Second semester of our Masters of Physiotherapy degree and the topic of electrophysical agents (EPAs) has emerged; in particular electrical stimulation (estim) for therapeutic purposes. All estim devices should produce some physiological response, however this may not be the best response. Therefore, we are focusing on the importance of the safe and effective use of these devices in achieving the desired therapeutic effects to optimise treatment. There are many devices out there, all with specific indications for use which relate to the therapeutic effects desired. It is our job as future physiotherapists to be able to select the best device for all clinical scenarios.
To get our heads around this, we were all given different EPA devices to research.
Our topic is high voltage pulsed current (HVPC), also known as:
· high voltage stimulation (HVS)
· high voltage galvanic stimulation (HVG)
· direct current stimulation (DC)
There are many names to describe this device, but it pretty much includes anything with the terms high voltage current. Although the term galvanic is used often, the term is incorrect as the current is pulsed, not constant.
In the upcoming weeks, we will do our best to explore and discuss the relevant issues relating to HVS to ensure the safe and effective application of this device. . But before we get into more specifics, let’s quickly touch on the history of HVPC.
History
The first high voltage stimulator was developed by Bell Telephone Laboratories in 1945 (Belanger, 2002). It was noted that by decreasing the pulse duration and increasing the voltage, deep tissues could be stimulated without producing tissue damage.
HVS has been clinically used over the last 45 years with the first therapeutic application in humans being reported in 1971 by Thurman and colleagues (Belanger, 2002).
Major interest in HVS began a few years after this, being advertised as high-voltage galvanic current, believed to utilise galvanic current, which is continuous or direct in nature. However, it soon became known as high-voltage pulsed current as the basic current type used in this therapy is pulsed (Belanger, 2002).
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| HVPC - Past to present |
The first HVS machines to be manufactured were big and bulky. However, as time has passed and technology has dramatically evolved, the devices have become much smaller, compact and also portable. Over the years HVS machines have become more flexible in the selection of treatment parameters with an unlimited range of available settings for on and off times.
Over time the use of HVS has diminished as other devices with more specific applications such as TENS and Interferential therapy has evolved (Knight et al, 2007). It is because of this non-specific application that it is not used often these days because other types of estim are more effective in performing functions such as edema management, muscle re-education and spasm reduction and pain modulation.
Over time the use of HVS has diminished as other devices with more specific applications such as TENS and Interferential therapy has evolved (Knight et al, 2007). It is because of this non-specific application that it is not used often these days because other types of estim are more effective in performing functions such as edema management, muscle re-education and spasm reduction and pain modulation.
As we stated earlier, HVPC machines used to be big and bulky, tormenting physiotherapists and their assistants at every use. Unlike other devices, HVPC uses 4 small ‘active’ electrodes and an ‘ineffective or dispersive’ large electrode to complete the circuit current. The electrodes are usually made of carbon rubber for durability and required the use of wet sponges on application.
The device has a polarity switch, giving the physio the option of placing positive (+) or negative (–) electrodes over the affected area depending on treatment goals. For example, it was believed (–) polarity over an injured area helped reduce edema (Snyder et al., 2010).We will discuss this further in the upcoming posts.
Another difference or characteristic of HVS distinguishing it from other devices is the design of the output channel leads – 2 output leads at one polarity are each used in conjunction with a single lead of opposite polarity (Robinson et al, 2007). This arrangement of leads reflects single channel stimulation however some HVS devices using this arrangement are classified as having 2 channels (Robinson et al, 2007).
Other distinguishing features setting HVS apart from other etsim devices include:
· Current: volts rather than amps
· DC or direct current rather than AC or alternating current used in TENS
o This is a distinguishing factor that aids in its use for wound healing
· Monophasic waveform compared to bi-phasic waveforms used in TENS
· deeper tissue penetration facilitating a more comprehensive physiological response
Not to leave you hanging over the cliff, but it’s looking like a busy week at uni. We hope to post a blog within the next week regarding HVPC parameters, applications and more. Stay tuned!
A & M
References:
· Bèlanger, A. (2002). Evidence-based guide to therapeutic physical agents. Lippincott Williams & Wilkins. pp. 109-122
· Knight, K.L. & Draper, D.O. (2007) Therapeutic modalities: the art and the science. Lippincott Williams & Wilkins.
· Robinson, A.J. & Snyder-Mackler, L. (2007) Clinical Electrophysiology: electrotherapy and electrophysiological testing, 3rd Ed. Lippincott & Wilkins
· Snyder, A.R., Perotti, A.L., Lam, K.C. & Bay, R.C. (2010). The influence of high-voltage electrical stimulation on edema formation after acute injury: a systematic review. Journal of Sport Rehabilitation, 19, 436-451. PMID: 21116012
Very good introduction. It has everything I had hoped for in a blogpost. Well done. You need a reference list or link to your sources. You should reference your statement that TENS etc are more effective than HVPG stim. CY
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