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Biomedical subjects

P L Weiss

Publications and source records attributed to P L Weiss.

18 recordsLinked to original sources
PubMed2005

Interactive virtual environment training for safe street crossing of right hemisphere stroke patients with unilateral spatial neglect.

PURPOSE: The goal of this study was to determine whether non immersive interactive virtual environments are an effective medium for training individuals who suffer from Unilateral Spatial Neglect (USN) as a result of a right hemisphere stroke, and to compare it to a standard computer visual scanning training. METHOD: Participants included 19 patients with right hemisphere stroke in two groups, 11 in an experimental group were given computer desktop-based Virtual Reality (VR) street crossing training and 8 in a control group who were given computer based visual scanning tasks, both for a total of twelve sessions, 9 hours total, over four weeks. Measures included: 1. Standard USN assessments, paper and pencil and ADL checklist; 2. Test on the VR street program; and 3. Actual street crossing videotaped. Testing was performed pre and post intervention. RESULTS: The VR group achieved on the USN measures results that equaled those achieved by the control group treated with conventional visual scanning tasks. They improved more on the VR test and they did better on some measures of the real street crossing. CONCLUSIONS: Despite several limitations in this study the present results support the effectiveness of the VR street program in the treatment of participants with USN, and further development of the program.

Accidents, Traffic↗
PubMed2000

Effect of seated posture on interface pressure in children who are able-bodied and who have myelomeningocele.

PURPOSE: The objective of this study was to investigate the relationship between sitting position and interface pressure distribution in seated children. METHOD: Fifteen able-bodied children and 15 children with myelomeningocele complete paraplegia, aged 7 to 18 years were included in the study. The body-seat interface pressure was measured with the QA pressure measurement system. Four sitting positions typically used to reduce body-seat interface pressure position (recline, tilt, combined and lean forward) were compared to a neutral position. RESULTS: Test/re-test Pearson correlation coefficients were greater than 0.94 for maximum pressure and greater than 0.88 for mean pressure at all test positions (p < 0.0001) and, for the risk area (defined as the percentage of sensors which recorded pressures greater than 40 mm Hg.) varied from 0.62 to 0.85 (p < 0.0005). Maximum pressures for the myelomeningocele group were significantly higher than those recorded for able-bodied subjects in the neutral, combined and lean forward positions (p < 0.001). For the able-bodied subjects, maximum pressures at the combined (p < 0.001), tilt (p < 0.05) and lean forward (p < 0.0001) positions were significantly lower than those measured at the neutral position. For the myelomeningocele subjects, maximum pressure at all tested positions was significantly lower than at the neutral position (p < 0.05). CONCLUSIONS: The results point to the importance of measuring body-seat interface pressure for each wheelchair user and of using the information to customize wheelchair utilization.

Adolescent↗
PubMed1998

Use of a computer simulator for training children with disabilities in the operation of a powered wheelchair.

OBJECTIVE: The purpose of this study was to evaluate the ability of a basic driving simulator program to evaluate and train children with disabilities in their ability to operate a powered wheelchair. METHOD: With a rating scale of skills considered essential for safe and efficient wheelchair operation, 22 children 7 to 22 years of age with either progressive muscular dystrophy or cerebral palsy were evaluated in their ability to drive a powered wheelchair through a driving course. They were divided into two groups: one without prior experience driving a powered wheelchair and the other with experience. After the driving assessment with an actual powered wheelchair, the inexperienced drivers were trained on a joystick-controlled computer game in which they navigated through labyrinths similar in layout to their own school environment. A test maze was administered before and after this training. Both groups were then evaluated on their ability to drive a powered wheelchair through the driving course. RESULTS: The inexperienced drivers significantly increased their simulator scores over the training period. Their wheelchair driving performance was significantly better after the simulator training, although their performance remained poorer than that of the experienced drivers. CONCLUSION: A simulator program can assist in the development and evaluation of the skills required to operate a powered wheelchair.

Adolescent↗
PubMed1995

Effect of maintained stretch on the range of motion of the human ankle joint.

The effectiveness of maintained stretch in expanding the range of motion of the human ankle joint was assessed in a population of normal adults. Controlled movements were imposed upon the ankle, and triceps surae and tibialis anterior electromyograms were monitored to ensure that only passive joint properties generated ankle torque. We found that a majority of subjects (7 of 12) showed evidence of muscle activity sufficient to distort a subjective assessment of changes in range of motion. For the remaining five subjects, a 60-s maintained stretch produced a small decrease in the torque subsequently generated by an imposed dorsiflexing movement, but this effect was transient and largely disappeared following 300 s of rest at a neutral position. This short-term effect is consistent with the viscoelastic properties of collagenous material stretched during such treatment and is unlikely to lead to long-term increases in range of motion. RELEVANCE: The results of these experiments indicate that subjective assessments of changes in joint range of motion may be distorted by voluntary and reflexive muscle activation. Moreover the presumed increases in range of motion produced by maintained stretch in our normal subjects were small and transient. These results suggest that future assessments of the long-term efficacy of this treatment must monitor muscle activity and take into account known viscoelastic properties of collagenous materials.

