Abstract:
A high-frequency surgical device having a high-frequency generator, which produces a high-frequency output signal for treating, in particular for cutting or coagulating, biological tissue, the high-frequency generator being designed in such a way that the output signal of the high-frequency generator has a predetermined fundamental frequency and a modulation apparatus being provided, which is used to modulate the output signal with a modulation frequency, the modulation frequency being smaller than the fundamental frequency. The high-frequency surgical device is characterized in that the modulation frequency is at least 100 kHz, and in that the output signal can be modulated in such a way that a crest factor of the modulated output signal suitable for a specific application of the high-frequency surgical device arises.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the invention relate to a high-frequency surgical device (HF surgical device). 
       BACKGROUND 
       [0002]    An HF surgical device are generally well-known, for example, from DE 10 2008 004 241 A1.  FIG. 6  of this application shows a basic diagram of a known HF surgical device  1  according to DE 10 2008 004 241 A1. It comprises an HF generator  3  which produces a high-frequency output signal a, in particular a high-frequency alternating current, which is supplied to an HF surgical instrument electrically connected to the HF generator  3 . The HF surgical instrument may, for example, be an instrument for argon plasma coagulation or for HF cutting which acts by means of one or a plurality of active electrodes on a patient&#39;s biological tissue  5  that is to be treated. The patient&#39;s tissue  5  to be treated acts in this case as a load impedance which is variable according to treatment level. The HF surgical device  1  further comprises a power supply unit  7  which converts the line voltage (50 Hz AC) into a voltage suitable for the HF generator. 
         [0003]    Normally, the high frequency power is initially generated in the HF generator  3  with a carrier or fundamental frequency and is amplified in downstream amplifier stages. Depending on the application, the output signal having the fundamental frequency that is produced by the HF generator  3  is modulated over time, in particular with a variable duty cycle. To do this, it is possible either to act directly on the HF generator  3  using a modulation apparatus  9  in such a manner that the output signal is modulated by pulsing or scanning the high frequency power, i.e. by correspondingly switching the output signal on and off. This is therefore pulse-width modulation (PWM), the pulse frequency or switching frequency determining the modulation depth of the output signal. The modulation frequency f Modulation  results in this case from the following formula: 
         [0000]        f   Modulation =1 /T,    
         [0004]    where T is the cycle duration of the square wave modulation signal. For this, the HF generator may have, for example, a circuit arrangement with MOSFET transistors which are switched on and off alternately. In this case, the modulation apparatus  9  is usually activated by a control device  11 . 
         [0005]    Another known possibility of modulating the output signal is direct activation of the power supply unit  7  by means of the control device  11 . As a result of this, it becomes possible to modulate the amplitude of the output signal of the HF generator  3 , the control device  11  acting as the modulation apparatus  9 . 
         [0006]    The fundamental frequency of the HF generator is normally around 300 to 500 kHz. Modulation normally takes place with frequencies between 1 kHz and 50 kHz. Preferably, however, modulation frequencies greater than 20 kHz are used to prevent the generation of unpleasant noises. However, with “pulsed argon plasma coagulation”, for example, lower modulation frequencies in the Hz range can also be used. 
         [0007]    It is generally specified for HF surgical devices that low-frequency current fractions which may flow via the patient and consequently may trigger neuromuscular stimulation (e.g. muscle twitching) must be limited to very low values. If this specification is met, certain parts of the application may be designated as CF (cardiac floating). One drawback of these conventional low modulation frequencies is that they are below the limit above which, according to current scientific knowledge, neuromuscular phenomena, such as muscle twitching, no longer occur. It has been ascertained that this limit is approx. 100 kHz. A relevant standard, IEC 60601-2-2, therefore rules that the fundamental frequency of HF surgical devices must be greater than 200 kHz. It is overlooked here, however, that the low modulation frequencies must be taken into account even with a fundamental frequency greater than 200 kHz because they are clearly visible in the frequency spectrum of the overall output signal and may therefore induce neuromuscular phenomena. 
         [0008]    Although it is known from the prior art to provide so-called decoupling capacitors in the patient circuit to avoid neuromuscular stimulation due to low-frequency and thus neuromuscularly effective modulation signals, said decoupling capacitors are unable to completely prevent neuromuscular stimulation which is induced in particular by the interaction of sparks between the active electrode of the surgical instrument and the tissue. 
       SUMMARY 
       [0009]    An object of embodiments of the present invention is, therefore, to create an HF surgical device which safely prevents the occurrence of neuromuscular phenomena. 
