Abstract:
An implantable drug infusion device includes a pump tube for holding a liquid to be pumped. A race is configured to support the tube. A roller assembly is configured to compress the tube against the race at one or more points along the path, and the roller assembly includes at least one roller. A drive assembly drives the roller assembly relative to the tube along the path so as to move the liquid through the tube. A biasing member is operably connected to the at least one roller to bias the at least one roller against the tube.

Description:
RELATED APPLICATIONS 
     The following applications are related to the present application: “Implantable Drug Delivery Device with Peristaltic Pump Having a Bobbin Roller Arm”, assigned Ser. No. 09/835,208, filed on Apr. 13, 2001; and “Implantable Drug Delivery Device with Peristaltic Pump Having Retractable Rollers, assigned Ser. No. 09/834,874, filed on Apr. 13, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an implantable drug delivery device for infusing a therapeutic agent into an organism, and more particularly, relates to an improved peristaltic implantable pump with improved occlusion along a fluid tube. 
     2. Description of the Related Art 
     Implantable drug infusion devices are well known in the art. These devices typically include a medication reservoir within a generally cylindrical housing. Some form of fluid flow control is also provided to control or regulate the flow of fluid medication from the reservoir to the outlet of the device for delivery of the medication to the desired location in a body, usually through a catheter. These devices are used to provide patients with a prolonged dosage or infusion of a drug or other therapeutic agent. 
     Active drug infusion devices feature a pump or a metering system to deliver the drug into the patient&#39;s system. An example of such a drug infusion pump currently available is the Medtronic SynchroMed programmable pump. Additionally, U.S. Pat. No. 4,692,147 (Duggan), U.S. Pat. No. 5,840,069 (Robinson), and U.S. Pat. No. 6,036,459 (Robinson), assigned to Medtronic, Inc., Minneapolis, Minn., disclose body-implantable electronic drug administration devices comprising a peristaltic (roller) pump for metering a measured amount of drug in response to an electronic pulse generated by control circuitry associated within the device. Each of these patents is incorporated herein by reference in their entirety for all purposes. Such pumps typically include a drug reservoir, a fill port, a peristaltic pump having a motor and a pumphead to pump out the drug from the reservoir, and a catheter port to transport the drug from the reservoir via the pump to a patient&#39;s anatomy. The drug reservoir, fill port, peristaltic pump, and catheter port are generally held in a housing, or bulkhead. The bulkhead typically has a series of passages extending from the drug reservoir and through the peristaltic pump that lead to the catheter port, which is typically located on the side of the housing. The peristaltic pumps use rollers which move along a pump tube, thereby moving liquid through the tube. 
     The prior art delivery devices, however, are limiting in that the load that the rollers place on the tube can vary as the rollers move along the tube. If the load is excessive, excess energy will be consumed and the tube life will be shortened, resulting in increased replacement costs. If the load is insufficient, inadequate occlusion of the tube will result in leakage of fluid past the roller, reducing the accuracy of the pump. Variation in the load is caused by variations in the gap between the rollers and the race in which the pump tube lies, the gap variance being due to manufacturing tolerances associated with the tube, the race and the pumphead. Prior art solutions to the load variance problem include tight manufacturing tolerances, sorting and matching of components, and placing shims of appropriate thickness between the rollers and the tube, each of which increases manufacturing costs and reduces manufacturing flexibility. 
     It is an object of the present invention to provide an implantable drug infusion device which reduces or wholly overcomes some or all of the difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of preferred embodiments. 
     SUMMARY OF THE INVENTION 
     The present invention provides an implantable drug infusion device which features a peristaltic pump having a new configuration, in which a spring biases a roller assembly against a pump tube, thereby minimizing the variation in the load that the roller assembly places on the pump tube. 
     In accordance with a first aspect, an implantable drug infusion device includes an implantable drug infusion device including a pump tube for holding a liquid to be pumped. A race is configured to support the tube along a path. A roller assembly is configured to compress the tube against the race at one or more points along the path, and the roller assembly includes at least one roller. A drive assembly drives the roller assembly relative to the tube along the path so as to move the liquid through the tube. A biasing member is operably connected to the at least one roller to adjustably bias the at least one roller against the tube. 
     In accordance with another aspect, an implantable drug infusion device includes a bulkhead having a race. A pump tube having an inlet and an outlet is positioned within the race. A roller assembly is configured to compress the tube against the race at at least one point along the path, and the roller assembly includes at least one roller. A drive assembly drives the roller assembly relative to the tube along the path so as to move a liquid through the tube. A biasing member is operably connected to the at least one roller to adjustably bias the at least one roller against the tube. 
     In accordance with yet another aspect, an implantable drug infusion device includes a bulkhead having a race, a first chamber, and a second chamber. A pump tube has an inlet and an outlet and is positioned within the race. A motor assembly is positioned within the first chamber, a pumphead assembly is positioned within the second chamber, and the motor assembly drives the pumphead assembly. The pumphead assembly includes a roller assembly having a hub and three trailing arms. Each trailing arm has a roller and is pivotally connected to the hub. A drive assembly drives the roller assembly relative to the tube along the path so the rollers compress the tube to move a liquid through the tube. A spring is operably connected to each trailing arm to bias a corresponding roller against the tube. 
