Patent Publication Number: US-6655934-B2

Title: Inverted peristaltic pumps and related methods

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/277,562 entitled Inverted Preistaltic Pumps and Related Methods filed on Mar. 21, 2001, the entire disclosure of such provisional application being expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to pumping devices, related equipment and methods and more particularly to inverted peristaltic pumps, tubing kits for use with such pumps and related methods for using such pumps. 
     BACKGROUND OF THE INVENTION 
     Numerous types of peristaltic pumps have been known in the prior art. In general, peristaltic pumps are devices that transfer fluid through one or more elongate, at least partially flexible, tube(s) by compressing each tube in a peristaltic manner. Such peristaltic compression of the tube serves to push or pull fluid through the lumen of each tube. The fluid transport is effectuated by moving the region of compression along the length of the tube. Such movement of the region of compression is typically achieved by way of one or more rollers driven by a mechanical drive mechanism that guides each roller along a re-circulating path. The path of each roller is typically configured such that each roller will pinch-off the inner lumen of the tube it moves along a portion of the length of the tube. Most commonly the roller rotates in a circular path about a central axis of rotation. 
     In order for a peristaltic pump to function as a positive displacement pump, it must effect at least first and second regions of compression on each tube and the second region of compression must be created before the fist region of compression is released. The length of the tube between the first and second regions of compression define a period. 
     Typically, the each peristaltic pump tube is mounted within the in a U-shaped or arc-shaped configuration whereby some portion of each tube overlaps a potion of a path traveled by a roller. In some peristaltic pumps, the desired compression or pinching-off of each tube is achieved by compressing the pump tube(s) between the roller(s) and an adjacent stationary member (a backing plate). In other peristaltic pumps, the desired compression or pinching-off of the tube(s) is achieved by stretching the tubes over the roller(s), without involvement of any stationarily member or backing plate, however such designs can be somewhat disadvantageous due to the propensity for most plastic tubes to stretch or creep thereby resulting in loosening of the tube(s) over time. 
     One advantageous feature of virtually all peristaltic pumps is that the fluid does not contact the pump&#39;s mechanical drive mechanism since the fluid is always confined within and moved through the flexible tube(s). Therefore, by using the peristaltic pumps for a medical application, the cost of the disposable or re-sterilizable portion of the medical instrument may be reduced. 
     One drawback associated with at least some peristaltic pumps is that the fluid outflow from a peristaltic pump tends pulsate. The prior art has included devices and methods that purport to reduce such pulsation, such as the reduced pulsation pump head described in U.S. Pat. No. 5,230,614 which has multiple rollers that compress the tube at relatively close intervals, thereby minimizing the pulsatile nature of the pump outflow. This method of fluid transfer may be costly and the wear and tear on the tubing can be high. Since each roller is collapsing a small portion of the tube at any given time, the likelihood of the tube to creep or become displaced is high. 
     Other prior art patents describe other modification to the traditional peristaltic pump designs including the use of a helical tubing arrangement as described in Canadian Patent No. 320,994, a multiple tube and cylindrical format as described in U.S. Pat. No. 5,688,112, a looped tube path as described in U.S. Pat. No. 5,630,711 and a single roller loop tube as described in U.S. Pat. No. 5,429,486. 
     The loading of the pump tubing on common peristaltic pumps is often cumbersome due to the fact that the flexible tubes are typically unsupported until loaded, and this my not be easy to maneuver into place. 
     The present invention overcomes at least some of the shortcomings of the prior art peristaltic pumps by providing peristaltic pumps that provide relatively non-pulsatile flow with tubing that is easily loadable and may be pre-mounted on a central core member. 
