Methods and devices for determination of flow reservoir volume

A novel enhanced flow metering device is adapted for disposing into a flow material reservoir a known volume of flow material whereby software used in conjunction with a pressure sensor may be calibrated. Additionally, by measuring the known amount of flow material returning to the flow material reservoir, checks are quickly made to ensure the pressure sensor is behaving as expected.

BACKGROUND

This disclosure relates to methods for the determination of flow reservoir volumes.

SUMMARY

A novel enhanced flow metering device is adapted for disposing into a flow material reservoir a known volume of flow material whereby software used in conjunction with a pressure sensor may be calibrated. Additionally, by knowing or determining the volume of a proximal flow space provides novel methods for determining the volume of flow material delivered, and with accuracy. Moreover, it provides for a novel safety device, whereby determination of the correct functioning of sensors measuring the volume reservoirs.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the present disclosure, reference is made to the accompanying drawings in which like references indicate similar elements, and in which is shown by way of illustration specific embodiments in which the present disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical, functional, and other changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims. As used in the present disclosure, the term “or” shall be understood to be defined as a logical disjunction and shall not indicate an exclusive disjunction unless expressly indicated as such or notated as “xor.”

As used herein, the term “real time” shall be understood to mean the instantaneous moment of an event or condition, or the instantaneous moment of an event or condition plus a short period of elapsed time used to make relevant measurements, computations, etc., and to communicate such measurement, computation, etc., wherein the state of an event or condition being measured is substantially the same as that of the instantaneous moment irrespective of the elapsed time interval. Used in this context “substantially the same” shall be understood to mean that the data for the event or condition remains useful for the purpose for which it is being gathered after the elapsed time period.

As used herein, the term “fluid” shall mean a gas or a liquid.

As used herein, the term “flow material” shall mean a fluid that is intended for delivery to a target.

As used herein, the term “fill” and “filling” shall mean increasing the amount of a fluid in a chamber by some percentage of the total volume of the chamber up to 100%.

Disclosed herein are methods and devices for determining the volume of flow material reservoirs and for calibrating sensors used to measure volumes in pumps, such as infusion pumps. The methods use flow metering devices disclosed herein to deliver a known volume of flow material back into a flow material reservoir in each metering cycle. Additionally, the present disclosure provides a method for detecting integrity or failure of the mechanical components of the pumps and the flow metering device.

Calculation of volume and overall flow rate of a pump are disclosed in U.S. Pat. Nos. 7,008,403; 7,341,581; and 7,374,556; U.S. Utility Patent Application Pub. Nos. 2007/0264130; and 2009/0191067 (the contents of each above listed patent or patent publication are incorporated herein by reference in their entirety) may be used as devices having flow material reservoirs and as the source of the flow material. These devices typically have sensors disposed therein to measure the volume of the flow material reservoir or to measure the volume of flow material dispersed from the pumps. Other pumps that have both a flow material reservoir and are able to measure the volume of the flow material reservoir or the flow material in the reservoir are expressly contemplated under this disclosure.

Methods for delivery of and determination of the volume of a fluid or flow material are expressly contemplated in this disclosure. Sensors, such as pressure transducers, may be used in connection with the apparatus and methods described herein. Acoustic sensors, including a loud speaker and one or more microphones, may be used to accurately determine the volume of flow material reservoirs, thereby allowing for direct or indirect calculation of the volume of flow material dispensed. Acoustic volume determination technology is disclosed in, e.g., U.S. Pat. Nos. 5,575,310 and 5,755,683 and U.S. Provisional Application Ser. No. 60/789,243, each of which is incorporated herein by reference in its entirety. U.S. Pat Application Publication No. 2007/0219496, which is incorporated herein by reference in its entirety, discloses still further methods for the determination of the volume of flow material reservoirs, including via optical, capacitive, deflection measurement methods (detecting deflection of a membrane as pressure changes), thermal time of flight methods, or other methods for measuring the volume of a chamber.

According to the embodiment illustrated inFIG. 1A, flow metering device100is shown. Flow metering device100comprises cavity109in which actuation shaft110is disposed. Actuation shaft110has a proximal end terminating with actuation device112and a distal end. Actuation shaft110further comprises optional actuation guide128and at least one fixed seal118a-118d. According to some embodiments, actuation shaft also comprises at least one shaft channel121(seeFIG. 5) being defined at the ends by at least one proximal shaft opening120and at least one distal shaft opening122. Flow metering device100also comprises at least first chamber136having first compressible member138. According to embodiments

The flow metering device100illustrated inFIG. 1Aalso comprises additional chambers, for example second chamber132having second compressible member134.

FIG. 1A-1Cillustrate in perspective view a two-chamber version of flow metering device100, whereby two chambers of varying size are filled with a flow material and one or both chambers136,132are used to dispense flow material to a target. According to the detail shown inFIGS. 1A-1C, flow metering device100houses first chamber136, second chamber132, and actuation shaft110.

In use, at least one of first chamber136and second chamber132is filled with flow material or other fluid through input conduit104. Input conduit104is a conduit through input device102terminating at proximal flow space124and used for moving flow materials from a flow material source to into flow metering device100. Input device102may be a connector or valve designed to be connected with tubing, conduit, piping, or other devices used to transport flow materials or other fluids.

Flow material is dispensed from flow metering device100through output conduit130. Output conduit130is a conduit that allows flow material to move from first chamber136or second chamber132to a target. Output conduit130, according to embodiments, may terminate in a connector, for example a luer connector or other industry standard connector, that connects to devices for delivery to the target. For example, if flow metering device100is delivering a pharmaceutical, the connector might be a luer device connected to a length of tubing ending in a hypodermic needle for injection of the pharmaceutical. According to embodiments, input conduit104and output conduit130are not in fluid communication. As illustrated, for example inFIG. 5, output conduit130comprises a conduit that transports from material from chamber136,132via output flow space125a, proximal shaft opening120, shaft channel121, distal shaft opening122, and distal flow space126. Generally, output conduit is a conduit that is in fluid communication with one or more chambers of flow metering device100when actuation shaft110is in a dispense position.

