TENS

Question 1

Describe volt, ampere, impedance and resistance

Answer 1

Electrical current (I)— is the flow of electrons from negative to positive as they are negatively charged - Measured in amperes (A)
• Ampere — rate of flow past a point
• 1 ampere = movement of 1 C per second.

Voltage (V)— is the electromotive force or the electrical potential difference or called electrical pressure
• Resistance (R)—opposition to the flow of electrons by the material
through which current travels

Tissue Impedance: resistance of the tissue to the passage of electrical current.
-bone and fat are high-impedance tissues, nerves and muscles are low impedance.

-If a low-impedance tissue is located iunder a large amount of high impedance tissue current will never become high enough to cause depolarisation

Question 2

Describe the difference between alternating, direct and pulsatile currents a

Answer 2

a

Question 3

Define duration, amplitude, phase charge and frequency

Answer 3

h

Question 4

Identify the different wave forms and pusle characteristic

Answer 4

a

Question 5

Describe the capacities of nerve and muscle tissue and how it effects the strength duration curve

Answer 5

h

Question 6

Understand the Duboid Reymold Law with respect to the application of electrical currents

Answer 6

The effectiveness of a current on target tissues is dependent on three factors:

1. Adequate intensity to reach threshold
2. Current onset rapid enough to avoid accomodation
3. Duration long enough to exceed capacitance of the tissue

Question 7

Describe the types of electrode configurations used with electrical stimulation

Answer 7

h

Question 8

Explain current flow through various biological tissue

Answer 8

h

Question 9

creat a safe working environment

Answer 9

a

Question 10

Ohm’s Law

Answer 10

Current = voltage/ resistance, or I=V/R

Question 11

Impedence- force that resists flow of electrons and is the sum of 3 component:

Answer 11

• Resistance
• Inductance- eddy current that forms around current
• Capacitance- the ability of a nerve to store an electrical charge

Electricity will chose the path of least resistance. Skin has teh greatest resistance to current flow.

Question 12

Electrical current have many applications in clinical practice inlcuidn:

Answer 12

• Muscle strengthening
• Pain control
• Wound healing and
• Inflammation and oedema management

Question 13

Effects of electrical currents:

Answer 13

A resting nerve normally has a resting membrane potential of around 60-90 mV.
The use of electric currents with pulse widths greater than 10Ms cause the muscle cell membrane to depolarise directly (Electrical Muscle Stimulation).
•The use of electric currents to induce muscle contraction is referred to a Neuromuscular Electrical Stimulation.

Amplitude (strength) has to be strong enough and the duration (phase duration) long enough to overcome nerve fibre capacitance to trigger the depolarization.

Question 14

Min amplitude to depolarise a nerve is called?

phase (time) duration required to depolarise a nerve fibre when the peak current is twice the rheobase.

Answer 14

Rheobase

Chronaxie

Question 15

Clinical Applications of Electrical currents

What are the differences between the physiologic and electrical stimulation of a muscle in terms of:

1. order of recruitment
2. synchrony of firing
3. Inhibition
4. Fatigue

Answer 15

The muscle contraction achieved through electrical stimulation is similar to that produced by physiological generation of action potentials, however there are some important differences.

See slide 22 (important)

Question 16

Muscular re-education

Answer 16

• After injury or surgery electrical stimulators can be used to retrain neuromuscular function.
• The muscular inhibition that results from injury needs to be overcome before the patient can participate in active rehabilitation.
• The is achieved by stimulation of the alpha motor neuron

If there is inhibition of a muscle from effusion or prolonged immobilisation, electrical stimulation can be used to help teach the athlete to contract the muscle. Thus, the force capacity or ability of the muscle to contract is enhanced, but the muscle is not truly strengthened.

Question 17

Therapeutic application of electric current is determined by the manipulation of parameters such as:

Answer 17

1. ElectrodePlacement
2. WaveForm
3. Amplitude
4. PulseDuration
5. Frequency
6. Duty Cycle
7. Rise time
8. TreatmentTime

Question 18

How does manipulating the electrod eplacement determine the manipulations of clinical parameters.

Sneosry tens
motor tens

Answer 18

• skin is insulator
• blood is best conductor
• muscle tendons are dense and low in water thus poor conductors
• bone is poor
• muscle is 75% water and propogates impulses more effectively in a longitudinal direction thus determine electrode placement.

-peripheral nerve is 6x the conductor of muscles

Sensory tens:
 Electrodes may be placed on or around the painful area
 Electrodes may be placed over the spinal cord segment or the
dermatome, myotome or sclerotome that corresponds to the
area
May be placed over trigger points
 Placed over the peripheral nerve that innervates the painful
area
 Also over the vascular structure which may contain neural
tissue
 Electrode placement may require several attempts for the best
site of pain relief

Motor Tens:
One electrode is placed over the muscle motor point & the second electrode is placed over the muscle so that the two electrodes are aligned parallel with the muscle fibres.
The electrode pads need to be placed at least 3.5 cm apart.
We will use bipolar applications – two electrodes of the same size and current density

Question 19

How does manipulating the wave form affect outcome?

Answer 19

Pulsed biphasic wave for muscle contraction is used.

1. Monophasic- D/c- the phase and pulse duration are the same.
2. Biphasic: there are 2 phase durations for each pulse.

Tissues only respond to the phase duration, not the pulse duration.

