Analysis of sway in Parkinson's disease using a new inclinometry-based method

A comprehensive multivariate analysis of the center of pressure during quiet standing in patients with Parkinson's disease

BACKGROUND

We hypothesized that postural instability observed in individuals with Parkinson's disease (PD) can be classified as distinct subtypes based on comprehensive analyses of various evaluated parameters obtained from time-series of center of pressure (CoP) data during quiet standing. The aim of this study was to characterize the postural control patterns in PD patients by performing an exploratory factor analysis and subsequent cluster analysis using CoP time-series data during quiet standing.

METHODS

127 PD patients, 47 aged 65 years or older healthy older adults, and 71 healthy young adults participated in this study. Subjects maintain quiet standing for 30 s on a force platform and 23 variables were calculated from the measured CoP time-series data. Exploratory factor analysis and cluster analysis with a Gaussian mixture model using factors were performed on each variable to classify subgroups based on differences in characteristics of postural instability in PD.

RESULTS

The factor analysis identified five factors (magnitude of sway, medio-lateral frequency, anterio-posterior frequency, component of high frequency, and closed-loop control). Based on the five extracted factors, six distinct subtypes were identified, which can be considered as subtypes of distinct manifestations of postural disorders in PD patients. Factor loading scores for the clinical classifications (younger, older, and PD severity) overlapped, but the cluster classification scores were clearly separated.

CONCLUSIONS

The cluster categorization clearly identifies symptom-dependent differences in the characteristics of the CoP, suggesting that the detected clusters can be regarded as subtypes of distinct manifestations of postural disorders in patients with PD.

The Effect of Sensory Reweighting on Postural Control and Cortical Activity in Parkinson's Disease

Aims

Balance requires the cortical control of visual, somatosensory, and vestibular inputs. The aim of this cross-sectional study was to compare the contributions of each of these systems on postural control and cortical activity using a sensory reweighting approach between participants with Parkinson's disease (PD) and controls.

Methods

Ten participants with PD (age: 72 ± 9; 3 women; Hoehn & Yahr: 2 [1.5 - 2.50]) and 11 controls (age: 70 ± 3; 4 women) completed a sensory organization test in virtual reality (VR-SOT) while cortical activity was being recorded using electroencephalography (EEG). Conditions 1 to 3 were completed on a stable platform; conditions 4 to 6 on a foam. Conditions 1 and 4 were done with eyes open; conditions 2 and 5 in a darkened VR environment; and conditions 3 and 6 in a moving VR environment. Linear mixed models were used to evaluate changes in center of pressure (COP) displacement and EEG alpha and theta/beta ratio power between the two groups across the postural control conditions. Condition 1 was used as reference in all analyses.

Results

Participants with PD showed greater COP displacement than controls in the anteroposterior (AP) direction when relying on vestibular input (condition 5; p<0.0001). The mediolateral (ML) COP sway was greater in PD than in controls when relying on the somatosensory (condition 2; p = 0.03), visual (condition 4; p = 0.002), and vestibular (condition 5; p < 0.0001) systems. Participants with PD exhibited greater alpha power compared to controls when relying on visual input (condition 2; p = 0.003) and greater theta/beta ratio power when relying on somatosensory input (condition 4; p = 0.001).

Conclusions

PD affects reweighting of postural control, exemplified by greater COP displacement and increased cortical activity. Further research is needed to establish the temporal dynamics between cortical activity and COP displacement.

Feasibility of Combining Disease-Specific and Balance-Related Measures as Risk Predictors of Future Falls in Patients with Parkinson's Disease

Evidence supports the view that postural sway in a quiet stance increases with clinical disease severity and dopaminergic therapy in idiopathic Parkinson’s disease (PD), which, in turn, increases the risk of falling. This study evaluated the feasibility of combining disease-specific and balance-related measures as risk predictors for future falls in patients with PD. The patients with PD underwent postural sway measurements (area, length, and velocity traveled by the excursion of the center of pressure) and clinical functional scores (Parkinson’s Disease Rating Scale [UPDRS] and Tinetti balance and gait score assessment) in both the on- and off-states of dopaminergic therapy. The outcome was defined as the development of a new fall. The sway area, velocity, and length increased after the medication administration. The Cox proportional hazards model showed that only previous fall history, Tinetti balance and gait score (on-state), and levodopa equivalent daily dose (LEDD) were associated with the development of future falls. The cumulative risk of fall development showed that the sway length and velocity were associated with future falls after more than six months. The combined LEDD, Tinetti balance and gait score (on-state), and velocity and length of postural sway (on-state) had the highest diagnostic accuracy (area under the curve = 0.9, p < 0.0001). Dopaminergic therapy can improve clinical functional scores but worsen balance-related measures. Increased sway length and velocity during the medication state are hallmarks of future falls, particularly in advanced PD. Combining disease-specific and balance-related measures can serve as an auxiliary diagnosis as risk predictors for future falls.

The Impact of Parkinson's Disease on Postural Control in Older People and How Sex can Mediate These Results: A Systematic Review

INTRODUCTION

Parkinson's disease is most prevalent among elderly people, 65 years and over, and leads to an alteration in motor control associated with postural instability. Current evidence shows that postural control decreases with the aging process. In addition, postural control is more altered in healthy aged men than in women. Until today, few studies have evaluated the combined impact of Parkinson's disease and sex on postural control. This review has allowed to evaluate the impact of Parkinson's disease and sex on postural control measurements in elderly people.

METHODOLOGY

Studies have been selected from two main databases: PubMed and EBSCO using the keywords "Parkinson", "postural control OR balance" and "sex". Articles related to the evaluation of postural control, including men and women with Parkinson's aged over 65 years old, regardless of stage, were included (n = 179). Articles were excluded if not written in French or English or not presenting original content.

RESULTS

Ten (10) studies out of 179 that fulfilled inclusion and exclusion criteria were reported in the final analysis, which cumulates a total of 944 individuals with Parkinson's (410 women). In general, results show greater postural instability among people with Parkinson's compared to healthy subjects, and this according to different objective measurements using stabilographic parameters from force platforms. Only two studies out of ten evaluated postural control while briefly considering distinctions between sex, but without showing a significant difference between men and women with Parkinson's. Parkinson's severity, length of time of Parkinson's disease and cognitive state of the person are the three variables with a negative impact on postural control.

