Abstract:
A laser energy delivery device is provided that is suitable for irradiating a body tissue with relatively long wavelength laser energy in the presence of an aqueous liquid without significant absorption of the laser energy by the liquid. The device includes an elongate hollow sheath that is open at its distal end and closed at its proximal end, a laser energy conduit such as an optical fiber or hollow wave guide, within the sheath, the distal end of the conduit being disposed near the open distal end of the sheath, and the proximal end of the conduit being adapted for connection to a source of long wavelength laser energy. The sheath also includes an inlet port, spaced from the proximal end of the sheath, and adapted to receive and deliver a biologically compatible gas through the sheath to a body tissue site in contact with the open distal end of the sheath. In use, the open distal end of the sheath is positioned in contact with a body tissue site. Gas infused through the sheath displaces an aqueous liquid from the region between the distal end of the sheath and the tissue. Laser energy emitted from the distal end of the conduit passes through the substantially liquid-free region at the distal end of the sheath and impinges on the tissue to be irradiated. The laser energy can be used to ablate, vaporize, coagulate or shrink tissue at the target zone without interference from aqueous liquids, which tend to absorb relatively large amounts of long wavelength laser energy and reduce the efficiency of tissue ablation.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to laser energy delivery devices and their method of use in an aqueous environment. More particularly, the invention relates to laser energy delivery devices useful for delivering laser energy at wavelengths of about 1,300 to 11,000 nanometers, to a body tissue site with reduced interference from surrounding aqueous fluid media.  
         BACKGROUND OF THE INVENTION  
         [0002]    Lasers that emit light energy at wavelengths in the range of about 1,300 to about 11,000 nanometers (long wavelength or “LW” laser energy) are excellent vaporizers of tissue, since their energy is highly absorbed by water, a major constituent of mammalian tissue. When exposed to such long wavelength laser energy, the water in the tissue is rapidly heated and converted to steam, causing ablation or vaporization of the tissue. These properties make long wavelength lasers particularly useful for nonsurgical removal or reduction of tissue.  
           [0003]    Typically, laser energy is delivered to a tissue site via an optical fiber or an optical wave guide device adapted for transmission of long wavelength laser energy. The emitting end of the fiber optic or wave guide is placed in close proximity to the desired tissue site. An endoscope is first positioned inside a duct, body cavity, hollow organ or surgically created passageway at the tissue site. The energy emitting end of the optical fiber or wave guide is then threaded through a channel in the endoscope to place the emitting end of the optical fiber or wave guide in the optical position near the tissue. Typically a fiber optic viewing device is also positioned at the working end of the endoscope to view the tissue site as it is being irradiated with laser light energy and to verify the correct positioning of the emitted laser energy.  
           [0004]    However, when water, saline, or other aqueous liquid is infused through the endoscope to provide a clear field of view of the tissue inside a duct, body cavity, hollow organ, or surgically created passageway, via the fiber optical viewing device, a substantial amount of the laser energy is wasted. The aqueous liquid between the distal end of the optical fiber and the target tissue absorbs a substantial part of the light energy and creates a steam bubble, which acts as an “optical cavity.” The remainder of the laser energy passes through the steam bubble and vaporizes or ablates the target tissue. However, as the steam bubble collapses between pulses of laser energy, liquid flows back into the space between the distal end of the optical fiber and the target tissue, requiring some of the laser energy to again be consumed in recreating the steam bubble between the optical fiber and the tissue, diminishing the amount of laser energy reaching the target tissue.  
           [0005]    The above phenomenon was first described by Jeffrey M. Isner et al. in “Mechanism of laser ablation in an absorbing fluid field,”  Lasers Surg. Med.  1988;8(6):543-54, and is commonly referred to as the “Moses Effect” or “parting the water.” 
           [0006]    Holmium lasers emitting long wavelength light were used in the mid to late 1990&#39;s to resect prostate tissue, as described above. However, while the procedure produced benefits comparable to a trans-urethral resection of the prostrate or “TURP” procedure, in which a wire loop is heated by radiofrequency (“RF”) energy to cut-out swaths of prostate tissue, the laser procedure typically took about 45 minutes to an hour for a small (20-30 gram prostate) and longer than an hour for larger prostates. As a result, the laser procedure never became popular and is presently used only infrequently.  
