Abstract:
The tissue cutting device comprises an elongated assembly including both an outer sleeve and an inner sleeve. The outer sleeve has a tissue-receiving window, and the inner sleeve has a distal end which cuts tissue as the inner sleeve is advanced past the window. The tissue is received into a lumen of the inner sleeve, and the inner sleeve lumen is typically enlarged in a proximal direction to reduce the tendency of resected tissue to lodge therein. The tissue displacement member is optionally provided at a distal end of the outer sleeve to further aid in dislodging tissue which becomes captured in a distal end of the inner sleeve of the lumen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/531,309, filed Jun. 22, 2012, now, U.S. Pat. No. 8,974,448, which claims the benefit of Provisional Application No. 61/501,101, filed on Jun. 24, 2011, the full disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates systems and methods for the cutting and extraction of 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 cutting instrument through a working channel in the hysteroscope. The cutting instrument may be a mechanical tissue cutter or an electrosurgical resection device such as a cutting 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 cutting device is disclosed in U.S. Pat. No. 5,906,615. 
     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 cut and remove fibroid tissue through a small diameter hysteroscope. 
     One particular challenge to cutting and removing fibroids using a small diameter hysteroscope is that resected tissue can easily become lodged in the small diameter lumens found in such small scopes. Therefore, it would be particularly useful to provide apparatus and methods which reduce the likelihood of resected tissue becoming lodged in the tissue removal lumens of such small diameter hysteroscopes. At least some of these objectives will be met by the inventions described herein below. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved tissue cutting devices, tissue extraction devices, and methods for their use, where the likelihood of resected tissue becoming lodged in the device is greatly reduced. The devices and methods may utilize one or more of a number of separate features, described in details below, where the individual features may be used independently or in combination in order to reduce the likelihood that tissue will become lodged in even very small tissue removal lumens used in hysteroscope and similar recectoscopes. 
     In a first aspect, a tissue cutting device comprises an elongated assembly including both an outer sleeve and an inner sleeve. The outer sleeve has a tissue-receiving window, typically near its distal end, which is open to an interior lumen of the outer sleeve. The inner sleeve is disposed coaxially in the lumen of the outer sleeve, and the sleeves are arranged so that the inner sleeve can reciprocate within the outer sleeve so that a tissue-cutting distal end of the inner sleeve can be advanced past the tissue-receiving window. In this way, by advancing the inner sleeve relative to the outer sleeve while tissue intrudes into the open window, typically fibroid tissue but other tissues as well, the intruding tissue may then be resected by advancing the inner sleeve to pass the cutting edge over the open window. The resected tissue is received through an open distal end of the inner sleeve into a distal portion of the inner sleeve lumen. Typically, a partial vacuum will be drawn on the inner sleeve lumen, to draw the resected tissue into the inner sleeve lumen. In order to reduce the chance that the resected tissue will become lodged in a distal portion of the inner sleeve lumen, a proximal portion of the inner sleeve lumen is provided with a cross sectional area which is larger than that of the distal portion. The increased in cross-sectional area need not be great, usually being at least 5%, and sometimes being 10% or more greater. 
     In another aspect of the present invention, the outer sleeve lumen may have a distal lumen portion extending distally of the window. The distal lumen portion will typically have a length which is at least as long as the length of the distal portion of the inner sleeve lumen. In this way, the inner sleeve may be advanced past the tissue-receiving window and into the distal lumen portion of the outer sleeve lumen. Such advancement not only allows a clean cut, it also allows for a displacement feature to be disposed in the distal lumen portion of the outer sleeve to engage and dislodge the tissue in the distal portion of the outer sleeve lumen as the inner sleeve is advanced distally into the distal lumen. The distance from a distal edge of the window to the distal end of the interior passage way will typically be at least 4 mm, often being 6 mm, sometimes being 8 mm or longer. The length of the distal lumen portion will typically be at least 5 mm, often being longer. Usually, the distal portion of the inner sleeve lumen will also have a length of at least 5 mm, typically being substantially the same as the length of the distal lumen portion of the outer sleeve. 
     The tissue-cutting distal end of the inner sleeve may comprise any conventional tissue-cutting structure, typically being a sharp-edged blade, a radiofrequency (RF) electrode, or the like. 
     Further optionally, an edge of the window may be surrounded by a dielectric material, typically having a width of at least 0.005 in. 
     Further optionally, the inner sleeve may have a first stroke portion which advances the tissue-cutting end across the window and a second stroke portion which advances the tissue-cutting end beyond the window, or a length of the second stroke portion is at least 5% of the combined lengths of the first and second stroke portions. 
