APPARATUS AND METHOD FOR TRANSFERRING LIQUID FROM AN EXTERNAL STORAGE CONTAINER TO AN IMPLANTED MEDICAL DEVICE

Abstract: An implantable drug pump (10) having a fluid storage reservoir (32) and an externally located syringe (20) for transferring fluid from the syringe (20) into the reservoir (32). More specifically, an implanted drum pump (10) includes a drug reservoir (32) and a volume (43), the reservoir (32) and volume (43) having a common wall defined by a flexible diaphragm (36). The volume (43) contains a liquid (42) having a vapor pressure at body temperature less than that of the ambient pressure surrounding the external syringe (20), thereby tending to provide a reservoir (32) pressure less than the ambient pressure. The syringe (20) includes a needle (22) having an orifice (24) located near its tip (26). The syringe (20) also includes a container (76) formed of a flexible material (78) which is in fluid communication with the orifice (24). An injection chamber (50) is in fluid communication with the reservoir (32). In operation, the needle (22) is forced through a pierceable septum (48) in the drug pump (10) so that the orifice (24) is in fluid communication with the reservoir (32). Because the ambient pressure surrounding the container (76) is greater than the pressure within the injection chamber (50) and the reservoir (32), fluid will flow from the container (76) into the reservoir (32) without any additional pressure being applied to the container (76). A unique valve responsive to the needle (22) piercing the septum (48) is also provided. Thus, a completely passive apparatus is disclosed in which a drug can be transferred from an external container into an implanted device only when a needle in fluid communication with the container is properly positioned with respect to the implanted device.

Description: Description Apparatus and Method for Transferring Liquid From an External Storage Container to an Implanted Medical Device Field of the Invention The invention relates to implantable* medical devices and, more specifically, to an i plantable drug pump and an associated external filling system. Background Art Implantable drug pumps having a drug-containing reservoir in which the pressure is less than the ambient pressure are known in the art. For example, such an implantable drug pump is disclosed in U.S. Patent 4,373,527 to R. E. Fischell. The purpose of a reduced-pressure reservoir is to prevent a drug contained within the reservoir from flowing outwardly into a user's body should a leak occur. Because the pressure within the reservoir is less than the ambient pressure, fluid will flow from the body into the reservoir whenever a leak occurs, thereby elimi ¬ nating the risk of traumatic effects associated with an excess amount of the drug being inserted into a user's body. Such drug pumps are usually filled with an external syringe-type device where pressure exerted by the syringe forces drug into the reservoir via a hypodermic needle. One disadvantage of such a system is that should the hypodermic needle be incor¬ rectly positioned with respect to an appropriate recepticle in the implanted drug pump, an excessive amount of concentrated drug could be injected into the user's body. Various systems have been devised to eliminate this problem. One system utilizes two needles and relies on an electrical continuity check to determine if the needles are located properly. Also, some prior art systems utilize sophisticated electronics to terminate filling when the reservoir is fill. The present invention eliminates the need for these complicated, expensive and potentially unreliable systems by providing a simple and reliable apparatus and method for refilling an implantable drug pump having a drug storage reservoir which is maintained at a pressure lower than the ambient pres¬ sure external to the user's body. The apparatus provided by the invention is completely passive, and allows fluid flow from the syringe to the implanted drug pump only when the needle is correctly posi¬ tioned within the " drug pump. * Summary of the Invention The invention provides an apparatus and method for transferring liquid, the apparatus including an implantable medical device having a first reservoir means, an externally located liquid storage means for storing a liquid at an ambient pressure, a pressure reducing means for providing a pressure within the first reservoir means that is less than the ambient pressure, and a fluid communication means for provi¬ ding fluid communications between the liquid storage means and the first reservoir means whereby fluid at the ambient pressure can flow from the liquid storage means to the first reservoir means. Thus, the invention provides an apparatus which includes an implantable drug pump having a fluid storage means which is maintained at a pressure less than that of the ambient pressure external to the implanted drug pump. The liquid storage means can be a syringe- type device located externally with respect to a user's body, the syringe-type device including a liquid storage means and a hypodermic needle in fluid communication with the liquid storage means. The liquid storage means is formed of a flexible material exposed to the ambient pressure. When the reservoir in the implantable drug pump needs refilling, the needle is inserted