GENERATOR TO SUPPLY A COAGULATION INSTRUMENT

Description

[0001] The invention relates to a generator for supplying a tissue fusion instrument, in particular an instrument for vascular fusion.

[0002] The surgical application of coagulation instruments, especially tissue fusion instruments, on patients is usually performed under considerable time pressure. If a surgical procedure requires numerous coagulation measures, particularly the closure and possible transection of many vessels, it is crucial that the vessels are closed as quickly as possible. The aim is to damage and coagulate as little surrounding tissue as possible to minimize unwanted lesions. At the same time, the closure must be performed securely to prevent closed and subsequently transected vessels from opening during or after the procedure and leading to bleeding.

[0003] Vascular fusion typically occurs between two branches of a fusion instrument, which are subjected to high-frequency coagulation voltage and compress a vessel held between them and heat it by means of current flow.

[0004] Such an instrument and associated coagulation processes can be found in US Pat. No. 8,216,223 B2. The instrument is assigned a device that delivers a test pulse to the instrument at the start of a coagulation process in order to measure tissue impedance. Additionally or alternatively, the system can determine characteristics of the electrosurgical instrument at the start of the treatment. The system then determines whether a tissue response is observed and uses this to determine a desired impedance trajectory. From this, the system determines the target value of the impedance based on a desired rate of change. The system then monitors compliance with this desired impedance curve, detecting temperature, tissue type, or similar factors.Additionally, the system can detect the amount of energy delivered to the tissue during the sealing process and stop further energy delivery for a predetermined period of time if the impedance exceeds a threshold that is higher than the initial impedance value. Once the energy application to the tissue is complete, the system can provide a cooling period. The cooling period serves to solidify the collagen in the sealed tissue. The cooling period can be a fixed period of time or an adaptive period depending on parameters related to the tissue fusion process. After the cooling period has elapsed, the sealing process is complete. The system can include active cooling elements to accelerate cooling, such as heat pipes or Peltier elements.

[0005] WO 2015 / 184446 A2 discloses a coagulation instrument that heats tissue held between the jaws of a tissue forceps by means of a flow of current. The phase angle of the alternating current sent through the tissue is recorded in order to maintain the tissue in a two-phase state at 100°C for fusion. US Pat. No. 5,827,271 also illustrates a tissue fusion instrument in which vessels are compressed between two energized jaws and a current is passed through them, thus heating them to fuse the tissue or vessel. After fusion has occurred, the power output to the instrument is reduced to a very low level in order to cool the tissue as quickly as possible. Alternatively, a very low power of approximately 1 watt can be delivered to the tissue to maintain the electrical circuit through the tissue. Such a low power output does not delay the cooling process.

[0006] The goal is to achieve the most homogeneous structure possible in the coagulated tissue. Achieving a homogeneous tissue structure and simultaneously achieving a short sealing time are a conflicting goal. The object of the invention is to provide a concept that improves the homogeneity and thus the reliability of the seal and shortens the sealing time.

[0007] This object is achieved with a generator according to claim 1 or 4.

[0008] The generator according to the invention generates a coagulation voltage for operating the instrument for tissue fusion in several stages. The generator is designed to initially heat the tissue to the boiling point of tissue fluid in a first stage, so that steam is formed. Once sufficient heating of the tissue has been achieved, the device according to a first aspect of the invention proceeds to a second stage. In this second stage, the tissue resistance is induced to oscillate. During this phase, the tissue resistance alternates between high and low values. Since high tissue resistances are associated with relatively dry tissue or vapor bubbles in the tissue, and low tissue resistances are associated with moist tissue or tissue without vapor bubbles, not only does the tissue resistance oscillate, but the tissue state also pulsates, which can result in pulsating mechanical stress on the tissue.In addition, by periodically reducing the electrical energy input into the tissue, an increase in moisture, vapor removal, or vapor liquefaction (e.g., through condensation or vapor escape) can be achieved. This can reduce tissue resistance, effectively and / or collectively achieving an increased total energy input. The periodic reduction in tissue resistance results in an increased current flow between the electrodes compared to coagulation processes, which operate with a constantly high tissue resistance.

