Principles of Electrical Stimulation

1. Principles of Electrical Stimulation

2. Current Types • Direct Current • Alternating Current • Pulsed Current

3. Direct Current Description: • One-directional flow of electrons • Constant positive and negative poles Use: • Iontophoresis • Low-voltage stimulation

4. Alternating Current Description: • Bidirectional flow of electrons • No true positive and negative poles Use: • Interferential stimulation • Premodulated currents

5. MONOPHASIC CURRENT Description: One-directional flow marked by periods of non-current flow Electrons stay on one side of the baseline or the other Use: High voltage pulsed stimulation BIPHASIC CURRENT Description: Bidirectional flow of electrons marked by periods of non-current flow Electrons flow on both sides of the baseline (positive and negative) Use: Neuromuscular electrical stimulation Three types of biphasic currents Pulsed Currents

6. Biphasic Current Types Symmetrical • Mirror images on each side of the baseline • No net positive or negative charges under the electrodes Balanced Asymmetrical • The shape of the pulse allows for anodal (positive) or cathodal (negative) effects • No net positive or negative charge Unbalanced Asymmetrical • Positive or negative effects • The imbalance in positive and negative charges results in a net change over time. Can cause skin irritation if used for long durations

7. Pulse Attributes

8. Time-dependent Attributes • Pulse duration • Phase duration • Interpulse interval • Intrapulse interval • Pulse period • Pulse frequency • Pulse trains (bursts) Note: These attributes do not apply to direct and alternating currents

9. Pulse Duration • The time (horizontal distance) from when the pulse rises to the baseline to the point where it terminates on the baseline. • [instructor note: click to start animation] Monophasic Pulse Biphasic Pulse

10. Phase Duration 1 1 2 • Phases are individual portions of the pulse that appear on one side of the baseline • For monophasic currents, pulse duration and phase duration are synonymous (only 1 phase). • Biphasic pulses have two phase durations • The phase duration determines which nerve type is affected. • [instructor note: click to start animation] Monophasic Pulse Biphasic Pulse

11. Interpulse Interval • The time between the end of one pulse and the start of the next pulse • Allows for mechanical changes in the tissues, such as when eliciting muscle contractions • Increasing the pulse frequency decreases the interpulse interval and vice-versa • [instructor note: click to start animation] Two Monophasic Pulses Two Biphasic Pulses

12. Intrapulse Interval • Intrapulse intervals are brief interruptions of current flow. • Are always shorter than the interpulse interval. • They allow for physiologic adaptations to the current and/or to decrease the total charge delivered by the pulse. • Are normally not adjustable on the unit. • Intrapulse intervals can also apply to monophasic currents. • [instructor note: click to start animation] Biphasic Pulse

13. Pulse Period • The pulse period is the amount of time from the start of one pulse to the start of the next pulse. • Includes the phase durations, intrapulse interval,and interpulse interval. • Inversely proportional to pulse frequency. As the pulse frequency increases, the pulse period decreases and vice-versa. • [instructor note: click to start animation] Two Monophasic Pulses Two Biphasic Pulses

14. Pulse Frequency • The number of times a pulse occurs per second • With alternating currents this measure is described as cycles per second

15. Pulse Trains (Bursts) • Trains contain individual pulses • Pulses in the train still have time-dependent characteristics: pulse duration, interpulse interval, etc. • Each train is separated by “off” times – the intertrain (or interburst) interval

16. Generator Attributes

17. Current Density • The amount of current per unit of area • The higher the current density, the more intense the effects 10 in2 300 V 30 V/in2 5 in2 300 V 60 V/in2

18. Duty Cycle • The amount (percentage of time) that the current is flowing relative to the time it is not flowing • Duty cycle = “ON”/(“ON + OFF”) * 100 • Example: • Current is on for 20 seconds and is off for 40 seconds • DC = 20/(20+40)*100 • DC = 20/60 * 100 • DC = 33.3%

19. Pulse Ramp • Used with a duty cycle • Gradually increases the current • Produces a more natural contraction • More comfortable

20. Electrical Currents

21. Measures of Electrical Current • Charge: • Microcoulomb, the charge delivered per pulse • Voltage: • The potential for electrical flow to occur. • The difference in charges between the positive (anode) and negative (cathode) poles • Current: • Amperage: The rate of electron flow • Wattage: • Measure of the ability to perform work • Calculated as W = Amperage * Voltage • Resistance: • Those structures (electrodes, wires, tissues) that do not transmit electrical energy

22. Average Current • The amount of charge delivered by one-half of a pulse or a cycle • Considers the amount of time required to deliver the charge

23. Circuit Types • Series Circuit • Electrons only have one path to flow • Parallel Circuit • Electrons have multiple paths to travel • The less the resistance within the path, the more flow that occurs • In the body, different tissues have different resistances • Nerves have relatively little resistance • Bone has high resistance