RU2772635C2 - Device and method for formation of plasma in aqueous environment - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: device for powering a medical instrument for the treatment of biological tissue by means of plasma effect is made in a special way for ignition and stable formation of plasma on an electrode of the instrument. For this purpose, the device has a control device, which, during the ignition attempt, preferably in a way specific for the instrument, limits current supplied to the instrument and/or limits electric power supplied to the instrument, and/or operates with decreased working voltage U_bb.

EFFECT: using such a measure, fast and stable formation of plasma with minor sparking is achieved for a large range of connected instruments in each case.

15 cl, 7 dwg

Description

SUBSTANCE: invention relates to a device for powering a medical instrument for processing biological tissue by means of plasma exposure, as well as to a method for igniting and maintaining plasma in an aqueous environment.

Medical instruments which act by means of plasma emanating from an electrode on biological tissue are in principle known and are in use.

In this area, for example, EP 2 514 380 A1 discloses an electric scalpel which serves to cut biological tissue. To this end, a plasma, referred to as a spark, is formed on the spatula-shaped electrode, which has a cutting effect on the tissue. Plasma is ignited in an aqueous or humid environment due to the fact that the water initially on the electrode is evaporated, and then a spark is ignited in the vapor layer. In order to form the necessary layer of steam and thus to achieve the fastest possible drying of the electrode during this heating phase, a high duty cycle is operated with pulses of a pulse-width modulated high-frequency voltage applied to the electrode, or even with an interruption-free high-frequency voltage, in while in the subsequent cutting process they work with a smaller pulse duty cycle.

DE 102014217362 A1 describes plasma evaporation by means of an instrument called a resectoscope, which is powered by a high frequency surgical instrument. In the context of the surgical intervention thus performed, the instrument is generally immersed in a saline solution, which serves as a rinsing fluid. By applying a high frequency voltage to the evaporator electrode of the tool, the plasma is ignited. To do this, initially a layer of steam is generated around the evaporator electrode, which requires high powers and currents, which allow the rinsing fluid and thus the surrounding biological tissue to be strongly heated. In order to prevent too much heating of the flushing solution and at the same time to facilitate ignition of the plasma, a blocking device is provided by which the flow of flushing fluid in the flushing fluid line can be blocked or reduced. This not only facilitates the ignition of the plasma, but also reduces the energy input for the ignition process.

To perform tissue resection, the operator may be provided with various instruments with different electrode shapes, which have different ignition tendencies and different plasma retention abilities. In addition, it is necessary to note the possible neuromuscular stimulations during the ignition of the plasma, which can irritate the operator or harm the processing process. Plasma instability or increased sparking during ignition can act just as harmfully.

The aim of the invention is to provide an apparatus and a method which or which contributes to the remediation of at least one of the above aspects.

This goal is achieved using the device or device according to claim 1 of the claims, as well as the method according to claim 13 of the claims.

The device includes a device that has a generator for supplying high-frequency alternating voltage, as well as a power supply from the network, which is connected to the generator to supply it with operating voltage. The generator is connected to the output to which the instrument is connected. In addition, the device contains a measuring device for determining the electrical resistance of the tool connected to the output. The resistance of the tool is understood to mean any value that can be interpreted as the quotient of the voltage applied to the output and the current flowing through the tool when a constant voltage is used for measurement. When an AC voltage is used for the measurement, the resistance is represented by the active component of the impedance, which is a quotient of voltage and current. Instead of resistance, impedance, impedance, reactance or active resistance can also be used in this invention. Thus, the resistance of the tool is essentially composed of the contact resistance of the electrode to the water environment, as well as the resistance of the water environment as such up to the return electrode.

In addition, the device contains a control device, which is designed to set, at least for a period of time, the operating voltage and/or the power supplied to the tool and/or the maximum current to be supplied to the tool in accordance with the measured resistance and for the corresponding control of the power supply from the mains and/or generator. Said period of time may be represented primarily by a predetermined variable or constant period of time, which is provided as the ignition attempt time for plasma formation. The measuring device can be represented as an integral part of the control device.

