Gait variability in Parkinson's disease: an indicator of non-dopaminergic contributors to gait dysfunction?

Limited Effect of Dopaminergic Medication on Straight Walking and Turning in Early-to-Moderate Parkinson's Disease during Single and Dual Tasking

Background

In Parkinson’s disease (PD), the effects of dopaminergic medication on straight walking and turning were mainly investigated under single tasking (ST) conditions. However, multitasking situations are considered more daily relevant.

Methods

Thirty-nine early-to-moderate PD patients performed the following standardized ST and dual tasks as fast as possible for 1 min during On- and Off-medication while wearing inertial sensors: straight walking and turning, checking boxes, and subtracting serial 7s. Quantitative gait parameters as well as velocity of the secondary tasks were analyzed.

Results

The following parameters improved significantly in On-medication during ST: gait velocity during straight walking (p = 0.03); step duration (p = 0.048) and peak velocity (p = 0.04) during turning; velocity of checking boxes during ST (p = 0.04) and DT (p = 0.04). Velocity of checking boxes was the only parameter that also improved during DT.

Conclusion

These results suggest that dopaminergic medication does not relevantly influence straight walking and turning in early-to-moderate PD during DT.

Dual-task-related neural connectivity changes in patients with Parkinson' disease

BACKGROUND AND OBJECTIVES

Dual-task (DT) gait impairment in people with Parkinson's disease (PD) and specifically in those with freezing of gait (FOG), reflects attentional dependency of movement. This study aimed to elucidate resting-state brain connectivity alterations related to DT gait abnormalities in PD with and without FOG.

METHODS

PD patients (n=73) and healthy age-matched controls (n=20) underwent DT gait analysis and resting-state functional Magnetic Resonance Imaging (rs-MRI) while 'off' medication. Patients were classified as freezer (n=13) or non-freezer (n=60). Functional connectivity (FC) alterations between PD and controls and between patient subgroups were assessed in regions of interest (ROIs) within the fronto-parietal and motor network.

RESULTS

PD had longer stance times, shorter swing times and more step length asymmetry during DT gait and needed more time and steps during DT turning compared to controls. Additionally, freezers showed similar impairments and longer double support times compared to non-freezers during DT gait. PD demonstrated hyper-connectivity between the inferior parietal lobule and premotor cortex (PMC) and between the cerebellum and the PMC and M1. FOG-specific hypo-connectivity within the striatum and between the caudate and superior temporal lobe and hyper-connectivity between the dorsal putamen and precuneus was correlated with worse DT performance.

CONCLUSION

PD showed FC alterations in DT-related networks, which were not correlated to DT performance. However, FOG-specific FC alterations in DT-related regions involving the precuneus and striatum were correlated to worse DT performance, suggesting that the balance between cognitive and motor networks is altered.

Effect of augmenting cholinergic function on gait and balance

Background

Impaired mobility and falls are clinically important complications of Parkinson’s disease (PD) and a major detractor from quality of life for which there are limited therapies. Pathological, neuroimaging and clinical evidence suggest that degeneration of cholinergic systems may contribute to impairments of balance and gait in PD. The proposed trial will examine the effects of augmentation of the cholinergic system on balance and gait.

Design

The study is a single-site, proof of concept, randomized, double-blind, cross-over trial in patients with PD. Each treatment period will be 6 weeks with a 6-week washout between treatments for a total of 18 weeks for each subject. Donepezil in 2.5 mg capsules or identical appearing placebo capsules will be increased from two per day (5 mg) to four capsules (10 mg) after 3 weeks, if tolerated. Subjects will have idiopathic Parkinson’s disease, Hoehn and Yahr stages 2 to 4. We anticipate recruiting up to 100 subjects for screening to have 54 enrolled and 44 subjects complete both phases of treatment. Dropouts will be replaced. As this is a crossover trial, all subjects will be exposed to both donepezil and to placebo. The primary outcome measures will be the root mean square of the mediolateral sway when standing and the variability of the stride duration when walking for two minutes. Secondary outcomes will be the computerized Attention Network Test to examine three domains of attention and the Short-latency Afferent Inhibition (SAI), a physiological marker obtained with transcranial magnetic stimulation as a putative marker of cholinergic activity.

Discussion

The results of this study will be the most direct test of the hypothesized role of cholinergic neurotransmission in gait and balance. The study is exploratory because we do not know whether donepezil will affect gait, balance or attention, nor which measures of gait, balance or attention will be sensitive to drug manipulation. We hypothesize that change in cholinergic activity, as measured with SAI, will predict the relative effectiveness of donepezil on gait and balance. Our immediate goal is to determine the potential utility of cholinergic manipulation as a strategy for preventing or treating balance and gait dysfunction in PD. The findings of this trial are intended to lead to more sharply focused questions about the role of cholinergic neurotransmission in balance and gait and eventually to Phase II B trials to determine clinical utility of cholinergic manipulation to prevent falls and improve mobility.

