Biomedical subjects

P S Lum

Publications and source records attributed to P S Lum.

5 recordsLinked to original sources

PubMed1999

Quantification of force abnormalities during passive and active-assisted upper-limb reaching movements in post-stroke hemiparesis.

We evaluated a method for measuring abnormal upper-limb motor performance in post-stroke hemiparetic subjects. A servomechanism (MIME) moved the forearm in simple planar trajectories, directly controlling hand position and forearm orientation. Design specifications are presented, along with system performance data during an initial test of 13 stroke subjects with a wide range of impairment levels. Performance of subjects was quantified by measuring the forces and torques between the paretic limb and the servomechanism as the subjects relaxed (passive), or attempted to generate force in the direction of movement (active). During passive movements, the more severely impaired subjects resisted movement, producing higher levels of negative work than less-impaired subjects and neurologically normal controls. During active movements, the more severely impaired subjects produced forces with larger directional errors, and were less efficient in producing work. These metrics had significant test-retest repeatability. These motor performance metrics can potentially detect smaller within-subject changes than motor function scales. This method could complement currently used measurement tools for the evaluation of subjects during recovery from stroke, or during therapeutic interventions.

Activities of Daily Living↗

PubMed1992

Human control of a simple two-hand grasp.

We investigated how people control fast, accurate movements of a load using a simple two-hand grasp. By providing a clear instruction to several subjects, we isolated a single control strategy. The kinematics produced by this control strategy are nearly indistinguishable from those produced during singlehand movements, but the torques are quite different: one hand accelerates not only itself, but also the load and the other hand, while the other hand brakes the hand-load-hand system. As a result, the hands squeeze the load with a large force during the movement. The dynamics of the hand-load-hand system are of the same form as the dynamics of a single-hand system. Apparently, by taking advantage of this dynamic similarity and of the spring-like properties of muscle, the human motor control system can control the two-hand grasp system simply by modifying the muscle activation patterns used to control single-hand movements. The task dynamics of two-hand grasp do not require that the load be squeezed during the movement, and squeezing the load wastes torque that could be used to move more quickly. However, the human motor control system may choose this squeezing strategy because it reliably brakes the hand-load-hand system despite inherent variability in the braking of individual hands.

Acceleration↗

PubMed1992

Feedforward stabilization in a bimanual unloading task.

When one hand removes a load from the other hand, feedforward motor commands stabilize the position of the unloaded hand. We studied the stabilization of the postural hand using a novel apparatus that allowed unloading at different rates, and unexpected uncoupling of the unloading force from the postural hand. Feedforward stabilization of hand position was observed in all subjects. This stabilization was achieved both by deactivation of postural agonist muscles and by activation of postural antagonist muscles. The neural feedforward command apparently increased with unloading rate. However, the command only partially canceled the interaction torque generated by removing the load, and stabilization became less effective as unloading rate increased.

Electromyography↗

PubMedDate not supplied

Development of robots for rehabilitation therapy: the Palo Alto VA/Stanford experience.

For over 25 years, personal assistant robots for severely disabled individuals have been in development. More recently, using robots to deliver rehabilitation therapy has been proposed. This paper summarizes the development and clinical testing of three mechatronic systems for post-stroke therapy conducted at the VA Palo Alto in collaboration with Stanford University. We describe the philosophy and experiences that guided their evolution. Unique to the Palo Alto approach is provision for bimanual, mirror-image, patient-controlled therapeutic exercise. Proof-of-concept was established with a 2-degree-of-freedom (DOF) elbow/forearm manipulator. Tests of a second-generation therapy robot producing planar forearm movements in 19 hemiplegic and control subjects confirmed the validity and reliability of interaction forces during mechanically assisted upper-limb movements. Clinical trials comparing 3-D robot-assisted therapy to traditional therapy in 21 chronic stroke subjects showed significant improvement in the Fugl-Meyer (FM) measure of motor recovery in the robot group, which exceeded improvements in the control group.

Adult↗

PubMedDate not supplied

Management of malpositioned central venous catheters.

Through research and clinical trials at The University of Texas M. D. Anderson Cancer Center, central venous catheters have gained wide acceptance and are being used for an increasing number of applications. More than 30,000 patients have had a CVC placed since the inception of the M. D. Anderson program in 1976. The soft and less thrombogenic silicone elastomer catheter is the most commonly used catheter in the institution. This study found that most commonly observed malpositions are related to the puncture site and technique, venous anatomy, and catheter characteristics. The study also indicated that the majority of malpositioned central venous catheters need not be removed but can be safely repositioned using rapid flushing, patient positioning, partial withdrawal, or simple or deflective guidewire techniques. Early recognition and management of malpositioned central venous catheters not only guard against serious complications but also allow proper catheter function and prevent delay of intravenous therapy.

Catheterization, Central Venous↗