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

Precision Balance Assessment in Parkinson's Disease: Utilizing Vision-Based 3D Pose Tracking for Pull Test Analysis

Postural instability is a common complication in advanced Parkinson's disease (PD) associated with recurrent falls and fall-related injuries. The test of retropulsion, consisting of a rapid balance perturbation by a pull in the backward direction, is regarded as the gold standard for evaluating postural instability in PD and is a key component of the neurological examination and clinical rating in PD (e.g., MDS-UPDRS). However, significant variability in test execution and interpretation contributes to a low intra- and inter-rater test reliability. Here, we explore the potential for objective, vision-based assessment of the pull test (vPull) using 3D pose tracking applied to single-sensor RGB-Depth recordings of clinical assessments. The initial results in a cohort of healthy individuals (n = 15) demonstrate overall excellent agreement of vPull-derived metrics with the gold standard marker-based motion capture. Subsequently, in a cohort of PD patients and controls (n = 15 each), we assessed the inter-rater reliability of vPull and analyzed PD-related impairments in postural response (including pull-to-step latency, number of steps, retropulsion angle). These quantitative metrics effectively distinguish healthy performance from and within varying degrees of postural impairment in PD. vPull shows promise for straightforward clinical implementation with the potential to enhance the sensitivity and specificity of postural instability assessment and fall risk prediction in PD.

Extraction of the pull force from inertial sensors during the pull test for Parkinson's disease: A reliability study

OBJECTIVE

To examine the inter- and intra-rater reliability of the pull test in patients with Parkinson's disease (PD) using the extracted pull force.

METHODS

In this inter- and intra-rater reliability study, two raters performed a pull test on 30 patients with PD. The pull force was quantified using inertial sensors attached to the rater's right hand and the patient's lower trunk. In this study, the pull force was calculated as an extracted three-dimensional vector quantity, the resultant acceleration, and was expressed in m/s2. Inter- and intra-rater reliabilities were analyzed using the interclass correlation coefficient (ICC) for the pull force and Cohen's weighted kappa (κw) for the pull test score. Furthermore, Bland-Altman analysis was used to investigate systematic errors.

RESULTS

The inter- and intra-rater reliability of the pull force was very poor (ICC = 0.033-0.214). Bland-Altman analysis revealed no systematic errors in the pull forces between the two test points. Conversely, κw for the pull test scores ranged from 0.763 to 0.920, indicating substantial to almost perfect agreement.

CONCLUSION

The pull test score was reliable despite variations in the quantified pull force for inter- and intra-rater reliability. Our findings suggest that the pull test is a robust tool for evaluating postural instability in patients with PD and that the pull force probably does not affect scoring performance.

Does Impaired Plantar Cutaneous Vibration Perception Contribute to Axial Motor Symptoms in Parkinson's Disease? Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation

OBJECTIVE

To investigate whether impaired plantar cutaneous vibration perception contributes to axial motor symptoms in Parkinson's disease (PD) and whether anti-parkinsonian medication and subthalamic nucleus deep brain stimulation (STN-DBS) show different effects.

METHODS

Three groups were evaluated: PD patients in the medication "on" state (PD-MED), PD patients in the medication "on" state and additionally "on" STN-DBS (PD-MED-DBS), as well as healthy subjects (HS) as reference. Motor performance was analyzed using a pressure distribution platform. Plantar cutaneous vibration perception thresholds (VPT) were investigated using a customized vibration exciter at 30 Hz.

RESULTS

Motor performance of PD-MED and PD-MED-DBS was characterized by greater postural sway, smaller limits of stability ranges, and slower gait due to shorter strides, fewer steps per minute, and broader stride widths compared to HS. Comparing patient groups, PD-MED-DBS showed better overall motor performance than PD-MED, particularly for the functional limits of stability and gait. VPTs were significantly higher for PD-MED compared to those of HS, which suggests impaired plantar cutaneous vibration perception in PD. However, PD-MED-DBS showed less impaired cutaneous vibration perception than PD-MED.

CONCLUSIONS

PD patients suffer from poor motor performance compared to healthy subjects. Anti-parkinsonian medication in tandem with STN-DBS seems to be superior for normalizing axial motor symptoms compared to medication alone. Plantar cutaneous vibration perception is impaired in PD patients, whereas anti-parkinsonian medication together with STN-DBS is superior for normalizing tactile cutaneous perception compared to medication alone. Consequently, based on our results and the findings of the literature, impaired plantar cutaneous vibration perception might contribute to axial motor symptoms in PD.

A non-expensive bidimensional kinematic balance assessment can detect early postural instability in people with Parkinson's disease

Background

Postural instability is a debilitating cardinal symptom of Parkinson’s disease (PD). Its onset marks a pivotal milestone in PD when balance impairment results in disability in many activities of daily living. Early detection of postural instability by non-expensive tools that can be widely used in clinical practice is a key factor in the prevention of falls in widespread population and their negative consequences.

Objective

This study aimed to investigate the effectiveness of a two-dimensional balance assessment to identify the decline in postural control associated with PD progression.

Methods

This study recruited 55 people with PD, of which 37 were men. Eleven participants were in stage I, twenty-three in stage II, and twenty-one in stage III. According to the Hoehn and Yahr (H&Y) rating scale, three clinical balance tests (Timed Up and Go test, Balance Evaluation Systems Test, and Push and Release test) were carried out in addition to a static stance test recorded by a two-dimensional movement analysis software. Based on kinematic variables generated by the software, a Postural Instability Index (PII) was created, allowing a comparison between its results and those obtained by clinical tests.