     SUMMARY OF THE INVENTION 
     The present invention provides new peristaltic pump devices in which the tube(s) is/are mounted on an arched or round central core member and one or more compression members (e.g., rollers, feet, a cylinder, etc.)) rotate, circulate, traverse or otherwise move about the central core member so as to cause the desired regions of compression in the pump tube(s). This arrangement results in comparatively smooth, non-pulsatile fluid transfer. Also, this arrangement allows for perpendicular rather than tangential compression of the tube(s), thereby minimizing the potential for creeping of the tube(s). In the peristaltic pumps of the present invention, the central core member may be stationary and the compression member(s) (e.g., rollers, feet, a cylinder, etc.) may rotate about the stationary core member. In pumps of the present invention, the tub(s) may be formed or mounted on a reusable or disposable core member to form a unitary tubing/core member assembly that is insertable as a unit or cartridge into the pump, thereby eliminating leakage as tubing is replaced and resultant potential for contamination of the pump components and/or the user&#39;s body. Also, in pumps of the present invention, the central core member (e.g, central backing plate) may provides an effective means to maintain or change the temperature of fluid being pumped through the pump tube(s) and, thus, may incorporate or include a heating or cooling element. 
     In accordance with the present invention, there are provided peristaltic pumps that are of an inverted design (i.e., wherein the fluid conduit (e.g., tubing) is mounted on a central core and a compression member revolves at least part way around the central core to compress the fluid conduit, thereby propelling fluid through the fluid conduit and methods of pumping fluids using such pumps. The inverted peristaltic pumps of the present invention provide economical and controlled fluid delivery with low pulsation and have applicability in many medical and non-medical applications. 
     Further in accordance with the present invention, the compressible fluid conduit (e.g., tubing) may be mounted or formed on the central core such that it is in abutting contact with the outer surface of the central core, thereby maintaining the desired size and shape of the fluid conduit with minimal stretching or deformation of the fluid conduit during use. Also, changing of the fluid conduit or tubing is simplified by the present invention because the central core having the compressible fluid conduit (e.g., tubing) pre-mounted or pre-formed thereon may be simply inserted into the pump in a position whereby the compression member will rotate at least partially around the core, thereby causing peristaltic compression of the fluid conduit (e.g., tubing) against the central core. Also, the central core may be provided with heating or cooling elements so as to heat or cool fluid as it passes through the fluid conduit(s) mounted or formed on the central core. 
     Still further in accordance with the present invention, in at least some embodiments, one or more grooves may be formed in the outer surface of the central core and the fluid conduit (e.g., tubing) may be mounted or formed within such groove(s). In some embodiments, a single helical groove may be formed in the outer surface of the core and the fluid conduit (e.g., tubing) may be mounted or formed within such helical groove. In many embodiments, it will be desirable for the fluid conduit (e.g., tubing) to make at least one full rotation around the central core. As described more fully herebelow, in some embodiments wherein the fluid conduit (e.g., tubing) is mounted or formed within groove(s), the depth of such groove(s) may vary to facilitate gradual increasing and decreasing of the amount of compression being applied to the fluid conduit as the compression member moves about the central core. In this regard, the ends of the groove(s) may be deeper than the center of the groove(s) so as to provide for gradual compression of the fluid conduit (e.g., tubing) from one end of the groove where the lumen of the fluid conduit is fully open to a point of complete compression (i.e., where the lumen of the fluid conduit is completely pinched off) followed by gradual decompression to the other end of the groove where the lumen of the fluid conduit is once again fully open. 
     These general aspects of the invention, as well as numerous other aspects and advantages of the invention, will become apparent to persons of skill in the art who read and understand the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic showing of a prior art peristaltic pump. 
     FIG. 2 is a schematic showing of one embodiment of an inverted peristaltic pump of the present invention wherein the compression member(s) comprise two (2) rollers. 
     FIG. 3 is a perspective view of the central core/tubing cartridge portion of the pump of FIG.  2 . 
     FIG. 4 is a partially rotated view of the central core/tubing cartridge of FIG.  3 . 
     FIG. 5 is a schematic showing of another embodiment of an inverted peristaltic pump of the present invention having a transversely loadable central core/tubing cartridge and an accompanying aspirant collection reservoir. 
     FIG. 6 is a schematic showing of another embodiment of an inverted peristaltic pump of the present invention wherein the compression member(s) comprise a single roller. 
     FIG. 7 is a perspective view of the central core/tubing cartridge component of the pump of FIG.  6 . 