     In a further aspect of the present invention, the tissue extraction device comprises a handle and a shaft assembly extending axially from the handle. The shaft assembly has a tissue-receiving window communicating with an interior extraction lumen for extracting tissue. The shaft assembly further comprises axially-extending first and second elements with at least one element being movable relative to the other element to move between a first position and a second position in order to resect tissue received in the window. A displacement feature coupled to the shaft is configured to displace resected tissue from the extraction lumen. 
     The first position of the first and second elements typically comprises an open-window configuration for receiving tissue therein. The second position is then a closed-window configuration, where movement of the elements from the first position toward the second position typically cuts tissue with a cutting edge on at least one of the elements. The cutting element will typically be a sharp-edged blade, an RF electrode, or the like. In exemplary embodiments, the displacement feature will comprise a projecting element that extends into the extraction lumen so that resected tissue is displaced as the elements are moved relative to each other. The projecting element will physically engage a tissue just after it has been resected and will act as a barrier to dislodge the tissue proximally as the cutting element is advanced further in the distal direction. The displacement feature may have a maximum cross-sectional dimension which is sufficient to extend substantially across a cross-section of the extraction lumen. In other embodiments, the displacement feature will have a cross-sectional area or “footprint” that substantially occupies the cross-section of the extraction lumen. In still other embodiments, the displacement feature may have a shape which is symmetric about a central axis of the extraction lumen but will not necessarily occupy the entire cross-section of the extraction lumen. Specific examples would be axially fluted configurations, star-shaped configurations, and the like. In other specific embodiments, the displacement feature may comprise a dielectric material and may be configured to extend axially into the extraction lumen by a distance of at least 2 mm, sometimes at least 4 mm, and other times at least 6 mm. In still other embodiments, the displacement feature will have a cross-sectional area which is at least 50% of the cross-sectional area of the extraction lumen in the region where the displacement feature enters the lumen. 
     The present invention also provides methods for cutting and extracting tissue from a body cavity, such as fibroids from a uterus. The methods comprise cutting tissue with a reciprocating inner sleeve having an extending stroke and a retracting stroke within an outer sleeve. The extending stroke cuts and captures tissue received through a tissue-receiving window in the outer sleeve. Tissue which is cut can become captured in a distal portion of a lumen of the inner sleeve, and if it is, the captured tissue is pushed in a proximal direction from the distal portion of the lumen in the inner sleeve where the displacement member, when the cutting sleeve is in a transition range between the extending stroke and the retracting stroke. The displacement member is able to push the captured tissue from the distal region into a proximal region of the inner sleeve lumen. Typically, the proximal region of the inner sleeve lumen has a cross-sectional area which is larger than that of the distal region of the inner sleeve lumen. This enlargement of the lumen allows the tissue to be extracted, typically by a partial vacuum applied at a proximal end of the lumen, with a reduced risk of becoming caught or captured. Usually, the displacement member is fixedly attached to the outer sleeve and axially aligned with the distal portion of the inner sleeve lumen so that the captured tissue is engaged and pushed proximally into the proximal portion of the inner sleeve as the inner sleeve is advanced fully into the outer sleeve. In other specific embodiments, the inner sleeve is advanced over a first stroke portion which advances a tissue-cutting end of the inner sleeve across the window and then further advanced over a second stroke portion which causes the tissue-cutting end to move beyond the window. The length of the second stroke portion is at least 5% of the combined lengths of the first and second stroke portions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of an assembly including a hysteroscope and a tissue-cutting 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 cutting and extraction. 
         FIG. 3  is a cross-sectional view of the shaft of the hysteroscope of  FIG. 1  showing various channels therein. 
         FIG. 4A  is a schematic view of the working end of the electrosurgical tissue-cutting device of  FIG. 1  showing an outer sleeve with a reciprocating inner cutting sleeve in a partially advanced position. 
         FIG. 4B  is a schematic view of the working end of  FIG. 4A  with the reciprocating inner cutting sleeve in a fully advanced position. 
         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 cutting 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 cutting sleeve. 
         FIG. 7A  is a cross sectional view of the inner RF cutting 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 cutting 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 cutting sleeve. 
         FIG. 9A  is a cross sectional view of the RF cutting sleeve of  FIG. 8  taken along line  9 A- 9 A of  FIG. 8 . 
         FIG. 9B  is a cross sectional view of the RF cutting sleeve of  FIG. 8  taken along line  9 B- 9 B of  FIG. 8 . 
         FIG. 10  is an enlarged cross sectional view of a working end with an RF cutting sleeve in advanced position and a tissue displacement member pushing a tissue strip proximally in the extraction lumen. 
