Abstract:
An electrosurgical medical device and technique for creating thermal welds in the transected margin of engaged tissue. The working end of the invention carries a bi-polar electrode arrangement that provides a novel type of Rf current flow for tissue welding described as an subfascial-to-fascial (or medial-to-surface) bi-polar approach. The working end of the device carries an openable and closable jaw assembly with paired first and second jaws for engaging tissue. The paired jaws have an axial channel for receiving a sliding (blade) member for transecting the captured tissue. The paired jaws carry electrode surfaces having a common polarity so that Rf current will not flow directly between the jaws which engage the surface or fascial tissue layers. The transecting member, when fully extended after transecting the captured tissue, carries an elongate electrode of an opposing polarity that engages the medial or subfascial layers of the tissue. Thus, bi-polar current is directed to flow from the transecting member electrode that engages medial tissue layers to both jaws that engage opposing surface tissue layers to create effective current densities in the medial tissue layers, even when transecting thick tissue volumes or vessels with thick non-uniform fascial layers.

Description:
FIELD OF THE INVENTION 
     This invention relates to medical devices and techniques and more particularly relates to an electrosurgical device for thermally sealing or welding the margins of a transected tissue volume, as well as a novel jaw structure that allows substantially elongate jaws to provide high compressive forces the captured tissue volume. 
     BACKGROUND OF THE INVENTION 
     In various open and laparoscopic surgeries, it is necessary to seal or weld the margins of transected tissue volumes, for example, a transected blood vessel or a tissue volume containing blood vessels. In a typical procedure, a deformable metal clip may be used seal a blood vessel, or a stapling instrument may be used to apply a series of mechanically deformable staples to seal the transected edge a larger tissue volume. Such mechanical devices may create a seal that leaks which can result in later complications. 
     Various radiofrequency (Rf) surgical instruments for sealing transected structures have been developed. For example, FIG. 1A shows a sectional view of paired electrode-jaws  2   a  and  2   b  of a typical prior art bi-polar Rf grasper grasping a blood vessel. In a typical bi-polar jaw arrangement, each jaw face comprises an electrode and Rf current flows across the tissue between the first and second polarities in the opposing jaws that engage opposing exterior surfaces of the tissue. FIG. 1A shows typical lines of bi-polar current flow between the jaws. Each jaw in FIG. 1A has a central slot adapted to receive a reciprocating blade member as is known in the art for transecting the captured vessel after it is sealed. 
     While bi-polar gapers as in FIG. 1A can adequately seal or weld tissue volumes that have a small cross-section, such bi-polar instruments are often ineffective in sealing or welding many types of anatomic structures, e.g., (i) substantially thick structures, (ii) large diameter blood vessels having walls with thick fascia layers f (see FIG.  1 A), (iii) bundles of disparate anatomic structures, (iv) structures having walls with irregular fibrous content. 
     As depicted in FIG. 1A, a relatively large diameter blood vessel falls into a category that is difficult to effectively weld utilizing prior art instruments. A large blood vessel wall has substantially thick, dense and non-uniform fascia layers underlying its exterior surface. As depicted in FIG. 1A, the fascia layers f prevent a uniform flow of current from the first exterior surface S to the second exterior surface  9  of the vessel that are in contact with electrodes  2   a  and  2   b . The lack of uniform bi-polar current across the fascia layers f causes non-uniform thermal effects that typically result in localized tissue desiccation and charring indicated at c. Such tissue charring can elevate impedance levels in the captured tissue so that current flow across the tissue is terminated altogether. FIG. 1B depicts an exemplary result of attempting to weld across a vessel with thick fascia layers f with a prior art bi-polar instrument. FIGS. 1A-1B show localized surface charring c and non-uniform weld regions w in the medial layers m of vessel. Further, FIG. 1B depicts a common undesirable characteristic of prior art welding wherein thermal effects propagate laterally from the targeted tissue causing unwanted collateral (thermal) damage indicated at d. 