In addition, the control device can be configured to set for the operating voltage and/or the power supplied to the tool and/or the maximum current to be supplied to the tool, after the ignition attempt time has elapsed, other pre-assigned values that are different from the pre-assigned values for the time ignition attempts.

By means of a specific pre-assigned voltage value (i.e., value) of the high-frequency alternating voltage and/or the operating voltage provided by the power supply from the mains for the duration of the ignition attempt and/or by limiting the power during the ignition attempt and/or limiting the supply to be supplied from the power supply from the mains and/or a high-frequency generator of maximum current, in each case, based on the measured minimum resistance of the electrode immersed in the solution, but not ignited, an adaptation of the ignition process on different instruments with different electrode shapes can be achieved. It was found that there is a reproducible relationship between the minimum resistance measured on the tool and those values for operating voltage, maximum power and/or maximum current at which it is possible to achieve reliable and stable ignition of the plasma with minimal sparking and minimal or at least negligible neuromuscular stimulations.

First of all, it has been found that by means of an ignition time-specific assignment of an operating voltage, in particular an assignment of an operating voltage (for example, a maximum required value of 550 V _p (B _p means peak voltage)) which exceeds the operating voltage available for further maintenance of the plasma (eg, maximum 460 B _p ), neuromuscular stimulation can be minimized, and there is less significant intensity of sparking during the transition from the unignited state to the formation of plasma. Similarly, there is a limitation of the maximum current flowing with a wet electrode without sparks, as well as the power for the ignition mode, especially the tool-specific limitation of the maximum current and maximum power, which alleviates, up to elimination, neuromuscular stimulations.

In this sense, current limiting and/or power limiting, i.e. limiting the maximum current on the mains power supply or on the high frequency generator, can help to improve the ignition process and plasma stabilization by preventing the formation of excessively large vapor bubbles and their separation from the electrode. tool.

To control the operating voltage, the power supply from the mains may have a voltage regulation input, which is connected to the control device. Via this voltage regulation input, the operating voltage supplied by the mains power supply is set. However, it must be borne in mind that, contrary to the usual presence in the mains supply unit of a control loop for adjusting the required operating voltage at the output of the mains supply unit, fluctuations in the operating voltage may occur, namely, in particular, voltage changes due to rapid load changes. Load changes cause the mains power supply to increase the operating voltage due to the energy stored in the output filter of the mains power supply.

In addition, voltage changes can occur due to the finite response time of the voltage regulation loop in the power supply unit. Limiting the operating voltage during the ignition mode to a reduced value ensures that the operating voltage does not rise excessively for a short time due to an abrupt rise in resistance at the electrode due to ignition of the plasma and thus an abrupt decrease in current. Due to this, in the transition phase (in other words, at the transition from a practically short circuit with a wet electrode to vaporization and plasma formation), an excess of the power load can be prevented. At the same time, the formation of bubbles is reduced, and thus plasma stabilization is achieved. In this way, excessive sparking as well as unwanted neuromuscular stimulation can be prevented or reduced.

Alternatively or additionally, the mains power supply and/or the generator has a current limiting input that is connected to the control device. This limits the maximum current supplied from the tool, and thus the unignited plasma current, which flows from the tool into the surrounding aqueous solution. On the one hand, due to this, the power load in solution and tissue is limited, and the process of plasma ignition is also stabilized.

Additionally or alternatively, the mains power supply and/or the generator may have a power limit input that is connected to the control device. The signal applied to the power limit input sets the maximum power supplied from the generator. Power limitation thus implemented prevents tissue damage, instrument damage and excessive sparking, and also stabilizes the ignition process.