     FIG. 8 is a partially rotated and canted view of the central core/tubing cartridge component shown in FIG.  7 . 
     FIG. 9 is a showing of the central core/tubing cartridge component shown in FIG. 7, with the tubing removed. 
     FIG. 10 is a schematic showing of another embodiment of an inverted peristaltic pump of the present invention wherein the compression member(s) comprise a single cylindrical compression member. 
     FIG. 11 is a showing of the central core/tubing cartridge component of the pump shown in FIG.  10 . 
     FIG. 12 is a cross sectional view of a pump of the type shown in FIGS. 10-11 with an associated pump drive assembly. 
     FIG. 13 is a schematic diagram of an inverted peristaltic pump of the present invention having a cylindrical core and straight cylindrical rollers. 
     FIG. 14 is a schematic diagram of an inverted peristaltic pump of the present invention having a frusto-conical core and angled, frusto-conical rollers. 
     FIG. 15 is a schematic diagram of an inverted peristaltic pump of the present invention having a frusto-conical, grooved core and angled, frusto-conical rollers. 
     FIG. 16 is a schematic diagram of an inverted peristaltic pump of the present invention having a convex-walled, grooved core sized to accommodate one full revolution of tubing and angled, concave walled rollers. 
     FIG. 17 is a schematic diagram of an inverted peristaltic pump of the present invention having a convex-walled, grooved core sized to accommodate two full revolutions of tubing and angled, concave walled rollers. 
     FIG. 18 is a shematic diagram of an inverted peristaltic pump of the present invention having a frusto-conical, grooved core and angled, frusto-conical rollers, the core being designed for easy demoldability from a two-piece mold. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     I. Inverted Peristaltic Roller Pump 
     The following detailed description refers to the accompanying drawings (FIGS. 1-12) which show certain embodiments of the present invention. 
     Peristaltic roller pumps are commonly used for fluid transfer. Conventional curvilinear configurations (FIG. 1) incorporate an array of two or more rollers  120  mounted on a rotating roller carrier  125  providing for an ex-centric mount for the axis of rotation of the rollers carried thereon and therefore a circular path for said rollers. A flexible tube  110  is placed between a stationary outer shell  130  (the backing plate) and the roller assembly such that the inner lumen of flexible tube  110  is pinched-off between the roller  120  and the outer shell  130  over an occlusion region  112 . Rotation of the roller carrier  125  indirection  126  causes the occlusion region  112  to move along the axis of flexible tube  110  in direction  113 , and for rollers  120  to rotate in direction  121  due to friction in contact with the concave side of the tube. Fluid is thus pumped from tube inlet  140  to tube outlet  150 . 
     It is often desirable, for example in medical products, to be able to easily change the pump tubing. Loading of the tubing into conventional peristaltic pumps as described in FIG. 1 can be difficult. During the pumping action, the tubing tends to be pulled along its axis, and thus the inlet portion of the tubing must be secured so the tubing will not migrate. Linear peristaltic pumps were developed that address many of these issues. In a linear peristaltic pump, a flexible tube is pressed against a flat stationary shell along a linear axis by one or more moving rollers or cam-sequenced squeezing elements. For such a linear configuration, the flexible tube can be pre-stretched and mounted into a cartridge for easy installation and removal. 