         FIG. 11  is a cross-sectional of a variation of the tissue displacement member of  FIG. 10 . 
         FIG. 12  is a perspective view of another embodiment of working end having a tissue-receiving window with a dielectric edge. 
         FIG. 13  is a cross section of the tissue-receiving window of  FIG. 12  showing the dielectric edge and interior dielectric layer. 
         FIG. 14  is a perspective view of another embodiment of working end with a tissue-receiving window that has an asymmetric configuration. 
         FIG. 15  is a perspective view of another variation with a tissue-receiving window that is configured with tissue-gripping features. 
         FIG. 16  is a perspective view of another variation with an exterior sleeve with a distal dielectric body portion. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an assembly that comprises an endoscope  50  used for hysteroscopy together with a tissue-extraction 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 5 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 valve-connectors  110   a ,  110   b  configured for coupling to a fluid inflow source  120  thereto, 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  (which can comprise an operating room wall suction source) coupled to the tissue-cutting 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  also 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-cutting 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-cutting 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-cutting 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 cut targeted fibroid tissue. The tissue-cutting device  100  has subsystems coupled to its handle  142  to enable electrosurgical cutting of targeted tissue. A radio frequency 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 extraction device  100  ( FIG. 4A ). 
       FIG. 1  further illustrates a seal housing  162  that carries a flexible seal  164  carried by the hysteroscope handle  104  for sealing the shaft  140  of the tissue-cutting 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-cutting device  100  includes a motor drive  165  for reciprocating or otherwise moving a cutting 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 cutting 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 4A , an electrosurgical tissue-cutting 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 cut tissue as is known in that art of such tubular cutters. 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. 4A , the distal end  177  of inner sleeve  175  comprises a first polarity electrode with distal cutting electrode edge  180  about which plasma can be generated. The electrode edge  180  also can be described as an active electrode during tissue cutting since the electrode edge  180  then has a substantially smaller surface area than the opposing polarity or return electrode. In one embodiment in  FIG. 4A , 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 cutting sleeve  175  has an interior tissue extraction lumen  160  with first and second interior diameters that are adapted to electrosurgically cut tissue volumes rapidly—and thereafter consistently extract the cut tissue strips through the highly elongated lumen  160  without clogging. Referring to  FIGS. 5 and 6A , it can be seen that the inner sleeve  175  has a first diameter portion  190 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 cutting 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 illustrates 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 a plasma around the electrode edge  180  of electrode sleeve  195  as is known in the art. Thus, the plasma generated at electrode edge  180  can cut and ablate a path P in the tissue  220 , and is suited for cutting fibroid tissue and other abnormal uterine tissue. In  FIG. 6B , the distal portion of the cutting sleeve  175  includes a ceramic collar  222  which is adjacent the distal edge  180  of the electrode sleeve  195 . The ceramic  222  collar 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 cutting sleeve  175  during operation. In one aspect of the invention, the path P cut 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 removal and vaporization of tissue in path P is substantially different than the effect of cutting 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 cut. In contrast, the plasma at the electrode edge  180  can vaporize a path P in tissue without applying any substantial force on the tissue to thus cut larger cross sections or slugs of strips of tissue. Further, the plasma cutting effect reduces the cross section of tissue strip  225  received in the tissue-extraction lumen  190 B.  FIG. 6B  depicts a tissue strip to  225  entering lumen  190 B which has such a smaller cross-section than the lumen due to the vaporization of tissue. Further, the cross section of tissue  225  as it enters the larger cross-section lumen  190 A results in even greater free space  196  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  to clog the lumen. Prior art resection devices with such small diameter tissue-extraction lumen typically have problems with tissue clogging. 
     In another aspect of the invention, the negative pressure source  225  coupled to the proximal end of tissue-extraction lumen  160  (see  FIGS. 1 and 4A ) 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 device. 
       FIGS. 7A-7B  illustrate the change in lumen diameter of cutting sleeve  175  of  FIG. 6B .  FIG. 8  illustrates the distal end of a variation of cutting sleeve  175 ′ which is configured with an electrode cutting 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 cutting sleeve  175 ′ of  FIG. 8 . Thus, the functionality remains the same whether the cutting electrode element  195 ′ is tubular or partly tubular. In  FIG. 8 , the ceramic collar  222 ′ is shown, in one variation, as extending only partially around sleeve  175  to cooperate with the radial angle of cutting 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 cutting and extracting device ( FIGS. 4A-4B ) 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-extraction 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 A proximate the plasma cutting 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 B 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-cutting device  100  for hysteroscopic fibroid cutting and extraction ( FIG. 1 ), the shaft assembly  140  of the tissue-cutting device is 35 cm in length. 
