Electrical Stimulation

1. ELECTRICAL
STIMULATION
AVANIANBAN CHAKKARAPANI
1

2. Outline
 Diagnosis
 Therapeutic
2

3. Review: Polarization & Action
Potentials
 Stimulation requires a polarized
membrane (between inside and
outside of nerve membrane).
 More positive ions than negative
ions outside nerve and more
negative ions than positive ions
inside membrane
 When polarized, membranes have
a potential of −70 to −90 mV
between inside and outside of
membrane
3

4. Review: Polarization and Action
Potentials
 Nerve action potential eventually causes
 An ascending sensory impulse to the brain
Or
 A descending muscle action potential
 Muscle action potential causes muscle
contraction.
4

5. Review: Polarization and Action
Potentials
 Nerve repolarizes
quickly.
 Absolute refractory
periods vary from 0.4
to 2 msec
 Depends on specific
nerve
5

6. Diagnosis
 Faradic Galvanic Test
 Measurement of Rheobase and Chronaxie
 Strength Duration Curve
 Nerve Conduction Velocity Studies
6

7. Faradic Galvanic Test
 Faradic stimulus evoked no response in
denervated muscle.
 Galvanic stimulus produce sluggish response.
 Based on various researches it has been
shown that the reaction to FG test applied to
muscle are correctly interpreted only in 50% of
cases.
 This test is inaccurate and unreliable.
7

8. Measurement of Rheobase and
Chronaxie
 Rheobase: minimum current for infinite
duration(in practice 100msec or more) will
cause contraction.
 Chronaxie: minimum time for which a current
of intensity twice rheobase will cause
contraction.
 Both are increased in denervated muscle.
 These values are greatly varies with few
variables like temp, blood supply, electrode
size and skin resistance.
8

9. NORMAL VALUE OF RHEOBASE
OF DIFFERENT MUSCLE
Deltoid 14 volts, 5mA
Triceps 18 volts, 5mA
Abductor digiti minimi 30volts, 8mA
Frontalis 14volts,4mA
9

10. FACTORS AFFECTING
RHEOBASE
 Resistance of skin and subcutaneous tissue
 Edema and inflammation
 Ischemia and underlying pain
 Temperature variation
 Position of electrode
 Amount of subcutaneous tissue
 Degeneration
 Deneravtion
 Partial denervation generally produce no changes
in rheobase.
 Re-innervation can show a sharp rise in rheobase
which indicates clinical recovery.
10

11. NORMAL VALUE OF
CHRONAXIE OF DIFFERENT
MUSCLE
Muscle Constant voltage Constant current
Deltoid 0.01ms 0.1ms
Abductor digiti minimi 0.04ms 0.2ms
Tibialis anterior 0.04ms 0.1ms
11

12. FACTORS AFFECTING
CHRONAXIE
 Texture of skin
 Ischemia
 Oedema
 Fatigue
 Position of stimulating electrode
 Denervation
 Partial denervation
 Re-inervation
 Nerve root lesion
 Peripheral neuropathy
 Myopathy (No significant change)
12

13.  Strength duration curve is a graph between
electrical stimuli of different intensities and
recording the time needed by each stimulus to
start the response.
 S-D curve should be plotted after 20th
day of
injury/lesion.
 After 21st
/22nd
day, regeneration of nerve will start,
generally it take about 270 days to regenerate.
 The purpose of S-D curve plotting is to know
whether the stimulated muscle is innervated,
denervated or partially denervated.
 There are also other method for this purpose like
EMG and NCV.
Strength Duration Curve
13

14. APPARATUS
 The apparatus with rectangular impulses of
different duration.
 Impulse with duration of 0.01, 0.03, 0.1, 0.3,
10, 30, 100, 300 ms are required.
 The stimulator may be of either the constant
current or constant voltage type.
 The constant current stimulator was thought to
produce the more accurate result but constant
voltage stimulator is rather more comfortable
for patient.
14

