Abstract:
A universal spark gap electrode with inner conductor formed as an elongate rod, an insulative sheath fit over the inner conductor, and an inner electrode tip soldered or brazed into the inner conductor. The inner conductor passes through an adapter and into an annular base with a spark gap cage and second electrode tip mounted thereon. The adapter is equipped with a molded annular jacket-type adapter mounted exteriorly thereon for engagement with the connecting receptacle of a lithotripsy machine. The annular base has a double-threaded collar that couples over the insulative sheath, and the adapter body screw-couples over the threaded collar of the annular base. This, the annular base, adapter body and insulative sheath are screw-coupled together in a coaxial configuration. Once the electrode is connected, the electrode tips generate a spark at the spark gap that vaporizes a small quantity of water, which creates an acoustic shock wave, which can be focused into the tissue of the patient and at a focal point corresponding to the position of a kidney stone or the like. A main advantage of the foregoing design is that the adapter can easily be substituted and replaced by an alternately-configured adapter to mate with other brands of lithotripters.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application derives priority from U.S. provisional application Ser. No. 60/861,757 filed 30 Nov. 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to lithotripsy equipment and, more particularly, to an improved electrode design that can be universally adapted for use with a range of lithotripters of various manufacturers. 
     2. Description of the Background 
     A lithotripter is a device that pulverizes kidney stones and gallstones by passing shock waves through a water-filled membrane that presses against the side of the patient. Extracorporeal shockwave lithotripters (ESWLs) in particular are used for treating kidney and biliary stones. The first ESWL lithotripter was developed in West Germany, and the US Food and Drug Administration (FDA) approved its use in the United States in Dec. 1984. Since then hundreds of thousands of patients have been treated. Lithotripters can use a number of methods of generating shock waves. Most typically, shock waves are generated by an electrode or “spark plug” placed at the focus of an ellipsoidal reflector. The spark from the plug vaporizes a small amount of water, creates a shock wave, and the ellipsoid reflector focuses each shock wave to a point about half a foot above it. A bombardment of successive shock waves has been found effective at disintegrating many stones including kidney stones. 
     The spark plug electrodes are usually constructed with an inner conductor which is surrounded by an insulating layer. The inner conductor extends beyond the insulation to an electrode tip. An opposing second electrode tip is spaced from the first electrode tip to provide a spark gap there between. A cage surrounds the electrodes and provides a conductor and necessary structure. 
     Examples of electrodes appear in several U.S. patents. 
     U.S. Pat. No. 5,105,801 to Cathignol et al. (Technomed) suggests that decreasing the resistance of the water decreases the latency time of the shockwave and actually increases the acoustic pressure. 
     U.S. Pat. No. 5,251,614 to Cathignol et al. discloses a lithotryptor electrode with closely-spaced discharge electrodes forming part of a discharge circuit having an inductance L and a capacitance C defining a critical resistance Rc equal to the square root of (L/C), 
     U.S. Pat. No. 5,195,508 to Muller et al. (Dornier Medizintechnik) issued Mar. 23, 1993 shows a spark gap unit for lithotripsy with a pencil conductor with an inner electrode, and insulation that envelops the pencil conductor. An external cage conductor is formed with a bow and an outer electrode. The patent illustrates a hollow inner space inside the insulation of the pencil conductor, the space being open rearwardly for easy placement of a current-feeding plug (connected to the inner electrode). 
     U.S. Pat. No. 4,905,673 to Pimiskern issued Mar. 6, 1990 (Dornier System GmbH) shows a lithotripsy probe with an inner and an outer conductor with electrode tips. The two electrodes have tips of initially different diameter, the tips being flattened (truncated cones) and facing each other, the diameter of inner electrode being initially larger than the diameter of the tip of the outer electrode. 
     U.S. Pat. No. 6,217,531 to Reitmajer (ITS Medical Technologies &amp; Services GmbH) issued Apr. 17, 2001 shows an adjustable electrode that self-measures the discharge voltage, compares it to a reference voltage, issues a correction signal, and operates an adjusting mechanism that repositions the electrodes, thus optimizing the spark gap. 
     U.S. Pat. No. 5,047,685 to Nowacki et al. issued Sep. 10, 1991 shows an electrode structure for lithotripters having inwardly turned tips with spaced confronting faces lying on opposite sides of the axis of the reflector. 
