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Biomedical subjects

A Beuter

Publications and source records attributed to A Beuter.

At least 37 records · Page 2Linked to original sources
PubMed1994

Diadochokinesimetry: a study of patients with Parkinson's disease and manganese exposed workers.

Diadochokinesia, the ability to perform rapid alternating movements is often impaired in patients with extrapyramidal disease. It is a common sign among patients with Parkinsonism or manganism. In the present study we compare patients with Parkinson's disease (n = 11), workers formerly exposed to manganese (n = 10) and control subjects (n = 11) performing rapid alternating hand movements for 5 s under four conditions repeated twice (natural cadence and maximal speed with one or two hands). Data recorded using a diadochokinesimeter built in our laboratory and connected to a 486/33 microcomputer were digitized in real time while subjects rotated back and forth hand held foam spheres connected to flexible rods articulated with optical encoders. Significant differences were found between control subjects and patients with Parkinson's disease, but not with manganese exposed workers, in most variables examined. However, trajectory length (a combination of movement amplitude and velocity) indicated that manganese exposed workers and patients with Parkinson's disease were significantly different from the controls in functional asymmetries between right and left hand. In addition, workers and patients tend to have marked differences between the performance of right and left hands. Improved quantitative measurement of rapid alternating movements may prove to be an important tool in early and differential diagnosis of Parkinson's disease and manganese exposure.

Humans↗
PubMed1993

Effects of noise on a delayed visual feedback system.

Experimentally it is known that some patients with Parkinson's disease are not able to use visual information in a normal manner in a simple motor tracking task involving a time delay. We considered the possibility that pathological tremor present in these individuals acts as noise and prevents them from performing normally. To test this hypothesis the effects of adding coloured noise was investigated experimentally and theoretically. Ten adult subjects with no known neurological disease were asked to track their own delayed finger position with different levels of coloured noise and delays introduced. Also, a model for the task utilizing first-order delay-differential equations was constructed and coloured noise was injected into simulations. The theoretical implications of the inclusion of a stochastic component are considered, and the prospect of the dynamics being driven by noise is discussed. Experimental and numerical results indicate that augmented noise tends to corrupt and curtail the oscillations normally induced by time delays. This augmented noise may explain why some patients with Parkinson's disease are not able to utilize visual information in a normal manner.

Adult↗
PubMed1993

Feedback and delays in neurological diseases: a modeling study using dynamical systems.

Numerous regulatory mechanisms in motor control involve the presence of time delays in the controlled behavior of the system. Experimentally, we have shown that an increase of the time delay in visual feedback induces different oscillations in control subjects and in patients with neurological diseases during the performance of a simple compensatory tracking task. A preliminary model is proposed to describe the oscillations observed in control subjects and in patients with neurological diseases. The influence of delays in two feedback loops are the main components of the motor control circuitry involved in this task and are studied from an analytical and physiological perspective. We analytically determine the influence in the model of each of these delays on the stability of the finger position. In addition, the influence of stochastic elements ("noise") in the modeling equation is seen to contribute qualitatively to a more accurate reproduction of experimental traces in patients with Parkinson's disease but not in patients with cerebellar disease.

Cerebellar Diseases↗
PubMed1992

The organization of stepping in patients with Parkinson's disease: bradykinesia or discoordination?

The purpose of this experiment was to quantify and analyse multijoint coordination of patients with Parkinson's disease (N = 5) and control subjects (N = 5) during forward and backward stepping motions executed at different cadences. Coordinates of reflective markers placed on the shoulder, hip, knee, ankle and metatarsal joints were recorded in the sagittal plane using a video motion analysis system. Kinematic and kinetic analyses provided angular displacements and velocities as well as joint moments of force and powers. Results suggest the presence of two types of discoordination: one type is velocity-dependent, hence related to bradykinesia, whereas the other type appears to reflect qualitatively different coordination patterns.

Aged↗
PubMed1990

Kinematic variability and relationships characterizing the development of walking.

The purposes of this study were: (1) to determine the pattern of variability and relationships in joint kinematics characterizing the development of walking and (2) to determine whether controlling for postural stability in new walkers results in less variability. The variability and relationships among hip, knee, and ankle motions were measured during 10 gait cycles of new walkers, supported new walkers, two-year-olds and seven-year-olds. Fourier series were generated for each joint motion and standard deviations were compared across groups. An age-related decline in variability was evident in select portions of the cycle. Stance and swing phase duration correlated with cycle duration for all ages. Postural support did not lessen variability in joint rotations for new walkers. Cross-correlations for hip-knee, knee-ankle, and hip-knee rotations were strong across all groups. These results suggest that a coordinative structure for walking produces strong intralimb coupling early in development, despite variability in select portions of joint motions.

