Chest surface recording of diaphragm potentials in man

The distribution of diaphragm potentials over the chest surface was recorded with electrode arrays along midaxillary, midclavicular, or sternal lines in 14 normal adults. The surface pattern of phasic inspiratory EMGs when subjects were supine, relaxed, and breathing quietly, was consistent with a diaphragm source. This pattern was obtained when the diaphragm alone was active (phrenic stimulation, 1 subject) and was absent when the diaphragm was inactive (unilateral paralysis, 1 subject). Static inspiratory efforts up to -40 cm H2O and voluntary breaths of twice tidal volume did not alter this characteristic voltage pattern if parasternal, pectoral, and abdominal recordings were near baseline. The peak voltage site moved down an interspace when inspirations exceeded 60% vital capacity. When subjects lay on their sides, the peak voltage site on the up-side shifted down one interspace, and the gradient on the down-side either shifted up or remained the same. We attribute these shifts to changes in diaphragm position. Muscular or positional artifacts which alter the timing and amplitude of surface diaphragm EMGs can be detected better with electrode arrays than single bipolar pair. Several laboratory and clinical applications for recording diaphragm potentials from the chest surface are discussed.