An internal combustion engine capable of optimizing the amount of oil in the crank chamber with a simplified structure of lubrication system, in which a U-shaped oil reservoir is formed surrounding and adjacent to a crank chamber. The thin electrodes suppress unevenness of potential, in particular, in a path away from the center axis of the reflector, which results in improvement of isochronism of an ion packet passing on the path. The one or more cardiac performance parameters are used for various diagnostic, monitoring, and therapy control purposes.