Patent Description:
The present invention is directed to a pump system as defined in claim <NUM>.

According to the present invention, the pump chamber has disposed therein a pair of plungers driven by a leadscrew having both left-hand and right-hand threads such that, when the leadscrew rotates in one direction, the plungers move toward each other and, when the leadscrew is rotated in the opposite direction, the plungers move away from each other.

The first conduit connecting the pump chamber to the reservoir connects to the pump chamber between the plungers, preferably in the middle of the pump chamber. Thereby, the movement of the plungers away from each other creates a negative pressure in the pump chamber which draws the liquid from the reservoir through the first conduit and into the pump chamber. The leadscrew is thus rotated in a direction such as to move the plungers away from each other to draw the liquid into the pump chamber. The liquid is prevented from returning to the reservoir by the one-way valve disposed in the conduit between the reservoir and the pump chamber.

Once the pump chamber is filled with an appropriate quantity of the liquid, the leadscrew is rotated in a second, opposite direction, thereby driving the plungers toward each other. A second conduit connected to the pump chamber between the plungers connects the pump chamber to a patient interface, typically a needle. Thus, motion of the plungers toward each other causes a movement of the liquid through the second conduit to the patient. The second conduit is also fitted with a one-way valve such that the suction created by the motion of the plungers away from each other to draw the liquid from the reservoir into the pump chamber does not also draw fluids from the patient through the patient interface and into the pump chamber.

In one embodiment of the invention, the rotation of the leadscrew can be driven by a drive coupled to the leadscrew either directly or via gearing.

The improved liquid delivery system disclosed herein thus addresses the problems identified in the Background section. By separating the reservoir from the pump chamber, the pump chamber can be configured with a cross-sectional area of any size, preferably small enough to overcome the difficulties associated with the larger diameter cross-sectional areas of conventional, prior art devices.

<FIG> is a cross-sectional view of a first embodiment of the pump chamber <NUM> of the present invention. Pump chamber <NUM> consists of an open-ended container comprising sidewall <NUM> and endcap <NUM>. Sidewall <NUM> may comprise a tube-like structure having a cross-sectional shape. In some instances, sidewall <NUM> and endcap <NUM> may be formed as an integral unit, however, in other instances, sidewall <NUM> and endcap <NUM> may be formed separately and joined together. Sidewall <NUM> and endcap <NUM> may be composed of, for example, glass, polypropylene or any other bio- or drug-compatible material. In certain embodiments, endcap <NUM> may be absent, with pump chamber <NUM> being open at both ends.

Sidewall <NUM> has formed therein inlet port <NUM> and outlet port <NUM>. Inlet port <NUM> connects, via a conduit, to a reservoir which may hold a quantity of a liquid. Outlet port <NUM> connects to a patient interface for delivery of the liquid to a patient. Preferably, inlet port <NUM> and outlet port <NUM> will be located midway between plungers 106a, 106b, such that when plungers 106a, 106b are in a touching, face-to-face configuration, access to both inlet port <NUM> and outlet port <NUM> are fully or partially blocked. This serves as a safety feature to prevent free-flow of the liquid from the reservoir to the patient interface in the event of valve failure. In preferred embodiments of the invention, inlet port <NUM> and outlet port <NUM> are located opposite each other along sidewall <NUM>; however, in other embodiments, inlet port <NUM> and outlet port <NUM> may be positioned at any convenient location along sidewall <NUM>.

Disposed within pump chamber <NUM> are plungers 106a, 106b. In some embodiments, plungers 106a, 106b may be composed of, for example, a butyl rubber or silicon rubber material or any other commonly known drug-compatible material. In other embodiments, plungers 106a, 106b may be composed of a polycarbonate derivative or cyclic olefin polymer (COP), in which case, plungers 106a, 106b may be surrounded by one or more O-rings composed of butyl rubber or silicon rubber. In some embodiments, plungers 106a, 106b are configured with flat facing surfaces. In other embodiments, other shapes may be used but preferably the plungers 106a, 106b will have mating shapes, for example, one concave and one convex, such that when plungers 106a, 106b are together, no volume remains therebetween. The faces of plungers 106a, 106b may be configured with channels to direct the movement of the liquid in a desired direction.