15. STRENGTH DURATION CURVE
15

16. Normal innervation
 The S-D Curve is of this typical shape
because the impulses of longer duration all
produce a response with same strength of
stimulus, irrespective of their duration, while
those of shorter duration, require an increase
in the strength of the stimulus each time the
duration is reduced.
 The point at which the curve begin to rise is
variable, but is usually at a duration of impulse
of 1 ms with constant current and 0.1 ms with
constant voltage stimulator.
16

17. 17

18. Complete Denervation
 S-D Curve of complete denervation is when
duration of impulse is 100 ms or less, the
strength of the stimulus must be increased
each time the duration the duration is reduced
and no response is obtained to the impulse of
very short duration.
 So the curve rises steeply and is further to the
right than of normally innervated muscle.
18

19. 19

20. Partial Deneravation
 S-D Curve of partial denervation is the impulses of longer
duration can stimulate both innervated and denervated
muscle fibers, so a contraction is obtained with a stimulus of
low intensity.
 As impulse are shortened, the denervation fibers responds
less readily, a stronger stimulus is required to produce a
perceptible contraction and the curve rises steeply like that of
denervated muscle.
 With the impulses of shorter durations, the innervated fibers
responds to a weaker stimulus than that required for the
denervated fibers.
 Kink in S-D Curve is seen at the point where two section
meet.
 The shape of curve indicates the proportion of denervation.
 A kink appears in the curve and as reinnervation progresses.
 Progressive denervation is indicated by the appearance of a
kink, increase in the slope and shift of the curve to the right.
20

21. 21

22. EQUIPEMENT REQUIRED FOR
S-D CURVE
 Low frequency generator with varying pulses
from 0.02 to 1000ms.
 Moist saline pad
 Electrodes
 Leads
 Bandage
 Plastic protactors
22

23. ADVANTAGES OF S-D CURVE
 It is simple, reliable and cheaper.
 Indicate proportion of denervation.
 Less time consuming.
23

24. DISADVANTEGES OF S-D
CURVE
 In large muscles, only proportion of fibers may
respond hence picture is not clearly shown.
 It’s a qualitative rather than quantitative
method of testing innervation.
 It won’t point out the site of lesion.
24

25. Nerve Conduction Velocity Studies
 Nerve conduction velocity (NCV) is a test to
see how fast electrical signals move through a
nerve.
 Surface electrodes are placed on the skin over
nerves at different spots. Each patch gives off
a very mild electrical impulse. This stimulates
the nerve.
25

26. Nerve Conduction Velocity Studies
 The nerve's resulting electrical activity is
recorded by the other electrodes.
 The distance between electrodes and the time
it takes for electrical impulses to travel
between electrodes are used to measure the
speed of the nerve signals.
 Electromyography (recording from needles
placed into the muscles) is often done at the
same time as this test.
26

27. THERAPEUTIC/REHABILIT
ATIVE
Neuro Muscular Electrical Stimulation
27

28. Muscle Fibre Types
 MOTOR UNIT - AHC + α motor neurone
+ muscle fibres.
28

29. Muscle Fibre Types
29

30. Muscle Fibre Types
30

31. Neuro Muscular Electrical
Stimulation
 NMES is used for
 Muscle re-education and prevention of
disuse atrophy
 Decreasing muscle spasm
 Decreasing edema
31

32. Why NMES?
 Used on patients who cannot perform a
voluntary muscle contraction
 Peripheral nerve innervation is intact, yet muscle
is too weak to contract from atrophy, pain,
immobilization, etc.
 Promotes early AROM in postsurgical and
immobilized limbs
 Break pain-spasm-pain cycle of muscle spasms
32

33. Don’t Replace Strength Training
with NMES
 NMES recruits fibers in the opposite order
than that of a voluntary contraction.
 Machine = large fibers followed by small
 Voluntary = small fibers followed by large
 Patient needs to move on to more traditional
weight training ASAP.
33