     From the foregoing disclosure, it will be readily apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this area of technology, that the present invention provides a significant advance over the prior art. Preferred embodiments of the implantable infusion device of the present invention can significantly reduce the variation in load placed by the roller assembly on the pump tube. This will allow for less stringent manufacturing tolerances, increased manufacturing flexibility, increased tube life, and improved performance. These and additional features and advantages of the invention disclosed here will be further understood from the following detailed disclosure of preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments are described in detail below with reference to the appended drawings. The accompanying drawings, which are incorporated into and form a part of this specification, together with the description, serve to explain the principles of the invention. The drawings are not drawn necessarily to scale, are only for the purpose of illustrating a preferred embodiment of the invention, and are not to be construed as limiting the invention. Some features of the implantable drug infusion device depicted in the drawings have been enlarged or distorted relative to others to facilitate explanation and understanding. The above mentioned and other advantages and features of the invention will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which: 
     FIG. 1 is an exploded perspective view of an implantable drug infusion device in accordance with the present invention; 
     FIG. 2 is an exploded perspective view of a pumphead assembly of the implantable device of FIG. 1; 
     FIG. 3 is perspective view, partially cut away, of the implantable device of FIG. 1, shown in its assembled state; 
     FIG. 4 is a section view, taken along lines  4 — 4  of FIG. 3, of the implantable device of FIG. 1; 
     FIG. 5 is a section view, taken along lines  5 — 5  of FIG. 2, of a trailing arm of the implantable device of FIG. 1; 
     FIG. 6 is an exploded perspective view of an alternative embodiment of the roller arm assembly of FIG. 1; 
     FIG. 7 is a plan view of the geometry of the race and inlet and outlet ramps of the implantable device of FIG. 1; 
     FIG. 8 is a section view of an alternative embodiment of the roller arm assembly of FIG. 1; 
     FIG. 9 is a plan view of the roller arm assembly of FIG. 8; 
     FIG. 10 is a plan view of the roller arm assembly of FIG. 8, showing the roller arm assembly before and after being compressed; and 
     FIG. 11 is a perspective view of an alternative embodiment of the roller arm assembly of FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, an implantable drug infusion device  2  in accordance with the invention comprises a bulkhead  4  containing a number of chambers and cavities sized and configured to house various subsystems of the implantable drug infusion device. In particular, bulkhead  4  has a first chamber  6  sized and configured to house a peristaltic pumphead assembly  8 . A second chamber  10 , sized and configured to house a motor assembly  12  which drives pumphead assembly  8 , is positioned adjacent first chamber  6  and separated therefrom by a wall  13 . Other chambers of bulkhead  4  house a battery and the electronic circuitry (not shown) used to operate implantable drug infusion device  2  and to control the dosage rate of the medication into the body. 
     Pumphead assembly  8  includes a compression member, such as roller arm assembly  20 , for compressing a pump tube  14  having an inlet  16  and an outlet  18 . First chamber  6  has a generally circular wall  24  defining a pump race  19 . Pump tube  14  is placed in first chamber  6  in close proximity to wall  24  so that roller arm assembly  20  may force the tube against the wall, thereby forcing medication to move through the tube in a known peristaltic manner. Flanges  21  extending outwardly from pumphead assembly  8  are received in recesses  23  formed in first chamber  6 , supporting pumphead assembly  8  in first chamber  6 . Inlet  16  is placed in a pump inlet cavity  26  formed in bulkhead  4 . Pump inlet cavity  26  is connected to the pump race  19  by a pump inlet race ramp  28 . Pump tube outlet  18  is placed in a pump outlet cavity  30  formed in bulkhead  4 . Pump tube outlet cavity  30  is connected to the pump race  19  by a pump outlet race ramp  32 . In a preferred embodiment, both pump inlet race ramp  28  and pump outlet race ramp  32  have an arcuate geometry to reduce pumphead torque, as described in greater detail below. A cover (not shown) is also provided for bulkhead  4  to provide protection for the components of drug infusion device  2 . Motor assembly  12  includes a motor (not shown) which drives a four-stage gear assembly  11 , only the fourth stage of which is visible. Teeth  15  are formed on the periphery of the fourth stage of gear assembly  11 . 
     Bulkhead  4  has an integral fill port cavity  34 , sized and configured to house a septum and components to retain the septum. Drugs are injected through the septum to fill a reservoir (not shown) contained within a lower portion of bulkhead  4 . A pathway is formed between the reservoir and pump inlet cavity  28 , through which drugs are introduced into pump tube  14 . The drugs exit pump outlet cavity  30  and travel through another pathway formed in bulkhead  4  to a catheter port on the periphery of bulkhead  4  from which the drug exits the device  2  and enters the anatomy of the individual. The structure of the septum, retaining components, pathways, and catheter port are known to one of skill in the art and are not shown here. 
     Referring now to FIG. 2, pumphead assembly  8  is shown in exploded form. Pumphead assembly  8  includes a drive gear  40  with teeth  44  formed about its periphery. A support plate  42  is positioned below drive gear  40 . Flanges  21  extend outwardly from support plate  42  and, as described above, are received in recesses  23  of bulkhead  4 , and preferably welded thereto. Roller arm assembly  20  is positioned below support plate  42 . Drive shaft  46  extends axially through apertures in roller arm assembly  20 , support plate  42 , and drive gear  40 , and is retained by retaining screw  48 . Drive shaft  46  is supported for rotation at its lower end by lower bearing  50 , and at a central location, between roller arm assembly  20  and support plate  42 , by upper bearing  52 . 
