Therapeutic application of electric current

 Electric current  is a flow of charged (positively or negatively) particles between a conductive medium. Good conductive mediums are the ones who have free charged particles (electrons or ions), because that characteristic allows a electric current to pass through them. The human body is an example of a good conductive medium (due to the high percentage of water and the presence of Cl- and Na+ ions).

Therapeutic application of electric current isn’t still nowadays generally accepted, because many people are sceptical when it comes to use electric energy as a medical treatment (though there are clinical evidences that electrical nerve stimulation provided successful relief of chronic pain, for example).

History
One of the oldest therapeutic applications of electric current is electrotherapy and it has a unique history, because it wasn’t discovered in a laboratory or clinic. Electrotherapy originates as early as 400 BC from contact with the torpedo fish, which could produce electric shocks between 100 and 150 volts. People would catch the fish alive and place it on a painful area of the body, the torpedo fish produced a series of electric shocks that reduced and controlled pain.

During the eighteenth century, the development of the battery provided the capacity of store electricity. As a result, physicians had more control over where, when, and how much current could be applied for therapeutic use. In the latter half of the nineteenth century most physicians in America possessed at least one electrical stimulator. However, as with any new medical technology, electrotherapy was not immediately accepted. This skepticism resulted in a decline of interest in electrotherapy toward the end of the century.

In 1965 electrotherapy regained its popularity when the gate control theory of pain was introduced. This theory proposed that an increase in large nerve fiber activity can potentially close the gate to information going to the brain from small pain fibers. When the gate is closed, the transmission of pain signals to the brain is blocked.

In 1967 clinical evidence came, reporting that electrical nerve stimulation provided successful relief of chronic pain. This therapeutic effectiveness in pain relief has led to other applications of electrotherapy by rehabilitative clinicians, including treating injured or diseased muscle and other soft-tissue conditions.

Electric Current
The electric current is related to three different unities which are the tension (measured in volts, V), the intensity (measured in amperes and miliamperes, A, mA) and the resistance (measured in ohms, Ω)

The factors that influence the resistance to the electric current of the human body include:
 * Skin (itself)
 * Hair (the presence of hair complicates the passage of the current)
 * Humidity of the skin (the presence and sweat facilitates passage of current; the gel is a good conductor)
 * Adipose tissue (the excessive presence of this tissue complicates the passage of the current)
 * Vascularization (a better vascularization causes a better passage of the current and the other way around)
 * Size of the electrodes1 (the larger the area of the electrodes, the easier the current passes through the tissue)

1 Electrode - electrical conductor used to make contact with a nonmetallic part of a circuit

Types of electric current
Electrotherapeutic devices used in rehabilitation generate different types of current that, when introduced into biological tissues (such as the skin), are capable of producing specific physiologic changes. There are many types of electric current used for therapies, being the principals:


 * 1) Alternating Current
 * 2) Direct Current
 * 3) Pulse Current
 * 4) Galvanic Current
 * 5) Interference Current

Alternating Current
In alternating current, the electrons constantly change directions, reversing its polarity. Electrons flowing in alternating current always move from the negative to positive pole, reversing direction when the polarities are reversed.

Direct Current
Direct current is a unidirectional flow of electrons toward the positive pole. However, on most modern direct-current devices, the polarity and thus the direction of current flow can be reversed. Electrotherapeutic devices are usually further classified as being either high-voltage generators or low-voltage generators.

Pulse Current
Pulsed current is the unidirectional or bidirectional flow of charged particles that periodically stop for a limited period of time before the next event. More specifically, a pulse is an isolated electrical event separated by a finite period of time from the next event. For most therapeutic applications, a constant current source is better. Therefore, pulsed current is more used for electrostimulation rather than long rehabilitation therapies.

Galvanic Current
The terms galvanic current and direct current are often used interchangeably. Historically, the term galvanic has been used to describe an uninterrupted direct-current form. High-volt galvanic electrical stimulators are considered to be useful in injuries associated with major tissue trauma accompanied by bleeding or swelling. Their direct current creates an electrical field over the damaged area that, theoretically, changes blood flow.

Interference Current
Interference current is based on the summation of two alternating-current signals of slightly different frequency. This results in current having a recurring modulation of amplitude, based on the difference in frequency between the two signals. This current flows and rests alternately performing different types of muscle activation, which is important in the muscular rehabilitation area.