Medication infusion pump with improved pressure reservoir

摘要

An implantable medication infusion pump is provided of the type having a pressure reservoir with a selected pressure fluid therein for maintaining liquid medication in an adjacent medication chamber under a substantially constant pressure. The reservoir comprises a hollow structural enclosure defined by at least one movable wall and adapted to be filled with a selected quantity of the pressure fluid, particularly such as a selected fluorocarbon in a liquid-vapor state. The movable wall of the pressure reservoir is shared with and defines one side of the medication chamber, with the pressure fluid undergoing appropriate change of state to expand or contract the pressure reservoir in a manner maintaining the medication under substantially constant pressure. The improved pressure reservoir includes an internal spacer element to prevent contraction of the pressure reservoir beyond a minimum volume at least slightly greater than the liquid state volume of the pressure fluid therein. With this construction, at least some pressure fluid within the pressure reservoir remains in a vapor state at all times.