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Biomedical subjects

Richard P Di Fabio

Publications and source records attributed to Richard P Di Fabio.

10 recordsLinked to original sources
PubMed2006

Gaze-shift strategies during functional activity in progressive supranuclear palsy.

The relative sparing of visual fixation in parallel with disruption of saccade function in progressive supranuclear palsy (PSP) creates a unique human model for the study of gaze-shift strategies which are adopted when vertical gaze palsy impairs primarily the eye-movement component of gaze control. It was hypothesized that people with PSP would rely on head pitch as a primary component of gaze shift during a platform stepping task and that there would be a predominance of fixation behavior (counter rotation of the eyes during head pitch) while attempting a down-gaze shift. Fourteen subjects with probable and 5 subjects with possible PSP participated in two experiments to measure visual fixation and gaze shift on the same continuum (using a derived vertical gaze fixation score, vGFS). Experiment #1 required gaze fixation during passive head pitch at 0.1-0.2 Hz, whereas experiment #2 required gaze shifts during a continuous platform step on, over, and off task. The primary gaze-shift strategy involved pitching the head downward to compensate for a loss in vertical saccade function. This strategy produced head pitch velocity that leads vertical eye velocity on the order of 200-500 ms. Gaze shifts during platform stepping showed greater fixation suppression (e.g., lower vGFS) in both groups of PSP compared to the visual stabilization task, but some subjects showed "fixation intrusion" during attempted gaze shift. The amount of eye movement was relatively constant when corrected for orbit height, whereas the extent of head pitch varied in proportion to the task demands. The mechanism controlling gaze in PSP, therefore appears to modulate head pitch independently of eye movement, but the gaze strategy seems dependent upon the extent of gaze dysfunction. These findings support the view that the desired gaze signal is parsed into separate eye and head pathways upstream from the burst neurons.

Adaptation, Physiological↗
PubMed2006

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.

Aged↗
PubMed2005

The validity of prospective and retrospective global change criterion measures.

OBJECTIVE: To assess the validity of retrospective versus prospective criterions of change. DESIGN: Single cohort pretest-posttest design. SETTING: Physical or occupational therapy outpatient clinics. PARTICIPANTS: Volunteer sample of 211 patients with upper-extremity musculoskeletal problems. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Disabilities of the Arm, Shoulder, and Hand questionnaire, the Shoulder Pain and Disability Index, the Patient-Rated Wrist Evaluation, the Medical Outcomes Study 12-Item Short-Form Health Survey; global disability rating (GDR), retrospective global rating of change (GRC), and patient satisfaction. RESULTS: Correlations were calculated among the baseline, 3-month follow-up, and change scores for each outcome measure with the change criterion instruments. Retrospective GRC and patient satisfaction ratings showed moderate correlations with the 3-month follow-up scores, but nonsignificant correlations with baseline scores. By contrast, the prospective GDR criterion showed significant correlations with both baseline and 3-month follow-up scores ranging between 0.3 and 0.4 (absolute value). CONCLUSIONS: Retrospective self-report measures of change do not accurately reflect true change over time. The retrospective GRC and patient satisfaction were heavily influenced by current (posttreatment) status whereas the prospective global change measure reflected both baseline and posttreatment status equally and thus appeared to be a more valid measure of change over time. This study demonstrates the need for an alternative criterion for establishing true individual change.

Adolescent↗
PubMed2004

Reliable change and minimum important difference (MID) proportions facilitated group responsiveness comparisons using individual threshold criteria.

