GALVANIC MUSCLE STIMULATORS
Galvanic Muscles Stimulators
Galvanic stimulators were first developed in the 1940’s and became popular in the mid-1970’s. Sometimes galvanic stimulators are referred to as direct current or uninterrupted direct current stimulators. The galvanic stimulator was one of the first stimulators used for horses in the early 1960’s. Due to this early use, galvanic stimulators have been referred to as ”the muscle stimulator” in past equine literature.
The waveform of galvanic devices is monophasic, meaning it has only one peak that is repeated over time. Galvanic stimulation uses direct current to create a unidirectional, continuous current.
Galvanic stimulators are used to produce ionic movement within the tissues toward one of the electrodes. This accumulation of ions to one polarity results in reflex vasodilatation due to the stimulation of the sensory nerve endings. However, the ion accumulation under the electrodes can create an unpleasant stinging sensation.
Damage to tissue, typically skin, can be caused by galvanic stimulators, even when used at low amplitudes because of the electrolytic reactions that occur when the current passes through the skin. The extent of damage is also affected by the length of time of the treatment, and the tissue impedance.
TYPES OF WAVEFORMS
Galvanic treatments are typically performed for 15 minutes or less at amplitudes of 5.0 mA. Electrodes must be of the size that current densities do not exceed 0.1 to 0.5 mA per cm squared of electrode surface area.
High-Voltage Pulsed- (Galvanic) Current Stimulators (HVPC)
Due to the limited use of galvanic stimulators, a new class has emerged called High-Voltage Pulsed-Current Stimulators (HVPC). Sometimes the term “galvanic” is still included in the name, however these stimulators are not direct current devices so the term is inaccurate.
HVPC stimulators typically generate a twin-spike monophasic pulsed waveform. Due to the monophasic waveform, the output polarity does not change during stimulation. Therefore, some forms of pulsed monophasic currents can have similar chemical effects to DC. However, very short duration monophasic pulsed currents do not always produce the negative electrochemical effects on the skin. Timing between the twin spikes can be reduced so that the two waveforms overlap, giving a stronger stimulation sensation. Switches exist on some devices to allow the user to switch the polarity of the electrodes.
TYPES OF WAVEFORMS