Pitfalls of intramuscular electromyographic recordings from the human costal diaphragm

Objective: Techniques for intramuscular recordings from the costal diaphragm have been described. This report describes procedures to assist with precise placement of these electrodes using ultrasound imaging and describes several sources of error that must be excluded when interpreting recordings made 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 electromyographic (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, despite precise electrode placement and use of intramuscular electrodes with small receptive areas, the EMG recording could be contaminated by cross-talk (discrete motor unit activity) from the adjacent internal intercostal muscle and from movement of the electrode relative to the muscle fibers during breathing. Furthermore, it is necessary to distinguish between expiratory intercostal muscle activity and units in the diaphragm that discharge tonically throughout expiration. Conclusions: While ultrasound guidance of intramuscular electrode insertion can assist with accurate electrode placement in the diaphragm, confirmation of the stability of the recording and absence of cross-talk is critical to avoid misinterpretation of diaphragm function.