     A first invention is a novel curvilinear peristaltic roller pump described in FIG. 2 configured by inverting the roller and backing plate. In this configuration, an array of two or more rollers  220  are mounted on a rotating support  225 . A flexible tube  210  is placed into a stationary pump cartridge  230 . In this novel configuration, the rollers  220  move over the convex surface of the flexible tube  210 . The flexible tube  210  is squeezed between the rollers  220  and the pump cartridge  230  to form an occlusion region  212 . In this configuration, rotation of the rotating support  225  in direction  226  causes the rollers  220  to rotate in direction  221  due to friction in contact with the convex side of the tube and for the occlusion region  212  to move along the axis of the flexible tube  210  in direction  213 . Fluid is pumped from the inlet port  242  to the outlet port  252  of the pump cartridge  230 . The pump cartridge is further described in FIGS. 3-4. In FIG. 3, flexible tube  210  is translucent, allowing visualization of tubing connector  255 . In pump cartridge  230 , the flexible tube  210  terminates into outlet connector 255 , which communicates through the body of pump cartridge  230  to outlet port  252 . A similar connector  245  arrangement terminates the opposite end of flexible tube  210  and communicates through the pump cartridge  230  to inlet port  242 . In FIG. 4, the flexible tube  210  is removed from the pump cartridge  230 , allowing for visualization of the channel  232  provided in pump cartridge  230  for the flexible tube  210 . This channel  232  keeps flexible tube  210  from migrating along the axis of pump cartridge  230 . In addition, the flexible tube  210  can be secured at either end or both ends to ports  245  and  255  to prevent migration of the flexible tube  210  along its axis. This novel configuration offers the advantage that an insertable pump cartridge  230  can be provided carrying the flexible tube  210  and is easily insertable into the pump assembly. One possible additional variation would comprise of a cartridge lacking ports and connectors and having an extended channel such that an independent tube carrying ports could be snapped and strung into it for subsequent insertion into the pump assembly. 
     FIG. 5 shows the pump of FIG. 2 with an optional aspirant reservoir  253  attached to the aspirant outlet port  242 . In this embodiment, the core member or tubing cartridge  230  having the pump tubing  210  mounted thereon may be transversely loaded into a position between the rollers  220  such that the rollers  220  may rotate about and compress the helically disposed pump tubing  210 . In this regard, it will be appreciated that the core member  230  having the tubing  210  mounted thereon and the aspirant reservoir  253  attached to its outlet port  242  may be lowered vertically into position between the compression members (which in this embodiment are rollers)  220 , as shown in FIG. 5. A vertical guide rail or track  255  or other guide surface or apparatus (e.g., a magnet) may be formed on the aspirant reservoir  253  and may interact with a corresponding rail, track, other guide surface or apparatus to guide the core or tubing cartridge  230  into position between the rollers  220 . Stated another way, the compression members, namely the rollers  220  rotate about axes of rotation AXR and the core member or tubing cartridge  230  is insertable into an operative position relative to the compression member advancing the core member in a direction DIR that is substantially perpendicular to the axis of rotation AXR. 
     II. Inverted Helical Roller Pump 
     A second invention is a novel single roller pump described in FIG. 6 that utilizes a helical tubing path as illustrated in FIGS. 7 through 9. If an ex-centric roller carrier is utilized then the pinch before release requirement translates into more than 360 degrees of tubing, which, in turn, requires a longitudinal or other displacement. One way, in which it can be implemented, is a helical path for the tube. 
     In this configuration, one roller  320  is mounted on a rotating support  325 . A flexible tube  310  is placed onto an inserted and than stationary pump cartridge  330 . In this novel configuration, the roller  320  moves over the convex surface of the flexible tube  310 . The flexible tube  310  is squeezed between the roller  320  and the pump cartridge  330  to form an occlusion region  312 . In this configuration, rotation of the rotating support  325  in direction  326  causes the roller  320  to rotate in direction  321  and for the occlusion region  312  to move along the axis of the flexible tube  310  in direction  313 . Fluid is pumped from the inlet port  342  to the outlet port  352  of the pump cartridge  330 . As appreciated from FIG. 7 a single roller  320  may be utilized because the flexible tube  310  can be simultaneously occluded at its inlet and outlet ends when roller  320  (not shown) passes through region  316 . The pump cartridge is further described in FIGS. 8 and 9. In FIG. 8 it is apparent that the flexible tube  310  follows a helical path on pump cartridge  332 . Region  316  where roller  320  (not shown) can simultaneously pinch two regions of the flexible tube  310  is also depicted. In FIG. 8, flexible tube  310  is translucent, allowing visualization of tubing connector  345  and  355 . In pump cartridge  330 , the flexible tube  310  terminates into inlet connector  345 , which communicates through the body of pump cartridge  330  to inlet port  342 . A similar outlet connector  355  arrangement terminates the opposite end of flexible tube  310  and communicates through the pump cartridge  330  to outlet port  352 . In FIG. 9, the flexible tube  310  is removed from the pump cartridge  330 , allowing for visualization of the helical channel  332  provided in pump cartridge  330  for the flexible tube  310 . The flexible tube  310  can be secured at either end or both ends to connectors  345  and  355  to prevent migration of the flexible tube  310  along its axis. Channel  332  is designed to have a radial depth that causes full occlusion of flexible tube  310  for one full helical loop around pump cartridge  330  beginning and ending in region  316 . In principle the depth of channel  332  in region  314  can be gradually varied to minimize inflow pulsation. Likewise, the depth of channel  332  in region  315  can be gradually varied to minimize outflow pulsations. 