CONCLUSION

Older people with Parkinson's disease have greater postural instability. Sex does not seem to influence the postural control of elderly people with Parkinson's, although more studies are necessary.

Synergic control of action in levodopa-naïve Parkinson's disease patients: II. Multi-muscle synergies stabilizing vertical posture

Postural instability is a major disabling feature in Parkinson's disease (PD). We quantified the organization of leg and trunk muscles into synergies stabilizing the center of pressure (COP) coordinate within the uncontrolled manifold hypothesis in levodopa-naïve patients with PD and age-matched control subjects. The main hypothesis was that changes in the synergic control of posture are present early in the PD process even before levodopa exposure. Eleven levodopa-naïve patients with PD and 11 healthy controls performed whole-body cyclical voluntary sway tasks and a self-initiated load-release task during standing on a force plate. Surface electromyographic activity in 13 muscles on the right side of the body was analyzed to identify muscle groups with parallel scaling of activation levels (M-modes). Data were collected both before ("off-drug") and approximately 60 min after the first dose of 25/100 carbidopa/levodopa ("on-drug"). COP-stabilizing synergies were quantified for the load-release task. Levodopa-naïve patients with PD showed no COP-stabilizing synergy "off-drug", whereas controls showed posture-stabilizing multi-M-mode synergy. "On-drug", patients with PD demonstrated a significant increase in the synergy index. There were no significant drug effects on the M-mode composition, anticipatory postural adjustments, indices of motor equivalence, or indices of COP variability. The results suggest that levodopa-naïve patients with PD already show impaired posture-stabilizing multi-muscle synergies that may be used as promising behavioral biomarkers for emerging postural disorders in PD. Moreover, levodopa modified synergy metrics differently in these levodopa-naïve patients compared to a previous study of patients on chronic antiparkinsonian medications (Falaki et al. in J Electromyogr Kinesiol 33:20-26, 2017a), suggesting different neurocircuitry involvement.

Postural Stability and Cognitive Performance of Subjects With Parkinson's Disease During a Dual-Task in an Upright Stance

Background

The reviewed studies on center of pressure (COP) displacement in Parkinson’s disease (PD) subjects show important methodological differences and contradictory results with regard to healthy subjects. The dual-task paradigm method has been used to examine cognitive prioritization strategies to control concurrent postural and cognitive tasks. The motor requirements, such as pronouncing words, involved in the cognitive tasks used in double-task conditions could be related to the heterogeneity of the results.

Research Objective

To compare postural sway and cognitive performance in subjects with PD and controls using a dual-task paradigm with a cognitive task free of motor demands. We tried to examine the prioritization strategy of PD patients regarding healthy adults to control for concurrent postural and cognitive tasks.

Materials and Methods

25 subjects with PD and 20 healthy controls carried out a postural task under both single-task and dual-task conditions. The postural task was to stand as still as possible, with eyes first open and then closed. The dual-task condition added a concurrent cognitive task based on phoneme monitoring. COP displacement variables and cognitive performance were compared between the groups and within-subject factors were also examined.

Results

PD participants showed higher COP displacement results than the controls. All participants shortened the mean sway radius in dual-task conditions compared with single-task conditions; only healthy subjects presented less transversal COP sway in dual-task conditions than in single-task conditions. The cognitive performance of PD patients on a phoneme monitoring task worsened when they carried it out while maintaining balance in a standing position compared to sitting. The opposite effect occurred in control subjects.

Conclusion

This study confirms the negative influence of Parkinson’s disease on the control of standing stability, increasing the COP sway amplitude. The attentional demands of a postural task, such as standing balance, may be greater in PD patients than in healthy subjects. This would affect the performance of patients during dual-task conditions to be able to control a postural task while performing other cognitive tasks. In these conditions, cognitive performance would be negatively affected. These results suggest that subjects with PD, at least during initial disease stages, prioritize postural control over other concurrent tasks, as is also seen in healthy subjects.

A Novel MRI Compatible Balance Simulator to Detect Postural Instability in Parkinson's Disease

Background: Postural instability is a debilitating and largely treatment-resistant symptom of Parkinson's disease (PD). A better understanding of the neural substrates contributing to postural instability could lead to new targets for improved pharmacological and neurosurgical interventions. However, investigating these neural substrates necessitates the use of functional MRI scanners, which are almost exclusively horizontally-based. Objective: We aimed to develop, and validate the use of, an MRI compatible balance simulator to study static and dynamic balance control in PD patients and elderly controls. Methods: Our MRI compatible balance simulator allowed participants to actively balance an inverted pendulum by activating postural muscles around the ankle joint while supine. Two studies were performed to compare static and dynamic balance performance between upright stance and simulated stance in PD patients and controls. Study 1 (14 PD; 20 controls) required participants to maintain static balance during upright and simulated stance for 120 s with eyes open and closed. In study 2 (20 PD; 22 controls) participants repeated the static balance task (80 s, eyes closed only), and also completed a dynamic balance task which required maintaining balance while experiencing random anterior-posterior perturbations applied to the trunk/pendulum. Postural sway of the body/pendulum was measured using an angular velocity sensor (SwayStar^TM, study 1) and Optotrak motion capture (study 2). Outcome measures were amplitude and frequency of center of mass sway for static balance, and peak and time-to-peak of center of mass displacement and velocity for dynamic balance. Results: PD patients had larger sway amplitude during both upright and simulated static balance compared to controls. PD patients had larger peak and time-to-peak sway, and larger time-to-peak sway velocity, during simulated, but not upright, dynamic balance compared to controls. Conclusions: Deficits in static and dynamic balance control can be detected in PD patients using a novel MRI compatible balance simulator. This technique allows for functional neuroimaging to be combined with balance-relevant tasks, and provides a new means to create insights into the neural substrates contributing to postural instability in PD.