Plungers 106a, 106b are connected by leadscrew <NUM>. In certain embodiments, leadscrew <NUM> may be composed of stainless steel, polypropylene, or any other well-known bio- or drug-compatible material. In preferred embodiments, leadscrew <NUM> comprises both left-handed threading 101a and right-handed threading 101b as an interface with plungers 106a, 106b, such that rotation of leadscrew <NUM> in a first direction will cause plungers 106a, 106b to move toward each other along the longitudinal axis of pump chamber <NUM> until touching, and such that rotation of leadscrew <NUM> in a second, opposite direction will cause plungers 106a, 106b to move away from each other along the longitudinal axis of pump chamber <NUM>.

<FIG> is a schematic representation of the first embodiment of the invention in which a linear-actuated drug dosing system <NUM> comprises two plungers 106a,106b disposed in pump chamber <NUM>. Reservoir <NUM> may contain a quantity of a liquid <NUM>, for example, a drug in liquid form. In some embodiments of the invention, reservoir <NUM> may be rigid, while, in other embodiments, the reservoir <NUM> may be flexible and collapsible to eliminate the need for a vent in the reservoir to prevent a vacuum performing therein as liquid <NUM> is drawn from reservoir <NUM> into pump chamber <NUM>. In some embodiments, reservoir <NUM> may be composed of high-density polyethylene or, in other embodiments, ACLAR®.

Reservoir <NUM> is fluidly coupled to pump chamber <NUM> through inlet port <NUM> via inlet conduit <NUM>. Likewise, pump chamber <NUM> is fluidly coupled to a patient interface through outlet port <NUM> via outlet conduit <NUM>. Inlet conduit <NUM> and outlet conduit <NUM> may be composed of, for example, stainless steel or Teflon and may be, for example, tubing of the type of which hypodermic needles are constructed. One-way valve <NUM> prevents liquid <NUM>, which has entered the pump chamber <NUM>, from returning to reservoir <NUM>. The patient interface may be, for example, a needle, a needle conduit or tubing that can be used as a fluid path to deliver the liquid <NUM> to a patient. One-way valve <NUM> prevents fluids from the patient from being drawn into pump chamber <NUM> as liquid <NUM> is being drawn into pump chamber <NUM> from reservoir <NUM>.

Plungers 106a, 106b are disposed within the pump chamber <NUM> and may be sealed against the inner surface of sidewall <NUM> of pump chamber <NUM>. It should be noted that the cross-sectional shape of pump chamber <NUM> may be any shape, including circular; however, in preferred embodiments, the cross-sectional shape of pump chamber <NUM> may be any one of a number of non-circular shapes, preferred examples of which are shown as reference number <NUM> in <FIG>. The non-circular, cross-sectional shape of pump chamber <NUM> is desirable to prevent plungers 106a, 106b from rotating within pump chamber <NUM> when leadscrew <NUM> is rotated. Non-rotation of plungers 106a, 106b is necessary to enable the movement of the plungers 106a, 106b along the longitudinal axis of pump chamber <NUM> driven by the rotation of leadscrew <NUM> as it rotates in either direction.

Leadscrew <NUM> may be driven by any one of a number of known methods. In one embodiment, the drive source may be motor <NUM>, which may be coupled to leadscrew <NUM> via gearing <NUM>. Leadscrew <NUM> is, in this embodiment of the invention, configured with both left-hand and right-hand threads, as shown in the figure. Thus, rotation of leadscrew <NUM> in a first direction (e.g. clockwise) will cause plungers 106a, 106b to move toward each other, while rotation of leadscrew <NUM> in an opposite direction (e.g. counter-clockwise) will cause plungers 106a, 106b to move away from each other.

