Patent Publication Number: US-2018043088-A1

Title: Compact medical infusion pumps

Description:
TECHNICAL FIELD 
     Embodiments of this disclosure generally relate to compact medical infusion pumps. More particularly, embodiments of this disclosure relate to compact medical infusion pumps and related systems and methods, which can be used in or with syringe pumps, ambulatory infusion pumps, and similar medical infusion devices. 
     BACKGROUND 
     In the field of medical infusion devices including “syringe pumps” and “ambulatory infusion pumps”, typically a pre-filled fluid syringe or reservoir is mechanically driven or controlled by a microprocessor to deliver a prescribed amount or dose of a drug or fluid at a controlled rate to a patient through an infusion line fluidly connected to the syringe or reservoir. Drugs or fluids delivered to a patient by way of syringe pumps and ambulatory infusion pumps can include, but are not limited to: therapeutic agents; nutrients; drugs; medicaments such as antibiotics, blood clotting agents, and analgesics; and other fluids. The devices can be used to introduce the drugs or fluids into patients&#39; bodies utilizing any of several routes such as, for example, intravenously, subcutaneously, arterially, or epidurally. 
     Examples of syringe pumps and related components are disclosed in U.S. Pat. No. 4,978,335 titled “Infusion Pump with Bar Code Input to Computer,” U.S. Pat. No. 8,182,461 titled “Syringe Pump Rapid Occlusion Detection System,” and U.S. Pat. No. 8,209,060 titled “Updating Syringe Profiles for a Syringe Pump.” Each of these patents is hereby incorporated by reference in its entirety. As used throughout this disclosure, the term “syringe pump” is intended to generally pertain to any device which acts on a syringe to controllably force fluid outwardly therefrom. As used throughout this disclosure, the term “ambulatory infusion pump” is intended to generally pertain to any device that acts on a reservoir to controllably force fluid outwardly therefrom, or otherwise regulate a flow of fluid to an ambulatory patient. 
     As with other technologies, throughout the evolution of infusion devices there has been increasing demand for reduction in their physical dimensions and overall sizes. However, reducing the dimensions and sizes of infusion devices has been problematic. For example, syringe pump dimensions and sizes may be limited or dictated by syringe sizes and the size of components necessary to manipulate these syringes. A typical syringe pump has a lead screw that actuates a plunger driver mechanism, which in turn acts on a plunger in the syringe to move the plunger forwardly and thereby dispense fluid outwardly from the syringe. A relatively large syringe, such as, for example, a 60 mL syringe, can require 5 inches of linear movement or travel of the plunger driver to deliver an entire volume of fluid from the syringe. Thus, the pump would need to be sufficiently large to accommodate 5 inches of linear travel of the plunger. Furthermore, when a 60 mL syringe is full, it may have an effective length of about 10 inches resulting from a syringe column or reservoir length of 5 inches plus a corresponding plunger length of about 5 inches to provide travel forwardly within the reservoir to force fluid outwardly therefrom. Thus, when a full 60 mL syringe is installed in a syringe pump, a total linear distance occupied by the combination may exceed 10 inches. Not only can an extended syringe arrangement be problematic based on the considerable length of physical space occupied on one side of the pump, but further the stability and mechanical integrity of such an extended arrangement can also be problematic. 
     It would therefore be useful and advantageous to provide pump mechanisms for infusion devices, such as, for example, syringe pumps, which would be compact, convenient, and provide desired stability and mechanical integrity in accurately delivering infusates to patients. 
     SUMMARY 
     This disclosure describes novel and inventive compact medical infusion pumps and related systems and methods, which can be used in or with syringe pumps, ambulatory infusion pumps, and similar medical infusion devices. In general, medical infusion pumps having split drive mechanisms provide compact pump arrangements beneficial to medical environments of limited space, and to stable, accurate fluid delivery. 
     In one embodiment, a compact medical infusion pump includes a base unit and a compact pump mechanism coupled to the base unit. The base unit includes a first stationary side panel and a second stationary side panel, and a drive train assembly generally centrally located in the base unit. The compact pump mechanism includes a carriage member, a plunger driver, and a rotatable drive member. The carriage member is shaped to support a medical syringe, movable in a first linear direction relative to the base unit, and fixed to a first guide rod arm that extends through the first stationary side panel. The plunger driver is shaped to selectively engage a plunger portion of the medical syringe, moveable in a second linear direction opposite the first linear direction, and fixed to a second guide rod arm that extends through the second stationary side panel. Further, the rotatable drive member is centrally located with respect to the base unit and driven by the drive train assembly. The rotatable drive engages both the first guide rod arm and the second guide rod arm to translate the carriage member and the plunger driver in opposite directions simultaneously, or approximately so, when rotated. 