     A number of bi-polar jawed instruments adapted for welding and transecting substantially small structures have been disclosed, for example: U.S. Pat. No. 5,735,848 to Yates et al.; U.S. Pat. No. 5,876,410 to Schulze et al.; and U.S. Pat. No. 5,833,690 to Yates et al. One other similar bi-polar instrument was disclosed by Yates et al. in U.S. Pat. No. 5,403,312. In that patent, paired bi-polar electrodes are provided in left and right portions of a jaw member to induce current flow therebetween. It is not known whether a jaw having the left-to-right or side-to-side bi-polar current flow of U.S. Pat. No. 5,403,312 was ever tested, but it seems likely that such an instrument would confine current flow to the tissue&#39;s exterior surface and facial layers f (see FIG.  1 B), thus aggravating the desiccation and charring of such surface layers. 
     What is needed is an instrument working end that can utilize Rf energy in new delivery modalities: (i) to weld a transected margin of a substantially thick anatomic structure; (ii) to weld or seal a margin of a blood vessel having thick or non-uniform fascia layers; (iii) to weld or seal tissue volumes that are not uniform in hydration, density and collagenous content; (iv) to weld a transected margin of a bundle of disparate anatomic structures; and (v) to weld a targeted tissue region while substantially preventing collateral thermal damage in regions lateral to the targeted tissue. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a novel technique—and an instrument working end capable of practicing the technique—for causing controlled Rf energy delivery and controlled thermal effects in a transected margin of tissues with thick facial layers, or other tissue with non-uniform fibrous content. For example, larger diameter blood vessels are a targeted application since such vessels have thick facials layers that can prevent uniform current flow and uniform resistive heating of the tissue. 
     As background, the biological mechanisms underlying tissue fusion by means of thermal effects are not folly understood. In general, the delivery of Rf energy to a captured tissue volume elevates the tissue temperature and thereby at least partly denatures proteins in the tissue. The objective is to denature such proteins, including collagen, into a proteinaceous amalgam that intermixes and fuses together as the proteins renature. As the treated region heals over time, the so-called weld is reabsorbed by the body&#39;s wound healing process. 
     In order to create an effective weld in a tissue volume with substantial fascial layers, it has been found that several factors are critical. The objective is to create a substantially even temperature distribution across the targeted tissue volume to thereby create a uniform weld or seal. Fibrous tissue layers (i.e., fascia) conduct Rf current differently than adjacent less-fibrous layers, and it is believed that differences in extra cellular fluid contents in such adjacent tissues contribute greatly to the differences in electrical resistance. It has been found that by applying very high compressive forces to a tissue volume comprising fascia layers and adjacent non-fibrous layers, the extracellular fluids either migrate from the non-fascial layers to the fascial layers or migrate from the captured tissue to collateral regions. In either event, high compressive forces tend to make the resistance more uniform regionally within the captured tissue volume. Further, it is believed that high compressive forces (i) cause protein denaturation at a lower temperature which is desirable, and (ii) cause enhanced intermixing of denatured proteins thereby creating a more effective weld upon tissue protein renaturation. 
     Of equal importance, it has been found that that a critical factor in creating an effective weld across adjacent fibrous (fascia) layers and non-fibrous (medial) layers is the deliver of bi-polar Rf energy from electrode surfaces engaging the medial layers and the surface or fascia layers. In other words, effective current flow through the fascia layers is best accomplished by engaging electrodes on opposing sides of the fascial layers. Prior art jaw structures that only deliver bi-polar Rf energy from outside the surface or fascial layers cannot cause effective regional heating inward of such fascial layers. For this reason, the novel technique causes Rf current flow to-and-from the medial (or just-transected) non-fascia layers of tissue at the interior of the structure, rather than to-and-from exterior surfaces only as in the prior art. This method is termed herein a medial-to-surface bi-polar delivery approach or a subfascia-to-fascia bi-polar approach. 
     Another aspect of the invention provides means for increasing the area of the engagement interface between an electrode and the just-exposed medial tissue layers. This is accomplished by providing a wedge-like slidable member having a electrode surface for compressing the just-transected tissue volume against inner faces of the paired jaw members. 
     More in particular, the working end of the instrument carries a jaw assembly with paired first and second jaws for engaging and compressing tissue along a line targeted for transection. The transected tissue margins thereby expose medial tissue layers m that can be engaged by an electrode. The jaw structure is moveable between a first (open) position and a second (closed) position by a slidable blade member that serves two functions: (i) to transect the captured tissue, and (ii) to contemporaneously lock together the elongate jaws by means of “I ” -beam flanges that span both sides of the paired jaws. 