         [0010]    The high-frequency surgical device that achieves this object comprises a high-frequency generator, which produces a high-frequency output signal for treating, in particular for cutting or coagulating, biological tissue, the high-frequency generator being designed in such a way that the output signal of the high-frequency generator has a predetermined fundamental frequency, and a modulation apparatus being provided, which is used to modulate the output signal with a modulation frequency, the modulation frequency being smaller than the fundamental frequency. The high-frequency surgical device is characterized in that the modulation frequency is at least 100 kHz, and in that the output signal can be modulated in such a way that a crest factor of the modulated output signal suitable for a specific application of the high-frequency surgical device arises. 
         [0011]    An essential point of embodiments of the invention is, therefore, that neuromuscular phenomena can be ruled out in that the modulation frequency does not fall below 100 kHz. It must be noted, however, that the frequency band gap between the modulation frequency and the fundamental frequency of the HF generator must not be too small since otherwise it will not be possible to set a large enough crest factor for a specific application of the HF surgical device, the crest factor describing the ratio of the peak amplitude of the output signal to its effective value. If, therefore, the modulation depth of the output signal and the fundamental frequency are not adapted to each other in a suitable manner, it is no longer possible to achieve the aim of a higher peak voltage with a low effective voltage, i.e. a higher crest factor. The crest factor is particularly important in HF surgery as it can mathematically describe the modulation depth of the HF generator&#39;s output signal. Different modulation depths and therefore crest factors of the output signal must be implemented depending on the HF generator&#39;s area of use. For instance, to obtain a suitable coagulation level for tissue coagulation of, for example, CF=2.5, the modulation depth of the HF generator&#39;s output current must consequently be set accordingly. Thus, according to embodiments of the invention, the fundamental frequency of the HF generator and the modulation depth of the output signal are adapted to each other in such a way that a suitable crest factor results, i.e. a crest factor sufficiently large for a specific application, on condition that the modulation frequency does not fall below 100 kHz. The fundamental frequency of the output signal and the modulation frequency are adapted to each other in such a way that crest factors ranging from 1.5 to 15, in particular ranging from 2 to 14, 3 to 13, 4 to 12, 5 to 11, 6 to 10, 7 to 9 or ranging from 1.5 to 14, 1.5 to 13, 1.5 to 12, . . . , 1.5 to 3 or 1.5 to 2 respectively can be adjusted. To be able to achieve the intended effects, crest factors between 1.4 (for unmodulated pure sinusoidal signals, such as are used during cutting or non-sparking contact coagulation) and 15 (for non-contact spray coagulation for example) or even larger are usually required. 
         [0012]    In one embodiment of the invention, the output signal is modulated by means of pulse width modulation. It may also be provided that the modulation frequency and the fundamental frequency are constant. In another embodiment of the invention, on the other hand, it may be provided that the modulation frequency is variable while the fundamental frequency is constant for modification of the crest factor. It may be further provided that a suitable crest factor is adjustable by varying the duty cycle of the modulation signal. This is particularly advantageous if the modulation frequency is kept constant. The invention preferably enables the adjustment of crest factors of the output signal (a) ranging from 1.5 to 15. 
         [0013]    The crest factor is preferably determined based on the output signal and should preferably not fall below a predetermined minimum value. A corresponding recording device which records the modulation frequency, the generator&#39;s fundamental frequency and the crest factor may be provided. 
         [0014]    Consequently, at a specified desired modulation frequency, which is greater than 100 kHz, modulation of the fundamental frequency is adjusted to the modulation frequency such that a predetermined crest factor to be set is achieved. For example, a crest factor can be adjusted for effective contact coagulation and/or for non-contact coagulation with low cutting effect. It is clear, therefore, that the crest factor can vary depending on the actual use of the surgical device, for example for cutting and/or coagulating tissue or a similar HF surgical treatment. 
         [0015]    A high frequency generator in which the modulation frequency is equal to or greater than 200 kHz is especially preferred. The value of the fundamental frequency must accordingly be greater, in particular significantly greater than 500 kHz. It is particularly advantageous if the fundamental frequency is greater than five times the modulation frequency. In particular, according to embodiments of the invention, the fundamental frequencies may be in the single-digit or even multi-digit megahertz range. 
         [0016]    A method for operating a high-frequency surgical device is additionally proposed for achieving the object referred to above. The method is characterised in that the fundamental frequency is modulated with a modulation frequency of at least 100 kHz and that the output signal is modulated in such a way that a crest factor of the modulated output signal suitable for a specific application of the high-frequency surgical device arises. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic representation of an output signal of an HF generator in the form of a continuous sinusoidal voltage; 
           [0018]      FIG. 2  a schematic representation of a modulated output signal with a crest factor modified compared to the unmodulated output signal; 
           [0019]      FIG. 3  a schematic representation of a modulated output signal of the HF generator with a crest factor even further modified compared to the unmodulated output signal; 
           [0020]      FIG. 4  a schematic representation of a modulated output signal of the HF generator with a crest factor even further modified compared to the unmodulated output signal; 
           [0021]      FIG. 5  a schematic representation of a modulated output signal of the HF generator with a crest factor modified compared to the unmodulated output signal; and 
           [0022]      FIG. 6  a schematic representation of an HF surgical device known from the prior art, for example, from DE 10 2008 004 241 A1. The reference numbers of  FIG. 6  are also used to explain a high-frequency surgical device according to embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows an output signal a with a generator frequency f Generator  which results from the following formula: 
         [0000]        f   Generator =1 /t,    
         [0024]    where t is the cycle duration of the output signal a and where the output signal a is presented as the output voltage in the present case. The output signal a of an HF generator  3  shown in  FIG. 1  is presented in its original form, i.e. unmodulated. The continuous sinusoidal signal according to  FIG. 1  has, by way of example, a crest factor of CF=1.41. 
