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Search Results: 1 - 10 of 179796 matches for " William E. McIlroy "
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Does It Really Matter Where You Look When Walking on Stairs? Insights from a Dual-Task Study
Veronica Miyasike-daSilva, William E. McIlroy
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044722
Abstract: Although the visual system is known to provide relevant information to guide stair locomotion, there is less understanding of the specific contributions of foveal and peripheral visual field information. The present study investigated the specific role of foveal vision during stair locomotion and ground-stairs transitions by using a dual-task paradigm to influence the ability to rely on foveal vision. Fifteen healthy adults (26.9±3.3 years; 8 females) ascended a 7-step staircase under four conditions: no secondary tasks (CONTROL); gaze fixation on a fixed target located at the end of the pathway (TARGET); visual reaction time task (VRT); and auditory reaction time task (ART). Gaze fixations towards stair features were significantly reduced in TARGET and VRT compared to CONTROL and ART. Despite the reduced fixations, participants were able to successfully ascend stairs and rarely used the handrail. Step time was increased during VRT compared to CONTROL in most stair steps. Navigating on the transition steps did not require more gaze fixations than the middle steps. However, reaction time tended to increase during locomotion on transitions suggesting additional executive demands during this phase. These findings suggest that foveal vision may not be an essential source of visual information regarding stair features to guide stair walking, despite the unique control challenges at transition phases as highlighted by phase-specific challenges in dual-tasking. Instead, the tendency to look at the steps in usual conditions likely provides a stable reference frame for extraction of visual information regarding step features from the entire visual field.
Ambulatory monitoring of activity levels of individuals in the sub-acute stage following stroke: a case series
William H Gage, Karl F Zabjek, Kathryn M Sibley, Ada Tang, Dina Brooks, William E McIlroy
Journal of NeuroEngineering and Rehabilitation , 2007, DOI: 10.1186/1743-0003-4-41
Abstract: Activities and physiologic measures were recorded during a continuous 8 hour period from 4 individuals in the sub-acute stage following stroke (ranging from 49 to 80 years old; 4 to 8 weeks post-stroke) in an in-patient rehabilitation hospital.Both heart rate (p = 0.0207) and ventilation rate (p < 0.0001) increased as intensity of activity increased. Results revealed individual differences in physiological response to daily activities, and large ranges in physiological response measures during 'moderately' and 'highly' therapeutic activities.Activity levels of individuals with stroke during the day were generally low, though task-related changes in physiologic measures were observed. Large variability in the physiological response to even the activities deemed to be greatest intensity suggests that inclusion of such extended measurement of physiologic measures may improve understanding of physiological profile that could guide elements of the physical therapy prescription.Considerable effort in the rehabilitation process of patients with stroke is orientated towards addressing sensori-motor dysfunction [1,2] and cognitive deficits [2,3]. Although the majority of patients with stroke have concomitant cardiovascular disease, and as such can benefit from aerobic exercise training, the effects of such exercise among these patients is only beginning to be considered in the literature [4,5]. A recent meta-analysis which included seven randomized controlled trials examining the efficacy of aerobic exercise training among patients with stroke reported that there is good evidence to support the use of aerobic exercise among patients with mild and moderate stroke for improving aerobic capacity [6]. Studies that have examined the effects of exercise [7,8] in sufficient dose and intensity have shown that improvements in cardiovascular fitness among individuals with stroke can be comparable to that of healthy, age-matched adults. The benefits of exercise for these individuals in
Cardiovascular Responses Associated with Daily Walking in Subacute Stroke
Sanjay K. Prajapati,Avril Mansfield,William H. Gage,Dina Brooks,William E. McIlroy
Stroke Research and Treatment , 2013, DOI: 10.1155/2013/612458