Actuation shaft110controls the filling and dispensing of first chamber136and second chamber132, depending of the position of actuation shaft110. Actuation shaft110may be disposed in flow metering device cavity109. As illustrated inFIG. 1A, actuation shaft110may be moved with actuation device112. Actuation device112may articulate via actuator202(see, e.g.,FIGS. 1B,1C) that effects movement of actuation shaft110. For example, actuation device112comprises a lead screw that is coupled with an actuator202, for example a motor having opposite threading and able to drive a lead screw. According to embodiments, actuator202is a motor, finger, spring, or other implement capable of effecting movement of actuation shaft110in cavity109. In some cases, actuator202operates in conjunction with an actuation device112. In other cases, actuator202operates by articulating directly with actuation shaft110.

In the example ofFIG. 1A, actuation device112is a series of screw-like threads that articulate with mated screw threads in a motor. Depending on the direction the motor rotates the mated screw threads, actuation shaft110moves towards the distal end or towards the proximal end of flow metering device100.

Actuation device112may comprise a nickel-titanium (nitinol) or other shape memory or non-shape memory alloy, metal, plastic material, composite, etc. Actuation device112may be a component such as a rigid or semi-rigid wire, rod, or shaft connected to actuator202, as shown inFIG. 1B. According to these embodiments, actuation device112in operation is pushed or pulled to effect movement of actuation shaft110. According to embodiments where a nitinol actuation device such as, for example, a wire, is used, a spring may be disposed to return the wire to its original position after it is actuated, or a second wire may be disposed to effect the same result. According to similar embodiments, a nitinol actuation device112may be returned to a native position through the use of the “self-return” properties of nitinol, e.g., temperature or strain-induced phase transition. Actuation device112, irrespective of the mechanical design or material used, effects movement of actuation shaft110both proximally and distally through flow metering device cavity109, as desired.

Actuation shaft110may be configured to translate along long axis111in cavity109and may also be configured to rotate around long axis111. For example and as illustrated inFIG. 1A, actuation guide128is disposed in actuation rotation channel129. As actuation shaft110moves in a proximal or distal direction, actuation guide128is forced by the walls of actuation rotation channel129to rotate actuation shaft110around long axis111of actuation shaft110. Rotating actuation shaft110helps actuation shaft110move proximally and distally through cavity109with less friction.

Fixed seals118a-118dprevent leakage of flow material around them. Fixed seals118a-118dare disposed around actuation shaft110and move with actuation shaft110. Articulation of fixed seals118a-118dwith actuation shaft110and the walls of flow metering device cavity109forms sealed spaces. Flow material in these sealed spaces are trapped therein; accordingly, as actuation shaft110moves, so does any fluid trapped in the sealed spaces. Fixed seals may be o-rings, quad-rings, or other devices that form sealed barriers to the flow of fluids, including flow material. Fixed seals118a-118d(shown in various configuration throughout the figures) are disposed along the length of actuation shaft110in various numbers and configurations.

In some embodiments, an additional seal, actuation shaft seal114, is disposed towards the proximal end of actuation shaft110. Actuation shaft seal114is fixed relative to cavity109and does not move together with actuation shaft110. In operation it is held in place by seal retainer116. As illustrated inFIG. 5, actuation shaft seal114may be disposed within flow metering device cavity109between seal retainer116and flange115.

As shown, e.g., inFIGS. 1A,1B, and5, fixed seals118a-118dand actuation shaft seal114may form a plurality of flow spaces: proximal flow space124, output flow space125a, sealed flow space125b, and distal flow space126. Each flow space is sealably defined by walls109aof flow metering device cavity109, fixed seals118a-118d(or in the case of proximal flow space124by fixed seal118aand actuation shaft seal114), and by outer surface110aof actuation shaft110. Each space is configured to accommodate the flow of flow material or other fluid.

Devices that have greater than one chamber utilize the multiple fixed seals118a-118dselectively to allow flow to and from desired chambers. For example, as shown inFIG. 5, shaft channel121forms a conduit or channel within actuation shaft110, allowing flow of fluid such as flow material therethrough. Shaft channel121terminates at proximal shaft opening120and distal shaft opening122. In other embodiments, multiple shaft channels121may be present. There may exist multiple distal shaft openings122(i.e., two or more openings in fluid communication with shaft channel121at about the same position along actuation shaft110), as well as multiple proximal shaft openings120to allow for an increased fluid flow rate through shaft channel121.

As illustrated, shaft channel121may be used to bypass one or more fixed seals118, thereby defining fluid flow paths. As shown in the example ofFIG. 5, shaft channel121bypasses fixed seals118b-118cand thereby effects flow from one flow space to another flow space. In particular, shaft channel121communicates with output flow space125a(via proximal shaft opening120) and distal flow space126(via distal shaft opening122), bypassing sealed flow space125b. Thus, sealed flow space125bmay be positioned over the conduits leading into the chambers to prevent flow in or out of the chamber over which sealed flow space125bis positioned, as described in more detail below.

Depending on where shaft channel121opens on the proximal end along actuation shaft110, various flow paths are defined. For example, in the particular configuration with the relative positions of the components shown inFIG. 5, proximal shaft opening120puts shaft channel121into fluid communication with output flow space125aand bypass sealed flow space125bdue to the presence of fixed seal118b. Thus, the contents of first chamber136(fluid or flow material) may be dispensed via first chamber conduit135. Axial movement of actuation shaft110within cavity109to put shaft channel121into fluid communication with second chamber conduit133via output flow space125awill allow any contents of second chamber132to be dispensed via second chamber conduit133. As illustrated inFIG. 5, the contents of first chamber136must be dispensed prior to dispensing the contents of second chamber132.