Postural balance and rifle stability in a standing shooting position after specific physical effort in biathletes

The aim of the study was to evaluate the effect of maximal specific physical effort on postural balance and rifle stability in biathletes in a standing shooting position. The study included 10 junior elite biathletes. The measurements were taken with the Vicon system and AMTI force platform. Postural balance and rifle stability characteristics were determined at rest as well as 1 and 5 min post maximal specific physical effort which was performed on a ski ergometer and continued until exhaustion. Maximal physical effort exerted a significant effect on all examined postural sway and rifle sway characteristics. The duration of the post-exercise changes was longer than 5 minutes. Higher post-effort rifle sway was observed in the vertical direction than in the across the shooting line direction. Post-effort postural balance impairment in the shooting line was much greater than in the across the shooting line direction. Moreover, a strong correlation was found between postural balance and rifle stability. Maximal physical effort influenced postural balance and rifle stability during aiming. Rifle sway during aiming in a standing shooting position seems to be coordinated with the postural sway of the biathlete's body. Thus, an increase in postural sway contributes to greater sway and lesser stability of the rifle.

Counteracting Postural Perturbations Through Body Weight Shift: a Pilot Study Using a Robotic Platform in Subjects with Parkinson's Disease

Abnormalities of body-weight transfer occur during several motor tasks in people with Parkinson's disease (PwPD). In this study, a novel robotic paradigm for assessment and training of dynamic balance was developed and applied to twelve healthy subjects (HS) and ten PwPD to verify its feasibility and to assess the capability of PwPD to counteract postural perturbations through body-weight shifts. At variance with other robotic paradigms, subjects had to react as fast as possible to the perturbation, bringing the platform back to the horizontal and keeping it until the end of the task. Four randomized perturbations, obtained varying the platform equilibrium angle from 0° to ±6° in sagittal (backward, forward) and frontal (right, left) planes, were repeated 3 times. Compared to HS, PwPD showed, in all perturbation directions, increased delay in counteraction phase onset (p<=0.01), prolonged time to stabilize the platform (p<=0.02), and higher deviation of the final plate inclination from the horizontal (p<=0.04), the deviation being larger during sagittal perturbations. PwPD showed also larger (p=0.01) postural sway around the stabilization angle following frontal perturbations. Results are in keeping with known hypo- and bradykinesia as well as proprioceptive and kinesthetic impairments in PD. We suggest that the proposed approach is feasible and might be included in balance evaluation and training in PD.

Postural sway in patients with early Parkinson's disease performing cognitive tasks while standing

OBJECTIVES

We investigated postural sway in patients with early Parkinson's disease (PD) to test the hypothesis that the postural control system was affected already at an early stage of PD. Moreover, we identified cases of dysfunction of stereopsis in PD patients.

METHODS

We examined 23 patients with early PD and 23 healthy, sex- and age-matched control subjects. Postural sway was measured with an accelerometer at the center of mass at the lower spine. Subjects were asked to stand quietly for 30 s under two usual conditions (eyes open and eyes closed) and two dual tasks conditions (eyes open with dual task, eyes closed with dual task). Stereopsis was assessed using the Titmus fly test.

RESULTS

In the usual conditions, no differences were found between the control group and PD group. With increasing task difficulty, PD patients showed an increase of RMS values of sway acceleration, compared to control subjects. These differences reached significance during cognitive task performance. PD patients showed larger JERK values with increasing difficulty of the sway task which also reached significance during cognitive task performance. Relative to controls, PD patients showed decreased stereopsis function. But, there were no statistically significant correlations between log seconds of arc of the Titmus test and JERK, even during cognitive task performance.

CONCLUSION

Our results indicate that patients with early PD have subtle signs of postural instability when their attention is diverted or reduced. In addition, deficits of stereopsis may be common in early PD patients. St Abbreviations: ACC: Accelerometers; ANOVA: Analysis of variance; AP: Antero-posterior; COP: Center of pressure; EC: Eyes closed; ECDT: eyes closed with dual task; EO: Eyes open; EODT: Eyes open with dual task; GDS: Geriatric depression scale; JERK: Jerkiness of sway; ML: Medio-lateral; MMSE: Mini mental state examination; MoCA: Montreal cognitive assessment; PD: Parkinson's disease; PDAbS: PD Patients with abnormal stereopsis; PDNrS: PD Patients with normal stereopsis; PIGD: Postural instability and gait disorder; RMS: Root mean square; UPDRS: Unified Parkinson's disease rating scale.

Motor Subtypes of Parkinson's Disease Can Be Identified by Frequency Component of Postural Stability

Parkinson’s disease (PD) can be divided into two subtypes based on clinical features—namely tremor dominant (TD) and postural instability and gait difficulty (PIGD). This categorization is important at the early stage of PD, since identifying the subtypes can help to predict the clinical progression of the disease. Accordingly, correctly diagnosing subtypes is critical in initiating appropriate early interventions and tracking the progression of the disease. However, as the disease progresses, it becomes increasingly difficult to further distinguish those attributes that are relevant to the subtypes. In this study, we investigated whether a method using the standing center of pressure (COP) time series data can separate two subtypes of PD by looking at the frequency component of COP (i.e., COP position and speed). Thirty-six participants diagnosed with PD were evaluated, with their bare feet on the force platform, and were instructed to stand upright with their arms by their sides for 20 s (with their eyes open and closed), which is consistent with the traditional COP measures. Fast Fourier transform (FFT) and wavelet transform (WT) were performed to distinguish between the motor subtypes using the COP measures. The TD group exhibited larger amplitudes at the frequency range of 3–7 Hz when compared to the PIGD group. Both the FFT and WT methods were able to differentiate the subtypes. COP time series information can be used to differentiate between the two motor subtypes of PD, using the frequency component of postural stability.

Deliberately Light Interpersonal Touch as an Aid to Balance Control in Neurologic Conditions

PURPOSE

We aimed to quantify the benefit of externally provided deliberately light interpersonal touch (IPT) on body sway in neurological patients.

DESIGN

IPT effect on sway was assessed experimentally across differing contacting conditions in a group of 12 patients with Parkinson's disease and a group of 11 patients with chronic hemiparetic stroke.