     Extracorporeal lithotripters are quite expensive, typically between $300,000 to $550,000, and their spark plug electrodes such as the foregoing are also expensive components. The rapid and frequent discharges of energy across the electrode tips has been found to erode and/or deteriorate the electrode tips, and replacement is often required. 
     U.S. Pat. No. 5,420,473 to Thomas issued May. 30, 1995 shows a partial solution in the form of a spark gap electrode assembly for lithotripters that allows easy replacement of both electrode tips without requiring manual adjustment of the spacing between the tips. 
     U.S. Pat. No. 6,849,994 to White et al. (Healthtronics) issued Feb. 1, 2005 is very similar to the above-noted &#39;473 patent to Howard. Specifically, it shows an electrode assembly for lithotripters with a pencil conductor removably connected to an insulating layer. External threads on the pencil conductor cooperate with internal threads in a bore of the insulating layer to fixably secure the insulating layer in a desired position relative to the inner conductor and discharge electrode tip.  FIG. 1  is an exploded view of the prior art &#39;994 White et al. device. This spark plug-type electrode assembly  10  included an inner conductor  12  having an insulating layer  22  inserted thereon. A discharge tip  26  is inserted into the inner conductor  12  and extends from opening  30  at the distal end  32  of the insulating layer  22 . A housing  34  has an internal bore  36  which allows the housing  34  to be disposed about the exterior surface  38  of the insulating layer  22 . The housing is equipped with a plastic clip  40  that connects to an electrical power connection in the lithotripter. In this and other prior art electrodes the clip  40  is keyed to the lithotripter. The housing  34  is joined to a cage base  50  which serves as an outer conductor, conducting electricity through arms  52  to upper tip holder  54  which receives the second electrode tip  56 . The cage base  50  surrounds bore  36  which extends over the insulating layer  22  as well as the upper housing  44 , and its arms  52  are spaced apart providing access to a spark gap, which is the space directly between the electrode tips  26 ,  56 . Accordingly, when a spark is generated, the acoustic shock waves may be transmitted from the spark gap through a reflector, and on through the tissue of a patient to break up the stones. 
     The &#39;473 Thomas and White &#39;994 patents suggests a partial solution to the problem in the form of a spark plug electrode having electrode tips that can be easily replaced. Nevertheless, with these and other known spark plug electrodes the electrode is keyed to the lithotripter and is available only as original equipment dedicated to a particular manufacturer&#39;s equipment. Spark plug electrodes from different manufacturers are not interchangeable. This effectively prevents replacement or substitution of the entire spark plug electrode assembly and compels purchase of an original equipment replacement 
     Accordingly an improved electrode design is needed to allow adaptation to numerous lithotripters from various manufacturers. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a spark gap electrode for lithotripsy machines with an interchangeable adapter that allows the same core electrode design to be interfitted to a variety of different machines from different manufacturers, most of which attempt to uniquely key their spark gap electrode to their particular machine by providing manufacturer-specific connecting receptacles. 
     It is another object to provide a spark gap electrode for lithotripsy machines as described above that employs a minimum of component parts. 
     It is still another object to provide a spark gap electrode as above that axially aligns and securely mounts the inner and outer electrode tips in an opposing relation within the spark gap. 
     In accordance with the foregoing object, the present invention is an improved universal spark gap electrode for use with a variety of lithotripsy machines having different connecting receptacles. The spark gap electrode generally comprises an inner conductor formed as an elongate rod and defined by a threaded receptacle at one end. An insulative sheath is press-fit over the inner conductor, the sheath being formed as a tubular covering for a major portion of the inner conductor. The insulative sheath has a screw threaded section and a pair of O-rings spaced along its length. An inner electrode tip is soldered or brazed into a distal receptacle of the inner conductor, protruding outward past the sheath, and the inner conductor/insulative sheath/electrode tip assembly is inserted through an adapter having a clip mounted exteriorly thereon for engagement with the connecting receptacle of a lithotripsy machine. The inner conductor within the insulative sheath passes through the housing, into an annular base, and into a spark gap cage on the base. The annular base has a double-threaded collar that screw-couples into the housing, and the insulative sheath likewise screw-couples into the threaded collar of the base. A second electrode tip is screw-inserted into the end of the spark gap cage of the base, and the two electrode tips remain opposed and coaxially spaced within the spark gap of the cage. Thus, once electrically connected, the electrode tips generates a spark at the spark gap that vaporizes a small quantity of water, which creates an acoustic shock wave, which can be focused into the tissue of the patient and at a focal point corresponding to the position of a kidney stone or the like. A main advantage of the foregoing design is that the adapter can easily be substituted and replaced by an alternately-configured adapter to mate with other brands of lithotripters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which: 
         FIG. 1  shows an exploded view of a prior art spark plug-type electrode assembly  10  from U.S. Pat. No. 6,849,994 to White et al. issued Feb. 1, 2005. 