Question 20

How does manipulating

Pulse Duration

Phase duration

Answer 20

The duration of each pulse indicates the length of time the current is flowing in one cycle.
 Phase and pulse duration are the same in monophasic current.
 Various machines will have the potential to change duration.
 Biphasic currents have the potential to combine phase durations, as do pulsatile currents (PC)
 Remember - When the current is applied, if the current does not flow in one direction long enough, there will not be an action potential. The strength-duration curve is important for describing the relationship of amplitude (strength) of the electrical current and the duration (phase duration). These two parameters are linked in the phase charge.

PHASE DURATION:
A tissue can store the electrical charge
• Phase duration must be long enough to overcome the capacitance of the target tissue to cause and AP
• Larger the nerve fibre the lower the capacitance

Question 21

How does manipulating amplitude effect

Answer 21

The amplitude refers to the intensity or magnitude of the current.
The peak current is the maximum amplitude of the current at any point during the pulse without regard to its duration.
The peak current must be high enough to exceed threshold for the nerve or muscle fibre.

Generally, large-diameter sensory and motor nerves (A-beta and A-alpha) have low thresholds, and smaller intensities of electrical current are needed to cause an action potential.
• The A-beta nerves are closer to the skin, so when the intensity on an electrical stimulator is turned up, a sensory response occurs before a motor response.
• A high peak current causes a greater depth of penetration of the electrical stimulation, which allows more fibers to be recruited.
• More nerves are stimulated with a higher amplitude, resulting in a stronger sensory or motor response.

Question 22

How does changing frequency affect outcome?

Answer 22

The frequency of the stimulation is the number of pulses generated per second (pps or Hz).
Each pulse indicates a rise & fall in amplitude
Although the same number of fibers are recruited, a higher frequency causes them to fire at a more rapid pace, which ultimately increases the tension generated.
Nerve membranes must repolarize, however, after discharging. There is an absolute refractory period in which the resting membrane potential is reinstated, and another action potential cannot be elicited during this time.
The absolute refractory period is the rate-limiting factor of the number of impulses that can be generated by a nerve.

Low frequency is 1000Hz – used to produce a physiologic effect of AP generation
• Medium frequency is 1000Hz-100,000Hz
• High frequency is >100,000Hz – used for heat generation purposes in diathermy

By increasing pulse rate with TENS >35 to 50Hz the body cant differentiate when one pulse ends and another begins, a tatanic muscle contraction may result. Below this a twitch response occurs.

-a continuous sensory effect is noted when the pulse rate exceeds 20 pps.

Question 23

How does manipulating rise time affect

Answer 23

The rate of rise refers to the time it takes to get from zero to maximal amplitude within each pulse.
Fast rates of rise times are necessary especially with low-capacitance tissues such as large motor nerves.
The rate of rise of the leading edge of the pulse is the preferred term to describe the onset of the stimulation, since rise time is often confused with ramp.

Ramp time has to do with a gradual increase in the amplitude of subsequent pulses so that the intensity does not come on abruptly when a duty cycle is used.

Question 24

Treatment time

Answer 24

For muscle strengthening the treatment time should allow for 10-20 contractions, thus a tx time of 10-20 minutes is required and should be repeated throughout the day numerous times.

Question 25

Electrode considerations:

Answer 25

Current density depends on the size of the electrodes and the distance they are apart. When unequal-sized electrodes are used, the current is more concentrated in the smaller electrode. This causes a perception of increased intensity under the smaller electrode. When electrodes are very different in size, such as with a point stimulator, the patient may not be able to perceive current in the larger electrode. The larger electrode becomes the dispersive electrode since the current is dispersed over a broad area.

THE NEGATIVE ELECTRIODE POSITIONED DISTALLY.

If the electrodes are placed very close together, the current is most dense or concentrated in the superficial tissues. If the electrodes are distant to each other, then the current has the potential to take a deeper path through the nerve and blood vessels that have less resistance.

Question 26

ELECTRODE configeration

review slide 60

Answer 26

There are two general types of electrode configurations: monopolar and bipolar. Either type may be used with monophasic or biphasic currents.
• Quadripolar electrode configurations are often used with interferential current.

monopolar:
Two or more unequal-sized electrodes are used.
• The larger electrode is the dispersive electrode (minimal or no sensation noticed)
• The smaller electrode is the active electrode
(sensory stimulation much greater than at the dispersive electrode), goes over the tx site
• Monopolar, when placed further apart produce deeper penetration & when a fixed polarity is required for iontophoresis to disperse Rx.

Bipolar electrode configurations can also be used with either monophasic or biphasic currents. In this case, equal-sized electrodes are used, with both placed over the treatment site. This setup is the most commonly used method in TENS.

Question 27

Gimme a summary

Answer 27

Electrical current is the movement of electrons by a voltage across a resistance.
• Electrical current can be used to depolarise selected nerve fibres, drive medications into tissues, stimulate denervated muscle, or promote tissue repair in some slow-to-heal lesions.
• There are multiple waveforms and parameter adjustments on electrotherapeutic devices, which can influence when and how a device is applied.
• The most common form of electrotherapy is TENS. Through appropriate selection of amplitude, phase duration, frequency, ramp, and duty cycle, TENS can be used for pain relief or to cause muscle contraction through stimulation of the alpha motor neuron.