Patent Application
20080287874
This invention relates generally to infusion devices. More particularly, the present invention is directed toward an adjustment mechanism to adjust the dead space of a piston pump by adjusting the end position of the piston's forward stroke.
Infusion devices may be used to deliver an infusion media (for example, a medication such as insulin) to a patient. Such devices may be implanted into a patient's body to deliver predetermined dosages of the infusion media to a particular location within the patient's body, for example, in the venous system, the spinal column, or within the peritoneal cavity.
A known infusion device of the type described above includes a drive mechanism that includes a reciprocating pumping element made of a ferrous material. The reciprocating pumping element includes an actuator member with a piston portion that is coupled to an armature portion, also known as a piston actuator or pole. The piston portion is configured to reciprocate within a piston channel when a solenoid coil is alternately energized and de-energized. That is, when the solenoid is energized, magnetic flux causes the actuator to move very quickly (on the order of 2-3 milliseconds) until it reaches a stop member. This corresponds to the pump's forward stroke and results in the delivery of a predetermined dosage of infusion media from an outlet chamber to the patient. When the solenoid is de-energized, the lack of magnetic flux allows the actuator to return to its original position under the force of a spring or other return mechanism. This, in turn, causes the pressure in the piston chamber to fall. The reduced pressure in the piston chamber causes infusion media to flow from a reservoir through an annulus between the actuator piston and the piston cylinder wall to refill the piston chamber, thus equalizing the pressure between the reservoir and the piston chamber and preparing the pump for its next pumping or delivery stroke. This is referred to as the refill stroke. The annulus between the actuator piston and the piston cylinder may be very small (i.e. in the order of 150 to 250 microinches radially), resulting in an outlet chamber refill process that takes between about 1 to 2 seconds. In contrast, the pump's forward (delivery) stroke may be approximately 500 times faster than the refill process.
Manufacturing tolerances in the production of the pump components may result in unwanted ullage (also known as “dead volume” or “dead space”) in the pumping chamber. Ullage may include space that the pump does not physically displace during the forward stroke, resulting in an inaccurate pumped volume. The dead space may lead to trapped air bubbles that are not displaced during the pumping strokes. The air bubbles can further lead to pump dysfunction that is, in part, due to the fact that the trapped air bubbles are compressible. A compressible air bubble in the pumping chamber may result in a smaller amount of displaced fluid from each pumping stroke due to piston movement, resulting in air compression rather than fluid displacement.
A need therefore exists for a method and apparatus to account for manufacturing tolerances in the assembly of the pump components. A need also exists to reduce or eliminate ullage in a piston type pump.
The present invention includes an apparatus and method for reducing or eliminating ullage in a piston type pump. The apparatus includes an adjustable stop member to selectively adjust the position of the piston during the forward stroke so as to reduce the volume that is not displaced.
On embodiment may be an apparatus for delivering a fluid, the apparatus including a housing, an inlet in the housing for receiving the fluid, an outlet in the housing for discharging the fluid, an actuator positioned within the housing and moveable between a first position and a second position to displace the fluid from the inlet and through the outlet, and an adjustable stop operatively positioned relative to the actuator whereby the second position is selected by adjustment of the adjustable stop.
Another embodiment may include an adjustable actuator for delivering fluid through a piston channel from an inlet to an outlet, the actuator including an armature configured to move between a forward position and a retracted position, a piston coupled to the armature and moveable within the piston channel, and an adjustable stop operably positioned to contact the armature to selectively adjust the forward position.
Yet another embodiment may be a method for manufacturing a piston pump that providing a pump assembly including a housing, an inlet in the housing for receiving the fluid, an outlet in the housing for discharging the fluid, a piston channel within the housing through which the fluid flows from the inlet to the outlet, and an actuator positioned within the housing and moveable between a first position and a second position, the actuator driving the fluid stored in the piston chamber toward the outlet when the actuator transitions from the first position to the second position, the actuator comprising an armature, and a piston coupled to the armature and moveable within the piston channel, placing the actuator in the first position, and adjusting a stop to selectively adjust the position of the actuator in the first position to a desired position in the piston channel.
