Diaphragm Motor Responses to phrenic nerve stimulation in ALS: Surface and Needle Recordings

Motor responses to nerve stimulation are generally recorded by surface electrodes placed on a target muscle using a belly-tendon montage, in which the active electrode is over the muscle end-plate zone. The compound muscle action potential (CMAP) amplitude represents the total number of innervated muscle fibres within motor units recordable by the electrode array. Loss of axons, or of muscle fibres, will reduce CMAP amplitude, as will increased distance between muscle fibres and recording electrode, incorrect electrode positioning and phase cancellation.

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