Electrical energy is used for tissue distraction mainly in two forms. In one form, radio-frequency (RF) energy is used to create thermal tissue destruction. The advantage of high frequency alternating current is pure thermal effect. At frequencies above 100 kHz the electrical current does not affect the nerves significantly, while the high density electrical current flowing through the tissue creates Joule heat increasing tissue temperature to the necrotic level. RF energy is actively used in electro-surgery and for tissue coagulation. Electro-surgery was pioneered by Bovie (U.S. Pat. No. 1,813,902) in 1928 and since that time different design of devices were suggested and multiple clinical applications were developed. RF is associated with surgical procedures and requires anesthesia to reduced pain associated with thermal tissue destruction. Recently, RF became popular for sub-necrotic tissue heating where the heat level is not high enough to generate tissue damage but stimulates physiological process in the warmed zone. For example, RF energy has been actively used for collagen remodeling in the skin. U.S. Pat. No. 6,749,626 describes the use of RF energy for collagen formation in the dermis. U.S. Pat. Nos. 6,470,216, 6,438,424, 6,430446 and 6,461,378 disclose methods and apparatuses for thermal treatment of the collagen matrix using RF, cooling and a special electrode structure that smoothes the skin surface. U.S. Pat. Nos. 6,381,498, 6,377,855, 5,919,219, 5,948,011, 5,755,753 describe methods of collagen contraction using RF energy, and a reverse temperature gradient on the skin surface. U.S. Pat. Nos. 6,378,380, 6,377,854 and 5,660,836 describe methods of liposculpturing using RF energy and external cooling to affect the collagen inside the adipose tissue. Another method to reduce and redistribute adipose issue is skin massaging. This method is based on improving blood circulation and increasing fat metabolism. U.S. Pat. No. 6,662,054 describes a method for skin massaging in combination with non-aggressive RF heating for increasing skin and fat metabolism.
Another, non-thermal method of destruction of adipose tissue is irreversible electroporation (IEP). This method is based on changing cell membranes using high electrical field leading to the apoptotic death of cells. US Patent Application Publications 2004/0019371 and 2003/0149451 describe devices and methods comprising at least two electrodes and generating electrical pulses with voltage above an electroporation threshold. U.S. Pat. No. 6,697,670 describes device with two pairs of electrodes where the first pair is used for electroporation of adipose tissue and second pair for electro-stimulation.
U.S. Pat. No. 6,697,670 and Patent Application Publication 2007/0161982 describe use of symmetrical bipolar pulses for IEP. This method allows a reduction in the shocking effect by maintaining zero average current, but subsequent pulses having similar amplitude but opposite polarity does not allow a cumulative effect from multiple pulses to be reached.
High voltage (HV) pulses used for IEP may create arcing around the electrode and damage the skin surface. Using pulses with single polarity may create a risk of electrical shock. According to the above mentioned patents and applications, electroporation effect becomes more consistent when an amplitude of electrical pulses is higher, pulse duration is longer and more HV pulses are applied. All these changes increase risk of electrical shock and create risk of potential harm to the patient.
Reduction of pulse duration below 10 microseconds may reduce electrical shock sensation but will require higher amplitude of HV pulses to generate clinical effect. (Nanosecond, high-intensity pulsed electric fields induce apoptosis in human cells. STEPHEN J. BEEBE, PAULA M. FOX, LAURA J. REC, E. LAUREN K. WILLIS, AND KARL H. SCHOENBACH, The FASEB Journal, Vol. 17 August 2003, pp. 1493-1495).
HV electrical pulses are also used for sterilization destroying bacteria. In the article “Electrical Sterilization of Juice by Discharged HV Impulse Waveform”, Hee-Kyu Lee, American Journal of Applied Sciences 2 (10): 2076-2078, 2006, it is shown that survivability of the cells is a strong function of temperature. Increase of temperature from 30° C. to 40° C. may provide the same survivability at an electric field strength two times lower. Pre-heating or pre-cooling of adipose tissue prior the electroporation treatment may reduce the treatment threshold to the level that is practical for use with less risk for the treated patient.
All the above mentioned methods may improve IEP treatment, but do not allow significantly reducing the electrical effect or significantly diminishing electrical shocking while providing efficient cell apoptotic destruction.