Cris Zampieri

iTUG, a Sensitive and Reliable Measure of Mobility

Timed Up and Go (TUG) test is a widely used clinical paradigm to evaluate balance and mobility. Although TUG includes several complex subcomponents, namely: sit-to-stand, gait, 180° turn, and turn-to-sit; the only outcome is the total time to perform the task. We have proposed an instrumented TUG, called iTUG, using portable inertial sensors to improve TUG in several ways: automatic detection and separation of subcomponents, detailed analysis of each one of them and a higher sensitivity than TUG. Twelve subjects in early stages of Parkinsons disease (PD) and 12 age matched control subjects were enrolled. Stopwatch measurements did not show a significant difference between the two groups. The iTUG, however, showed a significant difference in cadence between early PD and control subjects (111.1 ± 6.2 versus 120.4 ± 7.6 step/min, p <; 0.006) as well as in angular velocity of arm-swing (123 ± 32.0 versus 174.0 ± 50.4°/s, p <; 0.005), turning duration (2.18 ± 0.43 versus 1.79 ± 0.27 s, p <; 0.023), and time to perform turn-to-sits (2.96 ± 0.68 versus 2.40 ± 0.33 s, p <; 0.023). By repeating the tests for a second time, the test-retest reliability of iTUG was also evaluated. Among the subcomponents of iTUG, gait, turning, and turn-to-sit were the most reliable and sit-to-stand was the least reliable.

The instrumented timed up and go test: potential outcome measure for disease modifying therapies in Parkinson's disease

The Timed Up and Go (TUG) test has been used to assess balance and mobility in Parkinsons Disease (PD). However, it is not known if this test is sensitive to subtle abnormalities present in early stages of the disease, when balance and gait problems are not clinically evident but may be detected with instrumented analysis of movement. We hypothesise that postural transitions and arm swing during gait will be the most sensitive characteristics of the TUG for early PD. In the present study, we instrumented the TUG test (iTUG) using portable inertial sensors, and extended the walking distance from 3 m (traditional TUG) to 7 m. Twelve subjects with early-to-moderate, untreated PD and 12 healthy individuals participated. Our findings show that although the stopwatch measure of TUG duration did not detect any abnormalities in early-to-mid-stage PD, the peak arm swing velocity on the more affected side, average turning velocity, cadence and peak trunk rotation velocity were significantly slower. These iTUG parameters were also correlated with the Unified Parkinsons Disease Rating Motor Scale. Thus, the iTUG test is sensitive to untreated PD and could potentially detect progression of PD and response to symptomatic and disease-modifying treatments.

ISway: a sensitive, valid and reliable measure of postural control

BackgroundClinicians need a practical, objective test of postural control that is sensitive to mild neurological disease, shows experimental and clinical validity, and has good test-retest reliability. We developed an instrumented test of postural sway (ISway) using a body-worn accelerometer to offer an objective and practical measure of postural control.MethodsWe conducted two separate studies with two groups of subjects. Study I: sensitivity and experimental concurrent validity. Thirteen subjects with early, untreated Parkinson’s disease (PD) and 12 age-matched control subjects (CTR) were tested in the laboratory, to compare sway from force-plate COP and inertial sensors. Study II: test-retest reliability and clinical concurrent validity. A different set of 17 early-to-moderate, treated PD (tested ON medication), and 17 age-matched CTR subjects were tested in the clinic to compare clinical balance tests with sway from inertial sensors. For reliability, the sensor was removed, subjects rested for 30 min, and the protocol was repeated. Thirteen sway measures (7 time-domain, 5 frequency-domain measures, and JERK) were computed from the 2D time series acceleration (ACC) data to determine the best metrics for a clinical balance test.ResultsBoth center of pressure (COP) and ACC measures differentiated sway between CTR and untreated PD. JERK and time-domain measures showed the best test-retest reliability (JERK ICC was 0.86 in PD and 0.87 in CTR; time-domain measures ICC ranged from 0.55 to 0.84 in PD and from 0.60 to 0.89 in CTR). JERK, all but one time-domain measure, and one frequency measure were significantly correlated with the clinical postural stability score (r ranged from 0.50 to 0.63, 0.01 < p < 0.05).ConclusionsBased on these results, we recommend a subset of the most sensitive, reliable, and valid ISway measures to characterize posture control in PD: 1) JERK, 2) RMS amplitude and mean velocity from the time-domain measures, and 3) centroidal frequency as the best frequency measure, as valid and reliable measures of balance control from ISway.

