Patent ID: 7637892

Claim:
An implantable infusion pump for dispensing an active substance at varying flow rates to a patient comprising: a constant flow pump having a housing, said housing defining: an upper surface, an active substance chamber, a propellant chamber separated from the active substance chamber by a first flexible membrane, an outlet duct having a catheter attached thereto, an exit opening in fluid communication with the active substance chamber and a entrance opening in fluid communication with the outlet duct; and a removable module, said removable module including: a bottom surface contacting the upper surface of the constant flow pump, an entry formed in the bottom surface in fluid communication with the exit opening of the housing, an exit in fluid communication with the entrance opening of the housing, a needle valve portion having a longitudinally varying cross section along its length disposed within a valve body, means for longitudinally moving the needle portion within the valve body, a fixed flow restrictor in fluid communication between the entry of the removable module and the valve body of the removable module, and first and second pressure sensors for sensing pressure on either side of the fixed flow restrictor; wherein during operation of the pump system, a fluid dispelled from the active substance chamber by a force from the propellant chamber passes through the exit opening of the housing, through the entry of the removable module, into contact with the first pressure sensor, through the fixed flow restrictor, into contact with the second pressure sensor, through the valve body of the removable module, through the exit of the removable module, through the entrance opening of the housing, through the outlet duct, and through the catheter.