Investigation of the Relationship between the Motor Unit Number Estimate (MUNE) and the Mean Slope of the Stimulus-Response (SR) Curve of the Compound Muscle Action Potential (CMAP) Scan

Objective: The goal of this study is to elicit the relationship between the MUNE and the Mean Slope of the SR Curve of the CMAP Scan. Introduction: MUNE is used to diagnose and to monitor the Neuromuscular Disorders. CMAP Scan is a neurophysiological method based on the gradual stimulation of motor neurons and on recording their responses. As a result, a Stimulus-Response (SR) curve is plotted to study the progress of these diseases. In healthy subjects, SR curve is in the sigmoid form. As Motor Unit (MU) loss takes place, higher stimulus intensities are required in CMAP Scan. In addition, the shape of the SR curve becomes different form rather than sigmoid. This affects the slope of the SR curve. Therefore, a new more integrative variable called Mean Slope can be defined which might be correlated with MUNE. Material and Methods: Motor neuron groups including 5-to-300 axons were constituted via a simulation software and they were stimulated incrementally with currents from 0 to 99 mA. . The voltage differences were computed by using the CMAPs being the responses in the SR curve. The average of all slopes corresponding to each voltage differences was computed to find the Mean Slope. The correlation between MU number the Mean Slope was investigated statistically. Results and Discussion: The coefficient of determination and the Pearson correlation coefficient between MU number and the Mean Slope were found as 0.9974 and 0.999 respectively. A linear relationship between MU number and the Mean Slope was suggested.