Analysis of Body Response to Functional Electrical Stimulation on Hemiphlegic Subjects Using Higher Order Spectra

Hemiplegia is a clinical condition where one-half of the body loses its function. It often occurs after a stroke, head injury or other neurological disorders those disrupt the cerebral circulation. Functional Electrical Stimulation (FES) is a rehabilitation engineering method, used to restore or improve the lost functions. FES uses low levels of electrical current to stimulate the nerves and in turn contract the affected muscles. In our work, we use EMG signals as the input to evaluate the efficacy of FES in improving the body movement of hemiplegic subjects. The response of the muscle to the stimulation produced by FES is then captured in accelerometer signals. We measure EMG signals (a) with FES applied and (b) without FES. Higher Order Spectrum (HOS) has been used in the analysis of these accelerometer signals. We extracted HOS features from accelerometer signals with and without FES. Our results show higher values for HOS features in case of EMG without FES than when FES is applied, indicating that FES is able to restore the rhythmicity of the muscles of the hemiplegic subjects. For the analysis, Bispectrum plots and Bicoherence plots for the four cases of accelerometer signals has been taken into consideration, such as (i) no FES applied, (ii) FES applied to nerves only, (iii) FES applied to muscles only and (iv) FES applied to both nerves and muscles. We have found that all these plots are unique and can be used as a visual tool to clearly distinguish the cases from one another.