PATENT ABSTRACT
Tissue is resected and extracted from an interior location in a patient&#39;s body using a probe or tool which both effects resection and causes vaporization of a liquid or other fluid to propel the resected tissue through an extraction lumen of the resecting device. Resection is achieved using an electrosurgical electrode assembly including a first electrode on a resecting member and a second electrode within a resection probe or tool. Over a first resecting portion, radio frequency current helps resect the tissue and over a second or over transition region, the RF current initiates vaporization of the fluid or other liquid to propel the tissue from the resection device. In one embodiment, an extending element extends from a housing and into a channel in a resecting member as the resecting member moves toward a distal position.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 61/716,049, filed Oct. 19, 2012, the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to tissue resection devices and methods, for example, for use in resecting and extracting uterine fibroid tissue, polyps and other abnormal uterine tissue. 
     BACKGROUND OF THE INVENTION 
     Uterine fibroids are non-cancerous tumors that develop in the wall of uterus. Such fibroids occur in a large percentage of the female population with some studies indicating up to 40 percent of all women have fibroids. Uterine fibroids can grow over time to be several centimeters in diameter and symptoms can include menorrhagia, reproductive dysfunction, pelvic pressure and pain. 
     One current treatment of fibroids is hysteroscopic resection or myomectomy which involves transcervical access to the uterus with a hysteroscope together with insertion of a resecting instrument through a working channel in the hysteroscope. The resecting instrument may be a mechanical tissue cutter or an electrosurgical resection device such as an RF loop. Mechanical cutting devices are disclosed in U.S. Pat. Nos. 7,226,459; 6,032,673 and 5,730,752 and U.S. Published Patent Appl. 2009/0270898. An electrosurgical resecting device is disclosed in U.S. Pat. No. 5,906,615. 
     In a myomectomy or hysteroscopic resection, the initial step of the procedure includes distention of the uterine cavity to create a working space for assisting viewing through the hysteroscope. In a relaxed state, the uterine cavity collapses with the uterine walls in contact with one another. A fluid management system is used to distend the uterus to provide a working space by means of a fluid being introduced through a passageway in the hysteroscope under sufficient pressure to expand or distend the uterine cavity. The fluids used to distend the uterus are typically liquid aqueous solutions such as a saline solution or a sugar-based aqueous solution. 
     While hysteroscopic resection can be effective in removing uterine fibroids, many commercially available instrument are too large in diameter and thus require anesthesia in an operating room environment. Conventional resectoscopes require cervical dilation to about 9 mm. What is needed is a system that can effectively resect and remove fibroid tissue through a small diameter hysteroscope. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods for resecting and removing target tissue from a patient&#39;s body, such as fibroids from a uterus. The tissue is resected, captured in a probe, catheter, or other tissue-removal device, and expelled from the resecting device by vaporizing a liquid adjacent to the captured tissue in order to propel the tissue from the device, typically through an extraction or other lumen present in a body or shaft of the device. Exemplary embodiments of the tissue resecting device comprise an RF electrode, wherein the electrode can be advanced past a tissue-receiving window on the device in order to sever a tissue strip and capture the strip within an interior volume or receptacle on the device. The liquid or other expandable fluid is also present in the device, and energy is applied to the fluid in order to cause rapid expansion, e.g., vaporization, in order to propel the resected tissue strip through the extraction lumen. In this way, the dimensions of the extraction lumen can be reduced, particularly in the distal regions of the device where size is of critical importance. 
     In another aspect of the invention, a tubular resecting device has an inner resecting sleeve that reciprocates in a passageway in an outer sleeve or housing to resect tissue in a window of the outer sleeve. Within a distal portion of the stroke of the inner resecting sleeve, a projecting element extends into a tissue extraction channel in the inner sleeve. In a variation, the cross-section of the projecting element functions in a scissor-like manner to push the tissue against an electrode edge of the inner sleeve to resect the tissue. The projecting element can have an axial length of at least 2 mm. The projecting element also can have a tapered region for insuring that the inner sleeve when moving distally is guided over the projecting element even if there is flex in the distal portion of the outer sleeve in the region of the tissue-receiving window. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of an assembly including a hysteroscope and a tissue resecting device corresponding to the invention that is inserted through the working channel of the hysteroscope. 
         FIG. 2  is a schematic perspective view of a fluid management system used for distending the uterus and for assisting in electrosurgical tissue resection and extraction. 
         FIG. 3  is a cross-sectional view of the shaft of the hysteroscope of  FIG. 1  showing various channels therein. 
         FIG. 4  is a schematic side view of the working end of the electrosurgical tissue resecting device of  FIG. 1  showing an outer sleeve, a reciprocating inner sleeve and an electrode arrangement. 
         FIG. 5  is a schematic perspective view of the working end of the inner sleeve of  FIG. 4  showing its electrode edge. 
         FIG. 6A  is a schematic cut-away view of a portion of outer sleeve, inner RF resecting sleeve and a tissue-receiving window of the outer sleeve. 
         FIG. 6B  is a schematic view of a distal end portion another embodiment of inner RF resecting sleeve. 
         FIG. 7A  is a cross sectional view of the inner RF resecting sleeve of  FIG. 6B  taken along line  7 A- 7 A of  FIG. 6B . 
         FIG. 7B  is another cross sectional view of the inner RF resecting sleeve of  FIG. 6B  taken along line  7 B- 7 B of  FIG. 6B . 
         FIG. 8  is a schematic view of a distal end portion of another embodiment of inner RF resecting sleeve. 
         FIG. 9A  is a cross sectional view of the RF resecting sleeve of  FIG. 8  taken along line  9 A- 9 A of  FIG. 8 . 
         FIG. 9B  is a cross sectional view of the RF resecting sleeve of  FIG. 8  taken along line  9 B- 9 B of  FIG. 8 . 
         FIG. 10A  is a perspective view of the working end of the tissue resecting device of  FIG. 1  with the reciprocating RF resecting sleeve in a non-extended position. 
