Transcript Principles of Electrical Currents

Principles of Electrical
Currents
HuP 272
Electricity is an element of PT
modalities most frightening and least
understood.
Understanding the basis principles will
later aid you in establishing treatment
protocols.
General Therapeutic Uses of
Electricity
Controlling acute and chronic pain
Edema reduction
Muscle spasm reduction
Reducing joint contractures
Minimizing disuse/ atrophy
Facilitating tissue healing
Strengthening muscle
Facilitating fracture healing
Contraindications of Electrotherapy
Cardiac disability
Pacemakers
Pregnancy
Menstruation (over abdomen, lumbar or
pelvic region)
Cancerous lesions
Site of infection
Exposed metal implants
Nerve Sensitivity
Terms of electricity
Electrical current: the flow of energy
between two points
Needs
A driving force (voltage)
some material which will conduct the electricity
Amper: unit of measurement, the amount
of current (amp)
Conductors: Materials and tissues which
allow free flow of energy
Fundamentals of Electricity
Electricity is the force created by an
imbalance in the number of electrons at
two points
Negative pole an area of high electron
concentration (Cathode)
Positive pole and area of low electron
concentration (Anode)
Charge
An imbalance in energy. The charge of a
solution has significance when attempting
to “drive” medicinal drugs topically via
inotophoresis and in attempting to
artificially fires a denervated muscle
Charge: Factors to understand
Coulomb’s Law: Like charges repel,
unlike charges attract
Like charges repel
allow the drug to be “driven”
Reduce edema/blood
Charge: Factors
Membranes rest at a “resting potential”
which is an electrical balance of charges.
This balance must be disrupted to achieve
muscle firing
Muscle depolarization is difficult to achieve with
physical therapy modalities
Nerve depolarization occurs very easily with PT
modalities
Terms of electricity
Insulators: materials and tissues which
deter the passage of energy
Semiconductors: both insulators and
conductors. These materials will conduct
better in one direction than the other
Rate: How fast the energy travels. This
depends on two factors: the voltage (the
driving force) and the resistance.
Terms of electricity
Voltage: electromotive force or potential
difference between the two poles
Voltage: an electromotive force, a driving
force. Two modality classification are:
Hi Volt: greater than 100-150 V
Lo Volt: less than 100-150 V
Terms of electricity
Resistance: the opposition to flow of
current. Factors affecting resistance:
Material composition
Length (greater length yields greater
resistance)
Temperature (increased temperature, increase
resistance)
Clinical application of Electricity:
minimizing the resistance
Reduce the skin-electrode resistance
Minimize air-electrode interface
Keep electrode clean of oils, etc.
Clean the skill on oils, etc.
Use the shortest pathway for energy flow
Use the largest electrode that will
selectively stimulate the target tissues
If resistance increases, more voltage will
be needed to get the same current flow
Clinical application of Electricity:
Temperature
Relationship
An increase in temperature increases
resistance to current flow
Applicability
Preheating the tx area may increase the
comfort of the tx but also increases resistance
and need for higher output intensities
Clinical Application of Electricity:
Length of Circuit
Relationship:
Greater the cross-sectional area of a path the
less resistance to current flow
Application:
Nerves having a larger diameter are
depolarized before nerves having smaller
diameters
Clinical Application of Electricity:
Material of Circuit
 Not all of the body’s
tissues conduct
electrical current the
same
 Excitable Tissues
Nerves
Muscle fibers
blood cells
cell membranes
 Non-excitable tissues
Bone
Cartilage
Tendons
Ligaments
 Current prefers to
travel along excitable
tissues
Laws and Principles of Electricity
Ohm’s Law: V-IR (V is voltage, a measure
of the driving force which is equal to the
IxR where I is the Ampere (the amount of
current flow) and R is the resistance. Or,
expressed differently: The Ampere is
equal to the Voltage divided by the
resistance.
If you know the inter-relationship you can
understand if one increased what happens to
the other
Watt= electrical power=volt x amps- ohms
Stimulation Parameter:
Amplitude: the intensity of the current,
the magnitude of the charge. The
amplitude is associated with the depth
of penetration.
The deeper the penetration the more muscle
fiber recruitment possible
remember the all or none response and the
Arndt-Schultz Principle
Simulation Parameter
Pulse duration: the length of time the
electrical flow is “on” also known as the
pulse width. It is the time of 1 cycle to
take place (will be both phases in a
biphasic current)
phase duration important factor in
determining which tissue stimulated: if too
short there will be no action potential
Stimulation Parameter:
Pulse rise time: the time to peak
intensity of the pulse (ramp)
rapid rising pulses cause nerve
depolarization
Slow rise: the nerve accommodates to
stimulus and a action potential is not elicited
Good for muscle re-education with assisted
contraction - ramping (shock of current is
reduced)
Stimulation Parameters
Pulse Frequency: (PPS=Hertz) How many
pulses occur in a unit of time
Do not assume the lower the frequency the
longer the pulse duration
Low Frequency: 1K Hz and below (MENS .1-1K
Hz), muscle stim units)
Medium frequency: 1K to 100K Hz
(Interferential, Russian stim LVGS)
High Frequency: above 100K Hz (TENS,
HVGS, diathermies)
Stimulation Parameter:
Current types: alternating or Direct
Current (AC or DC)
AC indicates that the energy travels in a
positive and negative direction. The wave
form which occurs will be replicated on both
sides of the isoelectric line
DC indicated that the energy travels only in
the positive or on in the negative direction
DC
AC
Stimulation Parameter:
Waveforms; the path of the energy. May
be smooth (sine) spiked, square,,
continuous etc.
