Mechanomyography as an access pathway: corporeal contraindications

Purpose. The purpose of this study is to delineate the impairments of body functions and structures which specifically inhibit mechanomyography (MMG)-based switch control as an alternative access pathway.Method. Seven individuals with severe physical disabilities and varied diagnoses of neuromuscular or neurological conditions tested a MMG switch. A semi-structured protocol was used to gather quantitative and qualitative indications of the switch's performance, and descriptive perceptions of the participants and their care givers.Results. The participants controlled the switch by contracting muscles of their forehead, forearm or shoulder. Body functions and structures that negatively affect the signal-to-noise ratio (SNR) of the recorded MMG signal included involuntary dystonic movement, impaired muscle control, atrophied muscles, muscle spasticity and involuntary activity of neighbouring muscles.Conclusions. The MMG switch is strongly recommended where the muscle site and its control are intact and signal artefact is minimal. Its viability when muscle activity at the access site may be confounded by signal artefact is dependent on the strength of the voluntary muscle contraction relative to that of artefacts such as spastic contractions, involuntary dystonic movements, muscle spasms and physiological vibrations. Neurological conditions, such as spasticity, that compromise the user's ability to voluntarily contract or suppress muscle contractions may be considered contraindications to MMG-based access.