According to embodiments having more than one chamber, first chamber136and second chamber132(collectively chambers132,136), are disposed to be in fluid communication with the flow spaces via first chamber conduit135and second chamber conduit133, respectively.

Associated with each chamber are compressible members: first compressible member138(associated with first chamber136) and second compressible member134(associated with second chamber132). Compressible members may comprise an elastomeric membrane disposed over each chamber136,132. As shown inFIG. 5, for example, first compressible member138is an elastomeric membrane that covers first chamber136; second compressible member134is an elastomeric membrane that covers second chamber132. As fluid or flow material enters each chamber136,132through chamber conduits, for example first chamber conduit135or second chamber conduit133(respectively), the flow material contacts first compressible member138or second compressible member134, respectively, causing each compressible member138,134to distend into first chamber136or second chamber132, respectively.

Compressible members138,134may comprise other devices and materials as well. According to some embodiments, one or both of the compressible members comprise closed-cell foam. According to other embodiments, one or both of the compressible member comprises other elastomeric materials. According to still other embodiments, one or both compressible members138,134comprise pockets of air contained within a compressible bag or “pillow,” or separated by a mechanical device such as a piston or movable barrier. According to still other embodiments, one or both compressible members138,134comprise pneumatic chambers that are controlled via movement of air or vented outside of flow metering device100.

As illustrated inFIG. 5, first chamber136has a larger volume than second chamber132. Chambers136and132may have identical volumes or first chamber132may have a larger volume than first chamber136and be within the scope of the present disclosure. Having variable size chambers such as that shown inFIG. 5, for example, allows for variable aliquot sizes of flow material to be delivered to a target and adds a degree of fine tuning with respect to the overall flow rate of the flow material delivered to a target, for example, in dosing patients with a pharmaceutical. For example, as shown inFIG. 1A, chamber136,132are of different volumes. If insulin is being delivered as the flow material, the dosage may be carefully controlled over time depending on whether an aliquot of insulin from larger chamber136or an aliquot of insulin from smaller chamber132is delivered. Accordingly, multiple consecutive aliquots may be delivered from smaller chamber132to give a diabetic patient basal doses of insulin. However, when a bolus is needed, an aliquot may be delivered from the larger chamber136.

In other embodiments, devices of the present disclosure having only a single chamber are contemplated. As illustrated inFIGS. 2,4, and6, single chamber136associated with compressible member138is shown. Chamber conduit135allows chamber136to be in fluid communication with proximal flow space124and distal flow space126. A shaft channel may be used in one-chamber embodiments.

As exemplified inFIG. 6, one-chamber versions of the devices of the present disclosure have two fixed seals118b,118dthat are disposed along actuation shaft110. Thus, two flow spaces are defined: proximal flow space124, defined by actuation shaft seal114, actuation shaft surface110a, cavity wall109a, and fixed seal118b; and distal flow space126, defined by fixed seals118band118d, actuation shaft surface110a, and cavity wall109a. However, single chamber devices may also be designed with shaft channel121in actuation shaft110, as described above.

According to embodiments, sensors302may be disposed within flow metering device100, for example in the chambers132,136below compressible members134,138respectively (not shown), to measure pressure and thereby calculate the volume of fluid filling and dispensing from flow metering device100. Generally, sensors302are disposed in a chamber of known volume with a fixed volume of fluid contacting the pressures sensors. Temperature sensors may be likewise disposed within flow metering device100to increase the accuracy of the calculations.

Flow metering device100may be disposable. Indeed, disposable devices comprising flow metering device100and flow material reservoir may be pre-charged with a flow material in flow material reservoir300. The disposable device may be configured, for example, to integrally articulate with a reusable device that houses hardware such as user interfaces, sensor302, actuator202, and a microprocessor configured to operate flow metering device100.

According to embodiments, flow material reservoir300may be designed to hold a flow material and a gas, with sensor302placed directly in flow material reservoir300as illustrated in theFIG. 1A. According to other embodiments, flow material reservoir300is separated from a gas chamber holding a sensor, as described variously in the patents and publications incorporated by reference herein.

Flow material reservoir300may be pre-filled with flow material. In other words, flow material reservoir300may be filled with a flow material as a step in the manufacturing process, or in a separate step after manufacturing, but before it is offered to users of the device. According to other embodiments, an end user of the flow metering device100fills the device with the flow material.

According to alternate embodiments, flow metering device100is a non-disposable, reusable device in which an attached flow material reservoir may be periodically refilled. Indeed, flow metering device100may be, for example, disposed downstream from source300, such as a pump, and used as a flow rate regulator and safety device. As a flow rate regulator, it meters the rate at which flow material is delivered to a target because the input and output conduits are never in fluid communication simultaneously. As a safety device, if a pump or flow metering device100itself malfunctions, actuation shaft110is immediately arrested and the maximum additional flow material that can be delivered is the aliquot of flow material held in the chambers and spaces of flow metering device100.

The chambers in flow metering device100may be filled with a flow material when flow metering device100has actuation shaft110configured in a filling position, illustrated for a multichamber flow metering device100inFIG. 7. According to embodiments, the filling position occurs when the chambers, in this case first chamber136and second chamber132are in fluid communication with proximal flow space124via first chamber conduit135and second chamber conduit133.

In the filling position, actuation shaft110is located so that fixed seal118ais distal to first chamber conduit135and second chamber conduit133. To accomplish this, actuation shaft110may be moved distally, thereby causing fixed seals118a-118dto move distally with it. As illustrated inFIG. 7, once these components are in this position, actuation shaft connector112is in a distal position relative to its outer flow material dispense positions described below.