     The advantages of the inverted helical roller pump are that a single roller may be employed. In addition, extending the length of regions  314  and  315  to minimize inflow and outflow pulsations can be realized by extending the path length of the helical groove or channel  332  for one additional revolution each around pump cartridge  330 . In addition, because a single roller is utilized, the cartridge  330  may be easily inserted axially but laterally displaced such that no tube compression will occur during the axial insertion. Once fully inserted axially, the pump cartridge  330  may be moved lateral relative to the roller to effect the pinch-off of the tube, thus completing the cartridge loading operation. Such loading is a difficult problem for most conventional peristaltic pumps. 
     U.S. Pat. 5,630,711 teaches use of a full loop of flexible tubing around a modified helical path within a stationary outer shell to allow for the inlet and outlet of the flexible tubing to be on axis apart from a small lateral displacement. In this patent, two internal rollers are used to compress the tubing, as less than 360 degrees of the helical tubing path allow for occlusion between the rollers and the outer shell. This configuration does not allow for use of a single roller. 
     U.S. Pat. 5,429,486 describes a peristaltic pump utilizing a single internal roller and tubing contained within the outer shell that is passed through the pump in a helical geometry. This configuration is similar to the current invention but the rollers and shell are not inverted, but rather the inner roller and outer stationary shell are similar to non-inverted conventional peristaltic roller pumps. Canadian Patent 320,994 also describes placing a full loop of helical tube within a stationary outer shell and using a single internal a concentric roller to pump fluid along the tube. 
     U.S. Pat. 5,688,112 describes placing tubing along a helical path within an outer stationary shell and using multiple internal rollers to pump fluid through the tubing. This patent orients the tubes such that the tubes discharge along the axis of the rollers as opposed to tangentially exiting the pump. 
     III. Orbital, Single Concave Roller Pump 
     In some embodiments of single-roller pumps of the present invention, as described above, the surface of the roller that contacts the tube may be concave so as to make the pinching-off of the tube more gentle. This is illustrated in FIG. 10 wherein a single concave roller  420  comprises a thin walled cylinder and the surface of that roller  420  that pinches-off the tube is a single concave surface, as shown. Similar to a conventional single roller design an ex-centric drive  425  can be used and the thin wall cylinder should be free to rotate about the ex-centric axis, which is the center of the cylinder. 
     For this configuration (similar to the inverted helical single roller pump configuration above) a special loading mechanism is conceived: In operation the single concave roller  420  is ex-centric and pinches-off the tube (configured around the pump cartridge  330 ) on one side  412 . However, if during loading the pump cartridge  330  relative to the single concave roller can be made more concentric, then it is possible to have no contact with the tube  310  and therefore no friction during loading. Once inserted axially, the pump cartridge  330  may be moved lateral relative to the inner orbiting sleeve  420  by a the loading mechanism, thus completing the cartridge loading operation by bringing it into final position and pinching-off the tube  310 . 
     In this invention, the helical pump cartridge described in FIGS. 7-9 and  11  is mounted into an orbital, single concave roller pump drive as shown in FIGS. 10 and  12 . In this configuration, an ex-centric drive  425  is rotated by a motor drive in direction  426 . Rotationally mounted within and carried by ex-centric drive  425  is single concave roller  420 . Flexible tube  310  is occluded by compression between single concave roller  420  and stationary pump cartridge  330  in occlusion region  412 . Rotation of ex-centric drive  425  in direction  426  causes occlusion region  412  to move in direction  413  and for single concave roller  420  to rotate within ex-centric drive  425  in direction  421  due to friction in contact with the convex side of the tube. 
