Flush syringe assembly with controlled pulsatile flushing

Flush syringe assemblies capable of creating pulsatile movement of the plunger rod as it moves in the distal direction within a syringe barrel, while preventing overpressurization of the cathether are provided. An exemplary flush syringe assembly includes a syringe barrel with a first pulsing element and a chamber with flush solution, a plunger rod with a stopper and a second pulsing element that interacts with the first pulsing element to provide an engagement force that causes pulsatile movement of the plunger rod and a thumb press slidably attached to the plunger rod with a pulse control element. The pulse control element is compressible to create a compression force that is greater than the engagement force of the first pulsing element and the second pulsing element.

TECHNICAL FIELD

Aspects of the present invention relate to flush syringe assemblies that provide controlled pulsatile flushing of catheters and other vascular accessing devices (VADs) and methods of flushing a catheter.

BACKGROUND

VAD's are commonly used therapeutic devices and include IV catheters. There are two general classifications of VAD's, peripheral catheters and central venous catheters. If not properly maintained, VAD's can become occluded. To ensure VAD's are used properly and do not become occluded, standards of practice have been developed. These standards include a cleaning procedure, which is commonly referred to as a flush procedure or flushing a catheter.

VAD standards of practice usually recommend flush procedures be performed after catheter placement, before fluid infusion, and before and after drug administration, blood sampling, transfusions and parenteral nutrition. The goal of these flush procedures is to confirm catheter patency, avoid drug incompatibilities, ensure the complete drug dose administration, prevent thrombus formation and minimize the risk of blood stream infections. Flush procedures require different types and amounts of flush solutions. The most commonly used flush solutions are saline and or heparin lock solution. The type of flush solution and amount vary depending on the specific type of catheter. Flush solution volumes between 5 and 10 ml are most common but can range from 1 ml to 20 ml.

For flush procedures, an I.V. line refers to a system containing a VAD, a tubing set with clamp and may terminate with a port or valve. The most common types of ports are covered by pierceable septums or pre-slit septums and are known in the art and sometimes referred to as “PRN” from the Latin pro re nata meaning “as the need arises”. The septum is preferably made of rubber or another elastomeric material, which permits insertion of a sharp needle cannula in order to infuse fluids or to withdraw fluids from the catheter. Upon withdrawal of the needle cannula the septum seals itself. Ports having pre-slit septums are used with blunt cannula or the frusto-conically shaped tip of a syringe barrel. The syringe tip or the blunt cannula (which is usually attached to a syringe) is gently pushed through the pre-slit septum to establish fluid communication.

I.V. valves, another type of terminal I.V. access device that does not require a needle having a sharp tip, are activated by the frusto-conically shaped tip of a syringe barrel to allow fluid communication between the interior of the syringe and the catheter. These valves may contain structure for delivering fluid from a storage compartment in the valve to the catheter, and are referred to in the art as positive displacement valves. Such a valve is disclosed in U.S. Pat. No. 6,206,861.

Flush procedures may be enhanced by use of a “start-stop,” “push-pause” (also referred to as “push-pulse”) or turbulent flushing technique to remove debris or residue in the catheter that may cause occlusion or other undesirable effects. The removal of debris or residue is referred to as purging and prevents the build-up of deposits of blood, blood residue and IV drugs within a catheter or other VAD device. Such build-up can cause partial or complete blockage of the fluid pathway in a catheter system and can also require expensive and potentially dangerous methods for purging the affected catheter or a total catheter exchange. Often, such blockages lead to interruptions in therapy that may compromise patient care. The build-up of residue within a catheter can also increase infection risk by providing a breeding medium for microorganisms. For this reason, push-pulse is traditionally taught to healthcare workers.

As is understood by one skilled in the art, the push-pulse flushing technique introduces or creates turbulence within the syringe barrel when uneven pressure or force is applied to the plunger rod in the distal direction as the distal end of the plunger rod moves toward the barrel wall during expulsion of the flush solution contained within the barrel. In this disclosure, a convention is followed wherein the distal end of the device is the end closest to a patient and the proximal end of the device is the end away from the patient and closest to a practitioner. When such techniques are used in conjunction with catheters, turbulence is introduced within the catheter. Pulsing flow causes a swirling effect that moves any debris or residue attached to the catheter. Pulsing flow may also be referred to as pulsating flow and/or turbulent flow and includes flow that has a chaos or variations in its flow profile. Pulsing flow can be provided in a relatively controlled manner by a syringe that includes a plunger rod that interacts with the syringe barrel as the plunger rod is pushed forward to automatically create sharp pulses in fluid flow and pressure. In contrast to push-pulse and controlled pulsatile flow, conventional or “smooth” (also referred to as “straight” or “laminar”) flushing techniques require the application of substantially constant pressure or force to the plunger rod in the distal direction. Conventional or smooth flushing techniques may also include the application of pressure or force that increases or decreases substantially linearly to the plunger rod in the distal direction.

However, the use of features that provide the force differential that creates pulsing fluid flow generally cannot be applied with infusion pumps or other delivery systems that require slow and controlled delivery of medication to patients. For example, certain infusion pumps have high pressure alarms and the forces and/or pressures created by push-pulse techniques of flushing can set off the high pressure alarm. In addition, push-pulse techniques and flush syringes that provide push-pulse techniques often do not provide a way to control the increases in pressure within the flush syringe. Typical flush syringes that incorporate physical barriers to create pulsatile movement of the plunger rod through the barrel rely on the user to apply increased force on the plunger rod so the plunger rod can overcome the physical barriers. Other flush syringes without such physical barriers also rely on the user to stop and start movement of the plunger rod within the barrel to create pulsatile movement of the plunger rod. In these and other known flush syringes and procedures for, the user may exert a force on the plunger rod that could cause the pressure within the barrel to increase up to 25 psi and above. These pressure levels within the barrel can lead to overpressurizing catheters or other VADs that can also lead to interruptions in therapy that may compromise patient care. Further, high pressures within the barrel during flushing can also lead to vein blowout.