Results

There were differences between sociodemographic variables directly related to PD evolution. Although all tests were correlated with H&Y stages, only the PII was able to differentiate the first three stages of disease evolution (H&Y I and II: p = 0.03; H&Y I and III: p = 0.00001; H&Y II and III: p = 0.02). Other clinical tests were able to differentiate only people in the moderate PD stage (H&Y III).

Conclusion

Based on the PII index, it was possible to differentiate the postural control decline among the first three stages of PD evolution. This study offers a promising possibility of a low-cost, early identification of subtle changes in postural control in people with PD in clinical practice.

C-STIM: Protocol for a randomized, single-blind, crossover study of cerebellar repetitive transcranial magnetic stimulation (rTMS) for postural instability in people with progressive supranuclear palsy (PSP)

Background

Methods for modulating the cerebellum with transcranial magnetic stimulation (TMS) are well established, and preliminary data from our group and others has shown evidence of transient improvements in balance after cerebellar repetitive transcranial magnetic stimulation (rTMS) in progressive suprancuclear palsy (PSP). This study examines extensive posturography measures before and after 10 sessions of cerebellar rTMS and sham TMS in PSP.

Methods

Thirty subjects with PSP and postural instability will undergo cerebellar active and sham rTMS in a single-blind, crossover design with a randomized order of a 10-day intervention. Primary outcomes will be changes in sway area and medio-lateral range of sway with eyes open while standing on a stationary force-plate, and safety, tolerability, and blindedness. Secondary outcomes will include posturography and gait analysis with body-worn, triaxial inertial sensors, clinical balance scales and questionnaires, and a bedside test of vestibular function. Exploratory outcomes are changes in functional near infrared spectroscopy (fNIRS) signal over the prefrontal, supplementary motor, and primary motor cortices while standing and walking, and speech samples for future analysis.

Discussion

The C-STIM crossover intervention study adds a longer duration of stimulation and extensive posturography measures to more finely measure the improvements in balance and exploratory functional near-infrared spectroscopy (fNIRS) over the prefronal, supplementary motor, and primary motor cortices during balance assessments before and after 10 sessions of cerebellar rTMS and 10 sessions of sham cerebellar TMS. This project will improve our understanding of the importance of the cerebellum for control of postural stability in PSP.

Objective quantification of responses to the clinical pull-test in people with Parkinson's disease

BACKGROUND

Postural instability can occur in the later-stages of Parkinson's disease (PD). The clinical pull-test is scored on a 0-4 scale on the Unified Parkinson's disease rating scale (UPDRS), with postural instability scored 2 or higher. This ordinal scale does not adequately track progression in early-PD or predict development of postural instability.

RESEARCH QUESTION

To develop a test that quantifiably measured the backward stepping response on the pull-test in early-PD.

METHODS

Participants (35 controls and 79 PD participants) were prospectively enrolled in this study. Participants stepped backwards with each shoulder pull at four strengths on an instrumented gait mat. Four spatiotemporal parameters (reaction-time, step-back-time, step-back-distance, step-back-velocity) were quantified using Protokinetics Movement Analysis Software. Spatiotemporal pull-test parameters were compared to standard PD measures using linear regression and correlation coefficients. Repeated measures analysis was used to determine group differences in pull-test parameters. In a subset of participants repeated testing was performed and Bland-Altman plots were used to determine reproducibility of the pull-test parameters.

RESULT

Step-back-distance and step-back-velocity were inversely related to motor UPDRS and freezing of gait questionnaire scores. PD participants had shorter step-back-distance than controls adjusted for age and sex. Repeat assessments in 16 participants, on average 0.7 years apart, showed good agreement on most of the quantified parameters.

SIGNIFICANCE

The backward stepping response in PD participants was quantifiable, reproducible, and related to disease severity and could be used to quantify progression towards postural instability in early-PD.

Anticipatory Postural Adjustments and Compensatory Postural Responses to Multidirectional Perturbations-Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease

BACKGROUND

Postural instability is one of the most restricting motor symptoms for patients with Parkinson's disease (PD). While medication therapy only shows minor effects, it is still unclear whether medication in conjunction with deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves postural stability. Hence, the aim of this study was to investigate whether PD patients treated with medication in conjunction with STN-DBS have superior postural control compared to patients treated with medication alone.

METHODS

Three study groups were tested: PD patients on medication (PD-MED), PD patients on medication and on STN-DBS (PD-MED-DBS), and healthy elderly subjects (HS) as a reference. Postural performance, including anticipatory postural adjustments (APA) prior to perturbation onset and compensatory postural responses (CPR) following multidirectional horizontal perturbations, was analyzed using force plate and electromyography data.

RESULTS

Regardless of the treatment condition, both patient groups showed inadequate APA and CPR with early and pronounced antagonistic muscle co-contractions compared to healthy elderly subjects. Comparing the treatment conditions, study group PD-MED-DBS only showed minor advantages over group PD-MED. In particular, group PD-MED-DBS showed faster postural reflexes and tended to have more physiological co-contraction ratios.

CONCLUSION

medication in conjunction with STN-DBS may have positive effects on the timing and amplitude of postural control.

