Postural instability in Parkinson's disease: a comparison with and without a concurrent task

The purpose of this investigation was to determine the effects of dual task performance on postural instability in subjects with idiopathic Parkinson's disease (PD) compared with healthy elderly people. In particular, we aimed to divert attention to a secondary task so the full extent of balance disturbance could be revealed without compensation by attentional mechanisms. Forty-five subjects were tested: 15 PD subjects with a past history of falls; 15 PD subjects with no history of falls; and 15 unimpaired individuals. Groups were matched for age and sex and subjects with PD were tested at peak dose in the levodopa medication cycle. Each subject was tested on their ability to maintain stability in three conditions: (1) steady standing (feet apart, feet together, step stance, tandem stance, single leg stance); (2) in response to perturbations generated by self-initiated movements (arm raise test, step test); and (3) in response to an unexpected external perturbation in upright stance, the shoulder tug test. The concurrent task was verbal-cognitive and required subjects to recite the days of the week backwards. The concurrent task produced a significant deterioration in performance for the arm raise test in all groups, the step test for the PD fallers and controls and for tandem stance in the PD fallers. Ceiling effects were evident for timed tests with feet apart and feet together resulting in poor discriminative validity for these tests. The external perturbation test showed differences between the three groups for both unitask and concurrent task conditions, yet similar rates of change from unitask to dual task conditions. Because PD fallers had a more severe initial deficit than controls, deterioration placed them in that part of the balance continuum at high risk of losing equilibrium.     

Ambulatory monitoring of left ventricular function in patients with Parkinson's disease and postural hypotension

Left ventricular (LV) function was continuously monitored using a radionuclide detector (VEST) after intravenous injection of 25 mCi technetium-99m labelled red blood cells in nine patients with Parkinson's disease and postural hypotension (group 1) and ten patients with Parkinson's disease but without postural hypotension (group 2). LV function and blood pressure were monitored in the supine position for 15 min (period A), upon changing posture from the supine to the upright position for 10 min (period B), and upon returning to the supine position for 10 min (period C). In group 1, the passage from period A to period B induced a significant decrease in end-diastolic volume, end-systolic volume and ejection fraction (allP<0.01). In group 2, ejection fraction increased (P<0.05) upon changing posture from the supine to the upright position. Ejection fraction (F=33,P<0.01), end-diastolic volume (F=9,P<0.05) and end-systolic volume (F=10,P<0.05) were significantly different between the two groups. In group 1, stroke volume, cardiac output and vascular peripheral resistance decreased from period A to period B (allP<0.001). In group 2, no changes in stroke volume, cardiac output and vascular peripheral resistance were observed from period A to period B. All parameters were similar in the two groups during the periods A and C. Upon changing posture from the supine to the upright position, patients with Parkinson's disease and postural hypotension showed marked changes in parameters of LV function induced by vascular abnormalities. The results of this study may help to clarify the potential risk of sudden postural changes in such patients, which may cause fainting, syncope and increased risk of ischaemic coronary and cerebrovascular attacks and of lower limb fractures.     

A sensitivity comparison of clinical tests for postural instability in patients with Huntington's disease

Falls are a common complication in Huntington's disease (HD) and detection of postural instability (PI) may be useful for identifying patients who are at risk of falls.The aim of our study was to find the most sensitive clinical test for PI in patients with HD and to correlate PI with the other symptoms.20 HD patients were examined using: (1) The Unified Huntington's Disease Rating Scale (UHDRS), (2) The Mini Mental State Examination (MMSE) and (3) six clinical tests for PI. Inter-scale and test correlations were inspected and uni-dimensionality, validity, and measurement precision were analyzed using a factor analysis model/latent PI score. PI was compared with information obtained from surveys completed independently by patients and caregivers, and both reports were evaluated for absolute agreement using intraclass correlations (ICCs).PI was found in 16 patients; the tests correlated better with caregivers’ reports (r = 0.78) than patients’ responses. The validity of the patients’ answers decreased with the level of MMSE scores. PI correlated with MMSE (r = 0.64, p < 0.01), the subscale score for voluntary movements (r = 0.86, p < 0.01), the overall motor subscore (r = 0.73, p < 0.01), and the Luria test subscore (r = 0.87, p < 0.01).The stance with feet close together and tandem gait correlated best with the latent PI score, and factor loadings confirmed they were the most sensitive tests for PI detection in HD.     