     The combination of the first and second jaws together with a cooperating slidable transecting (or blade) member further provides a novel electrode arrangement that can accomplish the electrosurgical welding technique of the invention. The opposing jaws carry electrodes surfaces coupled to an Rf generator that have a common polarity. In other words, Rf current does not flow directly from the first jaw to the second jaw (in contrast to prior art, see FIG.  1 A). Rather, the extension portion of the slidable transecting member carries, or comprises, an electrode of an opposing polarity. Thus, when the transecting member is moved to the extended position after transecting the engaged tissue volume, the elongate electrode carried by the transecting member will thus engage the medial or interior layers of the transected margin. By this means, for the first time, bi-polar current flows can be directed from the transecting member that engages medal or sub-fascial tissue layers to both jaw faces that engage opposing surface or fascial tissue layers of the targeted tissue volume. It has been found that by engaging the medial portion of a just-transected structure with a first bi-polar electrode, and an exterior of the structure engaged with a second cooperating electrode, substantially uniform current flow through thick or non-uniform fascia layers can be accomplished. This novel medial-to-surface bi-polar approach of the invention also seems to greatly reduce tissue charring, and substantially prevents collateral thermal damage in the tissue by reducing stray Rf current flow through tissue lateral to the engaged tissue. 
     Of particular interest, the invention provides other (optional) features that enhance the effectiveness of an medial-to-surface bi-polar approach. More in particular, it has been found that increasing the electrode engagement area with the medial tissue layers can enhance thermal effects for tissue welding, For this reason, the elongate transecting member electrode may be configured as a wedge-type with an increasing cross-section that is adapted to plow into the medial tissue layers thereby increasing the electrode-tissue engagement area. 
     Also of particular interest, the invention provides means for compressing the engaged tissue between the electrode surface engagements, which has been found to assist in creating an effective weld. Such tissue compression again can be accomplished by using the increasing cross-section of the slidable transecting member to progressively press the tissue margins against a cooperating shape formed into the jaws. 
     In another embodiment of the invention, the jaw assembly further includes components of a sensor system which together with a power controller can control Rf energy delivery during a tissue welding procedure. For example, feedback circuitry for measuring temperatures at one or more temperature sensors in the jaws may be provided. Another type of feedback circuitry may be provided for measuring the impedance of tissue engaged between the transecting member and a jaw. The power controller may continuously modulate and control Rf delivery in order to achieve (or maintain) a particular parameter such as a particular temperature in tissue, an average of temperatures measured among multiple sensors, a temperature profile (change in energy delivery over time), or a particular impedance level or range. 
     Additional objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an illustration of current flow between the paired jaws of a prior art bi-polar radiofrequency device in a method of sealing a large blood vessel having substantially thick fascia layers. 
     FIG. 1B illustrates representative weld effects of the bi-polar current flow of FIG. 1A 
     FIG. 2 is a perspective cut-away view of the Rf working end of the present invention with the cooperating jaw members in a first (open) position and a sliding transecting or blade member in a first (retracted) position. 
     FIG. 3 is a different perspective cut-away view of the working end of FIG. 2 with the cooperating jaw members in a second (closed) position and the sliding transecting member in second (extended) position. 
     FIG. 4 is a perspective view of the slidable blade member of the working end of FIGS. 2-3 in first and second positions with the jaw members not shown. 
     FIG. 5A is an enlarged cross-sectional view showing an exemplary shape of the jaw faces of FIG. 2 taken along line  5 A— 5 A and depicting a tissue engagement plane. 
     FIG. 5B is an alternative cross-sectional shape (similar to FIG. 5A) of jaw faces defining an alternative engagement plane. 
     FIG. 6 is a view of the shape of the engagement plane of a prior art electrosurgical jaw wherein the jaw faces extend generally as a radial of the central axis. 
     FIGS. 7A-7B are sectional illustrations of steps of practicing the method of the invention in moving a jaw assembly to a closed position to provide high compressive forces in providing substantial electrode contact with surface layers and medial layers of the engaged tissue: 
     FIG. 7A being a sectional view of a large blood vessel with thick fascia layers being (i) captured and compressed by the jaw structure, and (ii) being transected by the leading edge of the blade member; 
     FIG. 7B being a sectional view of the increased diameter of an extension member electrode engaging a broad surface of the medial tissue layers as such layers are compressed outwardly against the cooperating jaw faces. 