Dopamine replacement therapy normalizes reactive step length to postural perturbations in Parkinson's disease

BACKGROUND

Postural instability is one of the most disabling motor symptoms of Parkinson's disease (PD) given its association with falls and loss of independence. Previous studies have assessed biomechanical measures of reactive stepping in response to perturbations, showing that individuals with PD exhibit inadequate postural responses to regain balance.

RESEARCH QUESTION

Does dopamine replacement therapy normalize step length in response to balance perturbations?

METHODS

In this study, we estimated reactive step length, to a postural perturbation, retrospectively from a dataset of frontal plane video using 2D motion tracking and direct linear transform methods. We compared two perturbation methods: support surface translation and shoulder pull (the clinical standard) in 14 individuals with PD and 13 without PD (on and off medication), with and without partial body weight support (BWS). The primary outcome was the length of the first step taken to regain balance after the perturbation analyzed with mixed effects ANOVA, with post hoc analysis of anteroposterior (AP) and mediolateral (ML) components.

RESULTS

PD OFF medication exhibited shorter reactive step length compared to PD ON and compared to control groups for the surface translation perturbations, but no significant difference was observed for the shoulder pull perturbations.

SIGNIFICANCE

Dopamine replacement therapy affects step length in response to perturbation more robustly for surface translations than for a pull by the shoulders.

Machine Learning and Wearable Sensors for the Early Detection of Balance Disorders in Parkinson's Disease

Dynamic posturography combined with wearable sensors has high sensitivity in recognizing subclinical balance abnormalities in patients with Parkinson's disease (PD). However, this approach is burdened by a high analytical load for motion analysis, potentially limiting a routine application in clinical practice. In this study, we used machine learning to distinguish PD patients from controls, as well as patients under and not under dopaminergic therapy (i.e., ON and OFF states), based on kinematic measures recorded during dynamic posturography through portable sensors. We compared 52 different classifiers derived from Decision Tree, K-Nearest Neighbor, Support Vector Machine and Artificial Neural Network with different kernel functions to automatically analyze reactive postural responses to yaw perturbations recorded through IMUs in 20 PD patients and 15 healthy subjects. To identify the most efficient machine learning algorithm, we applied three threshold-based selection criteria (i.e., accuracy, recall and precision) and one evaluation criterion (i.e., goodness index). Twenty-one out of 52 classifiers passed the three selection criteria based on a threshold of 80%. Among these, only nine classifiers were considered "optimum" in distinguishing PD patients from healthy subjects according to a goodness index ≤ 0.25. The Fine K-Nearest Neighbor was the best-performing algorithm in the automatic classification of PD patients and healthy subjects, irrespective of therapeutic condition. By contrast, none of the classifiers passed the three threshold-based selection criteria in the comparison of patients in ON and OFF states. Overall, machine learning is a suitable solution for the early identification of balance disorders in PD through the automatic analysis of kinematic data from dynamic posturography.

Using kinematics to re-define the pull test as a quantitative biomarker of the postural response in normal pressure hydrocephalus patients

Quantitative biomarkers are needed for the diagnosis, monitoring and therapeutic assessment of postural instability in movement disorder patients. The goal of this study was to create a practical, objective measure of postural instability using kinematic measurements of the pull test. Twenty-one patients with normal pressure hydrocephalus and 20 age-matched control subjects were fitted with inertial measurement units and underwent 10-20 pull tests of varying intensities performed by a trained clinician. Kinematic data were extracted for each pull test and aggregated. Patients participated in 103 sessions for a total of 1555 trials while controls participated in 20 sessions for a total of 299 trials. Patients were separated into groups by MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) pull test score. The center of mass velocity profile easily distinguished between patient groups such that score increases correlated with decreases in peak velocity and later peak velocity onset. All patients except those scored as "3" demonstrated an increase in step length and decrease in reaction time with increasing pull intensity. Groups were distinguished by differences in the relationship of step length to pull intensity (slope) and their overall step length or reaction time regardless of pull intensity (y-intercept). NPH patients scored as "normal" on the MDS-UPDRS scale were kinematically indistinguishable from age-matched control subjects during a standardized perturbation, but could be distinguished from controls by their response to a range of pull intensities. An instrumented, purposefully varied pull test produces kinematic metrics useful for distinguishing clinically meaningful differences within hydrocephalus patients as well as distinguishing these patients from healthy, control subjects.

Predicting Axial Impairment in Parkinson's Disease through a Single Inertial Sensor

Background: Current telemedicine approaches lack standardised procedures for the remote assessment of axial impairment in Parkinson’s disease (PD). Unobtrusive wearable sensors may be a feasible tool to provide clinicians with practical medical indices reflecting axial dysfunction in PD. This study aims to predict the postural instability/gait difficulty (PIGD) score in PD patients by monitoring gait through a single inertial measurement unit (IMU) and machine-learning algorithms. Methods: Thirty-one PD patients underwent a 7-m timed-up-and-go test while monitored through an IMU placed on the thigh, both under (ON) and not under (OFF) dopaminergic therapy. After pre-processing procedures and feature selection, a support vector regression model was implemented to predict PIGD scores and to investigate the impact of L-Dopa and freezing of gait (FOG) on regression models. Results: Specific time- and frequency-domain features correlated with PIGD scores. After optimizing the dimensionality reduction methods and the model parameters, regression algorithms demonstrated different performance in the PIGD prediction in patients OFF and ON therapy (r = 0.79 and 0.75 and RMSE = 0.19 and 0.20, respectively). Similarly, regression models showed different performances in the PIGD prediction, in patients with FOG, ON and OFF therapy (r = 0.71 and RMSE = 0.27; r = 0.83 and RMSE = 0.22, respectively) and in those without FOG, ON and OFF therapy (r = 0.85 and RMSE = 0.19; r = 0.79 and RMSE = 0.21, respectively). Conclusions: Optimized support vector regression models have high feasibility in predicting PIGD scores in PD. L-Dopa and FOG affect regression model performances. Overall, a single inertial sensor may help to remotely assess axial motor impairment in PD patients.

