Sliding core fluid delivery device

A pump for the delivery of a fluid includes a core, a restrictor, and an expandable bladder. The core is configured to extend longitudinally along an axis of the pump. The restrictor is configured to limit the longitudinal extension of the core to a predetermined maximum length. The expandable bladder is attached to the support core in at least one position and configured to receive a fluid.

FIELD OF THE INVENTION

This invention relates to a fluid delivery device.

BACKGROUND

Elastomeric pumps are widely used in healthcare settings to deliver fluids and medication to patients. In some pumps, fluid is stored in a drug reservoir or bladder made of silicon or another rubber polymer. The bladder is attached to a fixed length central support core at positions along the core that are separated by a non-variable distance. When filled, the bladder expands and the increased surface area of the bladder stores energy that exerts pressure on the fluid, driving the fluid out of the bladder. The flow rate of the fluid is often limited by a restricting orifice such as a glass capillary or a section of PVC tubing.

Referring toFIG. 1, a typical flow profile18(i.e., flow rate vs. time) for a standard elastomeric pump shows that the flow rate of fluid from the pump is not constant during fluid delivery. Flow begins with a strong initial spike20in flow rate, continues with a trough-shaped phase21having a lower flow rate, and finishes with a slight second spike22. While the troughs and peaks of such a profile may be averaged to provide a sufficient flow rate, in some cases, such as for the delivery of toxic medication or when a narrow therapeutic dose is required, the initial spike may result in an overdose or another undesirable situation.

The initial spike20is generated by the strong forces exerted on the fluid by the expanded bladder. To mitigate the initial spike in flow rate, a filled pump can be put aside for a waiting period before beginning fluid delivery in order to allow the bladder to lose some of its elasticity, thus reducing the forces exerted on the fluid therein.

The trough-shaped phase21results from a combination of two phenomena. As fluid exits the bladder, the bladder contracts and the energy stored in the bladder decreases. Thus, the pressure exerted by the bladder on the fluid decreases, causing the flow rate to drop. At the same time, however, the physical contraction of the bladder results in a thickening of the bladder walls, which causes the bladder to impose more pressure on the fluid. Initially, the first effect is prominent. As the bladder empties, the latter effect becomes progressively more prominent and manifests itself as the second spike22at the end of the fluid delivery.

If the thickness of the bladder walls is not uniform, the bladder will expand more rapidly in the thinner regions when receiving fluid, thus further accentuating the thickness variations. This effect causes the expanded bladder to have an asymmetrical shape, which in turn results in an uneven flow rate and variability in flow rate among like pumps. To combat this effect, the bladder is often enclosed in an outer cover that restricts its asymmetrical expansion, such as a rigid cover or a flexible and non-expandable cover. In some pumps, the bladder is formed of a rubber polymer that exerts force on the fluid therein and a silicone lining on the inside of the bladder that prevents the fluid from coming into contact with the rubber polymer.

SUMMARY

In a general aspect, a pump for the delivery of fluid includes a core configured to extend longitudinally along an axis of the pump, a restrictor configured to limit the longitudinal extension of the core to a predetermined maximum length, and an expandable bladder attached to the support core in at least one position and configured to receive a fluid.

Embodiments may include one or more of the following. The pump includes a cover enclosing the bladder and at least a portion of the support core. The cover has a size and shape such that when the bladder is filled with a fluid, the bladder has a size and position that are substantially independent of the size and shape of the cover. The cover is sized and dimensioned such that a gap exists between an outer surface of the bladder and an inner surface of the cover when the bladder is filled with fluid. The bladder is formed substantially of silicone. The position at which the bladder is attached to the core is selected based on at least one of a volume of the bladder when filled and a desired flow rate of a fluid delivered from the pump.

The core includes a first piece and a second piece configured to slide longitudinally relative to each other. The pump includes a connector for connecting the first piece and the second piece. The restrictor includes a ball bearing positioned in a channel. The length of the channel is determined based on the predetermined maximum length of the core. The support core is configured to expand longitudinally when fluid enters the bladder and to contract longitudinally when fluid exits the bladder. The pump is configured to deliver fluid at a substantially constant flow rate.

