Biomedical subjects

Derek G Kamper

Publications and source records attributed to Derek G Kamper.

13 recordsLinked to original sources

PubMed2006

A low cost instrumented glove for extended monitoring and functional hand assessment.

A wearable finger flexion monitor developed to measure hand function in individuals with hand dysfunction was evaluated for feasibility, measurement repeatability and reliability, fidelity of wireless transmission, and user acceptance. Configuration of the monitor allows use in situations when a traditional measurement glove cannot be worn. Five healthy individuals participated in the study of repeatability, while 10 healthy individuals and 10 individuals with acquired brain injury participated in trials to assess feasibility and user comfort. Repeatability results showed an overall error of 3.4 degrees , compared to 5.5 degrees and 5.7 degrees reported with other sensor gloves, and to manual measurements (5-8 degrees). Intraclass coefficient of reliability (using coefficient alpha) averaged 0.95. User feedback regarding comfort of the monitor was very high. Loss of data during wireless transmission was no greater than 1.2%. Results demonstrate that the monitor has a strong potential to be used as a tool for objective hand function evaluation in the home and community for both short- and long-term monitoring.

Adult↗

PubMed2006

Exaggerated interlimb neural coupling following stroke.

The patterns of interlimb coupling were examined in 10 stroke survivors with chronic hand impairment. In particular, the potential roles of postural state and motor tasks in promoting the flexed posture of the upper extremity were assessed. Through the use of electromyography analysis, joint angle measurements and a novel biomechanical apparatus to perturb the digits of the hand into extension, measurements of muscle activity and joint position were compared during multiple postural states, locomotion and voluntary muscle activity. The results demonstrated a significant increase in flexion of the digits (P < 0.001) and elbow (P < 0.005), during walking as compared with standing, sitting or laying supine. These results were indicative of an overall excessive activation coupling between the upper and lower extremities after stroke. Indeed both voluntary finger flexion and voluntary leg extension produced significant activity in the other impaired extremity, leg and arm, respectively, in the stroke as compared with the control subjects. Thus, rectus femoris in the impaired leg was active during finger flexion of the impaired hand in the stroke survivors and all four tested muscles in the impaired arm were active during extension of the legs (P < 0.05). These findings suggest an interlimb coupling related to active motor tasks, contributing to an upper extremity flexion bias following stroke.

Adult↗

PubMed2006

Impact of finger posture on mapping from muscle activation to joint torque.

BACKGROUND: The mapping from muscle activation to joint torque production can be difficult to determine for the multi-articular muscles of the fingers. This relationship was examined in vivo as a function of posture in the index finger. METHODS: Five healthy adults participated in an experiment in which the seven muscles of the index finger were sequentially electrically stimulated using intramuscular electrodes. Each muscle was stimulated at 12 different finger postures consisting of specified flexion of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints, while fingertip forces and moments were recorded. FINDINGS: Repeated measures analysis of variance revealed that joint torques resulting from the stimulation were significantly dependent upon finger posture (p < 0.05). The magnitude of the change in joint torque across postures was generally greater than 60%. This value is much larger than the difference attributable to the increase in active muscle force that occurs at longer muscle length, in accordance with the force-length curve (10-20% for the estimated length changes). In addition, the relative distribution of the joint torques generated by a given muscle activation was dependent upon finger posture for the intrinsic muscles and the long finger flexors (p < 0.05); the ratio of one joint torque to another varied with posture for these muscles, in some cases by more than 50%. INTERPRETATION: Joint torque is a product of both muscle force and the corresponding moment arm. As the change in active muscle force was limited, these data suggest that substantial changes in muscle moment arms occur with posture. Therefore, this postural dependence should be considered when constructing biomechanical models of the hand or planning tendon transfers for the fingers.

Adult↗

PubMed2006

Effects of changing wrist positions on finger flexor hypertonia in stroke survivors.