           [0007]    It would be desirable to enable a substantially greater amount of light energy from long wavelength lasers to be used in an aqueous liquid environment to vaporize tissue without significant quantities of energy being wasted by vaporizing the intervening aqueous liquid.  
         SUMMARY OF THE INVENTION  
         [0008]    A laser energy delivery device of the present invention comprises an elongate hollow sheath having an open distal end and a closed proximal end. The sheath defines a lumen and a gas inlet port. The gas inlet port is spaced from the closed proximal end of the sheath and is in open communication with the lumen. The gas inlet port is adapted for connection to a source of a biocompatible gas such as air, argon, carbon dioxide, helium, nitrogen, and the like, or a combination thereof.  
           [0009]    A laser energy conduit, such as an optical fiber or an optical wave guide is disposed within the lumen of the sheath. The proximal end of the conduit extends through the closed proximal end of the sheath. The proximal end of the laser energy conduit is adapted for connection to a source of a relatively long wavelength laser energy, i.e., at least about 1,300 nanometers and up to about 11,000 nanometers. The distal end of the laser energy conduit is positioned within the lumen of the sheath near the open distal end thereof. The distal end of the energy conduit is adapted to emit laser energy.  
           [0010]    The laser energy delivery device can also include a handpiece at the proximal end of the sheath to facilitate handling and placement of the sheath and energy conduit. The gas inlet port can be spaced from the handpiece or can be defined by the handpiece itself.  
           [0011]    The distal end of the sheath can be flared out in a bell or funnel-like shape, and can be beveled if desired. The distal end of the sheath, and its accompanying energy conduit, can be bent at an angle from the axis of the handpiece to facilitate placement of the open distal end of the sheath against the tissue that is to be irradiated by laser energy. The laser energy delivery device of the present invention is suitable for delivering relatively long wavelength laser energy to a tissue in an aqueous medium with minimal loss of laser energy to the medium.  
           [0012]    When an aqueous liquid is present at the tissue site, carbon dioxide or other biocompatible gas is infused into the sheath or handpiece and through the passageway defined between the optical fiber and the sheath, and displaces the liquid in the region between the distal end of the sheath and the adjacent tissue, creating a substantially liquid-free region between the distal end of the energy conduit, from which laser energy is emitted, and the tissue. The substantially liquid-free region enables a substantially greater portion of the laser energy to be utilized to vaporize the target tissue compared with irradiation through an aqueous liquid that necessarily absorbs and dissipates at least some of the laser energy.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    In the drawings,  
         [0014]    [0014]FIG. 1 is a chart showing the relative absorption in water of various wavelengths of light energy;  
         [0015]    [0015]FIG. 2 is an external view of an embodiment of the laser energy delivery device of the present invention;  
         [0016]    [0016]FIG. 3 is an external view of an alternative embodiment of the device of FIG. 2;  
         [0017]    [0017]FIG. 4 is a partial, cross-sectional view of the distal end portion of an embodiment of the device of FIG. 3;  
         [0018]    [0018]FIG. 5 is a partial cross-sectional view of a preferred embodiment of the device of the present invention; and  
         [0019]    [0019]FIG. 6 is a partial external view of the device of FIG. 5, positioned within the male urethra for the treatment of a urinary blockage due to an enlarged prostate. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and are described in detail herein specific embodiments of the invention, with the understanding that the present disclosure is an exemplification of the principles of the invention and is not limited to the specific embodiments illustrated.  
         [0021]    In the device and method of present invention, air or another biologically compatible gas, such as argon, carbon dioxide, helium, nitrogen, or a mixture thereof, preferably carbon dioxide, is infused into a sheath disposed over a laser energy conduit such as an optical fiber or optical wave guide, and displaces liquid at the distal end of the sheath. Light energy from a laser that is optically coupled to the laser energy conduit is emitted at a wavelength of at least about 1,300 nanometers (referred to herein as long wavelength laser energy, or LW laser energy) from the distal end of the laser energy conduit. The entire sheath has an inside diameter slightly larger than the outside diameter of the optical fiber or wave guide. Preferably, the distal end portion of the sheath has an inside diameter somewhat larger than the inside diameter of the body of the sheath. In a particularly preferred embodiment, the distal end portion of the sheath is flared outwardly into a funnel or bell-like shape. Preferably the LW laser energy has a wavelength in the range of about 1,300 nanometers to about 11,000 nanometers.  