Journal Article↗
PubMed1994

Using the Exos Handmaster to measure digital range of motion: reliability and validity.

Traditional assessment of digital range of motion via a standard goniometer is a weak correlate of hand function and task performance. Yet it remains one of the primary, quantitative methods of hand assessment used to determine an individual's ability to return to work or to assess his or her permanent functional impairment. Another technique more representative of functional performance would be immensely useful for clinicians, patients, employers and third-party payers. The objective of this research was to investigate the clinical feasibility of using the Exos Handmaster, a Hall-effect instrumented exoskeleton, to measure angular joint rotation of the metacarpophalangeal and interphalangeal joints. The work reported in this paper includes a description of modifications to the fixation technique and calibration procedures of the Handmaster and the results of an investigation of the unit's reliability and validity.

Activities of Daily Living↗
PubMed1992

Objective and subjective approaches to the force and displacement characteristics of input devices used by the disabled.

This study was designed to determine how well therapists were able to estimate the mechanical characteristics of adapted switches. This was accomplished using two related experiments. In the first experiment, objective data characterizing the activation force-displacement trajectories for eight commonly used adapted switches were collected. In the second experiment, subjective data identifying the relative ranking of activation force as well as activation displacement by experienced and novice therapists were compiled. The major finding was that although therapists' subjective estimates of activation force and displacement were reasonably good there were specific areas of weakness that should be rectified with quantitative, objective data. In particular, subjective estimates of the mechanical properties appeared to be inadequate when used to evaluate switches separated by only small differences in force or displacement and for those whose properties were larger or smaller than their expected values. Possible difficulties in dissociating activation force and displacement were also noted. The technical and clinical implications of these results are discussed.

Persons with Disabilities↗
PubMed1992

A human factors approach to adapted access device prescription and customization.

Adapted access device prescription and customization is often a lengthy and cumbersome process. To date, few objective procedures are available to assist in the prescription process. Rather, clinician and client rely on a trial-and-error approach that is often severely constrained by the size of their adaptive device collection as well as the extent of clinical expertise. Furthermore, the large number of available options and lack of information delineating the mechanical and physical characteristics of these devices means that therapists must take time away from direct clinical contact to probe each adaptation in detail. There is available in the human factors domain a body of literature that is highly relevant to adapted access. Of particular interest are the studies that have addressed issues related to the suitability of standard and alternative input devices in terms of task productivity (via improvements in input speed, accuracy, and endurance), and their ability to minimize the risk of acute and chronic work-related dysfunction. This paper aims to consider the relevance of human factors research for physically disabled individuals. Three human factors issues--digit travel, digit loading, and device positioning--have been selected as representative of factors important in the configuration of adapted access devices.

Adult↗
PubMed1990

Mechanical characteristics of micro-switches adapted for the physically disabled.

The object of this study was to measure the mechanical characteristics of several commonly used adapted switches in order to demonstrate the feasibility of collecting quantitative descriptions of switch performance. A stepping motor was used to drive a digital micrometer vertically towards the tested switch and proving-ring strain gauges recorded the operating force. Measures of activation and deactivation forces, travel and switch compliance were compared; several clinical examples illustrate the functional application of these results. It is anticipated that this information will permit clinicians to prescribe switches in a more accurate manner.

Adult↗
PubMed1988

Human ankle joint stiffness over the full range of muscle activation levels.

System identification techniques have been used to track changes in dynamic stiffness of the human ankle joint over a wide range of muscle contraction levels. Subjects lay supine on an experimental table with their left foot encased in a rigid, low-inertia cast which was fixed to an electro-hydraulic actuator operating as a position servo. Subjects generated tonic plantarflexor or dorsiflexor torques of different magnitudes ranging from rest to maximum voluntary contractions (MVC) during repeated presentations of a stochastic ankle angular position perturbation. Compliance impulse response functions (IRF) were determined from every 2.5 s perturbation sequence. The gain (G), natural frequency (omega n), and damping (zeta) parameters of the second-order model providing the best fit to each IRF were determined and used to compute the corresponding inertial (I), viscous (B) and elastic (K) stiffness parameters. The behaviour of these parameters with mean torque was found to follow two simple rules. First, the elastic parameter (K) increased in proportion to mean ankle torque as it was varied from rest to MVC; these changes were considerable involving increases of more than an order of magnitude. Second, the damping parameter (zeta) remained almost invariant over the entire range of contractions despite the dramatic changes in K.

