Diaphragm electromyogram measured with unilateral magnetic stimulation

The purpose of this study was to establish the phrenic nerve conduction tim e (PNCT) for magnetic stimulation and further assess the relatively new tec hnique of anterior unilateral magnetic stimulation (UMS) of the phrenic ner ves in evaluating the diaphragm electromyogram (EMG). An oesophageal electrode was used to record the diaphragm compound muscle a ction potential (CMAP) elicited by supramaximal percutaneous electrical phr enic nerve stimulation (ES) and UMS from eight normal subjects. The oesopha geal electrode used for recording the CMAP was positioned at the level of t he hiatus and 3 cm below. The diaphragm CMAP was also recorded from chest w all surface electrodes in five subjects. All of the phrenic nerves could be maximally stimulated with UMS. A clear p lateau of the amplitude of the CMAP was achieved for the right and left phr enic nerves. The mean amplitudes of the CMAP recorded from the oesophageal electrode were, for the right side, 0.74+/-0.29 mV (mean+/-SD) for ES and 0 .76+/-0.30 mV for UMS with maximal power output, and for the left side 0.88 +/-0.33 mV for ES and 0.80+/-0.24 mV for UMS. PNCT measured by the oesophag eal electrode with ES and UMS with maximal output were, for the right side, 7.0+/-0.8 ms and 6.9+/-0.8 ms, respectively, and for the left side 7.8+/-1 .2 ms and 7.7+/-1.3 ms, respectively. However, the CMAP recorded from chest wall surface electrodes with UMS was unsuitable for the measurement of PNC T. The results suggest that unilateral magnetic stimulation of the phrenic ner ves combined with an oesophageal electrode can be used to assess diaphragma tic electrical activity and measure the phrenic nerve conduction time.