDP) procedures. The estimated total number of lifetime alcoholic drinks was positively correlated with anteroposterior sway spectral power within the 2-4 Hz and 4-6 Hz frequency bands, in three Sensory Organization Test (SOT) conditions: eyes closed with stable support surface (SOT 2), eyes open with sway-referenced support (SOT 4), and eyes closed with sway-referenced support (SOT 5). All correlations remained significant after controlling for subject age, and were increased after excluding nine drug-abusing subjects. In contrast to the strong findings for frequency-based measures, no correlation was observed using conventional amplitude-based sway measures. These results suggest that 1) alcohol consumption compromises postural control in an exposure-dependent manner, and 2) sway frequency analysis reveals pathological processes not manifested in conventional CDP measures of sway amplitude.     

A quantitative analysis of postural control in elderly patients with vestibular disorders using visual stimulation by virtual reality

IntroductionPostural instability is one the most common disabling features in vestibular disorders.ObjectiveThis study aimed to analyze the limit of stability and the influence of manipulation of visual, somatosensorial and visual–vestibular information on postural control in older adults with vestibular disorder, with and without a history of falls.MethodsCross-sectional study. Participants – 76 elderly patients with vestibular disorder (G1, without falls; G2, with falls) and 41 healthy elderly subjects (control group; CG). Using posturography, analyzed were limit of stability area, body center of pressure, and velocity of oscillation in the standing position in 10 conditions, including open/closed eyes, unstable surface with eyes closed, saccadic and optokinetic stimuli, and visual–vestibular interaction.ResultsLimit of stability area in CG was better compared with G1-2, and center of pressure values were worse in G1 than in CG. Center of pressure area in all conditions and velocity of oscillation in the following conditions: open/closed eyes, optokinetic stimulation, and visual–vestibular interaction showed worse values in G2 than in CG. Center of pressure area in the following conditions: open/closed eyes, saccadic and optokinetic stimuli, visual–vestibular interaction, and unstable surface with eyes closed showed worse values in G2 than in G1.ConclusionOlder adults with vestibular disorder presented reduced limit of stability and increased postural sway in the following conditions: conflict between visual and somatosensory information and visual–vestibular interaction. Deterioration in postural control was significantly associated with history of falls.     

不同厚度海绵垫对健康人直立姿势稳定性的影响

目的分析健康人直立于不同厚度海绵垫时姿势特征的变化，探讨本体觉受到不同程度干扰时的姿势平衡改变。方法30例健康人分别站立于坚硬平板和不同厚度的海绵垫，海绵厚度依次从1到5块，每块厚度4．7cm。每种站立平面下，均睁眼和闭眼各站立30s。应用姿势描记仪记录人体直立时足底压力中心（center of pressure，COP）晃动的相关参数，包括总轨迹长、平均速度、单位面积轨迹长、外周面积、实效值面积、矩形面积。结果所有参数在睁眼和闭眼条件下均有随海绵垫厚度的增加而变化趋势（睁眼时F值为9．14～107．18，闭眼时F值为32．19～144．35，P值均〈0．0001），除单位面积轨迹长呈减少趋势外，其余参数均为增加趋势；对各参数在不同海绵垫间的差异进行比较，无统计学意义的情况有：①总轨迹长和速度：睁眼及闭眼时，4和5块之间；②单位面积轨迹长：睁眼时，0和1、1和3、2和3、3和4、4和5块之间；闭眼时，3和4、3和5、4和5块之间；③外周面积：睁眼时2和3、3和4、4和5块之间；闭眼时，3和4、3和5、4和5块之间；④实效值面积和矩形面积：睁眼时2和3、4和5块之间；闭眼时，3和4、3和5、4和5块之间。其余比较差异均有统计学意义（P〈0．05）或极显著统计学意义（P〈0．01）。结论在一定范围内，随着海绵垫厚度增加，直立其上的人体本体觉受到的干扰程度加剧，其姿势稳定性逐渐降低；应用海绵垫干扰本体觉同时，姿势描记仪记录的各参数中，COP晃动的轨迹长度和平均速度是较适宜描述姿势平衡变化的指标；应用海绵垫对直立人体足底本体觉进行干扰时，应考虑海绵厚度对结果的影响，选择适宜的厚度，以提高其临床应用价值。     

Visual influence on postural control,with and without visual motion feedback

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly (p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.     

