This chapter describes the different types of currents used for therapeutic electrical stimulation. The basic physics and principles of electricity are also presented to build a solid foundation on which to build a good understanding of electrical stimulation goals and techniques.
• The effects of electricity on the body can be difficult to comprehend, and the thought of actually sending 500 volts through a person's body can be intimidating. In this chapter, it will become apparent that electrotherapy, when used properly and appropriately, is a safe and effective form of therapy. Just as important, you will also see that electrical stimulation is an adjunct to other therapeutic modalities and rehabilitation exercises. However, electrical stimulation is not always an appropriate treatment approach.
Electricity is the force created by an imbalance in the number of negatively charged electrons • between two points, referred to as “poles.” This force, known as electromagnetic force, potential difference, or voltage, creates a situation in which electrons flow in an attempt to equalize the difference in charges, creating an electrical current. In its simplest form, an electrical current takes the path of least resistance from the negative pole (cathode), an area of high electron concentration, and flows to the positive pole (anode), an area of low electron concentration.
For electron flow to occur there must be a complete pathway, a closed circuit. An incomplete path, open circuit, prevents the electrons from flowing. When you walk into a room and flip a switch to turn on the light, you are closing a circuit that allows the electricity to flow from its source, through the light, and back to its source. Likewise, a closed circuit is created between your patient and an electrical stimulator by attaching opposite electrodes to the body. The electrons flow from the generator, through the patient's body in the form of ions, and then back to the generator via electrons.
Electrical Stimulating Currents
Generally, electrical currents are classified as either being a direct current (DC) or an alternating current (AC), depending on how the electrons flow. A third classification, pulsed current, represents a type of current that has been modified to produce specific biophysical effects (Box 11-1).
Box 11-1. CLASSIFICATION OF ELECTRICAL STIMULATING CURRENTS
|Current Classification ||Sample Waveform ||Uses |
Uninterrupted, unidirectional flow of electrons.
| ||DC can produce polarity-based changes in the tissue, resulting in ions being moved to and from the area. Long duration can directly affect muscle fibers and can alter local pH. |
Uninterrupted, bidirectional flow of electrons.
| || |
Iontophoresis: Medication delivery Low voltage stimulation: Eliciting contractions from denervated • muscle.
High frequency of the AC decreases skin resistance, leading to a more comfortable current.
Unidirectional flow of electrons marked by periods of non-current flow.