     FIGS. 8A-8B are sectional illustrations of steps of practicing the method of delivering bi-polar Rf current flow to seal or weld the transected margins the engaged blood vessel of FIGS. 7A-7B; 
     FIG. 8A being an illustration of Rf current flow from electrodes in contact with medial tissue layers to electrodes in contract with surface tissue layers; and 
     FIG. 8B being an illustration of the thermal weld effects caused of the novel form of bi-polar current flow of FIG.  8 A. 
     FIG. 9A is a perspective view of a Type “B” embodiment of electrosurgical working end (similar to FIG. 4) that provides a secondarily actuated slidable electrode member for compressing tissue laterally outward while providing increased electrode engagement area with medial tissue layers. 
     FIG. 9B is an enlarged sectional view of the Type “B” device of FIG. 9A taken along line  9 B— 9 B of FIG. 9A (showing one side of the jaw members in plain view) illustrating an increased area for electrode engagement with medial tissue layers. 
     FIG. 10 is a sectional view Type “C” working end of the present invention similar to the working end of FIG. 9A with thermoelectric cooling elements for preventing collateral thermal damage to tissue during the tissue-welding process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Type “A” Electrosurgical Working End for Sealing or Welding Tissue. Referring to FIG. 2, the working end  5  of an exemplary Type “A” embodiment is shown that is adapted for sealing or welding a tissue volume, such as a blood vessel, in an open or endoscopic procedure. The working end  5  has paired jaw portions  8 A and  8 B that are carried at the distal end of elongate introducer portion  10  (with handle not shown) extending along central longitudinal axis  15 . In this exemplary embodiment, the structural component of introducer portion  10  has a cylindrical cross-section and comprises a thin-wall tubular sleeve  16  that extends from a proximate handle (not shown). The diameter of sleeve  16  may range from about 3 mm. to 10 mm., e.g., to cooperate with a standard endoscopic Tracy sleeve. The handle may be any type of pistol-grip or other type of handle known in the art that carries actuator levers or slides as described below. 
     The first jaw member  8 A is actuated from the first open position of FIG. 2 to the second closed position of FIG. 3 by a novel jaw-closing system that applies very high compressive forces to captured tissue volumes over the length of substantially elongate jaws. Referring to FIG. 2, it can be seen that the upper (first) jaw member  8 A is actuatable about pivot pins  17   a  and  17   b  to open and close relative to the lower (second) jaw member  8 B that in this exemplary embodiment is configured as a fixed (non-actuatable) jaw. The pivot pins  17   a  and  17   b  are fit into a proximal portion  19  of lower jaw body member  20  that is fixedly coupled to the distal end of thin-wall sleeve  16 . 
     In this embodiment, the jaw structure is moved from the first open position (FIG. 2) to the second closed position (FIG. 3) by a dual-action jaw-closing system. In FIG. 2, it can be seen that upper jaw member  8 A has arcuate slots  22   a  and  22   b  in arm portions  23   a  and  23   b . Reciprocatable actuator rods  24   a  and  24   b  carry pins  26   a  and  26   b  in their distal ends that slide in arcuate slots  22   a  and  22   b  of the jaw arms to initially actuate upper jaw  8 A toward a closed position (FIG. 3) from the open position of FIG.  2 . It can be seen that the slidable actuator rods  24   a  and  24   b  comprise a first component of the jaw-closing system. The proximal ends of actuator rods  24   a  and  24   b  are coupled to a first actuator known in the art and carried in the handle portion (e.g., a lever arm or squeeze grip) that translates the rods to and fro. These rods  24   a  and  24   b  slide through parallel aligned bores  27   a  and  27   b  in body member  20 . This first mechanism for actuating upper jaw  8 A is adapted to cause an initial movement of the jaw toward the second closed position (see FIG.  3 ). A second actuator mechanism, described below, is provided for locking the paired elongate jaws in the second closed position (FIG. 3) to provide high tissue-compressing forces over the entire length of the elongate jaws, and to open the jaws. The axial length of jaws  8 A and  8 B indicated at a may be any suitable length depending on the anatomic structure targeted for transection and sealing and may range from about 100 mm. or more, for example for resecting and sealing lung, to as little as 5.0 mm. for a micro-surgery. 