Comparison of forward and backward postural perturbations in mild-to-moderate Parkinson's disease

BackgroundAssessing postural stability in Parkinson’s disease (PD) often relies on measuring the stepping response to an imposed postural perturbation. The standard clinical technique relies on a brisk backwards pull at the shoulders by the examiner and judgement by a trained rater. In research settings, various quantitative measures and perturbation directions have been tested, but it is unclear which metrics and perturbation direction differ most between people with PD and controls.Objectives(1) Use standardized forward vs. backward perturbations of a support surface to evaluate reactive stepping performance between PD and control participants. (2) Evaluate the utility of using principal components analysis to capture the dynamics of the reactive response and differences between groups.MethodsSixty-two individuals participated (40 mild-to-moderate PD, off medication). Standardized rapid translations of the support surface were applied, requiring at least one step, backward or forward, to restore balance. The number of steps taken and the projection of the first principal component (PC1) of the center of pressure (COP) time series were entered in linear repeated-measures mixed effect models.ResultsForward falls required significantly fewer steps to recover than backward falls. PC1 captured more than half of the variance in the COP trajectory. Analysis of the PC1 projection revealed a significant interaction effect of group (PD vs. controls) by direction, such that there was a group difference in forward stepping, but not backward.SignificanceForward reactive stepping in PD differed from controls more than backward-stepping. PC1 projections of the COP trajectory capture the dynamics of the postural response and differ between PD and controls.     

Between-leg asymmetry in automatic postural responses to stance perturbations in people with Parkinson's disease

BackgroundPeople with Parkinson's disease (PwPD) showed impairments of balance control which can be aggravated by the presence of higher interlateral postural asymmetry caused by a distinct dopaminergic loss in the substantia nigra between cerebral hemispheres.Research questionWe evaluate asymmetries between the more and the less affected leg in PwPD in responses to unanticipated stance perturbations.MethodsSixteen 16 PwPD participated in the experiment that consisted of recovering a stable upright stance, keeping the feet in place, in response to a perturbation caused by a sudden release of a load equivalent to 7 % of the participant's body mass. Anterior displacement and velocity of the center of pressure (CoP), the latency of gastrocnemius medialis muscle (GM) activation onset, rate of GM activation, and normalized magnitude of muscular activation were analyzed.ResultsAnalysis revealed significantly rate (p = 0.04) and magnitude (p = 0.02) higher activation of GM in the less affected limb. No significant effects of the leg were found for GM activation latency or CoP-related variables.SignificanceThere is a higher contribution of the less affected leg in automatic postural responses in PwPD.     

Coordination of axial rotation and step execution: deficits in Parkinson's disease

To determine why parkinsonian patients (PP) present some difficulties to initiate locomotion, a diagonal step has been investigated in two tasks in five control subjects (CS) and in ten PP. In the first task, the subjects had to perform one diagonal step without change in their orientation (WR); in the second task, they had to perform one diagonal step with a body rotation in the step direction (RO). The defended hypothesis is that the gait initiation deficits in Parkinson disease are a consequence of their difficulties to coordinate al the component of a complex movement. The analysed parameters were the duration of the postural and movement phases, the step length and velocity, and the amplitude of the horizontal ground reaction forces during each phase. Compared to CS, the PP showed a lengthening of the postural phase, a decrease in the step length and velocity and a reduction of the horizontal forces. The comparisons between the performances obtained in the WR versus those obtained the RO show in CS that the performances remained unchanged, whereas in PP the performances were significantly more altered in the RO. It illustrates the specific deficit occurring in PP while performing complex tasks where coordination between several components has to be achieved simultaneously.     