OBJECTIVE: This study contrasted the use of responsiveness indices at the group level vs. individual patient level. STUDY DESIGN AND SETTING: We followed a cohort of 211 patients (50% male; mean age 47.5 years; SD 14) with musculoskeletal upper extremity problems for a total of 3 months. Outcome measures included the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, Shoulder Pain and Disability Index (SPADI), Patient-Rated Wrist Evaluation (PRWE), and the Medical Outcomes Study 12-Item Short-Form Health Survey (SF-12). We calculated confidence intervals on various group-level responsiveness statistics based on effect size and correlation with global change. The proportion of patients exceeding the minimum detectable change (or reliable change proportion) and minimum important difference (MID proportion) were included as indices applicable to the individual patient. RESULTS: For the DASH, effect size ranged from 1.06 to 1.67 for various patient subgroups, and the reliable change and MID proportions indicated that 50%-70% of individuals exhibited change based on individual change scores. Only the SRM and reliable change proportion indicated differences among the outcome measures used in this study. CONCLUSION: The reliable change and MID proportions have an intuitive interpretation and facilitate quantitative responsiveness comparisons among outcome measures based on individual patient criteria.

Adult↗
PubMed2004

Footlift asymmetry during obstacle avoidance in high-risk elderly.

OBJECTIVES: To test the hypothesis that vertical footlift asymmetries and low obstacle clearing distance during obstacle avoidance are characteristics of elderly people classified as high risk for falls. DESIGN: Controlled cross-sectional design with two conditions to cue selection of the foot-for-step initiation: sound cue and visual cue. SETTING: Senior independent living facilities. PARTICIPANTS: Eighteen community-dwelling elderly with a history of falling or prolonged Timed Up and Go score greater than 13.5 seconds, 16 elderly with no fall history and Timed Up & Go score of 13.5 seconds or less, and 15 younger subjects. MEASUREMENTS: Video kinematic analysis of bilateral footlift displacement and velocity using reflective markers as subjects stepped over foam obstacles scaled to a maximum tolerated height. RESULTS: High-risk elders contacted the obstacle more frequently and had significantly greater vertical footlift asymmetries adjusted for obstacle/subject height (mean+/-standard error asymmetry index for sound cue 3.25+/-0.42 cm, for visual cue 2.51+/-0.45 cm) than low-risk and younger subjects (P<.001). In low-risk elderly and younger subjects, the asymmetry index approached 0, which indicated symmetrical lower limb movements when stepping over the obstacles. CONCLUSION: High-risk elderly show a marked asymmetry in foot clearance while stepping over an obstacle, with the lag foot clearing the obstacle at a much lower distance than the lead foot. Possible mechanisms responsible for these findings (limited hip extension and deficits in executive cognitive function) are discussed.

Accidental Falls↗
PubMed2003

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.

Adult↗
PubMed2003

Saccade-stepping interactions revise the motor plan for obstacle avoidance.

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.

Adult↗
PubMed2002

Eye-head coordination during postural perturbation as a predictor of falls in community-dwelling elderly women.

OBJECTIVES: To assess the functional significance of eye-head coordination during postural perturbations and to determine the contribution of angular vestibulo-ocular reflex (AVOR) suppression to the prediction of 1-year fall history in community-dwelling elderly women. DESIGN: Descriptive analysis of factors correlated with falls. SETTING: Community-based independent and senior assisted living facilities. PARTICIPANTS: Volunteer sample of 38 older women (mean age +/- standard deviation, 81.6+/-3.9y; range, 74-92y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Multiple and logistic regression variables (slope coefficients, partial R2, percent-correct fall history classifications) and fall prediction equations generated by using minimal sets of predictor variables. RESULTS: Instantaneous AVOR gain and sedative use were predictors of 1-year history of falls in all minimal sets of predictor variables. R2 for the prediction models varied from.47 to.62 and indicated substantial shared variance with the 1-year history of falling. Elderly women who failed to suppress the AVOR gain were 18 times more likely to have experienced a fall in the past year compared with elderly women who showed AVOR suppression (odds ratio=18; 95% confidence interval, 1.63-198.42). CONCLUSIONS: When controlling for all other variables in the model, instantaneous AVOR gain accounted for nearly 30% of the variance of fall history. The strong association between 1-year fall history, the use of sedatives, and changes in the AVOR gain supports a functional link between AVOR suppression and effective balance in elderly women.

Accidental Falls↗
PubMedDate not supplied

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 if normally 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.

Accidental Falls↗