Considering the many waveform parameters presented in Chapter 9, it should not be surprising that many clinicians feel intimidated or confused by clinical electrotherapy. However, a competent and clinically effective knowledge of electrotherapeutics can easily be obtained by understanding how parameters create the many effects produced with electrotherapy. Unfortunately, intimidation and confusion are perpetuated by commercial hype, poorly informed clinicians, complex-looking instrumentation, and sometimes misleading user's manuals. Waveforms vary in so many ways, and these variations are even more obvious when looking at the variety of dials, knobs, switches, and lights that are found on electrotherapeutic devices.
INSTRUMENTATION FOR ELECTROTHERAPY
Classifying Electrotherapeutic Devices
Electrotherapeutic devices can be described by the type of current generated and the power sources. Common clinical names used to describe devices include Russian, high-volt, microcurrent, and interferential. Although these names are common, use of more specific descriptors of the individual waveforms is encouraged. When classifying by power source, devices are either line-powered or battery-powered. Line-powered devices are powered by wall current (110 volt, 60 hertz [Hz] in North America) and are plugged into a wall outlet for use. These devices are sometimes referred to as clinical devices because their portability is limited. Battery-powered devices obtain their power from a variety of different battery sources, including the common AA, AAA, and 9-volt batteries as well as rechargeable batteries. The major advantage of battery-powered devices is their portability, allowing them to be used outside the clinic and while the patient is engaged in activity.
Line-powered devices have traditionally been capable of delivering greater current intensities than battery-powered devices. This was particularly true with stimulators delivering large-amplitude currents for muscle strengthening. For many years, evidence suggested that battery-powered stimulators used for muscle strengthening could not sufficiently activate skeletal muscle when compared to line-powered devices. However, evidence has altered this opinion. In studies of healthy, strong adults, Laufer et al1 and Lyons et al2 reported evidence that newer battery-powered devices can stimulate skeletal muscle to levels once considered achievable only by line-powered devices.
A common misconception is that, because batteries provide direct current (DC), battery-powered devices must deliver DC to the patient. This is for the most part inaccurate, the exception being devices used for iontophoresis. Although DC is provided by a battery, electrotherapeutic devices may provide a variety of other waveforms, none or only one of which may be DC. Likewise, line-powered devices receiving alternating current (AC) from the wall outlet do not deliver true 60 Hz AC to the patient. Rather, the alteration of battery-provided DC and household AC to other therapeutic waveforms occurs through the use of rectifiers, transformers, filters, and regulators within electrical devices. These take an input current and modify the current into a waveform to be used for therapeutic purposes.
Therapeutic electrical devices generally consist of two ...