There is a need for a flush syringe assembly that can be used with manual IV therapies and therapies that use infusion pumps and that provide controlled pulsatile flushing.

SUMMARY

A first aspect of the present invention pertains to a flush syringe assembly. In one or more embodiments, the flush syringe assembly includes a barrel with a first pulsing element, a plunger rod with a second pulsing element disposed within the barrel, a thumb press attached to one end of the plunger rod, a pulse control element disposed between the thumb press and the plunger rod. The flush syringe assembly also includes a stopper attached to the other end of the plunger rod to form a fluid-tight seal with the inside surface of the barrel. The chamber of the barrel may include a pre-selected amount of flush solution in the chamber. The flush solution may include saline and/or heparin.

The first pulsing element of the barrel and the second pulsing element of the plunger rod engage to provide an engagement force that causes pulsatile movement of the plunger rod as it moves within the barrel in the distal direction. The engagement force may be described as resisting a distally directed force applied to the plunger rod. In one or more embodiments, the second pulsing element may be aligned to prevent engagement with the first pulsing element to cause continuous and unimpeded movement of the plunger rod as it moves within the barrel in the distal direction. The first pulsing element may be provided as a retaining ring disposed on the barrel that extends inwardly into the chamber of the barrel. The second pulsing element may be provided as a plurality of projections disposed along the plunger rod body that extend outwardly from the plunger rod body. The plurality of projections may be disposed at regular intervals along the plunger rod body.

The barrel may include a side wall with an inside surface defining a chamber for retaining fluid. The barrel may include an open proximal end and a distal end including a distal wall with a tip extending distally therefrom having a passageway therethrough in fluid communication with the chamber. The plunger rod disposed within the barrel includes a distal end, a proximal end, and a plunger rod body extending from the distal end to the proximal end. The second pulsing element may be disposed on the plunger rod body. The thumb press is slidably attached to the proximal end of the plunger rod.

The pulse control element of one or more embodiments may include a spring or a compression spring that compresses to provide a compression force upon application of a distally directed force on the thumb press and expands as the distally directed force is released. In one or more embodiments, the spring has a spring rate so that application of a continuous distally directed force on the thumb press increases the compression force until it is greater than the engagement force and causes the first pulsing element to disengage from the second pulsing element permitting the plunger rod to move in a distal direction. In another variant, the spring rate is such that the disengagement of the first pulsing element and the second pulsing element causes the spring to expand and the compression force to decrease.

In one or more embodiments, the thumb press includes a proximal end, a distal end, and a plurality of engagement tabs disposed at the distal end of the thumb press. The plunger rod of one or more embodiments may include a plurality of openings having a distal end, a proximal end and a length between the distal end and the proximal for receiving the engaging tabs. When the engagement tabs are engaged with the openings of the plunge rod, the engagement tabs may be configured to slide along the length of the plurality of openings as the compression force is applied to the thumb press in the distal direction and the compression force is released. Stated in other words, when the engagement tabs are engaged with the openings of the plunge rod, the engagement tabs may be configured to slide along the length of the plurality of openings as the a force is applied to the thumb press in the distal direction to cause the spring to compress and the same force is released. Therefore, in one or more embodiments, the expansion of the spring may also cause the engagement tabs to slide to the distal end of the plurality of openings and the compression of the spring allows the engagement tabs to slide to the proximal end of the plurality of openings.

In one or more embodiments, the thumb press may also include a locking element that engages with the first pulsing element to lock the thumb press at least partially within the barrel when the stopper is in contact with the distal wall of the barrel. When at least a portion of the thumb press is locked within the barrel, the pulse control element exerts a force on the plunger rod in a distal direction.

In one or more embodiments, the flush syringe assembly may include a barrel, a plunger rod disposed within the barrel and a stopper disposed on a distal end of the plunger rod for forming a fluid-tight seal with the inside surface of the barrel. In one or more embodiments, the barrel includes a side wall having an inside surface defining a chamber for retaining fluid. The barrel may also include an open proximal end and a distal end including a distal wall with a tip extending distally therefrom having a passageway therethrough in fluid communication with said chamber. The open proximal end of the barrel includes at least one protrusion extending inwardly into the chamber. The barrel may also include a pre-selected amount of flush solution in the chamber. The flush solution may include saline or heparin.

The plunger rod includes a distal end, a proximal end including a thumb press, a compressible plunger rod body extending from the distal end to the proximal end. The plunger rod body includes a plurality of projections disposed along the plunger rod body that, upon application of a distally directed force to the thumb press, engage the protrusion of the barrel to provide an interference force with variations and cause pulsatile movement of the plunger rod as it moves within the barrel in the distal direction and imparts pulsing flow to the flush solution and increases the pressure of the flush solution. In one variant, the plurality of projections of the plunger rod may be aligned to prevent cooperation with the protrusion of the barrel to cause continuous and unimpeded movement of the plunger rod as it moves within the barrel in the distal direction. The proximal end of the barrel comprises a portion that is free of any protrusions. In one or more embodiments, the plunger rod may be rotatable within the barrel such that the plurality of projections may be aligned with the portion that is free of any protrusions to cause continuous and unimpeded movement of the plunger rod as it moves within the barrel in the distal direction.

