Confirmation of the lead effect through the recording of compound muscle action potentials and electrocardiography - Implications for the interpretation of recorded potentials from humans -

Abstract

INTENTION: A lead in this study means an electric wire connected to an electric circuit at one point. Every part of a lead is equipotential because of the absence of current. This equipotentiality is termed the lead effect. We investigated through the recording of compound muscle action potentials (CMAPs) and electrocardiography (ECG) whether this characteristic nature of the lead is applicable in the human body. METHODS: First, we recorded CMAPs from two male persons connected to each other. Stimulation was delivered to subject 1 alone and subject 2 assumed the role of a lead. CMAPs of subject 1 were recorded from the abductor pollicis brevis muscle with the belly-tendon method. While subject 2 was touching the belly area of subject 1 with his right index finger, the potential was led from the left forearm of subject 2 with a reference on the tendon area of subject 1. When subject 2 was touching the tendon area, the potential was recorded from the belly area of subject 1 with a reference on the left forearm of subject 2. Second, we recorded ECG simultaneously from the two subjects connected to each other by their hands. RESULTS: The recording from the left forearm of subject 2 demonstrated potentials almost identical to the CMAPs of subject 1. This suggested that the potential at the area of subject 1 touched by subject 2 was ‘transmitted’ without significant alteration to the left forearm of subject 2, which was far from the generator of the CMAP. ECG activity of one person was also ‘transmitted’ to another. CONCLUSION: This study suggested that the human body works well as a lead. An area far away from a generator can register some potential through the lead or lead-like structure, such as extremities, and does not necessarily constitute an inactive site.