Abstract:
Disclosed is a fluid delivery system comprising a bladder to hold a fluid, the bladder being enclosed in a structure formed from a cap connected to a drive mechanism. The drive mechanism includes a piston driven by a constant force spring, the piston resting against the bladder. Activation of the drive mechanism delivers the fluid at a rate pre-determined by the design of the spring.

Description:
BACKGROUND 
     The present invention relates to delivery systems for fluids. In particular, the invention is directed to a easily assembled and portable system for infusion of fluids such as intravenous solutions, blood plasma or drug solutions at a controlled delivery rate. 
     Various devices and methods are known for delivery of fluids to a patient. The simplest method utilizes gravity feed from a bag or bottle filled with the fluid suspended above the patient, possibly with a flow restrictor or drip chamber in the tubing connecting the bag to the patient. However, the flow rate can vary depending on many variables such as the height of the fluid bag above the patient, the content of the bag or the tubing or needle size. Also, it is sometimes desirable to deliver the fluids at an accelerated rate or at controlled but nonconstant rate. This can not be readily managed by a gravity feed system. 
     One of the more complicated methods is to utilize a motor driven pump which is computer controlled and thus is capable of being programmed to deliver fluid at very precise rates. While such devices may be useful at the bed side in a stationary position they are expensive and easily damaged and thus are not preferred for ambulatory use. 
     Previous attempts to produce a portable device which is resistant to damage and tampering has resulted in expensive and cumbersome products which are not readily controllable. Examples of such devices include inflatable cuffs, pressurized bladders and spring loaded clamps or platforms. However, these devices generally do not offer means for controlling flow. 
     Thus, there is a need for a simple, portable fluid delivery system which also allows medical personnel to readily control delivery rates of the fluids to the patient. 
     SUMMARY 
     These needs are met by the present invention which comprises a fluid delivery system having a bladder carried within a cap and a drive mechanism attached to the cap and mounted over the bladder. In a preferred embodiment, the drive mechanism comprises a piston which rests on the bladder and a spring which forces the piston against the bladder expelling the fluid from the bladder at a controlled rate. The delivery rate is controlled by varying the manner of construction, materials, cross section, thickness, and other parameters of the spring. 
     Further embodiments of the present invention include a fluid delivery system in combination with tubing sets for delivery of the fluid to the patient. The tubing set can include flow restriction devices which act in cooperation with the drive mechanism to further control the flow of fluid. 
    
    
     DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where: 
     FIG. 1 is an exploded side view of a first embodiment of the fluid delivery system. 
     FIG. 2 is a top view of the cap portion of the fluid delivery system of FIG. 1. 
     FIG. 3 is a cutaway side view of the cap portion of the fluid delivery system taken along line 3--3 of FIG. 1. 
     FIG. 4 is a cutaway expanded side view of the fluid delivery system of FIG. 1 with the piston in its unloaded position, the cut away view taken along line 3--3 of FIG. 1. 
     FIG. 5 is a cut away side view of the fully assembled fluid delivery system of FIG. 1 with addition of a tubing set, the cut away view taken along line 1--1 of FIG. 1. 
     FIG. 6 is a bottom view of the knob portion of the fluid delivery system of FIG. 1. 
     FIG. 7 is a cut away side view of the fluid delivery system and delivery tube of FIG. 5 with the bladder empty, the cut away view taken along line 3--3 of FIG. 1. 
     FIG. 8 is a cut away side view of a second embodiment of the fluid delivery system of FIG. 1. 
     FIG. 9 is a side view of the piston used in the fluid delivery system of FIG. 8. 
     FIG. 10 is a graph showing the filled volume of bladders having different dimensions. 
     FIGS. 11a, 12a, 11b and 12b are side views and top views, respectively, of a spiral spring design and a dome spring design for use in the fluid delivery system of FIG. 1 or FIG. 8. 
     FIG. 13 shows a drive system based on the negator spring concept. 
     FIG. 14 shows a spring force curve for the constant rate springs shown in FIGS. 11 through 13. 
    
    
     DESCRIPTION 
     FIGS. 1 through 7 show a first embodiment of a fluid delivery system 10 embodying features of the invention. 
     The fluid delivery system 10 comprises a cap 12, a removable bladder 14 carried within the cap 12 and a drive mechanism 16 attached to the cap 12. A piston 18 is enclosed within the drive mechanism 16 in contact with the upper surface 20 of the bladder 14. 