The plunger rod body may include a hollow portion including a spring having a rate so that the spring is initially compressed to provide a force that is less than the interference force and upon further application of distally direct force to the thumb press, the spring is compressed to provide sufficient force that is greater than the interference force.

In one or more embodiments, the compressible plunger rod body includes a telescoping segment attached to the proximal end of the plunger rod. The telescoping segment may be configured to slide in and out of the plunger rod body to reduce and increase the length of the plunger rod body. In such embodiments, the spring may be disposed between the telescoping segment and the plunger rod body. The spring may compress to generate a compression force as a force is applied to the plunger rod in the distal direction and expand as the compression force is released. In one or more embodiments, the expansion of the spring causes the telescoping segment to slide out of the plunger rod body to increase the length of the plunger rod body and the compression of the spring allows the telescoping segment to slide into the plunger rod body to reduce the length of the plunger rod body.

In one or more embodiments, the interaction of the plurality of projections with the protrusion of the barrel generates an engagement force that exerts a force on the plunger rod in a proximal direction. In such embodiments, increasing the compression force allows the plunger rod to overcome the engagement force and causes the plurality of projections to disengage from the protrusion. The disengagement of the plurality of projections and the protrusion causes the compression force to decrease.

The plunger rod of one or more embodiments may include a locking element that engages with the protrusion of the barrel to lock at least a portion of the plunger rod within the barrel when the stopper is in contact with the distal wall of the barrel. The locking of at least a portion of the plunger rod within the barrel causes the spring to exert a force on the plunger rod in a distal direction.

DETAILED DESCRIPTION

A first aspect of the present invention pertains to a flush syringe assembly configured to permit pulsatile movement of the plunger rod. The pulsatile movement of the plunger rod imparts pulsing flow to the flush solution as it is expelled. The first aspect of the present invention also includes flush syringe assemblies with a pulse control element to control the pressure of the flush solution being expelled by the flush syringe assembly. A flush syringe assembly100according to an embodiment of the first aspect of the present invention is shown inFIGS. 1-16.

FIG. 1shows the flush syringe assembly100in an assembled state. The flush syringe assembly100includes a syringe barrel110, a plunger rod130disposed within the syringe barrel110, a stopper160attached to one end of the plunger rod130, a thumb press170attached to the second end of the plunger rod130and a pulse control element190disposed between the thumb press170and the plunger rod130.

The syringe barrel110includes110includes an open proximal end119and a distal end111and a distal wall112. A sidewall113extends from the distal end111to the open proximal end119and includes an interior surface114that defines a chamber115for retaining or holding fluids, which may include flush solution and/or other liquids. The distal end111may also include a tip116having an open passageway117therethrough in fluid communication with the chamber115. The syringe barrel110may include an optional finger flange120at the open proximal end119extending radially outwardly from the sidewall113. The distal end111of the syringe barrel110includes a threaded collar121surrounding the tip116that forms a channel122for receiving a tip cap124. The tip cap124more clearly shown inFIG. 2includes a threaded portion125that is inserted into the channel122and engages the threaded collar121of the syringe barrel110. The threaded collar121may also engage a needle hub (not shown).

The syringe barrel110includes a first pulsing element126that is configured to cooperate with the plunger rod or engage a portion of the plunge rod to cause pulsatile movement of the plunger rod as it moves within the barrel in at least the distal direction. The first pulsing element126is configured to cooperate or engage a portion of the plunger rod to cause pulsatile movement of the plunger rod as it moves within the barrel in the distal direction and proximal directions. In the embodiment shown, the first pulsing element126is disposed on the interior surface114of the syringe barrel. Specifically, the first pulsing element126is shown as a structure that reduces the cross-sectional width of the interior surface114of the syringe barrel at or adjacent to the open proximal end119of the syringe barrel. It will be understood that the first pulsing element126may be disposed at other locations along the interior surface114of the syringe barrel. In one variant, the first pulsing element126may be a separate component (not shown) attached to the open proximal end119of the syringe barrel that reduces the cross-sectional width of the open proximal end119of the syringe barrel. In another variant, the first pulsing element126may include a plurality of inwardly extending projections (not shown) disposed along the length of the interior surface114of the syringe barrel. The first pulsing element126may be provided in the form of a plurality of inwardly projecting rings (not shown) that extends around the circumference of the interior surface114and are disposed at intervals along the length of the barrel.

In the embodiment shown inFIGS. 1-16, the first pulsing element126is formed by a retaining ring127(shown inFIG. 9) that extends into the chamber115. The retaining ring may be described as an inwardly extending protrusion. The cross-sectional width of the interior surface114of the syringe barrel at the retaining ring127is less than the cross-sectional width of the interior surface114at the remaining portions of the syringe barrel. The interior surface114of the syringe barrel110may include an inclined portion128disposed proximally adjacent to the retaining ring127. The cross-sectional width of the interior surface114of the syringe barrel increases from the open proximal end119to the retaining ring127. The interior surface114may also have a declined portion129disposed distally adjacent to the retaining ring127. The interior surface114of the syringe barrel decreases from the retaining ring127to the distal end111of the syringe barrel.