         FIG. 2  is a front perspective view of the universal electrode  2  according to the present invention. 
         FIG. 3  shows an exploded perspective view of the universal electrode  2  of  FIG. 2 . 
         FIG. 4  is a side cross-section of the base  20  of  FIG. 2 . 
         FIG. 5  is a side cross-section of base  20  of  FIG. 4  rotated 90 degrees. 
         FIG. 6  illustrates a variety of other adapters  35 A- 35 D designed for other brands of lithotripters. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is an improved electrode design for lithotripsy that can be universally adapted for use with a range of lithotripters of various manufacturers. 
       FIG. 2  is a front perspective view of the universal electrode  2  according to the present invention. 
     The universal electrode  2  generally comprises an inner conductor  10  that is ensheathed in an insulator  12 , the insulator  12  being press-fit onto the inner conductor  10 . The inner conductor  10  extends through the insulator  12  to an inner electrode tip  14  which protrudes nominally outward from the insulator  12 . An opposing outer electrode tip  16  is coaxially spaced from the inner electrode tip  14  to provide a spark gap there between. A cage  18  surrounds the electrodes  14 ,  16  and provides a conductor and supporting structure therefore. The cage  18  is joined to a base  20 , and the base  20  is attached to an adapter  35  that covers the exterior of the insulator  12 . The adapter  35  includes a clip  30  that is fixedly attached about an adapter body  40 , and the clip  30  defines a coupling that is keyed to a particular lithotripter. In accordance with the present invention, the adapter  35  (inclusive of clip  30 ) and adapter body  40  are interchangeable as a unit, easily disconnected (as will be described) from the remaining components. The clip  30  may be a molded plastic component attached to the adapter body  40 . In the illustrated embodiment, the clip  30  is a molded plastic sleeve compression fit onto a brass adapter body  40 , these two components comprising the adapter  35  that may be varied depending in the intended lithotripter for which it is intended. A variety of adapters  35  with different external configurations (including different clips  30 ) but common internal configurations (to all fit on a common adapter body  40 ) are made available, and the adapter  35  and adapter body  40  may be easily interchanged with an alternate clip  30 /adapter body  40  to thereby accommodate numerous lithotripters from various manufacturers. This effectively allows replacement or substitution of the entire spark plug electrode assembly  2  using this standard configuration, with only the adapter  35  (inclusive of clip  30 ) changing from unit to unit. 
       FIG. 3  shows an exploded perspective view of the universal electrode  2  of  FIG. 2 . The inner conductor  10  comprises a cylindrical brass rod that protrudes to a distal receptacle into which the inner electrode tip  14  is soldered or brazed. The insulator  12  comprises a cylindrical plastic (Delrin™ or the like) ferrule with internal through-bore. The inner conductor  10  is inserted lengthwise through the bore of the insulator  12  and is press-fit thereon such that the blunt end protrudes on one side and the inner electrode tip  14  protrudes on the other, the majority of the inner conductor  10  remaining ensheathed inside the insulator  12 . The inner conductor  10  is preferably formed with a base section  11  of greater diameter that forms a shoulder which seats against a conforming shoulder within the through bore of the insulator  12 . In addition, the base section  11  of inner conductor  10  is preferably formed with surface features to ensure a secure press-fit, and the two annular ribs  13  serve this purpose. 