through the user's skin and into the pump so that an orifice near the tip of the needle is exposed to the less than ambient pressure within the implantable drug pump reservoir. Thus, the ambient pressure external to the reservoir forces liquid from the syringe into the reservoir without any external pressure being applied by the user. Liquid will automatically cease .flowing when the reservoir is full. Thus, the invention provides a completely passive apparatus for transferring liquid from the external storage device to the implanted reservoir without risk of the hypodermic needle being incorrectly positioned and liquid being forced from the external storage means directly into the user's body. The invention also provides a unique mechanical valve that can be utilized with both a negative pres¬ sure and positive pressure liquid storage reservoir in an implanted medical device. In a specific embodiment of the invention, two volumes are provided in the implantable drug pump, one volume containing a liquid having a vapor pressure lower than the ambient pressure external to the user's body, and the second volume defining a drug-containing reservoir. The two volumes share a common flexible wall. Thus, the reservoir is maintained at a pressure less than the ambient pressure because of the reduced pressure in the other volume. The reservoir is in fluid commu¬ nication with an injection chamber containing a novel mechanical valve. The injection chamber is adapted to receive the end of the external hypodermic needle through a pierceable septum. Thus, when the hypo¬ dermic needle is inserted through the pierceable septum and the mechanical valve, the pressure at an orifice near the end of the needle is less than the pressure external to the user's body. Thus, fluid drug will flow from the external drug-containing storage container into the injection chamber and then " into the drug-containing reservoir due to this pres- sure differential. It can therefore be readily appreciated that the invention provides an entirely passive apparatus and method for filling the reser¬ voir of the implanted medical device. Brief Description of Drawings Figure 1 is a perspective view of an implantable drug pump provided by the invention; Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1; Figure 3 is a perspective view of an embodiment of the valve means provided by the invention; Figure 4 is the cross-sectional view of a syringe to be provided by the invention; and Figure 5 is a cross-sectional view of a further embodiment of a syringe provided by the invention. Detailed Description Detailed illustrative embodiments of the invention are disclosed herein. These embodiments exemplify the invention and are currently considered to be the best embodiments for such purposes. However, it is to be recognized that the specific embodiments dis¬ closed are only representative in providing a basis for the claims which define the scope of the invention. As previously explained, an apparatus for trans¬ ferring liquid from an external storage device or syringe to an implanted drug pump having a liquid storage reservoir is disclosed. The implantable drug pump is configured so that liquid in the storage reservoir within the drug pump is maintained at a pressure below that of the ambient pressure external to a user's body. The syringe is configured so that liquid contained therein is subjected to the ambient pressure. A hollow hypodermic needle having an exit aperture near its tip is in fluid communication with liquid contained within the syringe so that liquid will flow through the exit aperture whenever it is subjected to a pressure less than that of the ambient pressure. The implantable drug pump includes a pierceable septum through which the end of the hypo¬ dermic needle can be inserted. Because the storage reservoir in the drug pump when not full is subjected to a pressure less that ambient pressure, fluid will flow from the syringe via the hypodermic needle into the storage reservoir so long as this pressure dif¬ ferential exists. The storage reservoir itself includes a movable diaphragm, one side of which pro¬ vides part of the storage reservoir surface. A fluid material having a vapor pressure at body temperature less than the ambient pressure is present in a volume on the other side of the diaphragm, this lower pressure tending to reduce the pressure within the reservoir to a pressure less than the ambient pressure. Thus, whenever the needle is inserted through the septum, fluid will flow from the needle into the storage reservoir. However should the needle be inadvertently positioned incorrectly within the user's boby, no fluid will flow because the pres¬ sure within the user's body will be equal to the ambient pressure. As will be more fully explained below, a unique valving scheme is disclosed in which a valve is opened by insertion of the needle through a septum, and is closed when the needle is removed from the septum. Referring now to Figure 1, an implantable drug pump 10 is shown having a dispensing conduit 12 through which a drug 14 can be injected into a user's body. An annular depression 16 is provided in one side of the drug pump 10 to appropriately guide a hypodermic needle for refilling a reservoir contained within the implantable drug pump 10. Referring now to Figure 2, a cross-sectional