The retaining ring127may be provided as a separate component. The separate retaining ring (not shown) may be provided in the form of a disc with an opening in the center of the disc. The disc and/or opening would be sized and shaped so the retaining ring127may be to be fitted onto the open proximal end119of the barrel. The separate retaining ring would include at least one extension that extends from the disc into the opening. The cross-sectional width of the opening is decreased at the extension. The remaining portions of the opening are free of extensions. The cross-sectional width of the opening at these remaining portions is greater than the cross-sectional width of the opening at the extension. The separate retaining ring may be rotated with respect to the syringe barrel or the syringe barrel and the separate retaining ring may be rotated such that the position of the extension can change with respect to the plunger rod. The extension may be aligned with the plunger rod such that the extension engages with the plunger rod to create pulsatile movement of the plunge rod. Alternatively, the plunger rod may be aligned with the portions of the opening that are free of extensions so there is no engagement between the extension and the plunger rod and the plunger rod may move within the barrel in a continuous and unimpeded manner. Such embodiments would enable the user to utilize existing syringe barrels with the plunger rods described herein in flushing procedures.

Still referring toFIGS. 1-16, the side wall113of the syringe barrel may be cylindrical or may have another shape. In addition, the chamber115of the syringe barrel may include a desired amount of flush solution. The sidewall113may also include measuring indicia to indicate the amount of flush solution contained within the chamber115.

The flush syringe assembly may be pre-filled with flush solution during or after the assembly of the syringe using sterile filling methods. In such prefilled syringes, the tip cap124is attached to the tip116to seal the passageway117of the barrel. In embodiments in which the chamber115is provided empty, to fill the chamber115with the desired amount of flush solution, a needle assembly or hub may be attached to the tip116. The needle assembly would include a needle cannula to pierce a pierceable septum or to be inserted into a pre-split septum of a vial or neck of a glass ampoule containing flush solution and the flush solution is drawn into the chamber115of the syringe barrel by pulling plunger rod130in the proximal direction while holding barrel, to draw fluid through the needle cannula into chamber115.

Exemplary flush solutions include saline flush solution and/or heparin lock flush solution. These solutions are known in the art and readily available. An example of a saline flush solution is 0.9% Sodium Chloride USP for injection. An example of a heparin lock flush solution is 0.9% Sodium Chloride with 100 USP units of Heparin Sodium per ml or 10 USP units of Heparin Sodium per ml.

As shown inFIGS. 1-5, the plunger rod130is disposed within the chamber115of the syringe barrel. The plunger rod130includes a distal end131and a proximal end139. A stopper160is attached to the distal end131of the plunger rod130and includes a sealing edge162for forming a fluid tight seal with the interior surface114of the syringe barrel to draw fluid into the chamber115and to drive fluid out of the chamber115. The stopper160includes a distal end161, a proximal end169and a stopper body164that extends from the distal end161to the proximal end169. The stopper body164includes an interior recess165defined by an inside surface166for receiving at least a portion of the plunger rod130.

The stopper160shown inFIGS. 1-16includes a distal end161having a conical shape. Accordingly, when the distal end161of the stopper is in contact with the distal wall112of the syringe barrel, the stopper160is in full contact with the distal wall112and drives as much of the flush solution out of the chamber115as possible.

In the embodiment shown, the distal end131of the plunger rod includes a distal attachment portion133that includes a plurality of plunger rod threads134disposed thereon for engaging corresponding stopper threads167disposed on the inside surface166of the stopper160. To attach the stopper160to the plunger rod130, the distal attachment portion133is inserted into interior recess165of the stopper160and one or both of the plunger rods130and the stopper160is rotated with respect to one another until the plurality of plunger rod threads134engages the stopper threads167. In one or more embodiments, the distal attachment portion133and the inside surface166of the stopper160may include corresponding structure to enable a friction interference fit, snap fit or other connection to attach the stopper160to the plunger rod130. In one variant, the distal end131of the plunger rod130may include an integrally formed sealing portion (not shown) that forms a fluid-tight seal with the interior surface114of the syringe barrel.

The plunger rod130includes an optional annular protrusion135that extends radially outwardly from the plunger rod body and is disposed proximally adjacent to the distal attachment portion133. The annular protrusion135provides stability to the plunger rod during use and/or provides a physical barrier to engagement between the plunger rod threads134and the stopper threads167.

The plunger rod130includes a plunger rod body132that extends from the annular protrusion135to the proximal end139of the plunger rod. In embodiments that do not utilize an annular protrusion135, the plunger rod body132extends from the distal end131to the proximal end139of the plunger rod. In the embodiments shown inFIGS. 1-16, the plunger rod body132includes an outside surface that forms a perimeter around the plunger rod body132and an axial length extending along the length of the plunger rod body132. The plunger rod body132may include a single beam or structure, which may have cylindrical or other shapes. As shown inFIGS. 1-16, the plunger rod body132may be formed by two perpendicularly intersecting beams137,138. The beams may each have a rectangular cross-section. In the embodiment shown, the two intersecting beams137,138intersect to form an outside surface defining four quadrants144,145,146,147(shown more clearly inFIG. 7A) that are open and face the interior surface114of the syringe barrel and extend along the axial length from the proximal end139to the annular protrusion135of the plunger rod.

In the embodiments shown inFIGS. 1-16, the plunger rod130includes a second pulsing element136that is disposed on the outside surface of the plunger rod body132. The second pulsing element may be integrally formed or may be provided as separate components that may be attached to the outside surface of the plunger rod body132. In such embodiments, the plunger rod may further include structure for the attachment of a separate second pulsing element136to the outside surface of the plunger rod body132.

