Intro to E-Stim 2 (10/17a) [Biomedical] Flashcards
Alternating Current (AC)
Uninterrupted bidirectional flow of charged particles
Descriptive characteristics
- Biphasic (bipolar)
- Symmetrical (usually) or asymmetrical
- Balanced (usually) or unbalanced
- Varied shapes — sine wave, rectangular, triangular
Direction of current flow — back and forth between - and +
Zero net current flow — no chemical effects
Burst modulated alternating current (BMAC)
AC current delivered in bursts (with a break), can be more comfortable
EX: Russian Current
Pulsed Current (PC)
Interrupted uni or bidirectional flow of charged particles
Flow ceases for a finite period
Descriptive characteristics of pulses
- Mono or biphasic pulses
- Symmetrical or asymmetrical
- Balanced or unbalanced
- Various shapes (waveforms) rectangular, twin peak, etc
Direction of current flow — back and forth between - and +
Wave form
Mono/Bi phasic
Symmetrical/Asymmetrical — symmetric has same shape, duration, and intensity on both sides
Balanced/Unbalanced — same duration and intensity on both sides
Shape — sinusoidal, rectangle, triangle, spike
Duration (pulse/phase)
Both measured in microseconds
Most stimulators talk about pulse duration
Phase duration — time elapsed from beginning to end of one phase (cross ‘0’)
Pulse duration — time elapsed from beginning to end of all phases
Amplitude
Peak — each phase
Peak to peak — entire pulse
RMS — 70% of peak
Average — 64% of peak
Pulse/Phase Charge
Pulse charge — area under the curve of all phases
Phase charge — area under the curve of one phase
2 pulses with different amplitudes and durations can have the same pulse/phase charge
Pulse duration could be too short to reach threshold
As pulse duration increases, lower amplitudes are needed to excite the tissue
RMP for nerves is ___ mV, for muscles is ___ mV
Nerves = -70 mV Muscles = -90 mV
Frequency - Related Definitions
Interpulse interval (IPI) — time between successive pulses, can be mono/biphasic
Period — time elapsed from one point in waveform to identical point in next waveform
- Period = pulse duration + interpulse interval
- Have to convert to seconds (he will likely give in milliseconds)
Frequency = number of pulses per second (pps, Hz)
- Freq = 1 / Period
Frequency - Usage
When using NMES for strengthening, we want high freq (30-50 pps)
- Has to do with having pulse stay on and create tetanic contraction
Frequency Modulation — we regulate frequency to achieve different stimulations
Carrier Frequency Modulation — used only for BMAC (Russian waveforms, interferential waveforms), you can put bursts at diff frequencies
Ion response around the nerve membrane
More Na+ outside of the cell, anions and K+ more inside the cell
When you have a negative electrode, cations will be attracted to it
You can change the polarity at both electrodes, and if you have a large enough amplitude you can depolarize
For AC or pulse current, this goes back and forth constantly
Resistive/Capacitive Model
Capacitance — property of a system of conductors and insulators to store charge
Resistance built into cell membrane that can block flow of ions/direct current
Allows alternating current to pass
C = q / V , with C measured in Farads (F)
Neuron Membrane
Stores energy because extracellular more +, intracellular more -
Neuron Activation - Successful Initiation
Local current produces increase in Na conductance which depolarizes the membrane which further depolarizes the membrane
When sodium influx greater than Potassium efflux, threshold is reached
When initiations are successful, depolarization occurs to threshold, more sodium channels open and creates action potential, sodium channels close and potassium channels, repolarization, potassium channels slow to close, brought back to resting potential
Neuron Activation - Failed Initiation
when you have depolarization but not enough to reach threshold
