SINGLE USE SYRINGE WITH IMPULSE REDUCTION SYSTEM
CROSS REFERENCE TO RELATED REQUESTS This application is a partial continuation of U.S. Patent Application Serial No. 10 / 835,848 filed April 30, 2004 which is a continuation of U.S. Patent Application Serial No. 10 / 256,607 filed on September 27, 2002, now abandoned, and a partial continuation of U.S. Patent Application Serial No. 10 / 706,795 filed on November 12, 2003, which is a continuation of the U.S. Patent Application Serial Number 09 / 941,030 filed August 28, 2001, now abandoned, which is a continuation of U.S. Patent Application Serial No. 09 / 274,117 filed March 23, 1999, now U.S. Patent No. 6,361 .525, which is a partial continuation of U.S. Patent Application No. 09 / 249,431 filed on February 12, 1999, now abandoned, which is a continuation Partial Application of United States Application No. 09 / 124,447 filed July 29, 1998, now abandoned. BACKGROUND Embodiments of the invention generally relate to breakable plunger impulse reduction devices for medical devices, such as syringes. The reuse of medical equipment destined for a single use is a source of great concern, because such reuse can lead to the transmission of contagious diseases. Syringes including a syringe barrel having an elongate tip and a fluid passage, which is typically the lumen of a needle attached to the syringe through which fluid is drawn out of the syringe, are an example of such devices. Such syringes further include a plunger having a proximal end on which the user applies force to advance the plunger to the barrel and a proximal end with a distal portion. After use, a certain amount of fluid is typically left in what is called dead space between the distal portion and the elongated tip of the barrel. Attempts have been made to avoid the reuse of syringes by providing breakable emboli as part of the syringe assembly, of which examples are described in U.S. Patent No. 6,217,550 (Capes), the entire contents of which are incorporated herein by reference. and in U.S. Patent Publication No. US 2004/0199113 (Capes et al.), the content of which is also incorporated herein by reference. Such breakable plunger assemblies provide a breakable connection between the main body of the plunger and the distal proximal portion. Such breakable connections possess sufficient structural integrity to resist breakage during normal use, but they break at the application of additional force. Thus, after injection of the liquid contents of the syringe to a patient or to a reservoir or suitable device such as through the pierceable septum of a catheter connector, the user applies additional force to the thumb seat of the plunger. This additional force makes the rupturable connection be cut, mechanically disconnecting the main body of the plunger from the distal portion, and therefore disabling the additional use of the syringe. After activating the breakable connection (i.e., breaking it), the main body of the plunger moves forward at a relatively high speed and collides with the distal portion. This creates a contact impulse that compresses the distal portion and expels fluids that remain within the dead space between the distal portion and the passage of the elongated tip of the medical device. These fluids can be expelled at high velocities, resulting in a spray coming out from the tip of the hole or lumen if a needle is attached to the syringe. Such spraying poses a risk of dispersion of contaminating fluids or blood. Therefore, it would be desirable to provide syringes and breakable plunger assemblies that mitigate the risk of liquids being sprayed from the nozzle of a medical device when the plunger is disabled. COMPENDI The embodiments of the invention relate to a syringe including a barrel and a plunger. The barrel includes a barrel that has a fluid chamber, an inner surface, a proximal end, a distal end and a tip extending from the distal end with a passage in fluid communication with the chamber. In one or more embodiments, the plunger includes a proximal portion connected by a breakable or collapsible connector to a distal portion. The proximal portion may have a flange on which a user can press along a longitudinal centerline of the plunger. In one or more embodiments, the distal portion has a distal end with a stop that provides a seal sliding with the inner surface of the barrel, to expel fluids from the passage. The breakable or collapsible connection is broken or crushed when the force applied by the user exceeds a breaking or crushing force. In one or more embodiments, a pulse reduction system is provided between the stop and the flange to reduce the contact impulse that occurs between the proximal portion and the distal portion when the breakable connection is broken. In one embodiment, the pulse reduction system includes a first braking surface that is disposed in the proximal portion, and a second braking surface that is disposed in the distal portion. The braking surfaces are designed to slidably engage with one another in order to create a resistance to movement between the proximal portion and the distal portion. In another embodiment, the first braking surface is inclined with respect to the longitudinal centerline of the plunger. In another embodiment, the second braking surface is inclined with respect to the longitudinal centerline of the plunger. The surfaces can be rough to increase the coefficient of friction between the surfaces, and therefore the braking force. In another embodiment, the pulse reduction system includes an elastic member, such as a spring or similar device, disposed within a range separating the proximal portion of the distal portion along the longitudinal center line. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a syringe including a breakable plunger disposed within the syringe barrel. Figure 2 is an exploded perspective view of the syringe including the breakable plunger of Figure 1 with a needle and hub attached to the syringe. Figure 3 is a perspective view of a distal portion of the breakable plunger illustrated in Figure 1 before activation. Figure 4 is a side view of a distal portion of the breakable plunger illustrated in Figure 1 before activation. Figure 5 is a perspective view of a distal portion of the breakable plunger illustrated in Figure 1 after activation. Figure 6A is a side elevational view of the syringe of Figure 1 illustrated with a force applied to break the connection between the proximal and distal portions of the plunger. Figure 6B is a side view of a distal portion of the breakable plunger illustrated in Figure 6A after activation. Figure 7 is a perspective view of a distal portion of another breakable plunger. Figure 8 is a side view of the breakable plunger shown in Figure 7. Figure 9 is a perspective view of a distal portion of another breakable plunger. And Figure 10 is a side view of the breakable plunger shown in Figure 9. DETAILED DESCRIPTION Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description and the drawings. The invention is capable of other embodiments and of carrying out or being carried out in various ways. A convention used in this application is that the term "next" denotes a direction closer to the doctor, while the term "distal" denotes a direction further from the doctor. According to an embodiment of the invention illustrated in figures 1 and 2, a syringe 10 includes a barrel 20 having an internal surface 26 defining a fluid chamber 18, a distal end 12, a proximal end 14, a distal tip
16, and a breakable or collapsible plunger 30. The collapsible plunger 30 may be slidably disposed within the barrel 20. The plunger 30 includes a distal portion 34, a proximal portion 36 and a stop 38 connected to the distal portion 34. The distal portion 34 and the proximal portion 36 are connected to each other by a collapsible or breakable connection 40. The stop 38 is slidably positioned in fluid-tight engagement with the inner surface 26, and is capable of sliding distally and proximally along the longitudinal center line 32. By moving the plunger distally, the stop 38 can expel fluids from the fluid passage or hole 24 in the distal tip 16. By moving it shortly, the stop 38 can suck fluids through the fluid passage 24 and to the fluid chamber 18. Those skilled in the art will appreciate that the distal tip 16 of the syringe 10 can be detachably or permanently connected to a needle assembly by a hub 22 as is in the art. Such needle assemblies include, but are not limited to, needle assemblies of the Luer lock type and needle assemblies of the Luer slip type. It also falls within the scope of this invention to include a needle assembly having a one-piece construction where the cannula and hub are formed in one piece. A proximal end of the proximal portion 36 may include a thumb flange 37 that a user can push to move the plunger 30 and the stop 38 distally, or pull it to move the plunger 30 and the stop 38 proximally. A pulse reduction system 50 is disposed on the plunger 30 between the stop 38 and the flange 37 to reduce the contact impulse between the proximal portion 36 and the distal portion 34 generated when the breakable connection 40 is broken. Figures 1 and 2 show an impulse reduction system 50 using friction surfaces, it will be appreciated that any suitable impulse reduction system 50 can be used inside the syringe 10. As shown in Figures 2-6, the connection rupturable 40 may include protrusions 42 that are transverse to the longitudinal center line 32, and that connect overlapping regions of the proximal portion 36 with corresponding regions in the distal portion 34. Figures 3 and 4 show the collapsible plunger 30 before breaking the breakable connection 40. Figures 5 and 6A-6B show the collapsible plunger 30 after the breakable connection 40 has been activated. The protuberances 42 are constructed so as to withstand shear forces of typical use generated when a user sucks fluids into the fluid passage 24, or expels them through the hole 