view of the drug pump 10 can be seen. A syringe 20 is shown having a hollow conduit or hypodermic needle 22 which has an orifice or exit aperture 24 located on the side of the needle 22 adjacent to the needle tip 26. Thus, any fluid flowing through the hollow conduit or needle 22, will exit through the orifice 24. " Whenever the pressure adjacent to the orifice 24 is less than the ambient pressure of the fluid in the syringe 20, fluid will flow from the syringe 20 through the orifice 24. The implantable drug pump 10 in Figure 2 is shown positioned below the skin 28 of the user. The drug pump 10 includes a pump 30 which draws fluid from a drug storage reservoir 32 and provides it to the dispensing conduit 12. Control electronics 34 are provided for controlling the pump 30 in accordance with either preprogrammed or telemetered program information which is stored within the control electronics 34. A flexible diaphragm 36 is pro¬ vided, the diaphragm 36 being configured to form an annular bellows 38 around its periphery. The bellows 38 allows the diaphragm 36 to extend down¬ wardly in the direction of the arrow 40 so as to enlarge the volume of the storage reservoir 32. Although a bellows 38 is shown, other means for allo¬ wing the diaphragm to extend downwardly could be utilized. For example, a somewhat corrugated diaph¬ ragm could be utilized which is formed of a flexible, impervious material such as titanium foil. As will be explained in further detail below, a liquid 42 is positioned in the volume 43 defined by the flexible diaphragm 36 and the case of the drug pump 10, the liquid 42 having a vapor pressure at the body temperature of the user which is less than the ambient pressure external to the user. Thus, so long as the flexible diaphragm 36 is positioned apart from the case of the implantable pump 10 (as shown in Figure 2) , the liquid 42 will tend to reduce the pressure within the volume 43 and the reservoir 32 to a value less than the ambient pressure external to the drug pump 10. Thus, the pressure within the reservoir 32 will be such as to tend to draw any liquid at ambient pressure into the reservoir 32. It has been found that Freon 113 is a satisfactory liquid 42 to use. Other Freon materials and solvent" mixtures will be readily apparent to those familiar in the art. There are many other techniques which could be utilized to reduce the pressure with the storage reservoir 32. For example, the bottom.of the flexible diaphragm could be connected to the inner surface of the drug pump case by a spring under tension, the spring being located where the arrow 40 is located. Alternatively, the volume 43 could be subjecting to a partial vacuum during manufacture, thereby exerting a downward pressure on the flexible diaphragm in the direction of the arrow 40. The annular depression 16 is formed of a hardened ceramic material 46, although it could also be the same material utilized for the case of the drug pump 10. The annular depression 16 is in the form of an inver- - ted truncated cone, the narrow portion of which is defined by a pierceable septum 48 which can be formed of any of a number of well-known, body-inert septum materials of the type which tend to be self-sealing subsequent to removal of a hypodermic needle. Referring now to Figures 2 and 3, an injection chamber 50 is formed by a hollow cylindrical struc¬ ture 52, the bottom portion of which rests on a sup¬ port platform 54, the lower surface of which defines the upper surface of the reservoir 32. The pierce- able septum 48, is supported by the upper portion of the hollow cylindrical structure 52, and is in sealing contact with the hardened ceramic material 46. The portion of the pierceable septum 48 which is exposed to the ambient pressure in the user's body defines a perforation area 56 through which the end portion of the needle 22 can enter the injection chamber 50. A valve is also provided which includes a circular plate 58 having an annular ridge 60 around the periphery of its upper surface. The circular plate 58 is guided by the cylindrical structure 52 as it is displaced. The annular ridge 60 is provided to make sealing contact with the lower surface of the pierceable septum 48 due to the action of a spring 62 which is chosen to exert a pressure against the bottom of the circular plate 58 which would prevent fluid at an " ambient pressure from flowing through the septum 48 and into the injection chamber 50 should be septum 48 become ruptured. An aperture 64 is provi- ded in the wall of the hollow cylindrical structure 52 so that fluid can flow therethrough and through an interconnecting conduit 66 into the -reservoir 32. The aperture 64 can be fitted with a suitable filter 68 to prevent material greater than a certain size from flowing out of the injection chamber 50 into the reservoir 32. Alternatively, the hollow cylindrical structure 52 could be formed of a ceramic filter material, thereby eliminating the need for a separate filter. An aperture 70 is provided for fluid with- drawal from the reservoir 32 by the pump 30. Al¬ though the particular valving scheme described above has been found to work satisfactorily, it should be readily apparent to one familiar with the art that many other types of valving schemes could be utilized for allowing the needle orifice 24 to to in fluid communication