Date of Award
Doctor of Philosophy in Biomedical Engineering - (Ph.D.)
Richard A. Foulds
Jorge M. Serrador
Gerard G. Fluet
In the desire to better understand spasticity mainly in Cerebral Palsy (CP) and to examine vestibular stimulation as a future intervention for .muscle tone reduction, and to be able to describe the change in level of spasticity in subjects with disability and describe interventions effects, a series of experiments are done on children with spasticity. In addition to understanding the otoliths in the vestibular system and their projections, properties and pathways a more important major objective of this work is to validate the changes in otoliths signal caused by vestibular stimulation based on the Equilibrium Point Hypothesis and the inclusion of EMG data in assessing the level of spasticity.
Stimulation to the saccule in the otolith is induced to reduce spasticity. The otoliths are sensitive to acceleration, and detect the direction and magnitude of gravity, as well as transient linear accelerations due to movement. This is a form of a biological accelerometer. The vestibular mechanical stimulation is provided using a vertical stimulation chair that moves up/down at a constant frequency of 2 Hz and amplitude of ~ 7.5 centimeter for time duration of 15 minutes. This form of stimulation targets the saccule organ in the vestibular system, which results in alterations 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 is caused by neural changes in the vestibular descending signal.
Preliminary studies done on subjects without disability comparing NASA jump test pre and post riding a rollercoaster indicate that there are significant differences in the knee and hip angles, which can be explained as a result of the change in muscle tone caused by the exposure to microgravity or cyclic gravity while being on rides. A preliminary study done on a 35 year old subject with CP, showed promising results in reducing spasticity after stimulating the vestibular system using the vestibular stimulation chair. Data from the Pendulum Knee Drop (PKD) test show a significant reduction in the knee stiffness (K), and virtual trajectory (θvt) that is noticed as a change in the shape of knee trajectory post stimulation when compared to pre stimulation.
The final work presented in this study includes seven subjects with spasticity due to cerebral palsy. The PKD test, along with EMG, is used to assess their level of spasticity. Alterations to the vestibular descending signals while passing through the vestibular nuclei and going down toward the alpha motor neurons command a change in the muscle activation patterns that are responsible for setting the level of spasticity or muscle tone. Furthermore, this effect was found to be retained for at least 15 minutes post stimulation. One subject’s data is excluded from the study due to her high initial baseline measure of muscle tone and spasticity which is determined with the extreme firing of EMG bursts. In all the other six 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 virtual trajectory (θvt) specifically in two subjects who have no dystonia. Four of the subjects have dystonic spasticity and the other three do not have dystonia along with spasticity. The vestibular stimulation effect is different between the two groups, and it is found that stimulation do not have the same effect on the level of dystonia as much as it do on spasticity. Subsequent analyses of EMG lead to a potential linkage between the EPH and the muscle reflexes (EMG).
It is important to note that: 1) this work cannot be claimed as a permanent treatment for children with CP, but a combination of the described stimulation along with the proper physical therapy might have a very positive effect on the disorder. 2) Another path that can have a similar impact on the described population is by changing the stimulation duration intensity and providing the stimulation more frequently for at least five consecutive weeks might have a major impact on reducing the level of spasticity in children with CP.
Androwis, Ghaith J., "The effect of mechanical vestibular stimulation on muscle tone and spasticity in individuals with neurological impairment" (2014). Dissertations. 138.