We sought to establish whether spastic hypertonia results from changes in intrinsic muscle properties or from altered stretch reflex properties. We hypothesized that finger flexor spastic hypertonia is primarily of neural origin, and that the dynamics of spastic muscle responses to stretch should therefore reflect the dynamics of muscle spindle receptor responses. In 12 stroke survivors, we recorded torque and electromyographic (EMG) responses of extrinsic finger flexors to constant-velocity rotation of the metacarpophalangeal (MCP) joints of the affected hand, over a range of initial muscle lengths. Stretch velocity was set to 6 degrees, 50 degrees, 150 degrees, or 300 degrees per second. Muscle length changes were imposed by changing wrist angle between 0 degree, 25 degrees, and 50 degrees of flexion. We found that reflex torque and EMG responses exhibited both velocity and length dependence, and there were significant interactions between velocity and length, replicating known characteristics of muscle spindle receptors. Our results support the hypothesis that finger flexor hypertonia is primarily of neural origin, and that it accurately reflects spindle receptor firing properties.

Adult↗

PubMed2006

Weakness is the primary contributor to finger impairment in chronic stroke.

OBJECTIVE: To assess the relative contributions of several neurologic and biomechanic impairment mechanisms to overall finger and hand impairment in chronic hemiparetic stroke survivors. DESIGN: Repeated-measures design. SETTING: Clinical research laboratory. PARTICIPANTS: Thirty stroke survivors with chronic hemiparesis. Fifteen subjects had severe hand motor impairment and 15 had moderate impairment, as measured with the Chedoke-McMaster Stroke Assessment. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The biomechanic factors stiffness and resting flexion torque, together with the neurologic factors spasticity, strength, and coactivation, were quantified by using a custom hand manipulator, a dynamometer, and electromyographic recordings. Both passive and active rotations of the metacarpophalangeal joints of the fingers were examined. RESULTS: Although subjects in the severely impaired group exhibited statistically greater passive stiffness and resting flexion torque than their moderately impaired counterparts (P<.05), the overall effect of these biomechanic changes appeared small in relation to the deficits attributable to neurologic changes such as spasticity and, especially, weakness. In fact, weakness in grip strength and isometric extension accounted for the greatest portion of the variance between the 2 groups (eta(2)=.40 and eta(2)=.23, respectively). CONCLUSIONS: Thus, deficits in hand motor control after stroke seem to derive mainly from weakness, which may be attributable to the loss of descending corticospinal pathway activation of motoneurons.

Biomechanical Phenomena↗

PubMed2006

Effects of neuromuscular electrical stimulation treatment of cerebral palsy on potential impairment mechanisms: a pilot study.

PURPOSE: This pilot study examined the effects of neuromuscular electrical stimulation (NMES) therapy on upper limb impairment in children with cerebral palsy, specifically addressing spasticity, heightened passive resistance to wrist rotation, coactivation, and weakness. METHODS: Eight subjects, aged five to 15 years, with spastic hemiparesis subsequent to brain injury, participated in three months of NMES therapy, targeting the wrist flexor and extensor muscles. Maximum voluntary wrist extension range of motion against gravity, spasticity, passive torque, maximum voluntary isometric torque, and coactivation were recorded prior to, during, and at the conclusion of the therapy. RESULTS: Seven of the eight subjects demonstrated a significant (>15 degrees) improvement in wrist extension range of motion against gravity following the NMES treatment, with an average gain of 38 degrees. Differences in spasticity (0.01 +/- 0.14 N-m, p = 0.80) and passive torque (0.03 +/- 0.11 N-m, p = 0.52) were not significant for these subjects. Isometric wrist extension torque, however, did increase significantly (p < 0.01), accompanied by a reduction in flexor coactivation (p < 0.01). CONCLUSIONS: Evidence suggests that the NMES treatment protocol affected wrist extension by improving the strength of the wrist extensor muscles, possibly through decreased flexor coactivation. Further studies are required, however, to determine whether electrical stimulation itself or other facets of the therapy paradigm played the key role in improvement.

Adolescent↗

PubMed2005

Design considerations for a wearable monitor to measure finger posture.