34. Physiological Sequence in
Contraction
 Asynchronous motor unit pattern -------->
smooth graded contraction
 Relates to : No of motor units firing
(spatial summation)
Rate of motor unit firing
(temporal summation)
34

35. Normal Contraction
 Increase no of motor units in early contraction
(to force)
 then increase firing rate to increase force
further.
 Type I MU fire first, then Type II. Type IIb
brought in last of all
35

36. Electrical Stimulation Pattern
 SYNCHRONOUS firing pattern (all MU’s fire
together)
 Type II neurons are LARGER (therefore have
a lower threshold, therefore fire first - reverse
of the natural sequence)
36

37. Effects of Electrical Stimulation
 Short Term
Contraction & altered (local) blood flow.
 Longer Term (‘chronic’)
strengthening
structural changes
biochemical changes
37

38. Mechanisms
Most likely NEURAL (due to speed of response
& lack of volume changes)
?spinal motor pool activation
?synaptic facilitation
?muscle motor unit firing pattern (change SO to
FOG or FG?)
38

39. Best effects for weak muscles
(Gibson et al 1988)
 30Hz @ 300μs, 2 sec ON 9 sec OFF 1 hr/day
Knee immobilisation.
 Treatment group no strength loss, Non
treatment group17% reduced Xsect Area
39

40. Waveforms Krameret al (1984), Walmsley et al (1984), Snyder-
Mackleret al 1989) have all published evidence which supports the asymmetric over
the symmetric waveform(max quadriceps force production).
40

41. INTENSITY AND FORCE OF
CONTRACTION
 Approximately linear relationship between
CURRENT INTENSITY and FORCE OF
CONTRACTION (Ferguson et al 1989,
Underwood et al 1990)
 The greatest effects with least current intensity
by using BIPHASIC PULSED or BURST AC
currents.
41

42. FORCE OF CONTRACTION
 Stronger muscle contractions with 300-400μs
pulses, BUT these will also produce significant
stimulation of sensory fibres.
 Stimulation frequency affects FORCE
GENERATION.
 Higher forces produced with tetanic
contractions, but also more discomfort and
potential for muscle damage, more especially
with patients (the tetanic stim is widely
researched with athletes/fit individuals rather
than those with muscle dysfunction)
42

43. Force Generation Vs Fatigue
 Maximum at 60 - 100Hz (Binder et al 1990),
BUT also get higher fatigue.
 20Hz stimulation will achieve about 65%
force, BUT also much less fatigue
43

44. Stimulation Parameters
 Duty Cycle : (ON : OFF ratio)
 Minimum is to use equal cycles (1:1) but only for the
stronger / end rehab / fit patients
 Use higher ratios for the weaker to allow stim with
minimal chance of fatigue
 Weaker / poorer state the muscles, larger rest time
proportion
 Might start at 1:9 for v weak patients and progressively
reduce (towards 1:1)
 For example, if using stim for quads in a very weak
patient (post TKR) might use a 1:9 ratio, so 10 sec stim
would be followed by 90 sec rest.
44

45. Ramp
45

46. Review Electrodes: Physical
Dimensions
 Shape is unimportant
 Most are round or square or rectangular.
 Size and placement determine the number
of motor units stimulated.
46

47. Review Electrode Function
 Active electrode
 Electrode under which the current density is
great enough to elicit the desired response
 Indifferent (dispersive) electrode
 Electrode under which the current density is
not great enough to elicit the desired
response
47

48. Electrodes
 Best if both electrodes on muscle belly
 Best if one is at or near motor point
 Larger electrodes better (less current density,
therefore less discomfort)
 ?advantage if electrodes placed in
LONGITUDINAL orientation (Brooks et al
1990) - stronger contraction with less
discomfort
 Special electrodes are available for pelvic floor
stimulation
48