Trial registration

This trial is registered at clinical trials.gov (NCT02206620).

Dopaminergic modulation of arm swing during gait among Parkinson's disease patients

BACKGROUND

Reduced arm swing amplitude, symmetry, and coordination during gait have been reported in Parkinson's disease (PD), but the relationship between dopaminergic depletion and these upper limb gait changes remains unclear.

OBJECTIVE

We aimed to investigate the effects of dopaminergic drugs on arm swing velocity, symmetry, and coordination in PD.

METHODS

Forearm angular velocity was recorded in 16 PD and 17 control subjects (Controls) during free walking trials. Angular velocity amplitude of each arm, arm swing asymmetry, and maximum cross-correlation were compared between control and PD groups, and between OFF- and ON-medication states among PD subjects.

RESULTS

Compared to Controls, PD subjects in the OFF-medication state exhibited lower angular velocity amplitude of the slower- (p = 0.0018), but not faster- (p = 0.2801) swinging arm. In addition, PD subjects demonstrated increased arm swing asymmetry (p = 0.0046) and lower maximum cross-correlation (p = 0.0026). Following dopaminergic treatment, angular velocity amplitude increased in the slower- (p = 0.0182), but not faster- (p = 0.2312) swinging arm among PD subjects. Furthermore, arm swing asymmetry decreased (p = 0.0386), whereas maximum cross-correlation showed no change (p = 0.7436). Pre-drug angular velocity amplitude of the slower-swinging arm was correlated inversely with the change in arm swing asymmetry (R = -0.73824, p = 0.0011).

CONCLUSIONS

This study provides quantitative evidence that reduced arm swing and symmetry in PD can be modulated by dopaminergic replacement. The lack of modulations of bilateral arm coordination suggests that additional neurotransmitters may also be involved in arm swing changes in PD. Further studies are warranted to investigate the longitudinal trajectory of arm swing dynamics throughout PD progression.

A Validated Smartphone-Based Assessment of Gait and Gait Variability in Parkinson's Disease

Background

A well-established connection exists between increased gait variability and greater fall likelihood in Parkinson’s disease (PD); however, a portable, validated means of quantifying gait variability (and testing the efficacy of any intervention) remains lacking. Furthermore, although rhythmic auditory cueing continues to receive attention as a promising gait therapy for PD, its widespread delivery remains bottlenecked. The present paper describes a smartphone-based mobile application (“SmartMOVE”) to address both needs.

Methods

The accuracy of smartphone-based gait analysis (utilizing the smartphone’s built-in tri-axial accelerometer and gyroscope to calculate successive step times and step lengths) was validated against two heel contact–based measurement devices: heel-mounted footswitch sensors (to capture step times) and an instrumented pressure sensor mat (to capture step lengths). 12 PD patients and 12 age-matched healthy controls walked along a 26-m path during self-paced and metronome-cued conditions, with all three devices recording simultaneously.

Results

Four outcome measures of gait and gait variability were calculated. Mixed-factorial analysis of variance revealed several instances in which between-group differences (e.g., increased gait variability in PD patients relative to healthy controls) yielded medium-to-large effect sizes (eta-squared values), and cueing-mediated changes (e.g., decreased gait variability when PD patients walked with auditory cues) yielded small-to-medium effect sizes—while at the same time, device-related measurement error yielded small-to-negligible effect sizes.

Conclusion

These findings highlight specific opportunities for smartphone-based gait analysis to serve as an alternative to conventional gait analysis methods (e.g., footswitch systems or sensor-embedded walkways), particularly when those methods are cost-prohibitive, cumbersome, or inconvenient.

Predicting Falls in Parkinson Disease: What Is the Value of Instrumented Testing in OFF Medication State?

Background

Falls are a common complication of advancing Parkinson's disease (PD). Although numerous risk factors are known, reliable predictors of future falls are still lacking. The objective of this prospective study was to investigate clinical and instrumented tests of balance and gait in both OFF and ON medication states and to verify their utility in the prediction of future falls in PD patients.

Methods

Forty-five patients with idiopathic PD were examined in defined OFF and ON medication states within one examination day including PD-specific clinical tests, instrumented Timed Up and Go test (iTUG) and computerized dynamic posturography. The same gait and balance tests were performed in 22 control subjects of comparable age and sex. Participants were then followed-up for 6 months using monthly fall diaries and phone calls.

Results

During the follow-up period, 27/45 PD patients and 4/22 control subjects fell one or more times. Previous falls, fear of falling, more severe motor impairment in the OFF state, higher PD stage, more pronounced depressive symptoms, higher daily levodopa dose and stride time variability in the OFF state were significant risk factors for future falls in PD patients. Increased stride time variability in the OFF state in combination with faster walking cadence appears to be the most significant predictor of future falls, superior to clinical predictors.

