Patent Publication Number: US-6905497-B2

Title: Jaw structure for electrosurgical instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit from Provisional U.S. Patent Application Ser. No. 60/384,429 filed May 31, 2002 having the same title, which application is incorporated herein by this reference. This application is a Continuation-In-Part of co-pending U.S. patent application Ser. No. 10/032,867 filed Oct. 22, 2001 titled Electrosurgical Jaw Structure for Controlled Energy Delivery, and U.S. patent application Ser. No. 10/079,728 filed Feb. 19, 2002 titles Electrosurgical Systems and Techniques for Sealing Tissue, both of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to medical devices and techniques and more particularly relates to an electrosurgical jaw structure. The jaw assembly, in one mode of operation, can be used for general grasping and dissecting purposes wherein the jaws close in a non-parallel manner so that the distalmost jaw tips only engage tissue with little movement of the actuator lever in the handle of the instrument. In another mode of operation, the jaw assembly closes in a parallel manner under very high compression to enable tissue welding. 
     2. Description of the Related Art 
     In various open and laparoscopic surgeries, it is necessary to coagulate, seal or weld tissues. One preferred means of tissue-sealing relies upon the application of electrical energy to captured tissue to cause thermal effects therein for sealing purposes. Various mono-polar and bi-polar radiofrequency (Rf) jaw structures have been developed for such purposes. In a typical bi-polar jaw arrangement, each jaw face comprises an electrode and Rf current flows across the captured tissue between the first and second polarity electrodes in the opposing jaws. While such bi-polar jaws can adequately seal or weld tissue volumes that have a small cross-section, such bi-polar instruments often are ineffective in sealing or welding many types of tissues, such as anatomic structures having walls with irregular or thick fibrous content, bundles of disparate anatomic structures, substantially thick anatomic structures, or tissues with thick fascia layers such as large diameter blood vessels. 
     Prior art Rf jaws that engage opposing sides of a tissue volume typically cannot cause uniform thermal effects in the tissue, whether the captured tissue is thin or substantially thick. As Rf energy density in tissue increases, the tissue surface becomes desiccated and resistant to additional ohmic heating. Localized tissue desiccation and charring can occur almost instantly as tissue impedance rises, which then can result in a non-uniform seal in the tissue. The typical prior art Rf jaws can cause further undesirable effects by propagating Rf density laterally from the engaged tissue to cause unwanted collateral thermal damage. 
     What is needed is an instrument with a jaw structure that can apply Rf energy to tissue in new modalities: (i) to weld or seal tissue volumes that have substantial fascia layers or tissues that are non-uniform in hydration, density and collagenous content; (ii) to weld a targeted tissue region while substantially preventing thermal damage in regions lateral to the targeted tissue; and (iii) to weld a bundle of disparate anatomic structures. 
     SUMMARY OF THE INVENTION 
     The principal objective of the present invention is to provide an electrosurgical jaw structure and Rf energy control system that is capable of precisely modulating energy to engaged tissue over a selected time interval to accomplish tissue welding. As background, the biological mechanisms underlying tissue fusion or welding by means of thermal effects are not fully understood. In general, the application of Rf energy to a captured tissue volume causes ohmic heating (alternatively described as active Rf heating herein) of the tissue to thereby at least partially denature proteins in the tissue. By ohmic heating, it is meant that the active Rf current flow within tissue between electrodes causes resistive heating of conductive compositions (e.g., water) in the tissue. 
     One objective of the invention is to denature tissue 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. A more particular objective of the invention is to provide a system that (i) instantly and automatically modulates ohmic heating of tissue to maintain a selected temperature in the tissue, and (ii) to instantly and automatically modulate total energy application between active Rf heating (resulting from tissue&#39;s resistance to current flow therethrough) and conductive heating of tissue cause by the thermal capacity of the jaw components. 
     In one exemplary embodiment, a jaw of the instrument defines a tissue engagement plane that engages the tissue targeted for welding. The engagement plane carries first and second surface portions that comprise, respectively an electrical conductor and a variable resistive body or positive temperature coefficient (PTC) material having a resistance that increases at higher temperatures. A variable resistive body of a dope polymer or ceramic can be engineered to exhibit a positively sloped curve of temperature-resistance over a temperature range of about 37° C. to 100° C. The region at the higher end of such a temperature range brackets a targeted “thermal treatment range” at which tissue can be effectively welded. The selected resistance of the variable resistive body at the upper end of the temperature range will substantially terminate current flow therethrough. 
     In operation, it can be understood that the engagement plane will apply active Rf energy (ohmic heating within) to the engaged tissue until the point in time that the variable resistive body is heated to exceed the maximum of the thermal treatment range. Thereafter, Rf current flow from the engagement surface will be lessened—depending on the relative surface areas of the first and second surface portions. This instant and automatic reduction of Rf energy application can be relied on to prevent any substantial dehydration of tissue proximate to the engagement plane. By thus maintaining an optimal level of moisture around the engagement plane, the working end can more effectively apply energy to the tissue—and provide a weld thicker tissues with limited collateral thermal effects. 
     The jaw assembly corresponding to the invention further provides a suitable cross-section and mass for providing a substantial heat capacity. Thus, when the variable resistive body is elevated in temperature to the selected thermal treatment range, the retained heat of the variable resistive matrix volume can effectively conduct thermal energy to the engaged tissue volume. Thus, in operation, the working end can automatically modulate the application of energy to tissue between active Rf heating and passive conductive heating of the targeted tissue to maintain the targeted temperature level. 
     The jaw assembly corresponding to the invention is moved between an open position and closed position about an engagement plane by the positive engagement of the proximally-facing cams and distally-facing cams carried by a reciprocating member. Thus, the jaw assembly can be used effectively to dissect tissue by inserting the tip of the jaw assembly into a tissue plane and then opening the jaws with substantial from to thus separate and dissect the tissue. This is not possible with many jaw assemblies of surgical instrumemts that use springs to move the jaws toward an open position. 
     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. 1  is a perspective view of a Type “A” introducer and electrosurgical jaw assembly illustrating the first and second cam surfaces of the jaws that are adapted for positive engagement with a reciprocating member for both closing and opening the jaws. 