     It may be observed that the occlusion region  412  is much extended along the axis of flexible tube  310  relative to the occlusion region  312  obtained for the single roller inverted helical pump of FIG.  6 . 
     IV. A Preferred Embodiment of the Orbital, Single Concave Roller Pump 
     Presented in FIG. 11 is a preferred embodiment of a helical cartridge for use in an orbital, single concave roller pump. In this design, the female luer fitting  542  and male Luer fitting  552  are used for the fluid ports. The helical channel is designed so that one full revolution of flexible tube  510  can be fully compressed beginning and ending at region  516 . The helical channel for the loop beginning and ending at region  514 , beginning at the inlet connector  545  and extending to region  516  (full compression) gradually reduces in depth and the bottom of the channel changes from a full radius to a flat bottom with much reduced corner radii to accommodate flattening of the flexible tube  510  as it is increasingly compressed. This channel design makes compression of the tube very gradual from fully uncompressed to fully compressed and occluded. Defining a pump period from full pinch-off to next full pinch-off in this case equivalent to 360 degrees it is appreciated that gradual compression by means of a ramp over one period can be optimized to eliminate the fundamental harmonic of the pulsation. In this way, pulsation is greatly reduced. If the ramp is implemented on the inlet side pulsation of the suction is reduced, if the ramp were to be implemented on the outlet side pulsation of the discharge would be reduced, if a ramp on each side were to be implemented both pulsation of the suction as well as the discharge would be reduced independently. In the configuration shown in FIG. 11 the ramp is implemented on the side of fitting  542  witch will exhibit the reduced pulsation. Depending on the direction of rotation of the orbital compression around the pump cartridge, either only the intake pulsation for clockwise rotation or only the discharge pulsation for counter clock wise rotation would be minimized by the design of the channel for the tubing loop beginning and ending at region  514 . Again, an additional variation would comprise of a cartridge lacking ports and connectors and having an extended channel such that an independent tube carrying ports could be snapped and strung into it for subsequent insertion into the pump assembly. 
     A preferred embodiment of the pump drive is presented in a cross section view in FIG.  12 . Referring to FIG. 11 a cross section cut is made between the simultaneous full compression region  516  and outlet connector  555 , consequently the pump cartridge  530  with the outlet port fitting  552  is shown in the middle region of the FIG.  12 . The flexible tube  510  is exhibited in 5 cross-sections, of which the middle upper one is pinched-off, to the left the beginning of ramp  514  with minimal compression is shown, and to the right of it the ramp to the port  555  (not shown) shows no compression. The concave roller  520  is positioned maximal to the lower side of the figure by means of the ex-centric drive  525 . Bearings  523  and  528  provide for free rotation of the components. The drive mechanism  570  includes an electric motor  571 , a gearbox  572 , and a low teeth number spur gear  573 . The ex-centric drive  525  carries on its outer perimeter a high teeth number spur gear to engage with the drive mechanism  570 . The gearbox  572  is mounted to the frame of the pump  500 , specifically its rear plate  505 , which also centers the pump cartridge  530  (shown partially hallow) in the rear. A swinging loading mechanism  560 , specifically its swing  561  with its front extension  562  (both distinct from the frame of the pump  500 ), are provide to implement the no tube compression loading sequence described above, and its two bearings  563  and  568  are shown attached to the front  501  and rear plate  505  of the frame of the pump. The front plate  501  of the frame of the pump also provides centering for the front of the pump cartridge  530 . The loading mechanism  560  works with a small rotation around bearings  563  and  568  in conjunction with an associated clocking of the ex-centric drive  525  (not shown). 
