F wave analysis based on the compound muscle action potential scan

Xiaoyan Li PhD, Maoqi Chen PhD, Paul E. Barkhaus MD, Sanjeev D. Nandedkar PhD, Brian Schmit PhD, Ping Zhou PhD

Introduction/Aims Conventional F wave analysis involves a relatively uniform physiological environment induced by supramaximal stimulations. The F wave characteristics in a dynamic physiological condition, however, are rarely investigated. This study aimed to improve understanding of F wave properties in the more dynamic process by introducing a novel method to analyze F waves based on the compound muscle action potential (CMAP) scan technique.

Methods Twenty four healthy subjects participated in the study. The CMAP scan was applied to record muscle responses in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles, respectively. F wave characteristics including mean F wave amplitude and latency (F-M latency), persistence and activating threshold were quantified.

Results An average of 200 F waves per muscle were obtained from the CMAP scan recording. Weak to moderate correlations between F wave amplitude and stimulating intensity were observed in most of the APB (19 muscles; r=0.33±0.14, all p<.05) and ADM (23 muscles, r=0.46±0.16, all p<.05) muscles. Significantly longer mean F latency and lower activating F-threshold were found in the ADM muscles (F-M latency: APB: 25.43±2.39 ms, ADM: 26.15±2.32 ms, p<.05; F-threshold: APB: 7.68 ± 8.96% CMAP, ADM: 2.35±2.42% CMAP, p<.05).

Discussion This study introduces new features of F waves using the CMAP scan technique and identifies differences of F wave characteristics between the hand muscles. The CMAP scan based F waves analysis can be combined with the motor unit number estimation to assess functional alterations in motor neurons in neurological disorders.

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