Patent Publication Number: US-2007098579-A1

Title: Fluid pressure sensing chamber

Description:
The application is a continuation-in-part of U.S. patent application Ser. No. 11/260,595, filed Oct. 27, 2005, currently co-pending and a continuation-in-part of U.S. patent application Ser. No. 11/260,596, filed Oct. 27, 2005, currently co-pending. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates generally to fluid pressure sensing chambers and more specifically to fluid pressure sensing chambers used in ophthalmic surgical equipment.  
      When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).  
      In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquifies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.  
      A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draws aspiration fluid from the eye through the handpiece assembly.  
      The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body&#39;s distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve.  
      In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source, usually a peristaltic pump, in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.  
      Prior art devices have used sensors that detect irrigation pressure or aspiration vacuum. Based on the information from these sensors, the surgical console can be programmed to respond in order to make the surgical procedure more efficient and safer. In order to reduce the risk of contamination by the aspirated fluid, recent surgical systems use closed pressure sensors, in which the fluid does not come into contact with the load cell or other device used to sense the fluid pressure. One such pressure sensor is illustrated in U.S. Pat. No. 5,392,653 (Zanger, et al.). Overall system performance, however; depends in large part on purging all of the air from the aspiration pathway of the system, including the pressure sensor. Air is much more compressible than the irrigating solution used in surgery, and air pockets or bubbles add compliance to the system. Compliance results in undesirable pressure variations and fluctuations. Common methods of purging air from sealed liquid systems (or “priming” the system) include avoiding sharp edges and abrupt shape changes and dead ends within the system as well as filling any chambers in the system with liquid from the bottom or low point of the chamber and allowing air to escape out of the top of the chamber. The inventors of the present invention have discovered that the initial priming of pressure sensor chambers found within closed surgical fluidic systems is relatively easy, but if bubbles of air are allowed to enter the chamber (for example, if the surgical handpiece is changed mid-procedure), these air bubbles are extremely difficult to purge from the system. This difficulty is the result of the surface tension of the air bubble (as opposed to the unencapsulated air generally involved in the initial priming of the system) causing the bubble to be relatively robust and not easily broken and drawn out of the pressure sensing chamber once introduced. In addition, the liquid “film” surrounding the air bubble is tacky, causing the bubble to stick or adhere to surfaces within the system and resist further movement, even with very high flow rates. One reference, U.S. Pat. No. 6,059,765 (Cole, et al.) has suggested that certain chamber shapes and outlet locations may assist in the removal of air from surgical systems. The inventors have found that the chamber shapes and designs discussed in this reference are insufficient to assure that air bubbles can be purged from the system.  
      Accordingly, a need continues to exist for a pressure sensing chamber that prevents air from entering the chamber and being trapped within the chamber.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention improves upon prior art peristaltic pumps by providing a pressure sensing chamber having a canted tubing extension with a reduced diameter portion extending through the chamber. The tubing contains a plurality of ports so as to allow the purging of air from the chamber, but the ports are sized so that bubbles entering the tubing cannot easily flow into the chamber. The reduced diameter portion creates a pressure differential between the holes. This differential pressure creates flow through the chamber under high liquid flow and turbulent liquid flow events.  
      One objective of the present invention is to provide a cassette a pressure sensing chamber that is easy to prime.  
      Another objective of the present invention is to provide a pressure sensing chamber that does not permit air bubbles from becoming trapped in the chamber.  
      Yet another objective of the present invention is to provide a pressure sensing chamber having a tubing extending through the chamber.  
      These and other advantages and objectives of the present invention will become apparent from the detailed description, drawings and claims that follow.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a surgical system that may be used with the present invention.  
       FIG. 2  is a perspective view of a surgical cassette that may be used with the present invention.  
       FIG. 3  is an enlarged perspective view of a first embodiment of the pressure sensing chamber of the present invention.  
       FIG. 4  is an enlarged perspective view of a second embodiment of the pressure sensing chamber of the present invention.  