     As can be seen best in FIG. 2, the upper and lower jaws  8 A and  8 B have axial slots therein indicated at  28   a  and  28   b  that cooperate to receive a thin translatable blade member  30  with sharp edge  31  for transecting tissue captured in the jaw assembly. To better explain the second mechanism for closing the jaws, FIG. 4 shows introducer sleeve  16  with blade member  30  (without showing jaws) in its first retracted position and its second extended position. The proximal end of extension member  32  (not shown) is coupled to a second actuation means known in the art and carried in the handle portion (not shown) of the device to translate blade member  30  distally and proximally. The actuator may be any type of lever arm or slider adapted to translate the blade member. The distal end  33  of extension member  32  is connected to the blade member. The blade portion of the assembly of FIG. 4 has an “I”-beam type cross-section  37  with upper flange member  35   a  and lower flange member  35   b . Of particular interest, as will described below, the upper and lower flanges  35   a  and  35   b  serve as functional components of the dual-action jaw-closing mechanism. The upper and lower flanges  35   a  and  35   b  are fixed to blade member  30  by any suitable means such as fittings with pins, adhesives or the like. Further, as can be seen in FIGS. 2 and 4, the rounded leading edge  36   a  of upper flange portion  35   a  is adapted to push against flat surface  38   a  of upper jaw  8 A as a cam to thus push the jaw toward the closed position of FIG.  3 . Besides being adapted to push moveable jaw  8 A toward the closed position, it can be understood that the paired upper and lower flanges  35   a  and  35   b  are adapted to lock the distal portions  40  of the jaws in the second closed position. As can be seen in FIG.  4  and FIG. 5A, the inner flees  42   a  and  42   b  of flanges  35   a  and  35   b  of the “I”-beam form  37  are spaced apart a fixed dimension and are thus adapted to engage against outer surfaces  35   a  and  38   b  of the jaws to thereby lock the distal jaw portions  40  together. The dimension (indicated at b in FIG. 4) between flange inner faces  42   a  and  42   b  determines and controls the thickness of the tissue that is compressed between the jaw faces. In sum, the proximal jaw portions  44  (FIG. 3) are maintained together by the pivot pins  17   a  and  17   b  to define a predetermined gap dimension g between jaw face portions  46   a  and  46   b  in the closed position, while the distal jaw portions  40  are locked together by the flanges of the blade member. The combination blade and jaw-locking mechanism built into the blade member  30  (see FIG. 4) allows very elongate jaws to be locked together at distal ends thereof to thereby apply high compressive forces to captured tissue—which forces could not be achieved with a conventional jaw-closing mechanism as used is prior art graspers. This first and second jaw-closing mechanisms are preferably actuated from a single suitable actuator (e g., a lever arm or squeeze grip) that (i) can move actuator rods  24   a  and  24   b  proximally to initiate the jaw closing process, and (ii) move the extension member  32  coupled to blade member  30  distally to close and lock the jaws in the second closed position (see FIG.  3 ). Such dual-actuation mechanical systems are known in the art and need not be described in detail herein. 
     Referring to FIG. 4, other novel features and functions of the blade member or assembly can now be described In this preferred embodiment, the extension member  32  of the blade assembly has a surface comprising an electrode  50  that is of any suitable conductive material. As will be described below, this core electrode or central electrode  50  is adapted to cooperate with electrodes  55 A and  55 B in the upper and lower jaws, respectively. The core electrode  50  is coupled to electrical source  60  by a lead wire indicated at  62  in FIGS. 2-3. As can be seen best in FIG. 4, the extension member  32  has a distal tapered portion  63  that is fixedly coupled to blade member  30 . The tapered portion  63  rapidly transitions to a greater cross-sectional medial portion  64  of extension member  32  that serves a compression member to press transected tissue outwardly against cooperating faces  66   a  and  66   b  of the jaws. In this embodiment, the cross-section of extension member  32  and electrode  50  is round, but it should be appreciated that any shape is possible that is designed to cooperate with the shape of cooperating jaws faces to compress tissue in the method of the invention described below. This core electrode  50  is adapted to contact and engage the inner or medial layers m of just-transected tissue, as well as to laterally compress the just-transected tissue against jaw faces  66   a  and  66   b , as will be described the practice of the method of the invention. 