The control device may include an operating state recognition device that is configured to recognize the start of an ignition attempt. When recognized as such, the control device during the ignition attempt has the ability to set the required value for the operating voltage, which exceeds the required value during operation with a stable plasma following the ignition attempt.

The operating state recognizer may also be configured to distinguish at the end of an ignition attempt between states of ignited stable plasma and no plasma of any kind. Based on this information, the subsequent operating mode of the device can be set. If stable plasma formation has been detected, subsequent ignition attempts are blocked and the operating voltage and/or maximum power and/or maximum current are set to values suitable for operation with stable plasma. If the formation of any stable plasma was not found, on the contrary, the ignition attempt is repeated. In addition, it can be prearranged that the control device, after a failed ignition attempt, first of all maintains a waiting phase before starting a new ignition attempt. This makes it possible to prevent the supply of excessively high energy into the aqueous solution and/or the biological tissue.

In addition, the control device can be designed to record the electrical work applied to the tool, which is understood as the integral of electrical power taken over a period of time. For example, a time period predetermined for recording electrical work may be, for example, one second, within which the electrical power is integrated or added in small increments. For example, this can be done in second intervals or also in different time intervals. In this case, in a preferred embodiment, it can be provided that the control device shortens the waiting phase between two ignition attempts or operates without a waiting phase until the maximum permissible electrical work for a given time interval is still not reached. This prevents both too much energy input and too long waiting times that annoy or disturb the operator between successive ignition attempts.

In addition, the control device may be configured to detect the approach of the instrument electrode to the lumen-limiting biological tissue. To this end, the electrical resistance between the electrode and a neutral electrode provided on the instrument or, alternatively, separately attached to the patient, can be measured, which changes as the electrode approaches the tissue. If such proximity is detected, the control device has the ability to start an ignition attempt. In a preferred embodiment, it can be provided that the control device, when it is in the waiting phase between two ignition attempts, shortens this phase or operates without a waiting phase until the maximum electrical work allowed for a given time interval is still not reached.

In addition, the device according to the invention can be designed to adapt not only the operating voltage and/or power and/or maximum current for the ignition phase, but also the operating voltage and/or power and/or maximum current for the next operating phase based on the measured resistance and , thus instrument-specific.

By means of some, some or the sum of all the above features, devices can be created which automatically feed the various connected instruments in such a way that only little or no neuromuscular stimulation occurs, while at the same time good plasma ignition properties with little sparking are achievable. as well as stable plasma confinement.

First of all, in order to control the power supply of a device for powering a medical instrument for processing biological tissue by exposure to plasma, the device may have:

- a generator for supplying a high frequency alternating voltage (high frequency voltage) and for supplying a high frequency current (high frequency current), the generator being connected to the output to which the tool is connected,

- a power supply from the mains, which is connected to the generator to supply it with operating voltage,

- a control unit for controlling the generator and/or the mains supply unit, which has a measuring device for detecting the high frequency current supplied to the output,

moreover, the control device is configured to set, at least for a certain period of time, the maximum high frequency current to be supplied to the output and/or the power supplied to the output and for the corresponding control of the power supply unit from the network and/or the generator.

Said period of time may in particular comprise the time during which a vapor bubble is formed on the still wet electrode in contact with the liquid body, and in this case an electrically conductive plasma is formed in the vapor bubble. As long as the electrode touches over a large area of the fluid body, the control device limits the high frequency current supplied to the output, that is, the generator operates with a current limit and the applied voltage is negligible. When a vapor bubble forms, the output electrical resistance rises sharply by at least one order of magnitude, and typically by several orders of magnitude, resulting in a rapid decrease in high frequency current, a rapid increase in high frequency voltage, and an increase in power delivered by the generator.

In the aforementioned device, it can be provided that the control device detects a decrease in the high frequency current and/or an increase in the high frequency voltage, and on this basis, re-sets the maximum value for the high frequency current and/or maximum power, first of all limits them. The current measurement and/or the voltage measurement and the assignment of the maximum power may be carried out periodically at short intervals, for example 10 µs or 100 µs.

