Longwave (Kilohertz) Ultrasound

Ultrasound, as a therapy, involves the application of sound energy at a frequency above the normal hearing range (approximately 16Hz - 20,000 Hz). Mechanical energy beyond this range is not audible, though the nature of the energy does not change – it is still a mechanical (pressure) wave. Therapeutic Ultrasound frequencies usually between 1 and 3 MHz (millions of cycles per second) whereas Longwave ultrasound in the 40 – 50 kHz range (tens of thousands of cycles per second). Whilst this is clearly still beyond the normal upper limit for audible sound, it is not as far removed as traditional (MHz) ultrasound. It is probably preferable to refer to this particular form of ultrasound therapy as kilohertz ultrasound (as a way to distinguish it from the more normal MHz (Megahertz) ultrasound therapy. For additional information relating to the ‘physics’ of ultrasound, the basic ultrasound page/handout should have the basic information that you need.

It is suggested that due to its lower frequency and therefore greater wavelength, the energy will penetrate further into the tissues and thus ‘reach’ deeper tissues and have effects that traditional ultrasound is unable to achieve. This may or may not in fact be the case, and the biggest problem lies with the lack of specific research into ‘longwave’ or ‘kiloherts’ ultrasound.
One of the major effects of this different frequency is that there is claimed to be a difference in the effective penetration depth. By employing a LOWER FREQUENCY, the wavelength will be greater (assuming the velocity in tissue is approximately constant). The relationship between sound wave frequency, tissue velocity and wavelength is denoted thus :
v = f.l
At 3MHz, the wavelength (l) will be in the order of 0.5mm
At 1MHz the wavelength will be in the order of 1.5mm
At 45kHz the wavelength will be in the order of several 10’s of cm’s (around 30cm at 45kHz)
The effective penetration depth is also related to frequency. It is known that 1MHz and 3MHz are absorbed at different rates in the tissues and therefore have different penetration depths. The penetration depth of kilohertz US is expected to be in excess of 20 times greater than MHz ultrasound.

Galvanic Stimulation (GS)

Galvanic stimulation is most useful in acute injuries associated with major tissue trauma with bleeding or swelling. In contrast to TENS and IFC units, which apply alternating current, galvanic stimulators apply direct current.
Direct current creates an electrical field over the treated area that, theoretically, changes blood flow. The positive pad behaves like ice, causing reduced circulation to the area under the pad and reduction in swelling. The negative pad behaves like heat, causing increased circulation, reportedly speeding healing.

Interferential Current (IFC)

Interferential current is essentially a deeper form of TENS. In essence, IFC modulates a high frequency (4000 Hz) carrier waveform with the same signal produced by a TENS unit. The high frequency carrier waveform penetrates the skin more deeply than a regular TENS unit, with less user discomfort for a given level of stimulation. Deep in the tissues, the carrier waveform is cancelled out, resulting in a TENS-like signal deep under the skin.
Anecdotal evidence suggests that the IFC units may be useful for patients who have not had relief from TENS. However, at $2000 per unit, IFC devices are significantly more expensive than TENS units.

Transcutaneous Electrical Nerve Stimulators (TENS)

The patient may use a TENS unit at home for back pain relief on a long-term basis. TENS units are about the size of a pack of cigarettes and typically cost $250 - $700. All units allow the user to adjust the intensity of the stimulation; some units also allow the user to select high-frequency stimulation (60 - 200 Hz) or low-frequency stimulation (<10 Hz).
High frequency stimulation, sometimes called "conventional", is tolerable for hours, but the resultant pain relief lasts for a shorter period of time. Low-frequency stimulation, sometimes called "acupuncture-like", is more uncomfortable and tolerable for only 20-30 minutes, but the resultant pain relief lasts longer.

TENS users should experiment with various electrode placements. Electrodes can be placed over the painful area, surrounding the painful area, over the nerve supplying the painful area, or even on the opposite side of the body. TENS users need to try the unit for several days with several electrode placements prior to deciding if it will be useful. A home trial for several days to weeks is preferable.

Common characteristics of electrotherapy stimulation

TENS, IFC, and GS all apply electrical stimulation to nerves and muscles via adhesive pads placed on the skin. These devices are powered by batteries, and some units have an adapter that allows powering from an outlet.

Side effects are rare, but include allergic skin irritation under the adhesive pads and transient pain from the electrical charge. Placing the pads over the heart or over pacemaker leads could conceivably cause cardiac arrhythmia; placing them over the throat could conceivably cause low blood pressure; and placing them over a pregnant uterus could conceivably cause fetal damage. Because of these risks, electrical stimulation over these areas should be avoided. Electrical stimulation should also not be applied over malignancies or infected areas.

what is electrotherapy

Electricity has been used to treat pain for over 100 years. Early proponents of electricity were labeled as charlatans, but recent scientific studies have proven that electricity can reduce both acute and chronic pain.
In This Article:

* Electrotherapy
* Transcutaneous Electrical Nerve Stimulators (TENS)
* Interferential Current (IFC)
* Galvanic Stimulation (GS)

The exact mechanism of electrical stimulation’s beneficial effect remains controversial. Electrical stimulation may directly block transmission of pain signals along nerves. In addition, electrical stimulation has been shown to promote the release of endorphins, which are natural painkillers produced by the body.

Several different electrical stimulation devices exist, each producing different frequencies, waveforms, and effects. Electrical modalities include

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Transcutaneous Electrical Nerve Stimulation (TENS) (the most commonly used)
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Interferential Current (IFC)
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Galvanic Stimulation (GS)