WO2014083203A1

WO2014083203A1 - New modus operandi of pulsed radio frequency

Info

Publication number: WO2014083203A1
Application number: PCT/EP2013/075258
Authority: WO
Inventors: Menno Emanuel Sluijter
Original assignee: Hitops Gmbh
Priority date: 2012-11-30
Filing date: 2013-12-02
Publication date: 2014-06-05

Abstract

The present invention now pertains to an irregular PRF signal, preferably a PRF signal wherein the pulse bursts in said signal are distributed according to a Poisson distribution or a combined Poisson distribution. In a further preferred embodiment such a signal has a frequency of 50.000 – 1.000.000 Hz, preferably 150.000 – 500.000 Hz, a pulse duration of 0.1 – 100 msec, preferably 5-20 msec, and a pulse frequency of 0.1 – 50/sec, preferably 2 - 5/sec. Preferably, such a PRF signal is applied in therapy, preferably in the treatment of pain, or alternatively in the treatment of cancer, infectious diseases, COPD, depression, sequences of allostatic load, immunosuppression or otherwise caused immunodeficiencies

Description

Title: New modus operandi of Pulsed Radio Frequency

FIELD OF THE INVENTION

The invention relates to the field of medicine, more particularly the field of treatment with electrical signals.

BACKGROUND OF THE INVENTION

Use of electrical current, especially in the area of anodynia, more specifically in the area of pain relief, has been known for several decades. The first reports of the use of electrical current for pain management appeared in the 1930's. Initially, DC was used to induce lesions of nerves through the temperature increase caused by the electrical current

(thermocoagulation). Later, this has been replaced by AC with a frequency of 400 to 500,000 Hz, which has been shown to deliver more precise lesions. In the past few decades this radiofrequency (RF) thermocoagulation has been established as an accepted treatment option for trigeminal neuralgia, for unilateral cancer pain and for zygoapophyseal joint pain. Further, RF has been used in other fields:

- in cardiology for thermocoagulation of conductive tissue in the heart that conduct aberrant stimulus patterns;

- in oncology for destroying tumor tissue;

- in orthopedics for treatments of cartilage defects in

osteoarthritis.

When RF electric fields, with a commonly used frequency of 420 KHz, are applied to a needle, and when the needle is insulated except for the distal 2 - 15 mm, heat is formed around the distal, uninsulated "active" tip of the needle. The therapeutic effect was mainly attributed to the destruction of tissue by the heat that was generated by the friction of molecules. However, the role of heat became the subject of discussion when it was found that RF could also be clinically effective when it was applied distal to the nociceptive focus, pulsed RF (PRF) was then developed as a potential less destructive replacement of RF.

With PRF, which was first described in 1998 (Sluijter, M.E. et al., 1998, Pain Clin. 11:109-117), current is delivered in pulses of short duration (1-100 msec) separated by a silent period of about 0,1 to 1 sec. Heat generated by the application of the current is dissipated between pulses. Output current and pulse width and frequency parameters may be set to prevent the electrode and the directly surrounding tissue to heat up to more than 42°C to prevent cell destruction. Radiofrequency fields are applied in short pulses, at a constant voltage of 30 - 80 V, most commonly 45 V.

Initially a duty cycle of 2 x 20 msec/sec was recommended. Later many doctors have varied the duty cycle, using frequencies of up to 5 Hz and a pulse width of 5 - 10 msec, always taking care not to exceed a total active phase of 40 msec/sec, in order to avoid neurodestructive temperatures.

Nowadays PRF is recognized as treatment for e.g. various forms of spinal and facial pain and peripheral neuralgias.

Although currently PRF has become a standard therapy for pail relief in the hospital environment, there is still room for improvement of this PRF therapy.