Conclusion

Incorporating instrumented gait measures into the baseline assessment battery as well as accounting for both OFF and ON medication states might improve future fall prediction in PD patients. However, instrumented testing in the OFF state is not routinely performed in clinical practice and has not been used in the development of fall prevention programs in PD. New assessment methods for daylong monitoring of gait, balance and falls are thus required to more effectively address the risk of falling in PD patients.

Contribution of a Trunk Accelerometer System to the Characterization of Gait in Patients With Mild-to-Moderate Parkinson's Disease

OBJECTIVE

Gait disturbances like shuffling and short steps are obvious at visual observation in patients with advanced Parkinson's disease (PD). However, quantitative methods are increasingly used to evaluate the wide range of gait abnormalities that may occur over the disease course. The goal of this study was to test the ability of a trunk accelerometer system to quantify the effects of PD on several gait features when walking at self-selected speed.

METHODS

We recruited 96 subjects split into three age-matched groups: 32 healthy controls (HC), 32 PD patients at Hoehn and Yahr stage < II (PD-1), and 32 patients at Hoehn and Yahr stage II-III (PD-2). The following outcomes were extracted from the signals of the triaxial accelerometer worn on the lower back: stride length, cadence, regularity index, symmetry index, and mechanical powers yielded in the cranial-caudal, anteroposterior, and medial-lateral directions. Walking speed was measured using a stopwatch.

RESULTS

Besides other gait features, the PD-1 and the PD-2 groups showed significantly reduced stride length normalized to height (p < 0.02) and symmetry index (p < 0.009) in comparison to the HC. Regularity index was the only feature significantly decreased in the PD-2 group as compared with the two other groups (p < 0.01). The clinical relevance of this finding was supported by significant correlations with mobility and gait scales (r is around -0.3; p < 0.05).

CONCLUSION

Gait quantified by a trunk accelerometer may provide clinically useful information for the screening and follow-up of PD patients.

Tai Chi Training may Reduce Dual Task Gait Variability, a Potential Mediator of Fall Risk, in Healthy Older Adults: Cross-Sectional and Randomized Trial Studies

Background

Tai Chi (TC) exercise improves balance and reduces falls in older, health-impaired adults. TC’s impact on dual task (DT) gait parameters predictive of falls, especially in healthy active older adults, however, is unknown.

Purpose

To compare differences in usual and DT gait between long-term TC-expert practitioners and age-/gender-matched TC-naïve adults, and to determine the effects of short-term TC training on gait in healthy, non-sedentary older adults.

Methods

A cross-sectional study compared gait in healthy TC-naïve and TC-expert (24.5 ± 12 years experience) older adults. TC-naïve adults then completed a 6-month, two-arm, wait-list randomized clinical trial of TC training. Gait speed and stride time variability (Coefficient of Variation %) were assessed during 90 s trials of undisturbed and cognitive DT (serial subtractions) conditions.

Results

During DT, gait speed decreased (p < 0.003) and stride time variability increased (p < 0.004) in all groups. Cross-sectional comparisons indicated that stride time variability was lower in the TC-expert vs. TC-naïve group, significantly so during DT (2.11 vs. 2.55%; p = 0.027); by contrast, gait speed during both undisturbed and DT conditions did not differ between groups. Longitudinal analyses of TC-naïve adults randomized to 6 months of TC training or usual care identified improvement in DT gait speed in both groups. A small improvement in DT stride time variability (effect size = 0.2) was estimated with TC training, but no significant differences between groups were observed. Potentially important improvements after TC training could not be excluded in this small study.

Conclusion

In healthy active older adults, positive effects of short- and long-term TC were observed only under cognitively challenging DT conditions and only for stride time variability. DT stride time variability offers a potentially sensitive metric for monitoring TC’s impact on fall risk with healthy older adults.

What can biomarkers tell us about cognition in Parkinson's disease?

Cognitive decline is common in Parkinson's disease (PD), even in the early motor stage, and this non-motor feature impacts quality of life and prognosis tremendously. In this article, we discuss marker candidates for cognitive decline in PD from different angles, including functional and structural imaging techniques, biological fluid markers in cerebrospinal fluid, and blood genetic predictors, as well as gait as a surrogate marker of cognitive decline. Specifically, imaging-based markers of cognitive impairment in PD include cortical atrophy, reduced cortical metabolism, loss of cortical cholinergic and frontal dopaminergic function, as well as an increased cortical amyloid load. Reduced β-amyloid(1-42) in cerebrospinal fluid and lower plasma levels of epidermal growth factor are predictors for cognitive decline in PD. In addition, genetic variation in the apolipoprotein E (APOE), catechol-O-methyltransferase (COMT), microtubule-associated protein tau (MAPT), and glucocerebrosidase (GBA) genes may confer risk for cognitive impairment in PD; and gait disturbance may also indicate an increased risk for dementia. Other marker candidates have been proposed and are discussed. All of the current studies are hampered by gaps in our knowledge about the molecular causes of cognitive decline, which will have to be considered in future biomarker studies.

