Patent ID: 6887216

Claim:
An electronic device for selectively injecting or withdrawing fluid from a patient's body comprising: a reservoir for injecting or collecting said fluid; a source of therapeutic fluid; a fluid delivery system having a first end coupled to a said reservoir and a second end adapted to be inserted into the patient's body; a sensor coupled to one of said reservoir, fluid delivery system and electrical drive mechanism for sensing an internal parameter indicative of a force generated by said drive mechanism and internal resistances within said reservoir and said fluid delivery system to said force; and a controller coupled to said sensor and said electrical drive mechanism, said controller including a calculator for calculating an entry/exit pressure at said second end as a function of said internal parameter, said controller generating said commands for said drive mechanism to control said entry/exit pressure; wherein said pump in said charging mode is advanced to an empty position and then the piston is retrieved to a full position with the reservoir connected to the source of therapeutic fluid thereby causing said therapeutic fluid to fill said container.