Ghaith J. Androwis

Alterations of neuromuscular signals as a result of vestibular stimulation

Interest in a better understanding of mechanical vestibular stimulation and its effect on changing the muscle tone in individuals with Cerebral Palsy (CP) is the motivation of this study. Stimulation to the otoliths has shown a reduction in the degree of spasticity in population with neuromuscular disabilities. Three children with CP were involved in this study of whom two are twins (12 year-old, female) and the third is a 14-year old, male. The pendulum knee drop (PKD) test was used to evaluate the degree of subjects spasticity. The vestibular stimulation consisted of vertical oscillation with 3 inches of amplitude, a frequency of 2 Hz and a 15 minute duration. This form of stimulation targets the saccule organ in the vestibular system, which results in alteration of the descending signals of the vestibular system responsible for setting tone of the antigravity muscles. Electromyography (EMG) is simultaneously recorded from the quadriceps (Vastus Lateralis) and hamstring (Biceps Femoris) muscles along with the PKD test. The activation of EMG during PKD can be understood in relationship to the flexion and extension of the lower leg. It is interesting that EMG activity for quadriceps is seen at every flexion cycle in the post stimulation data, while on the other hand EMG activity is nearly continuous in the initial cycles of PKD in the pre stimulation. This may be an indication of a change in the activation pattern of EMG from the agonist and antagonist muscles as a result of the vestibular stimulation, which causes neural changes in the vestibular descending signal. In all three subjects of this study, the knee stiffness and damping parameters show a dramatic decrease post vestibular stimulation, and a smaller change is also noticed in the parameter describing virtual trajectory.

Equilibrium point model of knee joint spasticity

Spasticity is a highly complex phenomenon, which has not been defined in precise and quantifiable terms. Although the muscle stretch reflex is thought to play an important role in spasticity generation, the pathophysiologic basis of spasticity is not completely understood. Utilizing Wartenbergs pendulum knee test, this research demonstrates that spasticity can be modeled as a disorder of equilibrium point control. The Equilibrium Point Hypothesis of motor control theorizes that the central nervous system (CNS) provides a virtual trajectory of joint motion, representing space and timing. A mathematical model has been developed that can reproduces kinematic data through the use of dynamic optimization techniques. The results of this study support the concept that spasticity may be part a disorder in which the virtual trajectory specified by the CNS is distorted.

Spasticity and dystonia differentiated via the equilibrium point hypothesis

Is the Equilibrium Point Hypothesis (EPH) able to explain the different motor behavior in subjects with Cerebral Palsy (CP) experiencing spasticity and/or dystonia? Can the Virtual trajectory of the EPH provide a plausible distinction between the two different neurological disorder characteristics? These questions and others will be discussed in this paper. Stimulation of the otolith organ is provided in this study as explained in previous work [8_New]. The data presented in this study belong to six children with CP (4 females and 2 males) and the pendulum knee drop (PKD) test was administered to evaluate their disorder. We anticipated improvement in spasticity due to the vestibular stimulation among all subjects with changes in the three optimized parameters that indicate a reduction of muscle tone. Contrary to expectations, the vestibular stimulation was very effective in some subjects and nearly completely ineffective in others. Further analysis showed that those subjects for whom the intervention was successful had a very different appearance in their pendulum knee trajectory that the subjects who did not respond. Un-blinding of the clinical diagnoses confirmed that the stimulation benefitted those diagnosed with spasticity only, while the stimulation had little to no effect on subjects diagnosed with dystonia or a combination of dystonia and spasticity. These preliminary findings suggest an objective differentiation between spasticity and dystonia may, for the first time be possible.

Estimation of intrinsic joint impedance using quasi-static passive and dynamic methods in individuals with and without Cerebral Palsy.

Modeling the passive behavior of the knee in subjects with spasticity involves the applied external torques (e.g. gravitational torque), the intrinsic moments due to tissue properties, as well as active, neurally defined moments resulting from the hypersensitivity of reflexes introduced by disability. In order to provide estimates of the necessary intrinsic terms in the equation of motion, the push-pull and Wartenberg Pendulum Knee Drop (PKD) tests were administered. Four subjects without disability and two subjects with Cerebral Palsy (CP) were evaluated for their active and intrinsic knee stiffness parameters. Separation of these two terms requires an additional stiffness term be added to the traditional equation of motion. This holds true for subjects with and without neurological disability. Very interestingly, the optimized non-disabled PKD produced lumped stiffness (K) that is similar to the push-pull passive stiffness (KI) for both populations. On the other hand the optimized K value in the PKD test for subjects with disability was approximately 19 times larger than the KI value found graphically from the push-pull test. This leads us to the conclusion that we can partition our lumped K as the sum of a neurally generated stiffness (Ka) and KI to complete the trajectory model. Therefore, this study shows that spasticity is a velocity dependent, that would not appear in disabled individuals unless the examined limb has a non-zero velocity.