Temporal dynamics of cortical activity and postural control in response to the first levodopa dose of the day in people with Parkinson's disease

BACKGROUND

Our understanding of how balance control responds to levodopa over the course of a single day in people with Parkinson's disease (PD) is limited with the majority of studies focused on isolated comparisons of ON vs. OFF levodopa medication.

OBJECTIVE

To evaluate the temporal dynamics of postural control following the first levodopa dose of the day during a challenging standing task in a group of people with PD.

METHODS

Changes in postural control were evaluated by monitoring cortical activity (covering frontal, motor, parietal and occipital areas), body sway parameters (force platform), and lower limb muscle activity (tibialis anterior and gastrocnemius medialis) in 15 individuals with PD during a semi-tandem standing task. Participants were assessed during two 60 second trials every 30 minutes (ON-30 ON-60 etc.) for 3 hours after the first matinal dose (ON-180).

RESULTS

Compared to when tested OFF-medication, cortical activity was increased across all four regions from ON-60 to ON-120 with early increases in alpha and beta band activity observed at ON-30. Levodopa was associated with increased gastrocnemius medialis activity (ON-30 to ON-120) and ankle co-contraction (ON-60 to ON-120). Changes in body sway outcomes (particularly in the anterior-posterior direction) were evident from ON-60 to ON-120.

CONCLUSIONS

Our results reveal a 60-minute window within which postural control outcomes may be obtained that are different compared to OFF-state and remain stable (from 60-minutes to 120-minutes after levodopa intake). Identifying a window of opportunity for measurement when individuals are optimally medicated is important for observations in a clinical and research setting.

Effect of LSVT® BIG on standing balance in a Parkinson's patient: A case report

BACKGROUND AND PURPOSE

There are no reports regarding the effect of Lee Silverman Voice Treatment® BIG (LSVT® BIG) on standing balance ability evaluated using quantitative assessment. This case report aimed to describe and evaluate the influence of LSVT® BIG on the center of pressure (COP) trajectory in a patient with Parkinson's disease (PD).

METHODS

Although this paper focused on one case, quantitative assessment on the effect of LSVT® BIG on standing balance ability was performed. A 67-year-old woman patient diagnosed with PD at age 59, with a Hoehn and Yahr stage 3 disability severity, underwent a 4-weeks supervised LSVT® BIG program. The total distances of the COP trajectory (two-dimensional [2D] horizontal plane, anterior-posterior [AP] direction, and medial-lateral [ML] direction), and the mean COP velocity for each direction, postural stability, and posture subsections of the Unified Parkinson's Disease Rating Scale (UPDRS) Part 3 were assessed at pre- and post-intervention.

RESULTS

The total distances of the COP trajectory, mean COP velocities, and scores of postural stability and posture subsections of the UPDRS Part 3 improved after intervention (from 124.6 to 76.6 cm [2D], 89.4 to 57.7 cm [AP], 77.4 to 38.5 cm [ML]; 4.0 to 2.6 cm/s [2D], 3.0 to 1.9 cm/s [AP], 2.6 to 1.3 cm/s [ML]; and 3 to 0, and 3 to 2, respectively).

DISCUSSION

LSVT® BIG may be effective in improving the total distance of the COP trajectory, mean COP velocity, and both postural stability and posture subsections of the UPDRS Part 3 in the presented PD case.

Early balance impairment in Parkinson's Disease: Evidence from Robot-assisted axial rotations

OBJECTIVE

Early postural instability (PI) is a red flag for the diagnosis of Parkinson's disease (PD). Several patients, however, fall within the first three years of disease, particularly when turning. We investigated whether PD patients, without clinically overt PI, manifest abnormal reactive postural responses to ecological perturbations resembling turning.

METHODS

Fifteen healthy subjects and 20 patients without clinically overt PI, under and not under L-Dopa, underwent dynamic posturography during axial rotations around the longitudinal axis, provided by a robotic mechatronic platform. We measured reactive postural responses, including body displacement and reciprocal movements of the head, trunk, and pelvis, by using a network of three wearable inertial sensors.

RESULTS

Patients showed higher body displacement of the head, trunk and pelvis, and lower joint movements at the lumbo-sacral junction than controls. Conversely, movements at the cranio-cervical junction were normal in PD. L-Dopa left reactive postural responses unchanged.

CONCLUSIONS

Patients with PD without clinically overt PI manifest abnormal reactive postural responses to axial rotations, unresponsive to L-Dopa. The biomechanical model resulting from our experimental approach supports novel pathophysiological hypotheses of abnormal axial rotations in PD.

SIGNIFICANCE

PD patients without clinically overt PI present subclinical balance impairment during axial rotations, unresponsive to L-Dopa.

