Question

Surgical diathermy causes electromagnetic interference and in this process, the lead wires and the subject serve as:

• A. Out-of-band noise source
• B. Antenna
• C. Shielding
• D. Attenuator

Hint:

In electrosurgical environments, long unshielded cables act as unintentional receiving antennas. To minimize electromagnetic interference (EMI) pickup: - Keep patient lead wires as short as possible and twist them tightly together to minimize the magnetic flux induction loop area. - Utilize shielded cables with proper multi-point grounding and high-frequency filtering networks (ferrite beads or low-pass filters) at the input stages of diagnostic monitoring equipment.

Answer 1

The Correct Option is B

Concept: Surgical diathermy (electrosurgery) utilizes high-frequency alternating electrical currents (typically in the radiofrequency range of $300\text{ kHz}$ to $3\text{ MHz}$) to cut tissue or achieve coagulation. Because of the extremely high power levels involved, these units act as potent emitters of electromagnetic radiation. Electromagnetic Interference (EMI) propagation requires three basic components:
• An EMI Source (the electrosurgical unit spark-gap discharges).
• A Coupling Path (radiative or conductive transmission paths).
• A Receptor/Victim (sensitive monitoring equipment such as ECG or EEG monitors).

Step 1: Investigating the role of the subject and lead wires.
Biological tissue behaves as a volume conductor. When a patient is undergoing surgery, their body is filled with ionic fluids that can carry high-frequency currents. Additionally, long monitoring cables (such as ECG or EEG electrode lead wires) running from the patient to diagnostic machinery form long conductive loops.

Step 2: Correlating with electromagnetic wave principles.
In radiofrequency physics, any unshielded conductor whose physical length is comparable to a fraction of the electromagnetic wavelength acts as an efficient structure for radiating or capturing electromagnetic energy. This structure is defined as an antenna. During electrosurgical procedures:
• The high-frequency electro-surgical current traveling through the patient distributes across the body.
• The unshielded bio-potential lead wires act as long receiving linear wire antennas.
• These elements pick up the radiated electromagnetic waves generated by the high-power diathermy unit and convert them back into unwanted high-frequency electrical noise voltages directly superimposed on the minute biological signals. Consequently, the lead wires and the human subject inadvertently function as an antenna system that couples electromagnetic interference into nearby monitoring instruments. This corresponds directly to Option (B).