In another aspect, a method for the delivery of a fluid from a pump includes receiving fluid into a bladder and delivering fluid from the pump. Receiving fluid into a bladder includes extending a support core longitudinally along an axis of the pump and expanding the bladder. The extension of the support core is limited to a predetermined maximum length by a restrictor. Delivering fluid from the pump includes contracting the bladder and retracting the support core along the longitudinal axis of the pump.

Embodiments may include one or more of the following. Delivering fluid from the pump includes delivering fluid at a substantially constant flow rate. Extending the support core includes sliding a first piece of the support core longitudinally relative to a second piece of the support core. Expanding the bladder includes expanding the bladder to a shape and position that is substantially independent of a size and shape of a cover enclosing the bladder. The bladder is formed substantially of silicone.

A pump as described above has a number of advantages. In particular, the sliding core of the pump supplies an additional degree of movement to the pump as the bladder is filled or as fluid is delivered from the pump. This additional degree of movement affects the flow profile of the fluid delivery, enabling the pump to deliver fluid with a reduced initial spike or even no initial spike in flow rate. Furthermore, the sliding core allows the bladder to expand substantially symmetrically as it is being filled even if there are slight variations in the thickness of the bladder walls. The composition of the bladder as primarily silicone further facilitates the symmetric expansion of the bladder. As a result of this symmetric expansion, the bladder exerts a uniform pressure to the fluid inside, making possible a consistent flow rate during fluid delivery. In this way, a relatively constant flow rate is maintained during a large portion of the delivery of fluid from the pump. The symmetric expansion of the bladder also helps to reduce or eliminate the spike in flow rate at the start of fluid delivery from the pump. A consistent flow rate is attainable as soon as the pump has been filled with fluid; no waiting period is necessary to relax the pressure exerted by the bladder on the fluid inside. Additionally, inter-device variability is reduced because the expansion of the bladder, and hence the pressure applied to the fluid contained therein, is consistent among like devices.

DETAILED DESCRIPTION

Referring toFIG. 2A, a sliding core pump30delivers fluids, such as antibiotics, pain relief drugs, chemotherapy agents, or other medications, to a patient. Pump30includes a generally cylindrical support core32carrying a bladder4and an outer cover34. Fluid is stored within bladder4, which exerts pressure on the fluid, forcing the fluid out of the pump through a fluid delivery line10. A patient connector13(e.g., a Luer adapter) coupled to the end of fluid delivery line10facilitates the delivery of fluid to a patient. In some embodiments, fluid delivery line10is coupled to other components, such as an air trap and anti-microbial filter9or a micro-bore restrictor tubing12, which can be, for instance, a glass capillary or a section of PVC tubing. A clamp11connected to fluid delivery line10starts and stops the flow of fluid from pump30.

Referring toFIGS. 2A and 3, support core32incorporates movable or telescopic components, including a first sliding core member1and a second sliding core member3. Sliding core members1and3are held together with a collar-like connector2. In another embodiment, first sliding core member1inserts into an annular cavity in second sliding core member3. Bladder4is affixed to support core32at two positions8aand8bthat are selected based on the desired fill volume of the bladder. First sliding core member1and second sliding core member3are longitudinally extendible relative to each other along an axis8of pump30. The extension of the sliding core members1and3guides the longitudinal and concentric extension of bladder4into an elliptical shape. This relative motion of sliding core members1and3causes a relative displacement of positions8aand8b, which are separated by a variable distance8c. While fluids are being introduced into bladder4, the distance8cincreases as bladder4expands and support core32elongates. While fluid is being delivered from bladder4, the distance8cdecreases as bladder4contracts and support core32retracts.FIG. 2Ashows support core32in its start position with little fluid in bladder4. Referring toFIG. 2B, as fluids are introduced into bladder4and sliding core member1extends longitudinally relative to sliding core member3, bladder4expands into a balloon-like shape.