     Now referring to  FIGS. 4A-4B  and  FIG. 10 , one aspect of the invention comprises a “tissue displacement” mechanism that is configured to displace and move tissue strips  225  (see  FIG. 10 ) in the proximal direction in lumen  160  of cutting sleeve  175  to thus ensure that tissue does not clog the lumen of the inner sleeve  175 . As can be seen in  FIGS. 4A, 4B and 10 , one tissue displacement mechanism comprises a projecting element  230  that extends proximally from distal tip or body  232  that 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 the interior surface of the distal tip  232 . In one embodiment depicted in  FIGS. 4A and 10 , the shaft-like projecting element  230  thus functions as a plunger or pusher member and can push a captured tissue strip  225  in the proximal direction from the small cross-section lumen  190 B of cutting sleeve  175  as the cutting sleeve  175  moves to its fully advanced or extended position (see.  FIG. 10 ). For this reason, the length D of the projecting element  230  is at least as great as the axial length E of the small cross-section lumen  190 B in the cutting sleeve. Further, as depicted in  FIG. 10 , the stroke Y of the cutting sleeve  175  extends at least about 3 mm, 4 mm or 5 mm distally beyond the distal edge of the window  290 . In another aspect, the stroke Y of the cutting sleeve  175  is at least 5% or 10% of the total stroke of the cutting sleeve (stroke X+stroke Y in  FIG. 10 ). 
     In general, a method of cutting tissue corresponding to the invention comprising cutting tissue with a reciprocating cutting sleeve having an extending stroke and a retracting stroke within an outer sleeve, wherein the extending stroke cuts and captures tissue received by a tissue-receiving window in the outer sleeve, and pushing the captured tissue in the proximal direction in the cutting sleeve with a displacement member when the cutting sleeve is in a transition range in which the cutting sleeve transitions from the extending stroke to the retracting stroke. Further, the displacement member is configured to push the captured tissue at least in part from a first smaller cross-section lumen to a second larger cross-section lumen in the cutting sleeve. Thereafter, the negative pressure source can more effectively extract and aspirate the tissue from the lumen. 
     In another aspect of the invention, the tissue cutting device comprises an elongated assembly comprising concentric outer and inner sleeves, with a tissue-receiving window in the outer sleeve open to an interior lumen with a distal lumen portion extending distal to the window, wherein the inner sleeve is configured with a first axially-extending channel having a lesser cross-sectional area and a second axially-extending channel portion having a second greater cross-sectional area and wherein the ratio of lengths of the distal lumen portion relative to the first channel is at least 1:1. In one embodiment, the device is configured with a length of the distal lumen portion that is at least 5 mm. In this embodiment, the length of first axially-extending channel is at least 5 mm. 
     In another aspect of the invention, a tissue cutting device is comprised of an elongated assembly comprising concentric outer and inner sleeves, with a tissue-receiving window in the outer sleeve open to an interior lumen with a distal lumen portion extending distal to the window, wherein the ratio of the length of the distal lumen portion relative to the diameter of the interior lumen is at least 1:1. In one embodiment, the ratio is at least 1.5:1. In this embodiment, the length of the distal lumen portion is at least 5 mm. In one variation, the diameter of the interior lumen is less than 5 mm. 
     In general, a tissue cutting device comprised of a handle coupled to an elongated tubular assembly comprising outer and inner concentric sleeves, a tissue-receiving window in the outer sleeve communicating with an interior passageway extending through the assembly wherein a distal edge of the window is a spaced at least 4 mm, 6 mm, 8 mm or 10 mm from the distal end of the interior passageway. In this variation, the mean cross section of the passageway is less than 5 mm, 4 mm or 3 mm. 
     One embodiment of a tissue cutting device comprises a handle coupled to an axially-extending shaft assembly defining a tissue-receiving window communicating with an interior extraction lumen for extracting tissue, the shaft assembly comprising axially-extending first and second elements with at least one element axially moveable relative to the other element between a first position and a second position, and a displacement feature configured to displace resected tissue from the extraction lumen. In this embodiment, the first position comprises an open-window configuration for receiving tissue therein and the second position is a closed-window configuration. The movement of the elements from the first position toward the second position cuts tissue with a cutting edge of an element. The cutting edge can comprise a sharp blade edge or an RF electrode edge. The displacement feature ( FIG. 4A ) or projecting element  230  can be coupled to the first element, can project axially relative to an axis of the extraction lumen. This embodiment is configured with an extraction lumen having first and second cross-sectional areas, wherein a distal region of the extraction lumen has a first lesser cross-sectional area and a medial portion of the extraction lumen has a second greater cross-sectional area. In one variation, the distal region of the extraction lumen having the first cross-sectional area extends axially at least 2 mm, 4 mm, 6 mm and 8 mm. In another variation, the displacement feature is configured to extend axially into the extraction lumen in the second closed-window configuration at least 2 mm, 4 mm, 6 mm and 8 mm. 
