Last blog, we quickly mentioned how we as physiotherapists can actually slow down the rate of healing or possibly cause more damage. It is thus very important that we as physiotherapists are properly educated regarding the use of electrophysical agents as they can be a danger to some of our patients. Don’t forget, 1 of the 4 absolute ethical principles of the Australian Physiotherapy Association (APA) is to cause no harm.
Please take special note to not apply HVPC if any of the following are present:
· cardiac pacemakers, all electronically implanted devices – may interfere with normal device functioning
· malignancy – possible risk of enhancing the spread of the tumour
· broken or anaesthetic skin – risk of skin burns or irritation
· thick scarring or adipose tissue – have high electrical resistance, restricting current flow and therefore the effectiveness of treatment
· pregnancy – possible risk of affecting normal fetal growth and development
· advanced heart disease or arrhythmias
· undiagnosed pain
· epilepsy
The device should not be applied:
· trans-cerebrally – that is leg to arm, arm to arm, anterior to posterior or left to right sides of the chest wall. We do not want any conduction going through the heart…not good!
· over the carotid sinus
As with the use of all estim devices, safety precautions must be followed including:
· hand washing before and after treatment
· informing the patient about the device and gaining their consent
· performing a sensory discrimination test on the patient
· testing the device on yourself to ensure appropriate function
· cleansing of the skin prior to use
· appropriate electrode position
· ensuring the patient stays awake at all times during treatment
· A bell or alerting device left with the patient when left alone
The patient can expect to feel the following sensations with the associated frequencies used for (Belanger, 2002):
· wound repair, acute edema reduction
o prickling pins and needles over the smaller electrodes
o little sensation over the large dispersive electrode
· acute pain reduction
o moderate prickling pins and needles
· muscle contraction
o moderate prickling pins and needles progressing to a strong contraction
The patient should not feel uncomfortable or any pain at any time throughout the treatment. It is vital the patient informs the therapist if this occurs so the cessation or moderation of treatment can occur immediately.
Considerations for Use
The type of electrode used with HVS, as well as electrode placement and arrangement depends on the treatment area as well as the type of therapy/ therapeutic effect required. As with the use of all estim devices the correct electrode placement is essential to ensure the current flows through the target tissue.
Electrode types (Belanger, 2002):
· Rubber carbon electrodes
· Stainless-steel hand held probes
· Sock or electromesh glove electrodes
Electrode arrangement:
HVG uses 4 small ‘active’ electrodes and one ‘ineffective or dispersive’ large electrode to complete the current circuit.
One large, dispersive electrode combined with any of the following (Belanger, 2002):
 |
| Carbon rubber electrodes with moist sponge |
· 1, 2, or 4 active electrodes
· 1 handheld active electrode
Electrodes should be used with:
· Electroconductive gel
· Moist sponge or gauze
Because HVS machines produce monophasic waveforms, the output polarity of electrode leads does not change during stimulation. Therefore, most devices allow the user to select and manually switch the polarity of the output leads.
A polarity switch is used to make the active electrode/s either positive or negative:
· Positive electrode:
o placed over the wound
o attracts macrophages and promotes epithelial growth.
o Blood clot formation around the wound
· Negative electrode:
o placed on the skin surface closest to the wound
o increases blood flow
o stimulates fibroblastic growth, collagen production, epidermal cell migration
o inhibits bacteria growth
Most treatment begins with negative polarity to encourage any blood clots to dissolve and to increase inflammatory by-products, which help to heal the damaged tissues.
Monopolar or bipolar techniques may be used:
· Monopolar: wound healing, when treatment is over a large area such as edema reduction
· Bipolar: muscle contraction, or chronic pain
Now that all of the safety issues have been considered, what are the advantages and disadvantages associated with a HVS device?
Advantages of HVS include:
· Safety
o constant voltage
o less pulse charge with shorter pulse duration
· shorter pulse duration
o enhances patient comfort
o reduces skin impedance resulting in optimised tissue penetration
clinically versatile in function and discrimination of these responses is easy to obtain
o sensory effects
o motor effects
o pain reducing effects
· may be used with water
o minimal chemical effects at the skin surface
o no salt is needed to neutralise skin surface chemical reactions
· promotes wound healing
· can be applied to immobilised body part
Disadvantages of HVS include:
· lower average current
o cannot produce as strong a contraction as NMES
· lack of evidence regarding some of its uses
o twin peak current
o use for muscle contraction
Unforunately, we are nearing the end of our informative blog on HVPC. Before we finish up on the topic, we will touch on how to get your hands on a HVPC device for your physiotherapy clinic or person use. We will quickly mention that there is an informative handout on HVPC which we have referenced throughout the blog. Please be sure to have a look if you are interested: https://arizonadme.com/uploads/Instructional_Handout_Sterling_Impulse_HVG_Part_2.pdf
Until next time,
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.