     Now turning to FIG. 5A, the novel shapes and surfaces of electrodes faces  55 A and  55 B in engaging faces  46   a  and  46   b  of jaws  8 A and  8 B can be described FIG. 5A shows that the paired jaws in the second closed position generally define an open central channel portion indicated at  65  that has a cross-sectional shape that cooperates with the cross-sectional shape of core electrode  50  (phantom view), in this case having a round cross-section. The distal ends  67   a  and  67   b  of jaws  8 A and  8 B extend around, and define, the distal end open channel  65  within the closed jaws as can be seen in FIG.  3 . 
     FIG  5 A further shows that engaging faces  46   a  and  46   b  of jaws  8 A and  8 B define an engagement plane P (dashed line) that represents the plane in which targeted tissue is captured or engaged between the jaws before being transected by blade  30 , as well as during Rf energy delivery. Of particular interest, the engagement plane P: (i) has a non-linear form or non-planar from transverse to central axis  15  of the jaw structure, and/or (ii) has no portions that comprise a radial r of the axis  15  of the jaws (see FIG.  5 A). In prior art jaws, such an engagement plane P of the jaws typically is linear and also comprises a radial of a central axis of the jaws as shown in FIG.  6 . By the term radial, it is meant that a radial line or plane is orthogonal to the central axis of the jaws and also be termed a radius (see FIG.  6 ). As can be seen in FIG. 6, such a radial r thus defines the shortest possible distance from central axis  15  to an exterior surface or edge of the jaw structure. In the present invention, it has been found that thermal welds are enhanced in medial-to-surface Rf current flows when increased electrode surface areas are provided for engaging tissue between the upper and lower jaws. The novel manner of providing such increased electrode engagement area, within a small diameter jaw form, is to not provide an engagement plane P that is a simple radial r of central jaw axis. Rather, the preferred embodiment of the invention provides non-radial forms for such an engagement plane P. As can be seen in FIG. 5A, a preferred engagement plane P is provided that extends at angles to a radial r thereby providing an increased dimension across the jaw faces  46   a  and  46   b  that carry the surfaces of electrodes  55 A and  55 B. While FIG. 5A depicts an engagement plane P that is suitable for accomplishing the method of the invention, FIG. 5B depicts another engagement plane P that has jaw faces  46   a  and  46   b  that define an undulating form and thus is somewhat further removed from a radial form. 
     The sharp leading edge  31  of blade  30  shown in FIG. 4 is preferred for cutting tissue. Alternatively, the leading edge of blade member  30  may be an electrode element that operates at high Rf intensities suitable for cutting tissue as is known in the art. For example, for tissue cutting purposes, Rf frequencies may range from 500 kHz to 2.5 MHz, with power levels ranging from about 50 W. to 750 W., and open circuit voltages ranging as high as 9 Kv. In this alternative configuration, such an electrode cutting element preferably is insulated from core electrode  50  that cooperates with paired electrodes  55 A and  55 B. Alternatively, the working end may have a singular electrode that is adapted to both transect the captured tissue and thereafter cooperate with electrodes  55 A and  55 B to seal the tissue as will be described below. 
     Of particular interest, it can now be seen the translation of medial portion  64  of the extension member  32  provides issue-compressing means for compressing a medial portion m of the transected and exposed margin of the anatomic structure between cooperating surfaces. More in particular, FIGS. 7A-7B illustrate sectional views of the exemplary cross-sectional shape formed into engaging surfaces  66   a  and  66   b  of central channel  65  of the jaws and central electrode  50 . Referring back to FIG. 4, it can be seen that extension member  32  and the surface of electrode  50  increase in cross-sectional dimension from distal taper portion  63 . Thus, the extension member  32 , besides functioning to compress the medial tissue m of the vessel walls outwardly against the inwardly-facing jaw faces  66   a  and  66   b , also functions to increase the surface area of electrode  50  in contact with medial tissue layers m of the transected structure. As shown schematically in FIGS. 7A-7B, electrodes  55 A and  55 B in the paired jaws have a common (first) polarity and are coupled to electrical generator  60  and controller  70 . The cooperating central electrode  50  carried by extension member  32  has an opposing (second) polarity, and again is coupled to generator  60  and controller  70 . FIG. 7B thus indicates that bi-polar Rf current will flow between the central extension member electrode  50  and either jaw face  46   a  and  46   b  (i.e., electrodes  55 A and  55 B carried therein). The views of FIGS. 2 and 3 indicate that a current carrying wire lead  62  extends from electrical source  60  to extension member electrode  50 . Leads  74   a  and  74   b  extend from Rf source  60  to each of electrode elements  55 A and  55 B carried within the jaws. The electrodes are of any suitable material such as aluminum, stainless steel, nickel titanium, platinum, gold, or copper. Each electrode surface preferably has a micro-texture (e.g., tiny serrations or surface asperities, etc.) for better engaging tissue and for delivering high Rf energy densities in engaged tissues as is known in the art. The bi-polar Rf current may be switched on and off by a foot pedal or any other suitable means such as a switch in handle (not shown). 