SUMMARY OF THE INVENTION

The present invention now pertains to an irregular PRF signal, preferably a PRF signal wherein the pulse bursts in said signal are distributed according to a Poisson distribution or a combined Poisson distribution. In a further preferred embodiment such a signal has a frequency of 50.000 - 1.000.000 Hz, preferably 150.000 - 500.000 Hz, a pulse duration of 0.001 - 100 msec, preferably 0.1 - 50 msec, more preferably 2-10 msec, and a pulse frequency of 0.1— 50/sec, preferably 1- 20/sec, more preferably 2 - 5/sec. Preferably, such a PRF signal is applied in therapy, preferably in the treatment of pain, or alternatively in the treatment of cancer, infectious diseases, COPD, autoimmune diseases such as rheumatoid arthritis and Crohn's disease, depression, sequences of allostatic load,

immunosuppression or otherwise caused immunodeficiencies.

Further part of the invention is a method for treating pain or treating cancer, infectious diseases, COPD, autoimmune diseases such as

rheumatoid arthritis and Crohn's disease, depression, sequences of allostatic load, immunosuppression or otherwise caused immunodeficiencies wherein an irregular PRF signal according to the present invention is applied to a patient.

The invention also relates to a method for in vitro treatment of plant or animal tissue, especially plant seeds, by applying an irregular PRF signal according to the invention to said tissue.

Further, the invention pertains to the use of an irregular PRF signal according to the invention in a method to treat biological tissue, preferably wherein said biological tissue is plant tissue or in vitro cultured animal tissue.

A further part of the present invention is the use of PRF for the treatment of depression and a method for treating depressed patients wherein PRF is applied intravascularly, preferably intravenously.

Also a generator that is capable of delivering irregular PRF signals according to the invention, and preferably also capable of varying the voltage of individual PRF pulses in a duty cycle of such an irregular PRF signal, is also part of the invention. LEGENDS TO THE FIGURES

Fig. 1. Fast Poisson rhythm with average pulse (burst) frequency = 9.2 Hz, pulse (burst) width = 3.7, CV = 1.63.

Fig. 2. Slow Poisson rhythm with average pulse (burst) frequency

= 1.2 Hz, pulse (burst) width = 6.5, CV = 1.88.

Fig. 3. Types A and B mixed at a p value of 0.83. Average frequency 4.1 Hz, pulse width 4.1. There is now a rise of CV to 3.59.

Fig. 4. Msec-to-msec computation of the temperature around the electrode tip with a duty cycle as presented in Fig. 3. The voltage has been reduced from 45 to 42 V.

Fig. 5. Schematic drawing of PRF application. Shown are three consecutive pulses and the appropriate nomenclature for pulse, pulse width and interval. During each pulse the signal has the RF frequency.

DETAILED DESCRIPTION DEFINITIONS:

In the present description, "pulse" denotes a period during which electric fields at RF frequency are applied, "pulse width" denotes the duration of said pulse and "pulse frequency" the number of said pulses per second. "Duty cycle" means the configuration of frequency and pulse width. The term "duty load" denotes the total "on"-time of the signal per second. In Fig. 5 the signal configuration has been schematically indicated.

The Poisson distribution according to its mathematical meaning is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time and/or space if these events occur with a known average rate and independently of the time since the last event. The PRF signal that is distributed according to a Poisson distribution is meant to define a PRF signal in which the pulse frequency and/or the pulse duration follow a Poisson probability distribution. Since the average pulse frequency normally will be predetermined and have a value in the range of about 1-10 Hz, i.e. 1 to 10 pulses per second, the Poisson distributed PRF signal having been predetermined at 5 Hz will have pulses that will have an average interval over time of 0.2 seconds.

For the interval length, i.e. the spread of the probability distribution, the constraints are minimal. At the downside a minimum time must be allowed for the dissipation of heat from the electrode, varying from about 30 to about 100 msec, depending on the applied voltage. At the upper side there is no limitation. The pulse width may be varied according to a Poisson distribution with a predetermined average as well, but for the duty cycle the constraints are more limited and the situation is reciprocal: there is virtually no constraint on the lower limit, but at the upper side exposure must be limited to prevent excessive heat formation. Depending on the voltage this means that the pulse width may not exceed 8 to 30 msec.

An "irregular" signal according to the present invention is defined as a signal in which the period as defined in Fig. 5 is changed according to a Poisson distribution or a combination of Poisson distributions.

