Patent ID: 8512286

Claim:
An implantable infusion device comprising: a housing; a collapsible member disposed within the housing and defining a reservoir for containing a variable volume of fluid and having an outer surface that moves between an empty position and a full position in response to a change in volume of fluid contained in the reservoir; an interference member disposed within the housing and configured to engage the outer surface of the collapsible member as the reservoir approaches the full position and to cause pressure in the reservoir to increase following engagement with the surface of the collapsible member and concomitant fluid introduction into the reservoir, wherein the collapsible member and the interference member are configured such that the reservoir is capable of further expansion after the surface of the collapsible member engages the interference member and additional fluid is added to the reservoir; a port in fluid communication with the reservoir for providing access to the reservoir through the housing; a pressure sensor in communication with the reservoir; and electronics operably coupled to the pressure sensor for detecting the increase in pressure associated with engagement of the interference member with the surface of the collapsible member and concomitant fluid introduction into the reservoir.