Embodiments of the present invention will hereinafter be described in conjunction with the following drawings wherein like reference numerals denote like elements throughout.
The present invention is an adjustment mechanism for selectively adjusting the forward position of an actuator member of a piston type pump in order to eliminate undesired dead space not pumped during the pumping stroke, also known as ullage. In particular, the adjustment mechanism is an adjustable stop member that can be positioned to contact a portion of the actuator member to halt the actuator in a desired position during a forward pumping stroke. Adjusting the position of the piston during the forward stroke of the actuator member allows for a user to eliminate any unwanted ullage, or dead space that may occur if the piston does not complete its stroke in the desired position.
The following detailed description is of the presently contemplated mode of implementing the invention. This description is not to be taken in a limiting sense, but is merely for the purpose of illustrating the general principles of embodiments of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. The scope of the invention is defined by the appended claims.
In further embodiments, the present invention actuator member may be included in pumping systems not related to infusion devices. An implantable infusion pump, however, will be utilized in the remainder of this description for the sake of simplicity.
A description of the implantable infusion pump and how it is installed in the body may help to provide some further context for the present invention. The device 10 may include a generally disc-shaped housing 14. While a generally circular disc-shaped embodiment is illustrated in
The housing 14 includes a reservoir 16 for holding a volume of infusion medium, such as, but not limited to, a liquid medication to be administered to the patient. Housing 14 may also contain a drive mechanism 18 (e.g. a pump), a power source 13, and control electronics 20. Pump 18 may be configured to receive infusion media from reservoir 16 via a pump inlet 22. Inlet structure 22 may provide a closeable and sealable fluid flow path to the reservoir 16 in the reservoir portion of the housing. The inlet structure may include a port for receiving a needle through which fluid may be transferred to the infusion device, for example, to fill or re-fill the reservoir 16 of the device with the infusion media or a rinsing fluid as will be more fully discussed below. In particular embodiments, the inlet structure may be configured to re-seal after a fill or re-fill operation, and to allow multiple re-fill and re-seal operations. One example of an inlet structure is described in U.S. Pat. No. 6,652,510, titled “Infusion Device and Reservoir for Same,” which is incorporated by reference herein in its entirety and for everything it teaches and discloses. However, further embodiments may employ other suitable inlet structures, including, but not limited to, those described in U.S. Pat. Nos. 5,514,103 and 5,176,644, each to Srisathapat et al.; U.S. Pat. No. 5,167,633 to Mann et al.; U.S. Pat. No. 4,697,622 to Swift; and U.S. Pat. No. 4,573,994 to Fischell et al., also incorporated by reference. Representative examples of reservoir housing portions and reservoirs which may be employed in embodiments of the invention are described in the above referred to U.S. Pat. No. 6,652,510, and further embodiments may employ other suitable reservoir configurations, including, but not limited to, those described in the above referred to U.S. Pat. Nos. 5,514,103; 5,176,644; 5,167,633; 4,697,622; and 4,573,994.
The medical device 10 and catheter 12 are typically implanted by a clinician (e.g., surgeon) within the body 15 during a surgical procedure. While the present invention also contemplates embodiments wherein the catheter is implanted with a proximal end outside the body 15 so that it may attach to an external infusion device, the remainder of this description is, for the sake of brevity, directed to implantable infusion systems that are entirely implanted in the body 15 of the patient.
Before implantation of the medical device 10, the catheter 12 may be positioned such that the fluid delivered to the patient through the catheter 12 reaches a selected internal delivery location 17 within the body 15 of the patient. As depicted, the infusion system is implanted such that the delivery site 17 is located within the intrathecal space of the spinal canal. As may be appreciated, the infusion systems of the present invention may be used to deliver fluid to any other selected internal delivery location, e.g., epidural, etc.
Catheter 12 may preferably disgorge fluid at other than at its distal end. For example, catheter 12 may intentionally have a delivery region that is not proximate the distal end of the catheter 12, e.g., a hole or valve positioned somewhere before reaching the distal end of the catheter 12. Thus, catheter 12 may be placed in patient with a delivery region of catheter 12 placed in or near to, generally proximate to, the selected internal delivery site 17.