Cognition and gait show a selective pattern of association dominated by phenotype in incident Parkinson's disease

Reports outlining the association between gait and cognition in Parkinson’s disease (PD) are limited because of methodological issues and a bias toward studying advanced disease. This study examines the association between gait and cognition in 121 early PD who were characterized according to motor phenotype, and 184 healthy older adults. Quantitative gait was captured using a 7 m GAITrite walkway while walking for 2 min under single-task conditions and described by five domains (pace, rhythm, variability, asymmetry, and postural control). Cognitive outcomes were summarized by six domains (attention, working memory, visual memory, executive function, visuospatial function, and global cognition). Partial correlations and multivariate linear regression were used to determine independent associations for all participants and for PD tremor-dominant (TD) and postural instability and gait disorder (PIGD) phenotypes, controlling for age, sex, and premorbid intelligence using the national adult reading test. Cognitive and gait outcomes were significantly worse for PD. Gait, but not cognitive outcomes, was selectively worse for the PIGD phenotype compared with TD. Significant associations emerged for two gait domains for controls (pace and postural control) and four gait domains for PD (pace, rhythm, variability, and postural control). The strongest correlation was for pace and attention for PD and controls. Associations were not significant for participants with the TD phenotype. In early PD, the cognitive correlates of gait are predominantly with fronto-executive functions, and are characterized by the PIGD PD phenotype. These associations provide a basis for understanding the complex role of cognition in parkinsonian gait.

Associations between cognitive and gait performance during single- and dual-task walking in people with Parkinson disease

BACKGROUND

Cognitive impairments in Parkinson disease (PD) manifest as deficits in speed of processing, working memory, and executive function and attention abilities. The gait impairment in PD is well documented to include reduced speed, shortened step lengths, and increased step-to-step variability. However, there is a paucity of research examining the relationship between overground walking and cognitive performance in people with PD.

OBJECTIVE

This study sought to examine the relationship between both the mean and variability of gait spatiotemporal parameters and cognitive performance across a broad range of cognitive domains.

DESIGN

A cross-sectional design was used.

METHODS

Thirty-five participants with no dementia and diagnosed with idiopathic PD completed a battery of 12 cognitive tests that yielded 3 orthogonal factors: processing speed, working memory, and executive function and attention. Participants completed 10 trials of overground walking (single-task walking) and 5 trials of overground walking while counting backward by 3's (dual-task walking).

RESULTS

All gait measures were impaired by the dual task. Cognitive processing speed correlated with stride length and walking speed. Executive function correlated with step width variability. There were no significant associations with working memory. Regression models relating speed of processing to gait spatiotemporal variables revealed that including dual-task costs in the model significantly improved the fit of the model.

LIMITATIONS

Participants with PD were tested only in the on-medication state.

CONCLUSIONS

Different characteristics of gait are related to distinct types of cognitive processing, which may be differentially affected by dual-task walking due to the pathology of PD.

Objective biomarkers of balance and gait for Parkinson's disease using body-worn sensors

Balance and gait impairments characterize the progression of Parkinson's disease (PD), predict the risk of falling, and are important contributors to reduced quality of life. Advances in technology of small, body-worn, inertial sensors have made it possible to develop quick, objective measures of balance and gait impairments in the clinic for research trials and clinical practice. Objective balance and gait metrics may eventually provide useful biomarkers for PD. In fact, objective balance and gait measures are already being used as surrogate endpoints for demonstrating clinical efficacy of new treatments, in place of counting falls from diaries, using stop-watch measures of gait speed, or clinical balance rating scales. This review summarizes the types of objective measures available from body-worn sensors. The metrics are organized based on the neural control system for mobility affected by PD: postural stability in stance, postural responses, gait initiation, gait (temporal-spatial lower and upper body coordination and dynamic equilibrium), postural transitions, and freezing of gait. However, the explosion of metrics derived by wearable sensors during prescribed balance and gait tasks, which are abnormal in individuals with PD, do not yet qualify as behavioral biomarkers, because many balance and gait impairments observed in PD are not specific to the disease, nor have they been related to specific pathophysiologic biomarkers. In the future, the most useful balance and gait biomarkers for PD will be those that are sensitive and specific for early PD and are related to the underlying disease process.

Dupla-tarefa na doença de Parkinson: uma revisão sistemática de ensaios clínicos aleatorizados

Dupla-tarefa, ou tarefas simultâneas, envolve a execução de uma tarefa primária, que é o foco principal de atenção, e uma tarefa secundária, executada ao mesmo tempo. Portadores da doença de Parkinson apresentam uma deterioração na marcha quando performances de dupla-tarefa são requeridas. Sendo assim, o objetivo desta pesquisa foi realizar uma revisão sistemática de ensaios clínicos aleatorizados do efeito da intervenção da dupla-tarefa na marcha em portadores da doença de Parkinson. Foi realizada uma busca, por ensaios clínicos aleatórios, nas bases de dados MEDLINE, LILACS, SciELO, Cochrane e PEDro. Dois revisores extraíram os dados de forma independente e a qualidade metodológica foi avaliada utilizando-se a escala PEDro. Foram selecionados dois artigos, que abrangeram 175 participantes. Foi demonstrado que o treino com marcadores externos e com a música, que são formas de se treinar a dupla-tarefa, apresentou durante a marcha melhora na performance da marcha. Entretanto, são necessários ainda muitos estudos do tipo ensaios clínicos aleatorizados para verificar, principalmente, os efeitos da intervenção com a dupla-tarefa na marcha em portadores da doença de Parkinson.

