Contents of this web site © Ray Jurewicz
| Direct CurrentThe simplest source of energy for direct current is a battery, where chemical reactions produce an excess of electrons at the one pole (cathode), and a deficiency of electrons at the other pole (anode). When connected through a closed circuit, electrons flow from an area of high concentration (cathode), to an area of low concentration (anode).Although the movement of particles is from negative to positive poles, by convention, current (I), is defined by moving from positive to negative terminals.
Voltage or EMF (electron moving force) may be thought of as the storage of energy behind a dam. This amount of stored energy is analogous to potential difference.
Current flow occurs only when a circuit is closed (or the dam is opened). Current will flow from area of excess to deficiency until the source is exhausted, or difference is eliminated. The strength of the current flow is measured in amperes, or milliamperes.
Historically described as galvanic current, unidirectional flow of charged particles is referred to as direct current, or monophasic. Flow of current may be continuous or interrupted. Interrupting the current into pulses (making and braking the circuit) will have the affect of depolarization of nerve or muscle. Continuous DC ( un-interrupted) current has applications in iontophoresis and wound healing.
Current waveform plotted in graph form by convention is represented by the X-axis as a function of time, and Y-axis as a function of current magnitude.
Interrupted DC current. Four monophasic pulses of undefined current strength or duration.
Each “twin peak” represents one mono-phasic pulse of undefined current amplitude. The pulse duration measures 100 usec.; phase duration undefined.
The duration of the phase along the X-axis is referred to as the phase duration.
Phase duration can be affected by the waveform configuration. In the first instance, the pulse and phase duration is equal; in the second the phase duration is shorter than the pulse duration, due to its configuration.
Alternating current is defined as bi-directional flow of charged particles. To produce this type of current, the voltage applied across the circuit is periodically reversed, allowing electrons to flow in one direction, and then the other. The result is a biphasic pulsed current. Each pulse contains a phase below and above the X-axis.
Each pulse may be further defined by whether or not opposing phase configurations is symmetric or asymmetric.
Top drawing-4 biphasic pulses; bottom drawing-2 biphasic pulses.
The duration of the phase above the x-axis is added to the duration of the phase below the x-axis to determine the pulse duration. Interpulse and interphase intervals are self-explanatory.
Polar affects and phase charge
The area under the curve of each phase is a function of the phase charge, expressed in coulombs. The greater the area, the greater the amount of phase charge. The amount of charge is applicable to how much energy is being introduced physiologically, and if any polar affects will occur.
Historically, a waveform referred to as faradic was introduced subsequent to simple make and brake galvanic (monophasic pulsed) current. It was more comfortable than pulsed DC, as its duration was usually shorter. It also had less polar effects due to its waveform.
Faradic current-assymetric biphasic pulse.
Developed as a tool for Russian athletes, it was thought that a high frequency pulse had the effect of lowering resistance and therefore allowing for more efficient delivery of current.
Continuous sine wave (polyphasic) waveform with a carrier frequency of 2500 Hz, modulated to yield 50 pulses.
“High Volt” Stimulation
Monophasic pulsed current with very short phase duration (5-20 usec) and very high peak current amplitude (2000 to 2500 mA). This waveform may prove beneficial for treating edema.
High voltage monophasic pulsed “twin peak” current
Regulation and Modulation of Electrical Stimulation
· Waveform selection controls
Many devices allow the selection of a particular type of waveform (russian, faradic, etc). Others will provide only one type of current waveform. It is important to review operation manuals to identify what type of current waveform that is available.
· Amplitude controls
Output is regulated in volts, amps, or both. Some sort of measurement scale is usually observed, but may have no direct relationship to the amount of current or voltage being applied.
· Balance controls
When more than two electrodes are available, this will allow more stimulation to be directed to one particular electrode set.
· Frequency controls
Permit the variation of number of pulses per second. This may be labeled rate, burst rate, or frequency. Some machines (russian) may have frequency established automatically.
· Duty cycle
Allows a cycle stimulation followed by a rest period during the treatment time established.
· Ramp time
Permit modulation of amplitude, frequency, or duration of the current gradually. Usually, ramping the amplitude is utilized to allow for gradual onset of a strong muscle contraction. Some machines also allow for “ramp off” allowing for gradual relaxation of muscle contraction. This may also be labeled surge time, or slope time. Some machines will automatically ramp certain waveform characteristics.
· Constant or continuous mode
Allow for “continuous” trains of stimulation at waveforms established automatically or manually, without a duty cycle. This will allow the clinician the ability to establish a certain level of stimulation and desired muscle contraction prior to choosing a particular duty cycle.
· Alternate or reciprocal mode
Permits the use of more than one set of electrodes; cycling stimulation between the sets of electrodes.
· Treatment timer
Self-explanatory. Allows clinician to set time of stimulation session.
· Wimp switch
Some machines permit a on/off switch to be utilized by the patient through a cord to the machine, in the event the patient needs to turn the current off.
Contents of this web site © Ray Jurewicz