METHODS

A pressure plate recorded sway when IPT was provided by a healthcare professional at various locations on a patient's back.

FINDINGS

IPT on the back reduced anteroposterior body sway in both groups. Numerically, IPT was more effective when applied more superior on the back, specifically at shoulder level, and when applied at two contact locations simultaneously.

CONCLUSION

Our findings demonstrate the benefit of deliberately light IPT on the back to facilitate patients' postural stability.

CLINICAL RELEVANCE

Deliberately light IPT resembles a manual handling strategy, which minimizes load imposed on healthcare professionals when providing balance support, while it facilitates patients' own sensorimotor control of body balance during standing.

Maintaining balance against force perturbations: impaired mechanisms unresponsive to levodopa in Parkinson's disease

We introduce a new method to investigate postural instability in Parkinson's disease (PD) using computer-controlled motors to deliver precise pulls to the shoulders of subjects while standing. It mimics the clinical pull test but uses forces with unpredictable timing, direction, and magnitude. It revealed a number of balance control deficits in PD. Notably, the identified deficits were not significantly altered by levodopa medication, suggesting that disruption to nondopaminergic systems contributes to postural instability in PD.

There is evidence that postural instability associated with Parkinson's disease (PD) is not adequately improved by levodopa, implying involvement of nondopaminergic pathways. However, the mechanisms contributing to postural instability have yet to be fully identified and tested for their levodopa responsiveness. In this report we investigate balance processes that resist external forces to the body when standing. These include in-place responses and the transition to protective stepping. Forward and backward shoulder pulls were delivered using two force-feedback-controlled motors and were randomized for direction, magnitude, and onset. Sixteen patients with PD were tested OFF and ON levodopa, and 16 healthy controls were tested twice. Response behavior was quantified from 3-dimensional ground reaction forces and kinematic measurements of body segments and total body center-of-mass (CoM) motion. In-place responses resisting the pull were significantly smaller in PD as reflected in reduced horizontal anteroposterior ground reaction force and increased CoM displacement. Ankle, knee, and hip moments contributing to this resistance were smaller in PD, with the knee extensor moment to backward pulls being the most affected. The threshold force needed to evoke a step was also smaller for PD in the forward direction. Protective steps evoked by suprathreshold pulls showed deficits in PD in the backward direction, with steps being shorter and more steps being required to arrest the body. Levodopa administration had no significant effect on either in-place or protective stepping deficits. We conclude that processes employed to maintain balance in the face of external forces show impairment in PD consistent with disruption to nondopaminergic systems.

Randomized controlled trial protocol: balance training with rhythmical cues to improve and maintain balance control in Parkinson's disease

Background

Postural instability is a particularly incapacitating disorder, whose loss of motor independence by Parkinson´s Disease (PD) patients marks a significant stage of disease onset. Evidence suggests that deficits in automatic motor control, sensory integration and attention are associated with the lack of balance in PD. Physiotherapy together with medication play an important role in the treatment of this state, although no consensus has been reached on the best treatment modality. The aim of this randomized controlled trial protocol is to evaluate the effects of balance training with rhythmical (BRT), which is a motor program to improve balance associated with rhythmical auditory cues (RACs). This study is ongoing in the stage 1.

Methods and design

A total of 150 PD patients at H&Y stages II–III and asymptomatic for depression and dementia are enrolled in a single-blind randomized study. Randomization is achieved via a computer-generated random-sequence table. All patients should also present a fall history. They will be assigned into one of three groups, and their balance and gait will be assessed before and after 10 training sessions, and after 4 and 30 weeks subsequent to the end of the training. The BRT group will receive a motor program to improve balance associated with RACs, the MT group will perform motor training with the same aims as those in the BRT group but without RACs, and the control group (CG) will be trained only in orientations. The exercise program specific to balance is of 5 weeks’ duration with two sessions per week, 45 min each, and consists of general physiotherapy exercises. Each session will be divided into five warm-up minutes—30 min for the main part and 10 min for the cool down. The training progresses and intensifies each week depending on the individual’s performance. The subjects should be able to execute 10 repetitions of the exercise sequences correctly to progress to the next movement.

Discussion

This randomized study protocol will evaluate the effects of a motor program designed to improve balance associated with RACs, and will also assess whether balance training leads to activation of balance reactions at the appropriate time. We hypothesize that if this motor program is maintained long-term, it will prevent falls.

Trial registration

Clinicaltrials.gov NCT02488265; Ethics Committee of the University of São Paulo Faculty of Medicine Clinics Hospital 1.102.464.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0418-x) contains supplementary material, which is available to authorized users.

Postural Sway and Effect of Levodopa in Early Parkinson's Disease

Objective:

To characterize postural stability control and levodopa responsiveness in early Parkinson's disease (PD).

Methods:

Postural sway was studied during quiet stance in ten patients within six years of PD onset, both before (OFF) and after (ON) regular oral levodopa dosing. Postural sway was recorded using a force platform during 30 sec with eyes open, and six dependent variables were examined.

Results:

Mild baseline subclinical changes in postural sway were recorded in our patients. Clear benefit was observed in five out of six characteristics (mean sway, transversal sway, sagittal sway, sway intensity, and sway area) in the ON condition.

Conclusion:

Postural control mechanisms are affected early in PD and modulated by dopamine.

A low-cost real time virtual system for postural stability assessment at home

BACKGROUND AND OBJECTIVE

The degeneration of the balance control system in the elderly and in many pathologies requires measuring the equilibrium conditions very often. In clinical practice, equilibrium control is commonly evaluated by using a force platform (stabilometric platform) in a clinical environment. In this paper, we demonstrate how a simple movement analysis system, based on a 3D video camera and a 3D real time model reconstruction of the human body, can be used to collect information usually recorded by a physical stabilometric platform.

METHODS

The algorithm used to reconstruct the human body model as a set of spheres is described and discussed. Moreover, experimental measurements and comparisons with data collected by a physical stabilometric platform are also reported. The measurements were collected on a set of 6 healthy subjects to whom a change in equilibrium condition was stimulated by performing an equilibrium task.