     In another embodiment, a compact medical syringe pump includes a base unit, a slideable carriage assembly, and a slideable plunger assembly. The slideable carriage assembly supports and selectively translates a barrel portion of a syringe relative to the base unit. The slideable plunger assembly supports and selectively translates a plunger driver member that engages a plunger portion of the syringe. Further, the slideable carriage assembly moves in an oppositely-disposed, coordinated linear manner relative to the slideable plunger assembly, so as to control dispensing of fluid from the syringe. The slideable plunger assembly moves at an equal distance and speed to the slideable carriage assembly when expanded and retracted. 
     A further embodiment relates to a compact medical syringe pump, including a lower stationary base unit and an upper syringe manipulation assembly. The lower stationary base unit having a first side panel and a second side panel and a drive train assembly. The upper syringe manipulation assembly disposed above the lower stationary base unit in a two-part split structure that extends and retracts in accordance with the size of a syringe supported on the assembly. The upper syringe manipulation assembly is operatively coupled in an arrangement that extends and retracts equally from the first side panel and the second side panel of the stationary housing when adjusted. 
     An embodiment includes a compact medical syringe pump including a base unit and a compact pump mechanism. The compact pump mechanism is coupled to the base unit and includes a first longitudinal half screw, a second longitudinal half screw, a drive nut, a plunger driver, and a carriage. The first longitudinal half screw having a first thread orientation. The second longitudinal half screw having a second thread orientation that is opposite to the first thread orientation. The first and second half screws are substantially parallel to each other and together comprise a lead screw. The drive nut has an interior surface including both the first thread orientation and the second thread orientation, the nut being rotatably engaged with the first and second half screws. The carriage is coupled to the first half screw and the plunger driver is coupled to the second half screw. Further, when the drive nut rotates, the first half screw moves in a substantially linear direction and the second half screw simultaneously, or approximately so, moves in a substantially linear direction that is opposite to movement of the first half screw, with the carriage and the plunger driver thereby moving in substantially parallel, opposite directions corresponding to movements of the first and second half screws respectively. 
     In an embodiment, a compact pump mechanism includes a rotatable drive member, a first track, a second track, a plunger driver, and a carriage. The first track being movably engaged with the rotatable drive member, the first track further being longitudinally moveable by rotation of the rotatable drive member. The second track being movably engaged with the rotatable drive member, the second track further being substantially parallel to the first track and longitudinally moveable by rotation of the rotatable drive member. The carriage coupled to a first guide rod arm providing the first track. The plunger driver coupled to a second guide rod arm providing the second track. When the rotatable drive member rotates, the first track moves in a substantially linear direction and the second track simultaneously, or approximately so, moves in a substantially linear direction that is opposite to movement of the first track, with the carriage and the plunger driver thereby moving in substantially parallel, opposite directions corresponding to movements of the first and second tracks respectively. 
     Another embodiment includes a method of compact infusate delivery. The method includes loading a syringe having a barrel portion filled with fluid infusate and a plunger portion into a syringe pump having a split drive assembly. The method further includes moving a barrel portion of a syringe in a first direction relative to a base unit of a syringe pump using the split drive assembly. The method also includes moving a plunger portion of the syringe in a second direction, opposite that of the first direction, relative to the base unit of the syringe pump using the split drive assembly, the barrel portion and the syringe portion being moved in a simultaneous, or approximately so, coordinated fashion with respect to one another. The method also includes delivering the fluid infusate with the syringe pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is an illustration of an example of a syringe pump of the prior art. 
         FIG. 2  is an example of a syringe pump including a compact pump mechanism, according to an embodiment. 
         FIG. 3  shows a cross-sectional perspective view of the syringe pump of  FIG. 2  in which a top portion of the syringe pump has been removed, according to an embodiment. 
         FIG. 4  is a plan view of some components of an example of a compact pump mechanism, according to an embodiment. 
         FIG. 5  is a plan view of some components of an example of a compact pump mechanism, according to an embodiment. 