Motor <NUM> may be coupled to leadscrew <NUM> via gearing <NUM>. In some embodiments of the invention, gearing <NUM> may be a planetary gear system, but any configuration of coupling between the motor <NUM> and leadscrew <NUM> may be used, including a direct connection. Motor <NUM> may be a continuous motion motor or stepper motor and is preferably controlled by a software-driven controller.

In alternate embodiments of the invention, a nitinol wire drive (not shown) may be used to drive gearing <NUM> in lieu of motor <NUM> and may be coupled to leadscrew <NUM> via gearing <NUM>.

<FIG> shows the device in a static state, with plungers 106a, 106b shown together. This is a likely state of the device just subsequent to the delivery of one or more units of liquid <NUM> and in ready state for filling of the pump chamber <NUM> with additional liquid <NUM> from reservoir <NUM>.

<FIG> is a schematic diagram showing the process of drawing liquid <NUM> from reservoir <NUM> into pump chamber <NUM>. Motor <NUM> may be activated in a direction such as to cause plungers 106a, 106b to move away from each other as shown by the arrows in pump chamber <NUM>. Movement of plungers 106a, 106b away from each other causes a negative pressure to form in the volume 104a between the plungers 106a, 106b, which serves to draw liquid <NUM> through conduit <NUM>, into pump chamber <NUM> and, more specifically, into volume 104a between plungers 106a, 106b. One-way valve <NUM> prevents fluids from the patient from being drawn through conduit <NUM> and into volume 104a of pump chamber <NUM> as plungers 106a, 106b create the negative pressure within volume 104a as they move away from each other.

Pump chamber <NUM> may be configured with a vent <NUM> on end wall <NUM> of pump chamber <NUM> to allow air between plunger 106b and end wall <NUM> of pump chamber <NUM> to escape as plunger 106b is moved toward end wall <NUM>, and to allow air to enter the space between end wall <NUM> and plunger 106b when plunger 106b is moved in the opposite direction, away from end wall <NUM>.

<FIG> is a schematic diagram illustrating the process of pumping liquid <NUM> from volume 104a through conduit <NUM> to the patient interface. Motor <NUM> may be rotated in a direction opposite the direction of rotation used to draw liquid <NUM> into volume 104a such as to move plungers 106a, 106b toward each other as shown by the arrows in <FIG>, thereby creating a positive pressure within volume 104a. The movement of plungers 106a, 106b toward each other reduces the size of volume 104a and forces liquid <NUM> into the conduit <NUM> and out to the patient through the patient interface. One-way valve <NUM> prevents liquid <NUM> from returning to reservoir <NUM> as plungers 106a, 106b move toward each other, ensuring that all of liquid <NUM> within volume 104a is forced into conduit <NUM>.

Once plungers 106a, 106b have reached a position where they are touching one another, as shown in <FIG>, all, or most of liquid <NUM> within volume 104a will have been forced into conduit <NUM> to the patient interface. Plungers 106a, 106b do not necessarily need to touch each other to complete a cycle of liquid delivery. However, to reduce the amount of residual liquid within the system, and hence reduce the amount of wasted liquid at the end of usage of system <NUM>, plungers 106a, 106b preferably come into contact at the end of each cycle of liquid delivery, or alternatively, at a final cycle of drug delivery when all or nearly all of liquid drug has been dispensed from reservoir <NUM>. Having plungers 106a, 106b come into contact only at a final cycle of drug delivery will reduce the impact that plungers 106a, 106b have on constituents of the liquid (e.g., molecules of insulin) during each cycle of liquid delivery, thereby prolonging the life or effectiveness of the liquid (e.g., protein molecules within the liquid).