In accordance with the embodiments shown more clearly inFIGS. 7 and 7A, the second pulsing element136is provided as a plurality of projections140disposed along the length of the plunger rod body132at regular intervals. In one or more embodiments, the second pulsing element136may be provided as a single projection (not shown) that engages with the first pulsing element126of the syringe barrel that includes a plurality of retaining rings127(not shown) disposed along the length of the interior surface114of the syringe barrel.

In embodiments utilizing two perpendicularly intersecting beams137,138to form the plunger rod body132, the second pulsing element136may be disposed at opposite ends of one beam, as shown inFIG. 7A. In another variant, the second pulsing element136may be disposed on opposite ends of both beams137,138. In embodiments utilizing a single beam or structure to form a plunger rod body, second pulsing element136may be disposed around the perimeter of the plunger rod body132at regular intervals. Optionally, the second pulsing element may be formed along a segment of the perimeter of the plunger rod, while the remaining segments of the outside surface are free of the second pulsing element. In such embodiments, the second pulsing element136may extend along the entire axial length. In a specific embodiment, the second pulsing element may be formed along two opposite segments of the perimeter of the plunger rod body, leaving two opposite segments of the perimeter of the plunger rod that are free of protrusions. In such embodiments, the second pulsing element136may also extend along the entire axial length.

In embodiments where the second pulsing element136is disposed on opposite ends of one beam, where two beams are used to form the plunger rod body132or the second pulsing element136is disposed at one or more segments of the perimeter of the plunger rod body132or other embodiments in which the second pulsing element136is positioned so it is not always in contact with the first pulsing element126while the plunger rod130is disposed within the syringe barrel110, the position of the second pulsing element136permits the plunger rod130to move in a pulsatile or continuous and unimpeded manner within the syringe barrel110. Moreover, such positions of the second pulsing element136also permit the user to select whether to impart pulsing flow to the flush solution being expelled by selecting whether the plunger rod130should move in a pulsatile manner or continuous and unimpeded manner within the syringe barrel110. The user would select between moving the plunger rod130in a pulsatile manner or continuous and unimpeded manner by rotating the plunger rod130so that the second pulsing element136does not engage or interact with the first pulsing element126.

In one or more embodiments, the plunger rod130may include a second pulsing element136that is shaped, positioned or otherwise disposed on the plunger rod boy132in such a manner that forces the user to impart pulsing flow to the flush solution being expelled because it forces alignment of the second pulsing element136with the first pulsing element126such that they must engage or interact. The first pulsing element126may also be shaped, positioned or disposed on the syringe barrel110such that engagement or interaction with the second pulsing element136cannot be avoided during use and the plunger rod130is only able to move in a pulsatile manner within the syringe barrel.

In the embodiment shown inFIGS. 7 and 7A, the plurality of projections140include a distally facing ramped surface141disposed that extends from the plunger rod body132such that the cross-sectional width of the plunger rod body132increases along the ramped surface141in the proximal direction. The plurality of projections140may also include a projection surface142disposed proximally adjacent to the ramped surface141and a perpendicular surface143disposed proximally adjacent to the projection surface142. The cross-sectional width of the plunger rod body132along the projection surface142may be constant or may optionally increase or decrease. In one or more alternative embodiments, the plurality of projections140may be provided as rounded extensions (not shown), where the cross-sectional width of the plunger rod body132increases proximally to a point and then decreases.

In one or more embodiments, the second pulsing element136may be provided in the form of partial discs (not shown) that extend between the two intersecting beams137,138. Specifically, the partial discs may be connected to the adjacent beams137,138and extend radially outwardly toward the inside surface of the barrel from at least one of the quadrants144,145,146,147formed by the beams137,138. In such embodiments, the cross-sectional width of the plunger rod body132increases at the quadrants in which the partial discs are disposed. Alternatively, the partial discs may be formed in two non-adjacent quadrants144,146and connect between the beams137,138. The partial discs may be positioned at regular intervals along the axial length of the plunger rod body132. In one or more alternative embodiments, the partial discs may be positioned at irregular intervals and/or may be positioned at or adjacent to the proximal end139or the annular protrusion135of the plunger rod.

The plurality of protrusions140may be provided as rings (not shown) that extend around the perimeter of the plunger rod body132. The rings may be disposed at intervals along the axial length of the plunger rod body132. The cross-sectional width of the plunger rod body132at the rings is greater than the cross-sectional width of the plunger rod body132at locations between the rings.

The plunger rod130also includes a proximal attachment portion150for attaching the thumb press170to the plunger rod in a frictional interference fit. The proximal attachment portion150may be attached or integrally formed at the proximal end139of the plunger rod. The proximal attachment portion150includes a closed distal end151adjacent to the proximal end139of the plunger rod, an open proximal end159and a proximal wall152extending from the distal end151to the proximal end159. The proximal wall152includes an inside surface that defines a hollow interior153in fluid communication with the open proximal end159and the thumb press, as will be described herein. The hollow interior153is shaped to receive the pulse control element190and at least a portion of the thumb press170. The open proximal end159may include an extending rim portion (not shown) that extends inwardly into the hollow interior153for retaining at least a portion of the thumb press170within the hollow interior153of the proximal attachment portion. The thumb press170may include a corresponding structure for engaging the rim portion.

The proximal wall152includes at least one opening154for engaging at least a portion of the thumb press170. In the embodiment shown inFIGS. 2,7and7A, the proximal wall152includes four openings154disposed at regular intervals along the proximal wall152. Each of the four openings154has an elongate shape having a distal end155, a proximal end156and a length157that extends therebetween. The length157of the opening154permits a portion of the thumb press170to slide from the distal end155of the opening154to the proximal end156of the opening. As will be described in more detail below, the length157of the opening154allows the thumb press to move relatively to the plunger rod. The length157also permits the combined length of the plunger rod130and the thumb press170to expand or increase and compress or decrease. Such relative movement or expansion and compression permits the pulse control element disposed between the thumb press170and the plunger rod130to expand and compress.