         [0025]      FIGS. 2 to 4  show schematic representations of modulated output signals a 1 , a 2  and a 3 , in which the fundamental frequency of an HF generator  3  f Generator  is constant and matches the fundamental frequency shown in  FIG. 1 . Unlike the output signal a shown in  FIG. 1 , output signals a 1 , a 2  and a 3  from  FIGS. 2 to 4  are modulated, however, by a corresponding modulation apparatus  9  and a corresponding modulation signal m. The modulation form chosen here is a pulse-width modulation which is brought about by means of the square wave modulation signal m. The square wave modulation signal m has an on time t on  and an off time t off  which together result in the cycle duration T 1  of the modulation signal. Pulse pauses  13  and pulse packets  15  which are separated from each other by the pulse pauses arise due to the on and off times of the output signal a 1 . The modulation frequency, which can be calculated according to the formula below, arises in turn from the cycle duration T 1  of the modulation signal m: 
         [0000]        f   Modulation =1 /T   1 . 
         [0026]    What is referred to as the duty cycle D can be determined from the ratio of the on time to the sum of the on and off time of the modulation signal m: 
         [0000]        D=t   on /( t   on   +t   off )= t   on   /T   1 . 
         [0027]      FIG. 2  shows a pulse-width-modulated output signal a 1 . In other words, the output signal a 1  was modulated by a square wave pulse which has a cycle duration T 1  that was chosen in such a way according to embodiments of the invention that the resulting modulation frequency is f Modulation =1/T 1 ≧100 kHz. It becomes clear that the crest factor CF of the output signal a 1  of the HF generator  3  shown in  FIG. 2  is larger than the crest factor of the unmodulated output signal a shown in  FIG. 1 , as the pulse pauses  13  between the pulse packets  15  ensure a reduction in the effective value of the output signal a 1 . Consequently, the crest factor which results from the ratio of the peak value, i.e. the maximum amplitude, to the effective value of the output signal becomes larger on reducing the effective value of the output signal a 1 . 
         [0028]      FIG. 3  shows a schematic representation of another modulated output signal a 2  which has a modified pulse width modulation such that an increased crest factor CF results compared to  FIGS. 1 and 2 . As in  FIG. 2 , the fundamental frequency of the generator f Generator  is also unchanged with output signal a 2  according to  FIG. 3  and, according to embodiments of the invention, the modulation frequency f Modulation  is also chosen to be greater than or equal to 100 kHz and corresponds to the modulation frequency shown in  FIG. 2  which is apparent in the corresponding cycle durations T 1 . 
         [0029]    Increasing the crest factor CF is achieved with the output signal a 2  according to  FIG. 3  by varying the duty cycle D while the modulation frequency f Modulation  remains constant at 100 kHz. At the same time,  FIG. 3  makes it clear that the pulse pauses  13  between the pulse packets  15  are greater than in the example according to  FIG. 2 . This is achieved by reducing the on time t on  while reducing the off time t off  of the square wave pulse m. As a result of this increase in the pulse pause  13  between the pulse packets  15 , there is a reduction in the effective value of the output signal a 2  such that the crest factor CF is increased. In other words, the number of cycles t per pulse packet  15  is decreased due to the increase in the pulse pause  13 . 
         [0030]      FIG. 4  shows yet another example for a modulated output signal a 3  of the HF generator  3  that has a crest factor CF which is increased even further compared to  FIGS. 1 to 3 . As was also the case in  FIGS. 2 and 3 , the fundamental frequency f Generator  of the HF generator  3  was not modified which manifests itself in the constant cycle duration t of the output signal in the pulse packets  15 . Accordingly, the modulation frequency f Modulation  was also not modified compared to the modulations shown in  FIGS. 2 and 3  which the constant cycle duration T 1  also shows. Nevertheless, the modulated output signal a 3  shown in  FIG. 4  has a crest factor CF which is increased even further compared to  FIGS. 2 and 3 . 