     In general, the displacement feature or projecting element  230  has a maximum cross-section that extends substantially across a cross-section of the extraction lumen. In one variation, the displacement feature has a cross-sectional area that substantially occupies the first cross-sectional area of the extraction lumen.  FIGS. 4A and 10  illustrate a projecting element  230  that is cylindrical.  FIG. 11  illustrates a section of a projecting element  230 ′ that has a symmetric shape relative to a central axis of the extraction lumen, and is star-shaped or fluted with ribs and channels to allow distension fluid to flow therethrough as the cutting sleeve  175  reciprocates in chamber  240 . In another embodiment, the projecting element can have an asymmetric cross sectional shape with any number or flutes, grooves, lumens or bore extending about its axis. In a typical embodiment, the projecting element  230  is a dielectric such as a ceramic or polymer. 
     In another embodiment depicted in  FIGS. 12-13 , the tissue cutting device again comprises an elongated assembly comprising concentric outer and inner sleeves, with a tissue-receiving window in the outer sleeve open to an interior lumen. In this embodiment, the edges of the window comprise a dielectric element  300  such as a polymer or ceramic that can be molded, formed and bonded around the edge of window  176  in the metal sleeve  170 . This prevents unwanted arcing from the electrode edge  180  to the exterior of sleeve  170  (or electrode  185 ) when plasma is generated at the electrode edge  180  during reciprocation. The width W ( FIG. 13 ) of the dielectric is at least 0.005″.  FIG. 13  illustrates a sectional view of an outer sleeve  170  at the window  176  comprising a conductive electrode and dielectric element  300  around the edge of the window. It can be seen that thin insulative layer  200  is configured to join and bond to the dielectric element  300 . 
       FIG. 14  depicts the working end of another embodiment of tissue cutting device similar to those described above with a window  310  opening to the interior bore  172  of outer sleeve  170  wherein the longitudinal window  310  is longitudinally asymmetrical and wherein the window depth increases in the distal direction. As can be understood from  FIG. 10 , the asymmetric window  310  of  FIG. 13  draws a lesser volume tissue into the proximal window portion and a greater volume of tissue into the distal window portion for cutting with electrode edge  190 . Thus, this window configuration allows for a lesser cross section of tissue strip  225  in the proximal direction and a greater cross section of tissue strip  225  in the distal direction. The variation in cross-section of the captured tissue increases the efficiency of the negative pressure source  225  ( FIG. 1 ) in applying effective aspiration forces on the tissue strip  225  in the lumen, which is further assisted by projecting member  230  which is configured to push the distal, greater cross-sectional end of tissue strip  225  in the lumen  160  of inner sleeve  175 . 
     Further, still referring to  FIG. 14 , the increased radius R allowed by the varied depth window  310  allow for greater strength of the assembly in the proximal region of the window as the outer sleeve  270  transitions to the full hoop strength of the sleeve. 
       FIG. 15  depicts another working end variation similar to those described above with a window  320  opening to interior bore  172  of outer sleeve  170 . In this embodiment, the longitudinal window  320  has an edge configured with gripping features  322  such as teeth or an abrasive surface which assist in maintaining tissue  220  (see  FIG. 10 ) in a non-sliding disposition as the cutting sleeve  175  is moving in its extending stroke. 
       FIG. 16  depicts another working end variation similar to those described above with a window  330  opening to interior bore  172  of outer sleeve  170 . In this embodiment, a distal body  332  of a dielectric is bonded to the sleeve to thus provide distal window edge  333  that is entirely of non-conductive material. The body  332  can comprise a ceramic or polymeric material that is useful in preventing plasma at the reciprocating electrode edge  180  (see  FIG. 10 ) of the cutting sleeve  170  from folding, flexing, abrading, delaminating or otherwise damaging the dielectric lining or layer  200  laminated in bore  172  of sleeve  170 . 
       FIG. 16  further depicts a marking  340  that marks the proximal end of window  320  opening to interior bore  172  of outer sleeve  170 . This marking is useful for orienting and rotating the working end  145  when viewing through the hysteroscope and the physician presses the window into contact with tissue. Further, the working end has another marker (not visible) on the exterior of outer sleeve  180  to further orient the physician to the window. 
     Although particular 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.