The proximal wall152is shown as having a circular cross-section, however, it will be understood that the proximal wall152may shaped to have a square cross-section or other shaped cross-section. The openings154are also shown as having a generally rectangular configuration, however, it will be understood that the distal end155and/or proximal end156of the opening154may be rounded or shaped otherwise.

In the embodiment shown, the thumb press170is attached to the proximal attachment portion150in a frictional interference fit. The thumb press170may alternatively include a threaded portion (not shown) that engages with a corresponding structure on the open proximal end159of the proximal attachment portion150. The thumb press170includes an open distal end171in fluid communication with the open proximal end159of the proximal attachment portion150and a closed proximal end179. A first annular disc172is attached to the proximal end179and provides a surface for the user to apply proximally directed and distally directed forces on the thumb press170and the plunger rod130. The thumb press170includes a body portion173that extends from the first annular disc172to a plunger-engaging portion174. A second annular disc175may optionally be disposed between the body portion173and the plunger-engaging portion. The second annular disc175may be shaped to lock the thumb press170into the syringe barrel with the first pulsing element126. In other words, the thumb press170has a cross-sectional width at the second annular disc175that is greater than the cross-sectional width of the syringe barrel at the first pulsing element126such that once the second annular disc175advances distally past the first pulsing element126, for example, the retaining ring127, at least a portion of the thumb press170is locked within the syringe barrel110. The second annular disc175may include a tapered surface (not shown) to facilitate movement distally past the first pulsing element126and may include a stop surface (not shown) to prevent movement of the thumb press in the proximal direction after the second annular disc175has moved distally past the first pulsing element126. Alternatively, the body portion173may be shaped and/or may have a size to enable the user to lock the thumb press170into the syringe barrel with the first pulsing element126.

The plunger-engaging portion174may be described as a telescoping segment of the plunger rod130. In other words, the plunger-engaging portion174may be described as an extension of the plunger rod that is moveable relative to the plunger rod body in a telescoping fashion that causes the length of the plunger rod to expand and compress. The plunger-engaging portion174may also be described as a separate portion that allows the thumb press170to be slidable attached to the plunger rod.

In the embodiment shown, the plunger-engaging portion174includes a plurality of fingers176that extend distally from the second annular disc175and/or the body portion173of the thumb press170to the open distal end171of the thumb press. The plurality of fingers176defines a recessed portion177within the plunger-engaging portion174. In the embodiment shown inFIG. 6, the recessed portion177has a circular cross-sectional shape; however, it may have any shape to accommodate the pulse control element190.

In the embodiment shown inFIG. 6, the thumb press170includes four fingers176. The four fingers176may also be described as a solid wall that extends distally from the second annular disc175and defines the recess portion177and includes four openings spaced around the solid wall. Outwardly projecting engagement tabs180are disposed on each of the plurality of fingers176for engaging the openings154of the proximal attachment portion150. In the embodiment shown, the engagement tabs180are disposed adjacent to the open distal end171of the thumb press170. The engagement tabs180may be shaped to have a tapered surface182adjacent to the distal end171of the thumb press and a locking surface184on the opposite end of the engagement tabs180from the tapered surface182. The locking surface184is perpendicularly disposed with respect to the fingers176such that when engaged in the opening154of the proximal attachment portion150, the locking surface184prevents the tab from disengaging from the opening154. The shape of the fingers176and the tapered surface182of the engagement tabs180, facilitate the initial engagement of the engagement tabs180with the openings154and attachment of the thumb press170to the plunger rod130. Specifically, to assemble the thumb press170and the plunger rod130, the fingers176are inserted into the hollow interior153of the proximal attachment portion. The engagement tabs180are aligned with the openings154such that the tapered surface182enters the openings154and the locking surface184engages with the openings. The fingers176may flex inwardly until the engagement tabs180enter the openings154.

The length of the openings154permit relative motion between the thumb press170and the plunger rod130. Specifically, when the engagement tabs180are disposed at the proximal end156of the openings154, the length of the plunger rod130and the thumb press170is maximized. When a force is applied to the thumb press170in the distal direction, the thumb press170moves within the hollow interior153of the proximal attachment portion until the engagement tabs180slide toward the distal end155of the openings154. In this position, the length of the plunger rod130and the thumb press170is reduced to its shortest length. The change in the relative position of the engagement tabs180with respect to the openings154indicates the amount of compression of the pulse control element190, as will be described below.

A pulse control element190is disposed within the recessed portion177of the plunger-engaging portion174and extends into the hollow interior153of the proximal attachment portion150. The pulse control element190is shown inFIGS. 1-16as a spring that is compressible and can expand as the thumb press170moves in the proximal and distal directions, relatively to the plunger rod130. The pulse control element190may be provided in the form of a spring192. The spring192may be characterized as a compression spring. In one or more embodiments, the spring192has a rate defined as the change in the force it exerts, divided by the change in deflection of the spring. The spring is compressible and has a spring force that is defined by the product of the spring rate or constant (k) and the spring displacement (x). In one or more embodiments, the spring192has a rate that provides a compression force within the spring192that can increase to cause the first pulsing element126and the second pulsing element136to disengage or to cause the second pulsing element136to move distally past the first pulsing element126, without rotation of the plunger rod. In one or more embodiments, the spring has a rate controls the pressure of the flush solution to an amount below about 25 psi. In one or more alternative embodiments, the spring has a rate that controls the pressure of the flush solution to an amount below about 20 psi. In one or more embodiments, the spring192has a rate such that the disengagement of the first pulsing element126and the second pulsing that causes the spring192to expand and the compression force to decrease.

