Establishment of motor unit number index detection method

Abstract

Objective: An electrophysiological technique was established to determine Motor Unit Number Index (MUNIX), and to investigate the stability of MUNIX. Methods: Fifty healthy subjects (25 males and 25 females) from the Outpatient Service of Peking University Third Hospital between December 2017 and September 2018 were included and divided into 5 groups according to age. The relevant parameters were detected in bilateral deltoid muscle (axillary nerve), double little finger abductor muscle (ulnar nerve), double quadriceps muscle (femoral nerve), double tibialis anterior muscle (peroneal nerve). The same muscle and the same healthy subjects were tested again three months later. Three-step detection were conducted: first, the surface electrode was attached to the muscle belly of each muscle, and the reference electrode was placed 2-3 cm away from the muscle belly. At the same time, the maximum compound muscle action potential (CMAP) of corresponding nerve was obtained, and the negative peak amplitude was measured. The second step was to collect the interference phase of the surface electromyography (SIP). There were 10 levels in total. And the measurement was repeated for three times, and the whole interference phase range was measured in the end. In the third step, the negative peak amplitude and SIP value of CMAP were substituted into the Excel table, and the MUNIX and motor unit number size (MUSIX) values were automatically calculated by the instrument through mathematical functions. Results: The mean MUNIX values of deltoid, extensor little finger, quadriceps femoris and tibial anterior were 193.2, 189.0, 159.7, 147.2, MUSIX were 46.9, 54.3, 49.6, 48.1 μV, respectively. The detection rates of MUNIX and MUSIX in the four muscles were 100%, respectively. With the increase of age, it could be seen that MUNIX declined, with statistically significant difference (P<0.05), but there was no significant change in MUSIX. There was no statistically significant difference in MUNIX and MUSIX between different gender, lateral sides and baseline and 3-month's reexamination results (P>0.05). Conclusions: MUNIX technology can improve the motor unit count of proximal upper limb and lower limb muscles. Its parameters are monitored using a mathematical model based on the composite muscle action potential and the interference phase of surface electromyography. Result is stable and reliable.