To control the operating voltage, to limit the high frequency current or power, the mains supply and/or the generator may have a corresponding adjustment input, which is connected to the control device. The operating voltage supplied by the mains supply unit and/or the maximum current supplied by the mains supply unit and/or the maximum power supplied by the mains supply unit can be set via the control input. If an adjustment input is provided on the generator, the maximum generator-delivered high frequency current and/or the maximum generator-delivered power and/or the maximum generator-delivered high-frequency voltage can be set therethrough.

To register a rapid decrease in current, which serves as an indicator of the formation of a vapor bubble, the ratio of the currently detected high frequency current to the high frequency current at an earlier time point can be used. With periodic current measurement, the earlier point in time can be one or two measurements earlier. If the ratio is close to 1, there is no formation of vapor bubbles. If the ratio is significantly less than 1, there is vapor bubble formation. This can be taken as a signal to reduce or limit the power of the generator. Such an event stabilizes the formation of plasma by preventing premature detachment of the vapor bubble from the electrode. The formation of sparks is also weakened.

Additional details of advantageous embodiments of the invention are the subject of the description, drawing or claims. Shown on:

Fig. 1 - the device according to the invention, the attached tool and the processed biological object, in a schematic representation,

Fig. 2 - an instrument in a hollow organ surrounded by an aqueous solution, in a schematic representation,

Fig. 3 shows various tools that can be used with the instrument of FIG. one,

Fig. 4 - diagrams for various adjustments of various plasma ignition tools,

Fig. 5 - characteristic of the current and voltage on the tool when the plasma is ignited,

Fig. 6 is a diagram of various ignition scenarios, and

Fig. 7 is a diagram for illustrating the various dependences of maximum current and maximum power on the measured resistance.

In FIG. 1 illustrates a device 10 for processing a biological tissue 11, which is bounded by a lumen 12. The lumen 12 can be represented by the interior of a hollow organ or also by another cavity formed in the tissue 11. Typically, the lumen 12 is partially or completely filled with an aqueous solution 13, such as, for example, a NaCl solution.

The device 10 includes a device 14, which serves to supply the tool 15 with electric current. To this end, the instrument 14 has an outlet 16 to which an instrument 15 is connected or can be connected. If the instrument 15, as illustrated in FIG. 1 is a bipolar instrument, both poles of output 16 are connected to instrument 15. If, on the other hand, instrument 15 is unipolar (see FIG. 3, bottom), line 17 from output pole 16 leads to instrument 15, while the other line 18 from the other pole of the output 16 leads to the counter electrode 19, which is electrically connected to the biological tissue 11. The first line 17 is a high frequency line, and the second line 18 is considered as a neutral conductor.

The device 14 comprises a mains supply unit 20 which can be connected to the electrical power supply network and provides between the two lines V and M the operating voltage U _b . It serves to supply the assembly that forms the generator 21. The generator 21 produces from the operating voltage U _b a high-frequency alternating voltage, which is fed to the output 16. The frequency of the alternating voltage can be set in the range from 100 kHz to 10 MHz.

To detect the current supplied to the tool 15 and/or to detect the voltage applied to the output 16, a measuring device 22 can be provided, for example between the generator 21 and the output 16 or also as part of the generator 21. The measuring device 22, in addition to the voltage applied to the output 16 and /or current flowing through the output 16 outward and inward, if necessary, also has the ability to detect values derived from them, such as, for example, the ohmic resistance acting at the output 16 and/or the effective power and/or reactive power supplied from the output 16. Registered and/or detected values (voltage, current, resistance, impedance, power, etc.) are transmitted to the control device 23. In this case, the measuring device 22 can be made not only as shown in FIG. 1, separate from the control device 23, but also, in whole or in part, as part of it. The control device 23 and the measuring device 22 should be understood, as well as the generator 21 and the power supply unit 20, as functional units that can be built on the same or on separate hardware building groups.