ANTICIPATORY POSTURAL ADJUSTMENTS PRIOR TO STEP INITIATION ARE HYPOMETRIC IN UNTREATED PARKINSON'S DISEASE: AN ACCELEROMETER-BASED APPROACH

Background and purpose:  Anticipatory postural adjustments (APAs), prior to step initiation, are bradykinetic in advanced Parkinson’s disease (PD) and may be one of the factors associated with ‘start hesitation’. However, little is known about APAs in the early stage of PD. In this study, we determined whether body‐worn accelerometers could be used to characterize step initiation deficits in subjects with early‐to‐moderate, untreated PD.

Aging and saccade-stepping interactions in humans

Saccade-stepping interactions were compared in older and young persons to determine if visual anchoring theory could be applied to stepping behavior in both groups. Subjects rapidly stepped onto a platform. In some trials, a translucent shield was used to prevent visual fixation. Both elderly and younger subjects initiated downward saccades prior to footlift, but saccade-step latency was significantly longer for the elderly. Regardless of age, working memory was not sufficient to guide stepping in the absence of visual fixation. The findings support visual anchoring theory by demonstrating that older and young persons generate anticipatory downward saccades which precede the stepping action. Changes in the latency of saccade-step coupling with aging were attributed to slowed processing of visual anchors for obstacle avoidance. The central nervous system appears to accommodate age-related processing delays by initiating the down saccade well in advance of platform footlift, independently from stepping velocity.

Influence of Elderly Executive Cognitive Function on Attention in the Lower Visual Field during Step Initiation

Background: There is a well-established relationship between poor executive cognitive abilities and elderly fall risk, but the precise mechanism underlying this relationship is unknown. Older persons frequently fall or trip on objects below eye level, and it was hypothesized that the pathological mechanism linking low executive function and fall risk is a selective impairment in the resolution of visual attention in the lower visual fields. Objective: To determine ifnormally sighted older persons living in the community with deficits in executive cognitive abilities have a reduced resolution of visual attention in the lower visual fields compared to elderly and younger subjects with high executive abilities. Methods: Eye and head angulations were monitored as subjects fixated on a point rear-projected at eye level at the end of a 3- meter walkway. Visual stimuli were briefly presented (<300 ms) in the peripheral visual field (with and without distractors) to directly cue the selection of the right or left foot to lead a step over a foam obstacle resting at the subject’s feet. No saccades were allowed until the stimulus was extinguished, at which time a down-saccade-step sequence moved the foot over the obstacle. The resolution of visual attention (tested with gratings) and the influence of target eccentricity in the upper and lower visual fields were evaluated. The primary outcome measures were step error and obstacle contact rate, saccade occurrence after extinguished stimulus and the log of cue-saccade latency (limb-independent reaction time). Results: All groups experienced greater stepping errors than expected by chance when stimuli were presented in the lower versus upper visual field and with increasing eccentricity. However, the obstacle contact rate was greater, cue-saccade latency was prolonged, and fewer down-saccades were generated in the elderly group with poor executive abilities compared to those with high executive function and younger subjects. Conclusions: Loss of visual attention in the lower visual fields was not unique to elderly subjects with poor executive function. However, slowed processing time and reduction in the frequency of down-saccades associated with a low level of executive function potentially account for the mechanism linking executive abilities and fall risk.

Saccade-Stepping Interactions Revise the Motor Plan for Obstacle Avoidance

Abstract The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of −500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately −300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.

