Evaluation Of Muscle Weakness Post Stroke By Analysis Of Surface Electromyography Interference Patterns

The most common disability following a hemispherical stroke is a motor dysfunction in the contralesional side of the body (i.e., hemiparesis). Its clinical manifestations include muscle weakness, spastic hypertonia and abnormal movement coordination. It has been reported that the weakness for voluntary muscle contraction is a primary cause of overall impairment in stroke survivors. The interruption of the corticospinal tract after stroke is widely accepted as a main contributor to weakness. However, how a cerebral lesion affects motor unit (MU) structure and function remains unclear.Electromyogram (EMG) is an electrical signal derived from muscle contraction, which can serve as a useful tool for diagnosing and assessing neuromuscular diseases and injuries. Substantially, the measured EMG signal is the summation of a variety of motor unit action potentials (MUAPs) discharged by a group of motor units (MUs). Surface EMG (sEMG) is the signal detected via surface electrodes placed over the skin surface. With its noninvasive, safe and easy-to-use features, it has achieved important applications along with a broad prospect in clinical practice. At some extent of contraction levels, the recorded surface EMG signal is very likely to emerge an interference pattern with a great many superimposed MUAPs. Without discriminating individual MUAPs, the quantitative analysis of surface EMG interference patterns was conducted in this thesis, with specific purpose to evaluate paretic muscles of stroke survivors.The work reported in this thesis can be summarized into following aspects:1) In total 40 subjects were recruited in our study, consisting of 22 stroke survivors with hemiparesis (denoted as a stroke group),11 healthy young and 7 age-matched elder subjects (denoted as a control group). The surface EMG signals were collected bilaterally from the thenar muscles of these subjects during their performance of thumb abduction at various levels of isometric muscle contractions. Three diagnostic markers which are capable of differentiating neurogenic and myopathic diseases, namely clustering index (CI), kurtosis of amplitude (KA) and kurtosis of crossing rate (KCR), were adopted for EMG interference pattern analysis. As compared with the neurologically intact muscles of the control subjects and the contralateral muscles of the stroke subjects, the paretic muscles had abnormal values when each of the three markers was applied. Some stroke subjects showed abnormal increase of CI/KA/KCR implying dominant neurogenic changes, which could be related to MU loss, muscle fiber reinnervation, increased MUAP synchronization and reduced firing rate. On the contrary, some stroke subjects had abnormal reduced CI/KA/KCR values indicating dominant myopathic changes, likely due to muscle fiber atrophy or a selective loss of large MU. Such abnormality of some stroke subjects was further highlighted using a modified CI/KA/KCR parameter that emphasizes between-side comparison for each individual subject. These findings suggested that there appear to be different central and peripheral processes at work in varying degrees after stroke.2) Seven stroke subjects were further selected from the above-mentioned 22 stroke survivors for collecting data following the same experimental protocol multiple times during their inpatient rehabilitation treatment. The CI analysis, along with root mean square (RMS), median frequency (MDF), was applied in EMG interference pattern analysis. Experimental results showed that all values of RMS, MDF and CI in the paretic side were approaching to those in the contralateral side for a given subject. These findings suggested that these three parameters were able to effectively reflect the therapeutic effect, which can also be used to monitor improvement of corresponding pathological changes during their rehabilitation treatment. The surface EMG monitoring using multiple markers serves as a useful tool for understanding mechanisms about improvement of pathological changes during stroke rehabilitation.This study helps to better understand the pathological mechanisms underlying muscle weakness poststroke. It also provides important guidelines for clinicians to design accurate and effective rehabilitation protocol for stroke survivors, thus yielding improved stroke rehabilitation.