Non-linear analysis of body responses to functional electrical stimulation on hemiplegic subjects

Ultrasound imaging and semi-automatic analysis of active muscle features in electrical stimulation by optical flow

Ultrasound imaging is an effective way to measure the muscle activity in electrical stimulation studies. However, it is a time consuming task to manually measure pennation angle and muscle thickness, which are the benchmark features to analyze muscle activity from the ultrasound imaging. In previous studies, the muscle features were measured by calculating optical flow of the pennation angle by using only fibers of a muscle from the ultrasound, without carefully considering moving muscle edges during active and passive contraction. Therefore, this study aimed to measure the pennation angle and muscle thickness by using the edges and fibers of a muscle in a quantitative way in a semi-automatic optical flow based approach. The results of the semi-automatic analysis were compared to that of manual measurement. Through the comparison, it is clear that the proposed algorithm could achieve higher accuracy in tracking the thickness and pennation angle for a sequence of ultrasound images.

Temporal muscle activation assessment by ultrasound imaging during flexor withdrawal reflex and voluntary contraction

Activating flexor reflexes by electrical stimulation has been used as a mechanism to initiate the swing phase or to enhance it for spinal cord injured patients. However, it is necessary to know their contraction dynamics in order to artificially induce them at the right moment of a walking cycle. This requires understanding the temporal activation pattern of both surface and deep muscles simultaneously. This study aimed at developing a system to measure and analyze the temporal activation of both surface and deep muscles during voluntary contraction and flexor reflexes (also called withdrawal reflexes) using ultrasound imaging. A set of experiments were done to verify the validity of the system, while exploring the temporal pattern of muscle activation during flexor reflexes. As a result, we were able to quantify the surface and deep muscle activity by measuring the muscle thickness, pennation angle and long-axis displacement, from the ultrasound images.

RECURRENCE QUANTIFICATION ANALYSIS OF BODY RESPONSE TO FUNCTIONAL ELECTRICAL STIMULATION ON HEMIPLEGIC SUBJECTS

Hemiplegia means paralysis of half of the body. It commonly occurs following "stroke", which is due to impedance of blood supply to the brain, hence also termed as "cerebrovascular accident" (CVA). As a consequence of this, the brain tissues suffer from ischemic damage resulting in several symptoms, such as mere weakness, numbness to complete loss of power (paralysis). In order to restore or improve the lost functional movement of the body of the stroke-affected and hemiplegic subjects, a method called functional electrical stimulation (FES) has often been employed as the measure of rehabilitation. FES makes use of low levels of electrical current to activate the nerves and then the muscles, affected. The response of the body to this electrically triggered nervous stimulation could be recorded through different bio-signals. In our work, we measured the accelerometers of hemiplegic patient in two states; with FES and without FES. The nonlinear and nonstationary walking-function-related accelerometers are analyzed using recurrence plots (RP), which helps to visualize the dynamic behavior of the signals. The RPs of electromyography (EMG) signals with stimulation showed distinct periodicity and rhythm when compared to that without stimulation. In addition, we extracted recurrence quantification analysis (RQA) parameters from RP to quantify the obtained information from the RP. Lower values were observed for most of the RQA parameters with FES than obtained without FES. This also confirmed the fact that FES is very useful in bringing more order, rhythm and better control in the physical activities of hemiplegic people.