Abstract: Despite the importance of regaining independent ambulation after stroke, the amount of daily walking completed during in-patient rehabilitation is low. The purpose of this study is to determine if (1) walking-related heart rate responses reached the minimum intensity necessary for therapeutic aerobic exercise (40%–60% heart rate reserve) or (2) heart rate responses during bouts of walking revealed excessive workload that may limit walking (>80% heart rate reserve). Eight individuals with subacute stroke attending in-patient rehabilitation were recruited. Participants wore heart rate monitors and accelerometers during a typical rehabilitation day. Walking-related changes in heart rate and walking bout duration were determined. Patients did not meet the minimum cumulative requirements of walking intensity (>40% heart rate reserve) and duration (>10?minutes continuously) necessary for cardiorespiratory benefit. Only one patient exceeded 80% heart rate reserve. The absence of significant increases in heart rate associated with walking reveals that patients chose to walk at speeds well below a level that has meaningful cardiorespiratory health benefits. Additionally, cardiorespiratory workload is unlikely to limit participation in walking. Measurement of heart rate and walking during in-patient rehabilitation may be a useful approach to encourage patients to increase the overall physical activity and to help facilitate recovery. 1. Background Regaining independent ambulation is important to those with stroke [1, 2] and is the most frequently reported rehabilitation goal [3, 4]. Therefore, walking should be an integral part of in-patient rehabilitation. However, accelerometer-based monitoring of walking activity has revealed that the amount of daily walking completed by individuals with stroke during in-patient rehabilitation is low [5, 6]. Importantly, the majority of walking bouts are of short duration (<1 minute) [5–7] and typically involve walking to essential activities (e.g., washroom, dining area, or therapy) [5]. While activity monitors provide insight into total daily activity [5–10], they do not inform the possible determinants or consequences of this activity. Aerobic capacity is reduced in the early months following stroke [11–13]. Furthermore, poststroke gait is inefficient, and there are increased aerobic demands on those with stroke when walking compared to healthy controls, even when walking at the same speed [14]. Therefore, individuals with stroke are closer to their maximal aerobic threshold when walking than healthy controls. This
Correlating lesion size and location to deficits after ischemic stroke: the influence of accounting for altered peri-necrotic tissue and incidental silent infarcts
Lisa D Alexander, Sandra E Black, Fuqiang Gao, Gregory Szilagyi, Cynthia J Danells, William E McIlroy
Behavioral and Brain Functions , 2010, DOI: 10.1186/1744-9081-6-6
Abstract: Chronic stroke lesions of 41 patients were manually traced from digital T1-MRI to sequentially include the: necrotic lesion core, altered peri-necrotic tissue, silent lesions in the same hemisphere as the index lesion, and silent lesions in the opposite hemisphere. Lesion volumes for each region were examined for correlation with motor impairment scores, and subtraction analysis was used to highlight anatomical lesion loci associated with this deficit.For subtraction lesion analysis, including peri-necrotic tissue resulted in a larger region of more frequent damage being seen in the basal ganglia. For correlational analysis, only the volume of the lesion core was significantly associated with motor impairment scores (r = -0.35, p = 0.025). In a sub-analysis of patients with small subcortical index lesions, adding silent lesions in the opposite hemisphere to the volume of the index stroke strengthened the volume-impairment association.Including peri-necrotic tissue strengthened lesion localization analysis, but the influence of peri-necrotic tissue and incidental lesions on lesion volume correlations with motor impairment was negligible barring a small index lesion. Overall, the potential influence of incidental lesions and peri-necrotic tissue on brain-behaviour relationships may depend on the characteristics of the index stroke and on whether one is examining the relationship between lesion volume and impairment or lesion location and impairment.The size and anatomical location of stroke lesions is frequently evaluated to help advance our understanding of links between brain structure and human behaviour [1-4]. Accordingly, it is important for stroke neuroimaging analysts to have well-crafted methods for delineating and quantifying brain lesions that are visualized using widely available modalities such as magnetic resonance imaging (MRI). Lesion-based brain-behaviour studies in domains such as neuroscience and neuropsychology often involve patients with chronic st
The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations
Sylvia Quant, Allan L Adkin, W Richard Staines, Brian E Maki, William E McIlroy
BMC Neuroscience , 2004, DOI: 10.1186/1471-2202-5-18
Abstract: Results revealed a significant decrease in the magnitude of early cortical activity (the N1 response, the first negative peak after perturbation onset) during the tracking task compared to the control condition. More pronounced AP COP peak displacements and EMG magnitudes were also observed for the tracking task and were possibly related to changes in the N1 response.Based on previous notions that the N1 response represents sensory processing of the balance disturbance, we suggest that the attenuation of the N1 response is an important central mechanism that may provide insight into the relationship between attention and postural control.Dual-task experiments, in which subjects simultaneously perform a postural task and a cognitive task, show alterations in the performance of the postural task [1-6], the cognitive task [7-10], or both tasks [11-20]. The results of these studies suggest that, in some