Adult↗
PubMed1986

Position dependence of stretch reflex dynamics at the human ankle.

The purpose of this study was to examine the effect of ankle position on the human ankle stretch reflexes during tonically-maintained contractions over most of the range of motion. The ankle was placed at randomly selected mean positions. Target levels of triceps surae (TS) or tibialis anterior (TA) tonic contractions were generated while the ankle was displaced by small amplitude, stochastic perturbations. System identification techniques were used to identify the stretch reflex dynamics at each combination of tonic level and ankle angle. As shown previously, the TS stretch reflex was characterized by an unidirectional, velocity-sensitive impulse response function whereas the TA stretch reflex was characterized by a linear impulse response function between ankle velocity and TA EMG. TS stretch reflexes showed a strong dependence on ankle position while TA stretch reflexes did not. Thus the TS stretch reflex magnitude increased greatly as the ankle was progressively dorsiflexed. In contrast, ankle mean position had only a minor effect on the TA stretch reflex magnitude. Our results indicate that the position-dependent facilitation of the TS stretch reflex is not due to changes in the level of skeletal motoneuron excitability. Rather, this effect may be accounted for by mechanisms that modulate the efficacy of the stochastic ankle perturbation. Such mechanisms could include position-induced: modulation of monosynaptic and polysynaptic afferent inputs to skeletal motoneurons, alterations in the extent of fusimotor drive and changes in the transmission of the joint perturbation to spindle receptors. Such mechanisms are discussed in terms of the differences between TS and TA stretch reflexes. Finally, the functional significance of position-dependent reflex responses are considered.

Adult↗
PubMed1986

Position dependence of ankle joint dynamics--I. Passive mechanics.

System identification techniques were used to examine the position dependence of passive ankle joint mechanics. The relaxed ankle was stochastically perturbed about different angles in the range of motion (ROM). The linear dynamic relation between ankle position and torque was identified and modelled as a second-order underdamped system, having inertial (I), viscous (B) and elastic (K) parameters. Mean joint torque changed as the ankle was rotated through the ROM; it was small at mid-range and became much larger toward either extreme. While I remained constant both B and K changed as a function of ankle angle. At the extremes of the ROM, K was much larger than previously assumed and the relation between stiffness and the passive torque generated when the ankle was placed at different mean positions was linear. These results show that large variations in joint mechanics are possible even in the absence of voluntary muscle contraction. Moreover, these changes appear to be related to the torque generated when passive joint structures are stretched.

Adult↗
PubMed1986

Position dependence of ankle joint dynamics--II. Active mechanics.

System identification techniques were used to examine the position dependence of active ankle joint mechanics. Subjects were required to maintain tonic contractions in either the tibialis anterior (TA) or triceps surae (TS) muscles while the ankle was stochastically displaced about different mean angular positions. The dynamic relation between ankle position and torque was determined for each mean position/tonic torque combination; a non-linear minimization technique was used to estimate the three parameters (inertial, viscous and elastic) of a second-order, underdamped system. Whereas the inertial parameter remained essentially invariant across all test conditions, the viscous and elastic (K) parameters became larger as the level of tonic activity increased and as the joint was rotated toward the extremes of the range of motion. The relation between K and torque was linear at all ankle angles. The slope of this relation remained constant at all mean positions during plantarflexor contractions; during dorsiflexor contractions the slope increased as the ankle was rotated from maximum plantarflexion to maximum dorsiflexion. These findings are discussed in terms of: the physiological correlates of ankle mean position, the relative significance of passive and active joint mechanics and contrasts in joint behaviour during active dorsiflexor and plantarflexor contractions.

Adult↗
PubMed1983

Upper and lower extremity EMG correlations during normal human gait.

The purpose of the present study was to determine whether diagonal intersegmental interactions are present during normal human gait. The demonstration of consistently synchronous phasing would indicate the feasibility of utilizing an electromyographic (EMG) signal to control functional electrical stimulation to a paralyzed lower extremity muscle during gait. The EMG activity of several muscles of the upper extremity and of the tibialis anterior (TA) were monitored with surface electrodes in 8 women. Variability in both the frequency of occurrence and duration of EMG activity was found in all muscles of the upper extremity. No single arm muscle common to all subjects was phased similarly to TA. However, 6 subjects demonstrated at least 1 muscle of the upper extremity that was working at the same time as TA. It is postulated that differences in upper limb kinematics may mask the existence of intersegmental interactions during gait.

Adult↗