A "pulse" according to the present invention is the short duration of time in which radiofrequency current is applied to the electrode. Within such a pulse the current is delivered at radiofrequency, i.e. a frequency of 50.000 - 1.000.000 Hz, preferably 150.000 - 500.000 Hz, herein also indicated as "radiofrequency". Preferably the voltage in between pulses is zero, but also a minimum level of current at a very low voltage may be applied.

The mode of action of PRF has so far not been elucidated. Three possibilities have been suggested. In chronological sequence these are the following: 1. PRF causes modulation of afferent signals in the dorsal horn of the spinal cord;

2. PRF causes ablation by strong electric fields around the needle tip, and possibly by temperature effects during the active phase of the duty cycle;

3. PRF causes a brief expression of pro -inflammatory cytokines, eventually triggering an anti-inflammatory effect by a change of phenotype of immune cells, such as T-lymphocytes. Ad 1. PRF is in fact a new entity. It does not cause ablation, like in continuous RF, and it also is not considered to be stimulation like in TENS (transcutaneous electrical neurostimulation) or in epidural

stimulation. The frequency during the pulse generally is around 420 KHz and this is far higher than the physiological range. This explains why PRF does not cause any sensation to the patient, even at considerable voltages. We may therefore assume that the first synapse in the afferent chain does not depolarize. That does not mean that PRF has no effect on the nervous system. Laboratory experiments have shown that applying PRF to a segmental nerve root is followed by expression of c-fos in the dorsal horn of the spinal cord (Higuchi, Y. et al., 2002, Neurosurgery 850-856; Van

Zundert, J. et al., 2005, Anestesiol. 102:125-131). This phenomenon has been named "transsynaptal induction". It is a sign that PRF causes presynaptal conditioning. The importance of this transsynaptal activity for the clinical effect of PRF is still a subject of discussion. There could be Long Term Depression (LTD) of higher afferent synapses, but the clinical course following PRF procedures does not seem to be synchronous with an LTD effect. Also, PRF may have an anti-inflammatory effect when an electrode is positioned intra- articularly, in a position that is at considerable distance from any afferent nerve (Sluijter, M.E. et al., 2008, Pain Pract. 8:57-61; WO 2008/069647). This would suggest that there are two parallel effects that may operate either independently or in concert. Any activity inside the central nervous system cannot be ignored however, and it is reasonable to assume that presynaptic conditioning plays at least an additional role in the mode of action.

Ad 2. Although the overall temperature changes in tissue during PRF application are minimal because of the relatively large pulse intervals, the electric fields close to the needle/electrode are very high during the active pulse. Because the high power deposition during the pulse causes a "heat spike", thermal effects could contribute to destruction too. It has been suggested that these effects could cause a "mini-ablation", a watered down version of what happens during continuous RF (Cosman, E.R., 2005, Pain Med. 6:405-424; Erdine, S. et al., 2009, Pain Pract. 9:407-417). There are strong arguments contradicting this theory. Both the electric fields and the temperatures around the needle tip fall off very rapidly (<0.2 mm) away from the tip. Tissue destruction during PRF is therefore limited to minuscule dimensions (Cahana, A. et al., 2003, Pain 4:197-202). Also ablation could never explain the beneficial effects of intra-articular PRF procedures.

Ad 3. There are many anecdotal observations of a reduction of the serum CRP level following PRF procedures, concordant with the theory that anti-inflammation plays a role in the mode of action. Possibly the triggering event of this effect is expression of pro -inflammatory cytokines (Van Duijn, B., 2011, "Exploration of anti-inflammatory effect of PRF at the cellular level", Int. Symp. "Invasive Procedures in Motion", Nottwil, Switzerland, January 21-22) by the shaking effect of the alternating electric fields on charged molecules in the cell membrane. In the meantime, it has been published by the present inventors that PRF has beneficial effects on seeds and the germination of seeds (WO 2008/094042) and can stimulate growth and differentiation in in vitro tissue cultures (WO 2010/016765). Although also the mechanism that causes these effects is not yet elucidated or follows clearly from the above hypotheses, it appears that PRF is capable of influencing biological tissue to perform better.