Child↗
PubMed1990

Delayed visual feedback and movement control in Parkinson's disease.

The dependence of movement on visual information was compared for healthy individuals and Stage II-III patients with Parkinson's disease (PD). A time delay (0-1400 ms) was introduced into a visually guided motor tracking task which required the subject to maintain constant index finger position relative to a stationary baseline on an oscilloscope. For healthy individuals, delayed visual feedback induced complex oscillations in finger displacement. Similar results were obtained for four of eight patients with PD. However, oscillations were not induced in four of eight patients with PD because of reduced gain and/or a higher tremor amplitude at zero delay which obscured the tracking error. These results suggest that some patients with PD are able to utilize visual information for controlling tracking in this motor task in the same manner as healthy individuals.

Adult↗
PubMed1989

Parameter optimization model of learning in stepping motion.

In this study we combine the representation of motion by a finite number of hardwired functions with parameter optimization to model learning during a stepping motion. Representation of experimental kinematic data by a finite number of predetermined functions and undetermined coefficients was analyzed. Least squares approximation was used to represent experimental data of stepping motions over obstacles of different heights. Functional relationships between coefficients and obstacles heights were also obtained. Learning of stepping over an obstacle was then formulated as a finite dimensional optimization problem. The pattern of foot path, and joint angles trajectories obtained by this learning model, were then compared to the experimental data. The results of the data fitting analysis and of the optimization process as a model for motion learning, indicate that motion can be adequately represented by a set of hardwired functions, and a finite number of task dependent coefficients.

Humans↗
PubMed1989

Complex oscillations in a human motor system.

Experiments were performed to investigate the oscillations arising in a human motor system with delayed visual feedback. Eight subjects were instructed to maintain a constant finger position relative to a stationary baseline. The finger displacement was measured using a microdisplacement transducer connected to the index finger, and was displayed on an oscilloscope. Time delays between 40 and 1,500 ms were inserted in the visual feedback loop for 100 s. Results show that, as the time delays increase, irregular rhythms appear with short intermittent periods of regular oscillations. These regular low-frequency oscillations have an amplitude that increases with the time delays and a period that is consistently about 2 to 4 times the time delay. Fast Fourier Transforms (FFT) show a peak between 8 and 12 Hz, corresponding to physiological tremor in half the subjects. No systematic variations in the FFT for the 2 to 15 Hz range were observed as time delay increased. In the 0 to 2 Hz range, the FFT show a consistent increase in power with the time delay. These results indicate that, under the conditions of this experiment, tremor is not affected by time delays in the visuomotor system, and time delays in the visuomotor feedback loop give rise to complex oscillatory behaviors.

Journal Article↗
PubMed1988

Fitting mathematical functions to joint kinematics during stepping: implications for motor control.

The present study extends past work on modeling and control of stepping. The relationship between joint space kinematic data and routine motor control (i.e., open loop) during human stepping is investigated. A model of open loop stepping control using joint kinematics is described. Different functional approximations are employed to simulate experimental joint kinematic data collected on a subject stepping repeatedly over an obstacle. Results indicate that joint kinematics can be characterized by a small number of functions yielding a simple analytical description of open loop motor control. The different basis functions used and their associated coefficients reflected the qualitative behavior of joint trajectories thus allowing flexibility in the formulation of system kinematics. This approach provides a tool to study movement pathologies and movement development by identifying the basis functions governing the kinematics of motion and their associated coefficients. The model presented here is helpful in studying the segmentation of multiarticular movements into their elementary components by analytically modeling the discrete organization of motor behavior.

Foot↗
PubMed1988

[A theoretical model of the transition phase in human locomotion].

