Séverine Bleuse

Auditory cueing of gait initiation in Parkinson's disease patients with freezing of gait

OBJECTIVEnImpaired gait initiation (GI) in patients with advanced Parkinsons disease (PD) is a typical functional sign of akinesia. Failure to initiate the first step is frequently presented by patients with freezing of gait (FOG) and is often considered a sub-type of freezing. The literature on the effects of cueing of GI preparation and execution remains controversial. Our objective was to establish whether auditory cueing improves the preparation and/or execution of GI in PD patients with a history of FOG.nnnMETHODSnWe recorded first-step preparation and execution in 30 PD patients with confirmed FOG under two randomised conditions: self-triggered (ST) gait and gait cued by a sound beep in off- and on-dopa conditions. Anticipatory postural adjustments (APAs) were evaluated by monitoring the trajectory of the centre of pressure.nnnRESULTSnWe compared the patients with 30 patients without history of FOG and 30 healthy controls (HCs). l-Dopa only slightly improved the characteristics of APAs in freezers but was effective to improve gait hypokinesia. Auditory cueing was effective in improving step preparation in freezers, who showed adequate APAs more frequently. As seen with HCs and patients without FOG, patients released their APAs more quickly when auditory cueing was applied. However, cueing did not have a significant effect on step length. Clinically, auditory cueing also improved start hesitation in freezers.nnnCONCLUSIONSnAuditory cueing improved step preparation but not step execution in PD patients.nnnSIGNIFICANCEnA failure to link step preparation and execution during GI may explain the poor first-step execution seen in PD freezers.

Kinematic angular parameters in PD: Reliability of joint angle curves and comparison with healthy subjects

BACKGROUNDnMost previous biomechanical studies of Parkinsons disease (PD) have been restricted to the description of spatiotemporal parameters and certain peak values for angular parameters. The reliability of joint angle curves and comparisons with control data are of major interest in PD, since variability in gait cycle timing is a feature of this pathology.nnnMETHODSnWe used a video motion analysis system to record kinematic, spatiotemporal and angular parameters in 32 off-drug PD patients. The reliability of the patients lower limb joint angle curves in the sagittal plane were analysed using the intra-class correlation coefficient (ICC), together with fast Fourier transform (FFT) analysis and hierarchical classification for discarding deviant curves. Lastly, we compared average curves (using a mixed model and the bootstrap method) for the less-affected and more-affected sides of PD patients and then compared the patient data with the results from 30 age-matched controls.nnnRESULTSnThe ICC-based procedure was easily applicable. Only 9.4% and 12.5% of the patients hip and knee curves (respectively) were deemed to be unreliable. However, the PD patients very high cycle-to-cycle variability in the sagittal plane ankle curves prevented us from applying to this joint. For the knee joint, the curves for the most disabled patients (who walked at below 0.5 m/s) were not reliable. We did not find any differences between the less and more disabled sides. The differences between patient and control curves concerned the double-support time during the stance phase and the time point for maximum knee flexion during the swing phase. Patients and controls differed in terms of the hip extension phase, with lower values in PD.nnnCONCLUSIONnWe have developed the use of validated statistic tools for unambiguously comparing PD patients and controls in terms of joint angle curve differences.

Anticipatory postural adjustments associated with arm movement in Parkinson’s disease: a biomechanical analysis

Objective: To study anticipatory postural adjustments (APAs) in Parkinson’s disease (PD) via a biomechanical analysis, including vertical torque (Tz). Methods: Ten patients with PD (in the “off-drug” condition) and 10 age matched controls were included. While standing on a force platform, the subject performed a right shoulder flexion in order to grasp a handle in front of him/her, under three conditions (all at maximal velocity): movement triggered by a sound signal and loaded/non-loaded, self-paced movement. The anteroposterior coordinates of the centre of pressure (COP) and Tz were calculated. Results: A group effect was observed for Tz and COP in patients with PD (compared with controls): the maximal velocity peak appeared later and the amplitude of the COP backward displacement and the area of the positive phase of Tz were lower, whereas the duration of the positive phase of Tz was greater. Interaction analysis showed that the area of Tz was especially affected in the triggered condition and the loaded, self-paced condition. The onset of the COP backward displacement was delayed in the triggered condition. Conclusion: Our biomechanical analysis revealed that patients with PD do indeed perform APAs prior to unilateral arm movement, although there were some abnormalities. The reduced APA magnitude appears to correspond to a strategy for not endangering postural balance.