         FIG. 10B  is a perspective view of the tissue resecting device of  FIG. 1  with the reciprocating RF resecting sleeve in a partially extended position. 
         FIG. 10C  is a perspective view of the tissue resecting device of  FIG. 1  with the reciprocating RF resecting sleeve in a fully extended position across the tissue-receiving window. 
         FIG. 11A  is a sectional view of the working end of the tissue resecting device of  FIG. 10A  with the reciprocating RF resecting sleeve in a non-extended position. 
         FIG. 11B  is a sectional view of the working end of  FIG. 10B  with the reciprocating RF resecting sleeve in a partially extended position. 
         FIG. 11C  is a sectional view of the working end of  FIG. 10C  with the reciprocating RF resecting sleeve in a fully extended position. 
         FIG. 12A  is an enlarged sectional view of the working end of tissue resecting device of  FIG. 11B  with the reciprocating RF resecting sleeve in a partially extended position showing the RF field in a first RF mode and plasma resection of tissue. 
         FIG. 12B  is an enlarged sectional view of the working end of  FIG. 11C  with the reciprocating RF resecting sleeve almost fully extended and showing the RF fields switching to a second RF mode from a first RF mode shown in  FIG. 12A . 
         FIG. 12C  is an enlarged sectional view of the working end of  FIG. 11C  with the reciprocating RF resecting sleeve again almost fully extended and showing the explosive vaporization of a captured liquid volume to expel resected tissue in the proximal direction. 
         FIG. 13  is an enlarged perspective view of a portion of the working end of  FIG. 12C  showing an interior chamber and a fluted projecting element. 
         FIG. 14  is a sectional view of the working end of  FIG. 12C  showing an interior chamber and a variation of a projecting element. 
         FIG. 15  is a sectional view of the working end of  FIG. 12C  showing an interior chamber and a variation of a projecting element configured to explosively vaporize the captured liquid volume. 
         FIG. 16A  is sectional view of a working end of a resection probe similar to that of  FIGS. 11A-12C  showing a variation of a projecting element and resecting sleeve. 
         FIG. 16B  is another view of the working end of  FIG. 16A  with the resecting sleeve moving distally over a tapered portion of the projecting element. 
         FIG. 17  is a schematic view of a system for fibroid removal including a fluid management system. 
         FIG. 18  is a schematic view of the fluid management system of  FIG. 17  with an enlarged view of the working end of a tissue resecting probe as generally described in  FIGS. 1-12C  in a position to resect and remove a fibroid. 
         FIG. 19  is a cut-away schematic view of a filter module of the fluid management system of  FIGS. 17-18 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an assembly that comprises an endoscope  50  used for hysteroscopy together with a tissue resecting and extracting device  100  extending through a working channel  102  of the endoscope. The endoscope or hysteroscope  50  has a handle  104  coupled to an elongated shaft  105  having a diameter of 3 mm to 7 mm. The working channel  102  therein may be round, D-shaped or any other suitable shape. The endoscope shaft  105  is further configured with an optics channel  106  and one or more fluid inflow/outflow channels  108   a ,  108   b  ( FIG. 3 ) that communicate with connectors  110   a ,  110   b  configured for coupling to a fluid inflow source  120 , or optionally a negative pressure source  125  ( FIGS. 1-2 ). The fluid inflow source  120  is a component of a fluid management system  126  as is known in the art ( FIG. 2 ) which comprises a fluid container  128  and pump mechanism  130  which pumps fluid through the hysteroscope  50  into the uterine cavity. As can be seen in  FIG. 2 , the fluid management system  126  further includes the negative pressure source  125  coupled to the tissue resecting device  100 . The handle  104  of the endoscope includes the angled extension portion  132  with optics to which a videoscopic camera  135  can be operatively coupled. A light source  136  is coupled to light coupling  138  on the handle of the hysteroscope  50 . The working channel  102  of the hysteroscope is configured for insertion and manipulation of the tissue resecting and extracting device  100 , for example to treat and remove fibroid tissue. In one embodiment, the hysteroscope shaft  105  has an axial length of 21 cm, and can comprise a 0° scope, or 15° to 30° scope. 
     Still referring to  FIG. 1 , the tissue resecting device  100  has a highly elongated shaft assembly  140  configured to extend through the working channel  102  in the hysteroscope. A handle  142  of the tissue resecting device  100  is adapted for manipulating the electrosurgical working end  145  of the device. In use, the handle  142  can be manipulated both rotationally and axially, for example, to orient the working end  145  to resect targeted fibroid tissue. The tissue resecting device  100  has subsystems coupled to its handle  142  to enable electrosurgical resection of targeted tissue. A radiofrequency generator or RF source  150  and controller  155  are coupled to at least one RF electrode carried by the working end  145  as will be described in detail below. In one embodiment shown in  FIG. 1 , an electrical cable  156  and negative pressure source  125  are operatively coupled to a connector  158  in handle  142 . The electrical cable couples the RF source  150  to the electrosurgical working end  145 . The negative pressure source  125  communicates with a tissue-extraction channel  160  in the shaft assembly  140  of the tissue resecting device  100  ( FIG. 4 ). 
       FIG. 1  further illustrates a seal housing  162  that carries a flexible seal  164  within the hysteroscope handle  104  for sealing the shaft  140  of the tissue resecting device  100  in the working channel  102  to prevent distending fluid from escaping from a uterine cavity. 
     In one embodiment as shown in  FIG. 1 , the handle  142  of tissue resecting device  100  includes a motor drive  165  for reciprocating or otherwise moving a resecting component of the electrosurgical working end  145  as will be described below. The handle  142  optionally includes one or more actuator buttons  166  for actuating the device. In another embodiment, a footswitch can be used to operate the device. In one embodiment, the system includes a switch or control mechanism to provide a plurality of reciprocation speeds, for example 1 Hz, 2 Hz, 3 Hz, 4 Hz and up to 8 Hz. Further, the system can include a mechanism for moving and locking the reciprocating resecting sleeve in a non-extended position and in an extended position. Further, the system can include a mechanism for actuating a single reciprocating stroke. 