As actuation shaft110moves, actuation guide128imparts rotational motion to actuation shaft110around long axis111of actuation shaft110; this causes moveable seals118a-118dto rotate as well. A small degree of rotation reduces friction as actuation shaft118a-118dmoves distal and proximal in flow metering device cavity109. Embodiments are expressly contemplated that do not have actuation guide128or actuation rotation channel129, and therefore do not provide a rotational capability to actuation shaft110and seals118a-118d. In the filling position depicted inFIG. 7, flow metering device100chambers132,136may be filled with a fluid such as a flow material via input conduit104of input device102from, e.g., flow material reservoir300shown inFIG. 1A. When flow metering device100is in the filling position, first chamber136and second chamber132are in fluid communication with input conduit104via proximal flow space124and first chamber conduit135and second chamber conduit133, respectively. According to embodiments and as shown in the Figs., e.g.,FIG. 5, fluid contacts compressible members138,134, which distend into chambers136,132respectively. According to other embodiments, fluid actually flows into each chamber and causes compression of compressible members within each chamber, for example closed-cell foam. The energy stored by the compressible members then cause the flow material to flow from the chambers to output conduit130and from the output conduit130to a target when actuation shaft110is in its dispense position(s).

In use, fluid such as flow material that is flowing into first chamber136and second chamber132may be pressurized. Thus, for example, as the flow material flows into each of first chamber136and second chamber132, first compressible member134and second compressible member134are compressed, thereby storing the energy of the pressurized flow material when input conduit104is no longer in fluid communication with first chamber136and second chamber132. Flow material may also enter unpressurized and compress compressible members136,134as addition flow material is pumped into each chamber.

As illustrated by the embodiment shown inFIG. 7, compressible members138,134may comprise an elastomeric membrane. As shown inFIG. 7and related embodiments, flow material never actually enters chambers136,132, but rather contacts compressible members138,134, each of which distends into first chamber136and second chamber132, respectively. According to other embodiments, however, flow material may directly enter the chambers and contact other compressible members within the chambers. For example, compressible members138,134comprise a closed cell foam disposed in each chamber136,132. If compressible members138,134are mechanical devices, each compressible member138,134may be a piston.

Filling may be considered complete when the flow material pressure at the source (or at a pumping pressure) and at the compressible members138,134come into equilibrium or near equilibrium. According to other embodiments, filling may be considered complete prior to such pressure reaching equilibrium when actuation shaft110is moved whereby input conduit104is no longer in fluid communication with first chamber136or second chamber132. It is possible that the chambers136,132are not filled with the same volume of flow material.

As illustrated inFIG. 8, after first chamber136is filled to the desired volume, actuation shaft110is moved proximally to a first dispense position whereby first chamber136is no longer in fluid communication with input conduit104. Note that in this position, second chamber132is still in fluid communication with input conduit104, but second chamber136is not. Second chamber132remains in fluid communication with input conduit104via proximal flow space124and second chamber conduit133. By varying any or a combination of the geometry, configuration, or number of fixed seals118, embodiments are contemplated whereby no output of flow material occurs until both first chamber136and second chamber132are no longer in fluid communication with input conduit104.

As shown according to the embodiment illustrated inFIG. 8, first chamber136is in fluid communication with output flow space125avia first chamber conduit135. The energy stored in first compressible member138causes flow material to flow via conduit135into output flow space125a, into shaft channel121via proximal shaft opening120, and from shaft channel121through distal shaft opening122into distal flow space126.

Distal flow space126comprises the space between actuation shaft110and the walls109aof cavity109at the distal end of flow metering device100. Distal flow space126is in fluid communication with output conduit130, from which flow material is delivered to a target. Flow of flow material is effected via the energy stored in compressible member138to the target.

According to some embodiments, output conduit130(seeFIGS. 1-2, for example) forms a conduit from connectors for connecting tubes, piping, or other flow facilitation devices. For example, in a medical context, output conduit130may comprise, in part, the conduit of a luer connector or hypodermic needle, according to exemplary embodiments.

According to embodiments of one chamber versions of flow metering device100(seeFIGS. 2,4, and6, for example) and as disclosed above, shaft channel121, proximal shaft opening120, and distal shaft opening122are omitted. Thus, chamber136is either in fluid communication with input conduit104via proximal flow space124, in fluid communication with output conduit130via distal flow space126, or not in fluid communication with either proximal flow space124or distal flow space126when fixed seal covers chamber conduit133. Embodiments of one chamber versions of flow metering device100having shaft channel121are, however, contemplated and would operate according to the principles of flow through shaft channel121disclosed above.

Referring again to a two chamber embodiment of flow metering device100illustrated in, e.g.,FIGS. 7-9, and referring specifically to the embodiment illustrated inFIG. 9in which actuation shaft110has been moved fully proximal into a second dispense position. In this position, as illustrated, input conduit104is not in fluid communication with either of chambers136,132. As shown, second chamber132is in fluid communication with output conduit130via output flow space125a, shaft channel121, and distal flow space124. First chamber136is in fluid communication only with sealed flow space125bvia first chamber conduit135. As sealed flow space125bis not in fluid communication with any other space or conduit, sealed flow space125bprevents flow of the flow material contained in first chamber136.

Various permutations may be made to any or a combination of the geometry, configuration or number, positioning or placement of fixed seals118along actuation shaft110, as well as the positions of shaft channel121, proximal shaft opening120, and distal shaft opening122relative to the various positions of fixed seals118on actuation shaft110. Indeed, configurations are possible whereby both first chamber136and second chamber132are in fluid communication with output conduit130, where second chamber132is in fluid communication with output conduit130prior to first chamber136being in fluid communication with output conduit130, and many other permutations depending on the configuration of the chambers, other components, and the objectives of the design.

According to embodiments, flow metering device100is a component of a disposable unit that works in conjunction with a reusable unit. For example, the disposable unit may comprise a flow material reservoir, and the components that comprise flow metering device100. The reusable unit may comprise hardware and sensors used to determine the volume of flow material reservoir300, including user interfaces and software for operating the device.

