PHYSICS FUNDAMENTAL
TENS builds a circuit where human body
(nerves) is part of the circuit
transcutaneous electrical nerve stimulation
PHYSICS EXPLAINED
‣ Nerves transmit signals to the brain via
electrical pulses
‣ Nerves can be affected by externally applied
electrical current
‣ TENS creates a circuit that incorporates the
human body
‣ *** TENS uses low frequency, short duration,
pulsed current
‣ Pulse duration (μs) and pulse rate (Hz) are
adjustable
PHYSIO AIM
Stimulate sensory nerves to facilitate the pain
inhibitory systems for pain relief
PHYSIOLOGICAL EFFECTS
‣ TENS targets different pain inhibitory systems
depending on the settings applied
1. Pain Gating through stimulation of large
diameter sensory nerves Aβ
2. Endogenous Analgesia through
stimulation of small diameter afferent
nerves Aδ or C
‣ Often portable, so can be used while the
patient is moving (ie exercises, walking or
ADLs)
‣ Encourages pain-free movement
PHYSICS TERMS
Electrical current: Flow of electrical charges
Amplitude (Intensity) of current: Maximum strength
of current
Pulsed current: Current is ON and OFF periodically
Pulse duration: Amount of time when pulsed
current is ON
Pulse rate / Frequency: Number of pulses per sec
CONTRAINDICATIONS
Vicinity of uterus in pregnancy ** UNLESS
using directly for assistance with labour.
Over inbuilt stimulator (eg. Pacemaker)
PRECAUTIONS
Circulatory Insufficiency Risk of dissemination Exacerbation of existing conditions Unable to communicate Sensory loss
warning
When having electrical
stimulation you should feel (for
Pain Gating) a mild tingling (for
Endogenous\ Analgesia) a
strong tingling
which may be uncomfortable but not painful. If you feel anything more than this or any pain you must call me
immediately otherwise you may risk skin or
other tissue damage under the electrodes.
Settings/Dosage
AMPLITUDE Gating: Comfortable level of sensory stimulation Endogenous: 2-3x sensory
DURATION OF TREATMENT Gating: 10-20 mins Endogenous: >20 mins
FREQUENCY
Gating: 80-200 Hz (high)
Endogenous: 1-25 HZ (low)
PULSE WIDTH/PULSE DURATION
Gating: 60-100 μs (narrow)
Endogenous: 150-300 μs (wide)
Mode = normal
safety
- Test sharp / blunt Ensure intact sensation
- No metal jewellery/piercings in area
Metals are conductors. They will change electrical fields and current. If jewellery makes contact with a live electrode, current will flow through it to body = electric shock. - Ensure good contact through electrodes. Areas without contact to skin can make contact with other electrical
conductor, allow current to flow and cause electrical shocks. - Turn up intensity gradually, Avoid over-stimulating or burning an area.
Do not move electrodes while
intensity turned up. Possibility of shorting the circuit, allowing current to flow without expected resistance and cause higher current flows. Uneven contact will cause sparks and can burn skin
Check skin for any irritation - under electrodes
With unbalanced current chemicals could accumulate near the electrode. - Use electrodes of the same size
(bipolar application)
Using different sizes of electrodes causes change in current density inside human body that concentrate the evergy over a smaller area.
Why can electric current affect the human body?
Human body is conductor and allows current to flow
inside it. Nerves work based on electricity and can be
affected by applied electric currents.
What is the frequency of periodic pulse current?
Frequency of periodic pulse current, or pulse-rate, is
number of pulses occurring in a second.
What type of current is TENS?
Pulsed and low frequency.
What are the advantages of using small TENS units? It’s portable so can be taken
What are the disadvantages of low frequency currents?
They do not penetrate very deep, so not useful for
deeper structures.
How long might you expect pain relief to last utilising
each of these systems?
Pain gating: short term pain relief.
Endogenous analgesia: longer term relief 6-8 hours, but
need to apply for > 20 mins.
For a repeated pulsed current what is the difference
between “pulse width” and “pulse rate” ?
Pulse width/duration is how long the current flows
during one cycle. Pulse rate is how many cycles there are
during 1 second.