     Referring to  FIGS. 1 and 4 , an electrosurgical tissue resecting device has an elongate shaft assembly  140  extending about longitudinal axis  168  comprising an exterior or first outer sleeve  170  with passageway or lumen  172  therein that accommodates a second or inner sleeve  175  that can reciprocate (and optionally rotate or oscillate) in lumen  172  to resect tissue as is known in that art. In one embodiment, the tissue-receiving window  176  in the outer sleeve  170  has an axial length ranging between 10 mm and 30 mm and extends in a radial angle about outer sleeve  170  from about 45° to 210° relative to axis  168  of the sleeve. The outer and inner sleeves  170  and  175  can comprise a thin-wall stainless steel material and function as opposing polarity electrodes as will be described in detail below.  FIGS. 6A-8  illustrate insulative layers carried by the outer and inner sleeves  170  and  175  to limit, control and/or prevent unwanted electrical current flows between certain portions of the sleeve. In one embodiment, a stainless steel outer sleeve  170  has an O.D. of 0.143″ with an I.D. of 0.133″ and with an inner insulative layer (described below) the sleeve has a nominal I.D. of 0.125″. In this embodiment, the stainless steel inner sleeve  175  has an O.D. of 0.120″ with an I.D. of 0.112″. The inner sleeve  175  with an outer insulative layer has a nominal O.D. of about 0.123″ to 0.124″ to reciprocate in lumen  172 . In other embodiments, outer and or inner sleeves can be fabricated of metal, plastic, ceramic of a combination thereof. The cross-section of the sleeves can be round, oval or any other suitable shape. 
     As can be seen in  FIG. 4 , the distal end  177  of inner sleeve  175  comprises a first polarity electrode with distal electrode edge  180  about which plasma can be generated. The electrode edge  180  also can be described as an active electrode during tissue resection since the electrode edge  180  then has a substantially smaller surface area than the opposing polarity or return electrode. In one embodiment in  FIG. 4 , the exposed surfaces of outer sleeve  170  comprises the second polarity electrode  185 , which thus can be described as the return electrode since during use such an electrode surface has a substantially larger surface area compared to the functionally exposed surface area of the active electrode edge  180 . 
     In one aspect of the invention, the inner sleeve or resecting sleeve  175  has an interior tissue extraction lumen  160  with first and second interior diameters that are adapted to electrosurgically resect tissue volumes rapidly—and thereafter consistently extract the resected tissue strips through the highly elongated lumen  160  without clogging. Now referring to  FIGS. 5 and 6A , it can be seen that the inner sleeve  175  has a first diameter portion  190 A (with diameter A) that extends from the handle  142  ( FIG. 1 ) to a distal region  192  of the sleeve  175  wherein the tissue extraction lumen transitions to a smaller second diameter lumen  190 B with a reduced diameter indicated at B which is defined by the electrode sleeve element  195  that provides the resection electrode edge  180 . The axial length C of the reduced cross-section lumen  190 B can range from about 2 mm to 20 mm. In one embodiment, the first diameter A is 0.112″ and the second reduced diameter B is 0.100″. As shown in  FIG. 5 , the inner sleeve  175  can be an electrically conductive stainless steel and the reduced diameter electrode portion also can comprise a stainless steel electrode sleeve element  195  that is welded in place by weld  196  ( FIG. 6A ). In another alternative embodiment, the electrode and reduced diameter electrode sleeve element  195  comprises a tungsten tube that can be press fit into the distal end  198  of inner sleeve  175 .  FIGS. 5 and 6A  further illustrate the interfacing insulation layers  202  and  204  carried by the first and second sleeves  170 ,  175 , respectively. In  FIG. 6A , the outer sleeve  170  is lined with a thin-wall insulative material  200 , such as PFA, or another material described below. Similarly, the inner sleeve  175  has an exterior insulative layer  202 . These coating materials can be lubricious as well as electrically insulative to reduce friction during reciprocation of the inner sleeve  175 . 
     The insulative layers  200  and  202  described above can comprise a lubricious, hydrophobic or hydrophilic polymeric material. For example, the material can comprise a bio-compatible material such as PFA, TEFLON®, polytetrafluroethylene (PTFE), FEP (Fluorinated ethylenepropylene), polyethylene, polyamide, ECTFE (Ethylenechlorotrifluoro-ethylene), ETFE, PVDF, polyvinyl chloride or silicone. 
     Now turning to  FIG. 6B , another variation of inner sleeve  175  is illustrated in a schematic view together with a tissue volume being resected with the plasma electrode edge  180 . In this embodiment, as in other embodiments in this disclosure, the RF source operates at selected operational parameters to create plasma around the edge  180  of electrode sleeve  195  as is known in the art. Thus, the plasma generated at electrode edge  180  can ablate a path P in the tissue  220  and is suited for resecting fibroid tissue and other abnormal uterine tissue. In  FIG. 6B , the distal portion of the resecting sleeve  175  includes a ceramic collar  222  which is proximate to the distal edge  180  of the electrode sleeve  195 . The ceramic collar  222  functions to confine plasma formation about the distal electrode edge  180  and functions further to prevent plasma from contacting and damaging the polymer insulative layer  202  on the resecting sleeve  175  during operation. In one aspect of the invention, the path P ablated in the tissue  220  with the plasma at electrode edge  180  provides a path P having an ablated width indicated at W, wherein such path width W is substantially wide due to tissue vaporization. This vaporization of tissue in path P to provide the resection is substantially different than the effect of resecting similar tissue with a sharp blade edge, as in various prior art devices. A sharp blade edge can divide tissue (without cauterization) but applies mechanical force to the tissue and may prevent a large cross section slug of tissue from being resected. In contrast, the plasma at the electrode edge  180  can vaporize a path Pin tissue without applying any substantial force on the tissue to thus resect larger cross sections or strips of tissue. Further, the plasma resecting effect reduces the cross section of tissue strip  225  received in the reduced cross-section region  190 B of the tissue extraction lumen  160 .  FIG. 6B  depicts a tissue strip  225  entering the reduced cross-section region  190 B, wherein the tissue strip has a smaller cross-section than the lumen due to the vaporization of tissue. Further, the cross section of tissue strip  225  as it enters the larger cross-section lumen  190 A results in even greater free space  197  around the tissue strip  225 . Thus, the resection of tissue with the plasma electrode edge  180 , together with the lumen transition from the smaller cross-section ( 190 B) to the larger cross-section ( 190 A) of the tissue-extraction lumen  160  can significantly reduce or eliminate the potential for successive resected tissue strips  225  clogging the lumen. Prior art resection devices with such a small diameter tissue-extraction lumen typically have problems with tissue clogging. 