Very recently (WO 2011/078676), the present inventors have found that PRF when applied intravascularly, has very surprising therapeutic effects on a variety of diseases or conditions, amongst which cancer, infectious diseases, immunosuppression or otherwise caused immunodeficiencies. These effects may be partly explainable from the effect on pro-inflammatory cytokines as described above. Nerve cells, or other cells that are instrumental in the mode of action of PRF, such as cells that belong to the immune system, receive many electric signals in resting condition. The basis behind the present invention is that these signals are never regular, and they are mostly not even random. Their distribution can best be compared to a Poisson distribution. Accordingly, if artificial stimulation of these cells is applied, it is best performed while most closely resembling the real situation, i.e. by using irregular signals, for example with a Poisson-like distribution. In synapse models it has been shown that the effectiveness of the signals is strongly dependent on the coefficient of variance (CV, = standard deviation/mean) (Migliori, M. and Lansky, P., 1999, Biol. Cybern. 81:291-298).

In brain stimulation, this has been tried successfully before (Wyckhuys, T. et al., 2010, Epilepsia:2297-22304). But PRF is different from such brain stimulation that has been successfully applied. Brain stimulation causes depolarization of nerve cells, whereas the frequencies that are used in PRF do not have such an effect, as has been known for many years (D'Arsonval A. Action physiologique des courants alternatifs a grande frequence. Arch Physiol Norm Pathol 1893; 5: 401-408). Also, in brain stimulation the applied voltages are much lower than the voltages that are applied during PRF and the frequencies are much lower than the high frequency (about 400 KHz) that is used during the active pulse of PRF.

Where, at one hand, this brings advantages to brain stimulation, since power deposition does not play a role and there are no constraints in varying the signal, the differences between PRF and brain stimulation do not justify a one-to-one translation of the applicability of such irregular stimuli.

Further, the advantageous effects of the irregular PRF signals may be considered independent from neural responses, since— as is shown in Example 2 of the present application— an irregular PRF signal has been shown to be very successful in the treatment of cancer metastases.

In PRF there are strict limits to the power deposition because neurodestructive temperatures must be avoided. This is true for the deposition during the active pulse, to limit the height of the heat spike. The pulse width may therefore not exceed a certain number of msec, depending on the voltage. It is also true for the total deposition over time, which controls the mean temperature. This affects both pulse width and pulse frequency. It has to be kept in mind that if an undesirable accumulation of heat occurs during an irregular input, this may be quite limited in time. It cannot be measured by monitoring the mean electrode tip temperature, because the thermocouples that are commercially available are much too slow to pick up these short changes. The safety of an irregular cycle must therefore be checked with a calculating model that calculates effects per msec and that records maximal temperatures and their time course.

Possible remedies for avoiding this temperature effect are the use of pulses of a smaller width, e.g. a width in the low msec or even in the microsec range. In such a case, pulses of less than 100 isec, such as between 10 and 500 μββο may be administered. Another possibility to avoid or minimize an increase in temperature at the tip of the electrode is by varying the voltage per pulse. In this way the voltage of a pulse with a large duration may be decreased by which the electrode is heated less.

Accordingly, it would also be possible to accommodate relatively large pulse widths in the Poisson scheme according to the invention by lowering the voltage for those larger pulse width pulses and increasing the voltage for small pulse width pulses. This will markedly increase the CV of the pulse width.

The art of constructing a Poisson distribution for PRF is therefore to find a safe sequence, within the constraints, with an optimal coefficient of variation (CV). Normally increasing the power of the simple Poisson distribution that can be calculated with the formula can increase the CV at will

NP = -In (l-n/100) where Np is the Poisson number and n is a random number between 1 and 99. A series of random numbers has a CV of 0.5 to 0.6. The Poisson series that is calculated with this formula has a CV of

approximately 0.95. If Np is empowered by executing Np2 = Power (Np;n) where n may have any chosen value, the value of CV may be increased to values of 3 - 4. For PRF this tool can only be used over a limited range, because at higher powers a high percentage of the numbers end up in the very low range. These can be used without limitation in stimulation, but not in PRF because after each signal there is a constraint of a minimum period that is needed to eliminate the energy that has been deposited. There is therefore an obligatory cut off at for example 40 msec (but of course the value of this cut-off depends on the height of the voltage that is used), and paradoxically such a cut off signal sequence becomes very monotonous again.