         FIG. 6  is an example of a syringe pump including a compact pump mechanism depicting some internal components of the compact pump mechanism within the syringe pump, according to an embodiment. 
         FIG. 7  is an example of a syringe pump including a compact pump mechanism, according to an embodiment. 
         FIG. 8  is an example of a syringe pump including a compact pump mechanism, according to an embodiment. 
         FIGS. 9A-C  show an example of a cross-threaded nut arrangement for use in a compact pump mechanism, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments of the invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive. 
     Compact pump mechanisms described in greater detail by way of examples herein can be beneficial in numerous ways. For example, in various embodiments, a compact pump mechanism may reduce the overall size of a medical infusion pump, reduce a length of extension of a particular component from a pump housing in a particular direction, provide greater stability and mechanical integrity to components extending from a pump housing due to short cantilever length of support members, or provide a desirable centralized syringe and pump drive arrangement. As will be described by example herein, a compact pump mechanism can be achieved by effectively separating or “splitting” a medical infusion pump drive into two substantially parallel and oppositely-moving components. Accordingly, embodiments disclosed herein describing a “split drive” assembly, mechanism, or arrangement refer to embodiments in which an actuating member translates multiple non-continuous components to govern device motion. 
     Referring to  FIG. 1 , an example of a syringe pump  10  of the prior art is shown. Typically, such a known pump  10  includes a base unit  100  having a user interface comprising a display screen and input controls such as push-buttons and the like as are visible in the drawing. Pump  10  also includes a curved surface or cradle  110  for receiving and supporting a barrel  112  of a syringe  114 , a clamp  116  for selectively securing barrel  112  in cradle  110 , and a plunger driver  120  for removably coupling a plunger  122  of syringe  114  to pump  10  and linearly driving plunger  122  within barrel  112 . In use of pump  10 , syringe  114  containing a desired volume of a flowable substance is installed by way of placement of barrel  112  in cradle  110 , with barrel  112  being removably and selectively secured therein by clamp  116 . Plunger driver  120  is removably coupled to a distal end of plunger  122  of syringe  114 . Upon activation and operation of pump  10 , driver  120  eventually advances forwardly (to the left in the drawing) which causes plunger  122  to also move forwardly in barrel  112  and thereby cause the flowable substance to be forced outwardly from syringe  114  at outlet  124 . Tubing  132  is connected at outlet  124  to serve as a conduit for the flowable substance from syringe  114  to a patient  134 . 
     In such known syringe pumps, a length of linear travel of plunger  122  in barrel  112  largely depends upon a corresponding possible length of linear travel of plunger driver  120  and that the entire length of travel of plunger driver  120  occurs in one direction. Thus, the overall dimensions of known syringe pumps are typically dependent upon maximum lengths of possible travel and directions of travel of their plunger drivers. With reference to  FIG. 1 , if plunger  122  of syringe  114  has a maximum travel of 5 inches within barrel  112 , plunger driver  120  would therefore extend approximately 5 inches outwardly away from the pump (to the right in the drawing) when syringe  114  is installed in pump  10  as shown. 
     Referring now to  FIG. 2 , an example of a syringe pump  20  having a compact pump mechanism  201  is shown. The syringe pump  20  generally includes a base unit  200  (also alternatively referred to as a lower housing or a lower stationary base unit in this disclosure) and a compact pump mechanism  201  (also alternatively referred to as an upper syringe manipulation assembly in this disclosure). The base unit  200  is coupled to the compact pump mechanism  201 , where the compact pump mechanism  201  is generally located above or partially within the upper portion of the base unit  200 . Such a base unit  200  would typically be equipped with a user interface (not shown in  FIGS. 2-3 and 6 ) comprising a display screen and input controls. The base unit  200  generally comprises a housing having a first stationary side panel  204  and a second stationary side panel  206  at opposite ends of the base unit  200 . In the example of  FIG. 2 , the compact pump mechanism  201  includes a carriage  210  that supports a barrel  212  of a syringe  214 , and a plunger driver  220  that removably couples a plunger  222  of the syringe  214  to pump  20 . The syringe  214  is generally a replaceable component that removably fits within the compact pump mechanism  201  and is not necessarily or explicitly a component of the mechanism itself. In some embodiments, however, the syringe  214  may be considered part of the compact pump mechanism  201 . The carriage  210  is at least partially supported by a first guide rod arm  226  that is generally parallel to the carriage  210  and extends through the first stationary side panel  204  of the base unit  200 . The carriage  210  generally moves in a linear path in accordance with the positioning of first guide rod arm  226 . The plunger driver  220  is supported by a second guide rod arm  228  that is generally disposed parallel to the first guide rod arm  226  and extends through the second stationary side panel  206  of the base unit  200 . The plunger driver  220  generally moves in a linear path in accordance with the positioning of a second guide rod arm  228 , with the path of linear travel of the carriage  210  generally being opposite that of the plunger driver  220 . The path may be generally perpendicular to the disposition of the first and second stationary side panels  204  and  206  of the base unit  200  in some embodiments. Although not illustrated, a clamp could also be provided for removably securing the barrel  212  of the syringe  214  in carriage  210 . 