     Roller arm assembly  20  comprises a central hub  53  having an aperture  55  through which drive shaft  46  extends. Flat  57  on drive shaft  46  mates with flat  59  of aperture  55  such that roller arm assembly  20  rotates as drive shaft  46  rotates. A plurality of trailing arms  54  are each pivotally secured by a pin  56  to hub  53 . Trailing arm  54  comprises upper plate  51  and lower plate  61 . A roller  58  is pivotally secured to each trailing arm  54  by an axle  60 . As seen in FIG. 5, axle  60  extends between upper and lower plates  51 ,  61 . Axle  60  passes through an inner race  63  of roller  58 . Inner race  63  is extended vertically to provide clearance between an outer race  65  of roller  58  and upper and lower plates  51 ,  61 . In the illustrated embodiment, roller arm assembly  20  is shown with three trailing arms  54  and three corresponding rollers  58 , however, the number of trailing arms  54  and rollers  58  may be greater or lesser than three. 
     As seen in FIGS. 3 and 4, teeth  15  of gear assembly  11  drivingly engage teeth  44  of drive gear  42 , thereby causing rollers  58  to move about race  19 , compressing and occluding tube  14  as they move and forcing the drug therethrough in known peristaltic fashion. As noted above, inlet race ramp  28  and outlet race ramp  32  each have an arcuate geometry, which reduces the torque required as each roller  58  engages pump tube  14  during rotation of roller arm assembly  20 . 
     Referring back to FIG. 2, each trailing arm  54  and its corresponding roller  58  is adjustably biased outwardly by a biasing member, such as spring  62 . In a preferred embodiment, spring  62  is a coil spring. As seen in FIG. 4, spring  62  is oriented to facilitate the occlusion, or compression, of tube  14  by roller  58 . Since manufacturing tolerances on the system components, i.e., roller  58 , tube  14  and race  19 , can result in variations in the gap A between roller  58  and race  19 , the biasing action of spring  62  can advantageously minimize the variation in load placed by roller  58  on tube  14 , greatly increasing the compliance of the system. Thus, for an incremental change in the gap between roller  58  and race  19 , the incremental load required is reduced. For example, in prior art devices, where the system compliance is accounted for by the tube itself, a 0.001″ decrease in a radial direction of the race could incur a 150 g load increase on roller  58 . With the present invention, however, spring  62  may be sized with a spring rate such that for a 0.001″ decrease in the race, a 1.5 g increase in load is realized. In a preferred embodiment, spring  62  is formed of a highly corrosion resistant and fatigue resistant alloy. Suitable materials include cobalt alloys and stainless steel. In other preferred embodiments, a nitinol shape memory alloy may be used for spring  62 . 
     The biasing member provides numerous advantages over the prior art devices. Reducing the variation in load prevents excessive loading, thereby providing increased tube life; minimizes the force needed to occlude the pump tube, thereby minimizing the torque requirement for occlusion; improves occlusion and, therefore, reducing leakage and improving the performance of the peristaltic pump; allows for looser manufacturing tolerances and minimizes the need for sorting and matching components, providing increased manufacturing flexibility and reducing costs. 
     In a preferred embodiment, as seen in FIG. 2, roller arm assembly  20  further includes a tube guide  66 . In the illustrated embodiment, tube guide  66  is connected to trailing arm  54  and is formed of an upper plate  68  and a lower plate  70 . In another preferred embodiment, tube guide  66  may be connected directly to hub  53 . Tube guide  66  serves to help keep pump tube  14  properly aligned to ensure that rollers  58  are centered with respect to pump tube  14 . 
     Another embodiment of a roller arm assembly  80  is shown in FIG.  6 . Roller arm assembly  80  comprises three trailing arms  82  pivotally secured to a hub  84 . Hub  84  comprises upper plate  86 , lower plate  88 , and center plate  90 . Rods  92  extend through apertures  94 ,  96  formed in upper plate  86  and lower plate  88 , respectively. Pivot pins  98  extend between upper plate  51 ′ and lower plate  61 ′ of each trailing arm  82 . Hooks  100 ,  102  formed on upper plate  86  and lower plate  88 , respectively, of hub  84 , capture pivot pins  98 . The force of springs  62  acting on trailing arms  82  helps maintain trailing arms  82  in position on hub  84 . 
     It is to be appreciated that other roller arm assembly constructions will be suitable, and are considered within the scope of the present invention. Suitable roller arm assembly constructions will provide a biasing member to ensure that a roller, or other suitable compression member, is biased against a pump tube, thereby minimizing the variation in load required to occlude the pump tube. Other suitable biasing members include, for example, leaf springs and springs of other constructions, elastomeric members, closed or open cell elastomeric foam members, torsion bars, magnetic members, and solenoids. 
     In a preferred embodiment, inlet and outlet ramps  28  and  32  have exit and entry ramps transitioning smoothly into and from race  19  in order to minimize drag torque on pumphead assembly  8 . As seen in FIG. 7, inlet ramp  28  transitions smoothly from a radius R of approximately 3.947 mm (0.1554 in) through point B to point A of race  19 . Race  19  then transitions from point A′ to point B and then through a radius R′ of approximately 4.02 mm (0.1583 mm). The angles D, D′ between points A and B, and A′ and B′, respectively are approximately 35.5°. Shown in the table below are the dimensions for the radius of race  19  along the arc between points A and B, and A′ and B′, in 0.5° increments. It is to be appreciated that the radius varies smoothly along race  19 . 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Angle 
                 Radius 
               