Although the problem may be solved by also applying a variable voltage per pulse, as has been argued above, a better option to accommodate to the constraints is mixing two - or more— distributions in a probability p that can be optimized by trial and error to obtain the highest CV In this sense. "A PRF stimulation according to a combined Poisson distribution" according to the present invention is defined as a PRF stimulation in which the pulses are distributed according to a mixture of two or more Poisson distributions. Mixing of Poisson distributions is done by listing two (or more) columns each filled with the numbers corresponding to a Poisson distribution of data points (ti, t2...t_m) with a different average pulse frequency. The resultant combined Poisson distribution then is obtained by choosing, for every data point of the distribution, one of the values from the columns. The choice for the 1^st or 2^nd (or n^th) column can be subject to a probability factor p that indicates for each column the probability for each data point of the distribution that the number from that column is chosen. The combined Poisson distribution then will contain e.g. ti of column 1, t2 of column 1, t3 of column 2, etc.

The PRF signals may be generated by RF lesion generators that are commercially available (such as NT 1100 or the NT 2000 RF generators from Neurotherm, Wilminigton, MA, USA). These only need to be adapted for the present invention by inserting a module that facilitates the development of an irregular signal. An irregular signal according to the present invention is defined as a PRF signal wherein the pulses are fired according to a Poisson distribution or a combination of Poisson distributions. Accordingly, the module that needs to be built in such a commercial PRF signal generator will be capable of producing a signal that has

radiofrequency pulses which occur with irregular length and/or interval. The irregularity behaves according to a Poisson distribution or a combined Poisson distribution. Further, since the commercially available PRF generators currently do not present this feature, a module that would enable to vary the voltage per individual pulse of PRF would be desirable to accommodate the use of occasional PRF pulses with a large pulse width. A skilled person would be able to build such a module, either in software or hardware, to generate such duty cycles with varying voltage. The signal could also be delivered by a separate generator of PRF signals that is not a part of the existing RF lesion generators. Such existing lesion generators monitor the temperature at the electrode tip. This is a drawback now that PRF may in the future be used by other disciplines, outside the field of pain treatment. The existing generators are relatively expensive, and measurement of temperature necessitates sterilization of thermal probes, further adding to the cost and making the procedure more cumbersome. This is unnecessary because the measurement of the average tip temperature during PRF has very limited value. Temperature

measurement is important for heat lesions using continuous RF, where it protects against gas formation by overheating and where it gives an approximation of the shaft temperature, which is just a few °C lower. But in PRF the situation is very different because the shaft does not heat up. Since the temperature falls off so rapidly away from the electrode and since the heat spikes are of such a short duration that many thermocouple measuring systems can not follow these rapid changes, it only provides global information on an area of less than 0.5 mm³. Therefore during PRF temperature measurement can safely be replaced either by a judicious limitation of the voltage or by limiting the duty load. These values can be determined by calculating the effects on tissue with worst case scenario properties, i.e. tissue with low impedance and with a blood flow of close to zero.

The instruments for invasive application of PRF to a patient comprise a needle-like electrode, connected to a PRF current source and a means for providing connection to earth. The PRF current source (or lesion- generator) will provide, next to the source for the current, also a stimulator function, to check for the proper positioning of the electrode, and the facility of measuring the impedance of the circuit between patient, earth and apparatus. These devices are commercially available. The procedure to apply PRF, whether it is given in the vicinity of a nerve, intra -articularly or intravascularly is easy to perform and does not need special skills. For intravascular PRF an insulated needle with an exposed tip of minimally 5 mm, but preferably 15-20 mm, is inserted into a blood vessel, preferably a vein. With such a needle the impedance of the system should be below 1000 Ω, preferably about 100-600 Ω, more preferably about 200-250 Ω. Any blood vessel of sufficient size can be used, but preferred are venous blood vessels that are easily accessible, such as the antecubital vein, or a vein in the thigh (vena saphena) or neck (vena jugularis). Preferably, in view of the role of the nervus vagus in the inflammatory reflex, a vein should be used which provides a minimal distance to the nuclei of the nervus vagus, such as the vena brachialis, the vena brachiocephalica or the vena jugularis.