Remote smartphone gait monitoring and fall prediction in Parkinson's disease during the COVID-19 lockdown

Background

Falls could be serious events in Parkinson’s disease (PD). Patient remote monitoring strategies are on the raise and may be an additional aid in identifying patients who are at risk of falling. The aim of the study was to evaluate if balance and timed-up-and-go data obtained by a smartphone application during COVID-19 lockdown were able to predict falls in PD patients.

Methods

A cohort of PD patients were monitored for 4 weeks during the COVID-19 lockdown with an application measuring static balance and timed-up-and-go test. The main outcome was the occurrence of falls (UPDRS-II item 13) during the observation period.

Results

Thirty-three patients completed the study, and 4 (12%) reported falls in the observation period. The rate of falls was reduced with respect to patient previous falls history (24%). The stand-up time and the mediolateral sway, acquired through the application, differed between “fallers” and “non-fallers” and related to the occurrence of new falls (OR 1.7 and 1.6 respectively, p < 0.05), together with previous falling (OR 7.5, p < 0.01). In a multivariate model, the stand-up time and the history of falling independently related to the outcome (p < 0.01).

Conclusions

Our study provides new data on falls in Parkinson’s disease during the lockdown. The reduction of falling events and the relationship with the stand-up time might suggest that a different quality of falls occurs when patient is forced to stay home — hence, clinicians should point their attention also on monitoring patients’ sit-to-stand body transition other than more acknowledged features based on step quality.

Associations Between Amantadine Usage, Gait, and Cognition in PSP: A post-hoc Analysis of the Davunetide Trial

Introduction: Amantadine anecdotally improves gait in progressive supranuclear palsy (PSP) but definitive data is lacking. We investigated associations between amantadine usage, gait, cognition, and activities of daily living in 310 subjects with PSP using data from the davunetide trial.

Method: We compared baseline demographics, PSP Rating Scale (PSPRS), Repeat Battery for the Assessment of Neuropsychological Status (RBANS), and Schwab and England Activities of Daily Living (SEADL) scores between subjects taking vs. not taking amantadine using chi-square tests for categorical variables and independent sample t-tests for continuous variables. Using the general linear model (GLM), we tested whether group status predicted total PSPRS, PSPRS-gait and midline, total RBANS, RBANS-attention, and SEADL before and after the 52-weeks follow-up.

Results: Subjects taking vs. not taking amantadine were similar at baseline, except subjects taking amantadine had a higher Clinical Global Impression (CGI) Score (p = 0.01). However, the CGI change score did not differ between groups at week 52 (p = 0.10). Using GLM models (controlling for covariates), we found that subjects taking vs. not taking amantadine did not significantly predict total PSPRS, PSPRS-gait and midline, total RBANS, RBANS-attention, or SEADL at baseline, week 52, or the change score between baseline and week 52.

Discussion: This post-hoc analysis of the davunetide trial did not find an association between amantadine and gait or cognitive measures in PSP, but was not powered to find such a difference. Future studies should still examine amantadine for symptomatic benefit in multiple PSP subtypes.

Dopamine-mediated improvements in dynamic balance control in Parkinson's disease

BACKGROUND

Impaired dynamic balance control increases fall risk and contributes to immobility in individuals with Parkinson's disease (PD). It is unclear whether higher-level neural processes of the central nervous system contribute to impaired balance control.

RESEARCH QUESTION

Are dopamine-mediated neural processes of the higher-level central nervous system important for dynamic balance control in PD?

METHODS

21 individuals with idiopathic PD performed step-threshold assessments before and after self-administered dopaminergic medication. Individuals withstood progressively larger postural perturbations, during which they were explicitly instructed to avoid stepping to recover balance. The perturbation magnitude which elicited stepping responses on four consecutive trials is referred to as the step-threshold. Dynamic balance control was quantified as the minimum margin of stability captured during the largest sub-threshold trial (i.e., the maximum amount of compensated postural instability during the task). We compared dynamic balance between off and on medication states and between individuals who exhibited motor adaptive behavior and those who did not.

RESULTS

Dopaminergic medications significantly improved step-thresholds and allowed individuals to withstand greater amounts of instability without stepping, indicating dopamine-mediated improvement in dynamic balance control. Individuals who displayed behavioral evidence for higher-level neural processes (motor adaptation across repeated perturbations) displayed superior dynamic balance control versus those who did not. Anteroposterior ground reaction forces captured during perturbations suggest that individuals alter force profiles to avoid stepping at ∼200 ms after perturbation onset-a latency consistent with a transcortical process.

SIGNIFICANCE

Combined, our results indicate that higher-level, dopamine-mediated neural processes are responsible for dynamic balance control in PD. We hypothesize that this process incorporates sensorimotor integration, motor response initiation/inhibition, and goal- and reward-driven behaviors. Interventions targeting these processes may improve dynamic postural control in individuals with PD.

Fifteen Years of Wireless Sensors for Balance Assessment in Neurological Disorders

Balance impairment is a major mechanism behind falling along with environmental hazards. Under physiological conditions, ageing leads to a progressive decline in balance control per se. Moreover, various neurological disorders further increase the risk of falls by deteriorating specific nervous system functions contributing to balance. Over the last 15 years, significant advancements in technology have provided wearable solutions for balance evaluation and the management of postural instability in patients with neurological disorders. This narrative review aims to address the topic of balance and wireless sensors in several neurological disorders, including Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, stroke, and other neurodegenerative and acute clinical syndromes. The review discusses the physiological and pathophysiological bases of balance in neurological disorders as well as the traditional and innovative instruments currently available for balance assessment. The technical and clinical perspectives of wearable technologies, as well as current challenges in the field of teleneurology, are also examined.