Are gait initiation parameters early markers of Huntington's disease in pre-manifest mutation carriers?

Huntingtons disease (HD) pre-manifest mutation carriers (PMCs) present early-onset gait disturbances. Gait initiation encompasses the preparation and execution of the first step. By using paradigms with and without external cues, a gait initiation analysis can highlight the interaction between motor and cognitive aspects of movement preparation and execution. Hence, gait initiation disorders may constitute particularly interesting early markers of HD. The objective of the present study was to quantify gait initiation in PMCs. In a case-control study, 17 PMCs (median age: 36.5) were compared with a group of 25 healthy controls (HCs, median age: 36) for gait initiation and a group of 57 HCs (median age: 38) for gait. Presymptomatic mutation carriers displayed a shorter first step duration and lower-amplitude postural adjustments. For the first step duration and speed, these impairments were more pronounced under self-triggered (ST) conditions. The PMCs displayed a lower gait speed, cadence and stride length and higher stride-to-stride variability. The latter parameter seemed capable of differentiating between PMCs and HCs with adequate sensitivity (0.81) and specificity (0.87). We confirmed the early-onset impairment of gait in general and first step execution in particular in PMCs (particularly under ST conditions). The temporal parameters of step execution (e.g. duration) and spatial parameters of postural adjustment (e.g. a backward shift in the centre of pressure) may be worth investigating as early markers of HD. However, two such parameters (stride-to-stride variability and first step duration under ST conditions) already appear to be sufficiently reliable diagnostic tools for differentiating between PMCs and HCs.

Ajustements posturaux anticipés lors de la flexion du membre supérieur : intérêt du moment de torsion

Resume Objectifs : Determiner s’il existe un parametre biomecanique capable de caracteriser les ajustements posturaux dans differentes conditions. Methodesxa0: L’elevation du membre superieur induit chez le sujet debout un moment de torsion vertical Tz mesure par une plate-forme de force. Ce moment a ete etudie chez 10 sujets jeunes grâce au systeme opto-electronique Vicon 370. Les sujets, debout sur une plate-forme de force, flechissaient leur bras droit pour attraper une poignee situee a leur portee devant eux, dans 5 conditionsxa0: auto-commandees a 3 vitesses (lente, intermediaire, maximale), declenchee (sur signal sonore), lestee (1xa0kg au poignet) toutes deux a vitesse maximale. Dans une sixieme condition, le bras etait passivement deplace par un experimentateur. Resultatsxa0: Tz comportait une phase negative (c’est-a-dire une rotation anti-horaire) dans toutes les conditions. Elle n’etait precedee d’une phase positive, precedant le debut du mouvement, que lorsque ce dernier etait volontaire. La phase positive de Tz etait retardee dans la condition declenchee (– 60xa0ms) par rapport a la condition auto-commandee a vitesse maximale (– 155xa0ms) et n’etait pas modifiee par la charge et la vitesse. Par contre son amplitude augmentait avec la vitesse, la charge et en condition declenchee. Conclusionxa0: Le moment de torsion Tz et notamment sa phase positive permet de mesurer la latence, la duree et l’intensite de la preparation posturale associee a un mouvement volontaire, en fonction des caracteristiques de ce dernier. Il caracterise donc les ajustements posturaux dans toutes les conditions, y compris pour des vitesses faibles.

Gait and attentional performance in freezers under methylphenidate.

BACKGROUNDnAttentional resources appear to be involved in the occurrence of FoG. The Parkgait study recently reported that methylphenidate reduces gait hypokinesia and freezing of gait (FoG) in advanced PD patients receiving STN-DBS in the off-dopaminergic drug condition. Methylphenidate is considered to improve attention. The primary objective of the present ancillary study was to determine whether methylphenidate reduced the interference between a cognitive task and gait in patients with FoG. The studys secondary objective was to compare attentional performance in methylphenidate-treated and placebo-treated patients.nnnMETHODSnA total of 24 patients (from two centers) were included in the study. Patients were randomly assigned 1:1 to a three-month course of methylphenidate (1mg/kg/day) or placebo. Patients were assessed after an acute L-dopa challenge. The primary outcome criterion was the stride length ratio ((dual-task stride length minus free gait stride length)/free gait stride length). Trials with FoG episodes were excluded from the analysis. Secondary outcomes included changes in reaction times for computerized attention tasks and FoG severity.nnnRESULTSnWhen comparing patients receiving methylphenidate with those receiving placebo, we did not observe any significant differences in the interaction between the dual task and gait or in attentional performance.nnnCONCLUSIONnAs in the main Parkgait study, methylphenidate did not reduce gait hypokinesia in patients receiving dopaminergic treatment. Our present results suggest that the reduction in the number of FoG episodes previously observed in patients on methylphenidate was neither due to interaction between a dual-task and gait nor an increase in attentional performance.