For intra-articular placement of the electrode, the electrodes which are currently used for (P)RF are unsuitable since they have a very sharp tip, which could damage the joint. Further, some joints are arcuated, which limits the use of rigid instruments. Examples of electrodes for this type of treatment are given in WO 2008/069647.

When the electrode is in the proper position and connected to the PRF current source, the patient will be connected to earth (e.g. by a so- called earth-plate) to establish an electrical circuit. Exposure to PRF is then applied. Usual values are a pulse duration of 10 msec and a pulse frequency of 2-5/sec; a voltage of 20 - 80 V depending on the impedance of the system; and a total duration of treatment of 10 - 30 minutes. There is however a wide variation in parameters that may be used:

Frequency: 50.000 - 1.000.000 Hz,

preferably 150.000 - 500.000 Hz Pulse width (duration): 0.001-100 msec, preferably 0.1 - 50 msec, more preferably 5-20 msec and most preferably 2— 10 msec.

Pulse frequency: 0.1 - 50/sec, preferably 1 - 20/sec,

more preferably 2 - 5/sec

Voltage: 10 - 80 V, preferably 40-60 V

Treatment time: 2— 30 minutes

Further the voltage may not be brought back to zero during the rest phase.

The pulse width may be lower than 100 microsec, e.g. in the range of 10-500 μββο to avoid temperature effects at the tip of the electrode.

The PRF treatment is painless (except for the initial insertion of the needle electrode) and no adverse reactions have thus far been observed.

PRF may also be applied non-invasively through skin electrodes of varying diameter. This method can be used for two purposes. For treatment of pain it has been used since 2004 (Balogh SE, Transcutaneous application of pulsed radiofrequency: four case reports. Pain Pract. 2004 Dec;4(4):310-3.) and its efficacy has recently been confirmed in a

randomized controlled trial (Taverner MG et al., Transcutaneous pulsed radiofrequency treatment in patients with painful knee awaiting total knee joint replacement., Clin J Pain. 2010 Jun;26(5):429-32.). The method has also been used in the treatment of conditions that are connected to allostatic load and other malfunctioning of the immune system. For this modality electrodes are placed over large blood vessels, such as the subclavian vascular bundle with a reference electrode over the vagus nerve. Other future applications may include posttraumatic conditions, rheumatic or arthritic hands and non-healing ulcers and bone fractures. For

transcutaneous use the voltage should be adapted to the distance of the electrodes. It should be in the range of 6 - 10 V for each cm distance.

Further, when PRF is applied in vitro, for treatment of animal or plant tissue, any electrode may be applied which is capable of delivering the radiofrequency stimulation to the tissue. Of course in such circumstances stimulus conditions such as voltage, distance to the tisse, and pulse width and frequency can be optimalized.

As an additional finding it has been found that PRF, and thus also the irregular PRF treatment of the present invention is especially suited in the therapy of depression. Accordingly, the invention also comprises the use of PRF for treatment of depression and a method of treating depressed patients by administration of PRF. In this respect, the term depression is used for any mood disorder that is characterized by depressive feelings, such as bipolar disorder, major depressive disorder, stress-mediated depression, dysthymia, post-natal depression, and the like.

Preferably, PRF is applied intravascularly, and more preferably intravenously, but transcutaneous application of PRF as described above is also feasible. EXAMPLE 1

A 69 year old woman had been diagnosed with an endogenous depression 8 years ago. Over the last three years a chronic fatigue syndrome had developed as well. She had extensively been treated with

antidepressants without effect. She was treated with intravenous PRF with a Poisson distribution with a CV of 1.9, an average pulse frequency of 4.1 and an average pulse width of 4.8 msec. A voltage of 60 V was applied for 15 minutes. She reported a marked improvement in her mental condition that has so far been stable.