24 during normal use in medical procedures. However, the application of a certain breaking force indicated by the arrow F in Figure 6A, which should not be so small as to endanger the unintentional activation of the breakable connection 40 during the application of force during normal use , not too large as to impose excessive effort on the user, the breakable connection 40 is activated. That is, when a user exerts pressure on the thumb flange 37 with the intention of disabling the syringe 10 using additional force, the protuberances 42 intersect the distal portion 34. Thus, the breaking force is the total force that includes the force applied in normal use plus some additional force required to break the breakable connection. As a result, the proximal portion 36 is mechanically disconnected from the distal portion 34, crushing the plunger, effectively disabling the distal portion 34 and thereby rendering the syringe 10 unusable. The breaking force depends on various dimensions of the syringe barrel and the plunger, the viscosity of the liquid dispensed and the mechanical and hydraulic forces encountered in the filling and administration process. If the breakable connection is too weak, the proximal and distal portions will separate during normal use of the syringe, and if the force necessary to break the breakable connection is too high, the user may not be able to easily break the breakable connection as intended. The skilled person can select the appropriate materials and / or connections to provide the appropriate break force to cause the connection to break and the plunger to fold for the design and / or use of a particular syringe. To prevent spraying from the passage of fluid 24 or lumen of a needle attached to the syringe that would otherwise be produced from the most distal end 39 of the proximal portion 36 that impacts the distal portion 34 after activation of the connection 40, the piston 30 is provided with a pulse reduction system 50. As shown in FIGS. 2-6, in the proximal portion 36 one or more first braking surfaces 52 may be disposed which may be located within the distal region of the proximal portion 36. The first braking surface 52 may be slightly inclined with respect to the >; longitudinal center line 32 so that the first braking surface 52 is more distant from the longitudinal center line 32 along the distal direction. The first braking surface 52 can define a relatively rough finish to increase the coefficient of friction of the first surface 52. The distal portion 34 is provided with one or more corresponding second braking surfaces 54, which are aligned with the first braking surfaces 52, and which may be disposed within the proximal region of the distal portion 3. The second braking surfaces 54 can also define roughened surfaces to increase their coefficients of friction. The braking surfaces 52, 54 may be located adjacent the breakable connection 40. As shown in Figures 5 and 6, when the breakable connection 40 is activated, the proximal portion 36 moves along the longitudinal center line 32. with respect to the distal portion 34. There is, immediately after the activation of the breakable connection 40, between the proximal portion 36 and the distal portion 34 a relative movement that places the braking surfaces 52, 54 in contact with each other. The first braking surface 52 thus slides against the second braking surface 54. The friction developed between the first braking surface 52 and the second braking surface 54 creates a resistance to movement between the proximal portion 36 and the distal portion. 34. The wedge-shaped alignment of the first braking surface 52 and the second braking surface 54 with respect to the longitudinal centerline 32 causes the resistance to movement to increase as a function of the distal movement of the portion. next 36 along the longitudinal center line 32 with respect to the distal portion 34. This movement resistance force tends to slow down the relative movement between the proximal portion 36 and the distal portion 34, and thus acts as a shock absorber that reduces the contact impulse between the proximal portion 36 and the distal portion 3. It will be appreciated that, prior to activation of the breakable connection 40, there is an interval 56, which will be called the contact interval, between the proximal portion 36 and the distal portion 34 through which the proximal portion 36 advances after activation. of the breakable connection 40. In the absence of any type of impulse reduction system 50, when this contact interval is closed, contact between the respective surfaces making up the contact interval gives rise to a pulse that compresses the stop 38, and thus resulting in a pronounced ejection of material from the fluid passage 24. The exact position of this contact gap, and its width along the longitudinal center line 32, will depend on the specific geometrical configurations of the proximal portion 36 and the distal portion 34. For the embodiment illustrated