Keywords: Electroceuticals; Electric sympathetic block; Pain
1. Introduction
Electroceutical medicine involves the use of electrical modalities of pharmaceutical strength. Along with electrodes of specific size, shape, and configuration, specialized medical devices can be utilized to obtain pharmacologic effects. The medical literature refers to alternating currents (a.c.) of 1000-100 000 Hz as middle frequency currents. While physical therapy devices utilize an a.c. of 1 4000 Hz and intensities of 1 20 mA, electroceutical devices utilize frequencies in the 20 kHz range. At these higher frequencies, both current perception thresholds (the intensity of current required for perception) and let-go thresholds (the amount of current tolerated before letting go) are increased [1,2]. As a result, it is possible to employ intensities up to 115 mA and 50 V.
The basic and physical science literature is replete with references demonstrating the effects of middle frequency a.c. upon cell membranes and voltage-dependant gates [3-11]. Computerized applications of a.c. parameters, which are derived from accepted research for different nerve fiber types and pathology, are now available [12-17]. This technology has been combined with higher frequencies and intensities to increase clinical potency.
In multiple clinical studies utilizing an a.c. of 4000 Hz and proper electrode montages, sympathetic blockade and perceived pain relief of 75% has been reported [18]. When a 20-kHz carrier frequency with a modulation frequency of 5-100 Hz is employed, intensities of up to 115 mA and 50 V become clinically usable. A clinical trial utilizing these parameters to achieve electric sympathetic block over a 1-week series not only produced pain relief of at least 75%, but also achieved thermographically proven vasodilatation which was greater on the ipsilateral side than the contralateral side in 60% and the presence of a Horner's in 40% of the patients studied. Due to its potency, electroceuticals should only be utilized be physicians familiar with all of the precautions and side effects than can occur with pharmaceuticals that produce similar results.
2. Molecular biochemistry and cell biology
All cells have a measurable potential difference across their membranes. The normal 35-Å cell membrane has a transmembrane potential of 70 mV. This is equivalent to 200 000 V/cm. Only a small number of ions must be affected to have a large impact upon cell transmembrane potential. The movement of less than 1 nmol of charged ion/mg of protein can create a greater than 200 mV potential difference [17, 19, 20].
For proper cell function, membranes contain gated channels that are voltage-dependent (Fig. 1). Voltage dependent gates are pores through cell membranes that have changing permeability when influenced by electromagnetic signals. Changes in cell surface energy lead to conformational and chemical changes within the membrane, cytoplasm, and exoplasm [21-23].
3. Basic electricity
Current is the movement of charged particles (ions and
electrons). Voltage is the tension that results from a difference in the supply of positive and negative charges between two points. Examples of voltage include electromagnetic forces created by different concentrations of Na+, K+, or Ca2+.
Resistance is the property that inhibits the flow of charged particles. Examples include cell membranes, mesenchym, and skin. Resistance is related to voltage by Ohm's Law: V = IR, where V = voltage, I = current and R = resistance. Typical values of tissue resistivity are: nerve 1, blood 1.6, muscle 5, skin 10, fat 20, and bone 160 (k W) [23, 24].
Capacitance is the property of storage charge. Capacitance and resistance are both found in skin. Impedance is the property of resistance to alternating current flow. Its components include self-inductance, capacitance, and ohmic resistance. The relationship of impedance to voltage and alternating current flow is described by the equation: Z = E/I, where Z= impedance, E= voltage and I = alternating current flow [25].
Conductance is the ease with which an electrical current flows through a substance. It is the reciprocal of resistance. Frequency defines the number of electrical events, which occur in a unit of time. Hertz (Hz) are defined as equivalent to the number of cycles per second (pulse per second). Resistance, impedance, and capacitance are inversely proportional to frequency [25].
4. Electroceutical concepts
Electromedicine configurations are either direct current (d.c.) or alternating current (a.c.). Alternating currents are referred to as apolar and direct currents as polar. Most d.c. devices have a net negative charge and most a.c. devices have no net charge. When applied to extracellular fluids, d.c. polar currents enhance net positive charge under the anode (+), and therefore increase transmembrane potential. The resulting hyperpolarization is called anodal block [23, 25, 26].