         FIG. 2  is another perspective view of the Type “A” jaw assembly of  FIG. 1  illustrating the engagement surfaces of the jaws. 
         FIG. 3  is a perspective view of the reciprocatable extension member of the Type “A” electrosurgical working end of  FIGS. 1-2  shown de-mated from the working end. 
         FIG. 4  is a plan view of the de-mated reciprocatable member of  FIG. 3  showing the first and second cam surfaces thereof. 
         FIG. 5A  is an end view of the reciprocatable member of  FIG. 3  with first and second jaws in phantom view. 
         FIG. 5B  is a sectional view of the reciprocatable member of  FIG. 3  taken along line  5 A— 5 A of FIG.  3 . 
         FIG. 6  is a perspective view of a de-mated jaw of the Type “A” electrosurgical working end of  FIGS. 1-2 . 
         FIG. 7A  is a side view of working end of  FIGS. 1 and 2  with the reciprocatable member being retracted to apply opening forces on the paired jaws. 
         FIG. 7B  is a side view similar to  FIG. 7A  showing the reciprocatable member fully extended to apply high compressive forces over the length of the paired jaws. 
         FIG. 8A  is a sectional view of the Type “A” electrosurgical jaw taken along line  8 A- 8 A of  FIG. 7B  illustrating the conductive component carried in one jaw and a variable resistive matrix carried in both jaws. 
         FIG. 8B  is a graph showing the temperature-resistance profile of a variable resistive matrix carried in the jaw of  FIG. 8A , the impedance of tissue and the combined resistance of the variable resistive matrix and tissue as measured by a system controller. 
         FIG. 8C  is a graph showing an alternative temperature-resistance profile of a variable resistive matrix carried in the jaw of FIG.  8 A. 
         FIG. 8D  is a sectional view of an alternative Type “A” electrosurgical jaw illustrating the conductive component and temperature-sensitive resistive matrix of the jaw assembly carried in a one jaw with the other jaw having a insulative engagement surface. 
         FIG. 8E  is a sectional view of another alternative Type “A” electrosurgical jaw illustrating the conductive component embedded in the temperature-sensitive resistive matrix in one jaw. 
         FIG. 9  is a perspective view of a Type “B” electrosurgical working end with the jaws in an open position showing first and second cam surfaces carried on a single rotatable jaw. 
         FIG. 10  is a perspective view of the Type “B” working end of  FIG. 9  with the jaws in a closed position again showing the first and second cam surfaces of the single rotatable jaw. 
         FIG. 11  is an enlarged view of a proximal (first) end portion of the Type “B” jaw of  FIGS. 9-10  showing a projecting pin of the upper jaw that rotatably cooperates with an arcuate bore in the lower jaw to provide a jaw pivot with a selected degree of freedom of movement. 
         FIG. 12A  shows a Type “C” jaw structure in an open position with the slidable extension member and jaws in a partially cut-away view to illustrate the jaw opening-closing mechanism. 
         FIG. 12B  shows the Type “C” jaw structure of  FIG. 12A  in a first closed position with the slidable extension member moving the jaws to a parallel condition. 
         FIG. 12C  shows the jaw structure of  FIGS. 12A-12B  in a second closed position with the slidable extension member moving the jaws to a non-parallel condition so that the distalmost jaw tips engage tissue. 
         FIG. 12D  shows the jaw structure of  FIGS. 12A-12C  in a third closed position with the slidable extension member moving the jaws to a high-compression parallel condition for tissue welding. 
         FIG. 13  shows the slidable extension member of  FIGS. 12A-12D  de-mated from the first and second jaws to show the first and second cam elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1. Type “A” jaw assembly. An exemplary Type “A” jaw assembly  100  of a surgical grasping instrument is illustrated in  FIGS. 1 and 2  which is adapted for transecting captured tissue and contemporaneous welding of the captured tissue with Rf energy delivery. The jaw assembly  100  is carried at the distal end  104  of an introducer sleeve member  106  that can be rigid, articulatable or deflectable in any suitable diameter. For example, the introducer sleeve portion  106  can have a diameter ranging from about 2 mm., to 20 mm. to cooperate with cannulae in endoscopic surgeries or for use in open surgical procedures. The introducer portion  106  extends from a proximal handle (not shown). The handle can be any type of pistol-grip or other type of handle known in the art that carries actuator levers, triggers or sliders for actuating the jaws as will be disclosed below, and need not be described in further detail. The introducer sleeve portion  106  has a bore  108  extending therethrough for carrying actuator mechanisms for actuating the jaws and for carrying electrical leads  109   a - 109   b  for the electrosurgical components of the working end. 
     As can be seen in  FIGS. 1 and 2 , the jaw assembly  100  has first (lower) jaw element  112 A and second (upper) jaw element  112 B that are adapted to close or approximate about axis  115 . The jaw elements may both be moveable or a single jaw may rotate to provide the open and closed positions. In the exemplary embodiment of  FIGS. 1 and 2 , both the lower and upper jaws  112 A- 112 B are moveable relative to a rolling pivot location  116  defined further below. Another exemplary embodiment with a fixed lower jaw portion  112 A and rotatable upper jaw  112 B is shown in  FIGS. 9 and 10 . 
     Of particular interest, the opening-closing mechanism of the jaw assembly  100  corresponding to the invention operates on the basis of cam mechanisms that provide a positive engagement of camming surfaces (i) for moving the jaw assembly to the (second) closed position to engage tissue under very high compressive forces, and (ii) for moving the jaws toward the (first) open position to apply substantially high opening forces for “dissecting” tissue. This important feature allows the surgeon to insert the tip of the closed jaws into a dissectable tissue plane—and thereafter open the jaws to apply such dissecting forces against the tissues (see FIG.  7 A). 
     Referring to  FIGS. 1 and 2 , the lower and upper jaws  112 A- 112 B have a first end  118 , in the open position, that defines first (proximally-facing) arcuate outer surface portions indicated at  120   a  and  120   b  that are engaged by a first surface portions  122   a  and  122   b  of reciprocatable member  140  that is adapted to slide over the jaw elements to thereby move the jaws toward closed position. The first end portion  118  of the lower and upper jaws, in the open position, further defines second (distally-facing) arcuate surface portions indicated at  130   a  and  130   b  that are engaged by second surface portions  132   a  and  132   b  of the reciprocatable member  140  for moving the jaw elements to the open position. The distal (second) end region  133  of the paired jaws is rounded with a lip  134  that can serve as an electrode for surface coagulation as will be described below. 