     Another embodiment of the invention (not shown) includes a sensor array of individual sensors (or a single sensor) carried in any part of the jaw assembly that is in contact with the tissue targeted for welding. Such sensors preferably are located slightly spaced apart from electrodes  55 A- 55 B for the purpose of measuring temperatures of tissue adjacent to the electrodes during a welding procedure. It should be appreciated however that the sensors also may measure temperature at the electrodes. The sensor array typically will consist of thermocouples or thermistors (temperature sensors that have resistances that vary with the temperature level). Thermocouples typically consist of paired dissimilar metals such as copper and constantan which form a T-type thermocouple as is known in the art Such a sensor system can be linked to feedback circuitry that together with a power controller can control Rf energy delivery during a tissue welding procure. The feedback circuitry can measure temperatures at one or more sensor locations, or sensors can measure the impedance of tissue, or voltage across the tissue, that is engaged between the transecting member and a jaw. The power controller then can modulate Rf delivery in order to achieve (or maintain) a particular parameter such as a particular temperature in tissue, an average of temperatures measured among multiple sensors, a temperature profile (change in energy delivery over time), a particular impedance level or range, or a voltage level as is known in the art. 
     Operation and use of the working end  5  of FIGS. 2-3 in performing a method of the invention can be briefly described as follows. FIG. 7A shows a targeted tissue volume t that is captured between first and second jaws  8 A and  8 B The targeted tissue t may be any soft tissue or anatomic structure of a patient&#39;s body and FIGS. 7A-7B depict a large diameter blood vessel  80  with vessel walls  82  having thick fascia layers indicated at f underlying exterior surfaces s, medial tissue layers m and endothelial layers en. FIG. 7A depicts the blood vessel as it is transected by blade member  30 . FIG. 7A further shows the paired electrodes  55 A and  55 B of first and second jaw faces  46   a  and  46   b  engaging exterior surfaces s of the targeted tissue t thereby defining electrode engagement areas indicated at e 1  (collectively) between the first polarity electrodes  55 A- 55 B and the exterior surfaces s of the vessel. 
     Referring to FIG. 7B, it can be easily understood that progressive slidable movement of blade  30  causes the increased cross-section of core electrode  50  to plow into walls  82  of the vessel to press the medial tissue m between the extension member  32  and the cooperating sides  66   a  and  66   b  of axial channel  65  in the opposing jaw members. At the same time, the slidable extension member  32  carries electrode surface  50  that is pressed into contact with the endothelium en and medial tissue volumes m to thereby provide a broad engagement surface indicated at e 2  between the second polarity core electrode  50  and such medial tissue m (defined as including endothelium en). In FIG. 7A, the electrodes  55 A and  55 B are shown as being insulated from the structural component of jaws, but it should be appreciated that these electrodes  55 A and  55 B may comprise the structural component of the jaws, for example in very small instruments. Thus, in such an embodiment, the electrode engagement surface area e 1  of electrodes  55 A and  55 B can comprise substantially the entire jaw face that contacts the targeted tissue. 
     Now tuning to FIG. 8A, an illustration is provided that indicates the sealing or welding effect that is achievable by the medial-to-surface bi-polar current flow (or vice versa) indicated by arrows A. It has been found that a substantially uniform weld w can be created across the entire tissue volume captured between the engagement surfaces e 1  and e 2  of the jaw electrodes  55 A- 55 B and central electrode  50 , respectively. In other words, the sectional illustration of FIG. 8B shows that a weld w can be created where the proteins (including collagen) are denature intermixed under high compressive forces, and then permanently fused upon cooling to seal or weld the margin of the transected vessel. Further, it is believed that the desired weld effects can be accomplished substantially without collateral thermal damage to adjacent tissues indicates at  92  in FIG.  8 B. 
