Indications for Use

Last blog post we discussed the parameters that are generally used for HVPC. Today, we will introduce you to the indications for HVS use.

The consensus is that HVS may be applied alone or in combination with other modalities to treat a wide range of clinical pathologies. HVS stimulates excitatory responses (Knight et al, 2007) of:

·         Sensory and motor nerves

·         Autonomic nervous system (ANS)

·         Pain fibres

The main functions of HVS are:

·         Promote wound healing

Wound healing is possibly the best indication for HVS use. HVS increases circulation and perfusion to the injured tissues, providing the damaged tissues with oxygen and nutrients. At the same time, waste and oedema are being removed, which facilitates the overall healing process and promotes wound healing. As the current flows through the body to complete the circuit between the dispersive pads, it penetrates tissues causing ionic movement within the body to attain the desired physiological effects (Belanger, 2002):

§  Increase fibroblast numbers, therefore collagen synthesis

§  Inhibit bacterial growth

§  Block SNS, therefore increasing blood supply to the tissue and healing capacity

·         Reduce edema

Edema formation is due to leakage of plasma proteins to the interstitial spaces of cells after injury, resulting in fluid accumulation in the area. HVS is thought to:

§  decrease the permeability between cells membranes and the interstitial space, especially when negatively charged electrodes are over the injury site (i.e. repels negatively charged plasma proteins)

§  produce muscle contraction which stimulates the lymphatic system and promotes the movement of fluid, hence reducing edema (Knight et al, 2007)

NMES may be a better choice for resolving edema as it can produce stronger muscle contraction and therefore increased muscle pumping action response to facilitate edema reduction (Knight et al, 2007).

There are 2 protocols that may be used to assist edema reduction (Belanger, 2002):

§  Water immersion technique: apply a negative polarity, but should be applied as soon as possible after injury

§  HVS stimulation accompanied by RICE – rest, ice, compression, elevation

·         Pain modulation

HVS modulates pain via the gating system:

§  Blocking pain nerve fibre conduction

§  Releasing endorphins

§  Reducing/blocking neuritis

However it must be noted that other estim devices, such as TENS achieve this analgesic effect more efficiently (Knight et al, 2007).

·         Muscle re-education

HVS has also been associated with muscle re-education, however this belief is controversial.

Muscle re-education may be achieved by stimulating muscle contraction via:

§  Muscle twitch – 1-10Hz pulse frequency

§  Tetany or sustained contraction – 30-80Hz pulse frequency

Those who disagree with the notion HVS can be used for muscle education have a valid theory. As we have previously mentioned, HVS uses a twin peak, pulsed, monophasic current. Due to the unique current, the peak may not be long enough in duration to depolarize muscle fibres. Which theory is right? We will let you decide, but we tend to agree with the latter – HVS is not effective for muscle re-education. There has not been any research supporting either side, it simply comes down to theroy. 

NMES is the better option for muscle stimulation as it can produce stronger muscle contraction than HVS anyways (Knight et al, 2007).

To achieve these effects, specific dosage parameters need to be set according to the desired therapeutic effects. The amplitude may range between 1-500V; however, whatever the patient perceives as most comfortable is what should be implemented. The patient should be comfortable and pain free at all times throughout treatment.

Continuous, higher frequencies of 1-200 pulses per second (Belanger, 2002) are associated with:

·         Wound Healing

Reversed electrode polarity is recommended for wound healing with a treatment time ranging from 10 minutes to 1 hour depending on available clinic time.

·         Analgesia or pain modulation

Recommended treatment time ranges from 10 minutes to 2 hours depending on available clinic time

Pulsed, lower frequencies of 30-60 pulses per second (Belanger, 2002) are associated with:

·         Muscle strengthening

o   Frequency must be high enough to produce a tetanic muscle contraction

·         Muscle spasm relaxation

o    Via muscle fatigue effects

·         Oedema

Treatment time ranges between 5 and 30 minutes, but can be gradually increased as therapeutic improvements occur with successive treatments (Belanger, 2002).

As with all physiotherapy modalities, it is important to have sound research supporting its use; after all, physiotherapy is synonymous with evidence based practice. We will present some supporting literature in our next blog post. Check back soon!