A proximal end of the catheter 12 may be tunneled through the tissue to the device implant location and coupled to a catheter port of the medical device 10. If implanted, the medical device 10 is typically positioned subcutaneously, e.g., from 1 centimeter (0.4 inches) to 2.5 centimeters (1 inch) beneath the skin, where there is sufficient tissue for supporting the medical device 10, e.g., with sutures or the like.
The medical device 10 is, in the illustrated embodiment, operable to infuse a fluid from an enclosed reservoir 16 into the body 15 through the catheter 12.
In order to fully understand the operation of the present invention, a review of an example embodiment pump in which the invention may be utilized may be first helpful.
As illustrated in
In particular embodiments, both the drive mechanism 18 and the reservoir 16 may be hermetically sealed. In such embodiments, the housing 14 containing drive mechanism 18 and control electronics 20 may be made from titanium or titanium alloy or other biocompatible metals. The reservoir portion 16 of the housing may be made from similar metals or a biocompatible and infusion medium compatible plastic that allows for the desired hermeticity.
The drive mechanism 18 may include mechanical and electromagnetic components that inhabit a volume of space within the housing 14 in which the components reside and operate. The device 10 is configured such that, once implanted, it functions for a relatively long period of time to administer infusion medium to the patient to periodically be replenished from the outside of patient's body.
As used herein, the term “therapeutic substance” refers to a substance intended to have a therapeutic effect on the patient, e.g., pharmaceutical compositions, genetic materials, biologics, and other substances. “Pharmaceutical compositions,” as used herein, may include chemical formulations intended to have a therapeutic effect such as intrathecal antispasmodics, pain medications, chemotherapeutic agents, and the like. Pharmaceutical compositions are often configured to function effectively in an implanted environment by possessing various characteristics including: stability at body temperature to retain therapeutic qualities; concentration to reduce the frequency of replenishment; and the like. “Genetic materials,” as used herein, may include substances intended to have a direct or indirect genetic therapeutic effect such as genetic vectors, genetic regulator elements, genetic structural elements, DNA, and the like. “Biologics,” as used herein, may include substances that are living matter, or derived from living matter, and offer a therapeutic effect to the patient such as stem cells, platelets, hormones, biologically produced chemicals, and the like. “Other substances” may include most any other substance that is intended to have a therapeutic effect, yet does not clearly fit within one of the categories identified above. Examples of other substances may include saline solutions, fluoroscopy agents, and the like.
In some embodiments, the fluid contained within a reservoir 16 of the medical device 10 may be replenished periodically after device implantation. Typically, replenishment is accomplished with a non-coring needle (not shown) connected to a syringe filled with the fluid. The needle may be inserted through the patient's skin and into a self-sealing septum located within the housing of the medical device 10.
