Following completion of this chapter, the student will be able to:
- Define the most common terminology related to electricity.
- Differentiate between monophasic, biphasic, and pulsatile currents.
- Categorize various waveforms and pulse characteristics.
- Contrast the various types of current modulation.
- Discriminate between series and parallel circuit arrangements.
- Explain current flow through various types of biologic tissue.
- Explain muscle, nerve, and nonexcitatory cell responses to electrical stimulation.
- Describe how current flows through biologic tissue.
- Discuss the various treatment parameters including frequency, intensity, duration, and polarity that must be considered with electrical stimulating currents.
- Differentiate between the various currents that can be selected on many modern generators including high volt, biphasic, microcurrent, Russian, interferential, premodulated interferential, and low volt.
- Compare techniques for modulating pain through the use of transcutaneous electrical nerve stimulators.
- Be able to create a safe environment when using electrical equipment.
Many of the modalities discussed in this book may be classified as electrical modalities. These pieces of equipment have the capabilities of taking the electrical current flowing from a wall outlet and modifying that current to produce a specific, desired physiologic effect in human biologic tissue.
Understanding the basic principles of electricity usually is difficult even for the clinician who is accustomed to using electrical modalities on a daily basis. To understand how current flow affects biologic tissue, it is first necessary to become familiar with some of the principles and terminology that describe how electricity is produced and how it behaves in an electrical circuit.172,180,186
All matter is composed of atoms that contain positively and negatively charged particles called ions. These charged particles possess electrical energy and thus have the ability to move about. They tend to move from an area of higher concentration toward an area of lower concentration. An electrical force is capable of propelling these particles from higher to lower energy levels, thus establishing electrical potentials. The more ions an object has, the higher its potential electrical energy is. Particles with a positive charge tend to move toward negatively charged particles, and those that are negatively charged tend to move toward positively charged particles (Figure 5–1).1
The difference between high potential and low potential is potential difference. Electrons tend to flow from areas of higher concentration to areas of lower concentration. A potential difference must exist if there is to be any movement of electrons.
Electrons are particles of matter possessing a negative charge and very small mass. The net movement of electrons is referred to as an electrical current. The movement or flow of these electrons will always go from a higher potential to a lower potential.2 An electrical force is oriented only in the direction of the applied force. This flow of electrons may be likened ...