A & M 

References:

Bèlanger, A. (2002). Evidence-based guide to therapeutic physical agents. Lippincott Williams & Wilkins. Pg 109-122

Knight, K.L., & Draper, D.O. (2007) Therapeutic modalities: the art and the science. Lippincott Williams & Wilkins.

https://arizonadme.com/uploads/Instructional_Handout_Sterling_Impulse_HVG_Part_2.pdf

http://www.flickr.com/photos/sthtbs/74026457/

Parameters

Hello everyone and welcome back! A big thanks to everyone who viewed and commented on our blog. As promised, we are back and ready to talk more high voltage pulsed current (HVPC). Last week we discussed a little bit of the history and physical presentation of the HVPC device. Today, we will introduce you to some of the parameters specific to HVPC.

As its name suggests, high voltage stimulation (HVS) uses high voltage current, which is the main difference between HVS and other estim devices. Due to the lower impedance associated with high voltage, HVS is able to penetrate the skin more easily. Because of this, the depth of tissue penetration is proportional to the current pulse amplitude (Belanger, 2002). Up to 500V may be used to facilitate wound and tissue healing, but to also produce analgesia and muscle contraction.

HVS can be used to produce both a mechanical contraction and a chemical change within the body. This is achieved via delivering a short duration (microsecond) micramperage current, being driven by a high voltage current, to the symptomatic region of the body (Belanger, 2002). Again, higher peak currents combined with short pulse duration allows for a deeper tissue penetration.

The dosage associated with HVS requires specific parameters to be set according to the desired therapeutic effects. The amplitude may range between 1-500V (Belanger, 2002); however what the patient perceives as most comfortable is what should be implemented. The patient should be comfortable and pain free at all times throughout treatment.

The most widely accepted parameters for HVS use include (Belanger, 2002):

·         Waveform: Monophasic

A twin peak pulse is used and may accumulate a weak charge in the tissues. However, the second peak is unlikely to be effective, as the second peak occurs within the refractory period – a period where no physiological responses can occur. The monophasic twin peak waveform is perceived to provide more comfort for the patient. Here's a comparison of the waveforms:

High voltage monophasic twin peak pulsed current

Biphasic pulsed current produced by AC devices such as TENS

·         Amplitude: Volts 

HVS utilises low amperage (microamps) which allows for deeper penetration of the tissues, with less risk of irritating or burning the skin and other tissues.

·         Pulse duration: 20-200 µs

HVS machines are called micropulse stimulators, hence the most correct name for these devices is high voltage (pulsed) stimulators (HVS). The pulse duration is fixed on most HVS devices by the manufacturer and cannot be altered by the operator. The output of HVS devices is dependent on the pulse interval – the longer the pulse interval the smaller the output. As the pulse duration decreases, higher voltage or current is needed to produce a response. Therefore, output may be as high as 300-400mA, but due to the longer pulse interval may be as low as 1.5-2mA.

·         Frequency:

o   Low frequency stimulators: 0-150Hz.

o   High frequency stimulators: greater than 150Hz

120-150Hz is the most common used range with clinical effects seen in frequencies up to 400Hz (Belanger, 2002). There is little evidence to indicate that frequencies greater than 800Hz provide additional therapeutic benefits (Belanger, 2002). Clinical effects may even be lost as the pulses are delivered during the refractory period where no response can occur. 

The combination of this very short pulse duration and high peak current, but overall low total current per second (microcurrent) allows a relatively comfortable stimulation sensation for the patient.  Stay tuned for more, when we next discuss what therapeutic effects HVS is capable of achieving.

Until next time.... A & M.

References:

Bèlanger, A. (2002). Evidence-based guide to therapeutic physical agents. Lippincott Williams & Wilkins. Pg 109-122

https://arizonadme.com/uploads/Instructional_Handout_Sterling_Impulse_HVG_Part_2.pdf

http://nervestudy.com/topics/estim.htm

Introduction & History

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).



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.

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:

·         https://arizonadme.com/uploads/Instructional_Handout_Sterling_Impulse_HVG_Part_2.pdf

·         Bèlanger, A. (2002). Evidence-based guide to therapeutic physical agents. Lippincott Williams & Wilkins. pp. 109-122

·         www.denmedpro.com

·         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, 3^rd 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