     In another aspect of the invention, the negative pressure source  125  coupled to the proximal end of tissue-extraction lumen  160  (see  FIGS. 1 and 4 ) also assists in aspirating and moving tissue strips  225  in the proximal direction to a collection reservoir (not shown) outside the handle  142  of the resecting device. 
       FIGS. 7A-7B  illustrate the change in lumen diameter of resecting sleeve  175  of  FIG. 6B .  FIG. 8  illustrates the distal end of a variation of resecting sleeve  175 ′ which is configured with an electrode resecting element  195 ′ that is partially tubular in contrast to the previously described tubular electrode element  195  ( FIGS. 5 and 6A ).  FIGS. 9A-9B  again illustrate the change in cross-section of the tissue-extraction lumen between reduced cross-section region  190 B′ and the increased cross-section region  190 A′ of the resecting sleeve  175 ′ of  FIG. 8 . Thus, the functionality remains the same whether the resecting electrode element  195 ′ is tubular or partly tubular. In  FIG. 8A , the ceramic collar  222 ′ is shown, in one variation, as extending only partially around sleeve  175 ′ to cooperate with the radial angle of resecting electrode element  195 ′. Further, the variation of  FIG. 8  illustrates that the ceramic collar  222 ′ has a larger outside diameter than insulative layer  202 . Thus, friction may be reduced since the short axial length of the ceramic collar  222 ′ interfaces and slides against the interfacing insulative layer  200  about the inner surface of lumen  172  of outer sleeve  170 . 
     In general, one aspect of the invention comprises a tissue resecting and extracting device ( FIGS. 10A-11C ) that includes first and second concentric sleeves having an axis and wherein the second (inner) sleeve  175  has an axially-extending tissue-extraction lumen therein, and wherein the second sleeve  175  is moveable between axially non-extended and extended positions relative to a tissue-receiving window  176  in first sleeve  170  to resect tissue, and wherein the tissue extraction lumen  160  has first and second cross-sections. The second sleeve  175  has a distal end configured as a plasma electrode edge  180  to resect tissue disposed in tissue-receiving window  176  of the first sleeve  170 . Further, the distal end of the second sleeve, and more particularly, the electrode edge  180  is configured for plasma ablation of a substantially wide path in the tissue. In general, the tissue resecting device is configured with a tissue extraction lumen  160  having a distal end portion with a reduced cross-section that is smaller than a cross-section of medial and proximal portions of the lumen  160 . 
     In one aspect of the invention, referring to  FIGS. 7A-7B and 9A-9B , the tissue-extraction lumen  160  has a reduced cross-sectional area in lumen region  190 B proximate the plasma resecting tip or electrode edge  180  wherein said reduced cross section is less than 95%, 90%, 85% or 80% than the cross sectional area of medial and proximal portions  190 A of the tissue-extraction lumen, and wherein the axial length of the tissue-extraction lumen is at least 10 cm, 20 cm, 30 cm or 40 cm. In one embodiment of tissue resecting device  100  for hysteroscopic fibroid resection and extraction ( FIG. 1 ), the shaft assembly  140  of the tissue resecting device is 35 cm in length. 
       FIGS. 10A-10C  illustrate the working end  145  of the tissue resecting device  100  with the reciprocating resecting sleeve or inner sleeve  175  in three different axial positions relative to the tissue receiving window  176  in outer sleeve  170 . In  FIG. 10A , the resecting sleeve  175  is shown in a retracted or non-extended position in which the sleeve  175  is at it proximal limit of motion and is prepared to advance distally to an extended position to thereby electrosurgically resect tissue positioned in and/or suctioned into window  176 .  FIG. 10B  shows the resecting sleeve  175  moved and advanced distally to a partially advanced or medial position relative to tissue resection window  176 .  FIG. 10C  illustrates the resecting sleeve  175  fully advanced and extended to the distal limit of its motion wherein the plasma resecting electrode  180  has extended past the distal end  226  of tissue-receiving window  176  at which moment the tissue strip  225  is resected from tissue volume  220  and captured in reduced cross-sectional lumen region  190 B. 
     Now referring to  FIGS. 10A-10C  and  FIGS. 11A-11C , another aspect of the invention comprises tissue displacement mechanisms provided by multiple elements and processes to displace and move tissue strips  225  in the proximal direction in lumen  160  of resecting sleeve  175  to thus ensure that tissue does not clog the lumen of the inner sleeve  175 . As can seen in  FIG. 10A  and the enlarged views of  FIGS. 11A-11C , one tissue displacement mechanism comprises a projecting element  230  that extends proximally from distal tip  232  which is fixedly attached to outer sleeve  170 . The projecting element  230  extends proximally along central axis  168  in a distal chamber  240  defined by outer sleeve  170  and distal tip  232 . In one embodiment depicted in  FIG. 11A , the shaft-like projecting element  230 , in a first functional aspect, comprises a mechanical pusher that functions to push a captured tissue strip  225  proximally from the small cross-section lumen  190 B of resecting sleeve  175  as the sleeve  175  moves to its fully advanced or extended position. In a second functional aspect, the chamber  240  in the distal end of sleeve  170  is configured to capture a volume of saline distending fluid  244  from the working space, and wherein the existing RF electrodes of the working end  145  are further configured to explosively vaporize the captured fluid  244  to generate proximally-directed forces on tissue strips  225  resected and disposed in lumen  160  of the resecting sleeve  175 . Both of these two functional elements and processes (tissue displacement mechanisms) can apply substantial mechanical force to captured tissue strips  225 . For example, the explosive vaporization of liquid in chamber  240  can function to move tissue strips  225  in the proximal direction in the tissue-extraction lumen  160 . It has been found that using the combination of multiple functional elements and processes can virtually eliminate the potential for tissue clogging the tissue extraction lumen  160 . 