In this study we examine the bifurcation of the transition between walking and running. Beuter and Lalonde (1986) have conjectured that the pertinent parameters separating walking and running can be described by a cusp singularity (Thom, 1972). In this model, the unidimensional state space is characterized by support duration and the bidimensional parameter space is characterized by the subject's weight and speed. To test this model eight males walked and ran on a motor driven treadmill at an increasing or decreasing speed with or without additional loads corresponding to 0%, 7% and 14% of their body weight. Velocities corresponding to transitions between the two modes of locomotion indicate that on the average the walk-run transition occurs at higher speed than the run-walk transition illustrating an hysteresis effect. In addition, the average difference between the transitions decreases as the load increases [mean 0 = 0.235 m/s, +/- 0.09 m/s, mean 7 = 0.104 m/s, +/- 0.07 m/s and mean 14 = 0.041 m/s, +/- 0.06 m/s] corresponding to an F ratio of F = 2.72, 0.05 less than p less than 0.1. A comparison of the differences in transition velocity at 0% and 14% is statistically different (t = 2.8, p less than 0.025). These results tend to support the existence of an elementary cusp singularity separating the two locomotion modes and suggest that the mechanisms controlling these transitions can be described by a hysterisis cycle and a small number of parameters.

Adipose Tissue↗
PubMed1987

Relationships between electromyography and kinematics in human stepping strategies.

Kinematic and electromyographic (EMG) parameters were analyzed on phase plane diagrams of human stepping motions performed over an obstacle of varying height. A videomotion analysis system was used to record the displacement of 5 reflective markers placed on the subject's lower limb joints. Surface bipolar electrodes were placed on the rectus and biceps femoris muscles. Results revealed systematic differences in the EMG patterns of the rectus femoris between initial and subsequent trials in the 3 conditions of obstacle height. In the initial trials there was an episode of EMG activity right before or during the transition from knee flexion to extension. In the subsequent trials this episode was shifted toward maximum knee extension velocity, leaving a period of silence between the initial burst and this episode. On the other hand, the biceps femoris was rarely silent and particularly active during the flexion phase, reflecting its possible role in active knee flexion and postural control during the dynamic phase of stepping. The increase in phase plane size with obstacle height appears related to the amplitude of the initial EMG burst of the rectus femoris. Phase plane diagrams combined with EMG appear to be an appropriate approach to explore the dynamics of human movement strategies. The results suggest that control mechanisms for the flexion and extension phases are different and may be involved in fine tuning the stepping strategy for subsequent trials.

Electromyography↗
PubMed1987

Modeling of control and learning in a stepping motion.

In a previous study (Beuter et al. 1986) the authors modeled a stepping motion using a three-body linkage with four degrees of freedom. Stepping was simulated by using three task parameters (i.e., step height, length, and duration) and sinusoidal joint angular velocity profiles. The results supported the concept of a hierarchical control structure with open-loop control during normal operation. In this study we refine the dynamic model and improve the simulation technique by incorporating the dynamics of the leg after landing, adding a foot segment to the model, and preprogramming the complete step motion using cycloids. The equations of the forces and torques developed on the ground by the foot during the landing phase are derived using the Lagrangian method. Simulation results are compared to experimental data collected on a subject stepping four times over an obstacle using a Selspot motion analysis system. A hierarchical control model that incorporates a learning process is proposed. The model allows an efficient combination of open and closed loop control strategies and involves hardwired movement segments. We also test the hypothesis of cycloidal velocity profiles in the joint programs against experimental data using a novel curve-fitting procedure based on analytical rather than numerical differentiation. The results suggest multiobjective optimization of the joint's motion. The control and learning model proposed here will help the understanding of the mechanisms responsible for assembling selected movement segments into goal-directed movement sequences in humans.

Adult↗
PubMed1986

Phase plane modeling of leg motion.

Phase plane analysis of dynamical systems, in which variables are plotted against their time derivatives, has been recently emphasized as a general method for reconstructing system dynamics from data. The purpose of this experiment was to develop a model of leg movement in a stepping task using the phase plane approach. In this model, the leg is represented as a three-body linkage and the motion of the leg is assumed to be planar with four degrees of freedom. Experimental data was collected on one subject stepping six times, using a two dimensional videomotion analysis system with reflective markers placed on the lower limb joints. A computer program able to solve the equations of motion and compute the state of the system for a given task was implemented. This computer program was written to generate the motion of the leg for a given task using inverse kinematics and a preplanned foot path. Foot trajectories with cycloidal, constant acceleration/deceleration and sinusoidal velocity profiles were studied. From the results, an attempt was made to identify the variables which are measured and to determine the motion characteristics during stepping. The preliminary results support the concept of a hierarchical control structure with open-loop control during normal operation. During routine activity there is no direct intervention of the Central Nervous System (CNS). The results support the existence of preprogramming and provide a starting point for the study of the development of control in multiarticulate movements.