Operation of Flow Metering Device

According to embodiments of methods of the present disclosure, and as illustrated inFIG. 10, the two-chambered flow metering device100of, e.g.,FIGS. 7-9is operated by moving actuation shaft110proximally and distally to fill and dispense flow material in a controlled way. In operation1002, actuation shaft110is positioned in a filling position (e.g.,FIG. 7) whereby first chamber136and second chamber132are filled with a flow material in operation1004. After filling, actuation shaft110is positioned in a first dispense position (e.g.,FIG. 8) in operation1006, whereby first chamber136dispenses flow material contained therein as previously described into output conduit130in operation1008thereafter to a target. Finally, in operation1010, actuation shaft110is positioned in a second dispense position (e.g.,FIG. 9). Flow material contained in second chamber132is dispensed as previously described into output conduit130in operation1012thereafter to a target.

Similarly, and as illustrated inFIG. 11, the operation of a one chamber embodiment of flow metering device100of, e.g.,FIGS. 2,4and6is illustrated. In operation1102, actuation shaft110is positioned in a filling position whereby chamber136is filled with a flow material in operation1104. Once filled, actuation shaft110is positioned in a dispense position1106whereby flow material is dispensed as previously described into output conduit130in operation1108thereafter to a target.

Backstroke Volume

According to embodiments, for each complete fill-dispense cycle, actuation shaft110moves distally to fill and proximally to dispense flow material. Because input conduit104always remains in fluid communication with proximal flow space124, and because proximal flow space124varies in volume according to the position of actuation shaft110, as actuation shaft110moves to its dispense position (i.e., moves proximally), the volume of proximal flow space124is reduced, which subsequently forces some of the flow material remaining in proximal flow space124to return to flow material reservoir300via input conduit104in a predictable way. The volume of such flow material returning out of proximal flow space124is termed “backstroke volume.” Because actuation shaft110is capable of moving to discrete positions at every cycle, the backstroke volume can be the same for each cycle. If the backstroke volume is known, then such volume can be used for a variety of calculations and advantages, including calculating, e.g., the volume of flow material reservoir300and to improve the safety of flow metering device100and devices used in conjunction with it.

Knowing a precise value of the backstroke volume provides a platform for accurately determining the volume of flow material reservoir300volume (or the volume of the fluid in flow material reservoir300) and its flow rate by eliminating cumulative error that can occur from the use of prior determinations of the volume of flow material reservoir300or from calculation errors due to sensor drift or offset. Because the backstroke volume should be constant, if a backstroke volume is returned that is unexpected, the system may be configured to halt operations or generate an error or warning message.

Moreover, some sensors such as pressure transducers accumulate error over time due to sensor fatigue and other factors. Increasing error may be introduced, for example, by using values determined in prior measurements, each of which may have small measurement errors. When subsequent volume determinations are based on prior measured values which are in and of themselves inaccurate, each subsequent cycle potentially becomes increasingly inaccurate by coupling the error from prior measurements with sensor error in subsequent measurements. For example, when flow material reservoir300is nearly empty, repeated use of Boyle's law to determine the volume of flow material chamber300will result in reduced accuracy because small errors occurring in the measurement of each pressure measurement (beginning when flow material reservoir300was, for example, full of flow material) can accumulate over time. Use of a known backstroke volume, however, provides a novel method accurately to determine the volume of flow material reservoir300at any given cycle, thus minimizing cumulative error from prior cycles or from sensor drift/offset.

Moreover, according to embodiments, use of a known backstroke volume provides an additional safety mechanism. The devices of this disclosure can be used in various ways to improve safety: for example, the maximum size aliquot that can be inadvertently delivered in the event of a catastrophic failure is small because the metering methods described herein does not allow flow material reservoir300to be in fluid communication with the target. Second, by knowing an accurate backstroke volume, the cumulative error of the pressure sensors is eliminated, resulting in more accurate dosing of flow material. In addition, knowing the backstroke volume allows for constant and real-time monitoring of the mechanical components of device100to ensure their proper functioning (i.e., the volume of flow material returned to flow material reservoir300on each backstroke should be constant). If an unexpected backstroke volume is returned, the system can automatically shut down, be temporarily disabled, generate an error message, etc. to avoid the possibility of inaccurate dosing of flow material due to mechanical failure of the device. To avail oneself of these safety features, one or more flow metering devices such as those described herein may be disposed along the flow path so to meter flow of fluid such as flow material.

According to embodiments, the flow metering device100is disposed downstream from the pump. According to alternative embodiments, however, flow metering device100may be disposed upstream of a pump; the principles disclosed herein apply irrespective of whether flow material reservoir300is disposed upstream or downstream from the flow metering device.

Because actuation shaft110may be moved back and forth in cavity109, each stroke (fill-dispense cycle) causes a quantity of flow material to be evacuated from or flow into the chambers and conduits of flow metering device100. For example, when actuation shaft110is moved proximally, the volume of proximal flow space124is reduced and the excess flow material volume (backstroke volume) back flows into flow material reservoir300. According to embodiments, if flow material reservoir300is disposed downstream of flow metering device100, then proximal movement of actuation shaft110causes backstroke of flow material into cavity109(the backstroke volume is constant because its volume may be determined by fixed mechanical components; namely, actuation shaft110, cavity109, actuation shaft seal114and fixed seal118a). The change in the volume of flow material reservoir300likewise can be measured. The following discussion assumes that flow material reservoir300is disposed upstream from flow metering device100, but the principles described herein may be adapted by a person of ordinary skill in the art and implemented in the case where flow material reservoir300is disposed downstream from flow metering device100.

As described above, the actuation shaft110of embodiments the flow metering device100may occupy at least two positions: a filling position for filling chambers132,136, and a dispense position for dispensing flow material from flow metering device100.FIG. 7illustrates actuation shaft110disposed in a fill position, where actuation shaft110is positioned distally, as described above. In this position, flow material may be transferred through input conduit104and proximal flow space124into at least one of first chamber136and second chamber132via first and second chamber conduits135,133, respectively. In so doing, proximal flow space124is likewise charged with flow material. The volume of proximal flow space124at this point is denoted by the length700A inFIG. 7.

