Pitfalls of intramuscular electromyographic recordings from the human costal diaphragm

Objective: Techniques for intramuscular recordings from the costal diaphrag m have been described. This report describes procedures to assist with prec ise placement of these electrodes using ultrasound imaging and describes se veral sources of error that must be excluded when interpreting recordings m ade with intramuscular electrodes. Methods: Fine-wire electrodes were inserted into the left costal diaphragm under the guidance of ultrasound imaging in 17 healthy volunteers. Various respiratory maneuvers were performed to confirm the accuracy of the electro myographic (EMG) recordings and the electrode placement was confirmed with intercostal nerve blocks in one subject. Results: EMG recordings can be made from the costal diaphragm. However, des pite precise electrode placement and use of intramuscular electrodes with s mall receptive areas, the EMG recording could be contaminated by cross-talk (discrete motor unit activity) from the adjacent internal intercostal musc le and from movement of the electrode relative to the muscle fibers during breathing. Furthermore, it is necessary to distinguish between expiratory i ntercostal muscle activity and units in the diaphragm that discharge tonica lly throughout expiration. Conclusions: While ultrasound guidance of intramuscular electrode insertion can assist with accurate electrode placement in the diaphragm, confirmatio n of the stability of the recording and absence of cross-talk is critical t o avoid misinterpretation of diaphragm function. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.