way, postural control requires attention or other cognitive resources. However, central mechanisms that might be responsible for alterations in postural control and/or the cognitive task during a dual-task challenge remain unclear.One method to examine the central mechanisms involved in postural control is to measure cortical potentials (perturbation-evoked potentials or PEPs) following mechanical perturbations to stability using scalp-recorded electrodes [21-27]. Early PEPs involve a variable initial positive peak (P1) followed by a stable negative peak (termed "the N1 response"). The N1 response typically peaks within 100 to 200 ms following perturbation onset, and is often followed by later cortical potentials (termed "late PEPs") that peak within 200 to 400 ms with respect to perturbation onset.Previous studies have suggested that early PEPs represent sensory processing of the postural disturbance. For example, Dietz et al. [22] observed attenuated and delayed cortical potentials during perturbed gait compared to perturbed stance, which were similar in direction (alt
Contribution of primary motor cortex to compensatory balance reactions
Bolton David A E,Williams Laura,Staines W,McIlroy William E
BMC Neuroscience , 2012, DOI: 10.1186/1471-2202-13-102
Abstract: Background Rapid compensatory arm reactions represent important response strategies following an unexpected loss of balance. While it has been assumed that early corrective actions arise largely from sub-cortical networks, recent findings have prompted speculation about the potential role of cortical involvement. To test the idea that cortical motor regions are involved in early compensatory arm reactions, we used continuous theta burst stimulation (cTBS) to temporarily suppress the hand area of primary motor cortex (M1) in participants prior to evoking upper limb balance reactions in response to whole body perturbation. We hypothesized that following cTBS to the M1 hand area evoked EMG responses in the stimulated hand would be diminished. To isolate balance reactions to the upper limb participants were seated in an elevated tilt-chair while holding a stable handle with both hands. The chair was held vertical by a magnet and was triggered to fall backward unpredictably. To regain balance, participants used the handle to restore upright stability as quickly as possible with both hands. Muscle activity was recorded from proximal and distal muscles of both upper limbs. Results Our results revealed an impact of cTBS on the amplitude of the EMG responses in the stimulated hand muscles often manifest as inhibition in the stimulated hand. The change in EMG amplitude was specific to the target hand muscles and occasionally their homologous pairs on the non-stimulated hand with no consistent effects on the remaining more proximal arm muscles. Conclusions Present findings offer support for cortical contributions to the control of early compensatory arm reactions following whole-body perturbation.
Electrophysiological Correlates of Changes in Reaction Time Based on Stimulus Intensity
Bimal Lakhani, Albert H. Vette, Avril Mansfield, Veronica Miyasike-daSilva, William E. McIlroy
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0036407
Abstract: Background Although reaction time is commonly used as an indicator of central nervous system integrity, little is currently understood about the mechanisms that determine processing time. In the current study, we are interested in determining the differences in electrophysiological events associated with significant changes in reaction time that could be elicited by changes in stimulus intensity. The primary objective is to assess the effect of increasing stimulus intensity on the latency and amplitude of afferent inputs to the somatosensory cortex, and their relation to reaction time. Methods Median nerve stimulation was applied to the non-dominant hand of 12 healthy young adults at two different stimulus intensities (HIGH & LOW). Participants were asked to either press a button as fast as possible with their dominant hand or remain quiet following the stimulus. Electroencephalography was used to measure somatosensory evoked potentials (SEPs) and event related potentials (ERPs). Electromyography from the flexor digitorum superficialis of the button-pressing hand was used to assess reaction time. Response time was the time of button press. Results Reaction time and response time were significantly shorter following the HIGH intensity stimulus compared to the LOW intensity stimulus. There were no differences in SEP (N20 & P24) peak latencies and peak-to-peak amplitude for the two stimulus intensities. ERPs, locked to response time, demonstrated a significantly larger pre-movement negativity to positivity following the HIGH intensity stimulus over the Cz electrode. Discussion This work demonstrates that rapid reaction times are not attributable to the latency of afferent processing from the stimulated site to the somatosensory cortex, and those latency reductions occur further along the sensorimotor transformation pathway. Evidence from ERPs indicates that frontal planning areas such as the supplementary motor area may play a role in transforming the elevated sensory volley from the somatosensory cortex into a more rapid motor response.