InFIG. 8, actuation shaft110is positioned into a first dispense position by positioning actuation shaft proximally. Thus, the length700A becomes length700B. As second chamber132is already filled, the volume of flow material that was in proximal flow space124(represented in the view ofFIG. 8by the difference in length between length700A and length700B) is removed through input conduit104and into flow material reservoir300due to an increase in pressure of the flow material in proximal flow space124. The volume of this removed flow material (backstroke volume) is known, as it can be derived mathematically or by an initial measurement. The same principle operates whether actuation shaft is positioned in the first dispense position illustrated inFIG. 8(length700B) or the second dispense position illustrated inFIG. 9(length700C).

FIG. 12is a schematic illustrating the relative volume of fluid such as flow material present in flow material reservoir300as a function of time when a pump is used in conjunction with the devices of the present disclosure. At time ti(dashed line1202), actuation shaft110is positioned in a charge or filling position (operation1302ofFIG. 13) and an initial known volume Viof flow material is present in reservoir300. Next, flow material flows from flow material reservoir300into at least one chamber132,136in flow metering device100as shown by solid line segment1210. At the end of this chamber filling process, indicated inFIG. 12as time tf(dashed line1204), the volume Vfof flow material remaining in reservoir300before the backstroke is measured or determined in operation1304ofFIG. 13.

At time tb(dashed line1206), actuation shaft110has been positioned into a dispense position (operation1306ofFIG. 13). Because actuation shaft110has moved proximally between time tfand time tb, (i.e., the “backstroke”) and the volume in proximal flow space124is reduced, flow material returns through input conduit104and ultimately back into flow material reservoir300(illustrated by line segment1212inFIG. 12). At the end of the period in which the system has been receiving this backstroke material into flow material reservoir300(time tb), the volume Vbof flow material residing in flow material reservoir300is determined in operation1308. The backstroke volume (Vbackstroke) may be calculated as the difference between Vband Vf:
Vbackstroke=Vb−Vf.  (1)

After time tf, no further appreciable backstroke volume is observed and the volume Vbof flow material in reservoir300remains relatively constant until actuation shaft110is repositioned back to a fill position. The interim time period after the backstroke but before the actuation shaft110is moved to its fill position is represented as line segment1214. The point along the line where the next drop in volume occurs represents the next fill-dispense cycle.

Device Integrity Using Backstroke Volume

Because the backstroke volume is approximately constant, the backstroke volume measured on each fill-dispense cycle should be the same Vbackstrokex=Vbackstrokeyfor any two arbitrary times x and y, as shown in operation1310ofFIG. 13.

By measuring the volume of flow material reservoir300immediately prior to repositioning of actuation shaft110to a dispense position (time tf; dashed line1204ofFIG. 12) and after the backstroke has stopped (time tb; dashed line1206ofFIG. 12), the integrity of the devices may be monitored on a continuous or semi-continuous basis. If a backstroke volume is determined to be significantly different (within a predetermined tolerance level) from the known backstroke volume expected or observed in prior fill-dispense cycles, then an error state can be triggered or initiated in operation1312ofFIG. 13.

In operation1314, if the backstroke volume is determined to be the same (within a predetermined tolerance level) from the volume expected or observed in prior fill-dispense cycles, the known backstroke volume is used to accurately determine the amount of flow material in flow material reservoir300. Determination of the volume of reservoir300in this way eliminates much of the error observed by measuring the difference in volume calculated on each cycle. Because the backstroke volume is known and relatively constant over time, it can be used to more accurately measure volume in flow material reservoir300.

Backstroke Volume Determination

To make use of the backstroke volume, the backstroke volume must initially be determined. To determine the backstroke volume initially, data from a sensor such as sensor302is obtained in an initialization procedure. To initially determine the backstroke volume, a complete initial fill-dispense cycle of flow metering device is performed (i.e.,1202to1206inFIG. 12). The complete cycle can be performed prior to filling flow material reservoir300with a flow material (using, for example, a gas that is held in flow material reservoir300) or performed after flow material reservoir300is filled with a flow material. In either case, the total initial volume of fluid in flow material reservoir300or the volume of flow material reservoir300must be known.

According to some embodiments, flow material reservoir300of known volume is disposed in a disposable chamber that is slightly pressurized and is in fluid communication with a pressure transducer. Initially, flow material reservoir300is empty (i.e., empty of flow material, but filled with another fluid, such as a slightly pressurized gas). In this state, the total volume of flow material reservoir300is known, but the backstroke volume is unknown. Therefore, prior to filling flow material reservoir300with flow material, a complete fill-dispense cycle is performed. Gas from the flow reservoir300flows into the chambers of flow metering device100, which effects changes in pressure in flow material reservoir300. The changes in pressure from a known configuration of volume and pressure is used to calculated the backstroke volume initially.

According to alternate embodiments, flow material reservoir300is filled with a flow material of a known volume. The process for determining the backstroke volume is performed exactly the same way, i.e., running one or more fill-dispense cycles.

Once the backstroke volume is known, it can be used to calculate the volume of flow material dispensed during each fill-dispense cycle, as disclosed herein.

Using the Backstroke Volume to Determine the Flow Material Reservoir Volume

The backstroke volume can be used accurately to measure the volume of flow material reservoir300using Boyle's law. The principles outlined below are based on use of Boyle's law with the assumption that temperature is constant. Increased accuracy is possible with the use of temperature sensors.

According to some embodiments, flow material reservoir is part of a pump having a fluid chamber with a known volume of flow material therein and a gas chamber having a sensor disposed within it. The total volume of fluid chamber and gas chamber is fixed and known. When the volume of the gas chamber changes, the volume of the fluid chamber likewise changes in inverse proportional thereto (i.e., as the volume of the fluid chamber decreases, the volume of the gas chamber increases by the same amount). The gas chamber is sealed and has a sensor, for example a pressure transducer or temperature transducer, disposed therein.