In one or more alternative embodiments, the pulse control element190may be provided as a lever arm (not shown) that includes a first end disposed adjacent to or attached to the thumb press body173and the second end disposed adjacent to the proximal end of the plunger rod. The lever arm may be made of metal or plastic. The lever arm may include a first lever arm and a second lever arm that form an acute angle. In such embodiments, the application of a force in the distal direction on the thumb press170and the plunger rod130would compress the first lever arm and the second lever arm and such compression would provide within the lever arm that can increase to cause the first pulsing element126and the second pulsing element136to disengage or to cause the second pulsing element136to move distally past the first pulsing element126, without rotation of the plunger rod.

Movement of the thumb press170relative to the plunger rod130causes the pulse control element190or the spring192to expand and compress. Specifically, when a force is applied to the thumb press170in the distal direction, the thumb press moves in the distal direction relative to the plunger rod and the tabs180of the thumb press170move from the proximal end156of the openings154of the proximal attachment portion150to the distal end155of the openings154. The space within the hollow interior153of the proximal attachment portion150and the recessed portion177of the plunger-engaging portion174decreases and the thumb press170exerts a force on the spring192in the distal direction. The closed distal end151of the proximal attachment portion150prevents movement or expansion of the spring192and, therefore, the spring is compressed as more clearly shown inFIG. 10. Moreover, the application of a force in the proximal direction on the plunger rod130or the thumb press170will cause the tabs180to move in the proximal direction until they are in contact with the proximal end156of the openings of the proximal attachment portion. The second annular disc175of the thumb press170prevents the spring from moving or expanding and, therefore, the spring192compresses. Release of the distally directed force on the thumb press or the proximally directed force on the plunger rod allows the spring192to expand to its original relaxed state.

To use the flush syringe assembly described herein to remove debris from a catheter or, in other words, to expel flush solution having pulsing flow into a catheter, the plunger rod130and stopper160are assembled and inserted into the syringe barrel110with a chamber115that is filled with the desired amount of flush solution, as shown inFIG. 9. The stopper160forms a fluid tight seal with the interior surface114of the syringe barrel110. The spring192is positioned between the thumb press170and the plunger rod130in an uncompressed or expanded state with a length of D1. The engagement tabs180are positioned at the distal end155of the openings154of the proximal attachment portion150of the plunger rod.

The movement of the plunger rod130within the syringe barrel110creates an interference force. The second pulsing element136of the plunger rod is aligned to interact or engage with the first pulsing element126of the syringe barrel to create an engagement force. In this configuration, the engagement force between the first pulsing element126and the second pulsing element136provide variations in the interference force between the plunger rod and the syringe barrel, which causes pulsatile movement of the plunger rod130as it moves in the at least the distal direction within the syringe barrel110. The engagement force between the first pulsing element126and the second pulsing element136may be described as a proximally directed force on the plunger rod. In other words, the engagement force resists the distally directed force applied to the plunger rod. The engagement force may enhance or facilitate compression of the pulse control element190.

FIG. 10illustrates the initial interaction between the first pulsing element126and the second pulsing element136as a force is applied to the plunger rod130in the distal direction, the interaction or engagement between the first pulsing element126and the second pulsing element136creates or provides the engagement force and provides resistance to movement of the plunger rod in the distal direction. As the user continues to apply a force on the thumb press170and the plunger rod130in the distal direction, the engagement tabs180move in the distal direction relative to the plunger rod and the proximal attachment portion150until the engagement tabs180are adjacent to the distal end155of the openings154.

In known flush syringe assemblies, the user would have to apply a greater force in the distal direction to overcome the engagement force. Moreover, the flow of the flush solution would be stopped abruptly requiring even more force being exerted by the user to overcome the engagement force. There is often no control over the amount of additional force that is applied in the distal direction to overcome the engagement force. This leads to excessive force being applied to the plunger rod that causes the flush solution have excessive fluid pressure that can lead to overpressurization of the catheter and could lead to vein blowout. The user would have no way sensing that the pressure in the catheter has reached such high levels.

In the embodiment shown, the pulse control element190is disposed between the thumb press170and the plunger rod130is compressed by the resistance caused by the engagement force between the first pulsing element126and the second pulsing element136and the continued application of a distally directed force by the user on the thumb press170and the plunger rod130. The user would not detect any substantial change in the force required to expel the flush solution due to the compression of the spring192. The compression of the spring192creates a compression force that increases as the spring is further compressed. Initially, as the user applies a distally directed force on the plunger rod130and the thumb press170, the engagement force between the first pulsing element126and the second pulsing element136is low or non-existent. At this time, the compression of the spring192remains low and the compression force is not greater than the engagement force between the first pulsing element126and the second pulsing element136. As the user continues to apply a distally directed force on the thumb press170and the plunger rod130, the spring further compresses until the spring192has a length of D2. The compression force of the spring increases until it is greater than the engagement force between the first pulsing element126and the second pulsing element136, as shown inFIGS. 10 and 11. The second pulsing element136of the plunger rod disengages from the first pulsing element136and moves distally past the first pulsing element126, as shown inFIG. 11. The disengagement of the first pulsing element126and the second pulsing element136and the movement of the plunger rod impart pulsing flow to the flush solution. At this time, the engagement force decreases or is no longer present. The length of the spring192expands to D1. The disengagement of the first pulsing element126and the second pulsing element136and the movement of the plunger rod allow the spring to expand and the compression force of the spring192is decreased. The removal of the engagement force and the expansion of the spring192cause the plunger rod to expand or the thumb press170to move in the proximal direction relatively to the plunger rod and the engagement tabs180move toward the proximal end156of the openings154of the proximal attachment portion150of the plunger rod.