     More in particular,  FIGS. 12A-12C  illustrate sequentially the functional aspects of the tissue displacement mechanisms and the explosive vaporization of fluid captured in chamber  240 . In  FIG. 12A , the reciprocating resecting sleeve  175  is shown in a medial position advancing distally wherein plasma at the electrode edge  180  is resecting a tissue strip  225  that is disposed within lumen  160  of the resecting sleeve  175 . In  FIG. 12A-12C , it can be seen that the system operates in first and second electrosurgical modes corresponding to the reciprocation and axial range of motion of resecting sleeve  175  relative to the tissue-receiving window  176 . As used herein, the term “electrosurgical mode” refers to which electrode of the two opposing polarity electrodes functions as an “active electrode” and which electrode functions as a “return electrode”. The terms “active electrode” and “return electrode” are used in accordance with convention in the art—wherein an active electrode has a smaller surface area than the return electrode which thus focuses RF energy density about such an active electrode. In the working end  145  of  FIGS. 10A-11C , the resecting electrode element  195  and its electrode edge  180  must comprise the active electrode to focus energy about the electrode to generate the plasma for tissue resection. Such a high-intensity, energetic plasma at the electrode edge  180  is needed throughout stroke X indicated in  FIGS. 12A-12B  to resect tissue. The first mode occurs over an axial length of travel of inner sleeve  175  as it crosses the tissue receiving window  176 , at which time the entire exterior surface of outer sleeve  170  comprises the return electrode indicated at  185 . The electrical fields EF of the first RF mode are indicated schematically generally in  FIG. 12A . 
       FIG. 12B  illustrates the moment in time at which the distal advancement or extension of inner resecting sleeve  175  entirely crosses the tissue-receiving window  176 . At this time, the electrode sleeve  195  and its electrode edge  180  are confined within the mostly insulated-wall chamber  240  defined by the outer sleeve  170  and distal tip  232 . At this moment, the system is configured to switch to the second RF mode in which the electric fields EF switch from those described previously in the first RF mode. As can be seen in  FIG. 12B , in this second mode, the limited interior surface area  250  of distal tip  232  that interfaces chamber  240  functions as an active electrode and the distal end portion of resecting sleeve  175  exposed to chamber  240  acts as a return electrode. In this mode, very high energy densities occur about surface  250  and such a contained electric field EF can explosively and instantly vaporize the fluid  244  captured in chamber  240 . The expansion of water vapor can be dramatic and can thus apply tremendous mechanical forces and fluid pressure on the tissue strip  225  to move the tissue strip in the proximal direction in the tissue extraction lumen  160 .  FIG. 12C  illustrates such explosive or expansive vaporization of the distention fluid  244  captured in chamber  240  and further shows the tissue strip  225  being expelled in the proximal direction in the lumen  160  of inner resecting sleeve  175 . In another variation,  FIG. 14  further shows the relative surface areas of the active and return electrodes at the extended range of motion of the resecting sleeve  175 , again illustrating that the surface area of the non-insulated distal end surface  250  is small compared to surface  255  of electrode sleeve which comprises the return electrode. 
     Still referring to  FIGS. 12A-12C , it has been found that a single power setting on the RF source  150  and controller  155  can be configured both (i) to create plasma at the electrode edge  180  of electrode sleeve  195  to resect tissue in the first mode, and (ii) to explosively vaporize the captured distention fluid  244  in the second mode. Further, it has been found that the system can function with RF mode-switching automatically at suitable reciprocation rates ranging from 0.5 cycles per second to 8 or 10 cycles per second. It has been found that the tissue resecting device described above can resect and extract tissue at the rate of from 4 grams/min to 20 grams/min without any potential for tissue strips  225  clogging the tissue-extraction lumen  160 , depending on the diameter of the device. In one embodiment, a negative pressure source  125  can be coupled to the tissue-extraction lumen  160  to apply additional tissue-extracting forces to tissue strips  225  in the system. 
     Of particular interest, the fluid-capture chamber  240  defined by sleeve  170  and distal tip  232  can be designed to have a selected volume, exposed electrode surface area, length and geometry to optimize the expelling forces applied to resected tissue strips  225 . In one embodiment, the diameter of the chamber is 3.175 mm and the length is 5.0 mm which taking into account the projecting element  230 , provides a captured fluid volume of approximately 0.040 mL. In other variations, the captured fluid volume can range from 0.004 to 0.080 mL. 
     In one example, a chamber  240  with a captured liquid volume of 0.040 mL together with 100% conversion efficiency in an instantaneous vaporization would require 103 Joules to heat the liquid from room temperature to water vapor. In operation, since a Joule is a W*s, and the system reciprocates at 3 Hz, the power required would be on the order of 311 W for full, instantaneous conversion of the captured liquid to water vapor. A corresponding theoretical expansion of 1700× would occur in the phase transition, which would results in up to 25,000 psi instantaneously (14.7 psi×1700), although due to losses in efficiency and non-instantaneous expansion, the actual pressures would be less. In any event, the pressures are substantial and can apply expelling forces sufficient to expel the captured tissue strips  225  along the length of the extraction channel  160  in the probe. 
     Referring to  FIG. 12A , the interior chamber  240  can have an axial length from about 0.5 mm to 10 mm to capture a liquid volume ranging from about 0.004 mL 0.01 mL. It can be understood in  FIG. 12A , that the interior wall of chamber  240  has an insulator layer  200  which thus limits the electrode surface area  250  exposed to chamber  240 . In one embodiment, the distal tip  232  is stainless steel and is welded to outer sleeve  170 . The post element  248  is welded to tip  232  or machined as a feature thereof. The projecting element  230  in this embodiment is a non-conductive ceramic. 