     In this embodiment of  FIGS. 1 and 2 , the reciprocating member  140  (see  FIGS. 3 and 4 ) is actuatable from the handle of the instrument by any suitable mechanism, such as a lever arm, as is known in the art that is coupled to a proximal end  141  of member  140 . The proximal end  141  and medial portion  141 ′ of member  140  are dimensioned to reciprocate within bore  108  of introducer sleeve  106 . The distal portion  142  of reciprocating member  140  carries first (lower) and second (upper) laterally-extending flanges or shoulder elements  144 A and  144 B that are coupled by intermediate transverse element  145 . The transverse element  145  further is adapted to transect tissue captured between the jaws with a leading edge  146  ( FIG. 3 ) that can be a blade or a cutting electrode. The transverse element  145  is adapted to slide within a channels  148   a  and  148   b  in the paired first and second jaws. As can be seen best in  FIGS. 3 and 4 , the laterally-extending shoulder elements  144 A and  144 B define the surfaces  122   a ,  122   b ,  132   a  and  132   b  that slidably engage the arcuate cam surfaces of the jaws and that apply high compressive forces to the jaws in the closed position (FIG.  7 B). 
     Referring back to  FIGS. 1 and 2 , the first and second jaws  112 A and  112 B define tissue-engaging surfaces or planes  150   a  and  150   b  that contact and deliver energy to engaged tissues, in part, from an Rf electrode arrangement therein indicated at  155 . The jaws can have any suitable length with teeth or serrations  156  in any location for gripping tissue. The embodiment of  FIGS. 1 and 2  depicts such serrations  156  at an inner portion of the jaws along channels  148   a  and  148   b  thus leaving engagement planes  150   a  and  150   b  laterally outward of the tissue-gripping elements. In the embodiments described below, the engagement planes  150   a  and  150   b  and electrode(s)  155  generally are shown with a non-serrated surface for clarity of explanation, but such engagement planes and electrodes themselves can be any non-smooth gripping surface. The axial length of jaws  112 A and  112 B indicated at L can be any suitable length depending on the anatomic structure targeted for transection and sealing and typically will range from about 10 mm. to 50 mm. The jaw assembly can apply very high compression over much longer lengths, for example up to about 200 mm. for example resecting and sealing organs such as a lung or liver. The scope of the invention also covers jaw assemblies for an instrument used in micro-surgeries wherein the jaw length can be as little as about 5.0 mm. 
     In the exemplary embodiment of  FIGS. 1 and 2 , the engagement plane  150   a  of the lower jaw  112 A is adapted to deliver energy to tissue, and the tissue-contacting surface  150   b  of upper jaw  112 B can be electrosurgically active or passive as will be described below. Alternatively, the engagement surfaces of the jaws can carry any of the electrode arrangements disclosed in co-pending U.S. patent application Ser. No. 09/032,867 filed Oct. 22, 2001 titled Electrosurgical Jaw Structure for Controlled Energy Delivery and Ser. No. 10/308,362 filed Dec. 3, 2002 titled Electrosurgical Jaw Structure for Controlled Energy Delivery both of which are incorporated herein by reference. 
     The perspective and plan views ( FIGS. 3 and 4 ) more particularly illustrate the cam surfaces of reciprocating member  140  de-mated from jaws  112 A and  112 B.  FIG. 5A  shows an end view of “I”-beam shape of the reciprocating member  140  with the jaws  112 A and  112 B in phantom view. From  FIGS. 3 ,  4  and  7 B, it can be easily understood how the jaw assembly  100  can apply very high compressive pressures to engaged tissue. The transverse element  145  of the reciprocating member  140  defines a transverse dimension d between the innermost surfaces  158   a  and  158   b  of the flanges of the reciprocating member and the cooperating medial and distal outer surfaces  160 A and  160 B of the jaws (see  FIGS. 6 ,  7 A and  7 B). The selected transverse dimension d between the flanges or shoulders  144 A and  144 B thus further defines the engagement gap g between the engagement planes  150   a  and  150   b  of the jaws in the closed position. It has been found that very high compression of tissue combined with controlled Rf energy delivery is optimal for welding the engaged tissue volume contemporaneous with transection of the tissue. Preferably, the engagement gap g between the engagement planes ranges from about 0.001″ to about 0.050″ for most tissue volumes. More preferably, the gap g between the engagement planes ranges from about 0.001″ to about 0.010″. As can be seen in  FIGS. 3 , and  5 B, the medial portion  141 ″ of the reciprocating member  140  retains an “I”-beam shape with inner surface portions  163   a  and  163   b  that engage the cooperating medial outer surfaces of the jaws. Thus, the entire length L of the jaws can be maintained in a fixed spaced-apart relationship to define a consistent engagement gap g—no matter the length of the jaws. 
     It should be appreciated that jaw assembly  100  can be provided with mechanisms for adjusting the transverse dimension d between the inner surfaces of flanges  144 A and  144 B of the reciprocating member  140  as are disclosed in co-pending U.S. patent application Ser. No. 09/017,452 filed Dec. 13, 2001 titled Electrosurgical Jaws for Controlled Application of Clamping Pressure which is incorporated herein by reference. That application discloses mechanisms that allow the operator (i) to adjust the transverse dimension d between the cam surfaces of shoulders  144 A and  144 B between pre-selected dimensions, or (ii) to allow for dynamic adjustment of the transverse dimension d in response to the tissue volume captured between the paired jaws. 
       FIG. 6  shows an exemplary jaw de-mated from the jaw assembly  100  that exposes the cam engagement surfaces  120   b  and  130   b  of the member. An additional unique feature of the invention is the fact that the cooperating jaws can be identical to one another, thus simplifying the manufacturing process. Since the jaw members can be identical, metal injection molds costs can be reduced. 
