electrical stimulation ( pain )

Mechanisms of electrical stimulation for pain relief ( pain gating )

Explanation	How to achieve the effect
Segmental inhibition ( peripheral aspect of pain gate: stimulation of beta fibres → inhibitory interneuron in spinal cord stimulated )  Sensory perception  Psychological effects  from A beta fibre stimulation	High freq  Intensity: to sensory threshold

Mechanism of electrical stimulation for pain relief ( endogenous analgesia )

Explanation	How to achieve the effect
Stimulation of A delta fibres/ C fibres → posterior horn interneurons activated → encephalin release → endorphin release	Low freq  Intensity: intensity to 2-3x sensory threshold

Aspects of electric current manipulated for desired effect ( pulse duration )

	Effect
Pulse duration ( ms/ microseconds ) * duration curve slide	Higher pulse duration: amplitude needed to stimulate sensory + motor + pain nerves is similar  At lower pulse duration: amplitude needed to stimulate sensory nerves only is lower → good for acute pain relief ( X stimulation to pain nerves or motor nerves bc they need higher pulse amplitude )

Aspects of electric current manipulated for desired effect ( frequency)

Longer the pulse duration → smaller the number of pulses per sec ( lower frequency )

Aspects of electric current manipulated for desired effect ( amplitude )

Total no of nerve fibres recruited 

Increased sensory or motor response caused by larger number of nerve fibres stimulated 

Accommodation: 

Ability of nerve/ muscle to adapt to slowly increase current intensities 

→ overcome by increasing intensity 

Sensory > motor nerves → increase intensity slowly for sensory nerves/ change waveform used

Intensity: how far into the waveform to hit peak amplitude

Aspects of electric current manipulated for desired effect ( phase )

Monophasic: 

1. Current moves in one direction 

2. More excitation under -ve active electrode 

3. Higher chance of skin irritation from charge building

Biphasic: 

1. Current moves in 2 directions → X charge accumulation 

2. Less excitation

Principle of electrical stimulus in pain relief

1. Electrical current stimulating action potential in nerves 

2. Stimulus must be > 15 mV to overcome threshold of action potential 

3. Ease of nerve membrane stimulation: strength ( amplitude ) + duration of stimulus 

Treatment parameters of TENs ( acute pain ) 

Intensity	Until tingling felt
Duration	50-100 μs
Frequency	80-200 Hz/ pps

Treatment parameters of TENs ( chronic pain ) 

Intensity	To tolerated
Duration	150-200 μs
Frequency	1-10 Hz/ pps

Treatment parameters of TENs ( acute + chronic pain )

Mode	Conventional: pain relief + accommodation likely  Modulated:  discomfort → pain relief Burst: some discomfort + less accommodation
Durtion	Conventional: 30-60 mins/ continuous  Modulated: 20-30 mins  Burst: ?
Position of electrodes	Over site of pain  Trigger points  Along peripheral nerve length  Same dermatome/ myotome

Shape + phase

Biphasic + symmetrical/ asymmetrical

Clinical application of TENs

1. MSK pain ( low back + neck/ knee + shoulder pain ) → before exercise 

2. primary dysmenorrhea

3. Chronic pain 

4. Intractable angina 

5. Painful procedures 

6. Labour 

Interferential therapy characteristics

1. Frequency: higher than TENs bc needs to get sufficient intensity of current w/ low frequency in deep tissue 

2. 2 currents at different frequencies → interfere to produce beat frequency → triggers AP in deep tissue

3. Frequency of beat frequency: difference bwt 2 original frequency  

4. Sweep mode: oscillation bwt pre-set frequencies over time 

5. Higher frequency → lower skin impedance 

Prescription parameters of IFT ( acute )

Frequency	High ( 80-150 Hz)
Intensity	Low
Treatment time	10-20 mins

Prescription parameters of IFT ( chronic)

Frequency	Low ( 1-25 Hz )
Intensity	High
Treatment time	20-60 mins

Electrode placement for IFT

1. Relative to tissue: contra-planar/ coplanar ( for LBP) 

2. Size of electrode: as large as possible 

3. Distance bwt electrodes: small electrodes close: superficial current/ large electrodes apart: deeper flow 

→ smaller electrode to focus current at a motor point 

4. X transthoracic applications 

5. ************ Channels must cross each other w/ target tissue in the middle → e.g. 

Right upper knee: L1; Left upper knee: L2

Right lower knee: L2 ; Left lower knee: L1

Advantage of IFT

1. Targeting deep tissue 

2. Reduction of swelling w/ sweep mode 

3. Reduction of accommodation w/ sweep mode

Procedure for electrical stimulation for pain

1. Educate the patient abt electrotherapy adjunct option + gain initial consent 

2. Check contraindications + precautions ( skin check + test sharp/ blunt ) 

• X put electrodes over areas of low/ high resistance 

low: cuts + abrasions 

High: warts/ scars 

3. Clean skin 

4. Turn machine on w/ intensity at 0 

5. Position patient + apply to patient 

6. Ask when pt first start feeling tingling → turn up intensity until perceptible → desired level 

7. Warnings + final consent → give bell + check after a few minutes that they feel ok 

8. End: turn intensity to 0, remove electrodes, check skin 

Contraindications for electrical stimulation for pain

1. Over pacemakers/ inbuilt stimulator 

2. Transthoracic application 

3. Over carotid sinus 

4. Venous thrombosis/ thrombophlebitis 

5. Pregnancy: pelvic region ( over uterus/ low back ) 

Precautions for electrical stimulation for pain

1. Regular testing by qualified electrician 

2. Warnings + informed consent 

3. Check precautions + contraindications 

4. Test sharp/ blunt 

5. Test machine 

6. Turn machine on w/ intensity at 0 

7. Turn machine power on + off w/ pt X attached 

8. Documentation