Relationships between gait and dynamic balance in early Parkinson's disease

This study examined the relationships between gait and dynamic balance in people with early-stage Parkinson's disease (PD). We assessed 18 participants diagnosed with stage I–II idiopathic PD and 17 healthy age-matched volunteers. Temporo-spatial gait variables were analyzed using the GAITRite^® system and participants were asked to walk at a comfortable walking speed. Dynamic balance was assessed using the Balance Master^®. Movement velocity (MV), maximal excursion (ME), and directional control (DC), obtained through the limits of stability test, quantified dynamic balance. People with early stage PD exhibited significantly slower walking speed, shorter stride length, and smaller forward MV than the comparison group. In the PD group, stride length and speed significantly correlated with forward MV, forward ME, and forward DC. Thus, in people with early PD, gait speed and stride length are correlated with dynamic balance, particularly in the forward direction in standing.     

Evidence of a different landing strategy in subjects with chronic ankle instability

The purpose of the study is to evaluate the discriminative validity of the multiple hop test (MHT) for chronic ankle instability (CAI). The dynamic postural control of 51 CAI subjects and 52 uninjured controls was assessed using the MHT. To evaluate dynamic postural control, the type and number of balance errors were analysed and the time to complete the MHT was measured. Between-group differences of time scores and balance errors, identified as being change-in-support strategy errors (CSS) or fixed-support strategy errors (FSS), were assessed. The area under curve of the outcomes was determined and likelihood ratios (LRs) were calculated based upon their most optimal cut off point. When compared to uninjured controls, CAI subjects needed significantly more time to perform the test (p < 0.001) and made significantly more CSS errors (p < 0.001). When 1 positive outcome (time score or CSS errors) was considered as a criterion, the LR⁺ was 2 and the LR⁻ 0.08. In the case of 2 positive outcomes (time score and CSS errors), the LR⁺ was 7.1 and the LR⁻ 0.49.CAI subjects have an impaired dynamic postural control and rely on a different postural strategy to restore balance. The MHT has good discriminative validity for CAI.     

Use of time-to-boundary to assess postural instability and predict functional mobility in people with diabetes mellitus and peripheral neuropathy

BackgroundPeople with diabetes mellitus and peripheral neuropathy (DMPN) often have balance and mobility deficits. Time-to-boundary (TTB) is a parameter of postural control that combines position and velocity center of pressure data. While not previously investigated, assessment of TTB may provide new insight regarding postural control in people with DMPN.Research questionIs TTB reduced and related to a measure of mobility in people with DMPN?MethodsThirteen people with DMPN without fall history and 13 healthy matched controls participated in this case-control study. Participants stood in double-limb stance on a force plate. The anterior-posterior and medial-lateral center of pressure position and velocity relative to the boundaries of the base of support were used to calculate TTB (s). Lower values indicate less postural control. Time-to-failure during single-limb stance was a secondary measure of postural control. Time to complete the Timed Up and Go (TUG) was our measure of mobility. Longer TUG times correspond to decreased mobility, strength, and balance. Independent t-tests or Mann-Whitney U tests were conducted to assess group differences. Bivariate correlations between task outcomes were conducted.ResultsAnterior-posterior TTB and single-limb stance times were shorter in people with DMPN (p ≤ 0.04). TUG times were longer in the DMPN group (p = 0.04). In the DMPN group, inverse relationships were observed between TTB and TUG (anterior-posterior R² = .34; medial-lateral R² = .49; both p = 0.01), but not between single-limb stance times and TTB or TUG.SignificanceTTB was a sensitive measure of postural control in people with DMPN. The detected relationship between TTB and TUG newly establishes TTB as a clinically meaningful indicator of balance and function. Study findings may serve to further guide balance screening and rehabilitation efforts in people with DMPN.     