Effect of bilateral subthalamic nucleus deep brain stimulation on postural adjustments during arm movement

OBJECTIVEnAlthough it is well known that postural adjustment (PA) is impaired in advanced Parkinsons disease (PD), the potentially compensatory effects of bilateral subthalamic nucleus deep brain stimulation (STN DBS) in this respect are less clear.nnnMETHODSnWhile standing on a force platform and in the absence of antiparkinsonian medication, 10 patients performed voluntary, unilateral arm movements before surgery (the off stim condition) and then afterwards (the on stim condition). The patients PAs were monitored by vertical torque (Tz) and compared with those recorded in control subjects.nnnRESULTSnPatients with STN DBS and control subjects showed similar values for PA amplitude, duration and latency.nnnCONCLUSIONSnSTN stimulation may induce better postural control during the movement preparation and execution phases. Our results argue in favour of a positive effect of STN DBS on PA.nnnSIGNIFICANCEnThe PA amplitude (provided by Tz) may be a strong marker reflecting the clinical improvement seen in stimulated PD patients.

Biomechanical mechanisms and centre of pressure trajectory during planned gait termination

AIMnAlthough gait initiation has been extensively studied, gait termination has received less attention. In particular, the trajectory of the centre of pressure (CoP) during gait termination, as well as the trajectorys determinants, has not yet been described. The purpose of the present study was to characterize the kinetic components of planned gait termination (including the CoP trajectory) with respect to the various gait events and centre of mass speed and trajectory.nnnMETHODSnThirty healthy subjects were asked to walk along a test track and stop on a force platform while an optoelectronic system recorded temporal and spatial parameters. A total of 90 trials were analysed.nnnRESULTSnSubjects needed two steps to stop on the force platform. The CoP trajectory during gait termination was composed of three phases. During the first phase, the CoP moved forward under the stance foot, which was in contact with the ground. The ground reaction forces exerted a sagittal braking action. The second phase showed a lateral CoP shift and was correlated with braking; this may correspond to anticipatory postural adjustments for gait termination. The third and last phase might correspond to compensatory adjustments before the stance phase.nnnCONCLUSIONSnCoP trajectory is more complex during gait termination than during gait initiation. Gait termination comprises several specific sequences in the gait-stance transition. A better understanding of the kinetic parameters in gait termination should enable us to identify which kinetic parameters could be considered as risk factors for falls.

Freezing/festination during motor tasks in early-stage Parkinson's disease: A prospective study.

Parkinsonian patients have a tendency to speed up during repetitive motor tasks (festination) and to experience sudden motor blocks (freezing). In this article, we prospectively studied the appearance and progression of these phenomena in 30 early‐stage PD patients.

Does overestimation of an object's mass during arm-raising modify postural adjustments?

By using a dummy weight during an arm-raising movement, we sought to determine whether (i) postural adjustments are modified and (ii) the required focal movement can be performed adequately. Standing on a force platform, 30 healthy young adults performed voluntary, arm-raising movements with cube-shaped boxes: a small 1 kg box, a large 4 kg box and a large 1 kg box (i.e. the dummy weight, which looked as if it weighed 4 kg). Postural adjustments were quantified in terms of the latency, intensity and duration of the positive phase of the vertical torque (Tz) and displacements of the center of pressure. Lifting the dummy and lifting the small 1 kg box were associated with similar arm velocity curves. The characteristics of the positive Tz phase for the dummy box were intermediate between those observed for the small 1 kg box and the large 4 kg box. There were no differences between the three box-lifting conditions in terms of the latency and duration of Tz. We conclude that overestimation of the dummys mass was rapidly corrected by a feedback mechanism. Postural control was modified online as soon as the dummys true weight was perceived, which therefore enabled the maintenance of balance and adequate execution of the voluntary (focal) movement.