[0009] For the oscillating control of tissue resistance, a target resistance curve is defined, with the function block comprising a tissue resistance controller. The controller measures the tissue resistance continuously or at short intervals and compares this with the tissue resistance currently specified by the target tissue resistance curve. From the resulting deviation, it determines the voltage to be applied to the tissue and supplies it to the coagulation electrodes, which thus receive a high-frequency coagulation voltage that is amplitude-modulated at a low frequency. Its magnitude oscillates at a few hertz, preferably less than 30 Hz (or less than 20 Hz), more preferably less than 20 Hz, or even less than 10 Hz. In many cases, a good effect is achieved with an oscillation frequency between 10 Hz and 20 Hz.The oscillation frequency can be fixed by a corresponding function block or variably specified by the function block, particularly depending on the generator setting, the tissue being treated, and especially the instrument. The oscillation frequency can thus assume different, situationally adapted values.

[0010] The controller preferably has an output voltage limiting device that sets a maximum voltage and / or a minimum voltage during the oscillation of the tissue resistance. The maximum voltage is preferably set such that sparking during phases of high tissue resistance or other thermal damage to the tissue to be coagulated or the surrounding tissue is avoided. For example, the maximum voltage can be set to a value between 80 V and 150 V, preferably 90 V to 120 V. Different values ​​are possible. The minimum voltage is preferably set to a value other than zero. This prevents excessively rapid cooling of the tissue and excessively rapid condensation of vapor present in the tissue. The minimum voltage is, for example, in a range of 20 V to 40 V.

[0011] The functional block is preferably designed to end the resistance oscillation at a high tissue resistance, in order to then transition to a controlled cooling process in a third stage, which forms a second aspect of the invention. During the controlled cooling process, the tissue is continuously energized with voltage, the amplitude of which decreases over time, thereby significantly slowing the cooling of the tissue, which would otherwise be very rapid. By continuously energizing the tissue held between the electrodes, the cooling of the tissue is significantly slowed compared to the intermediate cooling observed during the oscillation, thereby reducing the temperature gradient present in the tissue. Zones that reach the optimal temperature for protein cross-linking during the cooling process are enlarged as a result of the reduced temperature gradient in the tissue.This allows the proteins involved, especially collagen, more time and space to form mechanically strong, possibly fibrous structures. Proteins – especially collagen – of opposing, pressed-together vessel walls can fuse together.

[0012] Although the slowed cooling process results in a longer cooling period, the sum of the time required for coagulation with resistance oscillation and controlled cooling is less than it would be for coagulation without resistance oscillation and with uncontrolled cooling. This allows a shortening of the coagulation time, so that a total treatment time, including the cooling process, of less than 3 seconds, and in particular less than 2 seconds, can be achieved. Although the time from closing the instrument's branches to reopening them is so short, secure vessel sealing and thus a high-quality surgical result can be achieved.

[0013] To determine the process status and in particular to determine the start and end times of the various stages, the functional block can monitor at least one tissue property. Such a tissue property can be the voltage applied to the tissue, the current flowing through the tissue, the applied power, the amount of energy transferred to the tissue, the tissue resistance or the like. For example, during the first stage, at the beginning of the current application, the tissue resistance typically experiences a phase of decrease, after which it passes through a minimum and increases again. The renewed increase is associated with the formation of vapor in or on the tissue. According to a first aspect of the invention, oscillations in the tissue resistance are now generated in the second stage of the coagulation process. This can be achieved, for example, by specifying a target curve for the tissue resistance.The coagulation voltage applied to the tissue is adjusted by a controller so that the tissue resistance approximately corresponds to the specified target curve. Once the oscillations have occurred for a predetermined period of time (e.g., approximately 0.5 s) or when a certain number of oscillations (e.g., 5 to 15, preferably 7 to 10, preferably 8) have been recorded, the third stage, which constitutes a slower cooling process, can be initiated.

[0014] The resistance oscillations and / or the slowed cooling enable the fusion of blood vessels with increased safety. The resistance oscillations lead to a pulsed energy input into the tissue, with periodic rewetting of the tissue through condensation of the insulating vapor, thus increasing the energy input. This prepares the ground for an intimate connection between the pressed, opposing vessel walls. The delayed, i.e., slowed cooling process then results in effective recombination and protein chain formation of the proteins involved, particularly collagen. The slowed cooling process creates enlarged zones in the biological tissue in which optimal temperature conditions for the formation of long, cross-linked protein chains are maintained during the cooling phase.