Gait disturbances as specific predictive markers of the first fall onset in elderly people: a two-year prospective observational study

Falls are common in the elderly, and potentially result in injury and disability. Thus, preventing falls as soon as possible in older adults is a public health priority, yet there is no specific marker that is predictive of the first fall onset. We hypothesized that gait features should be the most relevant variables for predicting the first fall. Clinical baseline characteristics (e.g., gender, cognitive function) were assessed in 259 home-dwelling people aged 66 to 75 that had never fallen. Likewise, global kinetic behavior of gait was recorded from 22 variables in 1036 walking tests with an accelerometric gait analysis system. Afterward, monthly telephone monitoring reported the date of the first fall over 24 months. A principal components analysis was used to assess the relationship between gait variables and fall status in four groups: non-fallers, fallers from 0 to 6 months, fallers from 6 to 12 months and fallers from 12 to 24 months. The association of significant principal components (PC) with an increased risk of first fall was then evaluated using the area under the Receiver Operator Characteristic Curve (ROC). No effect of clinical confounding variables was shown as a function of groups. An eigenvalue decomposition of the correlation matrix identified a large statistical PC1 (termed “Global kinetics of gait pattern”), which accounted for 36.7% of total variance. Principal component loadings also revealed a PC2 (12.6% of total variance), related to the “Global gait regularity.” Subsequent ANOVAs showed that only PC1 discriminated the fall status during the first 6 months, while PC2 discriminated the first fall onset between 6 and 12 months. After one year, any PC was associated with falls. These results were bolstered by the ROC analyses, showing good predictive models of the first fall during the first six months or from 6 to 12 months. Overall, these findings suggest that the performance of a standardized walking test at least once a year is essential for fall prevention.

The nature of dual-task interference during gait in incident Parkinson's disease

Dual-task interference during gait is a common phenomenon in older adults and people with Parkinson's disease (PD). Dual-task performance is driven by cognitive processes involving executive function, attention and working memory which underpin resource capacity and allocation. The underlying processes that contribute to dual-task interference are poorly understood, and confounded by methodological differences. The aim of this study was to explore the nature of dual-task interference in PD with respect to age-matched controls. We examined 121 people with early PD and 189 controls and controlled for baseline task demand on both tasks allowing between-group differences to be attributed to dual-task interference rather than differences in baseline performance. We also compared a wide range of gait characteristics to evaluate the pattern of interference. Participants walked for two minutes at a preferred pace under single- and dual-task (test of working memory capacity-digit span recall) conditions. In a subgroup task demand was increased (digit span+1) (n=55 control, n=44 PD) to assess the influence of resource capacity. Finally the association between dual-task interference with motor and cognitive characteristics was examined to evaluate resource capacity and allocation. PD and controls responded similarly to the dual-task for all gait characteristics except for step width and step width variability and this was the same when task demand increased (dual+1). Control participants took wider steps (p=0.006) and step width variability increased significantly for controls (p=0.001) but not PD. Interference was specific to the gait characteristic rather than a global pattern of impairment. Digit span error rates were not significantly different between groups during dual-task performance. There were no significant correlations with dual-task interference and global cognition, motor deficit, and executive function for either group. Effects of dual-tasks on gait performance are twofold and specific to the gait characteristic. They reflect an age-related reduction in gait performance (especially forward progression) in PD and controls possibly due to reduced resource capacity; and secondly, show postural stability during walking in early PD is disproportionately affected highlighting a PD-specific dual-task co-ordination deficit. Further work is required to identify the cognitive, executive and motor correlates of dual-task interference from which inferences about underlying cognitive processes can be made. These findings inform an understanding of dual-task impairment in early PD and suggest that management should target postural control under dual-task conditions from the early stages.