The relative longitudinal movement of sliding core members1and3along axis8is limited by ball bearings5, which are typically made of glass or a medical grade polymer. Ball bearings5are located in slots6and/or channels or grooves7in sliding core members1and3. The limit of the extension of support core32is determined by the length of slots6and channels7. In the embodiment shown inFIGS. 4A and 4B, two slots6aand6band two channels7aand7bare utilized. In general, the number of ball bearings5, slots6, and channels7varies depending on the size of support core32and the desired relative displacement between positions8aand8b. In other embodiments, the longitudinal movement of sliding core members1and3is limited by a stopper and guide assembly or by any other design that permits free movement of sliding core members1and3along axis8while also providing predetermined end points or limits to this movement.

Bladder4is formed of a flexible membrane that enables air trapped within the bladder to slowly dissipate through the permeable membrane. In some embodiments, bladder4is made of a self-venting material. The material of bladder4is also compatible with pharmaceutical compounds. For instance, bladder4is made of silicone or another rubber polymer. In some embodiments, bladder4is made primarily of silicone.

Referring again toFIG. 2B, cover34protects bladder4(e.g., from puncture, abrasion, or dirt) and provides a surface area for printing variable manufacturing data and device identification, such as lot numbers, fill volume, flow rates, and flow duration. Cover34is formed to enclose bladder4in both its filled state and its unfilled state without deforming or otherwise affecting the general shape or position of the bladder relative to support core32as bladder4expands and contracts. That is, as bladder4is filled with fluid, the bladder takes on a shape and position that is independent of the size and shape of cover34. In one example, cover34is vacuum formed to have an air gap35between an inner surface38of the cover and an outer surface36of bladder4in its fully filled state. Cover34is secured (for example, with elastic bands, not shown) to support core32at positions40aand40b. Because cover34is affixed to support core32and moves in tandem with sliding core members1and3, the ends of cover34extend longitudinally away from each other as bladder4expands. Cover34may be a soft cover that is made, for instance, of PVC. In other examples, a hard rigid cover protects bladder4. The hard rigid cover may fully or partially enclose bladder4in its fully-expanded state without deforming or otherwise affecting the general shape or position of the bladder relative to support core32as bladder4expands and contracts.

Referring toFIG. 4C, pump30includes a filling port42at an open end44of support core32through which fluids are introduced into bladder4. Filling port42is compatible with most syringes and other standard filling devices. A one-way anti-siphon valve46on filling port42prevents leakage of fluid from bladder4during and after filling. A flip cap assembly48is attached to support core32to cover filling port42. At an opposite end49of support core32, an output port50is connected to fluid delivery line10. Two flow paths52and54extend within support core32. Flow path52couples filling port42with the inside of bladder4, while flow path54couples the inside of bladder4with output port50.

The construction of support core32to including sliding core members1and3imparts an additional degree of movement to pump30as the bladder is filled or as fluid is delivered from the pump. Referring again toFIG. 1, this additional degree of movement gives a flow profile24to sliding core pump30. As fluid is initially delivered from the pump, bladder4contracts and sliding core members1and3move longitudinally inwards. The motion of sliding core members1and3allows bladder4to exert less pressure on the fluid contained therein. The reduced force causes a minimal initial spike26at the beginning of fluid delivery.

Once sliding core members1and3have retreated to their home position (i.e., when sliding core members1and3are in contact or when distance8cis at a minimum), bladder4continues to contract and expel fluid but there is no further retraction of support core32. At this point, the flow rate enters a phase28that is comparable to the flow rate obtained during delivery from a pump without a sliding core. By adjusting the distance8cin relation to the dimensions, wall thickness, geometry, and elasticity of bladder4, an approximately flat flow rate profile can be achieved for sliding core pump30.

In some embodiments, various modes of fluid delivery are available, including continuous flow, continuous flow with Bolus effect, Bolus flow, and variable flow.

The foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. These and other embodiments are within the scope of the following claims.