[0015] Further details of advantageous embodiments of the generator according to the invention and the control method according to the invention can be found in the attached drawings, the description, and the dependent claims. They show: Figure 1 the generator, a connected instrument and a vessel to be fused, in a schematic representation, Figure 2 a vessel held between two branches for coagulation, in a schematic sectional view, Figure 3 the generator, in a schematic, partial functional block representation, Figure 4 the time course of the coagulation voltage delivered by the generator, Figure 5 the temporal course of the tissue resistance arising in response to the applied coagulation voltage, Figure 6 the power delivered by the generator to the tissue as well as the energy delivered and Figure 7 the current conducted by the instrument through the tissue over time.

[0016] In Figure 1 A generator 10, a tissue fusion instrument 11 powered by it, and a vessel 12 to be sealed are illustrated very schematically. The instrument 11 has two branches 13, 14, which serve to grasp the blood vessel 12. Guide and operating elements provided for this purpose, such as a handle with an actuating lever, a shorter or longer shaft, or the like, are not illustrated. The instrument 11 can, in principle, have any design of a known tissue fusion instrument, as used for open or laparoscopic surgery.

[0017] At least one of the branches 13, 14 is movable in order to move the vessel 12 held between them, as Figure 2illustrated, so that the inner sides of the vessel walls lie on top of one another and are pressed against one another. Furthermore, the instrument 11 can have a moving mechanical knife, an ultrasonic knife, a moving or stationary electric knife subjected to cutting voltage, or other types of cutting elements. The invention relates to the device 10 and, in this respect, to the energization of the branches 13, 14, and is in principle applicable to any tissue or vessel fusion instrument, regardless of whether the instrument has no, one, or multiple cutting devices for severing the fused element.

[0018] The device 10 has a generator 15, which provides a high-frequency coagulation voltage HF at an output 16, which is optionally passed to the instrument 11 via a sensor block 17 and lines 18, 19. The sensor block 17 serves to detect the magnitude of the HF voltage supplied by the generator 15 and / or the HF current supplied by the HF generator and to transmit it as signals u and / or i to a function block 20 or several function blocks 20a, 20b (see Figures 1 and 3 ) to control the generator 15.

[0019] The generator 15 has an input 21 via which the generator 15 can receive control signals. These can be analog or digital signals that specify the level of the coagulation voltage u output by the generator 15. The control signals can be supplied by a functional block 20 that is connected to the sensor block 17 so that it receives signals output therefrom. The signals can, for example, be signals that characterize the RF current supplied by the generator 15 and / or the RF voltage provided by the generator 15. The functional block 20 can be divided into two or more functional blocks 20a, 20b.

[0020] The function block 20 or the function blocks 20a, 20b can be designed as separate modules or as program component(s) of a generator control program or by any other suitable means with which the operation of the generator 15 can be controlled. They form a controller for a variable to be controlled depending on the stage, which can be, for example, the current i (e.g. in stage A), the tissue resistance R (e.g. in stage B), the coagulation voltage u (e.g. in stage C), or the power P (e.g. also in stage C). The controller can be set to control the generator 15 in at least one of the stages within specified voltage limits that are constant over time or follow a desired time profile.Additionally or alternatively, the controller can be configured to control the generator 15 in at least one of the stages within specified current limits, resistance limits, or power limits that are constant over time or follow a desired time profile. The desired time profiles can be rising or falling ramps or other continuous or discontinuous periodic or non-periodic functions.

[0021] For a better illustration of the structure and functioning of the function block 20, reference is made to the embodiment according to Figure 3Reference is made to the first functional block 20a, connected to the sensor block 17, detects the coagulation voltage u supplied by the generator 15 and applied to the branches 18, 19, and the current i flowing through the vessel 12 or other tissue. The magnitude of the current i depends on the magnitude of the applied coagulation voltage u and the magnitude of the tissue resistance R, the value of which changes during the coagulation of the vessel 12 or other tissue. From the measured current i and the coagulation voltage u, the functional block 20a can, if necessary (at least approximately), calculate the existing tissue resistance R=(u / i)*cos(Phi) and / or the power P=u*i*cos(Phi) and / or the phase shift Phi between the voltage u and the current i and pass it on to the functional block 20b. In addition, the function block 20a can pass on the detected coagulation voltage u and / or the detected current i and / or variables calculated therefrom to the function block 20b.