Foot↗
PubMedDate not supplied

Sensitivity and specificity of a portable system measuring postural tremor.

A portable, accelerometric system measuring tremor was evaluated. That is, the validity and consistency of measurements as well as its ability to discriminate pathologic from physiological tremor were investigated. Control subjects and patients with Parkinson's disease were tested with this portable system and with an independent system that gave precise displacement data using lasers. It was found that amplitude of postural tremor as measured by the two systems differed significantly, but further investigation revealed that this difference was due 1) to the difference between amplitude of acceleration and amplitude of displacement, and 2) to changes in tremor over the time between tests, rather than to any inaccuracy or unreliability in the portable system. The other characteristics of tremor reported by the portable system were also valid and reasonably reliable in test-retest experiments, with the exception of the "harmonic index," which proved less stable. Most of the reported characteristics were distributed differently for the control group and for the patients with Parkinson's disease, but the large overlaps between distributions would make diagnosis difficult when tremor is not very pronounced. These results suggest that until better discriminating measures of tremor are available, tremor tests should be repeated and combined with other tests of motor function.

Humans↗
PubMedDate not supplied

Tremor in Cree subjects exposed to methylmercury: a preliminary study.

Rest, postural, and kinetic tremors were recorded in Cree subjects (n = 36) exposed to low levels of methylmercury (MeHg) and control subjects (n = 30) using lasers designed to measure displacement. Displacement and derived velocity and acceleration time series were analyzed using quantitative characteristics in time and frequency domains. We found: 1) relatively low agreement between our results and those of a clinical examination done at the time of testing (r = 0.31 for postural tremor); 2) best discrimination with velocity of static (postural with visual feedback) and kinetic tremors for which significant differences between the two groups are found in many of the characteristics examined; 3) myoclonic-like finger microdisplacements in tremor of Cree subjects; 4) significant changes in static tremor of Cree subjects following a kinetic task; 5) significant differences among three age-matched subgroups of six subjects each (Cree with higher and lower MeHg level, and a control group) in characteristics that reflect difficulty with tracking, myoclonic-like microdisplacements and change in frequency composition of tremor after the tracking task. The subtle differences detected in this preliminary study suggest that further work is warranted to determine whether they can be unambiguously associated with exposure to MeHg.

Environmental Exposure↗
PubMedDate not supplied

Manganese neurotoxicity, a continuum of dysfunction: results from a community based study.

Excessive manganese (Mn) has been associated with neurobehavioral deficits and neurological and/or neuropsychiatric illness, but the level at which this metal can cause adverse neurotoxic effects, particularly with long-term exposure, is still unknown. The objective of the present study was to assess nervous system functions in residents exposed to manganese from a variety of environmental sources. A random stratified sampling procedure was used to select participants; persons with a history of workplace exposure to Mn and other neurotoxic substances were excluded. A self-administered questionnaire provided data on socio-demographic variables. Blood samples were analyzed for total manganese (MnB), lead, mercury and serum iron. Nervous system assessment included computer and hand-administered neurobehavioral tests, computerized neuromotor tests, sensory evaluation and a neurological examination. The present analyses include 273 persons (151 women and 122 men); MnB range: 2.5 micrograms/L-15.9 micrograms/L (median: 7.3 micrograms/L). Multivariate analyses were used and neuro-outcomes were examined with respect to MnB, taking into account potential confounders and covariables. Results were grouped according to neurofunctional areas and MANOVA analyses revealed that higher MnB (7.5 micrograms/L) was significantly associated with changes in coordinated upper limb movements (Wilks' lambda = 0.92; p = 0.04) and poorer learning and recall (men: Wilks' lambda = 0.77; p = 0.002; women: Wilks' lambda = 0.86; p = 0.04). Further analyses revealed that with increasing log MnB (Simple regression: p < 0.05) performance on a pointing task was poorer, frequency dispersion of hand-arm tremor decreased, while harmonic index increased, and the velocity of a pronation/supination arm movement was slower. An Mn-age interaction was observed for certain motor tasks, with the poorest performance observed among those _50 y and in the higher MnB category. Differences between genders suggest that men may be at greater risk than women, although effects were also observed in women. These findings are consistent with the hypothesis that Mn neurotoxicity can be viewed on a continuum of dysfunction, with early, subtle changes at lower exposure levels.

Adult↗