Abstract:
Irrigation fluid is aspirated from an eye and through an aspiration instrument by operating a vacuum pump, including moving first and second plungers between respective suction strokes and discharge strokes. Vacuum pressure at an input side of the pump is maintained at a desired vacuum pressure setting by controlling speeds and directions of the plungers, and controlling positions of input and output valves communicating with cylinders in which the plungers move. Controlling is based on the pressure setting and measured pressures in the cylinders. Vacuum pressure is maintained while transitioning from the suction stroke of the first plunger to the suction stroke of the second plunger, by synchronizing respective positions of the plungers and the valves, such that initiation of the suction stroke of the second plunger during the transitioning is delayed until a vacuum pressure in the second cylinder is equal to a vacuum pressure in the first cylinder.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 11/088,318, filed Mar. 23, 2005, titled “DUAL CYLINDER VACUUM PUMP FOR MEDICAL ASPIRATION SYSTEM,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/556,963, filed Mar. 26, 2004, titled “VACUUM PUMP”, which are both incorporated by reference herein in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a vacuum pump for a medical aspiration system and a method for aspirating fluid utilizing the vacuum pump. 
       BACKGROUND 
       [0003]    Ophthalmic procedures are typically performed with instruments that have a tip located at the distal end of a handpiece. The handpiece is held by a surgeon who inserts the tip into the inner ocular chamber of an eye. By way of example, the surgeon may remove a cataracteous lens, or reattach a retina with the instrument. 
         [0004]    During a procedure, irrigation fluid is introduced into the eye to maintain the ocular pressure of the anterior chamber. The handpiece tip is coupled to an aspiration system that pulls the irrigation fluid and possibly tissue out of the anterior chamber. The tissue and irrigation fluid flow through an inner channel in the tip. 
         [0005]    The aspiration system includes a pump coupled to an aspiration tube. The aspiration tube is connected to an outlet port of the handpiece. Most aspiration pumps are of the peristaltic type because the pump behavior is predictable. A peristaltic pump essentially pushes the air/fluid within the aspiration tube to create, a vacuum pressure within the tube. The operation of a peristaltic pump creates surges in the pressure within the system. Pressure surges can be undesirable when performing delicate procedures such as retinal reattachment. 
         [0006]    Some aspiration systems contain a venturi type pump. Venturi pumps do not create pressure surges and are thus typically used in delicate ophthalmic procedures. Commercially available venturi pumps require a tank of compressed nitrogen gas. It is generally undesirable to have a pressurized gas tank in an operating environment. Additionally, venturi pumps are energy inefficient in creating a vacuum. 
       SUMMARY 
       [0007]    According to one implementation, a pump for a medical aspiration system is provided. The pump includes a housing with an input port, an output port, a first cylinder and a second cylinder. A motor assembly of the pump moves a first plunger within the first cylinder and a second plunger within a second cylinder. The pump includes valve assemblies that control fluid communication between the input/output ports and the cylinders. 