Clinical experience of comprehensive treatment on the balance function of Parkinson's disease

To investigate the effect of multi-disciplinary teamwork on balance performance of Parkinson's disease (PD).Sixteen primary Parkinson's disease patients (8 male, 8 female) treated with bilateral subthalamic nucleus deep brain stimulation (STN-DBS) were included in the study. The median age of patients was 60.5 years; all patients were in the Hoehn&Yahr (H&Y) 3 stage; the median PD duration of the disease was 9 years. For each patient, multi-disciplinary teamwork treatment including DBS, medication, physical therapy and psychotherapy proceeded. levodopa equivalent daily dose (LEDD, mg/day), life quality (PDQ-39), Motor disability (MDS-UPDRSIII) and balance performance (MDS-UPDRS 3.12, Berg Balance Scale BBS, Limits of Stability LoS) were assessed in different time and status respectively: preoperation (Med-off, Med-on), postoperation (Stim-Off/Med-Off, Stim-On/Med-Off, Stim-On/Med-On), 6 months postoperation (Stim-On/ Med-Off, Stim-On/Med-On) and 12 months postoperation (Stim-On/Med-Off, Stim-On/Med-On).The LEDD, life quality (PDQ-39) continued to improve during the follow-up, statistical difference were found in both 6 months postoperation and 12 months postoperation compared with preoperation. The Motor disability (MDS-UPDRSIII), balance performance (MDS-UPDRS 3.12, BBS) and the LoS (target acquisition percentage, trunk swing angle standard deviation, time) showed significant improvement in Stim-On/med-Off 6 months postoperation and 12 months postoperation separately compared with Med-Off preoperation.Multi-disciplinary teamwork for PD patients with STN-DBS could improve balance performance.

Linearity and repeatability of postural responses in relation to peak force and impulse of manually delivered perturbations: a preliminary study

PURPOSE

Postural reactions (PR) of standing subjects have been mostly investigated in response to platform displacements or body perturbations of fixed magnitude. The objective of this study was to investigate the relationship between PR and the peak force and impulse of the perturbation.

METHODS

In ten healthy young men, standing balance was challenged by anteriorly directed perturbations (peak force: 20-60 N) delivered to the back, at the lumbar (L) or inter-scapular (IS) level, by means of a manual perturbator equipped with a force sensor. Postural reactions as expressed by the displacement of the center of pressure (CoP) were recorded using a force platform. Two sets of 20 randomly ordered perturbations (10 to each site) were delivered in two separate testing sessions.

RESULTS

The magnitude of CoP response (∆CoP) was better correlated with the impulse (I) than with the peak force of the perturbation. The normalized response, ∆CoP_n = ∆CoP/I, exhibited good reliability (ICCs of 0.93 for IS and 0.82 for L), was higher with IS than with L perturbations (p < 0.01), and was significantly correlated with the latency of CoP response: r = 0.69 and 0.71 for IS and L, respectively.

CONCLUSION

These preliminary findings support the concept that manually delivered perturbations can be used to reliably assess individual PR and that ∆CoP_n may effectively express a relevant aspect of postural control.

Visual field motion during a body pull affects compensatory standing and stepping responses

KEY POINTS

It is unclear whether the visual input that accompanies a perturbation of a standing person can affect whether a recovery step is taken. Visual motion speeds were manipulated during unexpected forward and backward shoulder pulls. Visual motion that appeared slower than actual body motion reduced the initial in-place resistance to the perturbation. As a result of the modulation of the in-place response, less pull force was needed to trigger a step when visual velocity appeared slower than normal. The visuomotor postural response occurred earlier and was larger when the full-field visual input was paired with a mechanical perturbation.

ABSTRACT

The present study aimed to determine how visual motion evoked by an upper body perturbation during standing affects compensatory postural responses. This was investigated by rotating the visual field forwards or backwards about the ankle, time-locked to a forwards or backwards shoulder pull. Kinematic, kinetic and electromyographic responses were recorded to a range of pull forces over 160 trials in 12 healthy adults (mean ± SD = 31 ± 5.8 years). Stepping threshold forces and in-place postural responses were compared between conditions. When the visual field moved in the same direction as the pull, so that the apparent velocity of the body was reduced (SLOW condition), the pull-force required to induce a step was less than when the visual field either rotated in the opposite direction (FAST) or was unaltered (NATURAL). For in-place responses, the body was displaced further in the direction of the pull in the SLOW condition. This was the result of a reduction in the resistive force from lower leg muscles 130 ms after the visual motion onset. In trials with no pull, the visual motion induced postural responses that were later (290 ms) and had smaller amplitudes compared to when visual motion is paired with an unexpected perturbation of the body. The results suggest that the apparent speed of the visual environment during a perturbation does influence whether a compensatory step is taken, not via a direct effect on the decision to step but by modulating the initial in-place response.