     Generally internal to the compact pump mechanism  201  is a rotatable drive member  230 , as shown in  FIG. 3 . Rotatable drive member  230  may be embodied in various shapes, designs, and configurations. In some embodiments, the rotatable drive member  230  may comprise a toothed sprocket as part of a rack and pinion type arrangement that includes the first guide rod arm  226  and second guide rod arm  228  although other shapes, designs, and configurations are possible as well. Mechanism  201  further includes a first track  240  as part of a first guide rod arm  226  that is movably engaged with rotatable drive member  230 . As particularly depicted in  FIG. 4 , track  240  may include slots  242  that mechanically engage the toothed sprocket of rotatable drive member  230 . Track  240  is thereby longitudinally moveable by rotation of rotatable drive member  230 . Referring again to  FIGS. 2 and 3 , carriage  210  is coupled to first guide rod arm  226  and first track  240 . Mechanism  201  further includes a second track  245  of second guide rod arm  228  that is also movably engaged with rotatable drive member  230 . Similarly to first track  240 , second track  245  includes slots  247  (again, as particularly depicted in  FIG. 4 ) that mechanically engage the toothed sprocket of rotatable drive member  230 . Second track  245  and second guide rod arm  228  are thereby also longitudinally moveable by rotation of rotatable drive member  230 . Plunger driver  220  is coupled to track  245  of second guide rod arm  228 . 
     With reference to  FIGS. 2-4 , it is to be appreciated and understood therefore that when rotatable drive member  230  rotates, first track  240  moves in a substantially linear direction and second track  245  simultaneously, or approximately so, moves in a substantially linear direction that is opposite to movement of first track  240 . Thus carriage  210  and plunger driver  220 , since they are coupled to tracks  240  and  245  respectively as aforesaid, move in substantially parallel but opposite directions corresponding to such opposite movements of their tracks  240  and  245  and guide rod arms  226  and  228 , respectively. 
     When using syringe pump  20  and compact pump mechanism  201 , a syringe  214  containing a desired volume of a flowable substance can be installed by way of removable placement or coupling of the syringe barrel  212  in carriage  210  (with, optionally, the barrel being secured by a clamp as aforementioned). Further, an end of a plunger  222  in the syringe  214  is removably coupled to plunger driver  220 . After activation and during operation of pump  20 , drive member  230  rotates which thereby causes tracks  240  and  245  to move in opposite directions. For example, when drive member  230  rotates in a clockwise (CW) direction as shown in the drawings, track  245  moves forwardly (to the left in  FIGS. 2 and 3  or upwardly in  FIG. 4 ) while track  240  moves backwardly (to the right in  FIGS. 2 and 3  or downwardly in  FIG. 4 ). Such movements would therefore advance plunger driver  220  forwardly (to the left in  FIGS. 2 and 3 ) toward carriage  210 , and simultaneously, or approximately so, move carriage  210  backwardly (to the right in  FIGS. 2 and 3 ) toward plunger driver  220 . Together, these movements would move the plunger forwardly in the barrel of the syringe and thereby cause the flowable substance to be forced outwardly therefrom as desired. It is to be appreciated and understood, therefore, that a compact pump mechanism, as described by example or otherwise contemplated herein, effectively provides a medical infusion pump that enables a full range of plunger travel in a device that can be relatively smaller than known pumps. 
