Optically pumped magnetometers disclose magnetic field components of the muscular action potential.

Abstract

Aim: To track the magnetic field generated by the propagating muscle action potential (MAP). Method: In this prospective, proof of principle study, the magnetic activity of the intrinsic foot muscle after electric stimulation of the tibial nerve was measured using optically pumped magnetometers (OPMs). A classical biophysical electric dipole model of the propagating MAP was implemented to model the source of the data. Results: The signal profile generated by the activity of the intrinsic foot muscles was measured by four OPM devices. Three devices were located above the same muscle to compare the direction and the strength of the magnetic signal while propagating along the muscle. Interpretation: OPM devices allow for a new, non-invasive way to study MAP patterns. Since magnetic fields are less altered by the tissue surrounding the dipole source compared to electric activity, a precise analysis of the spatial characteristics and temporal dynamics of the MAP is possible. The classic electric dipole model explains major but not all aspects of the magnetic field. The field has longitudinal components generated by intrinsic structures of the muscle fibre. By understanding these magnetic components, new methods could be developed to analyse the muscular signal transduction pathway in greater detail.