E-Stim (Lecture) Flashcards
what is the role of biophysical agents in neuro?
- control pain - reeducate lost or impaired motor function
what types of electrical modalities are used for sensory vs motor level stimulation
what are the therapeutc effects and indications of electrical stimulation?
- decrease or control pain
- decrease muscle spasm
- increase muscle force/function
- electrodiagnosis
describe the process of nerve cell conduction
-When an adequate stimulus arrives:
Na+ channels open rapidly and Na+ flows in
When the RMP reaches +30 mV, K+ channels open and permeability to Na+ ↓
Membrane is repolarized
- during this period, membrane can be excited by graded stimulation
what is excitation-contraction coupling?
- Muscle action potential reaches the sarcoplasmic reticulum via the transverse tubular system
- This signals the sarcoplasmic reticulum to release Ca++
- Ca++ ions bind to troponin
- Troponin binds to tropomyosin
- Allowing actin to interact with myosin
- Relaxation occurs when action potential cease
- Ca++ is pumped back into the sarcoplamic reticulum by Ca++ activated ATPase enzymes
- Troponin inhibition ceases
- Actin-myosin interaction stops
describe temporal summation
The activation phase (≈ 5 ms) is much more rapid than the contraction-relaxation phase (≈ 100 ms)
If the muscle is maximally stimulated once, a muscle twitch (Pt) is produced
If the second neural impulse occurs after the muscle has relaxed, a second Pt is formed
If the subsequent neural impulses occur before the muscle has relaxed, partial summation occurs
If the subsequent neural impulses occur during the contraction time of the first, a tetanic contraction occurs
describe rate coding
types of sensory and motor axons?
note: conduction velocity is the speed at which an electrochemical impulse propagates down a neural pathway.
sensory level vs motor level stimulation depends on what?
-depends on threshold of activation of nerve types
AND
-intensity of stimulating current
what determines the differences between voluntary and induced contractions
- Order of recruitment
- Differences in rate coding
- Smoothness of onset of the contraction
- Differences in fatigability
describe the muscle fibre recruitment order wrt estim vs naturally
describe muscular recruitment for electrical stimulation
what is tissue impedence
what is current density and how do you alter it
Current density refers to the volume of current in the tissues
Current density is highest at the surface and diminishes in deeper tissue
1) Change the spacing of electrodes: Moving electrodes further apart increases current density in deeper tissues
2) change size of electrodes (image)
what is the strength duration curve
A graphic representation of the amount of current versus the duration of the impulse that is required to produce an action potential
The amount of electrical current needed to cause an action potential depends on the type of nerve fibre
Used to determine the duration of the stimulating pulse used to trigger an action potential
what is rheobase and chronaxie
Rheobase: Minimum current needed to produce an action potential at a long (infinite) pulse duration
Chronaxie: Minimum duration that will produce an action potential at twice the rheobase
desribe how different uscle fibre types depend on their innervation
Type I (Slow Oxidative) – fatigue resistant – lowest force production -
Type IIa (Fast Oxidative Glycolytic) – some fatigue resistance
Type IIb (Fast Oxidative) – least fatigue resistant – highest force production
what are stimulation parameters for normally innervated muscle?
- Pulse duration should be below 1 ms, usually in the range of 100-350 μs
- The rate of rise of the current strength has to be fast to prevent accommodation of the nerve
- High stimulation frequency for Type IIb fibres
- Low stimulation frequency for Type I fibres
define waveform shape, duration, and frequency
Waveform shape (rise time, fall time)
Waveform duration (total charge)
Frequency (time between pulses)
general precautions and contra-indications for e-stim
precautions:
Cardiac disease, Cognitively impaired or impaired sensation, Cancer, Skin irritation or open wounds
contraindications:
Demand cardiac pacemakers or arrhythmias
Placing electrodes over carotid sinus: ↓ BP
Areas of venous or arterial thrombosis or thrombophlebitis: emboli
Pregnancy: around pregnant area
Trans-thoracic or trans-cranial applications
define DC vs AC
Direct current: “continuous unidirectional flow of charged particles”
Alternating current: “continuous bidirectional flow of charged particles”
diff waveform types
pulse train parameters
what is pulse duration?
what are monopolar, bipolar, and quadripolar techniques used for?
Monopolar technique: 2 electrodes of different sizes with the active electrode smaller than the reference electrode. Small electrodes have greater impedance and a higher density of current than larger electrodes. With this technique the larger electrode is a reference or dispersive electrode. The dispersive electrode should be placed proximal to the active electrode. Because of its size, the density of current in the dispersive electrode is too low to provoke a sensory of motor response. Common use: wound healing, electrophoresis and electrodiagnosis.
Bipolar technique: two electrodes, usually of the same size, are placed over the muscle to be stimulated. The size of the electrodes depends on the size of the target muscle. Common use: muscle reeducation, disuse atrophy, neuromuscular facilitation, ROM limitation, muscle spasm, circulatory disorders.
Quadripolar technique: the use of 4 electrodes over the targeted muscle. This technique can be used to stimulate large muscle such as the quadriceps or the trunk extensors.
Compare the sensations from the high frequency (100Hz) and low frequency (1Hz) stimulation.
High frequency felt like tingling, low felt like a pulse
*note the difference between sensory level stimulation (trains of pulses at frequencies between 4 to 150 Hz) and motor level stimulation (trains of pulses, with internal frequencies of 30-50 Hz, applied in bursts over seconds).
