Studying the Liason between Motor Unit Number Estimate (MUNE) and the Total Slope of a Stimulus-Response (SR) Curve of Compound Muscle Action Potential (CMAP) Scan

Objective: This study aims to reveal the connection between the MUNE and the Total Slope of the SR Curve of the CMAP Scan. Introduction: MUNE being a neurophysiological method is utilized in diagnosing and monitoring Neuromuscular Disorders. CMAP Scan relying on the gradual stimulation of motor neurons and recording their responses. A Stimulus-Response (SR) curve results in this process to observe the course of these disorders. In normal cases, SR curve almost represents a sigmoid function. In cases with Motor Unit (MU) loss, beside higher stimulus intensities required for CMAP Scan, the alteration in the shape of SR curve influences the slope of this curve. Thus, a new global variable referred as Total Slope might be described that can be associated with MUNE. Material and Methods: In a simulation software motor neuron groups possessing 5 to-300 axons were created and stimulated gradually with currents from 0 to 99 mA. The CMAPs being the responses in SR curve were used to compute the voltage differences. All slopes corresponding to each voltage differences were summed to compute the Total Slope. The correlation between MU number the Total Slope was investigated statistically. Results and Discussion: The coefficient of determination and the Pearson correlation coefficient between MU number and the Total Slope were found as 0.9973 and 0.999 respectively. This suggests a linear relationship between MU number and the Total Slope. Conclusion and Recommendation: The total slope can be regarded as a new feature in constructing new mathematical models as the mean slope recently described in a recent study. Moreover, new features associated with the slope of the SR curve can be identified in future studies.