Electrotherapy Flashcards
What is TENS and what does it aim to do?
A method of electrical stimulation which aims to provide a degree of symptomatic pain relief by exciting sensory nerves, thereby stimulating either the pain gate mechanism and/or the opioid system.
Different methods of applying TENS relate to different physiological mechanisms.
What does TENS stand for?
Transcutaneous electrical nerve stimulation
What are the two primary pain relief mechanisms
Pain gate mechanism
Endogenous opioid system
What is the pain gate mechanism?
Nocioceptors send pain signals to dorsal horn of SC through a delta or C fibres.
If A-beta fibres are excited, these can close the gate, reducing the transmission of pain signals.
A beta fibres appreciate being stimulated at a relatively high rate.
What is the endogenous opioid system?
Stimulates A delta fibres which respond to a much lower rate of stimulation.
This activates the opioid mechanisms.
Opioid peptides (encephalin) are released which bind to the A-delta fibres, reducing the pain transmission in the spinal cord.
Reduces activation of noxious sensory pathways.
What does a burst mode stimulation aim to do?
Stimulate both nerve types at the same time (A delta and A beta).
Types of TENS output
- traditional TENS (high freq. TENS)
- acupuncture-like TENS (low freq. TENS)
- brief intense TENS
- burst mode TENS
- modulation mode TENS
What does traditional TENS involve?
→ Uses stimulation at a relatively high frequency (90-130Hz) and employs relatively narrow (short duration) pulses (start at 100ms)
→ Stimulation delivered at ‘normal’ intensity ( should not be uncomfortable)
→ 30 mins
→ Limited “carry over” effect
Useful technique - short term pain relief may enable patient to comply with treatment techniques.
USEFUL FOR TREATING ACUTE PAIN
What does acupuncture-like tens involve?
→Uses a lower frequency stimulation (2-5Hz) with wider (longer) pulses (200 - 250ms).
→ Intensity used is greater than traditional TENS (strong tingling sensation)
→ 30 mins or more
→ Onset of pain relief slower than traditional mode
→ A-delta stimulation and descending inhibition
→ Once sufficient opioid has been released, it will keep working after stimulation has ended - “carry over” may last several hours
→ Many patients find stimulation at low frequency at intervals throughout the day is an effective Strat.
USEFUL MODE FOR TREATING CHRONIC PAIN.
What is involved in burst mode TENS?
Traditional TENS but the burst mode is switched in, therefore:
interrupting the stimulation outflow at a rate of 2 - 3 bursts / second.
The stimulation intensity will need to be relatively high, similar to Acupuncure TENS.
Proposed that the application of BURST mode TENS can effectively stimulate both the pain gate and opioid mechanisms simultaneously.
What is modulation mode TENS?
The machine delivers a less regular pattern of TENS stimulation, in an attempt to reduce or minimise the accommodation effects of regular, patterned stimulation.
How to decide stimulation intensity?
High frequency - traditional TENS - ‘definetly there but not painful’
Low frequency - acupuncture-like TENS - ‘ strong but not painful’
Where should electrodes be applied in TENS?
- dual channel output
- target stimulus at appropriate spinal cord level - place electrodes either side of the lesion or pain areas
What is ultrasound?
A form of mechanical energy which causes the vibration of molecules to produce sound.
It is used to influence soft tissue healing and repair.
SOUND WAVES ARE LONGITUDINAL WAVES OF COMPRESSION AND RAREFACTION WHICH CAUSE TISSUE CELLS TO VIBRATE.
What are ultrasound frequencies?
Beyond 20,000Hz and are beyond the normal hearing range in humans.
What is the thermal and non-thermal effect of ultrasound?
Thermal effect = vibrating cells generate heat
Non-thermal effect = generated energy can be absorbed by the tissues
- thought to aid early repair + tissue healing due to effect on cellular function.
What are the properties of US waves?
Frequency = number of times cells vibrate in a complete cycle in 1 second.
Wavelength = distance between 2 equivalent points on the waveform
Velocity = speed that the wave travels through the medium
How does absorption and attenuation of U/S in the tissues work?
→ Tissues with a high water and low protein content (fat) absorb less U/S which reduces the potential for therapeutic effect
→ Tissues with low water content and high protein content (tendons + ligs) absorb more U/S which increases the therapeutic effect.
What are the therapuetic effects of US (non-thermal effect - PULSED MODE)
Pulsed mode - stimulates cavitation and acoustic streaming in the tissues and body fluids, which excites the tissue cells.
ACUTE AND SUB-ACUTE CONDITIONS
What is cavitation?
Formation of gas bubbles in tissues + body fluids
What is acoustic streaming?
Eddying (move in a circular way) of fluids around a vibrating structure - increases permeability of cell membrane + increases cell metabolism (helps flush out things not needed).
What are the therapuetic effects of US (thermal effect - CONTINOUS MODE)
Continuous mode - stimulates beneficial heating of dense collagen in tissues and can also use hyperaemia (increase in blood flow).
Also promotes relaxation and can penetrate deeper tissues.
MOST EFFECTIVE FOR CHRONIC CONDITIONS.
How does US aid tissue repair?
→ US increases the efficiency of the repair process
→ Inflammatory phase of tissue repair - US stimulates mast cells, platelets, WBC and macrophages - encourages cells to progress to the proliferation phase
→ US stimulates fibroblasts in prolferation phase + endothelial cells and muofibroblasts to encourage scar tissue formation.
→ During remodelling, collagen fibres change from immature type 3 to mature type 1 to increase tensile strength and mobility of the tissue - THOUGH US INFLUENCES COLLAGEN FIBRE TYPE AND ORIENTATION
Other uses of US other than tissue healing?
Low intensity pulsed US is thought to stimulate fracture healing
US also stimulates healing of chronic wounds, e.g. cenous ulcers and pressure sores.