BACKGROUND: Objective measures of hand function as individuals participate in home and community activities are needed in order to better plan and evaluate rehabilitation treatments. Traditional measures collected in the clinical setting are often not reflective of actual functional performance. Recent advances in technology, however, enable the development of a lightweight, comfortable data collection monitor to measure hand kinematics. METHODS: This paper presents the design analysis of a wearable sensor glove with a specific focus on the sensors selected to measure bend. The most important requirement for the glove is easy donning and removal for individuals with significantly reduced range of motion in the hands and fingers. Additional requirements include comfort and durability, cost effectiveness, and measurement repeatability. These requirements eliminate existing measurement gloves from consideration. Glove construction is introduced, and the sensor selection and glove evaluation process are presented. RESULTS: Evaluation of commercial bend sensors shows that although most are not appropriate for repeatable measurements of finger flexion, one has been successfully identified. A case study for sensor glove repeatability using the final glove configuration and sensors does show a high degree of repeatability in both the gripped and flat hand positions (average coefficient of variability = 2.96% and 0.10%, respectively). CONCLUSION: Measuring functional outcomes in a portable manner can provide a wealth of information important to clinicians for the evaluation and treatment of movement disorders in the hand and fingers. This device is an important step in that direction as both a research and an evaluation method.

Journal Article↗

PubMed2005

The movement-specific effect of motor imagery on the premotor time.

The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.

Electrodes↗

PubMed2004

The effect of motor imagery on spinal segmental excitability.

The purpose of this study was to investigate the effect of motor imagery on spinal segmental excitability by recording the reflex responses to externally applied stretch of the extrinsic finger flexors and extensors during the performance of an imaginary task. Nine young healthy subjects performed a series of imagined flexion-extension movements of the fingers. Muscle stretch was imposed concurrently by applying rotations of the metacarpophalangeal joints at 100, 300, or 500 degrees /sec. Three of the nine tested subjects also generated 0.2 Newton meter voluntary flexion torque in preloading tasks before stretch. At 300 degrees /sec stretch, electromyogram (EMG) and torque reflex responses, which were observed in the finger flexors in four of nine subjects during motor imagery, were activated at a short latency (38.6 +/- 10.6 msec). This latency was similar to that recorded during a stretch of preactivated flexor muscles (34.4 +/- 3.6 msec), in which motoneurons are already suprathreshold and in which monosynaptic effects of muscle afferents are likely to be discernable. In a similar manner, for stretches imposed at 500 degrees /sec, responses to stretch of the flexors were observed in all five tested subjects in imaginary flexion tasks at very short latencies (26.4 +/- 3.7 msec), again similar to those induced by tendon taps (22.8 +/- 1.2 msec). No EMG response was observed at rest during stretches. These observations support the view that effects must have been mediated by imagery-related subthreshold activation of spinal motoneurons and/or interneurons, rather than by long-latency transcortical reflex responses. We conclude that motor imagery has a potent effect on the excitability of spinal reflex pathways.

Adult↗

PubMed2003

Modeling reaching impairment after stroke using a population vector model of movement control that incorporates neural firing-rate variability.

The directional control of reaching after stroke was simulated by including cell death and firing-rate noise in a population vector model of movement control. In this model, cortical activity was assumed to cause the hand to move in the direction of a population vector, defined by a summation of responses from neurons with cosine directional tuning. Two types of directional error were analyzed: the between-target variability, defined as the standard deviation of the directional error across a wide range of target directions, and the within-target variability, defined as the standard deviation of the directional error for many reaches to a single target. Both between- and within-target variability increased with increasing cell death. The increase in between-target variability arose because cell death caused a nonuniform distribution of preferred directions. The increase in within-target variability arose because the magnitude of the population vector decreased more quickly than its standard deviation for increasing cell death, provided appropriate levels of firing-rate noise were present. Comparisons to reaching data from 29 stroke subjects revealed similar increases in between- and within-target variability as clinical impairment severity increased. Relationships between simulated cell death and impairment severity were derived using the between- and within-target variability results. For both relationships, impairment severity increased similarly with decreasing percentage of surviving cells, consistent with results from previous imaging studies. These results demonstrate that a population vector model of movement control that incorporates cosine tuning, linear summation of unitary responses, firing-rate noise, and random cell death can account for some features of impaired arm movement after stroke.