         [0008]    According to another implementation, a method for aspirating irrigation fluid from an eye is provided. Irrigation fluid is introduced into the eye. An aspiration instrument is inserted into the eye. The aspiration instrument communicates with a first aspiration tube. Irrigation fluid is aspirated from the eye, through the aspiration instrument and into the first aspiration tube by operating a vacuum pump to create a vacuum pressure in the first aspiration tube. The vacuum pump includes a first cylinder communicating with the first aspiration tube and with a second aspiration tube, and a second cylinder communicating with the first aspiration tube and the second aspiration tube. Operating the vacuum pump includes moving a first plunger between a suction stroke and a discharge stroke and moving a second plunger between a suction stroke and a discharge stroke. During the suction stroke of the first plunger, irrigation fluid flows from the first aspiration tube into the first cylinder. During the discharge stroke of the first plunger, irrigation fluid flows from the first plunger into the second aspiration tube. During the suction stroke of the second plunger, irrigation fluid flows from the first aspiration tube into the second cylinder. During the discharge stroke of the second plunger, irrigation fluid flows from the second plunger into the second aspiration tube. Respective fluid flows into and out from the first cylinder and into and out from the second cylinder are controlled by controlling respective positions of a first input valve interposed between the first aspiration tube and the first cylinder, a first output valve interposed between the first cylinder and the second aspiration tube, a second input valve interposed between the first aspiration tube and the second cylinder, and a second output valve interposed between the second cylinder and the second aspiration tube. The vacuum pressure in the first aspiration tube is adjusted to a desired vacuum pressure setting by manipulating an input of a control device. The vacuum pressure in the first aspiration tube is maintained at the desired vacuum pressure setting by controlling respective movement speeds and directions of the first plunger and the second plunger relative to each other, and controlling respective positions of the first input valve, the first output valve, the second input valve and the second output valve. The controlling is based on the desired vacuum pressure setting and measurements of respective pressures in the first cylinder and the second cylinder. The vacuum pressure in the first aspiration tube is maintained at the desired vacuum pressure setting while transitioning from the suction stroke of the first plunger to the suction stroke of the second plunger, by synchronizing respective positions of the first plunger, the second plunger, the first input valve, the first output valve, the second input valve and the second output valve, such that initiation of the suction stroke of the second plunger during the transitioning is delayed until a vacuum pressure in the second cylinder is equal to a vacuum pressure in the first cylinder. 
         [0009]    According to another implementation, the method includes adjusting the vacuum pressure in the first aspiration tube to a new vacuum pressure setting by manipulating the control device. A pressure surge in the first aspiration tube is avoided during adjustment from the desired vacuum pressure setting to the new vacuum pressure setting, by synchronizing respective positions of the first plunger, the second plunger, the first input valve, the first output valve, the second input valve and the second output valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic of an embodiment of a medical system; 
           [0011]      FIG. 2  is an illustration of a dual cylinder pump of the medical system. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Disclosed is a dual cylinder pump that is used to create a vacuum in an aspiration tube of a medical system. The pump includes a first plunger that moves within a first cylinder and a second plunger that moves within a second cylinder. Movement of the plungers is controlled by a motor assembly. The pump includes valves that control the flow of fluid into and out of the cylinders so that one cylinder is pulling fluid from the aspiration tube while the other cylinder is discharging fluid. In this manner the pump is continuously pulling vacuum, thereby preventing vacuum surges found in peristaltic pumps of the prior art. Additionally, the pump is relatively energy efficient and does not require a separate nitrogen tank as required by commercially available venturi pumps of the prior art. The pump can be constructed as a cartridge that can be removed and disposed. 
         [0013]    Referring to the drawings more particularly by reference numbers,  FIG. 1  shows an embodiment of a medical system  10  of the present invention. The system  10  may be used by a surgeon to perform ophthalmic medical procedures such as cataract lens removal, or retina reattachment. 
         [0014]    The system  10  may include a surgical aspiration instrument  12  that is coupled to an aspiration system  14 . The aspiration instrument  12  may include a tip  16  that extends from a handpiece  18  and can be held by a surgeon. The tip  16  can be inserted into the eye of a patient. The tip  16  is hollow and thereby defines an inner channel  17  through which irrigation fluid and possibly tissue may flow. Accordingly, the inner channel  17  extends through the tip  16  and, in the illustrated example, through the handpiece  18  to the rear of the handpiece  18  opposite to the tip  16 . 
         [0015]    The aspiration system  14  may include an aspiration line or conduit  20  that is coupled to the aspiration instrument  12 . The aspiration line  20  is connected to a vacuum pump  22  and a collection canister  24 . The vacuum pump  22  creates a vacuum pressure within the aspiration line  20  and a flow of fluid from the aspiration instrument  12  to the collection canister  24 . The aspiration system  14  can pull (e.g., evacuate or aspirate) emulsified tissue and fluid from the aspiration instrument  12  and into the collection canister  24 . In the illustrated example, the aspiration line  20  includes a first aspiration tube  21  fluidly interconnecting the inner channel  17  of the aspiration instrument  12  and the input side of the vacuum pump  22 , and a second aspiration tube  23  fluidly interconnecting the output side of the vacuum pump  22  and the collection canister  24 . 