       FIGS. 7A and 7B  more particularly show the actuation of the reciprocating member  140  from a first retracted position to a second extended position to move the jaws  112 A and  112 A from the first open position to the second closed position. Referring to  FIG. 7A , it can be seen that the translatable member  140  is being moved in the proximal direction so that the proximal-facing surfaces  132   a  and  132   b  of reciprocating member  140  abut the outer surfaces  130   a  and  130   b  of the jaws thus forcing the jaws apart, for example to apply dissecting forces to tissues.  FIG. 7B  shows the reciprocating member  140  after having been fully extended in the distal direction so that the distal-facing surfaces  122   a  and  122   b  of reciprocating member  140  have ridden up and over the proximal arcuate surfaces  120   a  and  120   b  of the jaws (and medial outer surfaces  160 A′ and  160 B′) thus forcing the jaws together. 
     Of particular interest, the jaws can rollably contact one another along the interface  170  between inner surfaces  172   a - 172   b  of the first end  118  of the jaws (see  FIGS. 6 ,  7 A and  7 B). Thus, the jaw assembly does not need to define a true single pivot point as is typical of hinge-type jaws known in the art. The pivotable action of the jaws along interface  170  can best be described as a rolling pivot that optionally can allow for a degree of dynamic adjustment of the engagement gap g′ at the proximal end of the jaws. The jaws elements can be retained relative to one another and the introducer sleeve  106  by means of protruding elements  175  ( FIG. 6 ) that couple with arcuate slots  176  in an internal member  177  that is fixedly carried in bore  108  of introducer sleeve  106 . Alternatively, outwardly protruding elements  178  can cooperate with slots in the wall of introducer sleeve  106  (not shown). As also shown in  FIG. 6 , the jaw assembly can (optionally) include springs for urging the jaws toward the open position. Electrical leads indicated at  109   a - 109   b  are shown in  FIG. 6  for coupling a voltage source (radiofrequency generator)  180  and controller  182  to the electrode arrangement  155 . 
     In one preferred embodiment shown in  FIGS. 1 and 2 , the first (lower) jaw  112 A carries an exposed conductive material or electrode  155  together with an exposed variably resistive matrix  185  in the jaw&#39;s engagement plane  150   a . The jaw assembly carries a return electrode in any of three locations, or any combination thereof: (i) in a portion of the opposing engagement surface  150   b  of upper jaw  112 B, (ii) in the transverse element  145  of the reciprocating member  140 ; or (iii) in laterally outward portions of the lower jaw  112 A that surround the variably resistive matrix  185 . 
     The sectional view of  FIG. 8A  more particularly illustrates the relevant conductive and variably resistive components within the body of the lower jaw  112 A for controllably delivering energy to tissue for sealing or welding purposes. The engagement surface  150   a  of jaw  112 A has the exposed conductive material (electrode) indicated at  155  that is both electrically conductive and thermally conductive. For example, the conductive material  155  can comprise a machined metal, a formed metal or a molded metal having a substantial thickness—that can be conductively bonded to the positive temperature coefficient (PTC) variably resistive matrix  185  described next. Alternatively, the conductive material  155  can comprise a thin film deposit of any suitable material known in the art (e.g., gold, platinum, palladium, silver, stainless steel, etc.) having any suitable thickness dimension, for example, ranging from about of 0.0001″ to 0.020″. The width of the conductive material  155  can be any suitable dimension depending on the jaw dimension. 
     As can be seen in  FIG. 8A , the jaw  112 A has an engagement surface with an exposed conductive material  155  at least partially surrounded by PTC matrix  185  that is variably resistive in response to temperature changes therein is carried adjacent to, and inward of, the surface conductive material  155 . The structural body portion  186   a  of jaw  112 A can be any suitable metal or other material having sufficient strength to apply high compressive forces to the engaged tissue, and typically carries an insulative coating (at least on its outer portions). As shown in  FIG. 8A , the body portion  186   a  of jaw  112 A preferably (but optionally) has a thin insulated coating  187  about its surface to prevent electrical energy delivery to tissues about the exterior of the jaw assembly and between the body  186   a  and the PTC matrix  185 . 
     The conductive portion (electrode)  155  exposed in the engagement plane  150   a  is coupled by an electrical lead  109   a  to a voltage (Rf) source  180  and controller  182 . The matrix  185  can have any suitable cross-sectional dimensions, indicated generally at sd 1  and sd 2 , and preferably such a cross-section comprises a significant fractional volume of the jaw body to provide a thermal mass for optimizing passive conduction of heat to tissue as will be described below. 
     It can be seen in  FIG. 8A , a substantial portion of the surface area of engagement plane  150   a  comprises the PTC resistive matrix  185 . Preferably, the matrix  185  comprises at least 10% of the surface area of engagement plane  150   a  of an electrosurgical jaw, wherein the engagement plane is defined as the tissue-contacting surface of the jaw. More preferably, the PTC matrix  185  comprises at least 25% of the surface area of engagement plane  150   a  of such a jaw. Still more preferably, the PTC matrix  185  comprises at least 50% of the surface area of the jaw&#39;s engagement plane  150   a.    
     Of particular interest, still referring to  FIG. 8A , the variably conductive matrix  185  comprises a polymeric material having a temperature-dependent resistance. Such materials are sometimes known as polymer-based “temperature coefficient” materials that exhibit very large changes in resistance with a small change in body temperature. This change of resistance with a change in temperature can result in a “positive” coefficient of resistance wherein the resistance increases with an increase in temperature (a PTC or positive temperature coefficient material). The scope of the invention also includes a variably conductive matrix  185  with a “negative” coefficient of resistance (and NTC material) wherein its resistance decreases with an increase in temperature. 
     In one preferred embodiment, the PTC matrix  185  is a ceramic layer that is engineered to exhibit unique resistance vs. temperature characteristics that is represented by a positively slope temperature-resistance curve in FIG.  8 A. More in particular, the matrix  185  maintains a low base resistance over a selected temperature range with a dramatically increasing resistance above a selected narrow temperature range of the material (sometimes referred to herein as switching range; see FIG.  8 B). For example, the base resistance can be low, or electrical conductivity can be high, between about 37° C. and 65° C., with the resistance increasing greatly between about 55° C. and 80° C. In another embodiment, the PTC matrix  185  is characterized by a more continuously positively sloped temperature-resistance as shown curve in  FIG. 8C  over the range of 37° C. to about 80° C. 
