Download Electrical Stimulation Technique

Electrical Stimulation
Techniques
© 2005 – FA Davis
Current Flow
• Electron Flow
(shown in red)
– Between the generators and
electrodes
– To and from the generator
• Ion Flow
(shown in yellow)
– Occurs within the tissues
– Negative ions flow towards the
anode and away from the
cathode
– Positive ions flow towards the
cathode and away from the
anode
© 2005 – FA Davis
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Electrodes
• Purpose
– Completes the circuit between the generator and
body
– Interface between electron and ion flow
– Primary site of resistance to current
• Materials
–
–
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Metallic (uses sponges)
Silver
Carbon rubber
Self-adhesive
© 2005 – FA Davis
Electrode Size
• Determines the Current Density
• Equal size
– Bipolar arrangement
– Approximately equal effects under exach
© 2005 – FA Davis
Electrode Arrangements
• Based on:
Current Density
Proximity to Each Other
Anatomic Location (Stimulation Points)
© 2005 – FA Davis
Current Density
• Bipolar Technique
– Equal current densities
– Equal effects under each electrode
(all other factors being equal)
• Monopolar Technique
– Unequal current densities
• At least 4:1 difference
– Effects are concentrated under the smaller electrode
• “Active” electrode(s)
“Active”
“Dispersive”
– No effects under larger electrode
• “Dispersive” electrode
• Quadripolar Technique
– Two bipolar electrode arrangements
– Two independent electrical channels
– TENS is a common example
© 2005 – FA Davis
Electrode Proximity
• Determines the
number of parallel
paths
• The farther apart the
electrodes the more
parallel paths are
formed
• More current is
required to produce
effects as the number
of paths increases
© 2005 – FA Davis
Stimulation Points
• Motor Points
– Superficial location of motor nerve
– Predictably located
– Motor nerve charts
• Trigger Points
– Localized, hypersensitive muscle spasm
– Trigger referred pain
– Arise secondary to pathology
• Acupuncture Points
– Areas of skin having decreased electrical resistance
– May result in pain reduction
• Traumatized Areas
– Decreased electrical resistance (increased current flow)
© 2005 – FA Davis
Path of Least Resistance
• Ion flow will follow the path of
least resistance
– Nerves
– Blood vessels
• The current usually does not
flow from electrode-toelectrode (the shortest path)
• The path of least resistance
is not necessarily the
shortest path
© 2005 – FA Davis
Selective Stimulation of Nerves
• Nerves always depolarize in the same order
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Sensory nerves
Motor nerves
Pain nerves
Muscle fiber
• Based on the cross-sectional diameter
– Large-diameter nerves depolarize first
• Location of the nerve
– Superficial nerves depolarize first
© 2005 – FA Davis
Phase Duration and
Nerve Depolarization
• Phase duration selectively depolarizes
tissues
Phase Duration Tissue
Short
Sensory nerves
Medium
Motor nerves
Long
Pain nerves
DC
Muscle fiber
© 2005 – FA Davis
Adaptations
• Patients “get used” to the treatment
• More intense output needed
• Habituation
– Central nervous system
– Brain filters out nonmeaningful, repetitive information
• Accommodation
–
–
Peripheral nervous system
Depolarization threshold increases
• Preventing Adaptation
– Vary output (output modulation) to prevent
– The longer the current is flowing, the more the current must be
modulated.
© 2005 – FA Davis
Electrical Stimulation Goals
Muscle Contractions
[Instructor Note: More detail on these
techniques are found in the CH 13 ppt:
Treatment Strategies]
© 2005 – FA Davis
Motor-level Stimulation
Comparison of Voluntary and Electrically-Induced Contractions
Voluntary
• Type I fibers recruited
first
• Asynchronous
– Decreases fatigue
Electrically-induced
• Type II fibers
recruited first
• Synchronous
recruitment
• GTO protect muscles
– Based on PPS
• GTOs do not limit
contraction
© 2005 – FA Davis
Motor-level Stimulation
• Parameters:
Amplitude: Contraction strength increases as
amplitude increases
Phase duration: 300 to 500 µsec targets motor
nerves:
– The shorter the phase duration, the more amplitude
required
– Longer durations will also depolarize pain nerves
– Pain often limits quality and quantity of the contraction
Pulse frequency: Determines the type of
contraction
© 2005 – FA Davis
Pulse Frequency
• Frequency determines the time for mechanical
adaptation
• Lower pps allows more time (longer interpulse
interverals)
Label
Low
Medium
High
Range
< 15 pps*
15-40 pps*
>40 pps*
Result
Twitch: Individual contractions
Summation: Contractions blend
Tonic: Constant contraction
* Approximate values. The actual range varies from person-toperson and between muscle groups
© 2005 – FA Davis
Effect of Pulse Frequency on
Muscle Contractions
1 pulse per second
20 pulses per second
40 pulses per second
Twitch Contraction
Summation
Tonic Contraction
The amount of time
between pulses – the
interpulse interval – is
long enough to allow the
muscle fibers to return to
their original position
© 2005 – FA Davis
The amount of time
between pulses allows
some elongation of the
fibers, but not to their
starting point.
The current is flowing so
rapidly that there is not
sufficient time to allow the
fibers to elongate
Electrical Stimulation Goals
Pain Control
© 2005 – FA Davis
Pain Control
Sensory-level
Motor-Level
Noxious Level
Target
Tissue
A-beta fibers
Motor nerves
A-delta
Phase
Duration
< 60 µsec
C fibers
120 to 250 µsec
1 msec
Pulse
60 to 100 pps
Frequency 80 to 120 pps
2 to 4 pps
Variable
Intensity
Moderate to
To tolerance
Strong contraction
© 2005 – FA Davis
Submotor
Electrical Stimulation Goals
Edema Control and Reduction
© 2005 – FA Davis
Edema Control
• Cathode placed over
injured tissues
• High pulse frequency
• Submotor intensity
• Thought to decrease
capillary permeability
• Do not use if edema
has already formed
© 2005 – FA Davis
Edema Reduction
• Muscle contractions
“milk” edema from
extremity
• Electrodes follow the
vein’s path
• Alternating rate
targets muscle groups
• Elevate during
treatment
© 2005 – FA Davis
Electrical Stimulation Goals
Fracture Healing
© 2005 – FA Davis
Fracture Healing
• Electrical current triggers
bone growth
• Piezoelectric effect within
the collagen matrix
• Alternating current
– Applied transcutaneously
– Similar to diathermy units
(no heat production)
• Direct current
– Implanted electrodes
© 2005 – FA Davis
Contraindications and
Precautions
© 2005 – FA Davis
Contraindications and Precautions
• Areas of sensitivity
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Carotid sinus
Esophagus
Larynx
Pharynx
Around the eyes
Temporal region
Upper thorax
• Severe obesity
• Epilepsy
• In the presence of
electronic monitoring
equipment
© 2005 – FA Davis
• Cardiac disability
• Demand-type
pacemakers
• Pregnancy (over lumbar
and abdominal area)
• Menstruation (over
lumbar and abdominal
area)
• Cancerous lesions (over
area)
• Sites of infection (over
area)
• Exposed metal implants