         [0022]    When the laser energy delivery device of the present invention is used to vaporize tissue in a duct, hollow organ, body cavity, or surgically created passageway, which is filled with a biologically compatible, clear aqueous liquid, the distal end of the sheath is brought into contact with, or close to, the target tissue. A biologically compatible gas is infused through the sheath to displace the liquid between the distal end of the optical fiber and the target tissue, creating a gas bubble therebetween. As a consequence, the target tissue is vaporized, ablated, or cut without wasting the laser energy by vaporizing the aqueous liquid.  
         [0023]    [0023]FIG. 1 illustrates the relative absorption of various wavelengths of light energy in water, according to Y. Hashishin and U. Kubo in “Development of Laser Endoscope for Coagulation and Incision,” published in  Lasers in the Musculoskeletal System , Pg. 81-84, Springer Verlag Berlin (2001). As FIG. 1 shows, light energy from Holmium:YAG, Erbium:YAG, CO, and CO 2  lasers is highly absorbed by water.  
         [0024]    [0024]FIG. 2 illustrates a laser energy delivery system, which includes a LW laser energy source  110 , capable of providing continuous wave, gated, or pulsed laser energy at a wavelength in the range of about 1,300 to about 11,000 nanometers, and which is optically connected to a preferred long wavelength laser energy delivery device  10  of the present invention. Laser energy conduit  130  extends through handpiece  140 , which is provided to facilitate the handling of laser energy conduit  130 . The proximal end of laser energy conduit  130  includes a coupler  120 , adapted for connection to a long wavelength laser energy source  110 . Handpiece  140  includes luer lock  150 , which is in open communication with handpiece  140  and gas supply tube  160 . Gas supply tube  160  is removably attached to luer lock  150 , and allows transport of air or other biologically compatible gas from a supply source (not shown) into handpiece  140 . Sheath  170  extends from within the distal end of handpiece  140  and defines a lumen through which laser energy conduit  130  extends. The distal end portion  180 , of sheath  170 , is open and allows gas that is infused into sheath  170  through luer lock  150  to exit sheath  170  at its open distal end.  
         [0025]    Sheath  170  can be made of any biologically compatible rigid or semi-rigid material. Preferably, sheath  170  is made of stainless steel, a rigid or semi-rigid plastic material, or a flexible, shape-memory nickel-titanium alloy such as nitinol, available from Memry, Inc., Bethel, Conn. Suitable semi-rigid plastic materials include polyvinyl chloride, block polyether amides, and the like materials. Distal end portion  180  of sheath  170  can be made of the same material as sheath  170  or a different material such as a natural or synthetic rubber material or a soft plastic material to facilitate safe contact with biological tissue. Alternatively, distal end portion  180  of sheath  170  can be coated with a natural or synthetic rubber.  
         [0026]    [0026]FIG. 3 illustrates a preferred embodiment of the present invention. In device  15 , the distal end portion consists of an outwardly flared distal end portion  190 , instead of being cylindrical as shown in FIG. 2. Flared distal end portion  190  can be a continuation of sheath  170  or can be a separate piece that is fixedly attached to the distal end of sheath  170 . Sheath  170  and its flared distal end portion  190  can be made of the same or different materials as described for the embodiment depicted in FIG. 2.  
         [0027]    [0027]FIG. 4 is a partial, cross-sectional view of another preferred embodiment of the LW laser energy delivery device of the present invention. Device  20  includes a handpiece  220 , defining port  222  and chamber  224 , and a sheath  230 . Sheath  230  is fixedly attached to the distal end of handpiece  220  and defines a lumen  232  which is in open communication with chamber  224 . Sheath  230  includes a distal end portion  240 , which has a larger inside diameter than the inside diameter of the remaining portion of sheath  230 . Laser energy conduit  210  extends through handpiece  220 , chamber  224  and lumen  232 . The distal end  212  of laser energy conduit  210  is positioned approximately at the open distal end  242  of sheath  230 . The laser energy conduit  210  is adapted at its proximal end for connection to a LW laser energy source (not shown). Laser energy conduit  210  forms a liquid and gas-tight seal with the handpiece  220  in the region  226  where the conduit  210  extends into the chamber  224 .  