It should be noted that conduits <NUM>, <NUM> interface with pump chamber <NUM> in the volume 104a between plunger 106a, 106b. In preferred embodiments of the invention, conduits <NUM> and <NUM> will connect to volume 104a midway between the largest distance that plunger 106a, 106b can travel from each other, or, in other words, at the point where plungers 106a, 106b meet when they are touching each other or at the end of a cycle, such that when plungers 106a, 106b are in the position shown in <FIG>, both inlet port <NUM> and outlet port <NUM> are blocked.

It should be noted that multiple units of liquid <NUM> may be drawn into volume 104a at a single time and may be dispensed in separate units to the patient. It is not necessary that volume 104a be emptied each time that a unit of liquid <NUM> is delivered to the patient.

It should be further noted that the quantity of liquid <NUM> drawn into volume 104a is dependent upon the distance between plungers 106a, 106b at their furthest point of travel away from each other. Thus, the quantity of liquid <NUM> drawn into volume 104a can be controlled by varying the distance between plungers 106a, 106b. Larger distances between plungers 106a, 106b will result in a larger volume 104a and, thus, a larger quantity of liquid <NUM>, while smaller distances will result a smaller volume 104a and a smaller quantity of liquid <NUM> being drawn into volume 104a.

One advantage of the dual-plunger design is that the system is balanced axially such that it does not induce a thrust onto the bearing support (i.e. the portion where the leadscrew <NUM> interfaces with end wall <NUM> of pump chamber <NUM>. This translates into less frictional losses in the system. One further advantage is that the design prevents the free flow of liquid <NUM> directly from reservoir <NUM> to the patient when plungers 106a, <NUM> block inlet port <NUM> and outlet port <NUM>. This can be a safety mechanism in the case of an over-pressure situation or if squeezing of the device forces liquid <NUM> out of reservoir <NUM>.

Various other methods are possible in this embodiment of the invention for measuring the size of the volume 104a between plungers 106a, 106b, and thus the quantity of liquid <NUM> which is drawn into volume 104a. In one embodiment of the invention, the size of volume 104a may be determined algorithmically by calculation based on the number of turns of leadscrew <NUM> and the known distance that plungers 106a, 106b travel based on the determined number of turns. Other embodiments of determining the size of volume 104a utilizing sensors will now be discussed.

<FIG> shows one embodiment using a pressure gauge to calculate a volume change in the pump chamber <NUM> using the ideal gas law equation PV = nRT. A gas pressure gauge <NUM> may be configured to interface with pump chamber <NUM> through vent <NUM> in end wall <NUM>. Using air pressure in area <NUM> as measured by pressure gauge <NUM>, the change in the position of the plungers, and thus changes in the quantity of liquid <NUM> in volume 104a, can be derived from a measurement of the change in air pressure within area <NUM>. The actual quantity of liquid <NUM> drawn into volume 104a may be further dependent on other factors, for example, the size of conduit <NUM>.

<FIG> shows a second embodiment utilizing a three-segment custom linear encoder using simple analog techniques. In this embodiment, change in the length (length = l<NUM> + l<NUM> + l<NUM>) of conductive bar or wire <NUM> can alter its resistance / current and can be calibrated to the position of plunger 106b. The position of plunger 106a can thereafter be inferred from the position of plunger 106b.

<FIG> shows yet another embodiment utilizing an ultrasonic sensor. An ultrasonic source <NUM> may direct a beam of ultrasonic sound through vent <NUM>. The speed of sound through various media (i.e., air → plastic → aqueous spolution → plastic → air) is known and, as such, based on timing, with the known distance between the ultrasonic source <NUM> and an ultrasonic detector <NUM>, a quantity of the liquid <NUM> can be inferred.

<FIG> shows a flowchart showing process <NUM> for delivery of liquid <NUM> from the reservoir <NUM> to the patient interface. The system <NUM> begins from a start position <NUM>. The start position is preferably the position wherein the plungers 106a, 106b are in a touching, face-to-face configuration such that volume 104a is reduced to virtually zero.