Early Postural Instability in Parkinson's Disease: A Biomechanical Analysis of the Pull Test

Postural instability in Parkinson's disease (PD) is commonly assessed by the pull test. This clinical test may be biased by the variability of the pull force applied. Our objective was to study the postural responses elicited by reproducible pull forces in healthy subjects and PD patients at different stages of the disease. We performed a multimodal approach that included a systematic analysis of the pull force needed to reach the backward limit of stability (FBLoS) assessed by mechanically produced forces, the displacements of the center of pressure (CoP) recorded on a force platform, and the latencies and patterns of activation of the stabilizing muscles. Comparisons between groups were performed by univariate and multivariate statistical analyses. Sixty-four healthy subjects and 32 PD patients, 22 Hoehn-Yahr (H-Y) stages I-II and 10 H-Y stage III, were studied. In healthy subjects, FBLoS decreased with aging and was lower in females. Mean (SD) FBLoS was 98.1 (48.9) Newtons (N) in healthy subjects, 70.5 (39.8) N in PD patients H-Y stages I-II, and 37.7 (18.9) N in PD patients H-Y stage III. Compared to healthy subjects and when adjusted for age and gender, PD patients H-Y stages I-II exhibited the following: (a) a reduced FBLoS; (b) larger CoP displacements and higher velocities for the same applied force; and (c) combined ankle and hip strategies elicited by less intense pull forces. All of these abnormalities were more pronounced in H-Y stage III PD patients compared to H-Y stages I-II PD patients. In conclusion, patients in the early stages of PD already exhibit a degree of postural instability due to inefficient postural adjustments, and they can more easily be destabilized by small perturbations than healthy subjects. This balance impairment becomes more pronounced in more advanced PD. In the pull test, pull force to step back should be a variable to consider when testing balance in clinical practice.

Effects of Fatigue on Balance in Individuals With Parkinson Disease: Influence of Medication and Brain-Derived Neurotrophic Factor Genotype

BACKGROUND AND PURPOSE

Because falls can have deleterious consequences, it is important to understand the influence of fatigue and medications on balance in persons with Parkinson disease (PD). Thus, the purpose of this study was to investigate the effects of fatigue on balance in individuals with PD. Because brain-derived neurotrophic factor (BDNF) has been shown to be related to motor performance, we also explored its role.

METHODS

A total of 27 individuals (age = 65.4 ± 8.1 years; males = 14, females = 13) with neurologist-diagnosed PD with 13 genotyped for BDNF as Val66Val, 11 as Val66Met, 2 as Met66Met (1 refused). Participants were tested both on and off medication, 1 week apart. On both days, they completed a pre- and posttest separated by a fatiguing condition. Factorial analyses of variance were performed for the following balance domains: (1) anticipatory postural responses; (2) adaptive postural responses; (3) dynamic balance; (4) sensory orientation; and (5) gait kinematics. For BDNF, t-tests were conducted comparing genotype for the pre-post difference scores in both the on and off medication states.

RESULTS

There were no interactions between time (pre- and postintervention) and medication for any of the domains (Ps ≥ 0.187). Participants with BDNF Met alleles were not significantly different from Val66Val participants in balance (Ps ≥ 0.111) and response to a fatiguing condition (Ps ≥ 0.070).

DISCUSSION AND CONCLUSIONS

Fatigue does not appear to have a detrimental effect on balance, and there was not a differential effect of medication in individuals with PD. These results also indicate that participants with a BDNF Met allele did not have a greater decay in function after a fatiguing condition.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A196).

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.

Neurophysiological analysis of the clinical pull test

Postural reflexes are impaired in conditions such as Parkinson's disease, leading to difficulty walking and falls. In clinical practice, postural responses are assessed using the "pull test," where an examiner tugs the prewarned standing patient backward at the shoulders and grades the response. However, validity of the pull test is debated, with issues including scaling and variability in administration and interpretation. It is unclear whether to assess the first trial or only subsequent repeated trials. The ecological relevance of a forewarned backward challenge is also debated. We therefore developed an instrumented version of the pull test to characterize responses and clarify how the test should be performed and interpreted. In 33 healthy participants, "pulls" were manually administered and pull force measured. Trunk and step responses were assessed with motion tracking. We probed for the StartReact phenomenon (where preprepared responses are released early by a startling stimulus) by delivering concurrent normal or "startling" auditory stimuli. We found that the first pull triggers a different response, including a larger step size suggesting more destabilization. This is consistent with "first trial effects," reported by platform translation studies, where movement execution appears confounded by startle reflex-like activity. Thus, first pull test trials have clinical relevance and should not be discarded as practice. Supportive of ecological relevance, responses to repeated pulls exhibited StartReact, as previously reported with a variety of other postural challenges, including those delivered with unexpected timing and direction. Examiner pull force significantly affected the postural response, particularly the size of stepping. NEW & NOTEWORTHY We characterized postural responses elicited by the clinical "pull test" using instrumentation. The first pull triggers a different response, including a larger step size suggesting more destabilization. Thus, first trials likely have important clinical and ecological relevance and should not be discarded as practice. Responses to repeated pulls can be accelerated with a startling stimulus, as reported with a variety of other challenges. Examiner pull force was a significant factor influencing the postural response.

Maximum Step Length Test Performance in People With Parkinson Disease: A Cross-sectional Study

BACKGROUND AND PURPOSE

The Maximum Step Length Test (MSLT), a measure of one's capacity to produce a large step, has been studied in older adults, but not in people with Parkinson disease (PD). We characterized performance and construct validity of the MSLT in PD.