         [0028]    Needle valve  254  is sealably attached to port  222  of handpiece  220 . Knob  252  is operably attached to needle valve  254  such that turning knob  252  in a clockwise direction, for example, seals the needle valve  254  in a closed position. Subsequently, turning knob  252  in a counter-clockwise manner moves needle valve  254  to an open position. Luer lock  260  defines channel  262  and is joined to the proximal end of the needle valve  254 . When needle valve  254  is in the open position, channel  262  of luer lock  260  is in open communication with port  222  and chamber  224  of handpiece  220  and with lumen  232  of sheath  230 .  
         [0029]    [0029]FIG. 5 illustrates a particularly preferred embodiment of the present invention. Laser energy conduit  310  in device  30  extends through handpiece  320  and is fixedly attached thereto. Sheath  330  extends into handpiece  320  and is attached to handpiece  320  by an adhesive or like expedient. Sheath  330  is bent at an angle φ from axis A of handpiece  320 . Sheath  330  can be made, for example, from stainless steel, a rigid or semi-rigid plastic, or a shape-memory nickel-titanium alloy, such as nitinol, or a combination of any of these materials.  
         [0030]    When sheath  330  is made of stainless steel, the angle φ at which the sheath  330  can be bent is limited by the relative outside diameter of sheath  330  and the inside diameter of an endoscope through which sheath  330  will be positioned when the device  30  is used. When sheath  330  is made of a flexible, shape-memory alloy, or a flexible or semi-rigid plastic, bend angle φ of sheath  330  can be in the range of about 20° to about 120° from axis A, preferably in the range of about 30° to about 90° from axis A.  
         [0031]    When sheath  330  is made of a flexible material such as a flexible or semi-rigid plastic, or a flexible shape-memory alloy, angle φ will diminish when sheath  330  is constrained within an endoscope channel. When sheath  330  is extended through an endoscope channel, angle φ will increase as distal end portion  340  of sheath  330  emerges from the distal end of the endoscope channel. Sheath  330  is preferably made of a nickel-titanium shape-memory alloy such as nitinol.  
         [0032]    In device  30 , sheath  330  defines a lumen  332  and an opening  350  spaced from handpiece  320 . Fitting  360  including port  370  forms a liquid and gas-tight seal around sheath  330  and is positioned around sheath  330  such that port  370  is in open communication with opening  350  of sheath  330 . Luer lock  380  is secured to port  370  so that luer lock  380  and port  370  are in open communication with the lumen  332  of sheath  330 .  
         [0033]    As shown in FIG. 5, flared distal end portion  340  of sheath  330  is beveled so that the open end  342  of sheath  330  is roughly parallel to axis A of handpiece  320 . Button  390  on handpiece  320  is positioned to indicate the direction of the bend of sheath  330 .  
         [0034]    [0034]FIG. 6 illustrates sheath  330  of device  30  (FIG. 5) positioned for use in the treatment of a urethral restriction due to an enlarged prostate. Sheath  330  extends through channel  410  of endoscope  400 . Endoscope  400  is positioned within the male urethra  420 , just proximal to prostrate  430 . Flared distal end portion  340  of sheath  330  is positioned to contact the inner surface of urethra  430  over lobe  440  of prostate  430 . The flared distal end portion  340  of sheath  330  is beveled at an angle, as described above. The bevel angle of the flare is selected to complement the angle of the bend in sheath  330 , enabling the flared distal end portion  340  of sheath  330  to efficiently contact the inner surface of urethra  420  at contact zone  450 .  
         [0035]    In use, a biocompatible gas, such as air, nitrogen, helium, argon, carbon dioxide, or mixtures thereof is infused through sheath  330  to displace surrounding liquid and create gas bubble  460  within and around the contact zone  450 . Excess gas bubbles  480  are shown escaping from main gas bubble  460 . The gas bubble  460  displaces fluid from the contact zone  450 , creating a fluid-free region through which LW laser light energy can pass with relatively little loss. Light energy from a LW laser can then be emitted from the distal end portion  340  of sheath  330  through laser energy conduit  310  (not shown) positioned within sheath  330  as described above. Very little gas is required to displace the fluid at contact zone  450 , and excess gas bubbles  480  escape from gas bubble  460  at contact zone  450  and can be absorbed by the surrounding fluid.  
         [0036]    Clearance of fluid from contact zone  450  allows the LW laser energy to efficiently ablate or vaporize tissue from the underlying lobe  440  of prostate  430 . Flared distal end portion  340  of sheath  330  can be moved along lobe  440  or  470 , and gas can be infused as LW laser energy is emitted. Alternatively, when sufficient tissue has been removed from contact zone  450  by laser irradiation, the flared distal end portion  340  of sheath  330  can be repositioned to form another contact zone  450  with lobe  440  or lobe  470  of prostate  430 , and gas can be infused and LW laser energy again can be applied to the tissue as needed, to clear the urethral restriction within the prostate  430 .  