     2. Type “B” Working End for Scaling or Welding Tissue. A Type “B” working end  105  is substantially the same as shown in FIGS. 2-3 with the addition of an independently actuatable extension sleeve member  122  that carries core electrode  50  as shown in FIGS. 9A-9B. In the Type “B” system of FIG. 9A, all component parts that are identical to those of the Type “A” embodiment have the same reference numeral. FIG. 9A shows the blade member  30  is coupled to an inner extension member  132  that can be translated from a retraced position to an extended position (see FIG. 9A) to transect captured tissue as described previously. FIG. 9A shows the blade assembly without the jaw structure to illustrate that extension sleeve member  122  is adapted to independently slide over inner extension member  132 . By separating the components of the invention that actuate the blade member  30  and the extension sleeve  122  that carries the core electrode  50  as well as tissue-compression mean, the level of tissue compression can be better controlled. The extension sleeve  122  has a distal taper indicated at  134  with core electrode  50  covering the surface extension sleeve  122 . The extension sleeve  122  is actuatable from a first retraced position to an extended position (see FIG. 9A) by an independent lever or slider mechanism in the handle (not shown) of the instrument. It can be easily understood that the independently actuated extension sleeve  122  is adapted to plow into and compress the transected margin of the engaged tissue outwardly against the cooperating jaw surfaces. Referring to FIG. 9B, an enlarged sectional view of one side of the jaw structure is shown that provides increased electrode engagement surfaces e 1  and e 2 . In this embodiment, the electrode engagement area e 1  at the exterior surface s of the vessel is enhanced by cooperating undulations  77  in jaws faces  146   a  and  146   b . Further, the exemplary embodiment of FIG. 9B shows that electrode engagement area e 2  is enhanced by providing an oval shape to the core electrode  50  that cooperates with jaw faces  166   a  and  166   b . The embodiment of FIG. 9B also shows that the entire jaw members may comprise electrodes  55 A and  55 B, which may particularly suitable for very small diameter instruments. 
     3. Type “C” Working End for Sealing Tissue. FIG. 10 shows an alternative embodiment of a working end  205  and jaw structure that performs the previously-described tissue welding methods of the invention. The transecting blade member  30  cooperates with paired jaw members  208 A and  208 B similar to the previous embodiments. FIG. 10 shows that a novel feature of this embodiment comprises active tissue-cooling means carried within at least one lateral portion  211  of the lower jaw  208 B for cooling tissue volumes collateral to the transected margin that is targeted for welding. The tissue-cooling means comprises thermoelectric cooling elements (or Peltier elements)  210  comprising at least one layer of semiconductor blocks (e.g., bismuth telluride) within inner and outer heat conduction layers  216   a  and  216   b  of a plastic or other material that in not electrically conductive. The use of such semiconductor cooling of tissue engaged by jaw members of a working end (together with thermal energy delivery means) for tissue welding was first disclosed by an author in co-pending U.S. patent application Ser. No. 09/110,065 filed Jul. 3, 1998, which is incorporated herein by this reference. Such semi-conductor cooling elements are coupled to leads and a direct current electrical source (not shown) as is known in the art for drawing heat from the engaged tissue and radiating the heat into the environment from the outer surfaces  216   a  and  216   b . The desired parameters for such semi-conductor cooling elements can be derived from engineering manuals known in the art (see, e.g.,  Thermoelectric Product Catalog and Technical Reference Manual  published by Ferrotec America Corp., 1050 Perimeter Rd., Manchester, N.H. 03103). FIG. 10 further shows that the jaws of the invention optionally may be asymmetric. That is, the jaws may be designed to seal only one margin of the transected tissue, as would be useful in a lung resection or any other procedure in which it is not necessary to seal the margin of tissue that is transected and removed 
     Another embodiment of the invention (not shown) may combine linear stapling means with the welding techniques of the invention. In other words, rows of staples together with staple-driving means can be carried in elongate jaws lateral to the electrodes  55 A- 55 B (see FIG. 7A) carried in the jaws. Such stapling means are known in the art (see, e.g., U.S. Pat. No. 5,403,312 to Yates et al). 
     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. 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. Further variations will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.