with the injection chamber 50 while maintaining isolation between the injection chamber 50 and the user's body when the needle 22 is removed from the implantable drug pump 10. The novel valve disclosed herein can be utilized in conjunction with implantable drug pump reservoirs having pressures higher than the ambient pressure and pressures lower than the ambient pressure. It is very valuable in the case of a positive pressure reservoir because positive pressure tends to close the valve more firmly. It, therefore, provides a secure seal to prevent outward leakage of medication, the direction in which a positive pressure system would tend to leak. As the plate 58 is displaced downwardly due to insertion of the needle 22 through the pierceable septum 48, it is guided along a pre¬ determined path defined by the hollow cylindrical structure 52. Removal of the needle results in the annular ridge 60 making sealing contact with the lower surface of the pierceable syptum 48. If the implanted drug pump reservoir has a pressure higher than the ambient pressure, the annular ridge 60 becomes self-sealing in that pressure on the lower surface of the circular plate 58 will be greater than the ambient pressure on the upper surface of the plate 58, thereby forcing the ridge 60 into the sep¬ tum 48. If the implanted drug pump reservoir is maintained at a pressure lower than the ambient pressure, the spring 62 is chosen so that it will overcome the higher ambient pressure on the upper surface of the plate 58 and force the annular ridge 60 into sealing contact with the septum 48. Although a round plate 58 was chosen for illustrative purposes, the plate could have any suitable shape just so long as an annular ridge defines an area equal to or larger than the perforation area of the septum, and defines' an area that at least overlaps the perforation area. Thus, the valve disclosed herein provides a positive mechanical apparatus for ensuring that drugs contained within the implanted drug reservoir cannot flow outwardly through the septum when the reservoir is at a higher than ambient pressure, and that body liquids surrounding the implantable drug pump cannot flow through the septum and into the reservoir when the pressure within the reservoir is less than the ambient pressure. The syringe 20 can be seen in further detail in Figure 4. Here, a container 76 for containing a drug to be dispensed is formed of a flexible material 78 which is attached to a needle 22 having an orifice 24 at a side portion close to the needle tip 26. A movable piston 82 is provided should it be necessary to force liquid from the liquid container 76. Orifices 84 and 84' are provided to insure that the pressure surrounding the container 76 is an ambient pressure. When fluid is completely removed from the container 76, the movable piston 82* can be removed from the syringe case 86 and a new container 76 and associated needle 22 can be inserted. Although the piston 82 can be utilized to force fluid within the container 76 through the orifice 24, it should be understood that the purpose of this is only to estab¬ lish that there can be flow through the orifice 24 and to check fluid in the container 78. In accor¬ dance with the teachings of the invention, once the needle 22 is inserted within the implantable drug pump 10 so that the orifice 24 is in fluid communica¬ tion with the injection chamber 50, fluid will flow automatically from the container 76 into the reser¬ voir 32 without any external pressure applied by the movable piston 82 and will automatically stop when the reservoir 32 is full. Alternatively, a standard syringe and needle with a low force plunger could be utilized for filling the reservoir. A further embodiment of the syringe 20 can be seen in Figure 5. Here, a syringe-like device 88 is shown, the device 88 serving the purpose of the syringe 20 without use of a movable piston. A case 90 holds a container 92 for holding a drug to be dispensed. The walls of the container are formed of a flexible material as in the Figure 4 embodiment. A needle 94 in fluid communication with the volume defined by the container 92 has an orifice 96 through which drug contained within the container 92 can flow. The orifice 96 is located near the needle tip 98 and is located on the side of the needle 94. The top of the container 92 is formed by a pierceable septum 100 for filling the container 92, and is rein¬ forced by an annular, rubber-like material 102 defi¬ ning the upper portion of the container 92. As fluid is removed from the container 92, the container will tend to shrink in volume as shown by the dotted lines 104. A pressure relief orifice 106 is provided to ensure that the pressure surrounding the container 92 is the ambient pressure. Operation of an implantable drug pump and its associated syringe according to the invention can now be appreciated. Referring now to Figure 2, when the drug in the reservoir 32 is depleted through the action of the pump 30, the volume of the reservoir 32 will be at a minimum and the volume 43 containing the liquid 42 as previously explained will be at a maxi¬ mum. The vapor pressure within the volume 43 will be such as to tend to lower the flexible diaphragm 36 S U BS TITUTE SHEET l^ in the direction indicated by the arrow 40. The pressure within the reservoir 32 will be less than