EXAMPLE 2

A 60 year old woman was diagnosed with a metastatic breast cancer. A large metastasis (about 8 x 4 x 3 cm) was observed above the right clavicle. Because of this she was unable to turn her head or only with lots of pain, probably caused by the pressure of the tumor metastasis on the nerves of the forearm that run below the clavicle. She was treated with intravenous PRF with a Poisson distribution with a CV of 1.9, an average pulse frequency of 4.1 and an average pulse width of 4.8 msec. A voltage of 60 V was applied for 15 minutes.. Two days after treatment the metastasis was shrunk to half of the initial size, which allowed painless turning of the head. After a week only a little remainder of the metastasis was palpable. This effect outperformed the regular PRF (as described in WO 2011/078676), since such a speedy recovery has not been observed with regular PRF signals. EXAMPLE 3

An 81 year old man had a history of neurogenic claudication. Walking for more than 50 m provoked severe pain in the right buttock with radiation in the leg following an L5 pattern. The MRI scan showed a lateral stenosis of the R L5 foramen with an intraforaminal hernia L5/S1, compromising the L5 root. He was treated with a Dorsal Root Ganglion procedure at the R L5 level with Poisson type PRF, at 45 V for 10 minutes. The day after treatment the radiation into the leg had disappeared, but the buttock pain could still be provoked by walking for 200 m. His condition improved rapidly, and 10 days after treatment he was free of all pain. After treatment with regular PRF improvement takes at least 2 months in similar cases. EXAMPLE 4

A 28 year old man had a long history of Crohn's disease, since the age of 16. He had been a university student but he had to terminate his studies due to frequent absence because of exacerbations of his disease. There were also serious consequences for his social life. He was treated with intravenous Poisson type PRF at 60 V for 15 minutes. Before treatment his CRP level was 7.3 mg/L. Ten days after treatment the CRP level had diminished to 1.7 mg/L and his general condition had markedly improved.

Claims

1. An irregular PRF signal.

2. An irregular PRF signal according to claim 1, wherein the pulse bursts in said signal are distributed according to a Poisson distribution or a combined Poisson distribution.

3. An irregular PRF signal according to claim 1 or 2, wherein said signal has a frequency of 50.000 - 1.000.000 Hz, preferably 150.000 - 500.000 Hz, a pulse duration of 0.001 - 100 msec, preferably 0.1 - 50 msec, more preferably 5-20 msec and most preferably 2— 10 msec, and a pulse frequency of 0.1— 50/sec, preferably 1— 20/sec, more preferably 2 - 5/sec.

4. An irregular PRF signal according to any of claims 1-3 for use in therapy.

5. An irregular PRF signal according to claim 4, for use in the treatment of pain.

6. An irregular PRF signal according to claim 4, for use in the treatment of cancer, infectious diseases, COPD, autoimmune diseases, depression, sequences of allostatic load, immunosuppression or otherwise caused immunodeficiencies.

7. Method for treating pain or treating cancer, infectious diseases,

COPD, autoimmune diseases, depression, sequences of allostatic load, immunosuppression or otherwise caused immunodeficiencies wherein an irregular PRF signal as defined in any of claims 1 - 3 is applied to a patient.

8. Method for in vitro treatment of plant or animal tissue, especially plant seeds, by applying an irregular PRF signal as defined in any of claims 1 - 3 to said tissue.

9. Use of an irregular PRF signal as defined in any of claims 1-3 in a method to treat biological tissue.

10. Use according to claim 9, wherein said biological tissue is plant tissue or in vitro cultured animal tissue.

11. PRF for use in the treatment of depression.

12. Method for treating depressed patients wherein PRF is applied intravascularly, preferably intravenously.

13. A PRF generator capable of generating an irregular PRF signal.

14. A PRF generator according to claim 13, which is also capable of varying the voltage of individual PRF pulses in a duty cycle.