Vision,visuo-cognition and postural control in Parkinson's disease: An associative pilot study

IntroductionImpaired postural control (PC) is common in patients with Parkinson's disease (PD) and is a major contributor to falls, with significant consequences. Mechanisms underpinning PC are complex and include motor and non-motor features. Research has focused predominantly on motor and sensory inputs. Vision and visuo-cognitive function are also integral to PC but have largely been ignored to date. The aim of this observational cross-sectional pilot study was to explore the relationship of vision and visuo-cognition with PC in PD.MethodsTwelve people with PD and ten age-matched healthy controls (HC) underwent detailed assessments for vision, visuo-cognition and postural control. Vision assessments included visual acuity and contrast sensitivity. Visuo-cognition was measured by visuo-perception (object identification), visuo-construction (ability to copy a figure) and visuo-spatial ability (judge distances and location of object within environment). PC was measured by an accelerometer for a range of outcomes during a 2-min static stance. Spearman's correlations identified significant associations.ResultsContrast sensitivity, visuo-spatial ability and postural control (ellipsis) were significantly impaired in PD (p = 0.017; p = 0.001; and p = 0.017, respectively). For PD only, significant correlations were found for higher visuo-spatial function and larger ellipsis (r = 0.64; p = 0.024) and impaired attention and reduced visuo-spatial function (r = −0.62; p = 0.028).ConclusionsVisuo-spatial ability is associated with PC deficit in PD, but in an unexpected direction. This suggests a non-linear pattern of response. Further research is required to examine this novel and important finding.     

Differences in postural control between healthy and subjects with chronic ankle instability

IntroductionChronic ankle instability (CAI) is characterized by the occurrence of repetitive inversion mechanism of the ankle, resulting in numerous ankle sprains. CAI occurs in approximately 70% of patients with a history of a lateral ankle sprain. Many causes of functional ankle instability have been postulated and include deficits in proprioception, impaired neuromuscular-firing patterns, disturbed balance and postural control.ObjectiveThe purpose of this study was to compare postural control behaviour in subjects with chronic ankle instability and healthy subjects, using the traditional linear and nonlinear variables for the centre of pressure (CoP) displacement, during one-leg stance on stable and unstable surfaces.Methods16 CAI subjects and 20 healthy subjects were evaluated with the single leg stance on a stable surface and an unstable surface, for 60 s with a force plate. The traditional linear variables like CoP displacement, CoP amplitude and CoP velocity were calculated. Variability of CoP displacement was also submitted to nonlinear analysis and the approximated entropy, sample entropy, correlation dimension and Lyapunov exponent were calculated.ResultsOn the stable surface, no differences between groups for all the traditional variables were found but the correlation dimension of CoP mediolateral displacement had lower values on the CAI group with statistical significance (p < 0.05). On the unstable surface, no differences were found neither with linear variable neither with variability nonlinear analysis.ConclusionCorrelated dimension of CoP displacement during one-leg stance on a stable surface was the only variable that show significant differences between the two groups. The lower values of this variable in the CAI subjects may implicate a balance control system with more difficulties to adapt to the environment and the task demands. More studies are needed to better understand CAI subjects balance control.     

Priming overconfidence in belief systems reveals negative return on postural control mechanisms

BackgroundModulation of postural control strategies and heightened perceptual ratings of instability when exposed to postural threats, illustrates the association between anxiety and postural control.Research questionHere we test whether modulating prior expectations can engender postural-related anxiety which, in turn, may impair postural control and dissociate the well-established relationship between sway and subjective instability.MethodsWe modulated expectations of the difficulty posed by an upcoming postural task via priming. In the visual priming condition, participants watched a video of an actor performing the task with either a stable or unstable performance, before themselves proceeding with the postural task. In the verbal priming paradigm, participants were given erroneous verbal information regarding the amplitude of the forthcoming platform movement, or no prior information.ResultsFollowing the visual priming, the normal relationship between trunk sway and subjective instability was preserved only in those individuals that viewed the stable but not the unstable actor. In the verbal priming experiment we observed an increase in subjective instability and anxiety during task performance in individuals who were erroneously primed that sled amplitude would increase, when in fact it did not.SignificanceOur findings show that people’s subjective experiences of instability and anxiety during a balancing task are powerfully modulated by priming. The contextual provision of erroneous cognitive priors dissociates the normally ‘hard wired’ relationship between objective measures and subjective ratings of sway. Our findings have potential clinical significance for the development of enhanced cognitive retraining in patients with balance disorders, e.g. via modifying expectations.     