The control device 23 is connected to the voltage adjustment input 24 of the power supply unit 20 . Via this voltage regulation input 24, the control device 23 sets the mains supply unit 20 to the desired value for the operating voltage U _b . In this case, the control device provided in the mains supply unit 20 regulates the actual value of the operating voltage U _b to the desired value, whereby temporary deviations may occur during the control process. This regulator can also be implemented in the control device 23.

In addition, the control device 23 is connected to a current limiting input 25, which can be provided on the generator 21 or on the power supply unit 20 or also on the current limiting group. The current limiting constructive group can be located between the power supply unit 20 and the generator 21, or also between the generator 21 and the output 16. The signal applied to the current limit input 25 sets the maximum supplied current at the output 16. Upon reaching it, the operation of the power supply unit 20 from the network and/or the generator 21 is adapted to prevent the current limit being exceeded.

In addition, a power limit input 26 is provided, which can be provided on the generator 21, on the power supply unit 20, or on the structural group located between the generator 21 and the power supply unit 20. Served at the input 26 power limit signal sets the maximum supplied to the output 16 power.

The voltage limit input 24, the current limit input 25 and the power limit input 26 are to be considered as information channels which can be implemented in any manner from the field of electrical engineering and data communication. It is also possible to dispense with a separate power limit input and achieve power limit by matching the voltage limit input 24 and the current limit input 25 to each other.

Fig. 2 serves to illustrate the tool 15 and its application in the lumen 12. The tool 15 has an electrode 27 made, for example, in the form of a loop or arc, which is connected to the line 17. The electrode 27 in the unlit state is wet, and is in contact over its entire surface with solution 13, that is, thus, is in electrical contact with it. Therefore, between the electrode 27 and the counter electrode 19, shown in FIG. 1 by the dotted line resistance R, which is essentially given by the size and shape of the electrode 27. The resistance R is made up of the combination of the resistance between the electrode 27 and the surrounding solution 13, as well as the resistance of the current circuit through the solution 13 to the counter electrode 19. If the electrode 27 is located near the wall, there is still parallel current circuit through tissue. If the counter electrode 19 is not made on the instrument 15, but is attached separately to the patient, the electrical resistance is composed only of the series connection of the transition resistance between the electrode 27 and the surrounding solution 13, as well as the resistance of the current circuit through the solution 13 and the resistance through the body tissue to the counter electrode 19.

Fig. 3 symbolically illustrates the various instruments 15a, 15b, 15c, 15e and, respectively, the dashed line resistance R of the circuit to the respective neutral electrode. Whereas the instruments 15a-15c are designed as monopolar instruments, which are supplied only via the line 17, in the bipolar instrument 15e the counter electrode 19 is indicated as the counter electrode and is made directly on the instrument 15e, which in this case is connected to both lines 17, 18 In other respects, the tools 15a-15e may differ from each other in the size and shape of the respective electrodes 27a, 27b, 27c, 27e. For example, the electrodes 27a, 27b, 27c, 27e may be large or small wire loops, tape loops, mushroom-shaped or other flat electrodes.

The instruments 15a-15e, when they come into contact with the solution 13 and are connected to the device 14, have a characteristic resistance R _a , R _b , R _c or R _e , measured between the electrode 27 and the counter electrode 19, which can be registered by means of the measuring device 22 The registration can be carried out, for example, immediately before the production on the plasma electrode 27 or also at the very beginning of such an ignition attempt, as long as the still undisturbed solution 13 adjoins the electrode 27. It is also possible to carry out a measuring cycle before the ignition attempt is made.

