Investigator: Kevin C. McGill, PhD Project Staff: Zoia C. Lateva, PhD and M. Elise Johanson, MS, PT Project Categories: Stroke / Spinal Cord Injury - 2000 Assessment of neuromuscular function in persons with suspected neuromuscular disorders often involves analyzing the electrical signals produced by muscles and nerves. The objective of this project is to develop accurate quantitative ways to analyze these signals. We expect that this work will lead to more objective and sensitive methods for diagnosing neuromuscular disorders, planning aspects of curative and rehabilitation therapy, and evaluating response to treatment. Our approach involves (1) developing biophysical models to understand the way in which the morphology of neurophysiological signals is determined by the anatomical and physiological properties of the underlying tissue, (2) recording signals experimentally to investigate the way in which these properties are expressed in normal subjects and subjects with pathology, and (3) developing advanced signal-processing techniques to extract clinically relevant information from neurophysiological signals. Our recent work focused on the compound muscle action potential (CMAP), which is the signal recorded from a muscle in response to electrical stimulation of its motor nerve. CMAPs are recorded clinically to assess muscle function in suspected cases of nerve entrapment syndrome, demyelinating neuropathy, and neuromuscular junction disease. We recorded CMAPs from the thenar and hypothenar muscles of the hand in eleven normal subjects and simulated the results using biophysical models. Our results show: (1) Muscle anatomy plays a more important role in determining CMAP shape than previously realized. In particular, the duration of the CMAP is related to the length of the muscle, and thus should be expected to vary between muscles and between individuals. (2) The changes in CMAP parameters associated with changes in hand configuration are due to changes in the lengths of the muscle fibers. Hand configuration should thus be strictly controlled in order for quantitative comparisons between CMAPs to be meaningful. (3) The hypothenar CMAP contains a large contribution from the other ulnar-innervated muscles of the hand, particularly those of the third and fourth interosseous spaces. This contribution must be kept in mind when interpreting CMAPs altered by pathology. Our current work focuses on the motor-unit action potential (MUAP), which is the signal recorded from an individual group of muscle fibers during a voluntary contraction. Measurement of MUAP properties is an important approach to quantitative EMG analysis. We are investigating the way in which three specific stages of the MUAP-its initiation at the muscle endplate, its termination at the muscle/tendon junction, and the slow repolarization phase of the muscle fiber membrane-affect conventionally measured MUAP parameters. MUAPs are recorded at different points in the muscle using monopolar and concentric needle electrodes in normal subjects and subjects with myopathic disorders. Several muscles with different fiber lengths, pennation angles, and endplate organizations are being studied. The MUAPs are identified using computer-aided decomposition methods we have developed. Preliminary results suggest that conventional MUAP parameters, particularly duration, are strongly affected by muscle architecture. Our long-term goal is to develop new analysis methods which take muscle architecture into account in order to more precisely pinpoint physiological processes altered in pathology. Related Work:
Funding Source: VA Medical Merit Review |