     It is also to be appreciated and understood that mechanism  201  can be used for reversing direction of a plunger&#39;s travel such as when, for example, an occlusion is detected by the pump and the plunger is commanded to, intentionally, move backwardly or retreat a desired distance until the occlusion has been removed. In such an occurrence, drive member could be commanded to rotate in a counter-clockwise (CCW) direction as shown in  FIGS. 2-4 , which would cause track  245  to move backwardly (to the right in  FIGS. 2 and 3  or downwardly in  FIG. 4 ) while track  240  moves forwardly (to the left in  FIGS. 2 and 3  or upwardly in  FIG. 4 ). Such movements would therefore move plunger driver  220  backwardly (to the right in  FIGS. 2 and 3 ) away from carriage  210 , and simultaneously, or approximately so, move carriage  210  forwardly (to the left in  FIGS. 2 and 3 ) away from plunger driver  220 . Together, these movements would move the plunger backwardly in the barrel of the syringe and thereby stop, or possibly even reverse, the flow of the flowable substance from the syringe as may be desired in a particular situation. 
     Referring now to  FIG. 5 , therein illustrated is another example of certain components of a compact pump mechanism  301 . In this example of mechanism  301 , although not specifically illustrated but similarly to  FIGS. 2 and 3 , a carriage supports a barrel of a syringe and a plunger driver removably couples a plunger of the syringe to a pump including mechanism  301 . A clamp could also be provided for removably securing the barrel of the syringe in the carriage. Mechanism  301  includes a rotatable drive member  330 . In this example, rotatable drive member  330  comprises a magnetic component. Mechanism  301  further includes a first track  340  that is movably engaged with rotatable drive member  330 . First track  240  includes a material that magnetically engages the magnetic component of rotatable drive member  330 . Track  340  is thereby longitudinally moveable by rotation of drive member  330 , with the carriage (not illustrated) coupled to first track  340 . Mechanism  301  further includes a second track  345  that is also movably engaged with rotatable drive member  330 . Similarly to first track  340 , second track  345  includes a material that magnetically engages the magnetic component of rotatable drive member  330 , with the plunger driver (not illustrated) coupled to second track  345 . When rotatable drive member  330  rotates, first track  340  moves in a substantially linear direction and second track  345  simultaneously, or approximately so, moves in a substantially linear direction that is opposite to movement of first track  340 . Thus the carriage and the plunger driver, since they are coupled to tracks  340  and  345  respectively as aforesaid, move in substantially parallel but opposite directions corresponding to such opposite movements of their tracks  340  and  345  and guide rod arms  226  and  228 . Use of a pump with compact pump mechanism  301  for a syringe containing a flowable substance would be analogous to pump  20  with mechanism  201  as aforedescribed. Mechanism  301  can be used for reversing direction of a plunger&#39;s travel, analogously to pump  20  with mechanism  201  as aforedescribed. 
       FIGS. 6-8  show other examples of medical infusion pumps with compact pump designs.  FIG. 6  shows an internal view of the syringe pump  20  in which the drive train assembly  280  can be seen. The drive train  280  assembly is generally centrally located in the base unit  200  between the stationary side panels  204  and  206 . The drive train  280  comprises the motor, gears, and other components needed to drive the rotatable drive member  230 , including guide rod arms  226  and  228  and associated tracks  240  and  245 . For purposes of this disclosure the first guide rod arm  226  includes a rod-like portion  286  which extends internally and externally through the stationary side panel  204  of the base unit  200 . In this example, the first guide rod arm  226  further includes a multifaceted arm structure  288  that connects with the rod-like portion  286 . First guide rod arm  226  also includes first track  240  that interfaces with the rotatable drive member  230 . Accordingly, the combination of the first track  240 , rod like portion  286 , and multifaceted arm structure  288  comprises a first guide rod arm  226 . Similarly, the combination of second track  245 , rod-like portion  287 , and multifaceted arm structure  289  comprise the second guide rod arm  228 . Guide rod arms  226  and  228  can be embodied in various shapes and sizes in various embodiments and are not limited to those structures disclosed herein. 
     The central location of the drive train  280  and centralized drive movement of the rotatable drive member  230  provides a number of advantages. Known syringe pumps and similar devices generally position the motor and drive at one side of a pump housing unit in order to have a sufficiently long distance of possible plunger driver travel in one direction from a stationary or otherwise fixed carriage relative to base unit  200  to accommodate a fully extended or un-advanced syringe plunger with, for example, a filled syringe that is ready for use in dispensing a medicament contained in the syringe to a patient. Past guide rod arm members would extend a considerable distance from the drive component of the motor that was roughly equivalent to the length of such an extended or un-advanced syringe plunger. 
