Programmable CSF metering shunt

1. An implantable body fluid drainage system comprising:

a metering shunt including (a) a housing with an internal chamber, (b) a movable barrier dividing the chamber into a first section and a second section, wherein the barrier is configured to be displaced by a differential pressure;

a CSF inlet conduit configured to connect a CSF space to the first section of the internal chamber;

a first powered inlet valve configured to connect the first section of the internal chamber to the second section of the internal chamber;

a first powered drain valve providing a drain path from the first section of the chamber;

a CSF outlet conduit configured to connect the first powered drain valve to a discharge location; and

a controller configured to (a) open the first powered inlet valve and close the first powered drain valve to fill the second section of the internal chamber to a volume defined by the barrier and chamber geometry and (b) subsequently close the first powered inlet valve and open the first powered drain valve to discharge the filled volume from the first section through the CSF inlet outlet conduit.

2. An implantable body fluid drainage system as in claim 1 , wherein the movable barrier is configured to elastically return to a non-displaced position in the absence of a differential pressure thereacross.

3. An implantable body fluid drainage system as in claim 2 , wherein the first powered inlet valve is a three-way valve configured to selectively connect either the first section or the second section of the chamber to CSF inlet conduit and wherein the first powered outlet valve is a three-way valve configured to selectively connect either the first section or the second section of the chamber to the CSF outlet conduit, wherein the controller is further configured to (a) position the first powered three-way inlet valve to deliver CSF from the CSF inlet conduit to the first section while blocking the second section from the CSF inlet conduit and (b) position the first powered drain valve to discharge the filled volume from the first section through the outlet conduit while blocking the second section from the discharge conduit.

4. A method for draining cerebrospinal fluid (CSF) in a patient, said method comprising:

implanting a metering system including (a) a housing with an internal chamber, (b) a movable barrier dividing the chamber into a first section and a second section, wherein the barrier is configured to be displaced by a differential pressure, wherein a CSF inlet conduit is configured to connect the first section to a CSF space and a CSF outlet conduit is configured to connect the second section to an outlet site;

opening a first implanted inlet valve to fill the second section of a chamber in the implanted metering system with CSF and to displace the movable barrier toward the first section of the chamber, wherein the CSF flows into the second section in response to a differential pressure between CSF pressure and an outlet pressure and wherein a filled volume is defined by the barrier and chamber geometry;

closing the first implanted inlet valve to fill the first section of the chamber with CSF from the CSF inlet and to displace the moveable barrier toward the second section and opening a first implanted outlet valve to drain the filled volume of CSF from the second section through the CSF outlet conduit to an outlet site; and

opening the first implanted inlet valve and closing the first implanted outlet valve to refill the second section with CSF wherein the barrier moves back toward the first section.

5. A method for draining cerebrospinal fluid (CSF) in a patient as in claim 4 , wherein the first section of the chamber is exposed to the CSF inlet pressure while the second section is being filled with CSF.

6. A method for draining cerebrospinal fluid (CSF) in a patient as in claim 5 , wherein the first section of the chamber is exposed to CSF inlet pressure while CSF is being drained from the second section.

7. A method for draining cerebrospinal fluid (CSF) in a patient as in claim 6 , wherein the movable barrier is configured to be displaced by the differential between the CSF inlet pressure and the CSF outlet pressure when the first section is exposed to CSF pressure, the first implanted inlet valve is closed, and the first implanted outlet valve is open.

8. An implantable body fluid drainage system comprising:

a metering shunt including (a) a housing with an internal chamber, (b) a movable barrier dividing the chamber into a first section and a second section, wherein the barrier is displaced by a differential pressure, (c) a first powered inlet valve providing a fill path to the first section of the chamber, and (d) a first powered drain valve providing a drain path from the first section of the chamber;

a CSF inlet conduit configured to connect a CSF space to the first powered inlet valve;

a CSF outlet conduit configured to connect the first powered outlet valve to a discharge location;

first powered bleed valve configured to connect the second section of the chamber to CSF pressure;

a second powered bleed valve configured to connect the second section to a pressure of the discharge location, wherein the controller is further configured to (a) close the first powered bleed valve and open the second powered bleed valve to fill the first section and (b) open the first powered bleed valve and close the second powered bleed valve to discharge the filled volume from the first section through the outlet conduit; and

a controller configured to (a) open the first powered inlet valve and close the first powered drain valve to fill the first section to a volume defined by the barrier and chamber geometry, (b) close the first powered inlet valve and open the first powered drain valve to discharge the filled volume from the first section through the outlet conduit, wherein the movable barrier is configured to elastically return to a non-displaced position in the absence of a differential pressure thereacross, (c) close the first powered bleed valve and open the second powered bleed valve to fill the first section, and (d) open the first powered bleed valve and close the second powered bleed valve to discharge the filled volume from the first section through the outlet conduit.

9. A method for draining cerebrospinal fluid (CSF) in a patient, said method comprising:

opening a first implanted inlet valve to fill a first section of a chamber in an implanted metering system with CSF and to displace a movable barrier isolating the first section the chamber from a second section of the chamber, wherein the CSF flows into the first section in response to a differential pressure between CSF pressure and an outlet pressure and wherein a filled volume is defined by the barrier and chamber geometry; and

closing the first implanted inlet valve and opening a first implanted outlet valve to drain the filled volume of CSF from the first section to an outlet site wherein the barrier moves back to an original position to discharge the CSF from the first section;

wherein the second section of the chamber is exposed to the outlet pressure while the first section is being filled with CSF;

wherein the first section of the chamber is exposed to CSF pressure while CSF is being drained from the first section; and

wherein the movable barrier is configured to elastically return to a non-displaced position in the absence of a differential pressure thereacross, wherein the barrier is initially displaced while the first section is filling with CSF and the CSF is discharged by the force of the elated return of the barrier after opening the first implanted outlet valve and exposing the second section to CSF pressure.