[0022] Depending on the operating mode or stage of the coagulation process, the function block 20b receives at least one of the signals characterizing the tissue resistance R, the power P transmitted to the tissue, the phase shift Phi between the coagulation voltage u and the current i, the coagulation voltage u and / or the current i flowing through the tissue. The function block part 20b of the function block 20 controls the coagulation process by specifying a target curve for at least one of the variables R, P, Phi, u, i in each stage, which target curve is stored, for example, in a memory 22. The target curve can contain several sections, each of which applies to one (or more) of the variables R, P, u, i and specifies the respective target value for this variable. The target value(s) can vary depending on the type of connected instrument 11 or according to settings on a user interface of the device 10.

[0023] Function block 20b also contains a control block that determines the difference between the respective value (R, P, Phi, u, or i) specified by the target curve and the actual value of the respective controlled variable R, P, Phi, u, or i determined by function block 20a. From this TARGET-ACTUAL difference, a target voltage is derived within function block 20b by the control block, which is then passed on to generator 15.

[0024] The control blocks 20a, 20b can be designed as part of a program executed by a controller which operates as follows and controls the generator 15 as follows:

[0025] The generator 15 is capable of delivering a high-frequency coagulation voltage in the range of several hundred kHz, for example 350 kHz. The voltage generated by the generator 15 can, for example, be in the range from 0 to 150 V. Other generator voltages are applicable. In any case, however, the voltages are dimensioned such that sparking between the branches 13, 14 and the biological tissue, for example the blood vessel 12, is avoided. In addition, the generator 15 is preferably designed such that it can deliver a power of, for example, up to 120 W or even more. Furthermore, it is preferably designed such that it can supply an RF current of up to 2 A (or more). With these parameters, the generator 15 is fundamentally suitable for fusing the blood vessel 12 or other tissue, i.e., for permanently closing it using the instrument 11.

[0026] The blood vessel 12 has a vascular endothelium 24, which forms the inner lining, i.e., the tunica interna of the blood vessel 12. The vascular endothelium consists of endothelial cells forming a single-layer squamous epithelium, elastic fibers, and connective tissue. This sits on a middle layer 25, also referred to as the tunica media, which consists of muscle cells, collagen fibers, elastic fibers, and connective tissue. The outer layer 26, also referred to as the tunica externa, consists primarily of connective tissue and elastic fibers. In particular, the tunica media and the tunica externa contain collagen fibers, which are to fuse with each other during tissue fusion.

[0027] To carry out the tissue fusion process, the vessel 12 is first grasped between the branches 13, 14 and according to Figure 2compressed so that the opposing inner surfaces of the vessel walls touch, the blood is forced out between branches 13, 14, and the vessel 12 is completely clamped. Branches 13, 14 exert a contact pressure on the vessel 12.

[0028] The merger process begins according to Figures 4 to 7 with a first stage, which preferably lasts a maximum of about 1 s and during which the vessel 12 between the branches 13, 14 is heated by the current flow. In terms of the program, stage A can be limited to a fixed period of time, e.g., 2.5 s. For example, in stage A, the current i to be sent through the tissue is specified as a ramp, e.g., increasing linearly over time, as in Figure 7is shown with a dotted line 27. In this case, the function block 20a detects the current i and transmits it to the function block 20b, which operates as a controller. The function block 20b generates a control variable for the generator 15 and transmits it to its input 21. At the same time, the function block 20b can also take into account the coagulation voltage HF applied to the branches 13, 14 and, for example, according to a time-dependent function, e.g. a voltage ramp I ( Figure 4 ), e.g., to prevent harmful effects on the tissue. The limitation can, for example, initially be set according to a predetermined time-dependent function, for example, the Figure 4 set linear ramp I, and optionally also by a maximum voltage II. Due to the voltage limitation, the current i remains below the target curve 27 for a certain time (e.g., about 0.6 s).

[0029] Simultaneously with the increase in current, the tissue resistance R, which is Figure 5As shown, the resistance decreases with progressive tissue heating due to the release of tissue fluid and the increasing mobility of dissolved ions. As the resistance decreases, the current increases, so the current controller lowers the voltage. It falls below the limit, so that the current i now follows the specification 27.

[0030] As an alternative to this type of control, the coagulation voltage u can also be controlled according to a predefined time function, e.g., as a ramp, in steps, or similar. This can be specified by function block 20b via the correspondingly time-dependent target voltage.