Referring to
As shown in
When assembled, the coil cup 40 may be located in the hollow interior of the housing member 32, with the central portion 36 of the housing 32 extending through channel 42 of the coil cup 40 as shown in
The drive mechanism 18 may also includes an actuator member 58, which may include an armature portion 60 and a piston portion 62. The actuator member 58 is most often made of a generally rigid, biocompatible and infusion medium compatible material having a relatively high magnetic permeability such as, but not limited to, ferrous materials, ferritic stainless steel with high corrosion resistance, or the like. In the embodiment of
The armature 60 cooperates with the inner and outer walls of the coil cup 40 to provide a flux path for electromagnetic flux. The spacing between the pole surfaces on the armature 60 and the pole surfaces on the coil cup walls define gaps in the flux path. In particular embodiments, the spacing between the surface of outer pole 70 of the armature 60 and the surface of outer pole 52 of the outer wall 50 of the coil cup 40 is greater than the spacing between the surface of inner pole 72 of the armature and the pole surface 48 of the inner wall 46 of the coil cup (or the barrier 74) when the actuator is in the retracted position shown in
The radial struts 68 in the armature provide radial paths for electromagnetic flux between the outer and inner pole sections 70 and 72 of the armature. The configuration of openings is most often designed to provide a sufficient conductor for electromagnetic flux and yet minimize or reduce viscous resistance to actuator motion. With reference to
The actuator spring 78 in the illustrated embodiment is a coil spring disposed around the piston portion 62 of the actuator 58 adjacent the armature portion 60. One end of the coil spring abuts the armature portion 60 of the actuator, while the opposite end of the coil spring abuts a shoulder 81 in the piston channel 38 of the housing 32. In this manner, the actuator spring 78 imparts a spring force between the housing and the actuator 58 to urge the actuator toward its retracted position shown in
In the illustrated embodiment, by using a coil spring 78 located around and coaxial with the piston portion 62 and disposed partially within the piston channel 38, the actuator spring may have minimal or no contribution to the overall thickness dimension of the drive mechanism. However, in other embodiments, actuator springs may have other suitable forms and may be located in other positions suitable for urging the actuator toward its retracted position shown in
The drive mechanism 18 may further include a cover member 80 which attaches to the housing member 32 over the open side of the housing member and the barrier 74. The cover member 80 is most often made of a generally rigid, biocompatible and infusion medium compatible material having a relatively low magnetic permeability (being relatively magnetically opaque) such as, but not limited to, titanium, stainless steel, biocompatible plastic, ceramic, glass or the like.
The cover member 80 defines an interior volume 82 between the barrier 74 and the inner surface of the cover member. The armature portion 60 of the actuator member 58 resides within the interior volume 82 when the cover is attached to the housing. The armature 60 is moveable in the axial direction within the volume 82 between the retracted position shown in
A first adjusting stop 84, or adjustable plunger, may be located within the cover 80 for contacting the armature 60 to set the retracted position of the armature when the armature is in the fully retracted position shown in
As is further illustrated, in the present invention the pump 18 includes a second adjusting stop 87. The second stop 87, also known as an adjustable plunger, adjustable ullage stop, or ullage control, may be positioned to selectively adjust the position of the actuator member 58 at the desired forward stroke position during pumping. As is further described below, adjustment of the second stop 87 may reduce the ullage present in the infusion device 10 and therefore result in a more accurate pumping device. As may be appreciated, the second stop 87 may be located at other positions that allow for contact with the actuator member 58 to perform the adjustment.
As shown in
The actual radial spacing between the piston portion 62 and the wall of the channel 38 to achieve such results depends, in part, on the overall dimensions of those components, the pressure differentials created in the mechanism, and the viscosity of the infusion medium.
The valve assembly 96 in the embodiment of
The valve member 102 is most often made of generally rigid, biocompatible and infusion medium compatible material, such as, but not limited to, titanium, stainless steel, biocompatible plastic, ceramic, glass, gold, platinum or the like. A layer of silicon rubber or other suitable material may be attached to the rigid valve member material on the surface facing the channel 38 to help seal the opening to channel 38 when the valve member is in the closed position shown in
The valve spring 106 is most often made of biocompatible and infusion medium compatible material that exhibits a suitable spring force such as, but not limited to, titanium, stainless steel, MP35N cobalt steel or the like. In the illustrated embodiment, the valve spring 106 is a coil spring. In other embodiments, other suitable valve spring configurations may be employed, including, but not limited to, helical, flat, radial, spiral, barrel, hourglass, constant or variable pitch springs or the like.
The embodiment shown in
The coil 54 may be inserted into the annular interior of the coil cup 40 with the coil leads extended through a coil lead opening 56 in the coil cup. The coil may be impregnated or partially impregnated with a fill material of epoxy or the like for adhering the coil to the coil cup and for sealing or partially sealing the coil. The fill material may also be used to adhere the barrier plate to the coil members to avoid warping or bulging of the barrier plate after assembly.