       FIG. 13  shows the cross-section of the ceramic projecting element  230  which is fluted, which in one embodiment has three flute elements  260  in three corresponding axial grooves  262  in its surface. Any number of flutes, channels or the like is possible, for example from 2 to about 20. The purpose of this design is to provide a significant cross-sectional area at the proximal end of the projecting element  230  to push the tissue strip  225 , while at the same time the three grooves  262  permit the proximally-directed jetting of water vapor to impact the tissue exposed to the grooves  262 . In one embodiment, the axial length D of the projecting element  230  is configured to push tissue entirely out of the reduced cross-sectional region  190 B of the electrode sleeve element  195 . In another embodiment, the volume of the chamber  240  is configured to capture liquid that when explosively vaporized provides a gas (water vapor) volume sufficient to expand into and occupy at least the volume defined by a 10% of the total length of extraction channel  160  in the device, at least 20% of the extraction channel  160 , at least 40% of the extraction channel  160 , at least 60% of the extraction channel  160 , at least 80% of the extraction channel  160  or at least 100% of the extraction channel  160 . 
     As can be understood from  FIGS. 12A to 12C , the distention fluid  244  in the working space replenishes the captured fluid in chamber  240  as the resecting sleeve  175  moves in the proximal direction or towards its non-extended position. Thus, when the resecting sleeve  175  again moves in the distal direction to resect tissue, the interior chamber  240  is filled with fluid  244  which is then again contained and is then available for explosive vaporization as described above when the resecting sleeve  175  closes the tissue-receiving window  176 . In another embodiment, a one-way valve can be provided in the distal tip  232  to draw fluid directly into interior chamber  240  without the need for fluid to migrate through window  176 . 
       FIG. 15  illustrates another variation in which the active electrode surface area  250 ′ in the second mode comprises a projecting element  230  with conductive regions and nonconductive regions  261  which can have the effect of distributing the focused RF energy delivery over a plurality of discrete regions each in contact with the captured fluid  244 . This configuration can more efficiently vaporize the captured fluid volume in chamber  240 . In one embodiment, the conductive regions  250 ′ can comprise metal discs or washers on post  248 . In other variation (not shown) the conductive regions  250 ′ can comprise holes, ports or pores in a ceramic material  261  fixed over an electrically conductive post  248 . 
     In another embodiment, the RF source  150  and controller  155  can be programmed to modulate energy delivery parameters during stroke X and stroke Y in  FIGS. 12A-12C  to provide the optimal energy (i) for plasma resection with electrode edge  180 , and (ii) for explosively vaporizing the captured fluid in chamber  240 . 
       FIGS. 16A-16B  are sectional views of a working end  600  of a tissue resecting probe that is similar to previous embodiments. In  FIGS. 16A and 16B , the inner resecting member or sleeve  610  is shown in a distal portion of its stroke after resecting a tissue strip  225  captured in the window  612  in the outer sleeve  615  or housing as generally depicted in the tissue resecting sequence of  FIGS. 12A-12B . 
       FIGS. 16A-16B  illustrate another aspect of the invention wherein the inner resecting sleeve  610  moves in a passageway  620  in the outer sleeve  615  and in the distal portion of its stroke, a projecting or extending element  630  extends into the tissue extraction channel  632  in the inner sleeve  610 . In one variation, the cross-section of the extending element  630  is configured to extend into the distal reduced cross-section portion  635  of the tissue extraction channel  632  and function in a scissor-like manner to push the tissue against the electrode edge  640  of the inner sleeve  610  as depicted in  FIG. 16A . The extending element  630  can have an axial length of at least 2 mm. In a variation, the extending element  630  has a length can ranging from 4 mm to 10 mm. The extending element  630  can have a length that equals at least 50% of the axial length of the distal reduced cross-section region  635  of the extraction channel  632 . 
     In one variation, a method of resecting tissue comprises positioning a working end of a tissue resecting probe against tissue and moving a resecting sleeve or member  610  carried by the probe wherein the moveable resecting member  610  interfaces with an extending element  630  carried by the probe that extends into a channel  632  in the resecting sleeve to thereby resect tissue that is captured between the resecting member  610  and the extending element  630 . In such a variation, the step of resecting tissue is accomplished by plasma formed at the distal electrode edge  640  of the resecting member  610 , with electrical fields EF ( FIG. 16A ) as described above. 
     In one variation, still referring to  FIGS. 16A-16B , the extending element  630  has a tapered region  644  that tapers in the proximal direction. In use, the tapered region helps insure that the distally moving inner sleeve  610  is guided over the projecting element  630  even if there is some flex in the distal portion of the outer sleeve  615  in the region of window  612 . It can be understood that distal movement of the inner sleeve  610  will engage the tapered region  644  of element  630  if the outer sleeve is flexed in any direction and thereafter further distal movement of the inner sleeve  610  over the projecting element  630  will center the outer sleeve  615  relative to the inner sleeve  610 . 
     In general, a method of resecting and extracting tissue comprises positioning a window of a tubular resecting device against tissue, and reciprocating a resecting sleeve in forward and backward strokes across the window wherein a projecting member separate from the resecting sleeve projects into a bore in the resecting sleeve during a portion of its forward stroke to prevent flexing of the sleeve proximate the window. 
     In one embodiment shown in  FIGS. 16A-16B , the extending element  630  has a recessed region  648  therein for receiving a fluid volume. As can be seen in  FIG. 16B , the extending element  630  is a dielectric material (e.g., a ceramic) with a central bore  660  for mounting the element  630  over the post element  652  of metal endcap  655 . The proximal surface  658  of post element  652  functions as an electrode when vaporizing captured fluid as described previously and shown in  FIG. 16B . The electrical fields EF′ are shown in  FIG. 16B  which result in the explosive vaporization of the contained liquid. It can be seen in  FIG. 16B  that metal endcap  655  is fixed with annular weld  656  to outer sleeve  615  (electrode) so that endcap  655  and its post element  652  also function as an electrode.  FIG. 16B  further illustrates that the working end has insulative layers on all surfaces of the distal annular space  660  that receives the inner resecting sleeve  610  to focus RF current paths in the central bore  650  of the projecting element  630 . More in particular, the outer sleeve  615  is lined with an insulative layer  662  and the endcap  655  has an annular inner insulator  664  bonded thereto. 