Action Potentials↗

PubMed2002

Directional control of reaching is preserved following mild/moderate stroke and stochastically constrained following severe stroke.

Recent evidence suggests that brain injury can impair the ability to independently activate shoulder and elbow muscles. We hypothesized that if muscle activation patterns are constrained, then brain-injured subjects should not be able to accurately grade initial hand movement direction during reaching toward a broad range of target directions. To test this hypothesis, we measured hand trajectories during reaching in three-space by 16 hemiparetic stroke subjects to an array of 75 targets distributed throughout the workspace. Contrary to our hypothesis, we found that the ability to grade movement direction was largely preserved following mild and moderate stroke. However, the most severely impaired subjects exhibited a degradation of directional control consistent with a loss of independent muscle control. Initial and final hand movement directions for these subjects were grouped roughly in two opposing directions, in a plane parallel with the coronal plane of the body, rather than distributed across the normal range. Selection between the two movement directions appeared partially random, in that subjects initiated over 50% of movements in the direction generally opposite the intended target, for targets to one side of the body. These results suggest that individuals with severe stroke are constrained to use only two gross, stereotypical muscle coactivation patterns for reaching control, and that selection between these patterns is stochastically influenced as the actual direction of motion is not strictly predictable given the desired direction.

Adult↗

PubMed2002

Extrinsic flexor muscles generate concurrent flexion of all three finger joints.

The role of the forearm (extrinsic) finger flexor muscles in initiating rotation of the metacarpophalangeal (MCP) joint and in coordinating flexion at the MCP, the proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints remains a matter of some debate. To address the biomechanical feasibility of the extrinsic flexors performing these actions, a computer simulation of the index finger was created. The model consisted of a planar open-link chain comprised of three revolute joints and four links, driven by the change in length of the flexor muscles. Passive joint characteristics, included in the model, were obtained from system identification experiments involving the application of angular perturbations to the joint of interest. Simulation results reveal that in the absence of passive joint torque, shortening of the extrinsic flexors results in PIP flexion (80 degrees ), but DIP (8 degrees ) and MCP (7 degrees ) joint extension. The inclusion of normal physiological levels of passive joint torque, however, results in simultaneous flexion of all three joints (63 degrees for DIP, 75 degrees for PIP, and 43 degrees for MCP). Applicability of the simulation results was confirmed by recording finger motion produced by electrical stimulation of the extrinsic flexor muscles for the index finger. These findings support the view that the extrinsic flexor muscles can initiate MCP flexion, and produce simultaneous motion at the MCP, PIP, and DIP joints.

Adult↗

PubMed2002

Alterations in reaching after stroke and their relation to movement direction and impairment severity.

OBJECTIVES: To examine the effects of stroke severity and target location on reaching (1) to identify regions in space that are difficult to reach, (2) to determine whether specific alterations in reaching are associated with particular clinical impairment levels, and (3) to characterize relationships between reaching alterations. DESIGN: Participants reached toward a screen of 75 targets spanning an approximate range from +/-90 degrees side to side and from waist to head. SETTING: Rehabilitation research center. PARTICIPANTS: Sixteen chronic stroke patients with a wide range in residual arm function and 4 control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Chedoke-McMaster Stroke Arm Assessment, distance, velocity, smoothness, straightness, and direction of the hand path during each reach. Hand position trajectories were recorded with an electromagnetic sensor. RESULTS: Reaches performed with the impaired arms showed significant degradation in all performance measures. Although only modestly dependent on the target location, these features correlated strongly with impairment level, as well as with each other. Reaching distance showed the strongest correlations with the other parameters. CONCLUSIONS: Stroke alters a broad array of features of reaching, yet largely the same degree of movement control is preserved across a range of target locations. The only consistently problematic task is to reach far out from the torso, independent of the movement direction. Thus, active range of motion (AROM), rather than control over a specific subset of movement directions, is a logical focus for therapy. In addition, measuring AROM is a simple clinical measure that yields much information.

Adult↗