Improvement of Gaze Control After Balance and Eye Movement Training in Patients With Progressive Supranuclear Palsy: A Quasi-Randomized Controlled Trial

OBJECTIVE One of the main oculomotor findings in progressive supranuclear palsy (PSP) is the inability to saccade downward. In addition, people with PSP have difficulty suppressing fixation, which may contribute to vertical gaze palsy. The objective was to investigate the effectiveness of a rehabilitation intervention tailored to enhance suppression of fixation and gaze shift in participants with PSP. DESIGN Controlled trial with a quasi-randomized design. Measures occurred at week 1 and 5. Researchers assessing participants were blind to the group assignments. SETTING Movement disorders assessment laboratory. PARTICIPANTS Nineteen adults with possible or probable PSP who were ambulatory for short distances and had far visual acuity of 20/80 and a Folstein Mini-Mental State score of more than 23. INTERVENTIONS Balance training complemented with eye movement and visual awareness exercises was compared with balance training alone. MAIN OUTCOME MEASURES Gaze control was assessed using a vertical Gaze Fixation Score and a Gaze Error Index. RESULTS Gaze control after the balance plus eye exercise significantly improved, whereas no significant improvement was observed for the group that received balance training alone. CONCLUSIONS These preliminary findings support the use of balance and eye movement exercises to improve gaze control in PSP.

Gaze Control and Foot Kinematics During Stair Climbing: Characteristics Leading to Fall Risk in Progressive Supranuclear Palsy

Background and Purpose: Does gaze control influence lower-extremity motor coordination in people with neurological deficits? The purpose of this study was to determine whether foot kinematics during stair climbing are influenced by gaze shifts prior to stair step initiation. Subjects and Methods: Twelve subjects with gaze palsy (mild versus severe) secondary to progressive supranuclear palsy were evaluated during a stair-climbing task in a cross-sectional study of mechanisms influencing eye-foot coordination. Infrared oculography and electromagnetic tracking sensors measured eye and foot kinematics, respectively. The primary outcome measures were vertical gaze fixation scores, foot lift asymmetries, and sagittal-plane foot trajectories. Results: The subjects with severe gaze palsy had significantly lower lag foot lift relative to lead foot lift than those with a mild form of gaze palsy. The lag foot trajectory for the subjects with severe gaze palsy tended to be low, with a heading toward contact with the edge of the stair. Subjects with severe gaze palsy were 28 times more likely to experience “fixation intrusion” (high vertical gaze fixation score) during an attempted shift of gaze downward than those with mild ocular motor deficits (odds ratio [OR]=28.3, 95% confidence interval [CI]=6.4–124.8). Subjects with severe gaze shift deficits also were 4 times more likely to have lower lag foot lift with respect to lead foot lift than those with mild ocular motor dysfunction (OR=4.0, 95% CI=1.7–9.7). Discussion and Conclusion: The small number of subjects and the variation in symptom profiles make the generalization of findings preliminary. Deficits in gaze control may influence stepping behaviors and increase the risk of trips or falls during stair climbing. Neural and kinematic hypotheses are discussed as possible contributing mechanisms.

Association between vestibuloocular reflex suppression during smooth movements of the head and attention deficit in progressive supranuclear palsy

With head movement, suppression of vestibular inputs during visual exploration is necessary not only for reorienting gaze, but also to direct attention to new visual targets. People with progressive supranuclear palsy (PSP) have difficulty suppressing the vestibuloocular reflex (VOR) and it was hypothesized that the magnitude of VOR suppression deficit correlates with the degree of degradation of attention and visuospatial performance. We evaluated cognitive and visuomotor function in 8 subjects with PSP (4 men and 4 women; ages 59–83 years). Gaze control was studied by measuring the accuracy of eye–head coordination during passive vertical and horizontal head‐on‐trunk movements. Fixation was assessed when subjects viewed either an earth‐fixed or head‐fixed target. A gaze fixation score (GFS) was calculated to represent the amount of error between eye and head movement in each plane (eye–head root mean square error normalized to the range of head rotation). The vertical but not horizontal GFS during attempted suppression of the VOR was significantly related to attention (r = −0.70; P = 0.05) and visuospatial ability (r = −0.76; P = 0.03). These findings suggest that the ability to suppress the VOR during vertical smooth movements of the head is associated with the magnitude of cognitive deficit in PSP.