Abstract:
An improved rigid catheter is provided for lithotripsy. The catheter includes a rigid tube adapted to engage a lithotripsy transducer and power supply, with a restriction in an internal diameter of the rigid tube proximate a power delivery end of the rigid tube. The catheter may also include an enlargement on an external diameter of the tip. The tip may also be fabricated of a material considered to be very hard. The probe may also be solid with an enlarged tip.

Description:
FIELD OF THE INVENTION 
     The field of the invention relates to lithotrity and more particularly to the probes used for crushing urethral calculi. 
     BACKGROUND OF THE INVENTION 
     Lithotrity (also commonly referred to as lithotripsy) is a well-known process for removing concretions, such as calculus stones, within human ducts such as the ureter or kidney. Under the process, a rigid probe is inserted into the body of the subject with a first end juxtaposed against the concretion. An ultrasonic signal is imposed onto the probe from a second end to break up the concretion. 
     The ultrasonic signal is typically generated by use of an electrically stimulated ultrasonic motor which may be rigidly attached to the probe. A variable power supply is used to supply a controlling signal to the ultrasonic motor. 
     The probe used is often hollow and typically made of an impervious material such as stainless steel. Often the tip used to contact and break up calculus stones is fabricated of a harder material. 
     The length of the probe is usually selected to be an integer multiple of one-half wavelength at the operating frequency. Selecting the probe to be an integer multiple of one-half wavelength at the operating frequency (and appropriate selection of tube thickness and coupling components) causes the probe to function as a resonator. The use of the probe as a resonator reduces the net power required to operate effectively. 
     An internal passageway of the probe is used to carry away debris generated by break-up of the concretion. The flow of fluid also functions to cool the probe during lithotripsy. 
     While lithotripsy using a rigid.probe.is effective, it is subject to a number of difficulties. As a concretion is broken-up, debris often accumulates and clogs the internal passageway of the probe. Clogging of the internal passageways of the probe often causes overheating of the probe, especially at higher power settings. 
     During break-up of the concretion, the probe will often bore a hole into the concretion and become lodged inside. Where relative movement between the probe and concretion ceases, break-up of the concretion effectively stops. 
     Accordingly, it is an object of the invention to restrict entry of debris into the passageway inside the probe until break-up of the concretion has progressed to a point where clogging is avoided. 
     It is a further object of the invention to provide a mechanism that prevents lodging of the probe tip within the concretion during break-up of the concretion. 
     SUMMARY 
     Briefly, these and other objects are provided by a rigid catheter for use in lithotripsy. The catheter includes a rigid tube adapted to engage a lithotripsy power supply and a restriction in an internal diameter of the rigid tube proximate a power delivery end of the rigid tube. 
     The catheter may also include an enlargement on an external diameter of the tip. The tip may also be fabricated of a material considered to be very hard. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a side view of the catheter in accordance with an embodiment of the invention; 
     FIG. 2 depicts a partial side view of the tip of the catheter of FIG. 1; 
     FIG. 3 depicts an assembly view of a lithotriptor using the catheter of FIG. 1; and 
     FIG. 4 depicts a cut-away side view of the tip of the catheter of FIG. 1 under an alternate embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side view of a rigid probe assembly (catheter)  10  which can be inserted into the body of a patient so as to operate on a caculi, stone or concretion  36  (FIG.  3 ), in accordance with an embodiment of the invention. The catheter  10  has a collar  18  at a first end which may be used to join the catheter to an ultrasonic motor  30  (FIG.  3 ). 
     Under the embodiment, the length of the probe  10  for a particular application may be approximately 14 inches. The tubing  16  may be #9 grade with an external diameter of 0.148 inches and an internal diameter of 0.117 inches. The length  12  of the tubing  16  and mass of the components (e.g., wall thickness, collar size, etc.) of the catheter assembly  10  are chosen so as to resonate at an operating frequency of the ultrasonic motor  30 . 
     In addition to resonating at the operating frequency of the ultrasonic motor  30 , the length  14  of the tubing  16  is also chosen as being an integer multiple of one-half wavelength at the operating frequency. Choosing the length  14  of the tubing  16  as being an integer multiple of one-half wavelength of the operating frequency ensures that the tip  28  of the catheter  10  will be at an ultrasonic anti-node of the resonant structure of the catheter  10 . Placing the tip  28  at an ultrasonic anti-node results in a maximum vibration in that portion of the catheter  10  (i.e., the tip  28 ) which is in physical contact with the concretion  36 . 