         [0031]    Further increasing the crest factor is achieved by increasing the pulse pauses  13  between the pulse packets  15  even further while the cycle durations t per pulse packet  15  are further decreased. In  FIG. 4 , a pulse packet  15  has only a cycle t of the output signal a 3 . As a result, the effective value of the output signal a 3  is deceased in turn such that the crest factor CF becomes even larger compared to the examples shown in  FIGS. 2 and 3 . 
         [0032]    Thus, a modification of the duty cycle D also takes place in  FIGS. 3 and 4  by means of pulse width modulation in such a way that, with a fixed fundamental frequency f Generator  of the HF generator  3  and with a fixed modulation frequency f Modulation , the crest factor can be adapted to a wide range of applications, such as HF coagulation or an HF cutting procedure. 
         [0033]    Overall, it can thus be noted that with constant fundamental frequency f Generator  and constant modulation frequency f Modulation,  the crest factor can be increased by reducing the duty cycle D of the modulation signal. To do this, it is necessary to select the fundamental frequency and the modulation frequency in such a manner that crest factors can be adjusted by pulse-width modulation within a sufficiently large range, preferably from 1.5 to 15. This requires a relatively large gap between the fundamental frequency f Generator  and the modulation frequency f Modulation,  where the boundary condition f Modulation ≧100 kHz must be met in order to safely prevent neuromuscular stimulation. To meet the requirements referred to above, the fundamental frequency preferably amounts to five times the modulation frequency. 
         [0034]      FIG. 5  shows another embodiment of the invention in which the fundamental frequency f Generator  of the output signal a 4  is unchanged while an increase in the crest factor CF is produced by reducing the modulation frequency f Modulation,  as distinguished from the variation shown in  FIGS. 2-4 . According to this, the cycle duration T 2  of the modulation signal according to  FIG. 5  is greater than the cycle duration T 1  used in  FIG. 2 , while the cycles t of the pulse packets  15  match in the embodiments of  FIGS. 2 and 5 . However, instead of keeping the modulation frequency f Modulation  constant, as shown in  FIGS. 2 to 4 , and merely reducing the cycles t per pulse packet  15  or increasing the pulse pauses  13 , in  FIG. 5  only the pulse pause  13  was increased without decreasing or increasing the number of cycles per pulse packet  15 . It is therefore shown that the crest factor can also be increased by decreasing the modulation frequency f Modulation.    
         [0035]    However, it is also necessary in this embodiment of the invention for the boundary condition f Modulation =100 kHz to be met in order to safely prevent neuromuscular stimulation. Therefore, with this embodiment too there must also be a sufficiently large gap between the fundamental frequency of the generator and the modulation frequency to be able to implement crest factors within a sufficiently large range, preferably from 1.5 to 15, by varying the modulation frequency in the range =100 kHz. 
         [0036]    Overall,  FIGS. 2 to 5  show that the fundamental frequency of the generator must be increased by several times compared to the modulation frequency to be able to generate appropriately large and variable crest factors, particularly within the range from 1.5 to 15, for a wide range of applications. For example, it may be sufficient for a cutting procedure using an HF surgical instrument if the output signal has been modulated in such a manner that it has a crest factor of 1.5. For a coagulation procedure, on the other hand, larger crest factors, particularly within the range of approx. 2.5, should be present. In addition, it is possible to implement various mixed forms of cutting and coagulation procedures using an HF surgical device for which, in turn, other crest factors, particularly within the range between 1.5 and 2.5, should be present. Moreover, there are applications, e.g. non-contact spray coagulation, for which crest factors of 15 or even larger are required to achieve the desired treatment effect. 
         [0037]    It is crucial for embodiments of the present invention that not only the fundamental frequency of the generator is greater than 100 kHz, that is to say, it lies in particular within a range between 300 to 600 kHz, but also that the modulation frequency f Modulation  does not fall below 100 kHz. The crest factor which should be adjusted for a specific application of the HF surgical device  1  must then be adjusted via a suitable modulation method, on condition that the modulation frequency does not fall below 100 kHz. As mentioned, for this it is necessary for the fundamental frequency of the generator  3  to exceed the modulation frequency by several times. In particular, according to embodiments of the invention, the fundamental frequencies may be in the single-digit or even multi-digit megahertz range. 
         [0038]    Overall, therefore, it can be seen that embodiments of the present invention safely prevents the occurrence of neuromuscular stimulation in that the modulation frequency is at least 100 kHz and consequently lies above the limit above which, according to current scientific knowledge, neuromuscular phenomena, such as muscle twitching, no longer occur. At the same time, a suitable crest factor for a specific application, such as contact coagulation or a cutting procedure is achieved in that the fundamental frequency is significantly higher than the usual 350 kHz. As a result, an adequate gap is created between the frequency bands of the modulation frequency and the fundamental frequency, which permits the production of a sufficiently large crest factor that is in particular larger than  15 .