Clinical validity of novel postural stabilization experimental indices based on hyperbolic transformation

BackgroundPostural stabilization is the function which allows an individual, after a transitional movement, to recover balance in a quiet erect posture. An experimental method has been proposed (Rabuffetti, 2011) and proved valid for the assessment of balance disorders in individuals with neurological diseases. It would seem that the two original indices were not fully independent since their concurrent distribution was confined by a hyperbolic boundary.Research questionA methodological advancement involving non-linear transformation techniques is required to overcome the limitations of the original approach.MethodsA hyperbolic transformation is applied to the original indices related to the mechanics of the stabilization (instability at beginning of stabilization and time rate of stabilization), thus defining two novel indices (Instability and Promptness). These novel indices may be related to different functional domains concerning, respectively, peripheral force capacity and central nervous motor control. The validity of these novel indices is quantified by their correlation with clinical scales in an already validated group of patients with Charcot-Marie-Tooth disease (N = 47) or Multiple Sclerosis (N = 20).ResultsThe novel indices generally improved validity compared to the original indices (+66% of indices show a statistically significant concurrent validity on a clinical scale). Moreover, Instability was more related to the Charcot-Marie-Tooth group (9 out of 12 valid correlations), and Promptness to the Multiple Sclerosis group (4 out of 5, when also considering statistical trends), in accordance to the, respectively, more peripheral and more central nature of the two neurological diseases.SignificanceThe novel postural stabilization indices support a clinical application for two reasons: 1) they have shown improved validity, compared to the original indices, in two groups of patients affected by neurological pathologies of different nature, 2) they are more closely related, compared to the original indices, to different functional domains.     

Preserved flexibility of dynamic postural control in individuals with Parkinson's disease

BackgroundContinuous oscillation of the support base requires anticipatory and reactive postural adjustments to maintain a stable balance. In this context, postural control flexibility or the ability to adjust balance mechanisms following the requirements of the environment is needed to counterbalance the predictable, continuous perturbation of body balance. Considering the inflexibility of postural responses in individuals with Parkinson's disease (PD), maintaining stability in the support base's continuous oscillations may be challenging. Varying the frequency of platform oscillation is an exciting approach to assess the interactions between reactive and anticipatory adjustments.Research questionThis study aimed to analyze postural responses of individuals with PD on an oscillatory support base across different frequencies.MethodsThirty participants with moderate PD diagnosis (M = 64.47 years, SD = 8.59; Hoehn and Yahr scale 3) and fifteen healthy age-matched controls (M = 65.8 years, SD = 4.2) were tested. Subjects maintained a dynamic balance on a platform oscillating in sinusoidal translations. Four oscillation frequencies were evaluated in different trials that ranged from 0.2 to 0.8 Hz in steps of 0.2 Hz.ResultsAnalysis showed similar performance between PD and healthy participants, with modulation of amplitudes of head displacement, center of pressure, center of mass and feet-head coordination to platform oscillation frequency.DiscussionOur findings suggest a preserved ability of individuals with PD to dynamically control body balance on a support base with predictable oscillatory translations.     

The effect of cryotherapy on postural stabilization assessed by standardized horizontal perturbations of a movable platform

BackgroundCryotherapy is a frequently used therapy in the acute treatment of sports injuries, although it has possible negative effects on dynamic postural stabilization.Research questionWhat is the effect of cryotherapy on the postural stabilization assessed by imposed platform perturbations?MethodsTwenty-four healthy participants (15 male, 9 female) performed 2 test sessions (before and after cryotherapy) consisting of 4 trials each. Each trial included 30 s single leg stance (SLS) on both legs and 4 testing blocks (2 for each leg) of 30 s for the dynamic testing. A single testing block comprised 4 perturbations. After the first session, cryotherapy was applied to the right leg by placing it in ice water at a temperature between 10 °C and 12 ° for 20 min.Outcome measuresWe assessed the Center of Pressure speed (CoPs) and the mean force variation for both static and dynamic tests. Additionally, the Time To Stability (TTS) was calculated for the perturbations.ResultsIn the static trials there was an interaction between leg and session present for the mean force variation (p = 0.01) with a large η² of 0.24, which shows higher variation of vertical force after application of the cryotherapy on the right leg. During the dynamic trials we found an interaction between leg and session for the TTS suggesting increase of the TTS due to the cryotherapy (p = 0.04), with a large η² of 0.17. No interaction effect was present for the CoPs in the mediolateral and anteroposterior direction (p = 0.62 and p = 0.12, respectively).SignificanceCryotherapy applied to the lower extremity results in a worse postural stabilization when assessed by platform perturbations. This might be the result of an altered balance strategy, due to impaired proprioception from the affected body part. More research is needed to examine the duration of this effect.Level of evidenceLevel 3, associative study     