that of the ambient pressure external to the user's skin 28 because of the vapor pressure of the liquid 42 as previously explained. To refill the reservoir 32, either of the syringes shown in Figures 4 or 5 could be itulized. For ease of explanation, the syringe of Figure 4 is chosen. The needle 22 of the syringe 20 is inserted through the skin 28 at a posi- tion predetermined to be near the annular depression 16 in the outer surface of the implantable drug pump 10. The needle 22 is guided by the wall of the annular depression 16 until its tip 26 is in contact with the pierceable septum 48. As further pressure is exerted on the syringe case 86, the needle 22 is forced through the pierceable septum 48 until its tip 26 is in touching contact with the circular plate 58. Further pressure on the syringe case 86 "will force the annular ridge 60 of the circular plate 58 away from the lower surface of the pierceable septum 48 by depressing the spring 62. When the spring 62 has been sufficiently depressed, the orifice 24 will be within the injection chamber 50. Because of the lower pressure in the injection chamber 50 due to the lower vapor pressure of the liquid 42 and its effect on the pressure in the reservoir 32 as previously explained, fluid will flow from the container 78 through the orifice 24 into the injection chamber 50, and through the aperture 64 and filter 68 into the interconnecting conduit 66. From the interconnec¬ ting conduit 66, fluid will flow into the reservoir 32 until such time as its volume is no longer expan¬ dable by the action of the liquid 42. When fluid stops flowing from the container 78, the needle 22 can be removed, the reservoir 32 now being refilled. Because the liquid 42 is chose to have a vapor pressure at body temperature less than the ambient pressure, the pressure of the fluid within the reser¬ voir 32 will tend to be less than the pressure of the fluid surrounding the implantable drug pump 10. Thus, if a leak should occur, for example, within the pierceable septum 48, the liquid contained within the reservoir 32 will remain in the reservoir 32 and the flow of any liquid would be from the user's body into the implantable drug pump 10 only if there was damage to the septum and valve rather than from the implant¬ able drug pump 10 into the user's body. Another major advantage of a device according to the inven¬ tion is that should the needle 22 be incorrectly positioned in the user's body, fluid will not flow into the user's body because the pressure will be equalized between the orifice 24 and the' container 76. It is only when the pressure at the orifice 24 is less than the ambient pressure will fluid flow. Thus, a device according to the invention provides a safety factor to a user heretofore unknown by provi¬ ding the user with a completely passive method of filling an implanted drug pump reservoir.

Claims: Claims What is claimed is: 1. An apparatus for transferring liquid compri¬ sing: an implantable medical device comprising a first reservoir means; liquid storage means for storing a liquid at an ambient pressure, said storage means being externally located with respect to said medical device, pressure reducing means for providing a pressure within said first reservoir means that is less than said ambient pressure; and fluid communication means for providing fluid communication between said liquid storage means and said first reservoir means whereby fluid at said ambient pressure can flow from the liquid storage means to the first reservoir means. 2. The apparatus of Claim 1 wherein said first reservoir means comprises a movable wall portion for altering the volume of said first reservoir means, said pressure reducing means comprising: a second reservoir means having one wall portion being said movable wall portion; and means for reducing the pressure in said second reservoir means to less than said ambient pressure, thereby tending to reduce the pressure in said first reservoir means to less than said ambient pressure. 3. The apparatus of Claim 2 wherein said movable wall portion comprises a flexible diaphragm. 4. The apparatus of Claim 2 wherein said means for reducing comprises a fluid having a vapor pres¬ sure less than said ambient pressure when said fluid is at the temperature of said living body. 5. The apparatus of Claim 4 wherein said fluid comprises Freon 113. 6. The apparatus of Claim 1 wherein said liquid storage means comprises: a container means formed of a flexible material subject to said ambient pressure for containing said liquid; and a hollow conduit having one end in fluid communi¬ cation with liquid within said container means and forming an aperture near the other end through which said fluid can flow. 7. The apparatus of Claim 6 wherein said fluid communication means comprises: an injection chamber adapted to receive the por¬ tion of said hollow conduit containing said aperture; and conduit means for providing fluid communication between said injection chamber and said first reservoir. 8. The apparatus of Claim 7 wherein said implan- table medical device further comprises filter means through which said liquid must pass prior to entering said first reservoir. 