     Those of skill in the infusion arts will also appreciate that, although somewhat supported internally or structurally, typical cantilever arm lengths are significant in extension of plunger drivers in known pumps. Long cantilever arms supporting the plunger drivers of known pumps have potentially caused operational disadvantages related to, for example, stability and precision of components in those pumps. But in comparison, the presently disclosed examples of a split-drive arrangement advantageously includes two relatively short guide rod arms  226  and  228 . Each of these guide rod arms  226  and  228  provide, as compared to known pumps, a much reduced cantilever arm extending from the central rotatable drive member  230  or respective stationary side panel  206  at one side to the plunger driver  220 . Likewise the cantilever arm extending from the central rotatable drive member  230  or side panel  204  at one side to the end portion of the carriage  210  provides a much reduced length as comparted to known pumps. Accordingly, greater stability and accuracy can be achieved when a mechanism with reduced cantilever arms extend from the base unit  200 . In some embodiments, the length of the second guide rod arm  228  extending between stationary side panel  206  of the base unit  200  and the plunger driver  220  serves as a cantilever arm having a length less than the length of the plunger portion  222  of the medical syringe  214 . 
     Moreover, it is to be appreciated and understood that the novel and inventive arrangement of components according to subject matter hereof generally provides for approximately equal but opposite linear travel of the plunger driver  220  and carriage member  210  in a coordinated fashion from either side of the base unit  200  depending upon the size of the inserted syringe. In some embodiments, the first guide rod arm  226  extends partially beyond the first stationary side panel  204  and the second guide rod arm  228  extends partially beyond the second stationary side panel  206  when the syringe  14  is full and the plunger  222  extends outwardly from barrel  212 . The disclosed arrangement does not largely extend only one portion of the pump mechanism  201  from only one side of the pump  20 . Accordingly, any potential interference caused by extending features would generally be balanced and more restricted to the immediate proximity of the base unit  200  of the pump  20  itself due to centering. The pump  20  is largely a self-centered device with respect to lateral displacement of components from the sides. As compared to mechanisms of known pumps, this centering effect provides convenient and compact syringe pumps that are less likely to interfere with other devices and medical professionals attending to a patient connected to the novel and inventive pumps described by example or otherwise contemplated herein. The compactness provided can be extremely important in environments, such as emergency room settings, in which numerous devices and medical professionals are surrounding a patient and thus physical space is limited. 
     Accordingly, in some embodiments the compact medical syringe pump  20  includes a lower stationary base unit  201  with side panels  204  and  206  on the sides of a drive train assembly  280  that is generally centered in the base unit  201  between these side panels. Located above the base unit  201  is an upper syringe manipulation assembly  201  (or compact pump mechanism) that includes a two-part split structure that extends and retracts in accordance with the size or contained medicament volume of a syringe  214  thereby supported. The upper syringe manipulation assembly  201  is operatively coupled to extend and retract equally from the first side panel  204  and the second side panel  206  of the base unit  200  when the assembly is adjusted. Moreover, the upper syringe manipulation assembly  201  provides two separate cantilever support arms to support a syringe coupled to the two-part split structure. 
       FIG. 7  shows another example of an embodiment of a compact medical syringe pump  20  having a base unit  700  and compact pump mechanism  701  generally similar to that disclosed in  FIG. 2 . The compact pump mechanism  701 , however, contains a split drive with arm members  726  and  728  associated with the opposite sides of rotatable drive member  730 . For example, the first drive arm  726  that supports the carriage  710  includes and is associated with a track  745  located on the near side of the device in the drawing. The second drive arm  728  that supports the plunger driver  720  includes and is associated with the track  740  located on the far side of the pump. In general, however, rotation of the rotatable drive member  730  effectively urges the carriage  710  and plunger driver  720  either toward one another or away from one another depending upon the direction of rotation. Another feature that can be seen in the pump  20  of  FIG. 7  is a compact pump mechanism  701  that is able to retract the plunger driver  720  and end of the carriage  710  to a recessed arrangement. Specifically, they are recessed to be flush with or narrower than the ends of stationary side panels  704  and  706 . In such an embodiment, not even the plunger driver  720  will cause protrusions or interference beyond the spatial footprint of the base unit  700 . 