To determine the resistance value, a voltage is provided to output 16. It may be the same as the ignition voltage for the plasma, or it may also be below it. The current flowing at the output 16 can then be detected by the measuring device 22. From the measured voltage and the measured current, the impedance and/or resistance R _min can be detected. This value, prior to the first ignition attempt, has the values R _a , R _b , R _c , R _e , which can respectively be regarded as characteristic of the corresponding tool 15a-15e. In this connection, reference is made to FIG. 7. It illustrates on its horizontal axis the different values of R _min , namely R _a , R _e , R _c , R _b for different tools 15a, 15e, 15c and 15b. Typically, these values are between 20 ohms and 100 ohms, with other values also not excluded.

Fig. 7 also serves to illustrate the ignition control strategy implemented by the control device 23. For this further and additionally, reference is made to FIG. 4 and 5.

To ignite the plasma 28 within the solution 13 (see Fig. 2) or on the wall of the lumen 12, the device 14 provides a high-frequency alternating voltage, which entails the occurrence of a current through the solution 13 and, if the counter electrode 19 is not placed on the tool 15 as such, but on fabric 11, through fabric. Due to the direct wet contact between solution 13 and electrode 27, the resistance present is very low and maximum current flows. In this case, the control device 23 limits the current in the power supply unit 20 or in the generator 21, respectively, to a value suitable for the respective tool 15a, 15b, 15c or 15e. This value depends on the resistance R _a -R _e , which the measuring device 22 detects just now or at the time preceding the ignition attempt.

Fig. 7 illustrates, by means of a curve I, different maximum current values for different tools 15a, 15b, 15c or 15e with different resistances R _a -R _e . Correspondingly, the output characteristic of the generator is set, for example, for the tool 15 _b in FIG. 4 value i _b . Equally, for this tool 15b according to FIG. 7 set the maximum power p _b . Due to this, the power is limited according to the section of the curve p _b , since the current limitation is not activated due to the start of the formation of vapor bubbles on the electrode 27, which causes the current to decrease. During the entire ignition process, the generator 21 is supplied with an operating voltage U _bb that is preferably set below the operating voltage U _b that is provided to the generator when the plasma 278 is ignited. , on the contrary, when a vapor bubble is formed, the stress limits.

Reducing the operating voltage U _b to the value U _bb , limiting the power p _b and limiting the current i _b according to the diagram in FIG. 4 provide a tool-specific ignition process with low sparking and stable plasma generation. The harmful effects discussed so far are prevented. This is also shown in the simplified diagram of FIG. 5, which is devoted primarily to the ignition of the plasma 28. The diagram illustrates on its left half, with a voltage U initially applied to the electrode 27, a large current i _b , which is set by current limiting (vertical branch of the curve i _b , in Fig. 4). Due to the low resistance of the order of several tens of ohms, only a small voltage is applied to electrode 27b. However, the specified voltage value in this state exceeds the average value. This is necessary because, otherwise, the initially occurring overvoltage causes the voltage regulator to regulate the voltage too much downward, which can lead to attenuation of the plasma.

By the time t _za a vapor bubble has formed around the electrode 27, which initially does not conduct electricity and therefore interrupts or at least significantly limits the flow of current before an electrical breakdown occurs. Typically, a sudden interruption of current or reduction in current results in a voltage peak at the generator 21 or at the mains power supply 20, primarily due to the energy stored there in the inductance. This voltage peak is shown in Fig. 5 through U _p , and usually results in the production of harmful light and, in certain circumstances, sound pulses, which are also called "sparks". However, by reducing the operating voltage to a value U _bb (eg 550 V) and by limiting the power to a tool-specific value p _b , while passing the p _b curve according to the curve in FIG. 4, the resulting sparking is reduced to a minimum. Therefore, the voltage U after the time t _za until the time t _ze rises with little or no excess deviation, while the current in turn decreases to its operating value.