         [0016]    The system  10  may include one or more control devices. In the illustrated example, the system  10  includes a controller unit  26  that is connected to the aspiration instrument  12  and the vacuum pump  22 . The system  10  may further include a foot pedal  28  that is connected to the controller unit  26 . The surgeon can control the aspiration instrument  12  and/or the pump  22  by manipulating an input  27  or  29  of the controller unit  26  and/or the foot pedal  28 , such as to adjust the vacuum pressure in the first aspiration tube  21  to a desired vacuum pressure setting and readjust the vacuum pressure to new settings as needed during a particular surgical procedure. The controller unit  26  may be an electronic controller and include a processor, memory, etc. (not shown) that can operate the pump  22  in synchronization with the aspiration instrument  12 . Although the foot pedal  28  is shown as being connected to the controller unit  26 , the foot pedal  28  may be connected directly to the pump  22  and/or aspiration instrument  12 . 
         [0017]      FIG. 2  shows an embodiment of the vacuum pump  22 . The pump  22  may include a housing  30  that has a first cylinder  32  and a second cylinder  34 . The housing  30  also provides a fluid input and a fluid output. In the illustrated example, the fluid input includes a first input port  36  and a second input port  37 , and the fluid output includes a first output port  38  and a second output port  39 . A manifold tube  46  may be utilized to split the fluid flow from the first aspiration tube  21  into respective flows into the input ports  36  and  37 . Thus, the first and second input ports  36  and  37  provide fluid communication from the first aspiration tube  21  (via the manifold tube  46 ) to the first and second cylinders  32  and  34 , respectively. Likewise, the respective flows from the output ports  38  and  39  may be combined by a manifold tube (not shown) or otherwise connected to the second aspiration tube  23  in any suitable manner. Thus, the first and second output ports  38  and  39  provide fluid communication from the first and second cylinders  32  and  34 , respectively, to the second aspiration tube  23 . Also in the illustrated example, the housing  30  further includes inlet lines (channels, conduits, or the like)  40  and  42  in fluid communication with the first and second cylinders  32  and  34 , respectively, and with the respective input ports  36  and  37 . The housing  30  further includes outlet lines  54  and  56  in fluid communication with the first and second cylinders  32  and  34 , respectively, and with the respective output ports  38  and  39 . 
         [0018]    The pump  22  may have a first valve assembly  44  that controls the flow of fluid into the first and second cylinders  32  and  34 , from the first aspiration tube  21  and, in the illustrated example, via the input ports  36  and  37  and manifold tube  46 . As previously noted, the manifold tube  46  is connected to the first aspiration tube  21  of the aspiration system  14  ( FIG. 1 ). The first valve assembly  44  may include a first input valve  48  that interfaces with the first inlet line  40  to control the flow of fluid into the first cylinder  32 , and a second input valve  50  that interfaces with the second inlet line  42  to control the flow of fluid into the second cylinder  34 . 
         [0019]    The pump  22  may further have a second valve assembly  52  that controls the flow of fluid from the first and second cylinders  32  and  34  and respectively through the outlet lines  54  and  56  of the housing  30 . As previously noted, the outlet lines  54  and  56  are connected to the second aspiration tube  23  of the aspiration system  14  ( FIG. 1 ) via the output ports  38  and  39 . The second valve assembly  52  may include a first output valve  58  that interfaces with the first outlet line  38  to control the flow of fluid from the first cylinder  32 , and a second output valve  60  that interfaces with the second outlet line  39  to control the flow of fluid from the second cylinder  34 . The valves  48 ,  50 ,  58  and  60  may be controlled by actuators or motors that are connected to and controlled by the controller unit  26  shown in  FIG. 1 . 
         [0020]    The pump  22  may include pressure transducers or sensors  62  and  64  that sense the pressure within the first and second cylinders  32  and  34 , respectively. The pressure transducers  62  and  64  can be connected to the controller unit  26  shown in  FIG. 1 , and provide pressure feedback information that can be used in a feedback control loop of the pump  22 . 
