Is the cellular membrane potential positive or negative?
negative, until an action potential occurs
Define refractory period:
Period immediately after a nerve impulse where another impulse cannot be generated; absolute period - none can occur; relative refractory period - a higher than normal stimulus can trigger an impulse
What is salutory / jumping conduction?
On a myelinated nerve the impulse jumps between gaps (nodes of ranvier) making it faster and more efficient
avg conduction velocity for myelinated and unmyelinated?
myelinated ~130 m/s vs unmyelinated ~.5 m/s
What is an ion:
an atom or a group of atom that has a net electrical charge
What is ionization:
process of changing the electrically neutral states of an atom
What is an electrical current?
Atoms with valence shells that are almost full relate to conductivity how?
These are stable and are called insulators which impedes electron movement such as apidose tissue
Atoms with valence shells that only have one or two electrons relate to conductivity how?
These readily relenquish their atoms and are conductors which readily permit electron movement, such as metal
Clinically therapeutic intensities should not exceed what amperage?
What is electromotive force?
1 volt is the electromotive force required to move 1 amp of current through a resistance of 1 ohm
What role does voltage play in nerve cell membrane depolarization?
An adequate number of electrons must be forced to move through conductive tissues.
How does Ohm's law express the relationship between current, voltage, and resistance?
V=IR; when resistance increases, current decreases; when resistance decreases, current increases; when voltage decreases, current decreases; when voltage increases, current increases; when voltage is zero, current is zeo
what properties of a material tend to make it resist electrical currents?
conductors have low resistance, whereas insulators have high resistance. The actual resistance of a material is determined by the formula R(resistance) = P (resistivity = length of material / cross section)
Greater cross sectional effects resistance how?
Increased temperature changes resistance and conductivity how?
decreased resistance and increased conductivity
If the resistor is longer what happens to resistance?
it is increased
Factors that increase skin impedance?
cooler skin temperature, electrode type/surface factors, hair and old present, increased skin dryness, increased skin thickness
Factors that decrease skin impedance?
increasing electrode surface, removing excess hair, warming skin, washing skin
What criteria is used to describe direct current?
DC is flow of electrons in one direction for >1 second. Flow is unidirectional, polarity is constant, current produces a twitch response only at the time of make
Direct currents produce polar effects. what polar effects produced by the anode (positive)?
hyperpolarizes nerve fibers, repels bases, hardens tissues, stops hemorrhage, sedates and calms, reduces pain in acute situations
Direct currents produce polar effects. what polar effects produced by the cathode (negative)?
depolarizes nerve fibers, attracts bases, softens tissues, increases hemorrhage, stimulates, reduces pain in chronic situations
What are the criteria used to describe alternating current (AC)?
The magnitude of flow of electrons changes, the direction of flow reverses, there are no polar effects, constantly flucuates
List the typical frequencies (change of currents, if applicable) used in therapeutic applications)
Frequency (Hz): 0 = direct current, 0-1000 = low frequency, 1000-100000 = medium frequency, 100000+ = high frequency
Does medium-frequency stimulation differ from low frequency stimulation in terms of skin resistance (capacitive impedance)
yes, capacitance impedance decreases as the frequency increases
Describe key attributes of interferential currents (IFC):
- two separate force generators that vary in relation to one another in amplitude and/or frequency, the difference of the two frequencies bcreases a beat frequency which is felt by the patient
What is the frequency for a twitch contraction?
What is the frequency for a tetantic contraction?
What is the frequency for a nonfatiguing tetanic contraction?
What is the frequency for a fatiguing tetanic contraction?
When intrapulse interval is adjusted it can do what?
It is used to increase patient comfort
Interpulse interval is needed to do what?
Time needed to ensure absolute refractory period
Interburst interval is used for what?
as a form of modulation
Define rise time, fall time, duty cycle:
RIse time: time it takes a wave to travel from zero to its peak amplitude fall time: time it takes a peak amplitude to fall to zero duty cycle: relative proportion of time between the stimulation period and rest period
Describe the key attributes of high volt current:
Produces a twin peak monophasic waveform because the waveform is fixed and small in duration it takes two peaks to depolarize the nerve. Units are constant voltage. Two leads - one dispersive and one active - active is much smaller than the dispersive electrode. Polarity can typically be set.