Multiple modes of impulsivity in Parkinson's disease

Cognitive problems are a major factor determining quality of life of patients with Parkinson's disease. These include deficits in inhibitory control, ranging from subclinical alterations in decision-making to severe impulse control disorders. Based on preclinical studies, we proposed that Parkinson's disease does not cause a unified disorder of inhibitory control, but rather a set of impulsivity factors with distinct psychological profiles, anatomy and pharmacology. We assessed a broad set of measures of the cognitive, behavioural and temperamental/trait aspects of impulsivity. Sixty adults, including 30 idiopathic Parkinson's disease patients (Hoehn and Yahr stage I–III) and 30 healthy controls, completed a neuropsychological battery, objective behavioural measures and self-report questionnaires. Univariate analyses of variance confirmed group differences in nine out of eleven metrics. We then used factor analysis (principal components method) to identify the structure of impulsivity in Parkinson's disease. Four principal factors were identified, consistent with four different mechanisms of impulsivity, explaining 60% of variance. The factors were related to (1) tests of response conflict, interference and self assessment of impulsive behaviours on the Barrett Impulsivity Scale, (2) tests of motor inhibitory control, and the self-report behavioural approach system, (3) time estimation and delay aversion, and (4) reflection in hypothetical scenarios including temporal discounting. The different test profiles of these four factors were consistent with human and comparative studies of the pharmacology and functional anatomy of impulsivity. Relationships between each factor and clinical and demographic features were examined by regression against factor loadings. Levodopa dose equivalent was associated only with factors (2) and (3). The results confirm that impulsivity is common in Parkinson's disease, even in the absence of impulse control disorders, and that it is not a unitary phenomenon. A better understanding of the structure of impulsivity in Parkinson's disease will support more evidence-based and effective strategies to treat impulsivity.

Synthesis of walking sounds for alleviating gait disturbances in Parkinson's disease

Managing gait disturbances in people with Parkinson's disease is a pressing challenge, as symptoms can contribute to injury and morbidity through an increased risk of falls. While drug-based interventions have limited efficacy in alleviating gait impairments, certain nonpharmacological methods, such as cueing, can also induce transient improvements to gait. The approach adopted here is to use computationally-generated sounds to help guide and improve walking actions. The first method described uses recordings of force data taken from the steps of a healthy adult which in turn were used to synthesize realistic gravel-footstep sounds that represented different spatio-temporal parameters of gait, such as step duration and step length. The second method described involves a novel method of sonifying, in real time, the swing phase of gait using real-time motion-capture data to control a sound synthesis engine. Both approaches explore how simple but rich auditory representations of action based events can be used by people with Parkinson's to guide and improve the quality of their walking, reducing the risk of falls and injury. Studies with Parkinson's disease patients are reported which show positive results for both techniques in reducing step length variability. Potential future directions for how these sound approaches can be used to manage gait disturbances in Parkinson's are also discussed.

Variability of Stepping during a Virtual Reality Paradigm in Parkinson's Disease Patients with and without Freezing of Gait

BACKGROUND

Freezing of gait is a common and debilitating symptom affecting many patients with advanced Parkinson's disease. Although the pathophysiology of freezing of gait is not fully understood, a number of observations regarding the pattern of gait in patients with this symptom have been made. Increased 'Stride Time Variability' has been one of the most robust of these features. In this study we sought to identify whether patients with freezing of gait demonstrated similar fluctuations in their stepping rhythm whilst performing a seated virtual reality gait task that has recently been used to demonstrate the neural correlate of the freezing phenomenon.

METHODS

Seventeen patients with freezing and eleven non-freezers performed the virtual reality task twice, once whilst 'On' their regular Parkinsonian medication and once in their practically defined 'Off' state.

RESULTS

All patients displayed greater step time variability during their 'Off' state assessment compared to when medicated. Additionally, in the 'Off' state, patients with freezing of gait had greater step time variability compared to non-freezers. The five steps leading up to a freezing episode in the virtual reality environment showed a significant increase in step time variability although the final three steps preceding the freeze were not characterized by a progressive shortening of latency.

CONCLUSIONS

The results of this study suggest that characteristic features of gait disturbance observed in patients with freezing of gait can also be demonstrated with a virtual reality paradigm. These findings suggest that virtual reality may offer the potential to further explore the freezing phenomenon in Parkinson's disease.

Gait variability and disability in multiple sclerosis

Gait variability is clinically relevant in some populations, but there is limited documentation of gait variability in persons with multiple sclerosis (MS). This investigation examined average and variability of spatiotemporal gait parameters in persons with MS and healthy controls and subsequent associations with disability status. 88 individuals with MS (age 52.4±11.1) and 20 healthy controls (age 50.9±8.7) performed two self-paced walking trials on a 7.9-m electronic walkway to determine gait parameters. Disability was indexed by the Expanded Disability Status Scale (EDSS) and ranged between 2.5 and 6.5. Gait variability was indexed by standard deviation (SD) and coefficient of variation (CV=SD/mean) of step time, step length, and step width. Average gait parameters were significantly correlated with EDSS (ρ=0.756-0.609) and were significantly different in individuals with MS compared to controls (p≤0.002). Also, step length (p<0.001) and step time (p<0.001) variability were both significantly greater in MS compared to controls. EDSS was positively correlated with step length variability and individuals with MS who used assistive devices to walk had significantly greater step length variability than those who walked independently (p's<.05). EDSS was correlated with step time and length variability even when age was taken into account. Additionally, Fisher's z test of partial correlations revealed that average gait parameters were more closely related to disability status than gait variability in individuals with MS. This suggests that focusing on average gait parameters may be more important than variability in therapeutic interventions in MS.