As shown inFIGS. 12-14, as the user continues to apply a distally directed force on the thumb press170and the plunger rod130to expel the flush solution, the first pulsing element126and the second pulsing element136continue to engage and disengage. As the first pulsing element126and the second pulsing element136engage and disengage, the spring192compresses and expands such that the engagement force and the compression force increase and decrease relative to one another to allow the plunger rod to expel the flush solution having pulsing flow from the syringe barrel. The compression force of the spring192prevents the user from actively applying excessive force to the plunger rod130and thumb press170to overcome the engagement force between the first pulsing element126and the second pulsing element136and prevent overpressurization of the catheter. After all of the flush solution is expelled from the syringe barrel110, the spring192is positioned in an expanded state with a length of D1, as shown inFIGS. 13 and 14.

In one embodiment, the flush syringe assembly100includes structure for preventing reflux, which minimizes the use of heparin to lock catheters or the need for positive displacement valves. Typically, to prevent reflux, the user is encouraged to maintain a positive pressure in the line during the flush procedure to prevent reflux or compression of the stopper that can draw blood back into the catheter, where it can clot and seal the catheter. The compression of the spring192by application of a distally directed force on the thumb press170and the plunger rod130after the stopper160is in contact with the distal wall112of the syringe barrel, as shown inFIGS. 15 and 16, applies positive pressure and prevents reflux. The user may also maintain such positive pressure by applying a sufficient force in the distal direction to the thumb press170or continuing to apply a distally directed force to the thumb press to lock the thumb press170into the barrel. Specifically, as shown inFIG. 15-16, the application of sufficient force to the thumb press170causes the second annular disc175to engage the first pulsing element126or the retaining ring127of the barrel. Thereafter, the retaining ring127continues to apply a distally directed force on the thumb press170and the spring192remains compressed and exerts a compression force on the plunger rod130and stopper160in the distal direction.

An alternative embodiment of the flush syringe assembly200is shown inFIGS. 17-18. Specifically, the flush syringe assembly200permits the user to select whether to utilize pulsating flow or continuous flow to flush a syringe. As discussed above, the syringe barrel110and/or plunger rod130includes a first pulse element126and a second pulse element136that are positioned, shaped or disposed thereon in a manner that allows the user to select whether or not the first pulsing element126and the second pulsing element136engage and cause pulsatile movement. For example, if continuous and unimpeded movement of the plunger rod is desired, instead of the pulsatile movement, the user may rotate the plunger rod130, barrel110or the retaining ring so that the first pulsing element126and the second pulsing element136are not aligned. As shown inFIG. 17, the flush syringe assembly200includes a syringe barrel210with a first pulsing element226and the plunger rod230with a plunger rod body232a second pulsing element236(not shown) that is disposed on the plunger rod body232in such a manner that the plunger rod230may be rotated within the syringe barrel210to prevent engagement or interaction with the first pulsing element226. The flush syringe assembly200also includes a thumb press270attached the plunger rod by a proximal attachment portion250. As the user applies a distally directed force on the thumb press and the plunger rod230, the lack of interaction or engagement between the first pulsing element226and the second pulsing element236causes the plunger rod230to moves within the syringe barrel in a continuous and uninterrupted manner. Specifically, the interaction force between the plunger rod230and the syringe barrel210remains constant and without the variations that are caused by pulsatile movement of the plunger rod. As the flush solution is expelled, as shown inFIG. 18, the user may continue to apply a force on the thumb press in the distal direction such that the second annular disc to engage the first pulsing element226. The pulse control element290disposed within the thumb press270and the proximal attachment portion250is compressed and continues to exert the compression force to the plunger rod230and stopper260in the distal direction.

The flush syringe assemblies described herein may also include visual or other indication elements to indicate the position of the first and second pulsing elements with respect to each other and thus, indicate whether movement of the plunger rod within the barrel will be pulsatile or continuous and unimpeded. For example, the thumb press may have a color disposed on a portion of the thereon that is aligned with the second pulsing element disposed on the plunger rod, as described herein. The barrel may include corresponding color disposed on the finger flange or other portion of the barrel that is aligned with the first pulsing element disposed on the barrel. Accordingly, in use the alignment of the colored portions on the thumb press and the barrel indicates to the user that the flush syringe assembly is configured for pulsatile movement of the plunger rod within the barrel. Other visual markers may also be utilized, for example, symbols and words may be disposed on the thumb press and barrel.

A second aspect of the present invention pertains to a method for flushing a catheter. In one or more embodiments, the method includes attaching a flush syringe assembly as described herein to a cathether. The flush syringe assembly may be filled or pre-filled with the desired amount of flush solution. The method includes applying a continuous force in the distal direction to the plunger rod to create sufficient compression force within the spring until it overcomes the engagement force between the first pulsing element and the second pulsing element. In one or more embodiments, the method further includes continuing to apply the force in the distal direction on the thumb press170and the plunger rod130until the thumb press170and/or plunger rod130is locked within the syringe barrel when the stopper is in contact with the distal wall of the syringe barrel.