METHODS

Forty participants (mean age: 65.12 ± 8.20 years; 45% female) with idiopathic PD completed the MSLT while "OFF" and "ON" anti-PD medication. Construct validity was investigated by examining relationships between MSLT and measures of motor performance. The following measures were collected: Mini-Balance Evaluation Systems Test (Mini-BESTest), Activities-specific Balance Confidence (ABC) scale, gait velocity, 6-minute walk test (6MWT), Movement Disorder Society-Unified Parkinson Disease Rating Scale subsection III (MDS-UPDRS III), and Timed Up and Go (TUG) test. A repeated-measures analysis of variance tested for main effects of medication and stepping direction and the interaction between the 2. Pearson or Spearman correlations were used to assess the relationships between MSLT and motor performance measures (α = 0.05).

RESULTS

Regardless of medication status, participants stepped further in the forward direction compared with the backward and lateral directions (P < 0.001). Participants increased MSLT performance when ON-medication compared with OFF-medication (P = 0.004). Regardless of medication status, MSLT was moderately to strongly related to Mini-BESTest, TUG, and 6MWT.

DISCUSSION AND CONCLUSIONS

People with PD stepped furthest in the forward direction when performing the MSLT. Increased MSLT performance was observed in the ON-medication state compared with OFF-medication; however, the small increase may not be clinically meaningful. Given the relationships between the MSLT and the Mini-BESTest, 6MWT, and TUG, MSLT performance appears to be associated with balance and gait hypokinesia in people with PD.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A186).

Abnormal gait pattern emerges during curved trajectories in high-functioning Parkinsonian patients walking in line at normal speed

Background

Several patients with Parkinson´s disease (PD) can walk normally along straight trajectories, and impairment in their stride length and cadence may not be easily discernible. Do obvious abnormalities occur in these high-functioning patients when more challenging trajectories are travelled, such as circular paths, which normally implicate a graded modulation in the duration of the interlimb gait cycle phases?

Methods

We compared a cohort of well-treated mildly to moderately affected PD patients to a group of age-matched healthy subjects (HS), by deliberately including HS spontaneously walking at the same speed of the patients with PD. All participants performed, in random order: linear and circular walking (clockwise and counter-clockwise) at self-selected speed. By means of pressure-sensitive insoles, we recorded walking speed, cadence, duration of single support, double support, swing phase, and stride time. Stride length-cadence relationships were built for linear and curved walking. Stride-to-stride variability of temporal gait parameters was also estimated.

Results

Walking speed, cadence or stride length were not different between PD and HS during linear walking. Speed, cadence and stride length diminished during curved walking in both groups, stride length more in PD than HS. In PD compared to HS, the stride length-cadence relationship was altered during curved walking. Duration of the double-support phase was also increased during curved walking, as was variability of the single support, swing phase and double support phase.

Conclusion

The spatio-temporal gait pattern and variability are significantly modified in well-treated, high-functioning patients with PD walking along circular trajectories, even when they exhibit no changes in speed in straight-line walking. The increased variability of the gait phases during curved walking is an identifying characteristic of PD. We discuss our findings in term of interplay between control of balance and of locomotor progression: the former is challenged by curved trajectories even in high-functioning patients, while the latter may not be critically affected.

Instrumental or Physical-Exercise Rehabilitation of Balance Improves Both Balance and Gait in Parkinson's Disease

We hypothesised that rehabilitation specifically addressing balance in Parkinson's disease patients might improve not only balance but locomotion as well. Two balance-training protocols (standing on a moving platform and traditional balance exercises) were assessed by assigning patients to two groups (Platform, n = 15, and Exercises, n = 17). The platform moved periodically in the anteroposterior, laterolateral, and oblique direction, with and without vision in different trials. Balance exercises were based on the Otago Exercise Program. Both platform and exercise sessions were administered from easy to difficult. Outcome measures were (a) balancing behaviour, assessed by both Index of Stability (IS) on platform and Mini-BESTest, and (b) gait, assessed by both baropodometry and Timed Up and Go (TUG) test. Falls Efficacy Scale-International (FES-I) and Parkinson's Disease Questionnaire (PDQ-8) were administered. Both groups exhibited better balance control, as assessed both by IS and by Mini-BESTest. Gait speed at baropodometry also improved in both groups, while TUG was less sensitive to improvement. Scores of FES-I and PDQ-8 showed a marginal improvement. A four-week treatment featuring no gait training but focused on challenging balance tasks produces considerable gait enhancement in mildly to moderately affected patients. Walking problems in PD depend on postural instability and are successfully relieved by appropriate balance rehabilitation. This trial is registered with ClinicalTrials.gov NCT03314597.

Parkinson disease

Parkinson disease (PD) is a complex, multisystem disorder with both neurologic and systemic nonmotor manifestations. It is neurodegenerative in nature in which disordered balance, gait, and falls are universal problems that can be present at initial diagnosis, and which progress over time. Freezing of gait is a particularly debilitating feature of PD that becomes more prevalent over time with disease progression, being present in approximately 7% after 2 years of disease and 28% after 5 years. Approximately 60% of people with PD fall each year, with around 70% of fallers falling recurrently, and some recurrent fallers falling multiple times per week. Many risk factors for falls in people with PD have been identified; these include a history of falls, freezing of gait, and abnormalities in measures of balance, leg muscle strength, mobility, cognition, and fear of falling. Therapies for improving physical function and mobility include levodopa, cholinesterase inhibitors, methylphenidate, deep-brain stimulation, cuing for freezing of gait, and exercise. This chapter reviews the clinical, pathologic, and physiologic correlates of gait disturbance and falls in PD, as well as the evidence for medical and nonmedical interventions.