Abstract:
A system and method for optimizing tissue separation using modulated or duty cycle controlled waveforms on desiccated tissue, where the desiccated tissue has a high electrical impedance. In bipolar electrosurgical procedures, tissue separation is separated with the application of an electrical signal. When tissue does not completely separate and becomes desiccated, generator may generate a duty cycle controlled waveform with specified duty cycle and frequency or modulated waveform. Modulated waveform is generated by adding or multiplying one or more waveforms together. Modulated or duty cycle waveforms create power pulses with higher voltages and a low RMS value. Power pulses drive power and create heat in the high impedance tissue. The creation of heat helps to mobilize water content adjacent to the desiccated tissue. The heating and mobilization of water induces motion into the tissue and aids in the complete separation of tissue while keeping the RMS power low.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to an electrosurgical system and method and, more particularly, to duty cycle controlled waveforms and modulated waveforms for use in optimizing tissue separation. 
         [0003]    2. Background of Related Art 
         [0004]    Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ohmic, resistive, ultrasonic, microwave, cryogenic, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. 
         [0005]    During the cutting process, the generator supplies an electrical signal at a fixed sinusoidal frequency to an electrosurgical instrument to cut the tissue. Occasionally, the tissue will not completely separate and become completely desiccated because the tissue dries or loses moisture as the electrical signal is applied to the tissue. The desiccated tissue has a very high electrical impedance. An object of the invention is to provide modulated or duty cycle controlled waveforms with higher voltages to completely separate the tissue while keeping the root mean square (RMS) power low. 
       SUMMARY 
       [0006]    A system and method for optimizing tissue separation using modulated or duty cycle controlled waveforms on desiccated tissue, where the desiccated tissue has a high electrical impedance. In bipolar electrosurgical procedures, tissue separation is separated with the application of an electrical signal. When tissue does not completely separate and becomes desiccated, a generator may generate a duty cycle controlled waveform with a specified duty cycle and frequency or a modulated waveform. The modulated waveform is generated by adding or multiplying one or more waveforms together. The modulated or duty cycle controlled waveforms create power pulses with higher voltages and a low RMS value. The power pulses drive power and create heat in the high impedance tissue. The creation of heat helps to mobilize water content adjacent to the desiccated tissue. The heating and mobilization of water induces motion into the tissue and aids in the complete separation of tissue while keeping the RMS power low. 
         [0007]    According to an embodiment of the present disclosure, a method for optimizing tissue separation including the steps of grasping a section of tissue with an electrosurgical instrument and sending a pulse waveform to the instrument to seal the tissue. The method further includes the steps of sending a sinusoidal waveform to the instrument to cut the tissue and determining if the tissue is completely separated. In response to determining the tissue is not completely separated, the method further includes the step of generating a duty cycle controlled waveform or a modulated waveform. The duty cycle controlled and the modulated waveform have a larger voltage than the sinusoidal waveform used to cut the tissue and a low root mean square (RMS) power value. The method then sends the duty cycle controlled or the modulated waveform to the instrument to completely separate the tissue. 
         [0008]    According to another embodiment of the present disclosure, a method for performing a surgical procedure includes the step of grasping a section of tissue with an electrosurgical instrument and sending a pulse waveform to the instrument to seal the tissue. The method also includes the steps of sending a sinusoidal waveform to the instrument to cut the tissue and determining if the tissue is completely separated. In response to determining the tissue is not completely separated, the method further includes the step of generating with a generator a duty cycle controlled waveform from pulsing a fundamental frequency at a specified duty cycle. The duty cycle controlled waveform has a larger voltage than the sinusoidal waveform used to cut the tissue and a low root mean square (RMS) power value. The method then sends the duty cycle controlled waveform to the instrument to completely separate the tissue. 
         [0009]    According to another embodiment of the present disclosure, a system for performing a surgical procedure includes an electrosurgical instrument configured to grasp a section of tissue and a generator. The generator is configured to selectively supply an electrical signal to the electrosurgical instrument in three phases. In a first phase, the generator sends a pulsed waveform to the electrosurgical instrument to seal the tissue. In a second phase, the generator sends a sinusoidal waveform to the instrument to cut the tissue. In a third phase, the generator sends a duty controlled waveform or a modulated waveform to cut unseparated tissue with a larger voltage than the sinusoidal waveform used to cut the tissue and a low root mean square (RMS) power value. 