         [0037]    The device and method of the present invention also can be utilized through an endoscope in a liquid medium to rapidly vaporize, ablate, resect or coagulate tumor tissue or non-malignant fibroid tissue in the female uterus, coagulate the surface of the uterus to treat menorrhagia, or to vaporize or coagulate tumor tissue elsewhere in the body, including the kidney, stomach or other organ. Using the devices of the present invention LW laser light energy can effectively coagulate bleeding vessels at a lower level of laser energy than conventional laser devices, enabling the devices of the present invention to be used, after the vaporization or resection procedure, to coagulate or cauterize any remaining bleeding vessels. Lower energy laser energy can also be used to shrink tissues, for example, the nucleus pulposa or annulus of a spinal disc.  
         [0038]    The present invention also provides a method of delivering relatively long wavelength laser energy to a body tissue in an aqueous liquid medium. The method involves positioning a laser energy delivery device of the present invention in a body lumen or cavity such as the made urethra, the female uterine cavity, a blood vessel, or a surgically prepared channel. The device is positioned so that the distal end of the device is in contact with a tissue site to be irradiated with laser energy. A gas supply source, operably linked to the gas inlet port provides a stream of biologically compatible gas through the lumen of the device sheath, which exits the lumen at its open distal end in contact with the tissue. The gas is supplied at a pressure and flow rate sufficient to displace the aqueous fluid medium surrounding the tissue site at the point of contact with the distal end of the sheath and maintain a substantially liquid-free zone between the distal end of the laser energy conduit component of the device and the tissue to be treated.  
         [0039]    In a preferred embodiment, the method comprises the steps of:  
         [0040]    (a) providing an endoscope defining at least one channel having an open distal end and an open proximal end;  
         [0041]    (b) providing a source of long wavelength laser energy, a laser energy delivery device of the present invention operably coupled to the source of laser energy, and a source of biocompatible gas operably connected to the laser energy delivery device;  
         [0042]    (c) positioning the endoscope within a body tissue lumen or cavity such that the open distal end of the endoscope channel is disposed opposite or near a tissue site in need of laser energy treatment;  
         [0043]    (d) positioning the laser energy delivery device through the endoscope channel such that the distal end of the device extends through the open distal end of the endoscope channel and contacts a body tissue site in need of laser energy treatment;  
         [0044]    (e) supplying gas from the source of biocompatible gas through the laser energy delivery device to the tissue site at a pressure and flow rate sufficient to displace liquid from the tissue site in contact with the open distal end of the sheath and maintain a substantially liquid-free region between the distal end of the laser energy conduit and the body tissue; and  
         [0045]    (f) supplying long wavelength laser energy from the laser energy source through the substantially liquid-free region to the tissue for a period of time and at a laser energy intensity sufficient to treat the tissue.  
         [0046]    The devices of the present invention can be used for treatments such as to effectively fragment or vaporize stones in the urinary tract (a procedure called lithotripsy), to vaporize bone of the lamina or other extensions of the vertebra to open the foraminal space in the spine and enable a portion of a herniated, ruptured or degenerated spinal disc to be vaporized or, at a lower energy level, to be shrunk, to clear a urethral restriction due to an enlarged prostate, to vaporize or coagulate tumor tissue, to cauterize tissue, and the like.  
         [0047]    Sources of laser energy useful in conjunction with the device and method of the present invention include filtered, third harmonic Nd:YAG lasers, emitting at about 1,440 nanometers, Holmium:YAG lasers and the like, emitting at about 2,100 nanometers, Erbium:YAG lasers and the like, emitting at about 2,940 nanometers, carbon monoxide (CO) lasers, emitting at about 6000 nanometers, and carbon dioxide (CO 2 ) lasers, emitting at about 10,600 nanometers.  
         [0048]    A preferred source of laser energy is the 80 watt Omnipulse™ MAX Holmium:YAG laser manufactured by Trimedyne, Inc. of Irvine, Calif. This laser emits light energy at a wavelength of about 2,100 nanometers, in pulses with a duration of about 250 to 350 microseconds, with a repetition rate up to 60 pulses per second. The peak energy output of the Omnipulse™ MAX is up to about 3.5 joules per pulse at a repetition rate of about 23 pulses per second (up to about 7 joules per pulse in the Double Pulse™ mode at a repetition rate of about 11 pulses per second).  