[0031] In the first stage, the resistance R of the tissue drops with increasing current and increasing heating to a value R min , which is typically below 50 ohms. Due to the increasing tissue temperature, the ohmic resistance R of the biological tissue drops to very low values, for example, barely more than 20 ohms, in many cases even below 10, 5 or 2 ohms. With increasing tissue heating and the onset of steam formation, the tissue resistance R increases again, as shown in Figure 5 can be seen at point 29. This point in time is reached after approximately 1 second. During this process, the power transferred to the tissue is relatively high, as Figure 6 shows. If the tissue resistance R reaches or exceeds a limit value of e.g. 50 Ohm and / or a multiple of R min and / or a certain phase shift Phi between the voltage u and the current i, stage A is completed.

[0032] At this point in time (approximately 1 s), the power P transferred to the vessel 12 has exceeded its maximum and decreases due to the increasing tissue resistance resulting from increasing vapor formation or tissue drying. The energy W transferred to the vessel 12 has reached approximately 50 J at this point in time in the present embodiment. Other energy values ​​may be provided alternatively.

[0033] Function block 20b can be configured to determine the process status based on the elapsed time, alternatively based on the electrical energy W transferred to vessel 12, alternatively based on the magnitude and / or temporal progression of tissue resistance R, or further alternatively based on the magnitude and / or temporal progression of current i. A characteristic value for the process status is the incipient boiling of the tissue fluid, which is accompanied by at least parts of vessel 12 having reached boiling temperature. If function block 20b monitors the current, this can be detected by function block 20b based on current progression 27. If function block 20b monitors the energy W transferred to vessel 12, function block 20b can detect the incipient boiling of tissue fluid when a specific amount of energy transferred to vessel 12 (for example, 50 watt-seconds) is reached.If the function block 20 monitors the tissue resistance R, it can detect the beginning of boiling of tissue fluid by exceeding a resistance limit of, for example, 42.5 ohms after passing through a resistance minimum.

[0034] Regardless of which of the above-mentioned variables is monitored by the functional block 20, 20b, it recognizes the end of stage A as the functional status (e.g., by the beginning of boiling of tissue fluid based on the resistance R) and now controls the generator 15 into a tissue fusion phase, which preferably lasts about half a second or slightly longer. During this phase, the generator 15 can be controlled by the functional block 20b in such a way that it generates the coagulation voltage u or the tissue resistance R with a setpoint value that progresses over time according to a predetermined function 31 and periodic voltage dips or voltage reductions 32 to 39. The predetermined maximum value of the coagulation voltage u can be constant over time or, as Figure 4suggests, follow a decreasing, time-varying function, e.g., a decreasing straight line. Other voltage curves, e.g., in the form of a decreasing e-function or even an increasing voltage curve, can be used.

[0035] In stage B, the function block 20b preferably operates as a controller for the tissue resistance R. For this purpose, the memory 22 specifies a desired time function for the desired tissue resistance R desired and supplies this function to the control block. This desired time function is, for example, a periodic time-dependent function, e.g., a sine function, which Figure 5is shown in dashed lines. The function block 20a determines the actual tissue resistance R actual and also supplies this to the control block. This controls the generator 15 accordingly, taking into account the voltage limit II, which still limits the maximum voltage that can be output by the generator 15 to a maximum value, e.g. 90 V to 120 V. In addition, the function block 20b either limits the coagulation voltage u downwards so that it does not fall below a minimum value of e.g. 25 V. By limiting the voltage upwards, sparking on the tissue or other thermal tissue damage can be avoided. By limiting the voltage downwards, too rapid or excessive condensation of steam is avoided.

[0036] As a result of the regulation of tissue resistance, Figure 4Voltage reductions 32 to 39 occur, during which the generator 15 briefly reduces its power, so that the output voltage drops from a value of approximately 90 V to 120 V to a minimum value of, for example, 20 V or 25 V. Each time the voltage drops, the power transmitted to the vessel 12 also initially drops, as Figure 6 However, due to the simultaneous decrease in tissue resistance, increased power is transferred to the tissue during the periodically subsequent voltage increase. On average, however, the power transferred to the tissue is greater during a periodic reduction in tissue resistance than if coagulation were performed entirely at a high coagulation voltage u of, for example, 100 V and thus a constantly high tissue resistance.

