GIMA SpA
DIATERMO MB250 – DIATERMO MB400
MA303IGBa-19-03-2007 Manuale
d’Istruzioni / Instruction’s Manual
31
2.
ELECTROPHYSICAL PRINCIPLES
In the electrosurgical interventations the traditional use of bade surgical is substitued by electrosurgical needle that allows to
make in a fast, simple and effective way the cut and coagulation of tissues.
The electrosurgical needle is made on the principle of electrical energy conversion in heat and it’s constitued by:
a sinusoidal oscillator in radiofrequency (0.4 – 2MHz)
a generator of wave packets, with repetition frequency of packets equal to 15 – 30 kHz
a mixer for the transfer, to the power amplification block, of the only wave form adapt to the cut, or the only wave form
for the coagulum, or a signal obtained by an opportune mixing of the two;
a power amplification block able to supply the necessary power in terms of current and to transmit to the electrods, by
transformer, the amplified signal;
a security circuit for the return electrode, to take possible cable interruptions and disarm the radiofrequency supply;
by an active electrode opportunely shaped (handle);
by a return electrode (neutral) that close the circuit by the patient.
The current that crosses the biological tissue can cause:
1.
Joule Effect
2.
Faradic Effect
3.
Electrolitic Effect
1) Joule Effect
In the biological tissue, crossed by electrical current, it’s produced an heating (thermical effect), dependent by the electrical
resistance of the tissue, by the current density, by the application time and that can determine many cellular transformations.
Q = I
2
x R x T
The thermical effect influence (Joule Effect) is made by:
Current Intensity and output power
Modulation levelGrado di modulazione
Parameters interpretable by the wave form of the high frequency current produced by the generator.
Electrode shape
The electrode shape can be needle or rounded according to the necessity, it has reduced dimension; for this the current
density on the point surface [A
·
m
-2
] is highest. The electrodes with a thin section create an high current density, an high
temperature, favouring the cut action. Those with a big surface create a smaller current density, a smaller temperature,
realizing a coagulation effect.
State of active electrode
The thermical effects can be reported to the human body resistance, to which must be added the electrode contact
resistance. It’s indispensable to maintain the active electrodes perfectly clean to not have a reduction of the effects.
Characteristics of the tissueo
The resistive characteristics change according to the biological tissues.
Biological tissue
(range from 0,3 to 1 MHz)
Metals
Blood 0,16 x 10
3
Silver 0,16 x 10
-5
Muscle, kidney, heart 0,2 x 10
3
Branch 0,17 x 10
-5
Liver, milza 0,3 x 10
3
Gold 0,22 x 10
-5
Brain 0,7 x 10
3
Aluminum 0,29 x 10
-5
Lung 1,0 x 10
3
Fat 3,3 x 10
3
(Example of specific resistances of organic and metallic materials )
According to the come temperature and in function of used pulse form, it’s possible to recognize many types of effects
produced by the current in radiofrequency on the human body:
Coagulation
Temperatures from 60 to 70 ºC in the area arround the active electrode cause a slow heating of intra-cellular liquid, the water
contained in the cell evaporates and an action of coagulum is obtained, so the blood flow is stopped.
Cut
Temperature over 100 ºC in the area arround the active electrode determine the evaporation of the intracellular liquid and the
cell explosion. The vapour arround the electrode baits a chain reaction in the direction where the active electrode is worked,
transmitting the evaporation energy to the tissues arround it.
The cut isn’t, for this, a mechanical resection.
If the temperature comes to 500 °C it’s verify the tissue with an action of cauterization.
Mixed currents
They are obtained by the mixing of coagulation and cut effects. There is a reduction of blood loss during the cut procedure, or
like cut that develops a substantial eschar coat.