     One aspect of the invention relates to the use of a PTC matrix  185  as described in  FIG. 8B  in a jaw&#39;s engagement plane with a selected switching range between a first temperature (T 1 ) and a second temperature (T 2 ) that approximates the targeted tissue temperature for a contemplated tissue sealing or welding objective. The selected switching range, for example, can be any substantially narrow 1°-10° C. range that is determined to be optimal for tissue sealing or welding (e.g., any 5° C. range between about 50°-200° C.) or for another thermotherpy. A more preferred switching range can fall within the larger range of about 50°-90° C. 
     No matter the character of the slope of the temperature-resistance curve of the PTC matrix  185  (see FIGS.  8 B and  8 C), a preferred embodiment has a matrix  185  that is engineered to have a selected resistance to current flow across its selected dimensions in the jaw assembly when at 37° C. ranging from about 0.0001 ohms to 1000 ohms. More preferably, the matrix  185  has a designed resistance across its selected dimensions in the jaw when at 37° C. ranging from about 1.0 ohm to 1000 ohms. Still more preferably, the matrix  185  has with a designed resistance across its selected dimensions when at 37° C. ranging from about 25 ohms to 150 ohms. In any event, the selected resistance across the matrix  185  in an exemplary jaw at 37° C. exceeds the resistance of the tissue or body structure targeted for treatment. The matrix  185  further is engineered to have a selected resistance that substantially prevents current flow therethrough corresponding to a selected temperature that constitutes the high end (maximum) of the targeted thermal treatment range. Such a maximum temperature for tissue welding can be a selected temperature between about 50° C. and 100° C. More preferably, the selected temperature at which the matrix&#39;s selected resistance substantially prevents current flow occurs at between about 60° C. and 90° C. 
     In a first mode of operation, it can be understood that the initial delivery of Rf energy to conductor or electrode  155  will thereby apply Rf energy to (or cause active ohmic heating of) tissue engaged between jaws  112 A and  112 B. Further, the delivery of Rf energy to electrode  155  will be conducted, in part, through the PTC matrix  185  in a path to a return electrode—no matter the location of the return electrode (or and combination thereof) as described above. The engaged tissue is thus elevated in temperature by ohmic or “active” Rf heating. The paired jaws&#39; components, including the PTC matrix  185 , will increase in temperature as caused by conduction of heat from the transient high temperatures of tissue—which were heated by caused by Rf densities therein (ohmic heating). 
     At a selected temperature at the maximum of the targeted treatment range, the PTC matrix  185  will no longer contribute to ohmic tissue heating due to termination of current flow therethrough. However, the mass of the PTC matrix  185  will still conduct heat to engaged tissue. As the PTC matrix  185  falls below the targeted treatment range, the matrix  185  again will contribute to ohmic tissue heating via current paths therethrough from electrode  155 . By this means of energy delivery, the mass of the jaw body will be modulated in temperature, similar to the engaged tissue, at or about the targeted treatment range. Of particular interest, the jaw body will apply energy to engaged tissue by ohmic heating, or by conduction (or radiation) of thermal effects in a self-modulating manner. 
     A suitable PTC material can be fabricated from high purity semi-conducting ceramics, for example, based on titanate chemical compositions (e.g., BaTiO 3 , SrTiO 3 , etc.). The specific resistance-temperature characteristics of the material can be designed by the addition of dopants and/or unique materials processing, such as high pressure forming techniques and precision sintering. Suitable PTC materials are manufactured by several sources and can be obtained, for example, from Western Electronic Components Corp., 1250-A Avenida Acaso, Camarillo, Calif. 93012. Another manner of fabricating the PTC resistive matrix  185  is to use a commercially available epoxy that is doped with a type of carbon. In fabricating a PTC matrix  185  in this manner, it is preferable to use a carbon type that has single molecular bonds. It is less preferable to use a carbon type with double bonds which has the potential of breaking down when used in thin layers, thus creating the potential of an electrical short circuit between the conductor (electrode)  155  and a return electrode carried within the jaw assembly. 
     As can be seen in  FIG. 8A , the conductive material or electrode  155  is operatively connected to the voltage (Rf) source  180  by electrical lead  109   a  that defines a first polarity. As described previously, return electrode functionality can be carried in any of three components of the jaw assembly, or any combination thereof: (i) in a portion of the opposing engagement surface  150   b  of upper jaw  112 B, (ii) in the transverse element  145  of the reciprocating member  140 ; or (iii) in laterally outward portions of the lower jaw  112 A outwardly adjacent to the PTC matrix  185 . In the embodiment of  FIG. 8A , the body portions  186   a  and  186   b  of the lower and upper jaws  112 A and  112 B have an opposing polarity as defined by coupling to electrical source by lead  109   b . Further, the slidable contact of the jaw body portions  186   a  and  186   b  with transverse element  145  of reciprocating member  140  makes it function with the opposing polarity. In the preferred embodiment depicted in  FIG. 8A , the upper jaw  112 B also carries a PTC matrix  185  that covers a substantial portion of the engagement surface  150   b . The material of the PTC matrix can be identical in both the lower and upper jaws. 
     The manner of utilizing the jaw assembly  100  of  FIG. 8A  to perform a method of the invention can be understood as engaging and compressing tissue between the first and second engagement surfaces  150   a  and  150   b  of jaws  112 A and  112 B and thereafter delivering Rf energy from conductor  155  and PTC matrix  185  to maintain a selected temperature in the engaged tissue for a selected time interval. For example, the jaw assembly is provided with a PTC matrix  185  that has a targeted treatment range in a region below about 90° C. With the jaws in the closed position and the engagement planes  150   a  and  150   b  engaging tissue, the operator actuates a switch that delivers Rf energy from the voltage (Rf) source  180  to the conductor  155 . At normal tissue temperature, the low base resistance of the PTC matrix  185  allows unimpeded Rf current flow from the voltage source  180  through engagement surface  150   a  and tissue to the return electrode components as described above via lead  109   b . It can be understood that the engaged tissue initially will have a substantially uniform impedance to electrical current flow, which will increase substantially in proximity to engagement surfaces  150   a  and  150   b  as the engaged tissue loses moisture due to ohmic heating. 