[0037] Due to the periodic resistance modulation, already generated steam and / or fabric of the vessel 12 can be re-moistened. This results in the following Figure 5illustrated resistance oscillations and subsequent power peaks according to Figure 6 Pressure pulsations that can contribute to penetrating the vascular endothelium 24. This allows protein components of the tunica media 25 and, if necessary, the tunica externa 26 of opposing vessel walls to come into contact with each other and fuse together.

[0038] The functional block 20 can specify the procedure status of the vessel 12, for example, based on a time curve for the course of the tissue resistance with a fixed or variable number of oscillations of the tissue resistance R or voltage reductions 32 to 39. Alternatively, it is also possible to specify the oscillations with amplitude and frequency and to record the number of voltage reductions 32 to 39 or resistance oscillations. For this purpose, the voltage reductions carried out can be counted and, when a limit of, for example, 8 or 9 is reached, stage B can be ended. Stage B ends in any case with a high tissue resistance and thus also with a high (non-reduced) coagulation voltage u. Similarly, in a further modified embodiment, the functional block 20 can determine the power maxima and / or power minima according to Figure 6 or the current peaks after Figure 7monitor and count to record the procedure status and detect the end of Stage B.

[0039] If the function block 20 determines in any of the ways described above that the second stage B has been completed, the function block 20 changes the control of the generator 15 so that it enters a controlled tissue cooling phase, stage C. During this phase, current continues to be supplied to the vessel 12 in order to specifically slow down the tissue cooling. Thus, the tissue resistance R decreases according to Figure 5in this phase, which begins at a time ta, the decrease is less steep than during the coagulation phase during the voltage reductions 32 to 39. This is achieved, for example, by controlling the coagulation voltage u according to a specified temporal voltage profile that is stored in the memory 22. The function block 20b specifies the coagulation voltage according to a time-dependent function, e.g., as a falling ramp. The specified voltage can be sent as a control signal either directly to the generator or, alternatively, to the control block, which, on the other hand, receives the coagulation voltage u actually output by the generator 15 and controls the generator based on the difference formed.

[0040] The coagulation voltage u is preferably reduced at a predetermined rate of, for example, -200 V / s. Other reduction rates (for example, -150 V / s or -250 V / s) may also be used. Furthermore, the reduction rate can be varied during the cooling phase, if desired.

[0041] During the cooling phase, the tissue becomes moist again, with the tissue cooling through different temperature ranges starting from approximately 150°C to 170°C in zones. This is accompanied by a decrease in tissue resistance R, which, however, is significantly slower than the resistance decreases during the resistance oscillations in stage B due to the continued current flow. As a result, the temperature gradient in the biological tissue is reduced by the slowed cooling compared to uncontrolled cooling. Relatively large-volume zones with an extended duration of existence form, whose temperature lies within a temperature window that is favorable for protein linkage. This allows more time for the formation of mechanically durable protein structures at each point in the affected tissue.

[0042] As the vapor decomposes or evaporates, the tissue resistance R decreases below a limit value. This limit value can be a predefined limit value or, alternatively, a limit value resulting from the tissue resistance during the resistance oscillations or from the resistance curve from stage A. For example, in stage B, the tissue resistance does not decrease as far as the target resistance curve specifies due to the minimum voltage of the generator 15 that cannot be undershot. However, the minimum tissue resistance R min that occurs can be recorded. If the tissue resistance R reaches the recorded minimum tissue resistance R min or a specified multiple thereof (e.g., 1.5*R min), this can be used as an event to terminate the voltage-controlled cooling phase of stage C. At this time te, the function block 20 switches to power control. The tissue is now supplied with a coagulation voltage u such that the power P, as Figure 6 shows, continues to decrease after the time te, for example linearly or according to another predetermined curve. The end of coagulation and thus the switching off of the generator 15 is then initiated by the function block 20 or 20b, for example in a time-controlled manner and / or after reaching a certain amount of energy W and / or upon reaching a certain power or according to other criteria at a time tc .

[0043] Alternatively, the resistance limit value can also be, for example, the value R min that the tissue resistance reaches as a minimum before its increase 28 and / or the value to which the tissue resistance drops during the voltage reductions 32 - 39. The function block 20, 20b can determine and store this value in order to then use it as a limit value to detect the end of the cooling phase.