     The exterior of the insulator  12  is defined by a cylindrical body with substantially uniform diameter along a majority of its length, and leading into a section of reduced diameter  122 . The section of reduced diameter  122  at the junction is defined by a plurality of screw threads  124  for screw-coupling into the adapter body  40 . The reduced diameter section  122  is dimensioned to fit snugly inside and through the adapter body  40 . In addition, a pair of O-rings  126  encircle the cylindrical body of insulator  12  in advance of the screw-threads  124  to provide a fluid seal within the adapter body  40 . O-rings  126  are preferably seated within annular notches defined in the body of insulator  12 . Again, the inner electrode tip  14  protrudes slightly outward from insulator  12 . 
     The adapter  35  comprises both the adapter body  40  and clip  30  which is mounted thereon, and while for purposes of illustration the clip  30  is formed as a discrete molded component attached to the adapter body  40 , one skilled in the art should understand that the entire adapter  35  may be formed as one unitary component. The adapter body  40  comprises a hollow cylindrical length of brass tube with internal screw-threads at the end  132 . The clip  30  is formed with a through-hole and is friction fit overtop adapter body  40 . If desired, the clip  30  may additionally be bonded to adapter body  40 . 
     The clip  30  is defined by three separate sections, including a cylindrical section  132  leading to a flange  134 , and a detent clip  138  extending from the opposite side of the flange  134 . The cylindrical section  132  fits over the internally-threaded end  142  of adapter body  40  as a collar, and abuts the base  20  when the base  20  is screw-inserted into the adapter body  40 . The flange  134  limits insertion of the electrode  2  into the lithotripter. The collar  136  fits snugly into the lithotripter for stability, and locks the electrode therein. As shown, the illustrated detent clip  138  is a raised resilient annular member with an outwardly disposed lip for snap-fit insertion into one particular brand of lithotripter. Other lithotripter brands employ different locking mechanisms and the adapter  35  can easily be configured to mate with other brands of lithotripters. 
     When the base  20  is screw-inserted into the adapter body  40  the inner electrode tip  14  extends into the base  20  and out the other side, extending into the cage  18  opposite outer electrode tip  18 . The cage  18  and outer electrode tip  16  are formed as an integral component attached, such as by welding, to the base  20  as shown in  FIG. 3 . This renders the cage  18  and outer electrode tip  16  replaceable as is the inner electrode tip  14 . The insulator  12 , adapter  35  (with exemplary clip  30  and adapter body  40 ), base  20  and cage  18 , and outer electrode tip  16  form a precision-axially-aligned structure. The distal male screw-coupling  123  of base  20  threads into the threaded aperture  140  at one end of adapter body  40 . Note that both inner and outer surfaces of the threaded aperture  140  are threaded. The insulator  12  with internally-fit conductor  10  is inserted through the adapter body  40  (protruding inner electrode tip  14  first), and the threads  124  of insulator  12  are screw-inserted axially into the distal male screw-coupling  123  of base  20 . One O-ring  126  circles the threads  123  of the base  20  and the other circles the threads of the insulator  12  to prevents water from entering the adaptor  35 . This configuration axially aligns and securely mounts adapter  35 , base  20  and cage  18 , and outer electrode tip  16  together such that the inner and outer electrode tips  14 ,  16  are held in an opposing relation centrally in the aperture of cage  18 . 
       FIG. 4  is a side cross-section of the base  20 , and  FIG. 5  is a side cross-section of base  20  rotated 90 degrees. The base  20  is an annular brass member with a distal male screw-coupling  123  for insertion into the adapter body  40 . The screw-coupling  123  leads to a flange that limits screw-insertion into the adapter body  40 , and an annular notch is formed in advance of the flange to seat one of the O-rings  126 . When assembled, the flange of base  20  is offset slightly from the shoulder defined by the base section  11  of the inner conductor  10 . This shoulder limits screw-insertion of the base  20  as shown in  FIG. 3  and a second O-ring  126  seals this intersection. 
