Practical Approach to

Practical Approach to Pain Gate Theories

Pain pathway • First order neurons Acute pain – A delta Chronic pain – C fibers

• Terminate in dorsal horn – Second order neurons- fibers cross to midline – Spino thalamic tract – fast component – Spino reticulothalamic- slow component

• Conducts through spinal cord , medulla, pons and mid brain • Terminate in thalamus Subin Solomen MPT(m'pal)

Pain gate theory-1

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Pain gate theory-2

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Pain gate theory-3 Raphae nucleus

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Classification of nerve fibers Nerve fibre Function Velocity

Frequency blocking

A alpha 1a

Motor eff Muscle sp aff

120-70

10-50

>50 tetanic

A beta, 11

Mechano receptors

70-30

80-100

>135

A gamma

intrafusal

30-15

NA

NA

A delta

Fast pain

30-12

25-40

>40

B

Pre ganglionic

10-3

1-10

>15

C

Post ganglionic

2-0.5

10-15

>15

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TENS • • • • •

Conventional Tens Acupuncture Tens Burst Tens Intense Tens Dual Tens

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TENS Settings HIGH TENS • • • • • • •

LOW TENS

Conventional Relieves acute pain Rapid onset Rapid offset Frequency >80Hz Pulse width=100-500μs Intensity =12-30mA

• • • • • • •

Acupuncture Relieves chronic pain Delayed onset Delayed off set Frequency =1-5Hz Pulse width=100-150μs Intensity >30mA

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Conventional tens

Cathode

Anode skin

TENS currents

A beta A delta C fibres

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Acupuncture tens

anode

Cathode skin

TENS currents

Aβ Aα

muscle

Muscle contracts

Aδ Subin Solomen MPT(m'pal)

Intense tens

Cathode

Anode skin

TENS currents

A beta

A delta C fibres

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Peripheral mechanisms Tens electrodes skin

Tens currents

Pain Stimulus Impulses generated by Noxious event Subin Solomen MPT(m'pal)

Tens induced Impulses Travel to CNS

For sensory- cathode proximal to anode For motor- anode proximal to cathode

Cathode

Anode skin ++++++ ++++++

-- - - - -- - - - -

-- - - - ----Hyper polarised

X

++++++ ++++++ Depolarized Nerve impulse

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Mechanism of Acute pain relief High TENS (80-100Hz)

Stimulation of Aβ fibers

1

Low TENS (>40Hz)

Blocks Aδ fibers

2

Relieves acute pain Subin Solomen MPT(m'pal)

Low TENS (1-10Hz) 1

Stimulation of A α fibres

Mechanism of chronic pain relief

Causes muscle fibers to contract 4

Muscle twitch

Low TENS (25-40 Hz)

Produces Acute Pain

2 Carried by A δ Fibers

Low TENS (>15 Hz)

Blocks C fibers At spinal level

3 Relieves Chronic pain Subin Solomen MPT(m'pal)

Stimulate C fibers

Descending pain pathway

Static AMF • By Varying frequency of second circuit relative to Constant frequency of first, • It is possible to produce a range of beat frequency deep in the patients tissues • Types – Constant or selective beat frequency ( Base 80, Spectrum 80Hz) – Variable or automatic beat frequency (Base 80. Spectrum 100) • Purpose – To prevent nerve habituation – It can also extend the range of nerve types that can be stimulated Subin Solomen MPT(m'pal)

Dynamic AMF • Vector or scanning • Types 45 degree and 90 degree • 45 degree -By varying the intensity of second circuit relative to the constant intensity of the first • 90 degree – increasing intensity of first while decreasing the intensity of second Or vice versa • Current is varied from 50 to 100 % • Purpose – – 45 degree large area – 90 degree diffused or cannot be localized Subin Solomen MPT(m'pal)

Frequency Knob 2 KHz • Motor stimulation • Young age

4 KHz Pain relief Old age

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Frequency Sweep In the classic ‘triangular’ sweep pattern, the machine gradually changes from the base to the top frequency, usually over a time period of 6 or3 or 1sec In the example illustrated, the machine is set to sweep from 90 to 130Hz employing a triangular sweep pattern. All frequencies between the base and top frequencies are delivered in equal proportion.

(A) Triangular sweep pattern

Subin Solomen MPT(m'pal)

Frequency Sweep This produces a very different stimulation pattern in that the base and top frequencies are set, but the machine then ‘switches’ between these two specific frequencies rather than gradually changing from one to the other. The diagram illustrates the effect of setting a 90 – 130Hz rectangular sweep.

(B) Rectangular Sweep Pattern

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(or step) sweep

Frequency Sweep There is a clear difference between Rectangular & trapezoidal– even though the same ‘numbers’ are set. One will deliver a full range of stimulation frequencies between the set frequency levels and the other will switch from one frequency to the other.

(C) Trapezoidal Sweep Pattern

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Acute pain TENS

IFT

• Stimulate A β(80 upto100 HZ) • Triangular – Base 80, Spectrum 100 Hz • Block A δ(>40 Hz) OR – Base 41 , Spectrum 60 Hz

• Rectangular – Base 42,Spectrum 100 Hz

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Chronic Pain IFT TENS • • • •

• Triangular

Stimulate A δ(26-40Hz) Stimulate Aα(1-10Hz) Block C (>15Hz) Stimulate C(10-15Hz)

– Base 26, Spectrum 39 Hz OR – Base 1 spectrum 10 HZ OR – Base 16 spectrum 26

• Rectangular – Base 5, Spectrum 30 Hz or – Base 5, spectrum 20 Hz or – Base 20, spectrum 30Hz

• Trapezoidal – Base 5, Spectrum 30 Hz Subin Solomen MPT(m'pal)