         [0049]    Typically, a source of laser energy having a wavelength in the range of about 1,300 to about 2,500 nanometers is optically coupled to a laser energy conduit such as an optical fiber or, through mirrors mounted on an articulated arm, to a hollow waveguide. Ordinary quartz or fused silica optical fibers may be used with Alexandrite lasers, but optical fibers with a low hydroxyl content, called “low OH” optical fibers, such as manufactured by the 3M Company of St. Paul, Minn., must be used with Holmium lasers. Laser energy of wavelengths of in the range of about 2,500 nanometers to about 11,000 nanometers is best delivered through a series of mirrors attached to an articulated arm, to whose distal end a short length of hollow waveguide or an optical fiber of a special composition, such as sapphire, zirconium fluoride (ZrF 4 ), chalcogenide (As 2 S 3 ), and the like, is attached.  
         [0050]    In one preferred embodiment, to facilitate handling of the optical fiber, the handpiece is disposed about 5 to 40 cm, preferably about 10 to 30 cm, from the distal end of the optical fiber. The sheath extends over the laser energy conduit from within the distal end of the handpiece to the distal end of the laser energy conduit. The sheath can be made wholly of metal or plastic or may consist of a metal shaft with an attached soft plastic distal end, a semi-rigid plastic shaft with an attached soft plastic distal end, or a semi-rigid plastic shaft with an attached metal distal end.  
         [0051]    The gas inlet port in the sheath or handpiece enables carbon dioxide or other biologically compatible gas to be infused through the space between the exterior of the optical fiber and the interior of the sheath. The sheath can have an inside diameter larger than the outside diameter of the optical fiber, the distal end portion of the sheath may have a somewhat larger diameter than its shaft, or the distal end portion of the sheath can be flared-out into a bell or funnel-like shape.  
         [0052]    Flaring-out the distal end of the sheath reduces the risk of the light energy inadvertently striking and burning the distal end of the sheath and creates a reservoir of gas at its distal end. The flared-out end portion of the sheath can be about 0.3 to 2 cm in length, preferably about 0.5 to 1.5 cm long, and can have an inside diameter in the range of about 1.5 to about 5 times the outside diameter of the optical fiber, preferably about 2 to about 3 times the outside diameter of the optical fiber.  
         [0053]    The proximal end of the laser energy conduit of a device of the present invention is optically coupled to an appropriate laser energy source. The energy transmitted from the laser source through the energy conduit, such as an optical fiber or hollow waveguide, can be used, for example, to vaporize or resect (cut into sections) an enlarged prostate gland that is blocking urine flow through the urethra, or to vaporize bone to open the foraminal space in the spine.  
         [0054]    Typically, for treatment of enlarged prostate, an endoscope is inserted into the urethra through the penis and the distal end of the endoscope is positioned near the prostate. A liquid, such as sterile water, saline, a glucose or dextrose solution, or other clear liquid is infused into the urethra through the distal end of the endoscope. Alternatively, the clear liquid can be simultaneously infused and withdrawn (circulated) to carry away debris and maintain a clear field of view at the distal end of the endoscope. The sheath and optical fiber portion of the device of the present invention is extended through a channel in the endoscope, such that the distal ends of the optical fiber and the sheath project outwardly from the open distal end of the endoscope channel and the distal end of the sheath contacts the tissue to be irradiated.  
         [0055]    A biocompatible gas, such as carbon dioxide, is infused through the gas inlet port and into the lumen of the sheath. A gas bubble at the open distal end of the sheath creates a gas “cavity” between the tissue that is to be irradiated and the distal end of the optical fiber. Light energy from the laser is emitted from the distal end of an optical fiber, passes through the gas cavity and into the tissue, where the long wavelength laser energy vaporizes or ablates the tissue. The gas bubble at the distal end of the sheath prevents the aqueous liquid around the tissue from absorbing laser energy being emitted from the optical fiber.  
         [0056]    Numerous variations and modifications of the embodiments described above can be effected without departing from the spirit and scope of the novel features of the invention. No limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. The appended claims are intended to cover all such modifications as fall within the scope of the claims.