49. Strengthening Protocols Athletes +
Non Injured Subjects
 2500Hz burst AC [Kramer et al 1984, Snyder-
Mackler 1989, Walmsley et al 1984]
 Symmetric and asymmetric biphasic pulsed
[Alon et al 1987, Grimb et al 1989]
 Frequency usually at around 60Hz + Stim
intensity at max tollerance
 BUT can get an effect at 25-50% MVC
(ISOMETRIC)
 PULSE WIDTH 300-400μS may be best
49

50. Strengthening Protocols Athletes +
Non Injured Subjects
 Duty cycle relates to fatigue
 If less fatigue resistant 1:8 - 1:5
 Once less likely to fatigue drop to 1:3 - 1:2 -
1:1
50

51. Strengthening Protocols Athletes +
Non Injured Subjects
 Ramp - no definitive rules, BUT with stronger
stimulation use longer ramp.
 Usually 2-4 sec ramp up and 1-2 sec ramp
down
 8 - 15 max contractions / session ; 3 - 5
sessions / week ; 3 - 6 weeks for significant
effect
51

52. Strengthening Protocols :
Rehabilitation Programmes
 Similar ideas BUT tend to use LOWER
frequencies - (minimum required to get tetany
- 20 - 35 Hz).
 Continue for longer (per session) and use a
Duty Cycle which minimises fatigue (at least
1:4 or more).
 The most effective treatment approach (??)
may employ 100 - 200 contractions per
session, usually over 1 - 2 hours
52

53. Suggested Clinical Treatment
Parameters
Muscle Strengthening
 30 - 35Hz @ 400 μs
 4 sec ON / 4 sec OFF (minimum) but usually
10 sec ON / OFF at least 15 mins alt days, but
usually 30 min / day
 Need strong contraction (not just mild twitch) +
voluntary as well
53

54. Suggested Clinical Treatment
Parameters
Muscle Endurance
 20Hz @ 400 μs
 2 sec ON / 2 sec OFF (minimum) at least 1 hr
day
 Minimal contractions
54

55. Suggested Clinical Treatment
Parameters
Very WeakMuscles /Marked Atrophy
 10Hz @ 400 μs
 2 sec ON / 2 sec OFF (minimum)
 minimum 1 hr day
 Minimal contraction
55

56. Tetanic Contraction to break
Muscle Spasm
 Goals
 Increase local circulation
 Remove metabolic wastes
 Mechanically stimulate muscle fibers
 Induce some muscle spasm fatigue
56

57. NMES for Decreasing Edema
 Produce cyclic muscle contractions to help
pump chronic edema
 5–10 sec on; 5–10 sec off
57

58. NMES Effects
Effects
1. Muscle contraction
a. Increase blood flow
b. Retard atrophy development
c. Decrease and retard neuromuscular
inhibitions
d. Increase muscle relaxation; decrease
spasm
2. Decrease pain
a. Possibly by decreasing muscle spasm
58

59. NMES Advantages & Disadvantages
C. Advantages
1. Can be applied to
immobilized body
part
D. Disadvantages
1. Sometimes
becomes a
panacea
59

60. NMES Indications &
Contraindications
Indications
1. Residual or chronic
muscle spasm
2. Any time normal
neuromuscular function
is not possible
3. Muscle strains
4. During cast
immobilization or disuse
atrophy
5. Pain owing to muscle
spasm
Contraindications
1. Do not use:
a. On a person with a
pacemaker
b. Over the heart or brain
c. Over recent or non-union
fractures
d. Over potential
malignancies
60

61. NMES Precautions
G. Precautions
1. Be cautious over an area with:
a. Impaired sensation
b. Skin lesions (cuts, abrasions, new skin,
recent scar tissue)
c. Decreased range of motion
d. Extensive torn tissue
61

62. Technique of Application
 Group muscle stimulation; and
 Motor Point stimulation.

63. Group Muscle Stimulation
 Stationary stimulation
 Active electrode & Passive electrode will be
kept stationary

64. Motor Point Stimulation

75. 75

79. Reference

80. Thank You