     Referring back to  FIGS. 4-5 , the preferred embodiment of the base  20  includes a pair of opposing brackets  119  protruding up from the body of the base  20  to provide a mounting for the cage  18 . Here the opposing brackets  119  are formed with a slots for receiving the ends of the prongs of cage  18 , which are also welded therein. The cage  18  itself is a two-pronged support structure converging to a forward hub, the prongs of the cage being adapted to surround the opposed electrodes  14 ,  16  and yet provide open access to a partially-enclosed space therein. The cage  18  and base  20  also serve as a conductor to the outer electrode tip  16 , which protrudes inward from the forward hub of cage  18 , protruding into the partially-enclosed space in cage  18 . Given this structure, the outer electrode tip  16  faces the inner electrode tip  14  within the confines of the partially-enclosed space in cage  18  to provide a spark gap there between. Accordingly, when a spark is generated, the acoustic shock waves may be transmitted from the spark gap through a reflector (not shown), and on through the tissue of a patient to break up stones. 
       FIG. 6  illustrates a variety of adapter assemblies  35 ,  35 A,  35 B,  35 C and  35 D each configured for a particular brand of lithotripters. 
     Adapter  35  (left) is as described above. However, the diameter and length of the inner conductor  10  and insulator  12  may vary with each lithotripter. The cage  18  surrounding the electrodes  14 ,  16  will remain substantially the same, except that its diameter may change. The adaptor  35  must be designed so that the electrode gap is precisely located at the focus of the partial elliptical bowl, e.g., the gap of the universal electrode  2  must be at the same place and of the same thickness (e.g., 0.5 mm) as the gap of the original equipment electrode supplied with the lithotripter. 
     Adapter  35 A (top left) is similar but is formed with a prolonged and tapered cylindrical section  132 A, and a longer raised collar  136 A on the opposite side of the flange  134 A. 
     Adapter  35 B (top second from left) is formed as a unitary machined part with a pronounced flange  134 B and seated O-ring  139  for sealed coupling to the lithotripter. Some lithotripters use a clip type adaptor as described previously while others use a metal ring-type adaptor. Adapter  35 B is designed for the latter. In all such cases the universal electrode  2  is able to screw into a receiving hole in the appropriate lithotripter. 
     Adapter  35 C (top second from right) is likewise formed as a unitary machined part similar to  35 B but with a shorter flange  134 B and no O-ring. 
     Adapter  35 D (right) is likewise formed as a unitary machined part and includes as hort broad collar  137  and pronounced O-ring protruding sidewardly there from. 
     In all the foregoing examples all such adapters  35 ,  35 A,  35 B,  35 C and  35 D are uniform in certain respects including the same dimensioned through-hole, as illustrated in  FIG. 3  to accommodate a uniform adapter base  40  (the latter likewise having internal threads to couple to base  20 . Thus, the basic adapter  35  is the only component that must change for each brand of lithotripter (albeit it may be necessary to change the inner conductor  10  and insulator  12  slightly to accommodate other lithotripters since each lithotripter electrode may vary in overall length and diameter of the inner conductor  10 ), and it is easy to swap out various adapter assemblies (inclusive of adapter  35  and base  40 ). 
     In use, the proper adapter  35  is selected and installed as per the foregoing in accordance with the particular brand of lithotripter into which the electrode  2  will be installed. Once installed, the electrode  2  will generate a spark at the spark gap between electrode tips  14 ,  16  and inside cage  18 . This spark vaporizes a small quantity of water, and the vaporization process emits an acoustic shock wave. The spark gap will be positioned at one focus of a partial elliptical reflector filled with a fluid, as known in the art. Thus, the acoustic shock wave is focused into the tissue of the patient and at a focal point corresponding to the position of a kidney stone or the like. A rapid succession of such shock waves is highly effective at disintegrating kidney stones. 
     Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications thereto may obviously occur to those skilled in the art upon becoming familiar with the underlying concept. 
     For example, it is possible to use one or two press fits instead of threads  123  for the coupling of the cage  18  to the adaptor  35  and/or for coupling of the insulator  12  to the cage  18 . Also, the center conductor  10  might be formed with an integral inner electrode tip  14  rather than a receptacle with soldered or brazed tip  14 . Finally, there are currently two categories of commercial lithotripters that require two different cage  18  diameters, and for manufacturing convenience it is presently envisioned that two different universal electrodes  2  will be offered with the two cage widths, one for the Lithotron™, HM3™, Medstone™ and Lithodiamond™ lithotripters, and one for the Medispec™ and Direx™ lithotripters. Therefore, in all such cases it is to be understood, that the invention may be practiced otherwise than as specifically set forth herein.