     The tubing  16  of the catheter  10  may be fabricated of a material appropriate for the environment of use (e.g.,  301  stainless steel). The collar  18  may also be fabricated of stainless steel. The tubing  16  may be joined to the collar  18  by some appropriate technique (e.g., welding, brazing, etc.). 
     FIG. 2 depicts a portion of the tip  28  of the catheter  10 . As shown, the tip  28  of the catheter  10  may be subject to a processing technique (e.g., swaging) appropriate to deform the tip  28  in such a way as to decrease the interior diameter  24 . The probe  10  may also be processed to produce an enlargement  40  proximate the tip  28 . 
     Swaging the tip  28  creates a restriction  42  of an appropriate reduced diameter  24  (e.g., a 17% reduction, or a final size of 0.100 inch for #9 tubing) inside the tip  28 . The restriction  42  prevents debris from the concretion  36  from entering internal passageway  38  of the tube  16  until it has been reduced to a sufficiently small size to allow it to be aspirated through the tube  16  without plugging. 
     The enlargement  40  represents an increase  26  in the diameter of the tube  16  (e.g., a 3% increase in diameter to 0.152 inch for a #9 tube) proximate the tip  28 . The enlargement  40  serves another important purpose. The enlargement  40  prevents the tip  28  of the probe  10  from entering and becoming lodged within the concretion  36  as it penetrates and breaks up the concretion  36 . 
     During use (FIG.  3 ), the catheter  10  is inserted into the body of the patient and a tip  28  on a first, power delivery end of the catheter  10  is placed into contact with the concretion  36 . An ultrasonic motor  30  is connected to a second end of the catheter  10  along with an aspiration tube  46  from an aspirator  44 . A power supply  34  is connected to the ultrasonic motor  30  for purposes of driving the ultrasonic motor  34 . The power supply  34  is adjusted to an appropriate frequency (e.g., 28 kHz) and power level and.lithotripsy is.allowed to begin. 
     As the catheter  10  begins to vibrate at an ultrasonic frequency under control of the ultrasonic motor  30  and power supply  34 , power begins to be dissipated within the tubing  16  of the catheter  10 . To cool the tubing  16 , fluid  46  is aspirated through the restriction  42  along the channel  38  of the tubing  15 , through the connecting handle  30  and tubing  46  and into an outflow collector within the aspirator  44 . 
     Also as power is applied to the catheter  10 , particles of the concretion  36  begin to abrade away due to an intimate contact and differential vibration between the tip  28  of the catheter  10  and the concretion  36 . As the particles are abraded away they are drawn into and become entrained within the cooling fluid flowing through the passageway  38  of the catheter  10 . 
     Alternatively, as power is applied to the catheter  10 , the concretion  36  may break up, or large sections of the concretion  36  may break away from the concretion which are too large to pass through the passageway  38  without interfering with the walls of the passageway  38 . The restriction  42  of the tip  28  of the catheter  10  prevents entry of the large sections of debris until the vibration of the tip  28  has reduced the debris to a size which will easily pass through the passageway  38  of the tubing  16  and aspiration device  44 . 
     As the concretion  36  is abraded away, the tip  28  of the catheter  10  may progress into the concretion  36 , effectively creating a hole in the concretion  36 . The enlarged edge  40  of the tip  28  prevents lateral jamming of the tip  28  of the catheter  10  inside a hole of the concretion  36  and seizing between the tip  28  and concretion. 
     FIG. 4 is a cut-away view of a the tip  28  of the catheter  10  under another embodiment of the invention. Under the embodiment, the tip  28  is fabricated of a material (e.g., carbide, Nitronic  50 , etc.) which may be much harder than the material of the tubing  16 . The use of a harder tip material may provide enhanced durability over stainless steel or other more malleable materials. 
     As shown the tip  28  (FIG. 4) may be sleeved onto the tubing  16 , through use of an interference fit. The tip  28  may also be joined to the tubing  16  by any other appropriate joining technology (e.g., brazing, welding, staking, etc.). 
     Specific embodiments of a novel apparatus for performing lithotripsy according to the present invention have been described for the purpose of illustrating the manner in which the invention is made and used. It should be understood that the implementation of other variations and modifications of the invention and its various aspects will be apparent to one skilled in the art, and that the invention is not limited by the specific embodiments described. Therefore, it is contemplated to cover the present invention any and all modifications, variations, or equivalents that fall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.