RESULTS

The experimental results showed that more than 95% of data collected by the proposed method were not significantly different from those collected by the classic platform, thus confirming the usefulness of the proposed system.

CONCLUSIONS

The proposed virtual balance assessment system can be implemented at low cost (about 500$) and, for this reason, can be considered a home use medical device. On the contrary, astabilometric platform has a cost of about 10,000$ and requires periodical calibration. The proposed system does not require periodical calibration, as is necessary for stabilometric force platforms, and it is easy to use. In future, the proposed system with little integration can be used, besides being an emulator of a stabilometric platform, also to recognize and track, in real time, head, legs, arms and trunk, that is to collect information actually obtained by sophisticated optoelectronic systems.

Age-related changes in cognitive function and postural control in Parkinson's disease

BACKGROUND AND AIMS

This study objectively analyzed postural instability and cognitive function in patients with Parkinson's disease (PD) and a group of healthy elderly and middle-aged individuals.

METHODS

The study included ten healthy middle-aged individuals (range 42-57 years), 14 healthy elderly individuals (range 60-90 years) and 15 PD patients (range 58-93 years). Center of pressure (COP) parameters were determined by means of computed static posturography during free standing with open and closed eyes. The level of cognitive functioning was examined with mini mental state examination (MMSE) and counting backwards test (CBT).

RESULTS

Parkinson's disease patients showed significantly lower MMSE scores compared to healthy middle-aged (p = 0.004) and elderly individuals (p = 0.03). Mean duration of CBT in PD patients was significantly longer than in healthy subjects. COP parameters correlated with age of subjects and cognitive function (MMSE score). No significant differences in any stabilographic parameters were observed between healthy elderly subjects and PD patients.

CONCLUSIONS

Age is the most significant factor impacting upon the static balance of older individuals during free standing. Compared to middle-aged and elderly individuals without central nervous system impairment, patients with PD present with significant delay in cognitive processes associated with executive function.

Comparing the Fullerton Advanced Balance Scale with the Mini-BESTest and Berg Balance Scale to assess postural control in patients with Parkinson disease

OBJECTIVES

To validate the Fullerton Advanced Balance (FAB) Scale for patients with idiopathic Parkinson disease (PD); and to compare the FAB Scale with the Mini-Balance Evaluation Systems Test (Mini-BESTest) and Berg Balance Scale (BBS).

DESIGN

Observational study to assess concurrent validity, test-retest, and interrater reliability of the FAB Scale in patients with PD and to compare the distribution of the scale with the Mini-BESTest and BBS.

SETTING

University hospital in an urban community.

PARTICIPANTS

Patients with idiopathic PD (N=85; Hoehn and Yahr stages 1-4).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

FAB Scale, Mini-BESTest, BBS, timed Up and Go test, Unified Parkinson's Disease Rating Scale, and visual analog scale.

RESULTS

Interrater (3 raters) and test-retest (3±1 d) reliability were high for all scales (ICCs≥.95). The FAB Scale was highly correlated with the Mini-BESTest (Spearman ρ=.87) and timed Up and Go test item of the Mini-BESTest (Spearman ρ=.83). In contrast with the BBS, the FAB Scale and Mini-BESTest have only minimal ceiling effects. The FAB Scale demonstrated the most symmetric distribution when compared with the Mini-BESTest and BBS (skewness: FAB scale: -.54; Mini-BESTest: -1.07; BBS: -2.14).

CONCLUSIONS

The FAB Scale is a valid and reliable tool to assess postural control in patients with PD. No ceiling effect was noted for the FAB Scale. Although the items of the FAB Scale are more detailed when compared with the Mini-BESTest, interrater and test-retest reliability were excellent. The scale is a promising tool to detect small changes of the postural control system in individuals with PD.

Light and heavy touch reduces postural sway and modifies axial tone in Parkinson's disease

BACKGROUND

Light touch with a stable object reduces postural sway by increasing axial postural tone in healthy subjects. However, it is unknown whether subjects with Parkinson's disease (PD), who have more postural sway and higher axial postural tone than healthy subjects, can benefit from haptic touch.

OBJECTIVE

To investigate the effect of light and heavy touch on postural stability and hip tone in subjects with PD.

METHODS

Fourteen subjects with mid-stage PD and 14 healthy control subjects were evaluated during quiet standing with eyes closed with their arms (a) crossed, (b) lightly touching a fixed rigid bar in front of them, and (c) firmly gripping the bar. Postural sway was measured with a forceplate, and axial hip tone was quantified using a unique device that measures the resistance of the hips to yaw rotation while maintaining active stance.

RESULTS

Subjects with PD significantly decreased their postural sway with light or heavy touch (P < .001 vs arms crossed), similarly as control subjects. Without touch, hip tone was larger in PD subjects. With touch, however, tone values were similar in both groups. This change in hip tone with touch was highly correlated with the initial amount of tone (PD, r = -.72 to -.95; controls, r = -.74 to -.85).

CONCLUSIONS

The authors showed, for the first time, that subjects with PD benefit from touch similarly to control subjects and that despite higher axial postural tone, PD subjects are able to modulate their tone with touch. Future studies should investigate the complex relationship between touch and postural tone.

A Classification of Postural Sway Patterns During Upright Stance in Healthy Adults and Patients with Parkinson’s Disease

The intermittent control during human quiet upright stance is a new hypothesis which claims that the active neural feedback control generating the ankle muscle torque is switched off and on intermittently at appropriate timings. The intermittent strategy is capable of providing compliant posture while ensuring robust stability. Contrastingly, impairment of postural reflexes in patients with Parkinson’s disease (PD) causes postural instability. Here we hypothesize that the instability in PD patients might be due to a loss of appropriate intermittent activations in the feedback muscle torque during stance. In order to provide evidence for this hypothesis, we characterized stochastic postural sway patterns measured as changes in center of pressure (CoP) and activities of ankle muscles during quiet stance in healthy young and elderly subjects as well as PD patients. To this end, sway patterns and associated ankle muscle activities were quantified by several indices including the CoP sway area, scaling factors of double-power-law power spectra of the sway, as well as levels and patterns of the muscle activations. Hierarchical cluster analysis was performed to suggest that the sway patterns could be classified into two major types. The first type consisted mainly of sway and muscle activation patterns from healthy subjects and some PD patients with the mild level of severity, and they showed features indicating the intermittent control. The second type, consisting mainly of PD patients with relatively severe levels of motor symptoms, was accompanied with non-intermittent but tonic muscle activities and sway areas either smaller or larger than those in the first type. Moreover, the major two types were further classified into several subtypes with distinguishable characteristics. Results suggested that a loss of the intermittent activations in the ankle muscles could be a cause of the postural instability for a population of PD patients.