               
                   
                   
               
             
             
               
                   
                 0.0° 
                 11.0000 
               
               
                   
                 .5 
                 11.0054 
               
               
                   
                 1.0 
                 11.0108 
               
               
                   
                 1.5 
                 11.0162 
               
               
                   
                 2.0 
                 11.0216 
               
               
                   
                 2.5 
                 11.0270 
               
               
                   
                 3.0 
                 11.0324 
               
               
                   
                 3.5 
                 11.0378 
               
               
                   
                 4.0 
                 11.0432 
               
               
                   
                 4.5 
                 11.0486 
               
               
                   
                 5.0 
                 11.0540 
               
               
                   
                 5.5 
                 11.0594 
               
               
                   
                 6.0 
                 11.0648 
               
               
                   
                 6.5 
                 11.0702 
               
               
                   
                 7.0 
                 11.0756 
               
               
                   
                 7.5 
                 11.0810 
               
               
                   
                 8.0 
                 11.0864 
               
               
                   
                 8.5 
                 11.0918 
               
               
                   
                 9.0 
                 11.0972 
               
               
                   
                 9.5 
                 11.1026 
               
               
                   
                 10.0 
                 11.1080 
               
               
                   
                 10.5 
                 11.1134 
               
               
                   
                 11.0 
                 11.1188 
               
               
                   
                 11.5 
                 11.1242 
               
               
                   
                 12.0 
                 11.1296 
               
               
                   
                 12.5 
                 11.1350 
               
               
                   
                 13.0 
                 11.1404 
               
               
                   
                 13.5 
                 11.1458 
               
               
                   
                 14.0 
                 11.1512 
               
               
                   
