Abstract:
A pump installed inside a graft in a body such as the human body to force fluid such as blood through that graft. The pump can be one which operates totally from the outside of the graft, forcing fluid through the graft without extending inside the graft. The pump can be an impedance pump, that operates based on the fluidic mismatches between the graft, and other fluid carrying vessels within the human body.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application 60/643,915, filed Jan. 10, 2005. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 
     
    
     BACKGROUND 
       [0002]    U.S. Pat. No. 6,254,355 describes an impedance pump which causes a pumping action that is based on fluidic impedance differences between different sections of a fluidic conduit. Basically, two or more different conduit sections have different fluidic characteristics or “fluidic impedances”. The fluidic impedance is dependant on the elasticity, size and area of the conduits, among other things. 
         [0003]    One of the conduit sections is actuated to change its inner area. The change in area causes a pressure increase in that section. The corresponding pressure increase in other sections is different because of the different fluidic characteristics of those other sections. The pressure difference causes the fluid to flow from the higher pressure area, to the lower pressure area. By continuing to change the fluidic characteristic before the system has an opportunity to return to its equilibrium state, fluid is caused to flow. 
         [0004]    The frequency, duty cycle and timing of the pressure increase can be adjusted to change different characteristics of the fluid flow, including speed of fluid flow and direction of fluid flow. Any actuation that can reduce the inner area of a fluidic conduit can be used to actuate the pump. 
       SUMMARY 
       [0005]    The present application describes an impedance pump used in cardiovascular bypass grafts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the drawings: 
           [0007]      FIG. 1  shows an illustration of a coronary bypass graft with an impedance pump on the graft; and 
           [0008]      FIG. 2  shows a detailed diagram of the impedance pump assembly and controller on a conduit carrying human blood. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    The general structure and techniques, and more specific embodiments which can be used to effect different ways of carrying out the more general goals are described herein. 
         [0010]    Blockage of arteries may be addressed during medical operations by using a graft. The graft may be a separate blood-carrying conduit, which extends in parallel with the blocked blood carrying vessel in the human body or any other body. 
         [0011]      FIG. 1  illustrates a coronary bypass graft. The coronary artery  100  is bypassed by a graft conduit  110 . In the embodiment, an impedance pump  120  is placed on the graft  110  to enhance the flow rate in the graft. This may improve the anistomosis hemodynamic and can also prevent or reduce graft occlusion, and improve patency. While the above describes a graft being used as a shunt, as an alternative, the graft can be used for other purposes, such as replacement of a diseased arterial or vein section rather than a shunt of that section. 
         [0012]      FIG. 1  shows the impedance pump actuator  120  being implanted on a graft  110 . In the embodiment, the actuator  120  forms an impedance pump, using the different fluidic characteristics of the graft  100  and the fluidic characteristics of the remaining blood conduits  100 . 
         [0013]    The actuator  120  includes a pinching portion shown as  200 , located around the walls  112  of the graft  110 . The pinching portion  200  is actuated to compress the walls of the pinching portion  200  towards one another, to reduce the area in the section between the walls of the pinching portion. A self-contained housing may also include an energy source shown as  210 , and a controller, shown as  220 , driven by the energy source. The controller may control the periodicity of the pinching, the duty cycle of the pinching to adjust the pressure increase and decrease to pump body fluid, e.g., blood, in a desired way. A non contact monitor  232  may be used to monitor the type and quantity of the flow. The controller  220  may include an interface  240 , which may be a wired interface, with a wire leading outside the body, or may be a wireless interface allowing monitoring and control from the outside. For example, a controller may operate to control the speed of pinching to maintain a certain level of flow in the graft artery. The controller can be any kind of computer or microcontroller, suitably programmed, and/or controlled from programmed instructions. 
         [0014]    Since the fluidic characteristics of the system as a whole may not be easily modeled prior to installation of the pump, it may also be highly desirable to be able to control the operation, e.g., period, duty cycle etc, of the pump after its installation. 
         [0015]    The pincher can be any one of a number of actuation devices which cause constriction of the outer wall of the graft. The actuation devices can be, for example, any of electromagnetic, piezoelectric, ferroelectric, or electrostatic. Other techniques may also be used, including actuation of polymers, and the like. 
         [0016]    The energy source  210  can be a battery, but power supply can also be based on patient ATP, thermal energy, or kinetic energy. 
         [0017]    The graft  110  can be any biocompatible compliant material. The graft must be an elastic material, and is preferably near the proximal and distal most ends. 
         [0018]    While the embodiment describes use of an impedance pump, it should be understood that other pumps may be used so long as the pumps are valveless and do not have any parts that extend within the walls forming the conduit holding blood. The impedance pump operates by exploiting the fluidic impedance mismatch between the graft and the native vessels at the anastomoses, and therefore may have special advantages, since those fluidic impedance mismatches will inherently exist. In addition, the impedance pump operates in a pulsatile manner, which may enhance the flow mixing and improve washout within the graft area. 
         [0019]    While the above has described using the impedance pump for a coronary graft, it should be understood that the pump can be used for other grafts, including arterial, vein, artificial, or engineered tissue. It can also be used for blood vessels of any diameter in order to increase the flow within such a blood vessel. 
         [0020]    Although only a few embodiments have been disclosed in detail above, other embodiments are possible and the inventor(s) intend these to be encompassed within this specification. The specification describes specific examples to accomplish a more general goal that may be accomplished in other way. This disclosure is intended to be exemplary, and the claims are intended to cover any modification or alternative which might be predictable to a person having ordinary skill in the art. For example, pumping of other bodily fluids is contemplated. This device can be used in other bodies beside a human body, for example in animals, also. 
         [0021]    Also, the inventor(s) intend that only those claims which use the words “means for” are intended to be interpreted under 35 USC 112, sixth paragraph. Moreover, no limitations from the specification are intended to be read into any claims, unless those limitations are expressly included in the claims.