         [0010]    Further, the generator can automatically initiate the third phase upon determining the tissue separation in the second phase was unsuccessful. A sensor determines an electrical impedance of the cut tissue. Alternatively, a user may be alerted to the unsuccessful tissue separation in the second phase. The user is then prompted to initiate the generator to supply energy using the third phase. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Various embodiments of the present disclosure are described herein with reference to the drawings wherein: 
           [0012]      FIG. 1  is a schematic block diagram of a bipolar electrosurgical system in accordance with an embodiment of the present disclosure; 
           [0013]      FIG. 2  is an enlarged, schematic end view showing one embodiment of an electrode assembly of the present disclosure; 
           [0014]      FIG. 3  is a schematic block diagram of a generator in accordance with an embodiment of the present disclosure; 
           [0015]      FIG. 4  illustrates a duty cycle controlled waveform according to an embodiment of the present disclosure; 
           [0016]      FIG. 5(   a ) illustrates a beat frequency waveform according to an embodiment of the present disclosure; 
           [0017]      FIG. 5(   b ) illustrates a fundamental frequency waveform according to an embodiment of the present disclosure; 
           [0018]      FIG. 6  illustrates a modulated output according to an embodiment of the present disclosure; and 
           [0019]      FIG. 7  is a flow diagram of a process for optimizing tissue separation using duty cycle controlled and modulated waveforms according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
         [0021]    The generator according to the present disclosure can perform bipolar electrosurgical procedures, including vessel sealing procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes electronic circuitry configured for generating radio frequency power specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., bipolar, vessel sealing). 
         [0022]      FIG. 1  is a schematic illustration of a bipolar electrosurgical system according to the present disclosure. The system includes bipolar electrosurgical forceps  10  having one or more electrodes for treating tissue of a patient P. The electrosurgical forceps  10  include, opposing jaw members  11  and  16  having an active electrode  14  and a return electrode  13 , respectively, disposed therein. The active electrode  14  and the return electrode  13  are connected to the generator  30  through cable  18 , which includes the supply and return lines  4 ,  8  coupled to the active terminal  31  and return terminal  32 , respectively (see  FIG. 3 ). The electrosurgical forceps  10  are coupled to the generator  30  at a connector  21  having connections to the active terminal  31  and return terminal  32  (e.g., pins) via a plug disposed at the end of the cable  18 , wherein the plug includes contacts from the supply and return lines  4 ,  8 . 
         [0023]    The generator  30  includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator  30 . In addition, the generator  30  may include one or more display screens for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the user to adjust power of the RF energy, waveform parameters including a fundamental frequency, a beat frequency, duty cycle, and/or other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, intensity setting, etc.). 
         [0024]      FIG. 2  is an enlarged, schematic end view showing one embodiment of an electrode assembly  20  of the present disclosure. During the so called “sealing phase”, the jaw members  11  and  16  are closed about tissue and the cutting element  26  may be configured to form a requisite gap between opposing sealing surfaces  22   a,    24   a,  and  22   b,    24   b.  During activation of the sealing phase, the cutting element  26  is not necessarily energized such that the majority of the current is concentrated between diametrically opposing sealing surfaces between  22   a  and  24   a  and  22   b  and  24   b  to effectively seal the tissue. Additionally, stop members (not shown) may be disposed on the sealing surfaces, adjacent to the sealing surfaces, or on the insulators  28 ,  29  to regulate the gap distance between opposing sealing surfaces  22   a,    24   a  and  22   a,    24   b.    
         [0025]    The electrode assembly  20  in this embodiment only includes one cutting element  26 . The cutting element  26  is disposed opposite insulator  29  which provides a dual function during activation of the electrode assembly  20 : 1) provides a uniform gap between sealing surfaces  22   a  and  24   a  and  22   b  and  24   b  during the sealing phase (eliminating a need for the above-mentioned stop members); and 2) prevents the electrode  20  from shorting during the sealing and cutting phases. During activation, the cutting element  26  is energized to a first potential “+” and the opposing sealing surfaces  22   a,    24   a,  and  22   b,    24   b  are energized to a second electrical potential “−” which creates an area of high power density between the two previously formed tissue seals and cuts the tissue. Additionally,  FIG. 2  is one example of electrode assembly  20 , other embodiments of electrode assemblies are disclosed in U.S. Pat. No. 7,276,068, issued on Oct. 2, 2007, entitled “Vessel Sealing Instrument with Electrical Cutting Mechanism”, the disclosure of which is herein incorporated by reference in its entirety. 
         [0026]      FIG. 3  shows a schematic block diagram of the generator  30  having a controller  34 , a DC power supply  37 , and an RF output stage  38 . The power supply  37  is connected to a conventional AC source (e.g., electrical wall outlet) and is adapted to provide high voltage DC power to an RF output stage  38  that converts high voltage DC power into RF energy. RF output stage  38  delivers the RF energy to an active terminal  31 . The energy is returned thereto via the return terminal  32 . 
         [0027]    The generator  30  may include a plurality of connectors (not shown) to accommodate various types of electrosurgical instruments (e.g., instrument, electrosurgical forceps  10 , etc.). Further, the generator  30  may be configured to operate in a variety of modes such as ablation, bipolar cutting, coagulation, sealing, etc. The generator  30  may also include a switching mechanism (e.g., relays) to switch the supply of RF energy between the connectors. 
         [0028]    The controller  34  includes a microprocessor  35  operably connected to a memory  36 , which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). The microprocessor  35  is operably connected to the power supply  37  and/or RF output stage  38  allowing the microprocessor  35  to control the output of the generator  30  according to either open and/or closed control loop schemes. Those skilled in the art will appreciate that the microprocessor  35  may be substituted by any logic processor (e.g., control circuit) adapted to perform the calculations discussed herein. 