       FIG. 8  illustrates another embodiment of a compact medical syringe pump  20  having a base unit  800  and compact pump mechanism  801  generally similar to that disclosed in  FIG. 7 . The compact pump mechanism  801 , specifically depicts the tracks  840  and  845  on the guide rod arms  826  and  828  in greater detail. As shown on in  FIG. 8 , the slots  842  and  847  are able to mate with and interact with the teeth  890  of the rotatable drive member  830 . Slots and corresponding teeth on the rotary drive member  830  can be varied to best accommodate the type of precise motion required. 
     Although not illustrated in  FIGS. 2-8 , it is to be understood that the aforedescribed examples of tracks in compact pump mechanisms could be moveably coupled or slideably secured in pumps in which compact pump mechanisms have been installed by way of, for example, longitudinal channels or slots formed in surfaces of the pumps on opposite sides of the rotatable drive members. Furthermore, but although also not illustrated in  FIGS. 2-8 , it is to be understood that rotation of the rotatable drive members could be provided by, for example, electrically-powered stepper motors in the pumps that are electro-mechanically coupled to the rotatable drive members by any suitable techniques. 
     Referring now to  FIGS. 9A-9C , therein illustrated is another example of a compact pump mechanism  901 . Specifically,  FIG. 9A  discloses a central cross threaded nut mechanism in assembled relation.  FIG. 9B  discloses the central cross threaded nut mechanism in an assembled relation in which a portion of the mechanism has advanced axially in opposing forward and backward directions based upon rotation of the central nut.  FIG. 9C  discloses the central cross threaded nut mechanism in an exploded view, such that each of the components can be better understood. Such a cross threaded nut mechanism could be implemented within a syringe pump to replace the centralized moving structure of a compact pump mechanism. For example, instead of a centrally mounted rack and pinion type assembly as disclosed by example in  FIGS. 1-8  herein, the cross thread nut mechanism could replace the rotatable drive mechanism with a nut that is driven by rotation proximate the center of the base unit. Further the guide rod arms could be at least partially replaced by the half lead screw structures discussed below. Using this cross threaded nut arrangement allows for another type of split drive device that can effectively provide a pump with enhanced compactness and advantageous shape. 
     In this example of mechanism  901 , although not specifically illustrated but similar to  FIGS. 2 and 3 , a carriage would support a barrel of a syringe and a plunger driver would removably couple a plunger of the syringe to a pump including mechanism  901 . Further, a clamp could also be provided for removably securing the barrel of the syringe in the carriage. The mechanism  901  shown in  FIGS. 9A-C  includes a drive nut  930  having an interior surface that includes a first thread orientation  932  and a second thread orientation  934  (as shown, in particular, in  FIG. 9C ). In this example, the first thread orientation comprises left-handed threads and the second thread orientation comprises right-handed threads. Mechanism  901  further includes a first longitudinal half screw  940  having a first thread orientation or left-handed threads, and a second longitudinal half screw  945  having a second thread orientation or right-handed threads. First and second half screws  940  and  945  are substantially parallel to each other and together comprise a lead screw  950  (as shown, in particular, in  FIG. 9A ). Drive nut  930 , having an interior surface that includes both the first and second thread orientations or left-handed and right-handed threads as aforesaid, is thereby rotatably engaged with first and second half screws  940  and  945  having corresponding left-handed and right-handed threads as aforesaid, respectively. Although not illustrated, it is to be understood that the plunger driver and any associated guide rod arm can be coupled to first half screw  940 , and the carriage and any associated guide rod arm can be coupled to second half screw  945 . When drive nut  930  rotates, half screw  940  moves in a substantially linear direction and half screw  945  simultaneously, or approximately so, moves in a substantially linear direction that is opposite to movement of half screw  940 . Thus the plunger driver and carriage, since they are coupled to half screws  940  and  945  respectively as aforesaid, move in substantially parallel but opposite directions corresponding to such opposite movements of their half screws  940  and  945 . Use of a pump with compact pump mechanism  901  for a syringe containing a flowable substance would be analogous to pump  20  with mechanisms  201  or  301  as aforedescribed; and mechanism  901  can be used for reversing direction of a plunger&#39;s travel, analogously to pump  20  with mechanisms  201  and  301  also as aforedescribed. 
     Although not illustrated in  FIGS. 9A-9C , it is to be understood that rotation of the drive nuts could be provided by, for example, electrically-powered stepper motors in the pumps that are electro-mechanically coupled to the drive nuts by any suitable techniques. 