Evaluation of a Robotic Exoskeleton for Gait Training in Acute Stroke: A Case Study

The application of robotic exoskeletons in gait therapy during stroke rehabilitation has grown rapidly over the past decade. The purpose of this investigation is to determine the impact of a robotic exoskeleton (RE) on temporal spatial gait parameters as compared to traditional standard of care gait training in a single inpatient after acute stroke. Outcome measures included temporal spatial gait parameters while walking with and without an RE during a single gait training session two weeks post stroke. During gait training in the RE, walking speed, and stride length increased while step width decreased on the affected and unaffected side. Total double support time decreased, and single support and swing time increased on the affected and unaffected limb during gait training in the RE. Gait training in the RE had a positive effect on the patients overall gait which included improved temporal spatial parameters and gait speed. Positive changes in temporal spatial parameters were evident on the affected and unaffected limb. Preliminary rehabilitative improvements with the RE device may include a gait training environment that is more symmetrical and may improve weight transfer and overall gait speed. Further research with a larger sample with various level of impairment utilizing an RE for gait training is needed to determine the potential utility of REs as an alternative to traditional gait training.

Vestibular stimulation frequency for altering spasticity in individuals with cerebral palsy

Mechanical vestibular stimulation for reducing spasticity is not yet well understood. It is crucial to identify the proper characteristics of mechanical stimulation needed to impact the otoliths. Therefore, vestibular stimulation was provided to 1 child with cerebral palsy (CP) and motor changes were evaluated with the Pendulum Knee Drop test (PKD), along with surface EMG before and after stimulation. The vestibular stimulation consisted of 7.5 cm of vertical oscillation at frequencies of 2 Hz and (5, 10, 15) minutes and 1 Hz and (5, 10, 15). The data in this study suggest that mechanical vestibular stimulation resulted in reduced muscle tone at both stimulation frequencies (1 and 2) Hz. Stimulation provided for 15 minutes at 2 Hz has a largest impact on the level of spasticity in an individual with CP.

Motor control investigation of dystonic cerebral palsy: A pilot study of passive knee trajectory.

The purpose of this study is to better understand dystonia in CP and be able to objectively distinguish between individuals who experience spasticity, dystonia, or a combination of these conditions while evaluating the effect of 2Hz vestibular stimulation. Selected outcome measures included knee ROM, angular velocity and acceleration and all measures increased post vestibular stimulation; these results are indications of a possible reduction in the level of disability. The current investigation also identified an unexpected and unique behavior of the knee in children with dystonic cerebral palsy (CP) that was noticed while administering the Pendulum Knee Drop test (PKD) at approximately 0.4 rad (a mid-angle between full extension and zero vertical). There was a catch-like phenomenon at the described mid-angle in dystonic individuals. These results may suggest that dystonia is not a velocity dependent hypersensitivity of reflexes, but may include position dependent muscle reflexes and co-contractions. This reinforces the need for a more precise objective measure or perhaps a modified measure such as a mid-angle PKD test. Furthermore, based on the results obtained through the modified technique, beneficial alterations can be made to the form of treatment such as: robotic therapy or physical therapy that specifically accommodates the unique motor control disorder in individuals with dystonic CP.

The Neural Contribution to Passive Joint Movement in Individuals with Cerebral Palsy

The original objective of this study was to quantify spasticity in a spastic subject using the Pendulum Knee Drop test. An interesting phenomenon was observed while analyzing the collected data. The neural contribution in defining or changing the set point for a passive joint movement is not well understood, therefore, the purpose of this paper is to explain the noted phenomenon according to the Equilibrium Point Hypothesis with which we can justify the changes in moments during PKD test. In passive limb movements the virtual trajectory follows the actual trajectory; in contrast for an active movement the desired trajectory precedes the actual trajectory. The present data explains passive knee movement during PKD for a CP individual and describe the changes in joint moment as function of θvt assigned by the CNS.

Modulation of Knee Range of Motion and Time to Rest in Cerebral Palsy Using Two Forms of Mechanical Stimulation

Spasticity and dystonia are challenging motor impairments that may interfere with the use of exoskeleton-based therapy. We suggest that two mechanical stimulation techniques that target and remediate these manifestations in cerebral palsy, will allow exoskeletons become a much more feasible rehabilitation technique. This will improve function and, importantly, safety. Our previous studies have shown the positive outcomes of vestibular stimulation, and published literature proposes the possible advantages of whole body vibration. Our current approach utilizes both techniques to define a rehabilitation method specific to the subject’s diagnosis of spasticity and dystonia. Our recent pilot data shows great potential in temporarily eliminating/reducing both spasticity and dystonia in a subject with CP. Results suggest a reduction in tone and possible improvements to mobility after a single session of stimulation. Therefore, this paper serves to propose the use of this approach to enable and enhance the benefits of robotic therapy.

Natural User-Controlled Ambulation of Lower Extremity Exoskeletons for Individuals with Spinal Cord Injury

Natural-quality, independent ambulation is a prerequisite for community use of lower extremity exoskeletons by individuals with disabilities. In general, current exoskeletons generate pre-programmed gait, where the user cannot exercise volitional control necessary to navigate over uneven surfaces and avoid obstacles. This project introduces an intuitive control strategy that allows the user to determine and sense the exoskeleton movement in real time using trajectories produced by the hands. The concept allows neurally defined ambulation control to be expressed through alternative biological articulators. This novel approach uses admittance control to compute each exoskeleton’s foot position from Cartesian forces exerted by the user’s hand on a trekking pole that is connected to foot through a multi-axis load cell. The algorithm has been evaluated by naive, non-disabled users who walked a 10 degree of freedom, ½ scale biped robot on a treadmill. The results show that the algorithm produced robot-generated gait kinematics that are similar to human gait kinematics. A human-scale exoskeleton has been developed to allow further exploration of this control method.