Method to direct current
Peaked - sharper
Sign - smoother
Stimulation Parameter:
Duty cycles: on-off time. May also be
called inter-pulse interval which is the
time between pulses. The more rest of
“off” time, the less muscle fatigue will
occur
1:1 Raito fatigues muscle rapidly
1:5 ratio less fatigue
1:7 no fatigue (passive muscle exercise)
Stimulation Parameter:
Average current (also called Root Mean
Square)
the “average” intensity
Factors effective the average current:
• pulse amplitude
• pulse duration
• waveform (DC has more net charge over time thus
causing a thermal effect. AC has a zero net charge
(ZNC). The DC may have long term adverse
physiological effects)
Stimulation Parameter:
Current Density
The amount of charge per unit area. This is
usually relative to the size of the electrode.
Density will be greater with a small electrode,
but also the small electrode offers more
resistance.
Capacitance:
The ability of tissue (or other material) to
store electricity. For a given current
intensity and pulse duration
The higher the capacitance the longer before a
response. Body tissues have different
capacitance. From least to most:
Nerve (will fire first, if healthy)
Muscle fiber
Muscle tissue
Capacitance:
Increase intensity (with decrease pulse
duration) is needed to stimulate tissues
with a higher capacitance.
Muscle membrane has 10x the
capacitance of nerve
Factors effecting the clinical
application of electricity
Factors effecting the clinical application of
electricity Rise Time: the time to peak
intensity
The onset of stimulation must be rapid
enough that tissue accommodation is
prevented
The lower the capacitance the less the
charge can be stored
If a stimulus is applied too slowly, it is
dispersed
Factors effecting the clinical
application of electricity
 An increase in the diameter of a nerve
decreased it’s capacitance and it will
respond more quickly. Thus, large nerves
will respond more quickly than small
nerves.
Denervated muscles will require a long rise
time to allow accommodation of sensory
nerves. Best source for denervated muscle
stimulation is continuous current DC
Factors effecting the clinical
application of electricity:
Ramp: A group of waveforms may be
ramped (surge function) which is an
increase of intensity over time.
The rise time is of the specific waveform and is
intrinsic to the machine.
Law of DuBois Reymond:
The amplitude of the individual stimulus
must be high enough so that depolarization
of the membrane will occur.
The rate of change of voltage must be
sufficiently rapid so that accommodation
does not occur
The duration of the individual stimulus must
be long enough so that the time course of
the latent period (capacitance), action
potential, and recovery can take place
Muscle Contractions
Are described according to the pulse width
1 pps = twitch
10 pps = summation
25-30 pps = tetanus (most fibers will reach
tetany by 50 pps)
Frequency selection:
100Hz - pain relief
50-60 Hz = muscle contraction
1-50 Hz = increased circulation
The higher the frequency (Hz) the more
quickly the muscle will fatigue
Electrodes used in clinical application
of current:
Electrodes used in clinical application of
current: At least two electrodes are required to
complete the circuit
The body becomes the conductor
Monophasic application requires one negative
electrode and one positive electrode
The strongest stimulation is where the current
exists the body
Electrodes placed close together will give a
superficial stimulation and be of high density
Electrodes used in clinical application
of current:
Electrodes spaced far apart will penetrate more
deeply with less current density
Generally the larger the electrode the less
density. If a large “dispersive” pad is creating
muscle contractions there may be areas of high
current concentration and other areas relatively
inactive, thus functionally reducing the total size
of the electrode
A multitude of placement techniques may be
used to create the clinical and physiological
effects you desire
General E-Stim Parameters
Pain
Edema
Muscle Re-ed.
Tissue Healing
Hz: 100+
Tens, HVGS, IFC
Hz: 100-150
HVGS, IFC
Hz: 50-60
Type: depends on purpose
Hz: 100+ or 1(? inc. circ)
IFC, Ionto, Mens (?)
PPS: 70-100
Polarity: purpose & comfort
PPS: 120
Polarity: negative
PPS: 1-20
Polarity: purpose & comfort
PPS: vary but typically tens like
Polarity: purpose & comfort
Time: 20-60 min
Time: 20 min
Time: Fatigue (1-15 min)
Time: 20 min
Other:
Electrode Spacing
Burst Option, Voltage/Acc.
Accupoint (1-5pps)
Other:
Electrode Spacing
Voltage/Acc.
With muscle cxn or pain reduction
Other:
Electrode Spacing, surge
Burst Option, Voltage/Acc.
Accupoint (1-5pps)
Other:
Electrode Spacing
Voltage/Acc.
Accupoint
E-Stim for Pain Control: typical
Settings
Neuromuscular Stimulation
High Volt Pulsed Stim
Gate Control Theory
High-Volt Pulsed Stim
Opiate Release
High-Volt Pulsed Stim
Brief-Intense (Probe)
High-Volt Pulsed Stim
Intensity: Stong & comfortable
Intensity: Sensory
Intensity: Motor level
Intensity: Noxious
Type title here
Pulse Rate: <15
35-50 for tonic contraction
Pulse Rate: 60-100 pps
Pulse Rate 2-4 pps
Pulse Rate: 120pps
Polarity: + or -
Phase Duration < 100 usec
Phase Duration: 150-250 usec
Phase Duration: 300-1000 usec
Alternating Rate: Alternating
Mode: continuous
Mode: Continuous
Mode: 15-60 sec at each site
Electrode Placement
Biopolar: Distal & Proximal to muscle
Monopolar: Over motor points
Electrode Placement
Directly over motor points
Electrode Placement
Directly over motor points
Electrode Placement
Grid Tech: distal & proximal to site