Feasibility and effects of adapted cardiac rehabilitation after stroke: a prospective trial
Ada Tang, Susan Marzolini, Paul Oh, William E McIlroy, Dina Brooks
BMC Neurology , 2010, DOI: 10.1186/1471-2377-10-40
Abstract: A repeated measures design was used with a 3-month baseline period and 6-month adapted CR intervention (n = 43, mean ± SD age 65 ± 12 years, 30 ± 28 months post stroke). Feasibility was determined by the number of participants who completed the study, occurrence of adverse events and frequency, duration and intensity of exercise performed. To determine effectiveness of the program, outcomes measured included aerobic capacity (VO2peak, ventilatory threshold), 6-Minute Walk Test (6MWT) distance, and risk factors. Descriptive statistics characterized the classes attended and number and intensity of exercise sessions. Paired t-tests, one-factor repeated measures analyses of variance contrasts and chi-square analyses were used to compare changes over time.Two participants withdrew during the baseline period. Of the remaining 41 participants who commenced the program, 38 (93%) completed all aspects. No serious adverse effects occurred. Post-intervention, VO2peak improved relative to the stable baseline period (P = 0.046) and the increase in ventilatory threshold approached significance (P = 0.062).CR is feasible after stroke and may be adapted to accommodate for those with a range of post-stroke disability. It is effective in increasing aerobic capacity. CR may be an untapped opportunity for stroke survivors to access programs of exercise and risk factor modification to lower future event risk.ClinicalTrials.gov registration number: NCT01067495Stroke is the leading cause of neurological disability in adults [1]. Poor levels of fitness, including low aerobic capacity [2] can compound the challenges by further limiting the ability to engage in many daily activities and impacting risk of subsequent stroke. Traditional stroke rehabilitation is effective in improving functional independence [3] yet insufficiently challenges the cardiorespiratory system to induce aerobic benefit [4].In contrast, cardiac rehabilitation (CR) is focused on exercise and risk factor management and i
Changes in spatiotemporal gait variables over time during a test of functional capacity after stroke
Kathryn M Sibley, Ada Tang, Kara K Patterson, Dina Brooks, William E McIlroy
Journal of NeuroEngineering and Rehabilitation , 2009, DOI: 10.1186/1743-0003-6-27
Abstract: 24 community dwelling, independently ambulating individuals greater than 3 months after stroke performed the Six-Minute Walk Test (6MWT). Participants walked over a pressure-sensitive mat on each pass of the 30 m course which recorded spatial and temporal parameters of gait. Mean gait speed and temporal symmetry ratio during each two-minute interval of the 6MWT were examined. Additional post hoc analyses examined the incidence of rests during the 6MWT and changes in gait speed and symmetry.On average, participants demonstrated a 3.4 ± 6.5 cm/s decrease in speed over time (p= 0.02). Participants who rested were also characterized by increased asymmetry in the final two minutes (p= 0.05). 30% of participants rested at some point during the test, and if a rest was taken, duration increased in the final two minutes (p= 0.001). Examination of factors which may have been associated with resting indicated that resters had poorer balance (p= 0.006) than non-resting participants.This study supports previous findings establishing that walking performance after stroke declines over relatively short bouts of functionally-relevant ambulation. Such changes may be associated with both cardiorespiratory and muscular fatigue mechanisms that influence performance. The findings also indicate that rest duration should be routinely quantified during the 6MWT after stroke, and consequently, further research is necessary to determine how to interpret 6MWT scores when resting occurs.Sensorimotor control is commonly impaired following stroke, and such changes in strength and coordination can significantly affect gait [1]. Gait impairments influence functional ambulation – the capacity to perform walking during activities of daily living – and are compounded by low cardiorespiratory fitness in stroke survivors [2,3]. Furthermore, fatigue is a commonly reported issue after stroke [4,5], and cardiorespiratory and muscular components of fatigue may mutually reinforce one another. For example, b
Do functional walk tests reflect cardiorespiratory fitness in sub-acute stroke?
Ada Tang, Kathryn M Sibley, Mark T Bayley, William E McIlroy, Dina Brooks
Journal of NeuroEngineering and Rehabilitation , 2006, DOI: 10.1186/1743-0003-3-23
Abstract: Thirty-six individuals (mean age ± SD, 64.6 ± 14.4 years; time post-stroke 16.2 ± 13.3 days) were evaluated using the 6MWT (distance, speed, heart rate), a maximal exercise test (VO2peak, heart rate, exercise test duration), and walking competency using a five meter walk (speed, symmetry ratio). Correlation analyses were used to examine the relationships between these outcomes.There was a strong correlation between the 6MWT and five meter walk velocity for preferred (r = 0.79) and fast (r = 0.82) speed (p < 0.001). On average, the 6MWT speed was faster than the preferred gait speed (94.9 cm/s vs. 83.8 cm/s, p = 0.003), but slower than the fast-paced walk (115.1 cm/s, p < 0.001). There was significant though more moderate association between 6MWT distance and VO2peak (r = 0.56, p < 0.001) and exercise test duration (r = 0.60, p < 0.001).The speed selected during the 6MWT was strongly related to the velocities selected during the five meter walk distance (intermediate to the selected preferred and fast speeds). Although the 6MWT may be challenging to the cardiorespiratory system, it appears to be more strongly influenced by potential limits to walking speed rather than cardiorespiratory capacity. As a result, this test is not, by itself, an adequate measure of aerobic fitness early after stroke.Stroke is the leading cause of adult disability in North America [1,2]. Functional ambulation is often compromised [3-6], and reduced independence in walking is a commonly reported concern among stroke survivors [7]. This is further complicated by reductions in cardiorespiratory fitness after stroke [4,8-10], changes in neuromotor control [5] and increased energy demands associated with performing everyday activities [6,10]. These issues underscore the need for valid testing procedures to evaluate aerobic fitness and walking ability following stroke.The measurement of maximal oxygen consumption during graded exercise testing is the gold standard for evaluating cardiorespiratory
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