9. The apparatus of Claim 7 wherein said injec¬ tion chamber is partially formed by a pierceable septum means one side of which ' is exposed to the ambient pressure environment, said septum means further comprising a peforation area to pass the end of said hollow conduit containing said aperture whereby said aperture is in fluid communication with said injection chamber. 10. The apparatus of Claim 9 wherein said injec¬ tion chamber further comprises valve means responsive to said hollow conduit located within said injection chamber for preventing fluid flow from the external environment past said injection chamber through said septum means. 11. The apparatus of Claim 10 wherein said valve means comprises: a movable member located within said injection chamber and having an upper surface configured to cover at lease said septum means perforation area; and spring means in contact with said movable member, said spring means adapted to hold said movable member in sealing contact with said septum means so that fluid will not flow therethrough, said spring means being adapted to allow said movable member to be displaced by said hollow conduit when it perforates said septum means, thereby allowing fluid to flow through said hollow conduit into said injection chamber. 12. The apparatus of Claim 11 wherein said movable member surface in sealing contact with said septum means defines a continuous ridge. 13. The apparatus of Claim 6 wherein said liquid storage means comprises a syringe defining an inner volume for retaining said container means, said syringe comprising a piston means for altering said ■ inner volume, said syringe further comprising means for subjecting said inner volume to said ambient pressure environment. 14. The apparatus of Claim 13 wherein said means for subjecting comprises at least one aperture in said syringe portion defining said inner volume. 15. The apparatus of Claim 6 wherein said con¬ tainer means further comprises a pierceable septum means through which said container means can be refilled. 16. A method for transferring liquid from an external medical container to an implanted device having a reservoir means comprising: storing a liquid at an ambient pressure external to said implanted device; reducing the pressure within said reservoir means to a value that is less than said ambient pressure; and providing fluid communication between said stored liquid and said implanted device reservoir means whereby said stored fluid will flow into said reservoir means. 17. An apparatus for transferring liquid compri¬ sing: an implantable medical device comprising a first reservoir means, liquid storage means for storing a liquid at an ambient pressure, said-.storage means being externally located with respect to said medical device; pressure reducing means for providing a pressure within said first reservoir means that is less than said ambient pressure; fluid communication means for providing fluid communication between said liquid storage means and said first reservoir means whereby fluid at said ambient pressure can flow from the liquid storage means to the first reservoir means; and valve means within said implantable medical device which is responsive to said fluid comunication means for allowing fluid to flow from said liquid storage means into said first reservoir means. 18. The apparatus of Claim 17 wherein said fluid communication means comprises a hollow conduit, said implantable medical device comprises septum means for receiving said hollow conduit, and said valve means comprises: a movable member for making sealing contact with said septum means; and spring means in contact with said movable member, said spring means being adapted to allow said movable member to be displaced by said hollow conduct when it perforates said septum means, thereby allowing fluid to flow through said hollow conduit into said first reservoir. 19. The apparatus of Claim 18 wherein said movable member surface making sealing contact with said septum means defines a continuous ridge. 20. In an implantable medical device having a liquid storage reservoir in fluid communication with an inner surface of a pierceable septum means, an improved valve means responsive to a liquid injection means piercing said septum means comprising: a movable member for making sealing contact with a portion of said septum means inner surface; and spring means tending to force said movable member to be in sealing contact with said portion of said septum means inner surface. 21. The improved valve means of Claim 20 wherein said movable member defines an upper surface having a continuous ridge portion for making said sealing contact. 22. The improved valve means of Claim 21 further comprising guide means for defining a predetermined displacement path for said movable member when dis¬ placed by said liquid injection means piercing said septum means. 23. The improved valve means of Claim 21 wherein said liquid storage reservoir is maintained at a pressure lower than the ambient pressure external to said implantable medical device, said spring means being chosen to maintain' said movable member in sealing contact with said septum means when said movable member is subjected to the pressure differen¬ tial defined by the ambient pressure and the lower pressure in the liquid storage reservoir.

Inventors: LORD PETER C, LORD, PETER, C.
Applicants: PACESETTER SYST, PACESETTER SYSTEMS, INC.
Application year: 1984
Main classification: A61M7
IPC codes: A61M5