     It can be appreciated that the configuration shown in FIG. 12 has a generally flat or narrow profile (apart from the slender motor  571  and gearbox  572 ) and may be useable in limited space applications which require a shallow of the pump mechanism. However, configurations with the ex-centric drive configured axially further backwards can provide a less shallow configuration with a significantly smaller front area, as may be desirable in other applications. This may be accomplished by re-configuring the bearing arrangement  528  such that is outer race caries an elongated ex-center drive  525  and its inner race attaches to the re-configured swing  561 . Both the ex-center drive  525  and the bearing arrangement  528  would than be located behind the pump cartridge  530 . 
     Referring now to FIGS. 13-18, there are shown a number of examples of various different ways in which the components of a inverted pumps  601 ,  602 ,  604 ,  606 ,  608  and  610  of the present invention may be configured and constructed. In particular, these examples show different configurations of the core members  612 ,  620 ,  630 ,  640 ,  650  and  660  and different configurations of the rollers  614 ,  622 ,  632 ,  642 ,  652  and  662 . These showings are not exhaustive of the multitude of different ways in which the core members and compression members (e.g., rollers) may be configured or constructed, but rather are merely examples of a few such configurations and constructions. 
     The embodiment shown in FIG. 13 comprises an inverted peristaltic pump  608  of the present invention having a cylindrical core  620  with flat side walls  624  and cylindrical rollers  622  having flat side walls  626 . 
     The embodiment shown in FIG. 14 comprises an inverted peristaltic pump  606  of the present invention having a frusto-conical core  612  the side walls  616  of which are flat and angled and frusto-conical rollers  614  which have flat, angled side walls  618 , such rollers  614  being mounted on slants or angles as shown to cause their side walls  618  to be substantially parallel to the side wall  616  of the core member  612 . 
     The embodiment shown in FIG. 15 is an inverted peristaltic pump  604  of the present invention having a frusto-conical, grooved core  630  and frusto-conical rollers  632  which have flat, angled side walls  618 . A helical projection or ridge  638  is formed about the side wall  634  of the core  630  so as to define a helical channel or groove  639  in which the pump tubing (not shown) is disposed. The rollers  614  of this embodiment are mounted on slants or at angles, as shown, such that their side walls  618  are substantially parallel to the side wall  616  of the core member  612 . 
     The embodiment shown in FIG. 16 comprises an inverted peristaltic pump  606  of the present invention having a grooved core  640  with a convex side wall  644  and rollers  642  which have convex side walls  646  and are mounted on slants or angles such that the concave roller sire walls  646  are substantially parallel to the convex core side wall  644 . A helical projection or ridge  648  is formed about the core side wall  644  so as to define a helical grove  649  within which one full revolution of pump tubing (not shown) may be disposed. 
     The embodiment shown in FIG. 17 comprises an inverted peristaltic pump  17  of the present invention having a grooved core  650  with a convex side wall  654  and rollers  652  which have convex side walls  656  and are mounted on slants or angles such that the concave roller sire walls  656  are substantially parallel to the convex core side wall  654 . A helical projection or ridge  658  is formed about the core side wall  654  so as to define a helical grove  659  within which two full revolutions of pump tubing (not shown) may be disposed. 
     The embodiment of FIG. 18 comprises an inverted peristaltic pump  610  of the present invention having a frusto-conical, grooved core  660  having a substantially flat side wall  654  and frusto-conical rollers  662  having substantially flat side walls  666 . The rollers  662  are mounted on slants or angles such that their side walls  666  are substantially parallel to the side wall  664  of the core  650 . A helical projection or ridge  668  is formed about the core side wall  664  so as to define a helical grove  669  within which the pump tubing (not shown) may be disposed. The helical projection  668  is configured such that the core  650  is devoid of undercuts or other design features that would complicate or deter demolding of the core from a typical two-piece plastic mold, such as may be used with an injection molding machine. 
     Although exemplary embodiments of the invention have been shown and described, many changes, modifications and substitutions may be made by those having ordinary skill in the art without necessarily departing from the spirit and scope of this invention. For example, elements, components or attributes of one embodiment or example may be combined with or may replace elements, components or attributes of another embodiment or example to whatever extent is possible without causing the embodiment or example so modified to become unuseable for its intended purpose. Accordingly, it is intended that all such additions, deletions, modifications and variations be included within the scope of the following claims.