[0044] The device 10 according to the invention and the method concept according to the invention each allow for a particularly rapid, gentle, and safe fusion of vessels 12 between two coagulation electrodes 13, 14. Resistance oscillations are generated in the biological tissue, during which a tissue resistance value of, for example, 50 ohms is alternately exceeded and undershot. This is followed by a phase of slowed tissue cooling, during which the tissue 12 is energized with a coagulation voltage that preferably decreases over time in order to achieve a cooling process that is significantly slower than with immediate voltage shutdown. This achieves, on the one hand, good fusion of the collagen of the pressed vessel walls and, on the other hand, mechanically stable solidification of the collagen.This process shortens the required fusion time compared to conventional methods, reduces unwanted damage to surrounding tissue due to the shortened exposure time of the high-frequency current, and makes vessel closure more secure.

[0045] Reference symbols: 10 Device 11 instrument 12 blood vessel 13, 14 Industries 15 generator HF coagulation voltage delivered by the generator 15 16 Output of generator 15 17 Sensor block 18, 19 lines u signal characterizing the coagulation voltage HF i signal indicating the current of generator 15 R Tissue resistance P power transferred to the tissue Phi Phase angle between u and i 20 Function block / controller 21 Input for controlling the generator 15 I Voltage limiting ramp II Voltage limit 22 memory 24 Vascular endothelium (tunica interna) 25 Tunica Media 26 External Tunic 27 Specification for the target current 28 Section of falling voltage u 29 Increase in tissue resistance W energy transferred to vessel 12 32 - 39 Voltage reductions ta, te Beginning and end of the voltage-controlled cooling phase tc End of power supply

Claims

1. A device (10) for supplying a tissue fusion instrument, in particular an instrument (11) for tissue fusion, comprising a generator (15) for generating a coagulation voltage (u) for operating the instrument (11), by means of which the coagulation voltage (u) is to be applied as the coagulation voltage to a tissue (12) to be fused for heating said tissue at least to the boiling temperature of tissue fluid, wherein the generator (15) is controllable at least with regard to the magnitude of the generated coagulation voltage (u), comprising a function block (20) for controlling the generator (15), which is configured to control the coagulation voltage (u) with low frequency in an amplitude-modulated manner, so that an oscillation of the tissue resistance (R) is caused and this alternately assumes high and low values, wherein the function block (20) has an output voltage limiting device which sets a maximum voltage during the oscillation of the tissue resistance (R), which is set such that sparking is avoided during the phases of high tissue resistance (R), characterized in that a nominal resistance curve is defined for the oscillating control of the tissue resistance (R) and that the function block comprises a controller for the tissue resistance (R), wherein the controller is configured to measure the tissue resistance continuously or in a tight time frame and to compare this to the tissue resistance currently specified by the nominal tissue resistance curve and to determine the voltage to be applied to the tissue from the resulting deviation and to deliver this voltage to the coagulation electrodes.

2. The device according to claim 1, characterized in that the controller comprises an output voltage limiting device that sets a maximum voltage and / or a minimum voltage during the oscillation of the tissue resistance.

3. The device according to one of the preceding claims, characterized in that the function block (20) is configured to terminate the resistance oscillation at a high tissue resistance.

4. A device (10) for supplying a tissue fusion instrument having two coagulation electrodes (13, 14), comprising a generator (15) for generating a coagulation voltage (u) for operating the instrument (11), by means of which the coagulation voltage (u) is to be applied via the two coagulation electrodes (13, 14) to a vessel (12) to be fused, which is held between the coagulation electrodes (13, 14), in order to heat it to a boiling temperature of tissue fluid and to fuse it when the vessel walls are pressed against one another, wherein the generator (15) is controllable at least with regard to the magnitude of the coagulation voltage (u) generated, comprising a function block (20) for controlling the generator (15) for performing a tissue cooling process under continuous current application to the instrument (11), when the vessel walls are pressed together between the electrodes (13, 14), with a coagulation voltage (u) of decreasing amplitude over time, characterized in that the function block (20) is configured to reduce the coagulation voltage (u) according to a predetermined curve.

5. The device according to claim 4, characterized in that the function block (20) is configured to reduce the coagulation voltage (u) continuously or in multiple steps during the tissue cooling process.

6. The device according to one of claims 4 or 5, characterized in that the function block (20) is additionally or alternatively controllable with respect to the magnitude of the output power (P) and is configured to continue monitoring the process status during the tissue cooling process and, based on the latter, to transition from current application with decreasing coagulation voltage (u) to current application with controlled power (P).

7. The device according to one of claims 1 to 3 and according to one of claims 4 to 6.