         [0021]    The pump  22  includes a first plunger  66  that moves within the first cylinder  32  and a second plunger  68  that moves within the second cylinder  34 . The plungers  66  and  68  are moved by a motor assembly  70 . The motor assembly  70  may include a first motor or motor unit  72  that moves the first plunger  66  and a second motor or motor unit  74  that moves the second plunger  68 . The motors  72  and  74  may move the plungers  66  and  68  out of phase relative to each other. By way of example, the plungers  66  and  68  may move 180 degrees out of phase relative to each other. The motors  72  and  74  may be connected to the controller unit  26  which controls the timing and phase of the plungers  66  and  68 . Although two motors  72  and  74  are shown and described, it is to be understood that the plungers could be coupled to a single motor. 
         [0022]    The motors  72  and  74  may be attached to the plungers  66  and  68  by couplers  76  and  78 . The couplers  76  and  78  may be of the quick disconnect type so that the plungers  66  and  68  and the housing  30  can be detached from the motor assembly  70 . This allows the housing  30  and plungers  66  and  68  to be packaged as a cartridge that can be detached after a medical procedure. The motor assembly  70  may include a first linkage  82  connected to the first plunger  66  and a second linkage  84  connected to the second plunger  68 . Thus, during the operation of the motor assembly  70 , movement of the first linkage  82  is translated into movement of the first plunger  66  alternately through its suction and discharge strokes, and movement of the second linkage  84  is translated into movement of the second plunger  68  alternately through its suction and discharge strokes. In the illustrated example, the first motor  72  is connected to the first linkage  82  and the second motor  74  is connected to the second linkage  84 . In the illustrated example, the first linkage  82  is releasably connected to the first plunger  66  by the first coupler  76 , and the second linkage  84  is releasably connected to the second plunger  68  by the second coupler  78 . The plungers  66  and  68  may be of the syringe type that can be readily discarded and replaced. The housing  30  can be sterilized for reuse in the system  10 . The valve actuators that actively control the valves  48 ,  50 ,  58  and  60  and the pressure transducers  62  and  64  may also be attached to the housing  30  in a sealed and readily detachable manner so that these components do not have to be sterilized after each procedure. 
         [0023]    The controller unit  26  may control the motors  72  and  74  and the  20  valve assemblies  44  and  52  in the following manner. The first input valve  48  may be opened to provide fluid communication between the manifold tube  46  and the first cylinder  32 . The second input valve  50  is closed. The first motor  72  may pull the first plunger  66  in a direction indicated by the arrow. Movement of the plunger  66  pulls fluid into the first cylinder  32 . 
         [0024]    When the first plunger  66  reaches an end of travel (suction stroke of first plunger  66 ), the first input valve  48  is closed and the second input valve  50  is opened. The second motor  74  then pulls the second plunger  68  to draw fluid into the second cylinder  34 . During this second plunger movement the first motor  72  pushes the first plunger  66  (discharge stroke of first plunger  66 ). The first output valve  58  is opened so that the fluid within the first cylinder  32  is pushed out of the pump  22 . The motors  72  and  74  and valves  48 ,  50 ,  58  and  60  are operated so that one of the cylinders  32  or  34  is pulling in fluid while the other cylinder  34  or  32  is pushing out fluid. In this manner a continuous vacuum is created in the aspiration line  20  (e.g., the first and second aspiration tubes  21  and  23 ). There are not sudden surges as found in prior art peristaltic pumps. 
         [0025]    To maintain a continuous vacuum level, the second plunger  68  may begin to pull a vacuum in the second cylinder  34  as the first plunger  66  nears the end of travel in the first cylinder  32  during the discharge stroke of the first plunger  66 . The second input valve  50  may be closed during movement of the second plunger  68  until the pressure transducers  62  and  64  sense the same pressure, wherein the second input valve  50  is opened and the first input valve  48  is closed. 
         [0026]    While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. 
         [0027]    For example, although multiple valves  48 ,  50 , and  60  are shown and described, it is to be understood that the pump  22  may have other valve arrangements. By way of example the pump  22  may have a single four-way valve.