How does high voltage current (galvanic) differ from direct current:
High voltage/Direct current: used to excite peripheral nerves/useless with peripheral nerves; useless in exciting denervated tissues/used to excite denervated tissues; creates no measurable thermal reaction under electrodes/creates thermal reaction under electrodes; not effective for ionto/effective; affects superficial and deep tissues/ only affects superficial tissue; useful in discriminating between sensory, motor, and painful stimulation/ stimulation is usually painful; used to resolve many clinical pathologies; used to resolve many pathologies/restricted benefit to limited number of
What is the relationship between interelectrode distance and depth penetration?
Current travels through areas of least resistance, electrodes placed at a greater distance result in a deeper penetration, provided all parameters remain constant.
List potential sites for electrode placement used in the treatment of pain:
site of pain, acupuncture points, trigger points, motor points, peripheral nerve roots, paravertebral, contralateral to the pain, distal or proximal
Name the two electrode placement strategies for NMES:
1. Unipolar method: the active electrode is placed on the motor point, and the dispersive electrode is placed on some other point such as the nerve trunk 2.) bipolar method: two electrodes of equal size are placed along the length of the muscle belly
LIst electrically excitable tissues:
abdominal organ cells, autonomic motor fibers, cardiac muscle fibers, cells that produce glandular secretion, nerve axons of all types, nerve cells of all types, voluntary motor fibers
List electrically nonexcitable tissues:
bone, blood, cartilage, collagen, extracellular fluid, ligaments, tendon
Discuss pfluger's law and its implications in the stimulation of human tissue:
healthy muscle contracts with less current if stimulated by the cathode compared with stimulation by the anode.
What is accommodation?
The increase threshold of excitable tissue when a slowly rising stimulus is used. Both nerve and muscle tissues are capable of accommodating to an electrical stimulus; nerve tissue accommodates more rapidly than muscle tissue.
Contraindications for electrotherapy:
cardiac pacemaker, prone to seizures, electrodes across or around the heart, electrodes over a pregnant uterus (especially first trimester), over an area suspected of arterial or venous thrombosis or thrombophlebitis, over the pharyngeal area, over protruding metal, over the carotid sinus
Precautions for electrotherapy:
allergies to tapes and gels, areas absent or decreased sensation, electrically sensitive pt, patients with advanced cardiac disease, severe hypo or hyper tension, an area with significant adipose tissue, over damaged skin, near stellate ganglion, on patients unable to communicate clearly
E-stim reported useful in literature for what conditions:
edema management, endurance training, improvement of muscle contractures, maintaining/improving ROM, management of spasticity and spasm, muscle strengthening, neuromuscular facilitation and reeducation, orthotic substitution.
What is the most effective way to use NMES for quad strengthening?
Recent evidence suggests that after TKA that voluntary exercise combined with NMES is most effective.
When is NMES indicated after knee surgery and immobilization?
- prevention of muscle atrophy associated with prolonged immobilizations - prevention of strength decrease - prevention of muscle mass decrease and muscle oxiadative capacity
Is there a difference between high-intensity e-stim and low intensity battery powered stimulators for quads s/p ACL rehab?
Yes, high intensity are supported, low intensity is not
Can NMES be used to augment ROM and strength of the shoulder musculature?
Yes, strength and girt in ortho patients, shoulder subluxation for neurological patients
Benefits of NMES after ACL reconstruction?
- decreased atrophy, increased muscle torgue, improved strength of quad, improved functional recovery with study of 2x./wk for 11-12 min tx increased max torque at 12 wks
Should ext lag be a criterion for using or not using NMES with ACL reconstruction?
No, there is no correlated relationship between lag and treatment outcomes
Is there a relationship between number of NMES training sessions per wk and strength outcomes?
yes, 3x/wk for 4 wks superior to 2x/wk for 4 wks
Is there a relationship between muscle contraction strength or fatigue and type of waveform used with electrical stimulation?
Recent evidence suggest that monophasic and biphasic waveforms generate greater torque and are less fatiguing than polyphasic waveforms.
TENS parameters and rationale for conventional, low rate, and brief intense TENS
Does TENS independently or adjunctly help with chronic low back pain?
no strong support, most effective as a placebo. Exercise and TENS follow through is poor in chronic back pain population.
Appropriate considerations for maintaining ROM:
Discuss appropriate considerations for edema control
Is EMG biofeedback helpful with quad recovery s/p ACL reconstruction?
yes. Biofeedback was more effective than e-stim in one study for peak torque and was more rapid in this process. Comparable in terms of muscle function.