Electromedical devices with 0 1000 Hz alternating currents are referred to as Low Frequency and those with 1000 100 kHz are called Middle Frequency. Low frequency currents cause a stimulatory effect between the electrodes [26]. The stimulatory effect of low frequency a.c. electrotherapy devices are thought to utilize the Gate Control Theory for their clinical effect [27, 28].
Unlike low frequency currents, middle frequency currents generate a cathodal effect referred to as ambipolar stimulation under each electrode [26]. Tissues have a lower impedance to middle frequency vs. low frequency currents (Fig. 2) [29]. Biologically significant effects can occur deeper within the tissue when middle frequencies are used due to the enhanced penetration and heightened disposition of current into the tissue depths [27].
Cell membrane responsiveness to an electrical stimulus is determined by the characteristics of its strength duration curve. Strength duration curves are derived from Weiss-Lipque relationships. These relationships describe the physical characteristics of nerve fiber responsiveness to electrical currents, controlling for factors such as charge, stimulus duration, and strength. Rheobase refers to the lowest possible stimulus strength that can be applied for an indefinite period of time and still obtain threshold.
Chronaxie describes the stimulus strength that is twice that of rheobase. All nerve fibers have unique and distinct characteristics that can be plotted out in the form of strength duration curves [30].
Middle frequency currents of at least 4000 Hz are needed to provide successive stimuli that fall within relative refractory periods such that repolarization cannot occur; the continuous refractory state that results is called Wedensky Inhibition. Wedensky inhibition and anodal block are both temporary phenomenon that cease as soon as the applied current is turned off [31, 32]. Tissues act like condensers they offer lower impedance at higher frequencies. When higher frequency currents are used, however, higher intensities are required for a tissue to reach threshold. This drawback is overshadowed by the fact that sensory perception are reduced at higher frequencies, both current tissue penetration and usable intensity can be increased as the frequency used is increased [1,2,29].
Weaver [33], Prausnitz [34], and Pliquett [35], have demonstrated that currents with sufficient voltage (50 150) and short pulse lengths (100 200 ms) can create 'pores' within the skin lipid bilayer, creating a transdermal channel into the depths of tissue. A 20-kHz carrier frequency, with a 50-V output, satisfies these criteria. Electroporation provides another explanation for the improved delivery of
current into the depths of the tissue with proper parameter selection.
With increasing concentration and intensity, greater current density occurs in the depths of the tissue. Joule's law states that as the resistance of a tissue increases, there is more electrical energy converted into heat. The relationship is expressed as follows: P = I2 X R where P = heat, I = current and R = resistance.
In order to avoid tissue destruction, limits have to be placed upon the total energy delivered into the tissue [24].
Total energy delivered into the tissue is limited by the patient's current perception threshold. At frequencies less then 100 kHz, patient perception will limit the intensity of electricity delivered before internal heating occurs. By limiting the flow of current
to 115 mA, with a 20-kHz carrier frequency, there is a very high margin of safety for any potential tissue destruction [2]. As shown in Figs. 2 and 3, at 20 kHz the benefits of middle frequency can be maximized. The unwanted electrical effect of increasing threshold with increasing frequency is minimized by dosing for a sufficient duration of time (Fig. 4) [36].
Electric Sympathetic Block High Frequency Electric, Pharmacologic Nerve Block Provides Relief For Sympathetic Pain
Electric Sympathetic Block: Current Theoretical Concepts and Clinical Results
Robert G. Schwartz, M.D.
Electric Sympathetic Block can be achieved by using high frequency electric, pharmaceutical currents through electroporation of the skin. Sympathetic nerve fiber activity is decreased as a result of the electroceutical's pharmacologic effect on the voltage dependant gate of the nerve membrane.
Electroceutical medicine involves the use of electrical modalities of pharmaceutical strength. Along with electrodes of specific size, shape, and configuration, specialized medical devices can be utilized to obtain pharmacologic effects. The medical literature refers to alternating currents (a.c.) of 1000-100 000 Hz as middle frequency currents. While physical therapy devices utilize an a.c. of 1 4000 Hz and intensities of 1 20 mA, electroceutical devices utilize frequencies in the 20 kHz range. At these higher frequencies, both current perception thresholds (the intensity of current required for perception) and let-go thresholds (the amount of current tolerated before letting go) are increased [1,2]. As a result, it is possible to employ intensities up to 115 mA and 50 V.
