The disclosed mechanical cardio-pulmonary resuscitation (CPR) apparatuses, systems, and devices have a plunger and a plunger displace sensor that can sense plunger displacement information during reciprocating cycles of the plunger. The disclosure CPR apparatuses, systems, and devices also have a microprocessor unit that can receive sensed plunger displacement information from the sensor and generate plunger driving instructions based on the plunger displacement information. The plunger driving instructions have one or both of a plunger driving force and a plunger amplitude for the reciprocating cycles.
