Liquid-vapor pressure reservoir for medication infusion pump

A pressure reservoir for use in an implantable medication infusion pump of the type having a hermetically sealed housing with a medication chamber for receiving a supply of a selected liquid medication disposed therein, the medication infusion pump also having pump means disposed within said housing for delivering the medication from the medication chamber to a patient, said pressure reservoir comprising:

• means defining an expansible structural enclosure having a liquid-vapor pressure fluid therein, said structural enclosure defining at least one flexible movable wall exposed to the medication chamber, said pressure fluid being adapted to undergo sufficient liquid-vapor phase change for varying the volumetric size of said structural enclosure in response to the quantity of the medication within the medication chamber to maintain the medication under a predetermined and substantially constant pressure, wherein said pressure fluid is selected to maintain the medication chamber under a pressure less than atmospheric pressure.

A pressure reservoir for use in an implantable medication infusion pump of the type having a hermetically sealed housing with a medication chamber for receiving a supply of a selected liquid medication disposed therein, the medication infusion pump also having pump means disposed within said housing for delivering the medication from the medication chamber to a patient, said pressure reservoir comprising:

• a structural enclosure having a selected liquid-vapor pressure fluid therein, said structural enclosure being mounted within the medication chamber and defining at least one flexible movable wall exposed to the medication chamber, said pressure fluid being adapted to undergo sufficient liquid-vapor phase change for varying the volumetric size of said structural enclosure in response to the quantity of the medication within the medication chamber to maintain the medication under a predetermined and substantially constant pressure, wherein said pressure fluid is selected to maintain the medication chamber under a pressure less than atmospheric pressure.

A pressure reservoir for use in an implantable medication infusion pump of the type having a hermetically sealed housing with a medication chamber for receiving a supply of a selected liquid medication disposed therein, the medication infusion pump also having pump means disposed within said housing for delivering the medication from the medication chamber to a patient, said pressure reservoir comprising:

• a pillow-shaped member having two sides made of a flexible material sealed about the periphery thereof to enclose a selected liquid-vapor pressure fluid therein, said pillow-shaped member being located within the medication chamber and defining a volumetric size within the medication chamber, said pressure fluid being adapted to undergo sufficient liquid-vapor phase change for varying the volumetric size of said pillow-shaped member in response to the quantity of the medication within the medication chamber to maintain the medication under a predetermined and substantially constant pressure, wherein said pressure fluid is selected to maintain the medication chamber under a pressure less than atmospheric pressure.

A method of maintaining a selected pressure in a medication chamber contained in an implantable liquid medication infusion pump, said method comprising:

• filling a structural enclosure having at least one flexible wall with a selected liquid-vapor pressure fluid;
• and
• installing said structural enclosure within the medication chamber, said pressure fluid being adapted to undergo sufficient liquid-vapor phase change for varying the volumetric size of said structural enclosure in response to the quantity of the medication within the medication chamber to maintain the medication under a predetermined and substantially constant pressure, wherein said pressure fluid is selected to maintain the medication chamber under a pressure less than atmospheric pressure.