                 14.5 
                 11.1566 
               
               
                   
                 15.0 
                 11.1620 
               
               
                   
                 15.5 
                 11.1674 
               
               
                   
                 16.0 
                 11.1728 
               
               
                   
                 16.5 
                 11.1782 
               
               
                   
                 17.0 
                 11.1836 
               
               
                   
                 17.5 
                 11.1890 
               
               
                   
                 18.0 
                 11.1944 
               
               
                   
                 18.5 
                 11.1998 
               
               
                   
                 19.0 
                 11.2052 
               
               
                   
                 19.5 
                 11.2106 
               
               
                   
                 20.0 
                 11.2160 
               
               
                   
                 20.5 
                 11.2214 
               
               
                   
                 21.0 
                 11.2268 
               
               
                   
                 21.5 
                 11.2322 
               
               
                   
                 22.0 
                 11.2376 
               
               
                   
                 22.5 
                 11.2430 
               
               
                   
                 23.0 
                 11.2484 
               
               
                   
                 23.5 
                 11.2538 
               
               
                   
                 24.0 
                 11.2592 
               
               
                   
                 24.5 
                 11.2646 
               
               
                   
                 25.0 
                 11.2700 
               
               
                   
                 25.5 
                 11.2754 
               
               
                   
                 26.0 
                 11.2808 
               
               
                   
                 26.5 
                 11.2862 
               
               
                   
                 27.0 
                 11.2916 
               
               
                   
                 27.5 
                 11.2970 
               
               
                   
                 28.0 
                 11.3024 
               
               
                   
                 28.5 
                 11.3078 
               
               
                   
                 29.0 
                 11.3132 
               
               
                   
                 29.5 
                 11.3186 
               
               
                   
                 30.0 
                 11.3240 
               
               
                   
                 30.5 
                 11.3294 
               
               
                   
                 31.0 
                 11.3348 
               
               
                   
                 31.5 
                 11.3402 
               
               
                   
                 32.0 
                 11.3456 
               
               
                   
                 32.5 
                 11.3510 
               
               
                   
                 33.0 
                 11.3564 
               
               
                   
                 33.5 
                 11.3618 
               
               
                   
                 34.0 
                 11.3672 
               
               
                   
                 34.5 
                 11.3726 
               
               
                   
                 35.0 
                 11.3780 
               
               
                   
                 35.5 
                 11.3834 
               
               
                   
                   
               
             
          
         
       
     
     Another preferred embodiment is shown in FIGS. 8 and 9, in which the biasing member is formed as an arm  112 . Arm  112  is formed of a length of wire bent into a desired shape. Roller  58  is secured to a hub  110  via an arm  112 . Arm  112  has a substantially U shaped profile forming upper and lower arms  113 ,  115  and extends through roller  58 . An end  114  of upper arm  113  is bent and received in an aperture  116  in an upper surface of hub  110 , and an end  118  of lower arm  115  is bent and received in an aperture  120  in a lower surface of hub  110 . The upper and lower arms  113 ,  115  are of unequal length L 1  and L 2 , respectively, such that apertures  116  and  120  are offset from one another in a radial direction with respect to hub  110  by a distance S 1 . Ends  114  and  118  may also be offset from one another in an axial direction with respect to hub  110  by a distance S 2 . In an equilibrium state, there is no stress on arm  112 , and, therefore, no stress placed on roller  58 . 
     As seen in FIG. 10, as arm  112  is rotated an angular amount θ with respect to hub  110  (to the position shown in dashed lines), the upper and lower arms  113 ,  115  become misaligned, placing stress on arm  112  and exerting a torque, and, therefore, a biasing effect on rollers  58 . The amount of torque can be varied by selecting appropriate lengths and diameters for upper and lower arms  113 ,  115 , varying the height of arm  112 , and varying the offsets S 1  and S 2  between upper and lower arms  113 ,  115 . 
     Another embodiment is shown in FIG. 11, wherein three arms  122 ,  124 ,  126 , each having a configuration similar to that described above with respect to FIGS. 8,  9 , are formed from a single wire  128 . As illustrated, wire  128  extends through a hub  110 , however, it is to be appreciated that hub  110  is not required, and the arms  122 ,  134 ,  126  may act as biasing members without the use of a hub. 
     In light of the foregoing disclosure of the invention and description of the preferred embodiments, those skilled in this area of technology will readily understand that various modifications and adaptations can be made without departing from the scope and spirit of the invention. All such modifications and adaptations are intended to be covered by the following claims.