         [0029]    A closed loop control scheme or feedback control loop is provided that includes sensor circuitry  39  having one or more sensors (not shown) for measuring a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output current and/or voltage, etc.). The sensor circuitry  39  provides feedback to the controller  34 . Such sensors are within the purview of those skilled in the art. The controller  34  then signals the HVPS  37  and/or RF output phase  38  which then adjusts the DC and/or RF power supply, respectively. The controller  34  also receives input signals from the input controls of the generator  30  or the instrument  10 . The controller  34  utilizes the input signals to adjust power outputted by the generator  30  and/or performs other control functions thereon. 
         [0030]    The forceps  10  is configured to operate in three modes or phases: (1) electrosurgical tissue sealing, (2) bipolar electrosurgical cutting, and (3) duty cycle controlled or modulated waveform bipolar electrosurgical cutting. The third mode or phase is applied when the tissue does not completely separate causing the tissue to have a very high electrical impedance. 
         [0031]      FIG. 4  illustrates a duty cycle controlled waveform  40  for use in the third phase. The waveform  40  is shown with a fundamental frequency  45  and a duty cycle  42 , where the duty cycle is the percentage of “on” time in a repetition rate  44 . The time difference between pulses is the percentage of “off” time  46  in the repetition rate  44 . 
         [0032]    The fundamental frequency  45  can range from 424 kHz to 520 kHz. More specifically, the fundamental frequency ranges from 448 KHz to 496 kHz. The duty cycle  42  can range from 5% to 50% of the “on” time in the repetition rate  44 , and more specifically from 5% to 20% of the “on” time in the repetition rate  44 . 
         [0033]    The duty cycle controlled waveform  40  allows for a higher voltage to be applied to the tissue while keeping the RMS power low. A high RMS power may damage the polymers used in the electrodes or cause other undeterminable effects. The duty cycle controlled waveform  40  creates power pulses, where the power and voltage are in an exponential relationship, as shown below: 
         [0000]    
       
      
       P=V 
       2 
       /R  
      
     
         [0000]    The power pulses drive power and create heat in the high impedance tissue. The creation of heat mobilizes water content next to the high impedance desiccated tissue. The heating and mobilization of water induces motion in the tissue and aids in complete separation of tissue. 
         [0034]      FIG. 5(   a ) illustrates a beat frequency waveform  50 . The beat frequency  47  can range from 0.5 kHz to 20 kHz.  FIG. 5(   b ) illustrates a fundamental frequency waveform  55 . 
         [0035]    Modulated waveform  60  in  FIG. 6  illustrates the multiplication of the beat frequency waveform  50  and the fundamental frequency waveform  55 . The resulting modulated waveform  60  creates a modulated effect that allows for a more smooth transition of energy delivery. Further, the resulting waveform  50  defines a technique of more complex energy delivery that results in a more destructive arc that improves tissue vaporization. Moreover, the modulated waveform  60  allows for a higher voltage to be applied to the tissue while keeping the RMS power low. The modulated waveform  60  creates power pulses, where the power and voltage are in a exponential relationship. The power pulses drive power and create heat in the high impedance tissue. The creation of heat mobilizes water content next to the high impedance desiccated tissue. The heating and mobilization of water induces motion in the tissue and aids in complete separation of tissue. 
         [0036]    In alternative embodiments, the beat frequency waveform  50  and the fundamental frequency waveform  55  can be added together to form a modulated waveform. Additionally, the fundamental frequency waveform  55  can be added or multiplied with itself, a sine wave, a square wave, a triangular wave, a duty cycle controlled waveform, or other waveform. Further, the beat frequency waveform  50  can be added or multiplied with itself, a sine wave, a square wave, a triangular wave, a duty cycle controlled waveform, or other waveform. Additionally, this modality of combining frequencies can be combined with other tissue degradation techniques to optimize the surgical procedure. 
         [0037]      FIG. 7  is a flow diagram of a process  700  for optimizing tissue separation by controlling waveform and duty cycle parameters. The process  700  starts with step  705 , which invokes clamping or grasping tissue with the instrument  710 . The generator then sends a pulse waveform to the instrument  10  to seal the tissue at step  715 . To cut the tissue at step  720 , the generator sends a small precise sinusoidal waveform to the instrument. Next, a sensor (not shown) on the instrument  10  and/or sensor circuitry  39  is used to determine if the tissue is completely separated at step  725  by measuring the electrical impedance of the cut tissue. If the sensor circuitry measures a high electrical impedance across the tissue, then the tissue is not completely separated. If the tissue is not completely separated, then the generator generates an electrical signal at step  730  with a duty cycle controlled waveform  40  or a modulated waveform  60 . The electrical signal sent in step  730  can automatically be sent by the generator  30  if the tissue is not completely separated in step  720 . Alternatively, a user may be prompted that the tissue was not completely separated in step  720 . Then, the user may be prompted to initiate the generator  30  to generate the electrical signal in step  730 . Then, the generator sends the electrical signal to the instrument  10  to finish cutting the tissue at step  740 . The process  700  then ends at step  745  after sending the electrical signal or after determining the tissue is completely separated. 
         [0038]    While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.