Postural sway in patients with mild to moderate Parkinson's disease

Clinical assessment of postural instability in persons with Parkinson's disease (PD) is done with the retropulsive pull test, but since this test does not assess the underlying causes of postural instability, there is a need for additional assessment tools. The aim of this study was to identify postural sway parameters for use in a multifactorial approach to quantify postural instability. Nineteen adults diagnosed with idiopathic PD, 14 healthy age-matched controls (EH), and 10 healthy young adults (YH) completed the study. Postural parameters were extracted during quiet standing in eyes open (EO) and eyes closed (EC) conditions. Removing visual feedback affected the groups in a similar way. Significant differences between the PD and the two control groups were found in sway path length, area, and ranges in the anterior-posterior (AP) and medial-lateral (ML) directions and the Hurst exponents. PD significantly increased AP sway path length compared with YH and ML sway path length compared with EH. The Hurst exponents in PD were significantly different than in EH. The results suggest that the ML direction is a successful discriminator between PD and age-matched controls and that the interaction between ML and AP directions should be considered in the method used to quantify postural instability.

Trunk accelerometry reveals postural instability in untreated Parkinson's disease

While several studies have shown that subjects with advanced Parkinson's disease (PD) exhibit abnormalities in sway parameters during quiet standing, abnormalities of postural sway associated with untreated PD have not been reported. Although not clinically apparent, we hypothesized that spontaneous sway in quiet stance is abnormal in people with untreated PD. We examined 13 subjects, recently diagnosed with PD, who were not yet taking any anti-parkinsonian medications and 12 healthy, age-matched control subjects. Postural sway was measured with a linear accelerometer on the posterior trunk (L5 level) and compared with traditional force plate measures of sway. Subjects stood for 2 min under two conditions: eyes open (EO) and eyes closed (EC). One of the most discriminative measures of postural changes in subjects with untreated PD was the increased 'JERK' of lower trunk in the EO condition, measured with the accelerometer. Root mean square and the frequency dispersion of postural sway in the EO condition also discriminated sway in untreated PD subjects compared to control subjects. We conclude that accelerometer-based sway metrics could be used as objective measures of postural instability in untreated PD. Accelerometer-based analysis of spontaneous sway may provide a powerful tool for early clinical trials and for monitoring the effects of treatment of balance disorders in subjects with PD.

Recurrent falls and mortality in Parkinson's disease: a prospective two-year follow-up study

OBJECTIVES

To evaluate the risk factors for recurrent falling and mortality in Parkinson's disease (PD) in a prospective study design.

MATERIALS AND METHODS

One hundred and twenty-five PD patients were included in the study. Baseline medical data were collected, and patients were clinically tested for mobility and balance. Falls were prospectively recorded for 2 years. Mortality was documented 4 years after the baseline.

RESULTS

Seventy-nine patients reported altogether 3125 falls during the follow-up, and 59 patients were classified as recurrent fallers. Altogether 126 fall injuries including six fractures were reported. Eighteen patients had died by the time of the hospital chart review. History of falling (OR 3.02, 95% CI 1.23-7.44) and the Unified Parkinson's Disease Rating Scale activities of daily living score (OR 1.13, 95% CI 1.04-1.22) were independent risk factors for recurrent falling in PD, whereas slow walking speed (OR 16.28, 95% CI 1.85-142.97) was an independent risk factor for mortality in PD.

CONCLUSIONS

History of falling and disease severity indicate increased risk of recurrent falls in PD, while patients with slow walking speed may have an increased risk of mortality. Recurrent falling was not associated with increased risk of mortality in PD in this study.

Postural sway approaches center of mass stability limits in Parkinson's disease

BACKGROUND

Although Parkinson's disease (PD) is a well recognised risk factor for falls, how this disease and its therapy affect postural stability and leaning balance remains unclear. The aim of this study was to examine the effects of PD and levodopa on postural sway and leaning balance.

METHODS

Performances of 28 PD participants {median [inter-quartile range (IQR)] duration of PD: 10 (6-13) years, median (IQR) UPDRS motor score "off": 22 (14-31) "on" and "off" levodopa were compared with 28 age- and gender-matched healthy controls on two measures of controlled leaning balance [ratio of anterior-posterior (AP) sway to maximal balance range (MBR) and coordinated stability].

RESULTS

PD participants had greater ratio of AP sway to MBR than controls (P < 0.001), indicating that they swayed more as a proportion of their limits of stability, both "off" and "on" levodopa (P < 0.001). They also performed poorer in the coordinated stability test both "off" and "on" levodopa compared to controls (P < 0.001, for both), suggesting greater difficulty in controlling the center of mass at or near the limits of stability. Levodopa improved PD "participants" leaning balance (P < 0.001) and reduced the AP sway to MBR ratio (P < 0.001), although not to the level of controls.

CONCLUSIONS

PD participants perform poorer than controls in leaning balance tests but significantly improve when "on" levodopa. Regardless of medication state, PD participants sway markedly more as a percentage of their limits of stability than controls suggesting a higher risk of falling.

Experimental calf muscle pain attenuates the postural stability during quiet stance and perturbation

BACKGROUND

The purpose of this study was to evaluate how acute pain changes the postural control and stability during quiet standing and after unexpected perturbations.