Visual Influence on Postural Control,With and Without Visual Motion Feedback

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly ( p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.     

First trial response to sudden support surface displacement: The effect of vestibular compensation

Conclusion: The effect of visual condition is more intense in the first trial response in normal subjects and patients and in last trial response only in patients. The first trial effect is more evident in compensated patients in the eyes open condition with any type of perturbation, and in non-compensated patients with the angular displacements in either visual condition. Objective: The study of body reaction to FTR can help to understand the complex mechanisms involved in the postural response and to develop new therapies to improve stability and prevent falls in unilateral vestibular deficit (UVD). This work describes the adaptation effect and the visual influence on the postural response to repetitive balance perturbation stimulus in normal subjects, compensated, and uncompensated UVD patients. Methods: The magnitude of displacement has been measured when the support surface is linearly or angularly displaced. The differences between results in the first and late trial, and the differences between the eyes open and eyes closed situation have been compared. Results: Compensated patients recover the adaptation ability to unexpected changes on the support surface through visual preference mechanism. Not compensated patients present hypermetric postural response with greater instability in the eyes open and eyes closed situations.     

Significance of pressor input from the human feet in lateral postural control. The effect of hypothermia on galvanically induced body-sway

The significance to human postural control of pressor information from the feet was investigated during vestibular disturbance in seven normal subjects who were exposed to bipolar biaural galvanic stimulation of the vestibular nerves before and after their feet were anaesthetized with hypothermia. The increase in body sway in the lateral plane induced by the galvanic stimulus was enhanced when the feet were anaesthetized, and adaptation of postural control to the galvanic stimulus was delayed. It is concluded that pressor information from the feet contributes significantly to postural control in humans and is important in compensating for vestibular disturbance.     

Long-term postural abnormalities in benign paroxysmal positional vertigo

Benign paroxysmal positional vertigo (BPPV) is a disorder in which patients suffer from acute rotatory vertigo due to the presence of free otoconial debris migrating into one or more semicircular canals during head movements and resulting in abnormal stimulation of the ampullary crest. A prolonged loss of equilibrium of unclear origin is also present. Static posturography is a useful tool for the study of postural control systems and their role in these abnormalities. The aim of the present study was to evaluate the frequency of body sway and long-term instability of BPPV patients by posturography frequency analysis. Twenty patients with canalithiasis of the posterior semicircular canal and 20 normal controls were subjected to static posturography. Informed consent was obtained from all subjects. Patients were tested 1 h after diagnosis, and 3 days and 12 weeks after the characteristic Epley repositioning maneuver. Patients with BPPV showed significantly increased body sway both on lateral (X) and anteroposterior (Y) planes compared to normal subjects. Corporal oscillation with a broad-frequency spectrum was observed in both closed and open eye tests. The repositioning maneuver decreased the X plane body sway, while the anteroposterior sway was unchanged. Twelve weeks after treatment, a normalization of the anteroposterior sway was observed. Results of this study suggest that the long-term postural disturbance associated with BPPV differs from the acute disequilibrium that subsides after canalith repositioning: the former is a sagittal plane/broad spectrum body sway, while the latter is primarily a frontal plane/low frequency sway. The Epley maneuver was shown to reduce frontal sway, a postural abnormality that might therefore be linked to posterior semicircular canal function. Conversely, the observed sagittal body sway was only partially relieved by the restoration of canal function, and therefore, may be more related to the chronic dizziness observed in these patients.     