       FIG. 5  is an enlarged perspective view of a third embodiment of the pressure sensing chamber of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As best seen in  FIG. 1 , commercially available surgical systems generally include surgical console  110  having attached, adjustable mayo tray  10  and handpiece  20  attached to console  110  by aspiration tubing  22 , irrigation tubing  24  and power cable  26 . Power to handpiece  20  as well as the flows of irrigation and aspiration fluid is controlled by console  110 , which contains appropriate hardware and software, such as power supplies, pumps, pressure sensors, valves, all of which are well-known in the art. As best seen in  FIG. 2 , cassette  200  that may be used with the present invention receives aspiration tubing  22  and irrigation tubing  24  and is installed within cassette receiving portion  25  of console  110 . Cassette  200  contains a pressure sensing chamber  210  which may consist of hollow void  230  formed within body  220  of cassette  200  and enclosed by pressure sensing diaphragm  215 . Cassette  200  may be any of a variety of commercially available surgical cassettes such as the INFINITI® Fluid Management System available from Alcon Laboratories, Inc., Fort Worth, Tex. Body  220  is generally molded from a suitable thermoplastic.  
      As best seen in  FIG. 3 , chamber  210  contains tubing extension  240  that extends through void  230 , essentially bisecting void  230  into two identical hemispheres, although other shapes from chamber  210  and void  230  may also be used. Tubing extension may be integrally molded into body  220 , or may be integrally formed with aspiration tubing  22 . In either case, tubing extension  240  fluidly communicates with aspiration tubing  22  so as to draw fluid through aspiration tubing  22  and into peristaltic pump  250 , as indicated by the flow arrows in  FIG. 3 . Penetrating through tubing extension  240  is one or more holes  260  that allow fluid communication between aspiration tubing  22 , void  230  and diaphragm  215 . Such fluid communication allows for changes in pressure within aspiration tubing  22  to be communicated to void  230 , causing deflection in diaphragm  215  which may be sensed by a load cell (not shown) mounted within cassette receiving portion  25  of console  110 . Holes  260  also allow void  230  to be purged of air during initial priming of cassette  200 . More importantly, holes  260  are sized and shaped so that any air bubbles entering aspiration line  22  cannot easily flow through holes  260  and enter void  230 . The hole(s)  260  locations and size promote good bubble retention within the tubing extension  240  and yet allow fluid flow through the lower hole(s)  260  during initial liquid filling of void  230 .  
      As best seen in  FIG. 4 , in order to promote initial liquid filling of void  230 ′ the internal size of tubing extension  240 ′ may have a reduced diameter portion  241  in order to create a flow restriction within tubing extension  240 ′. The flow restriction promotes liquid flow during initial liquid filling of void  230 ′ through the hole(s)  260 ′ below restrictor  242 . Flow restrictor  242  within tubing extension  240 ′ also creates a pressure differential between the hole(s)  260 ″ above restrictor  242  and hole(s)  260 ′ below restrictor  242 . This differential pressure creates flow through void  230 ′ under high liquid flow and turbulent liquid flow events. By way of example, holes  260 ,  260 ′ and  260 ″ are on the order of 0.0002 square inches to 0.02 square inches in area. Such precise sizing of holes  260 ,  260 ′ and  260 ″ prevents air bubbles and aspirated tissue from passing through holes  260 ,  260 ′ and  260 ″ because of the surface tension of the bubbles. The liquid film surrounding air bubbles suspended in a liquid are extremely tough and very resistant to puncturing or breaking. Therefore, the small size of holes  260 ,  260 ′ and  260 ″ prevents any air bubbles from passing through holes  260 ,  260 ′ and  260 ″. In addition, during use, a vacuum (negative pressure) is normally drawn in aspiration lines  22  and  22 ′ and tubing extensions  240  and  240 ′ because of the operation of pump  250 . As a result of this vacuum, very little, if any, liquid escapes out of tubing extension and into voids  230  and  230 ′. Therefore, there is virtually no fluid flowing into voids  230  and  230 ′ with which to carry any air bubbles into voids  230  and  230 ′.  
      As best seen in  FIG. 5 , the inventors have surprisingly discovered that angling or canting tubing extension  240 ″ relative to vertical centerline  500  further assists in preventing air bubbles from entering void  230 ″. Such canting takes advantage of the natural buoyancy and surface tension of air bubbles, which forces the air bubbles to cling to the upper surface of extension  240 ″ as the air bubbles are carried along in the flow stream. Such positioning of the air bubbles helps reduce the likelihood that any air bubbles can enter holes  261 , which are located along the middle of extension  240 ″. Too much canting, however, might cause the air bubbles to adhere to the top surface of extension  240 ″. The inventors have discovered that canting extension  240 ″ at an angle of between 10° and 20° from vertical centerline  500  is optimal, but any angle between 5° and 45° may be used.  
      This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that modifications may be made to the invention as herein described without departing from its scope or spirit.