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The authors determined which electrode types, sizes, and locations were best suited for impedance-based ventilation measurement. They compared 14 electrodes from two main groups: adhesive-gel and conductive rubber electrodes. Adhesive-gel electrodes were easy to apply, made good body contact, and did not slip during the course of the experiment. Higher signal-to-motion artifact ratios (SARs) were obtained when electrode area was increased by connecting several small electrodes together rather than by using a single electrode with a large area. The peak SAR was achieved when two electrode arrays (area=70 cm 2) were centered at the eighth intercostal spaces on opposite midaxillary lines. To determine the optimal electrode locations, the authors placed 32 electrodes on the trunk and recorded impedance between 171 electrode combinations on ten normal adult subjects. The data indicate that the SARs are highest when one electrode is place on the midpoint between the left and right second intercostal spaces on the sternum and the other electrode is placed in the opposite position on the back.