At block <NUM>, the plungers are moved apart by turning of leadscrew <NUM> and liquid <NUM> is drawn from reservoir <NUM> into the volume 104a between plungers 106a and 106b. At block <NUM>, it is determined whether the desired quantity of liquid <NUM> has been drawn into volume 104a of pump chamber <NUM> and, if not, control is returned to block <NUM>, where the plungers 106a, 106b continue to move away from each other until the desired quantity of liquid <NUM> is present in volume 104a. The determination of whether the desired quantity of liquid <NUM> has been drawn into volume 104a may be made algorithmically by calculating, for example, the number of turns of leadscrew <NUM> and its relationship to the size of volume 104a or with the assistance of one of the sensor arrangements shown in <FIG>(A-C), or through the use of any other sensor arrangement.

At block <NUM> it is determined if it is time for the delivery of the additional units of liquid <NUM> to the patient. If so, control is sent to block <NUM> and if not, system <NUM> loops at decision point <NUM> until triggered. The delivery of additional units of liquid <NUM> could be triggered automatically, for example, by a periodic timer, by manual initiation of the delivery by the patient, or by any other means, such as through an analysis of input received from sensors regarding the current condition of the patient.

At block <NUM>, the movement of plungers 106a, 106b toward each other is initiated by rotation of leadscrew <NUM> in an opposite direction, such as to force a quantity of liquid <NUM> from volume 104a and into conduit <NUM>, and from there to the patient interface. At <NUM> it is determined if the quantity so far delivered to the patient interface comprises the desired quantity and, if not, control returns to <NUM>, where the plungers continue to move toward each other to push a further quantity of liquid <NUM> to the patient interface. At <NUM>, if the desired quantity of liquid <NUM> has been delivered to the patient interface, the process is complete at <NUM>.

At decision point <NUM>, it is determined if the volume 104a is empty, that is, the last quantity of liquid <NUM> has been delivered to the patient. If volume 104a is empty, control returns to start position <NUM> and the process repeats with the loading of an additional quantity of liquid <NUM> from reservoir <NUM> to volume 104a. If volume 104a is not empty, control returns to decision point <NUM>, where the process loops until the delivery of the next unit of liquid <NUM> is triggered.

Note that the end position of the plungers when the pump chamber is empty at block <NUM> is the same as start position at <NUM>, wherein the plungers are in a touching, face-to-face configuration and are thereby ready to draw the next quantity of liquid <NUM> into volume 104a.

The second embodiment of the invention has components similar to the first embodiment in configuration and composition and operates in a similar manner. As such, the description of the second embodiment has been condensed for brevity and like reference numerals have been used for like components.

<FIG> is a cross-sectional view of an example of a pump chamber <NUM> in which only a single plunger <NUM> is used. Rotation of leadscrew <NUM> in a first direction moves plunger <NUM> toward end wall <NUM>, while movement of the leadscrew <NUM> in a second, opposite direction moves plunger <NUM> away from end wall <NUM>. Inlet port <NUM> and outlet port <NUM> are preferably located adjacent end wall <NUM>, such that movement of the plunger <NUM> toward the end wall forces any liquid within the pump chamber <NUM> into the output conduit <NUM>. Otherwise, the components and materials of the second embodiment of the pump chamber are identical to that of the first embodiment shown in <FIG>.

<FIG> is a schematic representation of the example of <FIG> in which a linear-actuated drug dosing system <NUM> comprises a single plunger <NUM> disposed in pump chamber <NUM>.

Reservoir <NUM> is fluidly coupled to pump chamber <NUM> through inlet port <NUM> via inlet conduit <NUM>. Likewise, pump chamber <NUM> is fluidly coupled to a patient interface through outlet port <NUM> via outlet conduit <NUM>. One-way valve <NUM> prevents liquid <NUM> which has entered the pump chamber <NUM>, from returning to reservoir <NUM>. One-way valve <NUM> prevents fluids from the patient from being drawn into pump chamber <NUM> as liquid <NUM> as being drawn into pump chamber <NUM> from reservoir <NUM>.

