TYPES OF ELECTRICAL STIMULATION

Iontophoresis

Iontophoresis, the process of increasing the penetration of drugs into the skin by application of an electric current, is commonly used by physical therapists for the purpose of delivering anti-inflammatory medications such as corticosteroids. The groundwork for iontophoresis dates back to the early 1900s, with initial scientific experiments performed by a researcher named LeDuc.

The majority of units consist of a compact phoresor that operates with a 9-volt battery and two wire leads, each connected to an electrode. One electrode is the drug-delivery electrode intended for the anti-inflammatory, and the other is used as a dispersive electrode charged opposite to the anti-inflammatory ion. When the electrodes contain solutions of ions, negatively charged anions are repelled from the cathode into the body and positively charged cations are repelled into the targeted body area from the anode.

This effect is specific for ions of the same polarity as the electrode and, conversely, ions of the opposite polarity are not transferred into the body. Physical therapists use iontophoresis based on this penetration and distribution of ions primarily for controlling and reducing inflammation. This is applied while minimizing the systemic concentration caused by circulatory removal of the desired medication from the targeted area.

Two typical prerequisites for treatment with iontophoresis are that the medication must be charged (or modified to carry a charge) and that the inflammatory process be near the body surface (i.e. a superficial muscle or tendon rather than a deeper muscle tendon bursa) (Costello, 1995).

In the physical therapy setting, constant direct current has been commonly used in iontophoresis applications. However because of concern over pH changes, some researchers contend that a method of producing a more "consistent" constant current should be used to provide current while the skin resistance is changing. Because of potential skin charge accumulation and skin irritation due to pH changes, modulated currents have been used with success on laboratory animals. Pulsed currents have proved to be as effective or more effective in the delivery of small ions. Such studies indicate the need for physical therapists to consider and investigate the use of currents other than the traditional continuous monophasic current for iontophoresis.

Still other clinicians propose a current of 2.0 mA for 20 minutes for more superficial areas with a chronic inflammatory condition. More recent advances in this technology have introduced a disposable single-use iontophoresis system with an internal battery and current limiting circuitry. This method provides a constant drug delivery for an 80 mA-minute treatment and can deliver both negatively and positively charged drug ions. It operates at a low current and is worn for 24 hours to deliver the desired dose. The unit is designed to begin a treatment as soon as it is hydrated and applied to the skin, and stop the treatment at approximately 80 mA-minutes (Morris, 2003; Reena Rai, 2005).

Thie zapper circuit above outputs a square wave signal at the supply voltage of 9 V in series with a resistor of 1 kΩ. This means that the maximum output current can never exceed 9 mA (when short-circuited), which keeps it safe to use. The frequency varies between about 28 kHz and 75 kHz. C3 is charged up via a constant current source so that the change in frequency is fairly linear. The LED used in the constant current circuit doubles as the ‘on’ indicator for the device. After about eight minutes the zapper turns itself off since output Q9 (pin 14) of IC2 then goes high. This stops the base current in T1, which turns off the supply voltage to the circuit via T2. The ground and output connection (R14) of the circuit is connected to the body via two hand or wrist electrodes (in the simplest case these could be two pieces of bare wire). For safety reasons, the circuit should only be powered by a 9 V battery 

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