Analysis of gastrocnemius compound muscle action potential in rat after death: significance for the estimation of early postmortem interval

The estimation of postmortem interval is of great importance in forensic medicine. Changes in the properties of excitable tissue provide another possible means by which the time of death can be estimated. This paper reports the monitorization of the compound action potentials recorded from gastrocnemius muscle by means of sciatic nerve stimulation in rats before and after death. The sciatic nerve was stimulated using rectangular impulses of 0.1 ms duration and intensities ranged between 1 and 100 mA while the rat was alive. Subsequently, the rat was killed by cervical dislocation. The similar measurement procedure was performed at the moment of death and every 5 min after sequentially. There was a progressive decline in amplitude values that began 10 min after death. The decrease in the amplitude of the compound muscle action potentials (CMAP) was most prominent especially when elicited with lower stimulus intensities. The mean area of the CMAPs also began to decrease beginning from 15 min after death. Fifteen minutes after death, the motor latencies began to prolong. Thirty-five minutes after death, the decline in amplitude and area of mean CMAP was most prominent as the mean motor latency. At the 40th minute, most of the CMAPs were unelicitable. During the early postmortem interval, these amplitude, area and motor latency alterations decrease in the amplitude and area, prolongation of motor latency seems to be well correlated with each other and this was statistically significant. These findings are discussed as possible basis of a forensic method for postmortem interval estimation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved

DESIGN OF AN EXPERIMENTAL SYSTEM FOR SCANNING ELECTROMYOGRAPHY METHOD TO INVESTIGATE ALTERATIONS OF MOTOR UNITS IN NEUROLOGICAL DISORDERS

The aim of this study is to establish an experimental system for scanning electromyography (EMG) to visualize the electrical activity of the motor unit (MU) territory in investigating the alterations in MU size in Juvenile Myoclonic Epilepsy (JME). MU is the basic unit of the skeletal muscle. Conventional EMG has already been used in routine clinical examinations to diagnose neuromuscular diseases. It provides information in terms of the amplitude and the duration. It reflects only a limited part of the MU. Scanning EMG method gives temporal and spatial information about the MU providing a map for the entire motor unit. An experimental system consisting of an EMG instrument, an actuator, a data acquisition system and a notebook for scanning EMG was designed and set up. The measurements are achieved by two concentric needle electrodes (CNE). An M-File in MATLAB 7.2 is used to construct 3-D plots of the MU territory. Measurements have been performed with seven JME patients and two healthy volunteers. The genetic origin of the JME suggested the subclinical anterior horn cell involvement in JME. Some evidences were found on the preponderance of the normal 'large' MUs using several electrophysiological methods. Scanning EMG system is used to confirm the presence of these large MUs. 3-D maps of the MU territories are constructed using the data acquired from the subjects. It has been demonstrated that the experimental system can be used to examine the motor unit territory different groups of diseases for clinical studies. This study will be extended to ten JME and to ten healthy volunteers, and by including three spinal muscular atrophy cases (SMA)