The coil cup 40 and the coil 54 may be inserted into the interior of the housing 32 with the coil leads (which may be wire leads or flexible conductive tabs) extending through a coil lead opening 56 in the housing 32. In particular embodiments, the coil cup and housing are configured to provide a tight friction fit that does not require additional means to adhere the two components together. In other embodiments, the coil cup 40 and housing 32 may be coupled together by a suitable adhesive material or other adhering methods, including, but not limited to, welding, brazing or the like.
The barrier 74 may be placed over the coil, coil cup and housing sub-assembly. The barrier 74 may be adhered to the housing by one or more adhering points or continuously secured along the circumference of the barrier 74 with any suitable adhesive material or other adhering methods including, but not limited to, welding, brazing, soldering, or the like. Alternatively, or in addition, the barrier 74 may be held in place by a shoulder portion of the cover 80, as shown in
After the barrier 74 is placed over the coil, coil cup and housing, the actuator 58 may be added to the sub-assembly. First, however, the actuator spring 78 is placed around the piston portion 62 adjacent the armature portion 60 of the actuator. Then the free end of the piston portion 62 is passed through the axial channel 38 of the housing 32 with the armature end of the actuator arranged adjacent the barrier 74.
A simplified schematic of the actuator member 58, including the armature portion 60 and the piston portion 62, is illustrated in
The position of the actuator 58 in the retracted position may be adjusted by adjusting the position of the first stop 84. In one particular embodiment, adjusting the first stop 84 includes adjusting a threaded cylindrical member that engages corresponding threads in the cover member 80. An exposed end of the first stop 84 may be provided with a tool-engagement depression for allowing engagement by a tool, such as a screw-driver, Allen wrench or the like, from outside of the cover member 80. By engaging and rotating the first stop 84 with a suitable tool, the depth that the stop extends into the cover member 80 may be adjusted to adjust the retracted position of the armature portion 60 and therefore the piston 62 in the piston channel 38. In one particular embodiment, adjustments of the first stop 84 are made during manufacture. In that embodiment, the adjusted position is set by welding or otherwise adhering the first stop 84 in the adjusted position during the manufacture. In other embodiments, the first stop 84 is not set and welded during manufacture to allow adjustment of the first stop 84 after manufacture.
In the present invention, the second stop 87 may be adjusted to help adjustably select the volume pumped during each pumping stroke, and eliminate any unwanted ullage, by adjusting the position of the piston 62 at the end of the forward stroke. The pumped volume is represented by space 110 in
During manufacturing, the position of the second stop 87 may be adjusted before the position of the first stop 84. In such an embodiment, the second stop 87 may be adjusted to set the forward position of the stroke for the actuator member 58. In the illustrated embodiment, the actuator member 58 forward stroke is limited by the armature portion 60 contacting the second stop 87. This end of forward stroke position may be selected such that the end of the piston 62 when the actuator 58 completes its pumping cycle is in a desired relationship with the end of the piston chamber. For example, as illustrated in
Once the forward position for the actuator 60 is selected, the volume of fluid to be pumped during each pumping stroke, represented by space 110, may then be selected. The volume is selected by moving the actuator 60 towards the first position such that the desired space 110 is left between piston 62 and valve 102. The first stop 84 is then adjusted to contact the actuator 58 at the desired actuator 58 position.
In one embodiment, the piston 62 may be purposefully made a little longer than necessary so as to require the actuator 58 to be dialed back so as to bring the piston 62 into an aligned position with piston channel 38 and the valve member 102.
Because of manufacturing tolerances, adjusting the forward and retracted positions of the actuator 58 in this manner may help to insure that each manufactured pump dispenses the same or nearly the same volume of fluid during each pumping stroke. The total volume of delivered fluids by the pump may therefore be extremely accurate.
The first and second stops 84 and 87 may be accurately adjusted using a variety of methods. One method may comprise the stops 84, 87 as screws such that each turn is equal to a set distance. In other embodiments the adjustment stops 84, 87 may include detents to indicate depths. Other adjustable stops with different kinds of indicators may be substituted without changing the nature and scope of the present invention.
In further embodiments, an adjusting member 108 may be included on the actuator member 58 to help control ullage. In one embodiment illustrated in
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.