       FIGS. 17-19  illustrate a fluid management system  500  that can be used when treating tissue in a body cavity, space or potential space  502  ( FIG. 18 ). The fluid management system  500  is depicted schematically in a hysteroscopic fibroid treatment system  510  that is adapted for resection and extraction of fibroids or other abnormal intra-uterine tissue using a hysteroscope  512  and tissue resection probe  515  that can be similar to those described above.  FIG. 17  depicts the probe  515  with handle  516  and extension member  518  with working end  520  ( FIG. 18 ) that can be introduced through working channel  522  extending through the body  523  and shaft  524  of the hysteroscope  512 .  FIG. 17  further shows a motor  525  in handle  516  of the probe that is coupled to a controller  545  and power supply by power cable  526 .  FIG. 18  illustrates the working end  520  of the resecting probe in a uterine cavity proximate a targeted fibroid  530 . 
     Referring to  FIGS. 17-18 , in general, the fluid management system  500  comprises a fluid source or reservoir  535  of a distention fluid  244 , a controller and pump system to provide fluid inflows and outflows adapted to maintain distension of a body space and a filter system  540  for filtering distention fluid  244  that is removed from the body cavity and thereafter returned to the fluid source  535 . The use of a recovered and filtered fluid  244  and the replenishment of the fluid source  535  is advantageous because (i) the closed-loop fluid management system can effectively measure fluid deficit to thereby monitor intravasation and insure patient safety, (ii) the system can be set up and operated in a very time-efficient manner, and (iii) the system can be compact and less expensive to thereby assist in enabling office-based procedures. 
     The fluid management system  500  ( FIG. 17 ) includes a computer control system that is integrated with the RF control system in an integrated controller  545 . The controller  545  is adapted to control first and second peristaltic pumps  546 A and  546 B for providing inflows and outflows of a distention fluid  244 , such as saline solution, from source  535  for the purpose of distending the body cavity and controlling the intra-cavity pressure during a tissue resecting and extracting procedure as depicted in  FIG. 18 . In one embodiment shown in  FIGS. 17-19 , the controller  545  controls peristaltic pump  546 A to provide positive pressure at the outflow side  548  of the pump ( FIG. 17 ) to provide inflows of distention fluid  244  through first flow line  550  which is in communication with fitting  561  and fluid flow channel  108   a  in hysteroscope  515 . The flow channel  108   a  is described above in a previous embodiment and is illustrated in  FIG. 3  above. The controller  545  further controls the second peristaltic pump  546 B to provide negative pressure at the inflow side  552  of the pump ( FIG. 18 ) to the second line  555  to assist in providing outflows of distention fluid  244  from the body cavity  502 . As described above, the explosive vaporization of fluid in the working end  525  of probe  515  functions to expel tissue strips  225  proximally in the extraction channel  160  of resecting sleeve  175 , which can operate in conjunction with negative pressures in line  555  provided by pump  546 B. In operation, the second peristaltic pump  546 B also operates to provide positive pressure on the outflow side  556  of pump  546 B in the second flow line portion  555 ′ to pump outflows of distention fluid  244  through the filter system  540  and back to the fluid source  535 . 
     In one system embodiment, the controller  545  operates to control pressure in cavity  502  by pressure signals from a disposable pressure sensor  560  that is coupled to a fitting  562  in hysterocope  512  which communicates with a flow channel  108   b  (see  FIG. 17 ) that extends through the hysteroscope. The pressure sensor  560  is operatively coupled to controller  545  by cable  564 . In one embodiment, the flow channel  108   b  has a diameter of at least 1.0 mm to allow highly accurate sensing of actual intra-cavity pressure. In prior art commercially-available fluid management systems, the intra-cavity pressure is typically estimated by various calculations using known flow rates through a pump or remote pressure sensors in the fluid inflow line that can measure back pressures. Such prior art fluid management systems are stand-alone systems and are adapted for use with a wide variety of hysteroscopes and endoscopes, most of which do not have a dedicated flow channel for communicating with a pressure sensor. For this reason, prior art fluid management systems rely on algorithms and calculations to estimate intra-cavity pressure. 
     The fluid channel or sensor channel  108   b  used by the pressure sensor  560  is independent of flow channel  108   a  used for distention fluid inflows into the body cavity. In the absence of fluid flows in the sensor channel  108   b , the fluid in the channel  108   b  then forms a static column of incompressible fluid that changes in pressure as the pressure in the body cavity changes. With a sensor channel cross-section of 1 mm or more, the pressure within the pressure channel column and the pressure in the body cavity are equivalent. Thus, the pressure sensor  560  is capable of a direct measurement of pressure within the body cavity. 
       FIG. 18  schematically illustrates the fluid management system  500  in operation. The uterine cavity  502  is a potential space and needs to be distended to allow for hysteroscopic viewing. A selected pressure can be set in the controller  545 , for example via a touch screen  565 , which the physician knows from experience is suited for distending the cavity  502  and/or for performing a procedure. In one embodiment, the selected pressure can be any pressure between 0 and 150 mm Hg. In one system embodiment, the first pump  546 A can operate as a variable speed pump that is actuated to provide a flow rate of up to 850 ml/min through first line  550 . In this embodiment, the second pump  546 B can operate at a fixed speed to move fluid in the second line  555 . In use, the controller  545  can operate the pumps  546 A and  546 B at selected matching or non-matching speeds to increase, decrease or maintain the volume of distention fluid  244  in the uterine cavity  502 . Thus, by independent control of the pumping rates of the first and second peristaltic pumps  546 A and  546 B, a selected set pressure in the body cavity can be achieved and maintained in response to signals of actual intra-cavity pressure provided by sensor  560 . 