     The cap 12 has a cylindrical wall 22, a closed end 24 and an open end 26. 
     The bladder 14 located inside the cap 12 contains the fluid 28 to be delivered. The bladder 14 has at least one access port in the wall 30 of the bladder 14 to allow removal of fluid 28 from the bladder 14. The access port may also be used to fill the bladder or a second filling means may be made available for this purpose. The access port is accessible through the cap 12 when the fluid delivery system 10 is assembled. In, the embodiment in the figures the access port is a tubing connector 32, which may also include a valve (not shown), which extends through an opening 33 in the closed end 24 of the cap. Preferentially, a one way valve is used to prevent retrograde flow. Alternate access or filling means include a septum which can be pierced by a needle or a spike or a tube with an external clamp. Other suitable access means standard in the art and connectors such as threaded, bayonet or luer lock connectors are also usable. 
     The bladder 14 can be chosen to have a capacity appropriate for the amount of fluid to be delivered and the time period for fluid delivery. FIG. 10 is a graph showing how the capacity of a cylindrical bladder varies with the height and diameter of the bladder. Other three-dimensional shapes, such as spherical or square bladders can also be used to expand or limit the quantity of fluid delivered with a fixed rate drive mechanism. 
     The drive mechanism 16 comprises a shell 34, a piston 36 which is free to move within the shell 34, a pressure means which forces the piston 18 against the upper surface 20 of the bladder 14 and a knob 36 on the top of the shell to retain the pressure means in a loaded position until released by the operator. The knob 36 is held on the shell 34 by a collar 37 integral with the shell 34, the collar surrounding the hole 46. A preferred pressure means is a specially designed spring 38, which is described below. The piston 18 shown in the drawings includes an upwardly extending shaft 40 with a barbed upper end 42, the shaft 40 extending through the center of the spring 38. The barbed end 42 is split so that it can be compressed during the assembly of the system. 
     The shell 34 has a upper end 44 with a hole 46 through the center thereof, a cylindrical wall 48 and an open lower end 50. The open lower end 50 is designed to connect to the open upper end 26 of the cap 12. The hole 46 in the shell upper end 44 is sized so that the compressed barbed end 42 of the shaft 40 can be inserted therethrough but can not be readily withdrawn once inserted without forcibly compressing the shaft 40. 
     Various different means can be used to hold the cap 12 to the shell. FIGS. 1 through 3 show inwardly extending tabs 52 on the inner surface 54 of the cap 12. The tabs 52 are sized to fit through grooves 56 on the lower end 50 of the shell 34 and lock into a matching recess 58 on the upper ledge 60 of the shell bottom end 50 when the shell 34 is connected to the cap 12. Along the bottom of the inner surface of the cap is a soft liner 35 which is compressibly deformed by the connection of the cap to the shell, thus, aiding in holding the parts together. Alternate connecting means include threaded surfaces, latching mechanisms, rivets or screws. 
     Enclosed within the shell 34 is piston 18 which has a pressure surface 62 perpendicular to the shell wall 48. Extending laterally from the piston 18 edge are several fingers 64 which ride in vertical slots 66 in the inner wall of the shell 34. Guided by the fingers 64 and the slots 66, the piston 18 is free to move up and down within the shell 34. Extending upward from the piston 18 is a piston shaft 40 designed to releasably latch outside the shell and interlock with the top of the shell. In the embodiment, shown the latch release is a knob 36 which has release means, such as a cammed surface 68, on its inner surface designed to mate with the top of the piston shaft 40. The knob protects the top of the shaft and the cammed surface compresses the barbed shaft 42 after assembly when release by the operator is desired. Release is accomplished by rotating the knob 36. 
     Located within the shell 34 between the shell upper end 44 and the piston 18 is the spring 38. The spring 38 is designed to push the piston 18 toward the shell lower end 50 with a constant force. This is accomplished by various different mechanisms. For example, the spring can be cut from a single piece of spring steel or molded from a stiff plastic material with the width of each turn of the spring increasing along the spring length. A second alternative is a spring with a thickness varying along its width. Thirdly, the spring can be formed from two different materials laminated together with the ratio of the materials varying along the spring length. In a like manner, the same variations in spring design can be used to produce a driving force which varies in a preset manner. 
     FIGS. 11 through 13 show various different spring designs which may be used in the fluid delivery system 10 of the invention. FIGS. 11a and 11b show side and top views of a coil spring 70. In this instance, the cross section of the winding has a greater height than width, the height being selected to obtained the desired force curve as the spring expands. FIGS. 12a and 12b show side and top views of a dome spring 72 which has a base portion 74 and a top portion 76 connected by integral struts 78. As the dome spring 72 is compressed the base and/or the top can flatten and the struts 78 bow. Again, the cross section of the struts 78, base 74 and cap 76 can be varied to control the force of the spring as it expands. 
     FIG. 13 shows a spring 80 based on the negator principle. A spring wire 80 is wound around left and right wheels 84, 86. The spring wire 80 is tensioned by moving the piston 88 upwards against the wire 82. 
     The above-described springs can be formed from various materials or combinations of materials. While spring steel is the preferred materials various other high modulus metals, plastics or a combination of materials may be used. Also, a combination of different grades of a material, where the different grades have different moduli may be used. FIG. 14 shows the spring force (delivery pressure) as a function of spring extension (% volume remaining) for the constant force springs described above. 
     FIGS. 8 and 9 are directed to a second embodiment, preferably for applications where the fluid delivery system 90 is not to be refilled. The piston 18 has a weakened portion which is designed to allow the piston 18 and lower shaft 92 to be separated from the upper shaft 94 which is connected to the knob 36. As best shown in FIG. 9, the shaft has a narrowed portion 96 and a hollow center 98 which results in a thin wall portion which is readily broken by applying a twisting force to the upper shaft portion 92 by rotating the knob 36. The fingers 64 riding in the slots 66 prevent the lower shaft 92 and the piston 18 from rotating when the knob 36 is turned. 
     FIGS. 5 and 7 show a tubing set 100 attached to the tubing connector 32 on the bladder 14. Different tubing set 100 configurations can be used to match the specific delivery requirements of the physician, patient and the fluid being delivered. The particular arrangement shown includes a spike 102 connected to the tubing connector 32, a filter system 104 for trapping particulate matter and to remove gas bubbles, a clamp or a valve 106 and an outlet for attachment to a tube or catheter which, in turn, is emplaced in the patient. In a further embodiment, the outlet 108 in the tubing set 100 can also contain one or more metering orifices which, in conjunction with the known spring force, further controls the flow rate. 
     Shown on FIG. 1 is an accessory holder 110 which snaps onto the bottom of the cap 12 to hold the tubing set 100 and other accessories which are used with the fluid delivery system. 
     To assemble the embodiment of FIGS. 1 through 7 the piston 18 is forced upward into the shell 34 so that the barbed end 42 of the piston shaft 40 is inserted through the hole 46 in the upper end 44 of the shell 34 and the barbed end 42 is allowed to expand. Forcing the piston 18 into the shell 34 compresses the spring 38 and thus loads the drive mechanism 16. As the barbed end 42 exits through the hole 46 in the upper end 44 of the shell 34 the barbs are inserted into the cammed inner surface 68 of the knob 36 and the knob 36 is twisted, catching the barbs within the cam. The filled bladder 14 is placed in the cap 12 and the cap 12 carrying the bladder 14 is connected to the shell 34 by placing the tabs 52 through the grooves 56 in the shell ledge 60 and pressing and twisting the cap 12 to place the tab 52 in the recess 58 on the shell ledge 80. The desired tubing set 100 is then attached to the tubing connector 32. To use the fluid delivery system 10 the knob 36 is turned compressing the barbed upper end 42 which allows the compressed barbs to pass through the hole 46 in the upper end 44 of the shell 34 driven by the expanding spring 38. The system 10 can be reused by removing the cap 12, replacing the empty bladder 14 with a full bladder 14 and reassembling the system 10. 
     The embodiment of FIGS. 8 and 9 is assembled in a similar manner except that the cap 12 snaps onto the shell 34 so that once assembled it is not readily disassembled. Also the piston shaft 40 is frangible so that untwisting the knob 36 after assembly does not release the shaft 40 but instead causes the shaft 40 to break at the narrowed portion 96, thus rendering the system non-reusable without replacing the piston 18 and shaft 40 assembly. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions and uses thereof, other versions and uses are possible. For example, various different means can be used to assemble the device or hold the components together, various different sizes and shapes of bladders can be used, and various different spring designs can be utilized to deliver a continuous constant drive force. Alternately, the spring can be designed to give several predetermined but different force cycles. For example, it may be desirable to deliver a bolus of fluid followed by a one or more periods of constant rate or fixed decreasing delivery rates. This can be accomplished by varying the spring design. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.