According to alternative embodiments, flow material reservoir may comprise an integral chamber having a gas, a sensor, and flow material. According to this example, flow material reservoir is disposed upstream of flow metering device100.

Flow material reservoir may be filled with fluid such as flow material, by the user. According to other embodiments, flow material reservoir is prefilled (for example, in the case where flow material reservoir is part of a disposable unit). According to embodiments, the flow material reservoir may be designed so that the volume of flow material reservoir300is known with accuracy either before, during, or after flow material has been dispensed.

The backstroke volume must be determined if it is to be used to determine the volume of flow material reservoir300in each fill-dispense cycle. According to other embodiments, the backstroke volume may be known because flow metering device100is manufactured such that the backstroke volume is accurately determinable to some tolerable error level, according to embodiments.

According to other embodiments, flow metering device100is initialized to determine the backstroke volume. To do so, flow material reservoir300contains a fluid, for example, a pressurized gas or flow material. The total volume of flow material reservoir300must be known or the volume of flow material in reservoir300must be known.

According to embodiments, the backstroke volume may be calculated using the sensor(s). The pressure of flow material reservoir300is measured. Let Videsignate the volume of flow material reservoir300at this point (seeFIG. 12, time ti). Actuation shaft110is then moved to its filling position. In this position, fluid flows from flow material reservoir300flows into chambers132,136via proximal flow space124of flow metering device100. Let the volume of flow material reservoir300after chambers of flow metering device are filled with fluid from the flow material reservoir300be designated Vf(seeFIG. 12, time tf). Finally, actuation shaft110is moved to its dispense position. This movement causes a backstroke volume of fluid to into flow material reservoir300. At the end of this process, the volume of flow material reservoir300is designed as Vb(seeFIG. 12, time tb). Because the initial volume of flow material reservoir300was known, Vfand Vbmay be determined by the following equations:

Vf=Pi⁢ViPf⁢⁢and⁢⁢Vb=Pi⁢ViPb,(2⁢a)⁢⁢and⁢⁢(2⁢b)
where Pi, Pf; and Pbare the measured pressure in the flow material reservoir300at the respective times ti, tf, and tb. The backstroke volume is the difference between Vband Vf. Thus, the volume of fluid returned to flow material reservoir300after the backstroke, and therefore the backstroke volume, can be calculated by:

The initialization procedure may be repeated a number of times and the Vbackstrokevalues calculated from each initialization procedure may be averaged or otherwise used to obtain an acceptable value for Vbackstroke.

It should be noted that in all cases the volume to be measured is the volume of the fluid in flow material reservoir300. In certain cases, the volume of the fluid in flow material reservoir300is substantially the same as the volume of flow material reservoir300. In either case, it is the change in volume, not the absolute volume that is used to determine the backstroke volume and the volume dispensed during each fill-dispense cycle. For each fill-dispense cycle, the change in volume of flow material reservoir or the fluid in flow material reservoir changes by the same amount. By observing the changes in volume, as well as knowing the initial volume of flow material in flow material reservoir300, the volume of flow material dispensed from flow metering device100can be substantially precisely determined.

According to some embodiments, the sensor directly measures the fluid volume in flow material reservoir300, for example via acoustic or other similar methods of volume determination disclosed herein or incorporated by reference herein. In other embodiments, the sensor(s) are disposed in separate chambers, for example gas chambers, and the volume of the fluid/flow material reservoir300are inferred because the total volume of the chamber and the flow material reservoir is fixed (i.e., the volume of the gas chamber is determined, which allows for determination of flow material reservoir by subtracting the volume of the gas chamber from the total, fixed volume of the flow material reservoir plus the gas chamber). Thus, the terms can be used interchangeably without taking away from the general principles for determining the backstroke volume and subsequent volumes for fluid or flow material dispensed from flow metering device100.

Calculation of Absolute Volume of Flow Material Reservoir

Once the backstroke volume (Vbackstroke) is known, it can be used to determine the volume of flow material reservoir300after each fill-dispense cycle. By calculating the difference in the volume of flow material reservoir300after each fill-dispense cycle from the volume of flow material reservoir300in the prior cycle, the precise volume of the aliquot metered to a target from flow material reservoir300via flow metering device100may be determined. Moreover, if the backstroke volumes for each fill-dispense cycle are not within a predetermined tolerance level, a mechanical breakdown may be more likely to have occurred and an error state may be initiated.

According to embodiments, to determine the absolute volume of flow material reservoir300at the end of each cycle (line1206inFIG. 12, time tb), the backstroke volume (Vbackstroke) may be used. Simplifying equation (3) and solving for PiViyields the equation:

Pi⁢Vi=Vbackstroke⁢Pb⁢PfPf-Pb.(4)
To solve for Vb(which is the volume of flow material reservoir300at the end of each cycle while actuation shaft110is in its dispense position), equation 2b is solved:

Because PiViwas previously solved in equation 4, Vbcan be determined using only the backstroke volume by substitution:

Vb=Vbackstroke⁢Pf(Pf-Pb).(5)
Thus, for any given cycle, the volume of flow material reservoir300(Vb) is determined. Note that Vbfrom the previous cycle becomes Vifor the current cycle.
Calculation of Delivered Aliquot Size

To determine the volume delivered from flow metering device100during any given cycle (i), the following equation is used:
Vdeliveredi=Vbi-1−Vbi.  (6)

Notably, when Vbackstrokeis measured initially, sensor drift becomes less relevant because all of the pressure measurement from which Vbis calculated occur within a very small window in which overall drift is negligible. Consequently, the problem of cumulative error due to sensor drift is reduced.