METHODS

Nine subjects stood as quiet as possible on a movable force platform that recorded the centre of pressure position and provided unexpected floor perturbations, before, during and after experimental calf muscle pain. Bilateral surface electromyography from the tibialis anterior and medial gastrocnemius muscles was recorded. The foot pressure distributions were measured using pressure insoles. Intramuscular injections of hypertonic saline were administrated (right leg) to induce acute pain in the tibialis anterior and/or medial gastrocnemius muscles, and an isotonic injection was used as control.

FINDINGS

Simultaneous pain in tibialis anterior and medial gastrocnemius altered the postural control. During quiet standing: higher medial-lateral centre of pressure speed and increased total sway displacement (P<0.05), weight moved to the non-painful side, (P<0.05) and plantar centre of pressure of the left foot was shifted towards the heel's direction (P<0.05). During forward perturbation: higher mean displacement in the medial-lateral direction (P<0.05). After the perturbation: larger sway area (P<0.05). Pain only in the medial gastrocnemius muscle increased medial-lateral centre of pressure speed (P<0.05) during the quiet standing. Pain only in the tibialis anterior muscle increased peak pressure on the contralateral foot (P<0.05).

INTERPRETATION

These findings suggest that large acute painful areas on the calf muscles impair the postural control and potentially increase the risk factors for falls. Further strategies aiming to reduce pain in patients may lead to improvement in balance.

Assessment of postural control in patients with Parkinson's disease: sway ratio analysis

Analysis of the postural stability impairments in neurodegenerative diseases is a very demanding task. Age-related declines in posturographic indices are usually superimposed on effects associated with the pathology and its treatment. We present the results of a novel postural sway ratio (SR) analysis in patients with Parkinson's disease (PD) and age-matched healthy subjects. The sway ratios have been assessed based upon center of foot-pressure (CP) signals recorded in 55 parkinsonians (Hoehn and Yahr: 1-3) and 55 age-matched healthy volunteers while standing quiet with eyes open (EO) and then with eyes closed (EC). Complementing classical sway measure abnormalities, the SR exhibited a high discriminative power for all controlled factors: pathology, vision, and direction of sway. Both the anteroposterior (AP) and mediolateral (ML) sway ratios were significantly increased in PD patients when compared to the control group. An additional SR increase was observed in the response to eyes closure. The sway ratio changes documented here can be attributed to a progressive decline of a postural stability control due to pathology. In fact, a significant correlation between the mediolateral SR under EO conditions and Motor Exam (section III) score of the UPDRS was found. The mediolateral sway ratios computed for EO and EC conditions significantly correlated with the CP path length (r = .87) and the mean anteroposterior CP position within the base of support (r = .38). Both indices reflect postural stability decline and fall tendency # in parkinsonians. The tremor-type PD patients (N=34) showed more pronounced relationships between the mediolateral SR and selected items from the UPDRS scale, including: falls (Kendall Tau=.47, p < .05), rigidity (.45, p < .05), postural stability (retropulsion) (.52), and the Motor Exam score (.73). The anteroposterior SR correlated only with tremor (Kendal Tau = .77, p < .05). It seems that in force plate posturography the SR can be recommended as a single reliable measure that allows for a better quantitative assessment of postural stability impairments.

Orthostatic hypotension, balance and falls in Parkinson's disease

Orthostatic hypotension (OH) is a common feature in Parkinson's disease (PD). As the control of balance and gait is already affected by PD per se, OH may further predispose patients to falls and accidents. The study was conducted to evaluate the clinical correlates of OH and its association with mobility and balance in PD. From a total population of 205,000 inhabitants, 120 PD patients were included in the study. Medical data including history of recent falls were collected, and patients were clinically examined using the orthostatic test, the Timed Up & Go test, walking speed, and the quantitative measurement of postural sway. Sixty-three (52.5%) patients had OH in the orthostatic test. Twenty-five (39.5%) patients with and 16 (28.1%) patients without OH (P = 0.614) had fallen during the past 3 months. Patients with OH had significantly increased postural sway in standing compared with patients without OH. However, OH was not associated with mobility or walking speed. The current results support the concept that the control of body balance and OH may be closely linked.

Postural sway and falls in Parkinson's disease: A regression approach

A population-based study was designed to evaluate the clinical associates of postural sway and to identify the risk factors for falls in Parkinson's disease (PD). From a total population of 205,000 inhabitants, 215 PD patients were identified of which 120 home-dwelling cases were finally included in the study. Medical data were collected and patients were clinically examined and tested for static balance using an inclinometric device. Recent falls occurred in 40 (33%) of the subjects and 27 (23%) subjects were recurrent fallers. The fallers had a significantly larger sway area (P = 0.021) and a larger maximum deflection in anterior-posterior (P = 0.016) and lateral directions (P = 0.006) than the nonfallers. A significant correlation was found between the sway measures and the UPDRS total score, motor subcore and UPDRS "bradykinesia" item. A higher UPDRS total score (OR: 1.04, 95% CI: 1.01-1.07) and an increased sway area (OR: 1.25, 95% CI: 1.02-1.54) were independent risk factors for recent falling in PD. In addition, the duration and severity of PD, antiparkinsonian medication, recent falling and the use of a walking aid were associated with increased sway measures. The results can be used to identify PD patients who are at a risk of falling. Both antiparkinsonian medication and nonmedical treatment should be optimized to reduce falls in PD.

Assessment of postural instability in patients with Parkinson’s disease

Postural instability is one of the most disabling features of idiopathic Parkinson's disease (PD). In this study, we focused on postural instability as the main factor predisposing parkinsonians to falls. For this purpose, changes in sway characteristics during quiet stance due to visual feedback exclusion were studied. We searched for postural sway measures that could be potential discriminators for an increased fall risk. A group of 110 subjects: 55 parkinsonians (Hoehn and Yahr: 1-3), and 55 age-matched healthy volunteers participated in the experiment. Their spontaneous sway characteristics while standing quiet with eyes open and eyes closed were analyzed. We found that an increased mediolateral sway and sway area while standing with eyes closed are characteristic of parkinsonian postural instability and may serve to quantify well a tendency to fall. These sway indices significantly correlated with disease severity rated both by the Hoehn and Yahr scale as well as by the Motor Section of the UPDRS. A forward shift of a mean COP position in parkinsonians which reflects their flexed posture was also significantly greater to compare with the elderly subjects and exhibited a high sensitivity to visual conditions. Both groups of postural sway abnormalities identified here may be used as accessible and reliable measures which allow for quantitative assessment of postural instability in Parkinson's disease.