     Following an arbitrary time interval, the impedance of tissue proximate to engagement surfaces  150   a  and  150   b  will be elevated, and the higher tissue temperature will instantly conduct heat to the PTC matrix  185  in each jaw. In turn, the PTC matrix  185  will reach its limit and terminate Rf current flow therethrough. Such automatic reduction of active Rf energy application can thus prevent any substantial dehydration of tissue proximate to PTC matrix  185 . By thus maintaining the desired level of moisture in tissue proximate to the engagement planes, the jaw assembly can more effectively apply energy to the tissue. Such energy application can extend through thick engaged tissue volumes while causing very limited collateral thermal effects. Thereafter, as the temperature of the engaged tissues falls by thermal relaxation and the lesser Rf energy density, the temperature of the matrix  185  will fall below the threshold of the targeted treatment range. This effect, in turn, will cause increased Rf current flow through the assembly and matrix to the engaged tissues to again increase the tissue temperature by increased ohmic heating. By the above-described mechanisms of causing the PTC matrix  185  to be maintained in the treatment range, the actual Rf energy applied to the engaged tissue can be precisely modulated to maintain the desired temperature in the tissue. Further, the composition that comprises matrix  185  can comprise a substantial volume of the jaws&#39; bodies and the thermal mass of the jaws, when elevated in temperature, can deliver energy to the engaged tissue by means of passive conductive heating—at the same time Rf energy delivery causes lesser active (ohmic) tissue heating. This balance of active Rf heating and passive conductive (or radiative) heating can maintain the targeted temperature for any selected time interval. 
     In summary, one method of the invention comprises the delivery of Rf energy from a voltage source  180  to tissue via a conductor in a jaw assembly at least partly through a PTC material  185  wherein the thermally-sensitive resistor material has a selected temperature-resistance profile to provides low resistance at low tissue temperatures and a very high resistance above the targeted temperature range for tissue sealing or welding. In operation, the working end automatically modulates active Rf energy density in the tissue as the temperature of the engaged tissue conducts heat back to the PTC material  185  to cause move the matrix along its selected temperature-resistance curve. In the treatment range, the Rf current flow thus can be modulated without the need for thermocouples or any other form of feedback circuitry mechanisms to modulate Rf power from the source. Most important, it is believed that this method of the invention will allow for immediate modulation of actual Rf energy application along the entire length of the jaws, which is to be contrasted with prior art instruments that utilize a temperature sensor and feedback circuitry. Such sensors or thermocouples measure temperature only at a single location in the jaws, which typically will not be optimal for energy delivery over the length of the jaws. Such temperature sensors also suffer from a time lag. Further, such temperature sensors provide only an indirect reading of actual tissue temperature—since a typical sensor can only measure the temperature of the electrode. 
     In another mode of operation, the system controller  182  coupled to source  180  can acquire data from the current flow circuitry that is coupled to first and second polarity electrodes in the jaw (in any locations described previously) to measure the blended impedance of current flow between the first and second polarity conductors through the combination of (i) the engaged tissue and (ii) the PTC matrix. Another method of the invention thus can include provide algorithms within the system controller  182  to modulate, or terminate, power delivery to working end based on the level of the blended impedance as defined above. The method can further include controlling energy delivery by means of power-on and power-off intervals, with each such interval having a selected duration ranging from about 1 microsecond to one second. The working end and system controller  182  can further be provided with circuitry and working end components of the type disclosed in Provisional U.S. Patent Application Ser. No. 60/339,501 filed Nov. 9, 2001 titled Electrosurgical Instrument which is incorporated herein by reference. 
     In another mode of operation, the system controller  182  can be provided with algorithms to derive the temperature of the resistive PTC matrix  185  from measure impedance levels—which is possible since the matrix is engineered to have a selected resistance at each selected temperature over the temperature-resistance curve (see  FIGS. 8B-8C . Such temperature measurements can be utilized by the system controller  182  to modulate, or terminate, power delivery to engagement surfaces based on the temperature of the PTC matrix  185 . This method also can control energy delivery by means of the power-on and power-off intervals as described above. 
     Referring back to  FIG. 2 , the distal (second) end  133  of the jaws carries a thin lip  134  extending outwardly from the jaw body. It has been found useful to provide an electrode in lip  134  for surface coagulation of tissues. In one preferred embodiment, an independent electrode  188  is carried in lip  134  that can be any thin film conductive material carried at the surface of jaws and coupled to an electrical source (not shown), for example cooperating with a ground pad. In another embodiment, the electrode  188  can comprise an exposed portion of the conductive lower jaw body  186   a  and upper jaw body  186   b  wherein the insulative layer  187  removed from the lips  134  (cf. FIG.  8 A). 
       FIG. 8D  shows an alternative embodiment of jaw assembly  190  that carries all the same components as described previously in the embodiment of FIG.  8 A. The difference is that the engagement plane  150   b  of upper jaw  112 B carries a fully insulated layer indicated at  192 . It has been found that such a configuration can function well in very small instruments adapted for engaging small tissue volumes. 
       FIG. 8E  illustrates another alternative embodiment of jaw assembly  195  that carries components that are similar to those described in the embodiments of  FIGS. 8A and 8D . However, in this embodiment, the conductor  155  of the lower jaw  112 A is carried in an interior portion of the PTC matrix  185 . Thus, the conductor  155  has no exposed surface in engagement plane  150   a  of the lower jaw  112 A. It has been found that such a configuration is useful in treating some very thin tissues since ohmic heating of tissue can be terminated altogether when the PTC matrix  185  reaches its selected switching range. In operation, the jaws can automatically modulate the application of energy to tissue between active Rf heating and passive conductive heating of the targeted tissue at a targeted temperature level. 