     In one system embodiment, as shown in  FIGS. 18-19 , the fluid management system  500  includes a filter module or system  540  that can include a first filter or tissue-capturing filter  570  that is adapted to catch tissue strips  225  that have been resected and extracted from the body cavity  502 . A second filter or molecular filter  575 , typically a hollow fiber filter, is provided beyond the first filter  570 , wherein the molecular filter  575  is adapted to remove blood and other body materials from the distention fluid  244 . In particular, the molecular filter  575  is capable of removing red blood cells, hemoglobin, particulate matter, proteins, bacteria, viruses and the like from the distention fluid  244  so that endoscopic viewing of the body cavity is not obscured or clouded by any such blood components or other contaminants. As can be understood from  FIGS. 16-18 , the second peristaltic pump  546 B at its outflow side  556  provides a positive pressure relative to fluid flows into the filter module  540  to move the distention fluid  244  and body media through the first and second filters,  570  and  575 , and in a circulatory flow back to the fluid source  535 . 
     Referring to  FIG. 19 , in an embodiment, the first filter  570  comprises a container portion or vial  576  with a removable cap  577 . The inflow of distention fluid  244  and body media flows though line portion  555  and through fitting  578  into a mesh sac or perforate structure  580  disposed in the interior chamber  582  of the vial  576 . The pore size of the perforate structure  580  can range from about 200 microns to 10 microns. The lumen diameter of hollow fibers  585  in the second filter  575  can be from about 400 microns to 20 microns. In general, the pore size of perforate structure  580  in the first filter  570  is less than the diameter of the lumens of hollow fibers  585  in the second filter  575 . In one embodiment, the pore size of the perforate structure  580  is 100 microns, and the lumen size of the hollow fibers  585  in the molecular filter  575  is 200 microns. In one embodiment, the molecular filter  575  is a Nephros DSU filter available from Nephros, Inc., 41 Grand Ave., River Edge, N.J. 07661. In one variation, the filter  575  is configured with hollow fibers having a nominal molecular weight limit (NMWL) of less than 50 kDa, 30 kDa or 20 kDa. 
     Referring to  FIG. 19 , it can be seen that the filter module  540  includes detachable connections between the various fluid flow lines to allow for rapid coupling and de-coupling of the filters and flow lines. More in particular, flow line  555  extending from the tissue resecting probe  515  has a connector portion  592  that connects to inlet fitting  578  in the first filter  570 . Flow line portion  555 ′ that is intermediate the filters  570  and  575  has connector portion  596   a  that connects to outlet fitting  596   b  in first filter  570 . The outflow end of flow line  555 ′ has connector  598   a  that connects to inlet fitting  598   b  of the second filter  575 . The portion  590  of the second flow line  555  that is intermediate the second filter  575  and fluid source  535  has connector portion  602   a  that connects to outlet fitting  602   b  in the second filter  575 . In one embodiment, at least one check valve  605  is provided in the flow path intermediate the filters  570 ,  575  which for example can be in line  555 ′, connectors  596   a ,  598   a  or fittings  596   b ,  598   b . In  FIG. 19 , a check valve  605  is integrated with the inlet end  608  of the second filter  575 . In use, the operation of the system will result in substantial fluid pressures in the interior of the second filter, and the check valve  605  allows for de-coupling the first filter without escape of pressure and release of fluid media into the environment, for example, when the tissue resection procedure is completed and the physician or nurse wishes to transport the vial  576  and tissue strips  225  therein to a different site for biopsy purposes. 
     In one aspect, a fluid management system comprising a first fluid line  550  configured to carry distention fluid  224  or influent from a fluid source  535  to a body space, a second fluid line  555 ,  555 ′ and  560  configured to carry fluid from the body space to a first filter  570  and then to a second filter  575  and then back to the fluid source  535 , a pump operatively coupled to the second fluid line to move the fluid and at least one check valve  605  in the second fluid line intermediate the first and second filters  570  and  575 . 
     In one embodiment, the controller  545  of the fluid management system  500  is configured for calculation of a fluid deficit that is measured as a difference between a fluid volume delivered to the body space  502  and a fluid volume recovered from the body space during a medical procedure such as fibroid removal (see  FIGS. 17-18 ). A method of fluid management in a hysteroscopic procedure comprises providing a distention fluid source  535  ( FIG. 18 ) having a predetermined volume, introducing fluid (e.g., saline) from the source  535  through a first flow path or line  550  into the uterine cavity and through a second flow line  555  out of the cavity into a filter module  540  and through a further portion  590  of the second flow line back to the fluid source  535  wherein the interior volume of the first and second flow lines and the filter module when subtracted from the predetermined volume of the source  535  equals 2.5 liters or less to thereby insure that saline intravasion is less than 2.5 liters. In this variation, the predetermined volume of the source  535  can be 3.0 liters, as in a standard 3 liter saline bag, and the interior system volume can be at least 0.5 liters. In one variation, the fluid management system  500  can include a sensor system for determining the volume of fluid remaining in the source  535 , and the sensor can provide a signal to the controller  545  which in turn can provide a visual or aural signal relating to remaining fluid volume in fluid source  535 . In one variation, the fluid source  535  can be a bag that hangs from a member including a load cell  625  ( FIGS. 17, 19 ) which is configured to send load signals to the controller  545 . The controller can have a screen  565  which continuously displays a fluid parameter such as calculated fluid deficit or fluid remaining in the source  535 . In other variations, the sensor adapted for sensing the weight or volume of fluid in the fluid source can be a float or level sensor in a fluid container, an impedance or capacitance sensor coupled to the fluid source container, an optical sensor operatively coupled to the fluid container or any other suitable type of weight or volume sensing mechanism. Any such sensor system can send signals to the controller for providing fluid deficit calculations or fluid intravasation warnings. 
     While certain embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration and the above description of the invention is not exhaustive. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims.