Abstract:
A multilayered impedance pump is formed by an inner tube and an outer tube which have different mechanical characteristics. The outer tube is relatively stiff, and can be used for a structural material. The inner tube is excitable, and a gel is placed between the inner and outer tube. The actuator actuates the gel to cause pressure waves along the inner tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Application 60/756,704, filed Jan. 6, 2006. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 
     
    
     BACKGROUND  
       [0002]     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.  
         [0003]     U.S. Pat. No. 6,254,355 discloses a pump that pumps fluid based on differences in fluidic characteristics, e.g., fluidic impedance, between various parts.  
         [0004]     Different applications for this impedance pump have been disclosed. The pump can be used to pump fluids within the body cavity. This pump may be very useful in biomedical applications since it can be a very energy efficient device, and can operate without any valve or impeller, or any structure on the inside of the tube or lumen.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     In the Drawings:  
         [0006]      FIG. 1  shows a side view of a multilayered pump;  
         [0007]      FIG. 2  shows a cross-sectional view of the pump along the line  2 - 2  in  FIG. 1 ; and  
         [0008]      FIG. 3  shows the pump in place inside the aorta; and  
         [0009]      FIG. 4  illustrates a pump embodiment that is suitable for such an aorta.  
       SUMMARY  
       [0010]     The present application describes a new impedance pump with multiple walls.  
         [0011]     In an embodiment, this impedance pump is formed of an inner lumen and an outer lumen with a material between the inner and outer lumens that can transmit forces.  
         [0012]     In another embodiment, waves are used that can constructively interfere, to allow a relatively small actuation wave to add and become a larger amplitude wave that is induced on the inner lumen.  
     
    
     DETAILED DESCRIPTION  
       [0013]      FIGS. 1-2  illustrate an embodiment of a double-walled impedance pump. In the embodiment, a first, inner lumen  120  is formed of a material that is elastically deformable. The inner lumen holds the fluid that is desired to be pumped. The first lumen  120  is surrounded by a second substantially unbending, e.g., rigid walled lumen  100 .  
         [0014]     The space between the inner lumen  120  and outer lumen  100  is filled with a fluid material  110 . For example, the fluid material  110  may be a gel that has mechanical properties allowing it to transmit periodically applied forces. The fluid  110  may resonate at a resonant frequency (or frequencies) of the system. The fluid  110  preferably has a viscosity higher than 1.5 centi-Poise (cP). The gel can be any material than can transmit the force from an actuator to the flexible walled tube  120 , however. Therefore, this application contemplates using fluids with gel-like consistencies, but also fluids with water-like consistencies, e.g., a viscosity of around 1 cP. Any fluid that can transmit applied force waves can be used.  
         [0015]     The resonant motion of the gel material  110  causes little or no motion to the second surrounding lumen  100 . Rather, a small amplitude excitation acting within the gel area between the lumens  100 ,  120  is, in effect, amplified by constructive interference caused by wave reflection at the boundary between the lumens. The amplitude amplification must be obtained by changing characteristics of the excitation, until the constructive interference is obtained. The system is also preferably operated at a resonant frequency. If so, this allows a small amplitude excitation within the area to be greatly amplified.  
         [0016]     The embodiment shows two lumens interacting with each other in this way, but it should be understood that there can be 3, 4, 5, or any number of lumens which operate in an analogous way.  
         [0017]     Any wave reflection boundary can be included as part of the system and can become part of the system and the resonant effect. Trial and error may be used to find optimum combinations.  
         [0018]     The embodiment uses a flexible lumen  120  which receives an asymmetric excitation. Both ends of the lumens are fluidically coupled to sections of varying fluidic characteristics, e.g. fluidic compliance, geometry or any other physical property. In the embodiment of  FIG. 2 , one end of the lumens is closed.  
         [0019]     The connection area between the lumens and the other materials creates a reflection site which causes fluidic wave reflection.  
         [0020]     The excitation is carried out over a specific range of frequencies which can cause the potential for constructive wave interactions. When the proper interactions occur, a low amplitude excitation of the gel is effectively amplified into a larger amplitude surface wave that is formed on the inner surface of the inner lumen  120 . This, in turn, creates a pressure gradient to drive fluid flow of fluid  110  within the inner lumen  120 .  
