Principles of Electromagnetic Radiation
In this chapter we will cover the use of exogenously applied, time-varying electromagnetic (EM) fields from the nonionizing radio frequency (RF) part of the EM spectrum, which, when placed near open or closed wounded soft and hard tissues, will induce a healing electric field inside those tissues that is proportional to the rate of change of the magnetic field. In this context we will present the evidence for the use of nonthermal pulsed electromagnetic fields (PEMF), pulsed radio frequency energy (PRF), and low-level thermal PRF, which may also be referred to as pulsed shortwave diathermy (PSWD), as adjunctive treatments for patients with chronic wounds. Please note that continuous shortwave diathermy (CSWD) is also derived from the 27.12-MHz frequency, but because it is capable of generating vigorous tissue heating if tissues are in well vascularized tissues, it is generally not used for wound healing applications. Table 27.1 lists devices and their acronyms.
Table 27•1List of Devices and Their Acronyms |Favorite Table|Download (.pdf) Table 27•1 List of Devices and Their Acronyms
|Acronym ||Device/EM Energy |
|PEMF ||Pulsed electromagnetic field |
|PRF ||Pulsed radio frequency |
|PSWD ||Pulsed shortwave diathermy |
|CSWD ||Continuous shortwave diathermy |
It is important to emphasize here that all of these alternative wound healing interventions are derived from a primary continuous RF sinusoidal wave (27.12 MHz) called a "carrier," which can be modulated to produce nonthermal PEMF and PRF and mild thermal PSWD, each of which will be described later.
What Is Electromagnetic Radiation?
EM radiation is a type of energy that is created when electric charges are accelerated. When electric charges move, they produce waves of electric and magnetic energy in space. A familiar example is electric charges that move back and forth as alternating current emitted from a radio station tower (antenna) and that travel (broadcast) at the speed of light through space as RF radiation. These waves have a distinctive frequency and wavelength and can be reflected, refracted, and absorbed when they interact with matter.
What Is Frequency and How Does It Affect Tissues?
The frequency of EM radiation corresponds to the number of waves per second that cross a fixed point in space. EM waves are typically sine waves that cover a vast range of frequencies and corresponding wavelengths. Lower energy levels represented by the spectrum are produced by lower-frequency sine waves (eg, 60 Hz for electric power), whereas very high frequencies (1019 Hz) produce high-energy level gamma rays. RF radiation is the area or band of the EM spectrum in which most radio communication takes place and consists of propagating sine waves typically between 10 kilohertz (kHz) and 300 gigahertz (GHz) (1 kHz = 1 × 103 Hz; 1 GHz = 1 × 109 Hz.)1 (Fig. 27.1) The electromagnetic spectrum ...