Effect of exercise on extraskeletal risk factors for hip fractures in elderly women with low BMD: a population-based randomized controlled trial

We conducted a 30-month population-based, randomized, controlled trial in 160 elderly women at risk for fractures on the basis of a low baseline BMD. Mainly home-based weight-bearing exercise was effective in improving strength, balance, and gait.

INTRODUCTION

Evidence on the effect of exercise on extraskeletal risk factors for hip fractures comes mainly from studies in voluntary low-risk women, and no population-based, long-term interventions have been performed in elderly women with low bone mass. The aim of this study was to determine the effect of long-term weight-bearing exercise on balance, muscle strength, and gait in elderly women at risk for fractures on the basis of a low baseline BMD.

MATERIALS AND METHODS

A birth cohort of 1690 women 70-73 years of age were invited to the radius and hip BMD measurements; 96 women were excluded because of medical reasons; 160 women with radius and hip BMD values of >2 SD below the reference value were included in the trial. The participants were randomly assigned to 30 months of impact, balancing, and strengthening exercises or to no intervention. Main outcome measures were body sway length and leg strength at month 30. Secondary endpoints included gait speed, endurance, and grip strength. Outcomes were assessed at 0, 12, 24, and 30 months using blinded operators. Repeated-measures ANOVA was used to determine statistical significance. The analyses were performed on an intention-to-treat basis.

RESULTS

Body sway increased more in the control group than in the exercise group over time (time-group interaction, p < 0.001). Leg strength improved in the exercise group and decreased in the control group (interaction, p < 0.001). A significant time-group interaction (p < 0.001) in favor of the exercise group was found on the following secondary endpoints: the timed up and go test score, walking speed, and distance walked in 2 minutes.

CONCLUSIONS

Weight-bearing exercise is an effective way of modifying extraskeletal risk factors for fractures in elderly women.

Deterministic center of pressure patterns characterize postural instability in Parkinson's disease

Static posturographic recordings were obtained from six Parkinson's patients and six age-matched, healthy control participants. The availability of vision and visuo-spatial cognitive load were manipulated. Postural sway patterns were analyzed using recurrence quantification analysis (RQA), which revealed differences in center of pressure (COP) dynamics between Parkinson's and control participants. AP COP trajectories for the Parkinson's group were not only significantly more variable than for the control group, but also exhibited distinct patterns of temporal dynamics. The visual manipulation did not differentially affect the two groups. No cognitive load effects were found. The results are generally consistent with the hypothesis that pathological physiological systems exhibit a tendency for less flexible, more deterministic dynamic patterns.

Postural stability of Parkinson's disease patients is improved by decreasing rigidity

Postural instability has a big impact on the quality of life of patients with Parkinson's disease (PD) as it often leads to an insecure stance and fall. We investigated if postural stability in these patients improves by decreasing rigidity with a dopaminergic agonist. In our study, we tested eight PD patients with no concomitant diseases. Their age was 61 +/- 2 years (mean +/- SE) and their Hoehn-Yahr score was 3 +/- 0.1. The patients were evaluated according to the Unified Parkinson's Disease Rating Scale for motor function (mUPDRS) and with stabilometric measurements of forward-backward and side-to-side body oscillations during free stance with eyes open. Both evaluations were performed in an "off "state and in an apomorphine-induced "on" state. As expected, the mUPDRS score was significantly decreased in the "on" state with posture being improved in six patients, gait in eight patients and postural stability in seven of eight patients. In addition, apomorphine caused a significant reduction of the relative amplitude of lower frequencies and an increase of the relative amplitude of higher frequencies of forward-backward body oscillations. The results of stabilometry and mUPDRS evaluations are in agreement with the effect of apomorphine on rigidity, indicating that postural stability of PD patients is improved by decreasing rigidity.

Falls and freezing of gait in Parkinson's disease: a review of two interconnected, episodic phenomena

Falls and freezing of gait are two "episodic" phenomena that are common in Parkinson's disease. Both symptoms are often incapacitating for affected patients, as the associated physical and psychosocial consequences have a great impact on the patients' quality of life, and survival is diminished. Furthermore, the resultant loss of independence and the treatment costs of injuries add substantially to the health care expenditures associated with Parkinson's disease. In this clinically oriented review, we summarise recent insights into falls and freezing of gait and highlight their similarities, differences, and links. Topics covered include the clinical presentation, recent ideas about the underlying pathophysiology, and the possibilities for treatment. A review of the literature and the current state-of-the-art suggests that clinicians should not feel deterred by the complex nature of falls and freezing of gait; a careful clinical approach may lead to an individually tailored treatment, which can offer at least partial relief for many affected patients.

Feature selection of stabilometric parameters based on principal component analysis

This study addresses the challenge of identifying the features of the Centre of pressure (COP) trajectory that are most sensitive to postural performance, with the aim of avoiding redundancy and allowing a straightforward interpretation of the results. Postural sway in 50 young, healthy subjects was measured by a force platform. Thirty-seven stabilometric parameters were computed from the one-dimensional and two-dimensional COP time series. After normalisation to the relevant biomechanical factors, by means of multiple regression models, a feature selection process was performed based on principal component analysis. Results suggest that COP two-dimensional time series can be primarily characterised by four parameters, describing the size of the COP path over the support surface; the principal sway direction; and the shape and bandwidth of the power spectral density plot. COP one-dimensional time series (antero-posterior (AP) and medio-lateral (ML)) can be characterised by six parameters describing COP dispersion along the AP direction; mean velocity along the ML and AP directions; the contrast between ML and AP regulatory activity; and two parameters describing the spectral characteristics of the COP along the AP direction. On the basis of the results obtained, some guidelines are suggested for the choice of stabilometric parameters to use, with the aim of promoting standardisation in quantitative posturography.