         [0021]     In addition, by selecting the excitation frequency to a frequency that causes resonant activity, the surface wave, and hence pumping may be greatly increased.  
         [0022]     In operation, a low amplitude wave is created on or near the outer lumen  100 , but preferably inside of the lumen  100 . For example, a low amplitude wave may be created at the location  102 , or at the location  131 . The external layer  100  is a relatively stiff but compliant structure. Even though the structure is compliant, it is not dispensable, enabling it to be used within a body cavity. The material is referred to herein as being substantially unbending.  
         [0023]     The low amplitude excitation avoids exciting the outer lumen, hence enabling its use in applications where high amplitude excitations could be harmful.  
         [0024]     The low amplitude excitation at either of areas  102  or  131  may be caused by any of a number of different technologies including piezoelectric, electromagnetic, or electrostatic induction. Alternatively, the low amplitude wave may be created sonically or ultrasonically.  
         [0025]     The low amplitude wave preferably is applied at a frequency that causes resonance within an internal gel layer  110  that is between the outer surface  100  and the inner surface  120 . The resonant frequency may be found, for example, by trial and error.  
         [0026]     Moreover, the gel allows the low amplitude excitation waves to be converted to large amplitude surface waves through the resonant reaction and through the wave reflection at an end surface  130 . The small amplitude waves combine to large amplitude waves, which themselves propagate in a relatively soft gelatinous layer  120 , and are effectively amplified by the constructive interference.  
         [0027]     This pump may be used as an auxiliary heart pump, or as an aortic pump to serve as a replacement for current balloon pump designs. An advantage of this pump is that the outer surface  100  is relatively stiff, and therefore it can be used where structurally needed. A robust assistance device may be used to augment the impaired cardiac pumping capability to replace current long-term pumps that added complication in both use and implementation.  
         [0028]      FIG. 3  illustrates the pump in place inside the aorta and  FIG. 4  illustrates a pump embodiment that is suitable for such an aorta. The pump  300  is shown within the aorta  310 . The device can be inserted by a catheter lying against the aortic walls. The pump can be delivered through the femoral artery inserted in a collapsed state. Thereafter, a stent can be used to expand the outer lumen so that the outer rigid surface of the pump lays flush against the inner walls of the aorta. Once in position, the gelatinous material, e.g., a hydrogel, can be injected to expand the outer lumen. Since the external wall is not dynamically excited, significantly less stress is exerted on the surrounding tissue as compared with intra-aortic balloon pumps, which may exert relatively large stresses on the aorta. In this embodiment, the actuator is shown at the location  305 , and the pump  300  is shown with the very elastic internal surface  310 , and the compliant but not dispensable outer surface  315 . The outer surface  315  is capable of inward but not outward motion. This outer surface  315  is in contact with the inside of the aortic walls.  
         [0029]     The actuator  305  may be, for example, an electromagnetic coil. It is actuated by controller  320  to periodically restrict and relax, either locally from a source of power, or remotely via a wire to a source of power or via some wireless mechanism. It may be a piezoelectric device that causes a constriction around the inner surface  310 . The actuator may alternatively be located within the gel itself.  
         [0030]     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.  
         [0031]     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 another 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, the pump can be used for other applications. Different materials can be used in place of the disclosed gel. The controller can control at a periodic frequency, or can control at aperiodic pulse periods. The lumens may be cylindrical, but may also be any other shape, including elliptical in cross section, or any other shape.  
         [0032]     Also, the inventors 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. The controller for the actuation that is described herein may be carried out by any kind of computer, either general purpose, or some specific purpose computer such as a workstation. The computer may be a Pentium class computer, running Windows or Linux, or may be a Macintosh computer. The computer may also be a handheld computer, such as a PDA, cellphone, or laptop.  
         [0033]     The programs may be written in C, or Java, Brew or any other programming language. The programs may be resident on a storage medium, e.g., magnetic or optical, e.g. the computer hard drive, a removable disk or media such as a memory stick or SD media, or other removable medium. The programs may also be run over a network, for example, with a server or other machine sending signals to the local machine, which allows the local machine to carry out the operations described.