Somatosensory shift of postural control in dizzy patients

Conclusions: Postural control is dependent on the visual system in normal conditions. Shift from visual to somatosensory dependence in dizzy patients suggests that utilizing the stable visual references is recommended for the rehabilitation of dizzy patients. Objectives: To investigate which of the visual or somatosensory system is mainly used for substitution of the impaired spatial orientation in dizzy patients. Methods: We recruited 189 consecutive patients with or without dizziness and vestibular dysfunction. Dizzy patients were divided into three groups: acute, episodic, and chronic dizziness. Vestibular function was assessed by caloric test, traditional head impulse test, and head shaking nystagmus. Visual or somatosensory dependence of spatial orientation was assessed by posturography on a solid surface or on foam in eyes open or closed condition. The foam ratio (posturography with/without foam) when eyes were closed was indicative of somatosensory dependence of postural control, whereas the Romberg ratio on foam showed visual dependence. (Romberg ratio on foam)/(foam ratio with eyes closed) was calculated and used as an index of the visual/somatosensory dependence of postural control. Results: The visual/somatosensory ratio of postural control was significantly lower in dizzy patients as well as patients with vestibular dysfunction, however, no differences were found between acute, episodic, and chronic dizziness.     

evaluation of postural stability in patients wit unilateral vestibular hypofunction:effect of feet orientation

To investigate effect of feet orientation on the evaluation of the postural stability in patients with unilateral vestibular hypofunction (UVH) by timed standing tests and static posturography (SPG). Methods 65 subjects with UVH and 92 healthy subjects regarded as control group took the posrural stability tests in four different stances including (1) standard Romberg test, (2) feet-apart stance test, (3) tandem and (4) unilateral standing tests. In each stance, the postural stability was measured in both eyes open (EO) and eyes closed(EC) conditions. The average time that subjects kept balance before falling in each test conditions was recorded by stopwatch as the timed result. In addition, the sway velocity (SV) of center of foot pressure in the upright stance during standard Romberg test and feet apart stance, regarded as postural stability, was also recorded as SPG. Results (1) The balance-maintain-ing time of the UVH group in tandem and unilateral standing with EO and EC was decreased (P< 0.001) compared with the control group. (2) The SVs during standard Romberg test and foot-apart stance withEO were not different between the UVH group and control group (P = 0.118 and 0.110 respectively), but significant with EC condition (P < 0.001). (3) For both groups, the SV during foot-apart standing was shorter than standard Romberg test both with EO and EC(P< 0.05 and P < 0.001). (4) There was no correlation between the balance time and SV for either groups (P > 0.05). Conclusions The results suggest that the tandem and unilateral stance tests may provide additional information about the upright stance to the SPG measurement in patients with UVH. The effect of feet orientation on SPG measurements should be considered.     

复位治疗对良性阵发性位置性眩晕患者姿势稳定性的影响

目的探讨耳石复位治疗（CanaIithrepositioningprocedure,CRP）对后半规管良性阵发性位置性眩晕（posterior semicircular canal benign paroxysmal positional vertigo, PSC-BPPV）患者姿势稳定性的影响。方法25例PSC—BPPV患者在CRP前、后进行4种站立条件下的姿势稳定性测试,①坚硬平板、睁眼（T1）;②坚硬平板、闭眼（T2）;③海绵垫、睁眼（T3）;④海绵垫、闭眼（T4）。以配对的25名正常人为健康对照组。采用身体直立时足底压力中心的平均晃动速度（swayvelocity,SV）为研究参数。结果①CRP前患者SV均较健康对照组增加,T1时有显著性差异（f=2．442,P=0．022）：T2NT4有极显著性差异（f值分别为3．529、5．799和4．312,P〈0．01）;②CRP后除T1外（f=1．808,P=0．083）,T2-T4时,患者身体晃动SV较治疗前降低,有显著性差异（f值分别为2．487、2．248和2．897,P〈0．05）：③CRP后患者姿势稳定性与健康对照组比较,T1gUT2时SV间比较,无显著性差异（f分别为1．388和2．022,P〉0．05）;T3和T4时SV间比较,有显著性差异（f分别为1．488和2．327,P〈0．05）。结论CRP可提高PSC—BPPV患者姿势稳定性,但与正常人仍有一定差异,提示PSC．BPPV患者可结合CRPgl前庭康复治疗提高姿势平衡能力。     