Weight, age and coefficients of variation in renal solute excretion

BACKGROUND

Homoscedasticity (constant variance over axes or among statistical factors) is an integral assumption of most statistical analyses. However, a number of empirical studies in model organisms and humans demonstrate significant differences in residual variance (that component of phenotype unexplained by known factors) or intra-individual variation among genotypes. Our work suggests that renal traits may be particularly susceptible to randomization by genetic and non-genetic factors, including endogenous variables like age and weight.

METHODS

We tested associations between age, weight and intra-individual variation in urinary calcium, citrate, chloride, creatinine, potassium, magnesium, sodium, ammonium, oxalate, phosphorus, sulfate, uric acid and urea nitrogen in 9,024 male and 6,758 female kidney stone patients. Coefficients of variation (CVs) were calculated for each individual for each solute from paired 24-hour urines. Analysis of CVs was corrected for inter-measurement collection variance in creatinine and urine volume. CVs for sodium and urea nitrogen were included to correct for dietary salt and protein.

RESULTS

Age was positively associated with individual CVs for calcium and negatively associated with CVs for potassium, ammonium and phosphorus (p(FDR) < 0.01). Weight was associated with CVs for creatinine, magnesium and uric acid, and negatively associated with CVs for calcium, potassium and oxalate (p(FDR) < 0.05).

CONCLUSION

Intra-individual variation changes over age and weight axes for numerous urinary solutes. Changing residual variance over age and weight could cause bias in the detection or estimation of genetic or environmental effects. New methodologies may need to account for such residual unpredictability, especially in diverse collections.

The effects of instructions on dual-task walking and cognitive task performance in people with Parkinson's disease

Gait impairments are prevalent among people with Parkinson's disease (PD). Instructions to focus on walking can improve walking in PD, but the use of such a cognitive strategy may be limited under dual-task walking conditions, when walking is performed simultaneously with concurrent cognitive or motor tasks. This study examined how dual-task performance of walking and a concurrent cognitive task was affected by instructions in people with PD compared to healthy young and older individuals. Dual-task walking and cognitive task performance was characterized under two sets of instructions as follows: (1) focus on walking and (2) focus on the cognitive task. People with PD and healthy adults walked faster when instructed to focus on walking. However, when focused on walking, people with PD and young adults demonstrated declines in the cognitive task. This suggests that dual-task performance is flexible and can be modified by instructions in people with PD, but walking improvements may come at a cost to cognitive task performance. The ability to modify dual-task performance in response to instructions or other task and environmental factors is critical to mobility in daily life. Future research should continue to examine factors that influence dual-task performance among people with PD.

Cholinergic dysfunction contributes to gait disturbance in early Parkinson's disease

Gait disturbance is an early feature in Parkinson's disease. Its pathophysiology is poorly understood; however, cholinergic dysfunction may be a non-dopaminergic contributor to gait. Short-latency afferent inhibition is a surrogate measure of cholinergic activity, allowing the contribution of cholinergic dysfunction to gait to be evaluated. We hypothesized that short-latency afferent inhibition would be an independent predictor of gait dysfunction in early Parkinson's disease. Twenty-two participants with Parkinson's disease and 22 age-matched control subjects took part in the study. Gait was measured objectively using an instrumented walkway (GAITRite), and subjects were asked to walk at their preferred speed for 2 min around a 25-m circuit. Spatiotemporal characteristics (speed, stride length, stride time and step width) and gait dynamics (variability described as the within subject standard deviation of: speed, stride time, stride length and step width) were determined. Short-latency afferent inhibition was measured by conditioning motor evoked potentials, elicited by transcranial magnetic stimulation of the motor cortex, with electrical stimuli delivered to the contralateral median nerve at intervals ranging from N20 (predetermined) to N20 + 4 ms. Short-latency afferent inhibition was determined as the percentage difference between test and conditioned response for all intervals and was described as the group mean. Participants were optimally medicated at the time of testing. Participants with Parkinson's disease had significantly reduced gait speed (P = 0.002), stride length (P = 0.008) and stride time standard deviation (P = 0.001). Short-latency afferent inhibition was also significantly reduced in participants with Parkinson's disease (P = 0.004). In participants with Parkinson's disease, but not control subjects, significant associations were found between gait speed, short-latency afferent inhibition, age and postural instability and gait disorder score (Movement Disorders Society Unified Parkinson's Disease Rating Scale) and attention, whereas global cognition and depression were marginally significant. No other gait variables were associated with short-latency afferent inhibition. A multiple hierarchical regression model explored the contribution of short-latency afferent inhibition to gait speed, controlling for age, posture and gait symptoms (Postural Instability and Gait Disorder score-Movement Disorders Society Unified Parkinson's Disease Rating Scale), attention and depression. Regression analysis in participants with Parkinson's disease showed that reduced short-latency afferent inhibition was an independent predictor of slower gait speed, explaining 37% of variability. The final model explained 72% of variability in gait speed with only short-latency afferent inhibition and attention emerging as independent determinants. The results suggest that cholinergic dysfunction may be an important and early contributor to gait dysfunction in Parkinson's disease. The findings also point to the contribution of non-motor mechanisms to gait dysfunction. Our study provides new insights into underlying mechanisms of non-dopaminergic gait dysfunction, and may help to direct future therapeutic approaches.