     2. Type “B” jaw assembly.  FIGS. 9-10  illustrate an exemplary Type “B” jaw assembly  200  adapted for electrosurgery that again can weld and transect an engaged tissue volume. The jaw assembly  200  is carried at the distal end  204  of an introducer member  206  that has a bore  208  extending therethrough. The Type “B” embodiment is similar to the Type “A” embodiment except that the first (lower) jaw  212 A is a fixed extension portion of rigid introducer member  206 . As can be seen in  FIGS. 9 and 10 , the second (upper) jaw  212 B is adapted to close or approximate about axis  215 . 
     The opening-closing mechanism of jaw assembly  200  corresponding to the invention again provides cam surfaces for positive engagement between reciprocatable member  240  and the jaws (i) for moving the jaws to a (second) closed position to engage tissue under high compressive forces, and (ii) for moving the jaws toward the (first) open position thereby providing high opening forces to dissect tissue with outer surfaces of the jaw tips. The reciprocating member  240  operates as described previously to reciprocate within bore  208  of the introducer member  206 . As can be seen in  FIG. 10 , the distal end portion  242  of reciprocating member  240  carries distal first and second laterally-extending flange portions  244 A and  244 B with the blade-carrying transverse element  245  extending therebetween. The blade-carrying member slides within channels  248   a  and  248   b  in the jaws. 
     In the exemplary embodiment of  FIGS. 9 and 10 , the first and second jaws  112 A and  112 B again define engagement surfaces or planes  250   a  and  250   b  that deliver energy to engaged tissue. The engagement planes carry a conductor  255  and a PTC matrix  285  in at least one of the jaws&#39; engagement surfaces  250   a  and  250   b . In the embodiment of  FIGS. 9 and 10 , the upper jaw  212 B has a first end region  258  that, in the open position, defines a first (proximally-facing) arcuate cam surface indicated at  260  that is engaged by a first surface portion  262  of the reciprocatable member  240 . The reciprocatable member  240  can be substantially identical to that of  FIGS. 3 and 4 . The first (proximal) end region  258  of the upper jaw, in the open position, further defines second (distally-facing) surface portions indicated at  270   a  and  270   a ′ that are engaged by second surface  272  of reciprocatable member  240  for moving the jaw assembly to an open position. 
     As can be seen best in  FIG. 10 , the cam surfaces  270   a  and  270   a′  are formed into pins or projecting elements  274  and  274 ′ that serve multiple purposes. Referring to  FIG. 11 , the pins  274  and  274 ′ extend through the upper jaw body  276   b  and are received within arcuate bores  277  in body  276   a  of lower jaw  212 A. The lower portions  278  (collectively) of the pins  274  and  274 ′ thus can retain upper jaw  212 A and prevent it from moving axially or laterally relative to the jaw axis  215  while still allowing the jaw&#39;s rotation for opening and closing. The pin mechanism further allows for greatly simplified assembly of the instrument. 
     Of particular interest, the pins  274  and  274 ′ provide additional functionality by providing a degree of “vertical” freedom of movement within the first (proximal) end portion  258  of the jaw. As can be seen in  FIGS. 10 and 11 , the distal laterally-extending flange portions  244 A and  244 B define a transverse dimension d (cf.  FIG. 3 ) that in turn determines the dimension of the engagement gap g of the distal end of the jaws in the jaw-closed position (FIG.  10 ). The transverse dimension d equals the dimension between inner surfaces of flange portions  244 A and  244 B that slidably contact the outer surfaces of both jaws. 
       FIG. 10  further illustrates that reciprocatable member  240  carries separate proximal laterally-extending flange portions  294 A and  294 B with an optional different transverse dimension d′ between inner surfaces thereof. A larger dimension d′ between flange portions  294 A and  294 B that slidably contacts the proximal surfaces of both jaws can thus provide a different engagement gap g′ at the proximal end of the jaws. This selected gap dimension g′ can be larger than the engagement gap g at the distal end of the jaws—an effect that would not be possible with a hinged jaw that allows no “vertical” freedom of movement between the proximal ends of the jaws. It has been found that such a floating pivot is useful for engaging thick tissues. Further, the inner surfaces of the flanges  244 A- 244 B and  294 A- 294 B can carry a very slightly compressible material such as a Teflon (not shown) wherein slight compression of such material would allow the jaws&#39; engagement surfaces to move slightly apart when engaging thick tissues. 
     3. Type “C” jaw assembly.  FIGS. 12A-12D  illustrate an exemplary Type “C” jaw assembly  300  that provides both electrosurgical functionality and improved grasping and dissecting functionality for endoscopic surgeries. In  FIGS. 12A-12D , both the upper and lower jaws are shown in cut-away views to show internal cam surfaces of the upper jaw  312 A and the reciprocatable member  240 . The jaw assembly  300  carries engagement surfaces for applying electrosurgical energy to tissue as in the previously described embodiments, as well as cutting means for transecting the engaged tissue volume. The improvement of the Type “C” jaw assembly  300  relates to the ability of the jaw structure, in one mode of operation, to be used for general grasping and dissecting purposes wherein the distalmost tips  313  of the jaws can close tightly on tissue with little movement of the actuator lever in the handle of the instrument. At the same time, in another mode of operation, the jaw assembly  300  can close to apply very high compressive forces on the tissue to enable welding. Thus, the jaw structure provides (i) a first non-parallel jaw-closed position for grasping tissue with the distal jaws tips (FIG.  12 C), and (ii) a second parallel jaw-closed position for high compression of tissue for the application of electrosurgical energy (FIG.  12 D). 
     Referring to  FIG. 12A , the Type “C” embodiment again has an introducer member  206  that is similar to the Type “B” embodiment with first (lower) jaw  312 A comprising a fixed extending portion  314  of the rigid introducer. As can be seen in  FIG. 12A , the second (upper) jaw  312 B is adapted to close or approximate about axis  315 . The opening-closing mechanism of jaw assembly  300  provides cam elements and cooperating jaw surfaces for positive engagement between the reciprocatable member  240  as described previously (i) for moving the jaws to a closed position to engage tissue, and (ii) for moving the jaws toward the open position thereby providing high opening forces to dissect tissue with outer surfaces of the jaw tips  313 . 