Plunger <NUM> is disposed within the pump chamber <NUM> and may be sealed against the inner surface sidewall <NUM> of pump chamber <NUM>. Leadscrew <NUM> may be driven by any one of a number of known methods. In one embodiment, the drive source may be motor <NUM>, which is coupled to leadscrew <NUM> via gearing <NUM>. Leadscrew <NUM> is, in this embodiment of the invention, configured with a single threading, as shown in the figure. Thus, rotation of leadscrew <NUM> in a first direction (e.g. clockwise) will cause plunger <NUM> to move toward end wall <NUM>, while rotation of leadscrew <NUM> in an opposite direction (e.g. counter-clockwise) will cause plunger <NUM> to move away from end wall <NUM>.

Motor <NUM> may be coupled to leadscrew <NUM> via gearing <NUM> to drive leadscrew <NUM> in either rotational direction.

<FIG> shows the device in a static state, with plunger <NUM> shown adjacent end wall <NUM> and blocking inlet port <NUM> and outlet port <NUM>.

<FIG> is a schematic diagram showing the process of drawing liquid <NUM> from reservoir <NUM> into pump chamber <NUM>. Motor <NUM> may be activated in a direction such as to cause plunger <NUM> to move away from end wall <NUM> as shown by the arrow in pump chamber <NUM>. Movement of plunger <NUM> away from end wall <NUM> causes a negative pressure to form in the volume 104a between the plunger and end wall <NUM>, which serves to draw liquid <NUM> through conduit <NUM>, into pump chamber <NUM> and, more specifically, into volume 104a between plunger <NUM> and end wall <NUM>. One-way valve <NUM> prevents fluids from the patient from being drawn through conduit <NUM> and into volume 104a as plunger <NUM> creates the negative pressure within volume 104a as it moves away from end wall <NUM>.

<FIG> is a schematic diagram illustrating the process of pumping liquid <NUM> from volume 104a through conduit <NUM> to the patient interface. Motor <NUM> may be rotated in a direction opposite the direction of rotation used to draw liquid <NUM> into volume 104a such as to move plunger <NUM> toward end wall <NUM> as shown by the arrow in <FIG>, thereby creating a positive pressure within volume 104a. The movement of plunger <NUM> toward end wall <NUM> reduces the size of volume 104a and forces liquid <NUM> into the conduit <NUM> and out to the patient through the patient interface. One-way valve <NUM> prevents liquid <NUM> from returning to reservoir <NUM> as plunger <NUM> moves toward end wall <NUM>, ensuring that all of liquid <NUM> within volume 104a is forced into conduit <NUM>.

Once plunger <NUM> has reached a position where it is touching end wall <NUM>, as shown in <FIG>, all, or most of liquid <NUM> within volume 104a will have been forced into conduit <NUM> to the patient interface. Plunger <NUM> does not necessarily need to touch end wall <NUM> to complete a cycle of liquid delivery. However, to reduce the amount of residual liquid within the system, and hence reduce the amount of wasted liquid at the end of usage of system <NUM>, plunger <NUM> preferably comes into contact with end wall <NUM> at the end of each cycle of liquid delivery, or alternatively, at a final cycle of drug delivery when all or nearly all of liquid drug has been dispensed from reservoir <NUM>. Having plunger <NUM> come into contact with end wall <NUM> only at a final cycle of drug delivery will reduce the impact that plunger <NUM> has on constituents of the liquid (e.g., molecules of insulin) during each cycle of liquid delivery, thereby prolonging the life or effectiveness of the liquid (e.g., protein molecules within the liquid).

It should be noted that conduits <NUM>, <NUM> must interface with pump chamber <NUM> in the volume 104a between plunger <NUM> and end wall <NUM>. In preferred embodiments of the invention, conduits <NUM> and <NUM> will connect to volume 104a directly adjacent end wall <NUM>, such that when plunger <NUM> is in the position shown in <FIG>, both inlet port <NUM> and outlet port <NUM> are blocked.