帕金森病立体定向手术靶点定位软件

目的设计并验证帕金森病立体定向手术靶点定位软件.方法推导出任意靶点两种坐标(大脑原点,即AC-PC线中点坐标系坐标和立体定位架坐标系坐标)之间的相互换算;数字化三维坐标重建Schaltenbrand-Wahren人脑立体定向图谱,形成随AC-PC长度缩放的导航图谱.编成软件实现(1)图谱中选靶点,得出其两种坐标;(2)输入两种坐标中的一项,得出另一项,并在图谱中显示靶点.对软件的实用性、准确性进行了验证.结果帕金森病立体定向手术靶点定位软件,靶点定位直观准确,消除了定向架的影响、简化了计算、提高了SW图谱的适应性.     

Evaluation of postural control in children with increased femoral anteversion

BackgroundFemoral anteversion is defined as the angular difference between the axis of the femoral neck and the transcondylar axis of the knee and the most common cause of an in-toe gait in children.Research questionDoes increased femoral anteversion (IFA) adversely affect postural stability and balance in healthy children?MethodsSixteen children with IFA aged 10–15 years and an age-matched control group of 16 children who were growing typically were included. Postural stability (PS), limits of stability (LoS), and the modified clinical test of sensory integration of balance (mCTSIB) were used to evaluate postural control by "Biodex Balance System® (BBS)" and Balance Error Scoring System (BESS), which is a visual observation of instability in 3 stance positions under 6 different conditions, were performed for all cases. SPSS v.20 program was used for data analysis. Independent Samples T-test or Mann Whitney U test were used for between-group comparisons depending on the distribution properties of the data. The significance level was set at p < 0.05.ResultsA significant difference was found between the groups for overall and anterior/posterior stability index in PS (p < 0.05), all parameters of LoS (p < 0.05) and mCTSIB (p < 0.05). Also there was a significant difference between the BESS firm surface (p = 0.007), BESS foam surface (p < 0.001), and total surface scores (p < 0.001).SignificanceThe results indicate that the children with IFA were significantly more unstable in all parameters of BBS and BESS when compared to their healthy peers. This shows that postural stability and balance are impaired in healthy children with IFA. To the extent of our knowledge, this study is the first to examine the postural control problems associated with IFA in healthy children.     

Impaired synergic control of posture in Parkinson's patients without postural instability

BackgroundPostural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of movement and postural stability.ObjectivesMulti-muscle synergies stabilizing vertical posture were studied in Parkinson's disease patients without clinical symptoms of postural instability (Hoehn-Yahr ≤ II) and age-matched controls. We tested the hypothesis that both synergy indices during quiet standing and synergy adjustments to self-triggered postural perturbations would be reduced in patients.MethodsEleven Parkinson's disease patients and 11 controls performed whole-body tasks while standing. Surface electromyography was used to quantify synergy indices stabilizing center of pressure shifts in the anterior–posterior direction during a load-release task.ResultsParkinson's disease patients showed a significantly lower percentage of variance in the muscle activation space accounted for by the first four principal components, significantly reduced synergy indices during steady state, and significantly reduced anticipatory synergy adjustments (a drop in the synergy index prior to the self-triggered unloading).ConclusionsThe study demonstrates for the first time that impaired synergic control in Parkinson's disease can be quantified in postural tasks, even in patients without clinical manifestations of postural instability. Synergy measurements may provide a biomarker sensitive for early problems with postural stability in Parkinson's disease.