     Accordingly, operation of compact infusate delivery of many of the above embodiments of a compact syringe can be carried out by an operator accordingly to a number of steps. First, a syringe having a barrel portion filled with fluid infusate and a plunger portion is loaded into a syringe pump having a split drive assembly. A barrel portion of a syringe is moved in a first direction relative to a base unit of a syringe pump using the split drive assembly. A plunger portion of the syringe is moved in a second direction, opposite that of the first direction, relative to the base unit of the syringe pump using the split drive assembly. This is done such that the barrel portion and the plunger portion are moved in a simultaneous, or approximately so, coordinated fashion with respect to one another. The fluid infusate accordingly is able to be delivered by the syringe pump. 
     Irrespective of a particular embodiment, it is to be appreciated and understood that compact pump mechanisms that have been described by example, or which are otherwise contemplated herein, can be characterized in that they provide movement of syringe barrels and plungers at substantially equal rates, but in linearly opposite directions. Thus, these novel and inventive compact pump mechanisms thereby provide substantially steady-state rates of delivery of flowable substances outwardly from the syringes. 
     It is also to be appreciated and understood that types, components, dimensions, fabrication processes, and other particulars and parameters of aforedescribed example embodiments can be substituted for others as desired, or that accessories can be added thereto. For example, the tracks could have any desired lengths provided that they are compatible with length dimensions of pumps in which they are installed. 
     While compact pump mechanisms have been particularly shown and described with reference to the accompanying figures and specification, it should be understood however that other modifications thereto are of course possible; and all of them are intended to be within the true spirit and scope of novel and inventive devices described herein. Thus, configurations and designs of various features could be modified or altered depending upon particular embodiments. For example, the carriage and the plunger driver could be coupled to the tracks in any order. Thus, although some examples herein have described the first tracks as being coupled to carriages and the second tracks as being coupled to plunger drivers, the first tracks could instead be coupled to plunger drivers with the second tracks therefore coupled instead to carriages. In such embodiments, the CW and CCW movements of the rotatable drive members would result in movements of the tracks, and their coupled carriages and plunger drivers, that would be analogous but opposite to the aforedescribed examples. 
     Compact pump mechanisms as described by example or otherwise contemplated herein could also include combinations of the aforedescribed examples of rotatable drive members having toothed sprockets or magnetic components, and tracks having slots or materials that magnetically engage the magnetic components, respectively. In those embodiments, magnetic sprockets could be coupled to slotted tracks having materials that magnetically engage the magnetic sprockets, with such compact pump mechanisms possibly being less susceptible to vibration and external forces than, for example, conventional pump mechanisms. 
     Furthermore, although not illustrated, compact pump mechanisms as described by example or otherwise contemplated herein could also include suitable vernier or “fine adjustment” controls for or with the rotatable drive members, tracks, drive nuts, and half screws, to possibly enable more precise movement of these components when in use. 
     Regardless of particular components or modes of action, it is to be appreciated and understood that compact pump mechanisms—such as have been described by example or are otherwise contemplated herein—can provide pump mechanisms for infusion devices which would be relatively compact and which would not be necessarily be defined in dimensions or sizes by syringes installed therein. 
     It is also to be appreciated and understood that compact pump mechanisms as have been described by example or otherwise contemplated herein could potentially be used for or with virtually any devices which control the delivery or movement of flowable substances from one location to another. 
     It is further to be understood that dimensioning and scaling of the drawings herein have been chosen to clearly show details of example embodiments. Thus, in some embodiments it is possible that spacing between, or orientations of, various features might be variable and visually different from those illustrated. In any event, dimensioning and scaling could vary significantly across various embodiments of compact pump mechanisms. 
     It is additionally to be understood in general that any suitable alternatives may be employed to provide novel and inventive compact pump mechanisms such as those that are described by example or otherwise contemplated herein. 
     Lastly, compositions, sizes, and strengths of various aforementioned components of compact pump mechanisms that are described by example or otherwise contemplated herein are all a matter of design choice depending upon intended uses thereof. 
     Accordingly, these and other various changes or modifications in form and detail may also be made, without departing from the true spirit and scope of compact pump mechanisms that may be defined by the appended claims. 
     It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with an enabling disclosure for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof. For example, in embodiments described with a syringe-type infusion pump, it is to be understood that an ambulatory type pump could have been alternatively employed. 
     The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 
     Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.