If, on the other hand, another tool is used, for example tool 15a, which, in contact with the solution 13, has a different, less significant resistance R _a (see FIG. 7), the control device 23 for the ignition process according to FIG. 4 specifies a higher maximum current i _a and a higher maximum power p _a , as well as, again, a suitable operating voltage U _ba , which may be greater or less than U _bb , or also the same as it. Again, an ignition process is obtained with minimal sparking and with a smooth transition to a stable plasma hold.

The control device 23 is further configured to terminate the ignition attempt after the ignition attempt time tvz has elapsed, provided that no ignition is detected. As the diagram in FIG. 6, this is followed by a waiting phase t _W within which no further ignition attempt is made. Typically, the timeout is a few hundred milliseconds, such as 0.8 s. Due to this, the power load in solution 13 and/or tissue 11 is limited.

To improve comfort, it can be provided that the control device 23, under given conditions, shortens the waiting time t _W or does not withstand it at all. To do this, the control device 23 can be configured to record the electrical work produced between the electrode 27 and the counter electrode 19 at a predetermined recording time interval. For example, this logging time interval may be 1 s, and the maximum work done on it is 400 Wts. After such a logging interval has elapsed, the logging may be restarted. If, for example, now the first ignition attempt (leftmost in Fig. 6) is located in the monitoring interval, in which, apart from the first ignition attempt during t _VZ ignition attempt, no subsequent ignition attempt has yet occurred, and in this monitoring interval the maximum electrical operation has not yet been reached, the waiting time t _W can be shortened, and the second ignition attempt, otherwise made only after the waiting time has elapsed, is carried out prematurely, as indicated in FIG. 6 by means of an arrow, in the form of an ignition attempt 30.

It is also possible to trigger a contraction or else prematurely interrupt the waiting time tw when proximity of the electrode 27 to the biological tissue 11 is detected. be used as a trigger event to abort the timeout interval, ie to initiate a premature ignition attempt 30 (FIG. 6). If necessary, several ignition attempts can be made in close succession. In an embodiment, this may be due to the fact that in a given monitoring time interval, a given limit for the electrical work performed has not yet been reached or exceeded.

The device for powering the medical instrument 15 for processing biological tissue 11 by means of plasma 28 is made according to the invention in a special way for ignition and stable formation of plasma 28 on the electrode 27 of the instrument 15. For this purpose, the device 14 has a control device 23, which during the ignition attempt, preferably for the tool in a way that limits the current supplied to the tool 15 and/or limits the electrical power supplied to the tool 15 and/or operates with a reduced operating voltage U _bb . With this measure, for a wide variety of attachable tools 15a-15e, fast, stable plasma generation with little sparking is achieved in each case.

LIST OF REFERENCES

10 Device

11 Biological tissue

12 Lumens

13 Solution

14 Instrument

15 Tool (by common reference)

15a - 15e Tool (by specific reference)

16 Exit

17 First line

18 Second line (neutral line)

19 Counter electrode

20 Mains power supply V, M Lines

Ub Operating voltage (e.g. 600 V _p )

21 Generator

22 Measuring device

23 Master

24 Voltage regulation input

25 Current limit input

26 Power limit input

27 Electrode (by common reference)

27a-27e Electrode (by specific reference)

R Resistance

R _min Minimum measured resistance value R

R _a -R _e Tool-specific minimum resistance R _min

28 Plasma

I Tool-dependent overcurrent curve

P Tool dependent maximum power curve

i _b Maximum current for tool 15b

i _a Maximum current for tool 15A

p _b Maximum power for tool 15b

p _a Maximum power for tool 15a

U _bb Operating voltage for tool 15b

U _ba Operating voltage for tool 15A

t _VZ Ignition attempt time (50ms-500ms),

t _W Waiting time interval (0.5 s-1 s),

29 Late ignition attempt

30 Premature ignition attempt

Claims (22)