<FIG> shows a flowchart showing process <NUM> for delivery of liquid <NUM> from the reservoir <NUM> to the patient interface. The system <NUM> begins from a start position <NUM>. The start position is preferably the position wherein plunger <NUM> is in contact with end wall <NUM> such that volume 104a is reduced to virtually zero.

At block <NUM>, the plunger <NUM> is moved away from end wall <NUM> by turning of leadscrew <NUM> and liquid <NUM> is drawn from reservoir <NUM> into the volume 104a between plunger <NUM> and end wall <NUM>. At block <NUM>, it is determined whether the desired quantity of liquid <NUM> has been drawn into volume 104a and, if not, control is returned to block <NUM>, where the plunger <NUM> continues to move away from end wall <NUM> until the desired quantity of liquid <NUM> is present in volume 104a.

At block <NUM> it is determined if it is time for the delivery of the additional units of liquid <NUM> to the patient. If so, control is sent to block <NUM> and if not, system <NUM> loops at decision point <NUM> until triggered.

At block <NUM>, the movement of plunger <NUM> toward end wall <NUM> is initiated by rotation of leadscrew <NUM> in an opposite direction, such as to force a quantity of liquid <NUM> from volume 104a and into conduit <NUM>, and from there to the patient interface. At <NUM> it is determined if the quantity so far delivered to the patient interface comprises the desired quantity and, if not, control returns to <NUM>, where the plunger <NUM> continues to move toward end wall <NUM> to push a further quantity of liquid <NUM> to the patient interface. At <NUM>, if the desired quantity of liquid <NUM> has been delivered to the patient interface, the process is complete at <NUM>.

At decision point <NUM>, it is determined if the volume 104a is empty and, if so, control returns to start position <NUM> and the process repeats with the loading of an additional quantity of liquid <NUM> from reservoir <NUM> to volume 104a. If volume 104a is not empty, control returns to decision point <NUM>, where the process loops until the delivery the next unit of liquid <NUM> is triggered.

Claim 1:
A pump system comprising:
a pump chamber (<NUM>) of which at least one end is open-ended,
a leadscrew (<NUM>) extending along a longitudinal axis of the pump chamber (<NUM>),
a first plunger (106a) and a second plunger (106b),
an inlet port (<NUM>) and an outlet port (<NUM>) defined in a sidewall of the pump chamber, wherein the inlet port and outlet port are located in an area of the sidewall between the first and second plungers,
a reservoir (<NUM>), in fluid communication with the pump chamber via an inlet conduit (<NUM>) which is coupled to the inlet port,
an inlet one-way valve (<NUM>), disposed between the reservoir and the pump chamber, the one-way valve allowing fluid to flow from the reservoir into the pump chamber and preventing fluid from flowing from the pump chamber to the reservoir,
a patient interface, in fluid communication with the pump chamber via an outlet conduit which is coupled to the outlet port,
an outlet one-way valve (<NUM>), disposed between the pump chamber and the patient interface, the one-way valve allowing fluid to flow from the pump chamber to the patient interface and preventing fluid from flowing from the patient interface to the pump chamber,
wherein
the leadscrew has left-hand and right-hand threads (101a, 101b) defined thereon, wherein the first plunger (106a) is coupled to the leadscrew via the left-hand threads (101a), and wherein the second plunger (106b) is coupled to the leadscrew via the right-hand threads (101b),
wherein rotation of the leadscrew (<NUM>) in a first direction causes the first and second plungers (106a, 106b) to move toward each other, and wherein rotation of the leadscrew (<NUM>) in a second, opposite direction causes the first and second plungers (106a, 106b) to move away from each other, and in that a drive is coupled to the leadscrew for rotating the leadscrew in the first and second directions.