Non-constant pressure infusion pump

Abstract

The present invention relates to an implantable infusion pump having a refillable infusate reservoir in fluid communication with a delivery site via a flow path. This flow path includes a flow resistance. The infusion pump includes a sensing device(s), positioned relative to the flow path, to provide data regarding a flow rate along the flow path. The infusion pump effects a division of a total flow period into at least a plurality of unit dose periods, each unit dose period effecting delivery of a unit dose of infusate. The cumulative effect of delivering the total number of unit dose periods is the delivery of a desired dose over the total flow period. The present invention permits a reservoir pressure to vary over any portion of total flow period but effects a constant-pressure state over each unit dose cycle.

1 . A system for infusing a fluid in a living body, said system comprising:
 a reservoir to transiently store a fluid infusate for transmission to a delivery site;   a flow restrictor disposed in a fluid path between said reservoir and said delivery site;   a pressure sensing device providing pressure information to determine a pressure differential across said flow restrictor; and   a valve disposed in said fluid path between said reservoir and said delivery site, said valve operable to control infusate output from said reservoir to said delivery site as a function of said pressure differential across said flow restrictor;   wherein said reservoir, said flow restrictor, said pressure sensing device, and said valve are provided in a configuration adapted for implantation in a living body.   
   
   
       2 . The system of  claim 1 , further comprising: an energy source to effect an expulsion of stored infusate from said reservoir. 
   
   
       3 . The system of  claim 2 , wherein said energy source provides a non-constant reservoir pressure, and wherein said valve is controlled to provide a desired flow of said infusate despite said non-constant reservoir pressure. 
   
   
       4 . The system of  claim 3 , further comprising:
 a controller coupled to said pressure sensing device and said valve, said controller operable to utilize said pressure information to determine said pressure differential across said flow restrictor, said controller further operable to subdivide a flow period into smaller unit dose periods over which said pressure differential across said flow restrictor is likely to remain constant and controlling said valve to deliver a total dose of said infusate through a series of sequential said unit dose periods.   
   
   
       5 . The system of  claim 4 , wherein said unit dose periods are selected at least in part to reduce battery consumption. 
   
   
       6 . The system of  claim 4 , wherein said unit dose periods are selected so that an open/close rate of said valve is pharmacologically insignificant. 
   
   
       7 . The system of  claim 1 , further comprising:
 a controller coupled to said pressure sensing device and said valve, said controller operable to utilize said pressure information to determine said pressure differential across said flow restrictor, said controller further operable to manipulate said valve as a function of said pressure differential across said flow restrictor and thereby control infusate output from said variable-volume chamber to said delivery site.   
   
   
       8 . The system of  claim 7 , wherein said controller provides an alert with respect to overfilling of said reservoir using said pressure differential across said flow restrictor. 
   
   
       9 . The system of  claim 7 , wherein said controller provides an alert with respect to depletion of said reservoir using said pressure differential across said flow restrictor. 
   
   
       10 . The system of  claim 7 , wherein said controller further determines a rate at which said pressure differential across said flow restrictor changes. 
   
   
       11 . The system of  claim 10 , wherein said controller alters timing of a period of said valve being opened as a function of said rate at which said pressure differential across said flow restrictor changes. 
   
   
       12 . The system of  claim 1 , wherein said pressure sensing device comprises:
 a first pressure sensor disposed in said fluid path between said outlet conduit and said flow restrictor; and   a second pressure sensor disposed in said fluid path between said flow restrictor and said delivery site.   
   
   
       13 . The system of  claim 12 , wherein said pressure sensing device further comprises:
 a third pressure sensor disposed in said fluid path between said second pressure sensor and said delivery site.   
   
   
       14 . The system of  claim 1 , further comprising:
 a temperature sensing device providing temperature information to determine a temperature of said infusate.   
   
   
       15 . The system of  claim 14 , wherein said valve is further operable to control infusate output from said reservoir as a function of said temperature of said infusate. 
   
   
       16 . A method for infusing a fluid in a living body, said method comprising:
 providing a reservoir, a flow restrictor, and a valve in a configuration adapted for implantation in a living body;   transiently storing a fluid infusate in said reservoir for transmission to a delivery site;   disposing said flow restrictor in a fluid path between said reservoir and said delivery site;   determining a pressure differential across said flow restrictor; and   controlling said valve disposed in said fluid path between said reservoir and said delivery site to control infusate output from said reservoir to said delivery site as a function of said pressure differential across said flow restrictor.   
   
   
       17 . The method of  claim 16 , wherein controlling said valve comprises:
 subdividing a flow period into smaller unit dose periods over which said pressure differential across said flow restrictor is likely to remain constant and controlling said valve to deliver a total dose of said infusate through a series of sequential said unit dose periods.   
   
   
       18 . The method of  claim 17 , wherein said unit dose periods are selected at least in part to reduce battery consumption. 
   
   
       19 . The method of  claim 17 , wherein said unit dose periods are selected so that an open/close rate of said valve is pharmacologically insignificant. 
   
   
       20 . The method of  claim 16 , further comprising:
 providing an alert with respect to overfilling of said reservoir using said pressure differential across said flow restrictor.    
   
   
       21 - 34 . (canceled)