1. Device (14) for powering a medical instrument (15) for processing biological tissue (11) by exposure to plasma (28), containing: - a generator (21) for supplying a high-frequency alternating voltage, and the generator (21) is connected to the output (16), to which the tool (15) is connected, - power supply unit (20) from the mains, which is connected to the generator (21) to supply it with operating voltage (U _b ), - a control device (23) for controlling the generator (21) and/or power supply unit (20), - a measuring device (22) for determining the electrical resistance (R _min ) connected to the output (22) of the tool (15), moreover, the control device (23) is designed to set, at least over a period of time (t _VZ ) the operating voltage (U _b ), and/or the power supplied to the tool (15) (P), and/or to be supplied to the tool (15) maximum current (i) in accordance with the measured resistance (R _min ) and for the appropriate control of the mains supply unit (20) and/or generator (21). 2. The device according to claim 1, characterized in that the power supply unit (20) has a voltage regulation input (24), which is connected to the control device (23). 3. A device according to one of the preceding claims, characterized in that the generator (21) has a current limiting input (25) which is connected to a control device (23). 4. Appliance according to one of the preceding claims, characterized in that the generator (21) has a power limiting input (26), which is connected to the control device (23). 5. The device according to one of the preceding claims, characterized in that the control device (23) has an operating state recognition device, which is designed to recognize the start of an ignition attempt, while the alternating voltage supplied from the generator (21) to the tool (15) forms on the tool (15) plasma (28). 6. Appliance according to one of the preceding claims, characterized in that the control device (23) is configured to set, during the ignition attempt, the required value for the operating voltage (U _b ), which is greater than that during operation after the ignition attempt. 7. The device according to one of the preceding claims, characterized in that the control device (23) has an operating state recognition device, which is designed to recognize the end of an attempt to ignite or extinguish the plasma, while supplied from the generator (21) to the tool (15) the alternating voltage led to the formation of a plasma (28) on the tool (15). 8. The device according to one of the preceding claims, characterized in that the control device (23) has an operating state recognition device, which is designed to recognize the end of an ignition attempt, while the alternating voltage supplied from the generator (21) to the tool (15) is not forms a plasma (28) on the tool (15). 9. The device according to one of the preceding claims, characterized in that the control device (23) is designed to maintain in the phase (t _W ) waiting for a predetermined pause time after a failed ignition attempt and to subsequently start a new ignition attempt. 10. The device according to claim 9, characterized in that the control device (23) is designed to register the electrical work (W) supplied to the tool (15). 11. The device according to claim 10, characterized in that the control device (23) is designed to register the approach of the instrument (15) placed in the lumen (12) with the biological tissue (11) and in the event that the control device (23) is in the waiting phase and the increase in impedance exceeds the limit value for terminating the waiting phase and starting a new ignition attempt. 12. The device according to one of the preceding claims, characterized in that the control device (23) is designed to set the operating voltage (U _b ), and/or the power supplied to the tool (15) (P), and/or to be delivered to the tool ( 15) maximum current (i) during the working phase adjacent to the ignition phase in accordance with the resistance (R _min ) measured before ignition of the plasma (28) and for the corresponding control of the power supply unit (20) from the mains and/or generator (21). 13. Method for igniting plasma (28) in an aqueous environment on an electrode (27) of a medical instrument (15), wherein the electrode (27) is in contact with an aqueous solution (13), moreover, the electrode (15) is connected to the device (14), which is designed to supply high-frequency voltage, moreover, before applying a high-frequency voltage to the electrode (27) to ignite the plasma (28), the electrical resistance (R) between the electrode and the water environment is calculated, and based on the value of this resistance (R), the operational settings of the device (14) are made. 14. The method according to claim 13, characterized in that the operational settings preferably include only the ignition phase, within which the water (13) adjacent to the electrode (27) evaporates and the plasma (28) is ignited in the resulting vapor bubble. 15. The method according to claim 14, characterized in that the operating settings include the no-load voltage (U) and / or the power supplied to the tool (15) (P), and / or the maximum current to be supplied to the tool (15) ( i).

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