Sensor Offset Calibration Using the Backstroke Volume

At certain times, if the volume of flow material reservoir300and the backstroke volume are known, sensor offset calibration may be accomplished. Some sensors, such as pressure transducers, tend to lose accuracy over time due to mechanical fatigue and other factors. For example, pressure transducers work by measuring the deflection of a strain gauge. The strain gauges tend to plastically deform over time, making them less accurate. Moreover, when measuring greatly different pressures, the strain gauges behave slightly differently, which also introduces error, especially when volume of flow material reservoir300is calculated from initial measurements when flow material reservoir300is full and later measurements when flow material reservoir300is empty. The deflection affects the measured voltage, which can be expressed as a line correlating pressure and voltage.

Deformation of the strain gauge affects pressure measurements in two ways: the slope of the line comparing voltage to pressure can change (drift) and the y-intercept of the line can change (offset).

As discussed above, use of the backstroke volume to calculate the absolute volume of flow material reservoir300greatly diminishes the effect of drift. However, it is believed that use of the backstroke volume to calculate the absolute volume of flow material reservoir300does not affect or increases potential error due to changes in the offset. Thus, a method of periodically calculating and adjusting the offset is presented.

According to embodiments, to calculate the offset, the volume of flow material reservoir300must be known at some point in the process with relative accuracy independent of calculating it using sensor302data. For example, prior to filling flow material reservoir300with flow material, its volume may be accurately known. Alternately, the volume of a pre-filled flow material reservoir300may be known. In another alternative, the volume of flow material reservoir300will be known with sufficient accuracy at given points in the fill-dispense cycle, for example when all flow material has been dispensed from reservoir300.

Turning again toFIG. 12, when flow material chamber is empty or holds a known volume prior to a backstroke, the point in each stroke cycle will correspond to line1204. Using the known backstroke volume and the known volume of flow material reservoir300, the offset can be calculated using Boyle's law between lines1204and1206, the difference in volume of which corresponds to Vbackstroke. The offset for each pressure measurement can be expressed as the measured pressure P plus an offset value Poffset. If sensor302is perfectly calibrated, the offset value will be zero.

Thus:
PbVb=PfVf(7).
Substituting pressure value to include the updated pressure offset yields:
(Pb+Poffset)(Vf+Vbackstroke)=(Pf+Poffset)Vf.  (8)
Note that the volume Vbis expressed on the left side of the equation is expressed in terms of Vf, namely:
Vb=Vf+Vbackstroke.  (1)

Solving for Poffsetyields the equation:

Thus, Poffsetcan be derived if the volume of flow material reservoir300(Vf) is known and the backstroke volume (Vbackstroke) is known.

Use of Flow Metering Device to Dispense Insulin from an Integrated Insulin Pump and Flow Metering Device

Flow metering device100is useful in the dispensing of insulin as the flow material. Flow metering device is disposed as part of an integrated infusion pump, such as those incorporated by reference herein, or can pump insulin straight from the insulin reservoir as disclosed herein. According to some embodiments, flow material reservoir300is disposed upstream from flow metering device100. Flow material reservoir300contains a pressure sensor and a temperature sensor for measuring the pressure and temperature in the insulin chamber, respectively. According to other embodiments, flow material reservoir comprises a bag or other collapsible member disposed in a chamber that can hold a pressurized gas and that also houses the sensors.

Prior to using the insulin pump to dispense insulin, the backstroke volume must be determined. As disclosed above, backstroke volume may be determined when the insulin reservoir is full of insulin, or when it holds another fluid, such as a slightly pressurized gas.

When the insulin reservoir is full of insulin when the initialization is performed, a user initializes the pump by running one or more fill-dispense cycles with the pressurized gas to establish the backstroke volume. Once the backstroke volume is determined, the user connects the insulin pump for actual delivery of insulin into the blood stream.

Alternately, the user initializes the insulin pump prior to filling the insulin reservoir with insulin. Rather than performing fill-dispense cycles with insulin, it is performed with a fluid being held in the flow material reservoir, such as a pressurized gas. After the backstroke volume has been determined, the user fills the insulin pump with a quantity of insulin and puts the pump into fluid communication with the blood stream. Thereafter, each fill-dispense cycle will dispense an aliquot of insulin to a user.

Thereafter, the insulin pump metering insulin to a patient as described herein. In multiple chamber versions, bolus volumes of insulin can be delivered, for example by dispensing for the larger chamber in the flow metering device as disclosed herein. Likewise, basal doses may be delivered by repeatedly filling and dispensing from the smaller chamber of flow metering device, depending on the configuration of the chamber in the flow metering device and the flow paths defined therein.

Use of Flow Metering Device to Dispense Insulin from a Disposable Insulin Reservoir Cartridge and Flow Metering Device

According to some embodiments, flow metering device is part of a disposable cartridge. The disposable cartridge contains the insulin (flow material) reservoir and the flow metering device. The disposable cartridge is adapted to mateably fit into a reusable device that houses the hardware, user interface, and pressure and temperature sensors. By mating the disposable cartridge and the reusable device, the sensors may be placed into fluid communication with the flow material reservoir.

According to embodiments, the sensors of the reusable device are disposed in a separate gas chamber designed to change in volume as the flow material reservoir changes in volume. For example, the insulin reservoir may comprise a bag of insulin that is placed in a pressurizable chamber. As insulin is dispensed, the volume of the bag is reduced, whereby the volume of the chamber housing the bag is increased by the same amount. In some embodiments, the disposable contains both the insulin bag (flow material reservoir) and the chamber that houses the bag. When mated to the reusable device, the chamber holding the bag is sealably placed into fluid communication with the sensors.

Once the disposable cartridge and the reusable device are mated together, the initialization procedure must be performed to determine the backstroke volume as described above. The volume of insulin in the insulin reservoir will be known prior to performing the initialization procedure. Accordingly, a small volume of insulin is dispensed during the initialization procedure, rather than quantities of pressurized gas as described above.

Thereafter the mated disposable cartridge and reusable device dispenses insulin as described above.