Postural control in patients with unilateral vestibular lesions is more impaired in the roll than in the pitch plane: a static and dynamic posturography study

The postural instability of patients with vestibular loss (11 with bilateral and 101 with unilateral vestibular loss) at different times following the lesion was investigated by means of posturography and compared to healthy subjects. In addition, subjects submitted to galvanic vestibular stimulation were also studied to compare their postural performances with those of patients with complete unilateral vestibular lesion. The platform consisted of a static computerized force platform, on which a seesaw platform could be placed to test the subjects in dynamic conditions. The displacement of the center of foot pressure was measured under different conditions: subjects standing on the fixed platform, eyes open and eyes closed and subjects standing on the seesaw platform, eyes open and eyes closed. In the last condition, balance was tested in the subject's pitch plane by allowing the platform to rotate forwards and backwards only and in the patient's roll plane by allowing the platform to rotate to the left and to the right. The results showed that in static conditions, only bilateral vestibular loss patients had abnormal values compared to controls. In contrast, in dynamic eyes-closed conditions, both bilateral and unilateral patients could be differentiated from controls. Bilateral patients were unable to stand up without falling in both pitch and roll planes. Unilateral patients fell in the first week following the lesion and exhibited increased postural oscillations in both planes from the 2-week up to the 1-year postlesion stage. In addition and more importantly, they fell more often or had higher sway in the roll than in the pitch plane. Therefore, this study suggests that dynamic posturography on a seesaw platform could be a valuable tool for clinical diagnosis and quantitative analysis of imbalance in patients suffering from a unilateral vestibular loss up to 1 year after the lesion.     

年龄和视觉对直立静态平衡的影响

为研究年龄和视觉系统对人体立位姿态平衡功能的影响，应用ST－939人体重心平衡仪，对127名正常人进行立位姿态平衡功能测试，观察重心移动的外围面积、路径总长和平均速度以及重心在不同圆内的分布图（即姿态图）结果显示：①正常人重心移动的外周面积、路径总长和平均速度随年龄增长而增大；②70岁组闭睁眼测试面积差值最大。本项研究结论认为在20～60岁年龄内姿态平衡功能最佳，60岁以后出现衰退。在年长者中视觉系统在控制立体姿态平衡中起重要作用。     

Cervical muscle afferents play a dominant role over vestibular afferents during bilateral vibration of neck muscles

A previous study showed that vibratory stimulation of neck muscles in humans induced short-latency electromyographic (EMG) activation of lower leg muscles, producing postural reactions at the feet. These findings indicated that cervical proprioception contributes to stabilization of stance through rapidly integrated pathways. However, as vibration may excite both proprioceptive and vestibular afferents, and because of the proximity of neck muscles to the vestibular apparatus, neck muscle vibration could also have activated the vestibular system thereby contributing to the effect observed. To investigate any possible contribution of vestibular stimulation, vibratory stimuli were applied bilaterally and separately to the splenius muscles of the neck and the planum mastoideum overlying the vestibular organs. Ten normal subjects, with eyes closed, were exposed to vibratory stimulation of two different amplitudes and frequencies. Responses were assessed by EMG activity recorded from tibialis anterior and gastrocnemius muscles of both legs and by changes in center of pressure as measured by a force platform. Results indicated that vibration induced reproducible EMG and postural responses in the anteroposterior direction, particularly on cessation of vibration. EMG and postural responses were considerably lower and less consistent with mastoid vibration compared with neck muscles vibration. Previous reports suggest that vibratory stimulation could propagate to the vestibular organs and generate a vestibular-induced postural activation. However, our findings indicate that cervical muscles afferents play a dominant role over vestibular afferents when vibration is directed towards the neck muscles.     