     The reciprocating member  240  ( FIG. 13 ) operates as described previously to reciprocate within bore  208  of the introducer member  206  (FIG.  12 A). As can be seen in  FIG. 12A , the distal end  242  of the reciprocating member  240  again carries distal flange portions  244 A and  244 B with a blade-carrying transverse portion  245  therebetween. The transverse portion  245  slides within channels  248   a  and  248   b  in the paired jaws. In the exemplary embodiment of  FIG. 12A , the first and second jaws  312 A and  312 B again define engagement surfaces  350   a  and  350   b  that can deliver electrosurgical energy to engaged tissue. The engagement planes preferably carry a conductive-resistive matrix  385  (not shown) in at least one of the jaws&#39; engagement surfaces. 
     In the embodiment of  FIG. 12A , the upper jaw  312 B has a proximal end  258  that defines a first (proximally-facing) arcuate jaw surface  260  that is engaged by a first cam surface element  262  of reciprocatable member  240  for opening the jaw. The proximal end  258  of the upper jaw further defines second (distally-facing) jaw surface portions indicated at  270   a  and  270   a′  that are engaged by second cam element  272  of reciprocatable member  240  for moving the jaw assembly to an open position. 
     The embodiment of  FIG. 12A  shows that the upper jaw  312 B has a floating primary pivot location indicated at P 1  that is provided by the projecting elements or rectangular pins  274  (collectively) on either side of the channel portions  248   a  that slidably extend into bores  277  (collectively) in the lower jaw body (cf. FIG.  11 ). The lower portions of the pins  274  thus allow upper jaw  312 B to rotate while at the same time the pin-and-bore mechanism allows the upper jaw to move upwardly away from the lower jaw. 
     Of particular interest, the degree of “vertical” freedom of movement of the upper jaw allows for the system to “tilt” the distal tip  313  of upper jaw  312 B toward the axis  315  to thereby allow the distal jaw tips  313  to grasp tissue. This is termed a non-parallel closed position herein. The tilting of the jaw is accomplished by providing a plurality of cam surfaces in the upper jaw  312 B and the reciprocatable member  240 . 
     As can be seen in  FIGS. 12A and 13 , the lower and upper laterally-extending flange portions  244 A and  244 B of the reciprocatable member  240  define a transverse dimension d that determines the dimension of gap g between the engagement surface of the jaws in the fully jaw-closed position (FIGS.  10  &amp;  12 D). The transverse dimension d equals the dimension between inner surfaces of flange portions  244 A and  244 B that slidably contact the outer surfaces of both jaws. 
       FIG. 13  best illustrates that the reciprocatable member  240  is configured with separate elevated step or cam surfaces  390  in the lower flange portions  244 A that are adapted to slidably engage the ends  395  of the rectangular pins  274  on either side of upper jaw  312 B. The elevated cam surfaces  390  of reciprocatable member  240  thus create another transverse dimension d′ between inner surfaces of the flange portions  244 A and  244 B that move the jaws toward either the first jaw-closed position or the second jaw-closed position. 
     Now turning to  FIGS. 12A-12D , the sequence of cut-away views illustrate how the multiple cam surfaces cause the jaws to move between a first “tilted” jaw-closed position to a second “high-compression” jaw-closed position. In  FIG. 12A , the jaws are in an open position. In  FIG. 12B , the reciprocatable extension member  240  is moved distally and its cam surface element  262  pushes on jaw surfaces  260  to move the jaws toward a closed position wherein the jaws rotate about primary pivot location P 1 . In  FIG. 12B , it can be seen that the elevated cam surfaces  390  in the lower flange  244 A have not yet engaged the ends  295  of the rectangular pins  274 . 
     Now turning to  FIG. 12C , the extension member  240  is moved further distally wherein the elevated cam surfaces  390  of lower flange  244 A have now engaged and elevated the ends  295  of rectangular pins  274  thereby tilting the upper jaw. The upper jaw  312 B is tilted slightly by forces in the direction of the arrows in  FIG. 12C  as the upper flange  244 B holds the upper jaw  312 B at a secondary pivoting location indicated at P 2 —at the same time that the step of the cam surface element  390  lifts the pins  274  and the proximal portion  258  of the upper jaw  312 B upward. 
     Thus, the system functions by providing a slidable cam mechanism for lifting the proximal end of the jaw while maintaining the medial jaw portion in a fixed position to thereby tilt the distal jaw to the second jaw-closed position, with the pivot occurring generally about secondary pivot P 2  which is distal from the primary pivot location P 1 . 
       FIG. 12D  next shows the reciprocatable extension member  240  moved further distally wherein the elevated cam surfaces  390  of lower flange  244 A slides distally beyond the ends  295  of rectangular pins  274  thus causing the flanges  244 A and  244 B together with the trailing edge portions  354 A and  354 B of the “I”-beam portion ( FIG. 13 ) of the member  240  to apply very high compression forces over the entire length of the jaws as indicated by the arrows in FIG.  12 D. This position is termed a parallel jaw-closed position herein. Another advantage of the invention is that the jaw structure is in a “locked” position when the extension member  240  is fully advanced. The instrument does not need a separate mechanism to maintain the jaws locked together as in prior art graspers. 
       FIG. 13  shows another optional feature of the reciprocatable extension member  240  that is adapted to maintain the proximal end  258  of the jaws in a selected spaced apart position that is substantially parallel. Whereas the upper and lower flange surfaces maintain the engagement surfaces  355 A and  355 B with a maximum gap therebetween—the flanges do not create a minimum gap which would occur, for example, if tissue were engaged at the distal end of the jaw but not at the proximal end of the jaws. Since the pivot is a “floating-type” pivot, the proximal jaw portion could be pinched together somewhat if tissue was only engaged by the distal jaws when the extension member is in its fully extended position.  FIG. 13  shows the extension member  240  with another cam or engagement surface indicated at  402  (phantom view) that is adapted to slide under and engage the ends  295  of the rectangular pins  274  thus cause the proximal jaw portion  258  to have a minimum gap. Thus, the jaws can be maintained with parallel engagement surfaces even with a “floating” pivot. In another embodiment (not shown), the ends  295  of the rectangular pins  274  can be fitted with rollers, bearing or a lubricious coating to insure ease of sliding of the extension member against the ends  295  of the rectangular pins  274 . 
     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.