Taken from Basics of Acupuncture, G. Stux and B. Pomeranz, 1998, Springer, pp. 272-273.
"Generally the red lead of each pair of wires is positive, and the black is negative. Pulses of electricity are applied to the needles in order to stimulate nerves, with the pulse width being from 0.1 to 1.0 ms in duration (Some stimulators have adjustable pulse width). More expensive, elaborate stimulators use biphasic pulses (negative followed by positive or vice versa) in order to reduce polarization of each needle due to electrolysis. (The negative pulse cleans the electrode of electrolytes deposited by the preceding positive pulse.) If the pulses are perfectly biphasic, then the net DC current is zero and no polarization occurs. Polarization is a nuisance as it raises the electrode resistance over time, thus reducing the intensity of stimulation. Also, it can cause the needle to break off in the tissue.
Another advantage of biphasic pulses is that the two needles of each pair receive symmetrical stimuli (one needle being the mirror image of the other). Hence the red lead has a positive pulse immediately by a negative pulse, while the black lead has a negative pulse followed by a positive pulse. Since negative pulses cause an action potential on the nerve, it is important that both needles in a pair receive negative pulses, which is only possible in a biphasic stimulator. The intensity of stimulation is under the control of an intensity knob. In less expensive stimulators in which the biphasic pulses are not perfectly matched (the negative wave is not equal to the positive wave); the negative, black lead will give a stronger needle sensation than the positive, red lead. In order to achieve an optimum effect for acupuncture analgesia, the strongest tolerable intensity is required for DeQi (to activate type II and III muscle nerves). If both leads of a pair deliver symmetrical, biphasic pulses then both needles will be optimally stimulated to give De Qi. With less expensive devices, however, only one needle of a pair is adequately activated (the needle attached to the black lead)."
Microcurrent electrotherapeutic devices have been on the market for many years and are normally designed to be used with TENS pads or Q-Tip cotton probes. The electrodes are applied externally to the skin for physical therapy or physiotherapy applications. When touching acupuncture points, a similar effect to electro-acupuncture occurs.
The classic microcurrent waveform is called a square wave (denoted technically as 50% duty cycle square wave, as explained below). Microcurrent stimulators designed for electrodes attached to the skin may not be appropriate or safe for use with electro-acupuncture where needles are inserted into the body (percutaneously).
Pantheon Research electro-acupuncture stimulators are designed with a microcurrent square wave that is fully safe and effective to use with percutaneous needle stimulation, as during electro-acupuncture. Slightly different than the 50% duty cycle waveform, the electro-acupuncture compatible waveform has a much faster pulse time of 5% or less.
Classical microcurrent devices for physical therapy apply the electrical stimulus to large electrodes, either a TENS pad or a Q-Tip cotton probe. Since the surface area of these electrodes is large and the electricity is passed through the epidermis, the current density, the available electrical current divided by the surface area of the electrode touching the skin, is small. In addition, the stratum corneum of the skin has a very high resistance to the passage of electricity, which also reduces the current passing into the body. This is a very safe technique and very therapeutic for many problems.
However, if this very safe 50% duty cycle square wave is passed into the tip of a needle inserted subcutaneously, different conditions occur. Since the surface area of a needle tip is very small and the available electricity is divided by the area of the needle shaft (or possibly the needle tip) under certain conditions, the current density is large in comparison to a 1 inch square TENS pad. Also, the resistance of the skin is not present.
The problematic condition is most acute when a very slow frequency is being used. Very slow frequencies of .5 Hz, 1 Hz, and 2 Hz are most common in electro-acupuncture. At 1 Hz, with a 50% duty cycle, the positive pulse will be .5 second in length. At .5 Hz, the positive pulse will be 1 second in length. At these slow frequencies the current begins to appear as DC current and the problems of electrolysis are possible.
Electrolysis will result in the metal components of the needle being electrically forced into the tissues, and the formation of gas bubbles under the skin and in tissue.
The following quote is taken from the paper by Yoshiaki Omura printed in Acupuncture and ElectroTherapeutics Res. Int. J., Vol. 12, pp. 201-225, 1987, entitled "Basic Electrical Parameters for Safe and Effective Electro-therapeutics (Electro-acupuncture, TES, TENMS (or TEMS), TENS and Electro-magnetic Field Stimulation with or without Drug Field) for Pain, Neuromuscular Skeletal Problems, and Circulatory Disturbances: Undesirable Electrolysis Phenomena Associated with DC Stimulation or Prolonged Application of Electrical Impulses with Excessively Large Pulse Width."
Prolonged electrical pulse stimulation with excessively wide pulse duration or DC electrical stimulation with a significantly large current may result in the following undesirable electrolysis phenomena: 1) strong acid (HCL) formation around the positive electrode and strong alkaline (NaOH) formation around the negative electrode, which may result in necrosis of tissue around the electrodes, 2) hydrogen gas bubble formation around the negative electrode and oxygen gas bubble formation around the positive electrode as a result of the electrolysis phenomena of water molecules in the body tissue which reduces the effectiveness of the electrical stimulation by decreasing current, as well as 3) breakage of the positive electrode after prolonged application of large DC currents."
With a very slow frequency, we may have excessively wide pulse duration with significantly large current, especially since the needle tip may be the location of the current movement. The 50% duty cycle microcurrent stimulation has been used now for a few years in electro-acupuncture applications, and there have not been widespread reports of electrolysis effects. However, when introducing a new technology into medical practice, a conservative design philosophy is safest and best until the years pass and all technical issues can be examined. The safety of patients is always the priority.
Whereas theoretically, a potential problem exists with the use of 50% duty cycle current, it has been the practice of Pantheon Research to design a system that is not in question. The microcurrent waveform used has a pulse time of only .4 milliseconds, even at very low frequencies. This corresponds to a duty cycle of 5% or less. This is analogous to standard pulse times on electro-acupuncture machines and is safe. The illustrations below demonstrate the images of the waveforms as seen on an oscilloscope.