外周性眩晕患者的平衡功能研究

目的评价外周性眩晕患者的平衡功能并分析视觉、本体觉在平衡维持中的特点,为平衡康复治疗提供基线数据。方法研究对象分两组,正常对照组47例,男性21例、女性26例,平均年龄（36．17±13．27）岁：外周性眩晕患者组45例,男性20例、女性25例,平均年龄（47．89±13．04）岁;分别进行硬平板和泡沫板的睁、闭眼共计6种感觉模式的平衡功能测试。结果①外周性眩晕组前后向和左右向的3种感觉评分与平衡评分均较正常对照组低;②除睁眼硬板条件外其余模式的Romberg商（RombergQuotient）,即静态闭眼时姿势面积与睁眼面积的比值、身体压力中心晃动的包络面积（statokinesigram,SKG）,EP90％身体晃动轨迹点的椭圆面积、最大晃动幅值等参数均较正常对照组增大;以上差异具有统计学意义。结论外周性眩晕患者平衡功能明显下降,而且涉及视觉和本体觉构成,平衡的康复与维持需借助视觉、本体觉补偿,平衡功能检查可为制定个体化前庭康复提供参考。     

Reliability of postural control measures in children and young adolescents

Although many studies have been carried out regarding postural stability during pediatric age, reliable information and a complete analysis of all age groups are still lacking. The purpose of this study was to verify the test–retest reliability of posturographic parameters in four sensory conditions and provide normative values for children and young adolescents. 289 subjects, aged 6–14 years, were assessed by means of the static posturography system SVeP. 173 elementary school pupils (114 males and 59 females, aged 6–10 years; mean age 8.80 ± 1.53) and 116 middle school students (60 males and 56 females, aged 11–14 years; mean age 12.6 ± 0.9) underwent static posturography in two consecutive trials with four testing conditions: eyes open and eyes closed with and without foam pads. The participants were divided into nine age groups. Thirty healthy young adults were also recruited for comparison. The analysis of test–retest reliability demonstrated an excellent reliability of velocity measurement and a moderate reliability of area measurement. Velocity and area decreased significantly with age in all sensory conditions, indicating an improvement in postural control from childhood to adolescence. Postural stability had not reached the adult level by the age of 13–14 years. Reliable information regarding postural stability can be obtained in children and young adolescents by means of stabilometric parameters. These data can be used as a reference for early detection of atypical postural development and for the assessment of dizziness and balance disorders in children.     

Effects of tinnitus on posture: a study of electrical tinnitus suppression

We investigated the effects of tinnitus on postural responses using posturography. Thirty-three tinnitus patients (19 female and 14 male) ranging in age from 33 to 67 years (mean age, 53) were selected randomly at our outpatient clinic. Nobody complained of dizziness. Posturographic examination was given before and after 30-minute electrical stimulation. Items tested were envelope area, area (root mean square), total length, total length-area, mean amplitude of lateral body sway (mx), and anteroposterior sway (my). Those parameters did not improve in patients without tinnitus relief. Two postural measures (envelope area and mx) showed significant improvement in patients with tinnitus relief. These effects appeared only on positions involving restricted visual feedback. In a comparison of postural measures in patients with and without tinnitus relief, all parameters except total length and mx improved significantly in patients with eyes open. Our study showed that aside from the auditory system, tinnitus can affect balance, implying that tinnitus may be a factor in increasing unsteadiness in patients with tinnitus.     

Dynamic posturography in humans imagining a fixed spatial reference

OBJECTIVE: To investigate the effect of imagining a fixed spatial reference on balance control. MATERIAL AND METHODS: Twenty-one healthy subjects were asked to remain as stable as possible while standing on a sway-referenced platform (NeuroCom Equitest posturography system). Subjects were instructed to keep their eyes open in the dark and to either look far into the distance without fixating on any particular point in space or to direct their gaze towards a remembered earth-fixed target (25-cm distant). Room lights were switched off immediately before each 20-s sway recording. Postural stability measures included equilibrium scores and root-mean-square sway amplitudes in the anterior-posterior plane. RESULTS: Postural sway was not influenced by the instruction to gaze towards a remembered target. CONCLUSION: Imagining a fixed spatial reference does not influence postural control, at least during sway-referenced dynamic posturography.