Reduced step length, not step length variability is central to gait hypokinesia in people with Parkinson's disease

OBJECTIVES

Previous studies found that people with Parkinson's disease (PD) walked at a slower speed and with significantly shorter stride length and/or increase in variability of stride length than control subjects. The present study aimed to examine whether difference existed in amplitude and variability of step length between control and PD subjects if they walked at a similar speed.

METHODS

This was a cross-sectional study. Thirteen PD patients and 15 healthy control subjects were instructed to walk at a similar speed on a treadmill under 2 randomized conditions: walking alone (Walk(o)) and walking with digit subtraction of 3 (Walk(calculation)). Amplitude of step length (cm), variability of step length (%), and percent accuracy of the calculation task (%) were recorded and analysed.

RESULTS

During both Walk(o) and Walk(calculation), PD patients had significantly shorter step length and larger step length variability than control subjects (p<0.05). When a cognitive task was added to walking, PD patients showed a significant decrease in step length without further change in step length variability (p<0.05).

CONCLUSION

As reduced step length persisted when the control subjects walked at a speed similar to that of patients, our finding suggests that PD patients had a fundamental problem in regulating the amplitude of step length during walking.

Medication improves balance and complex gait performance in Parkinson disease

Gait and balance impairments in people with Parkinson disease (PD) may lead to falls and serious injuries. Therefore, it is critical to improve our understanding of the nature of these impairments, including how they respond to prescribed anti-Parkinson medication. This is particularly important for complex balance and gait tasks that may be associated with falls. We evaluated motor function, functional balance, and gait performance during various gait tasks in 22 people with PD OFF and ON medication (PD OFF, PD ON) and 20 healthy older adults. Although MDS-UPDRS-III score, Berg Balance Scale, Mini-Balance Evaluations Systems test, and Timed-Up-and-Go improved in PD with medication, impairments persisted in all measures on medication, compared to controls. Dual task Timed-Up-and-Go did not improve with medication, and PD ON required more time than controls. Gait velocity and stride length improved similarly with medication in PD across forward, fast, backward, dual task forward, and dual task backward gait tasks. Cadence did not change with medication, nor did it differ between PD ON and controls. Velocity and stride length were reduced in PD ON compared to controls. Velocity reductions in PD ON during fast gait were cadence-mediated, while velocity reductions in backward gait were stride length-mediated. Our results suggest functional balance improves with medication in PD and gait performance improves with medication, regardless of task complexity. Remaining impairments on medication highlight the need to examine additional therapeutic options for individuals with PD to reduce the risk of falls.

A review of dual-task walking deficits in people with Parkinson's disease: motor and cognitive contributions, mechanisms, and clinical implications

Gait impairments in Parkinson's disease (PD) are exacerbated under dual-task conditions requiring the simultaneous performance of cognitive or motor tasks. Dual-task walking deficits impact functional mobility, which often requires walking while performing concurrent tasks such as talking or carrying an object. The consequences of gait impairments in PD are significant and include increased disability, increased fall risk, and reduced quality of life. However, effective therapeutic interventions for dual-task walking deficits are limited. The goals of this narrative review are to describe dual-task walking deficits in people with PD, to discuss motor and cognitive factors that may contribute to these deficits, to review potential mechanisms underlying dual-task deficits, and to discuss the effect of therapeutic interventions on dual-task walking deficits in persons with PD.

Gait variability in older adults: a structured review of testing protocol and clinimetric properties

Gait variability (stride-to-stride fluctuations) is used increasingly as a marker for gait performance and future mobility status, cognitive status, and falls. This structured review explicitly examined literature that reported on the reliability, validity and responsiveness of gait variability in older adults. We searched Medline, Embase, Web of Science, Scopus, CINAHL, PEDRO, Biomechanics, SportDiscus and PsycInfo databases. Two independent reviewers undertook data extraction, with adjudication by a third reviewer in cases of disagreement. Twenty-two full papers were screened and 10 met the predefined inclusion criteria, involving 1036 participants who were mainly community dwelling older adults in their 8th decade. A wide range of gait variability parameters, testing protocols and calculations of gait variability were reported. Reliability estimates varied, but were mostly fair to moderate. Concurrent validity was established for stance time variability and change estimates were reported for stance time and swing time. Standard of reporting was generally poor, with insufficient detail provided for aspects of measurement and testing protocols. Further research is required to standardise testing procedures and establish reliability, responsiveness and validity for confident use of gait variability as a robust measure.