in Figs. 2-6, and with specific reference to Fig. 4, the contact interval 56 extends from the end more distal 39 of the proximal portion 36 along the longitudinal centerline 32 to the surface 57 at the distal portion 34. The width, measured along the longitudinal centerline 32, of the contact interval 56 may be larger that the interval 58, also measured along the longitudinal center line 32, separates the most distal end of the first braking surface 52 from the closest end of the second braking surface 54 before the activation of the breakable connection 40 As a result, the impulse reduction system 50 has a wide distance along the longitudinal center line 32 to develop a braking force that slows down the relative movement between the proximal portion 36 and the distal portion 34, and thus, it reduces the contact impulse between the proximal portion 36 and the distal portion 34 to reduce the spraying of fluids from the fluid passage 24. Other types of mechanism can be used. We are shock absorbers to reduce the impulse developed between the proximal portion and the distal portion. For example, an elastic element may be disposed within a range separating the proximal portion of the distal portion. When the elastic member is compressed by the proximal portion, the elastic member reduces the speed of relative movement between the proximal portion and the distal portion, and thereby reduces the contact impulse between the proximal portion and the distal portion. An embodiment using an elastic element is illustrated in Figures 7 and 8. A collapsible plunger 100 is similar to the collapsible plunger 30 discussed above, having a proximal portion 110 connected to a distal portion 120 by means of a breakable connection 130. A The compressible elastic element 140 is disposed in a range between the proximal portion 110 and the distal portion 120. Specifically, the elastic member 140 is disposed adjacent the breakable connection 130, and just forward of the breakable connection in the distal direction. When the breakable connection 130 is separated from the distal portion 120, the proximal portion 110 begins to advance in the distal direction. When the proximal portion 110 advances, it compresses a first arm 142 of the elastic element towards a second arm 144 of the elastic element. The elastic member 140 creates a force that resists this compression, and thus slows the forward speed of the proximal portion 110. The elastic member 140 thus acts as a shock absorber that reduces the shock associated with the activation of the breakable connection 130, and thus reducing the contact impulse of the proximal portion 110 impacting the distal portion 120. An alternative embodiment using elastic elements as shock absorbers is illustrated in Figures 9 and 10. A collapsible plunger 200 uses springs 240 arranged at - those between the proximal portion 210 and the distal portion 220 to reduce the contact pulse of the proximal portion 210 which strikes the distal portion 220 when the breakable connection 230 is activated. In particular, the springs 240 may be disposed proximally adjacent to the breakable connection 230. Naturally, in both embodiments illustrated in Figures 7-8 and 9-10, any suitable elastic devices or devices may be used to slow relative movement between the proximal portion and the distal portion. It falls within the scope of the present invention to include plungers and plugs that are formed separately or integrally from the same or different materials such as two-color molding, or that are formed separately from identical or different materials and are joined together by mechanical means , adhesives, ultrasonic welding, heat sealing or other suitable means. The plugs are preferably made of elastomeric material such as natural rubber, synthetic rubber, thermoplastic elastomers and combinations thereof. It is understood that the plunger of the present embodiment simply illustrates these multiple possibilities. In use, the syringe of this embodiment can be filled from a vial, ampoule or other suitable reservoir using known safe methods. According to embodiments of the invention, the plunger can be moved back and forth along the barrel as many times as necessary to adequately fill the syringe barrel. For example, the syringe barrel can be filled with sterile water and the sterile water can then be injected into a vial containing a lyophilized medication which is then sucked back into the syringe barrel. Many single use syringes of the prior art only allow a close movement of the plunger with respect to the barrel. With these disposable syringes, once the plunger moves in a direction distal to the barrel, it can no longer be removed. Therefore, it is not possible to mix sterile water and a lyophilized medication as described above. Although the foregoing refers to embodiments of the present invention, other embodiments of the invention can be devised without departing from its basic scope, and its scope is determined by the claims that follow.