Eberhart's Manual of High Frequency Currents
Noble M. Eberhart, M.D., Ph.D., D.C.L., 1911
Characteristics and Synonyms. As Long ago as 1899, Prof.
D'Arsonval noticed that passing the D'Arsonval current through certain tissues of the body
produced a higher temperature in these tissues. Nagelschmidt, Doyon and others confirmed
these early observations, and the name diathermy was applied to this method of
increasing the temperature of the internal tissues of the body.
The direct D'Arsonval current is used and diathermy is
synonymous also with the terms thermo-penetration, electro-coagulation and electro-thermic
coagulation. The application is always bi-polar.
It really amounts to the application of electrically
generated heat, which may be made to cover certain definite areas between the poles of
the apparatus, and may be used to raise the temperature of the tissues or even carried to
the point of coagulation with the formation and separation of a slough. In the latter case
it is the equivalent of a surgical procedure.
We are familiar with the action of the galvanic
current. If we pass this current through water, owing to electrolysis, the water is
decomposed into hydrogen and oxygen which collect at the positive and negative poles
respectively, or, if the current is passed through a solution of potassium iodide and
starch, a dark color is immediately noticed at the negative pole, due to the decomposition
of the potassium iodide and consequent action of the iodine on the starch solution. If we
dip our hand into the water while the current is passing, there is a distinct tingling
If, now, instead of using the galvanic current, we pass
the direct D'Arsonval current through the water or solution, no electrolytic action is
apparent and the only effect is an increase of temperature in the solution, as is
evidenced by the introduction of a thermometer which shows the steady rise in temperature
until the water boils. It is estimated that with the diathermic current the internal
temperature of the body, located between the points of application can be raised to a
temperature of 110 to 140 degrees Fahrenheit, though many believe 110 degrees to be about
the limit of skin and tissue resistance.
Effects. On account of there being practically
no skin resistance to the passage of the diathermic current, the current passes directly
from one electrode to the other, heating the tissues that lie between the electrodes. The
current can be concentrated in this manner, and is always under absolute control. This is
of great value, as a little experience will enable the operator to gauge the amount of
current required to produce any given temperature in the tissues and reduces the
application of this current to exact measurement, so difficult to obtain when applying an
ordinary high frequency current.
If electrodes of the same amount of surface are used on
the opposite sides of a part, the same effect would be produced at each electrode or a
uniform effect produced between the two, making allowance for the fact that fatty tissues
heat quickly and that bones are slow to heat, but retain their heat longer, while muscular
tissues are slower to heat than either fat or bones.
If we decrease the size of one electrode, since the
same amount of current is passing, there will be a more intense heat over the area of the
smaller electrode. If sufficient current is used the heat acts like the cautery,
coagulating and destroying the tissue.
By regulating the size of the electrodes the heat may
be delivered wherever desired within the tissues, thus the value of this current in all
inflammatory conditions of joints, etc.
When the cauterizing effect is desired, the active
electrode is usually a metal point or a wire. In this form it represents one form of
fulguration. It is employed in papilloma of the bladder. (The technique is given under
this heading in Chapter VI.)
Diathermic currents are measured with the hot wire
Range of Usefulness. Outside of their use in one
form of fulguration as above referred to, they nave been very successfully used in
connection with deep Roentgen therapy in malignant growths, and in the form of increased
heat without carrying it to tissue coagulation, in arteriosclerosis, local or peripheral
disturbances, sciatica, neuralgia, lumbago, asthma neuritis, headaches and rheumatic or
other forms of arthritis. Many other conditions naturally suggest themselves where these
currents may be employed.
Techniques. For increased internal heat, the
method of the use of this current is as follows: Connecting cords are attached to
electrode of suitable size or shape for the part that is to be treated. These electrodes
are made either of solid discs, or a thin brass sheet covered with absorbent material. In
order to make better contact they are first covered with gauze saturated with a normal
salt solution, and the part to be treated is also moistened with this solution,. The
control of the current is easily maintained by using a meter and the exact amount that is
applied can be measured at all times. In general treatment, the current is slowly turned
on until the meter shows from 700 to 800 milliamperes passing, and then it is gradually
increased up to the tolerance of the patient. The operator should remember that it is
better to commence with a small current and gradually and uniformly heat the part between
the electrodes rather than to start with a heavier current where the greatest effect is
nearer the two electrodes, for if too much current is used, the tissues near the
electrodes will be heated beyond the pont of tolerance before the tissues that lie deeply
are heated as much as they should be, and burns will be produced.
Fig. 64b - A New Electrode for Modified Diathermy.
In the second method, where coagulation and
cauterization are desired, the active electrode must be metallic, and if extensive work is
to be done anaesthesia is required.
Dr. G. E. Pfahler (Journal Advanced Therapeutics, Dec.,
1914) has accomplished remarkable results by combining this method with deep Roentgen
therapy in malignant growths. The work is done under an anaesthetic, as the pain is
severe. In most of his cases ether was employed, but in mouth cases hypodermic injections
of one or one and a half HMC tablets (hyoseine hydrobromide gr. 1/100; morphine
hydrobromide gr. 1; and cactoid gr. 1/64) were used. These in some cases had to be
supplemented by ether.
Fig. 64c - Diathermy Electrodes.
He uses an instrument capable of generating 1,000 to 2,000
milliamperes. In removing a portion of a lip he uses a ball electrode inside, about
three-eights of an inch in diameter, and a needle-point electrode externally. He says;
"I would outline the area of the diseased tissue to be removed by allowing the
current to flow from this point toward the ball electrode on the inside, and then
coagulate the entire diseased tissue. At first I depended upon the needle electrode to
actually carve out the diseased tissues, but now I find it simpler to cut this away with a
pair of curved scissors after coagulation, always cutting within the coagulated tissues.
In this way there is no bleeding and the edges are completedly sealed off.
"In destroying an extensive lesion in the cheek I used a flat
electrode, one inch in diameter, on the inside and a point electrode on the outside. In
destroying a portion of the tongue I have used two point electrodes. The electrodes are
held in contact with the tissue."