Which statement about current modes and safety is true?

• A. Constant voltage is safer and preferred.
• B. Constant mode is not used in therapy.
• C. Constant current is safer and preferred.
• D. There is no difference in safety between modes.

Answer: (C)

In electrotherapy, safely delivering a predictable dose hinges on controlling the current through the body. The body’s impedance varies between people and even within a session, so keeping the current constant ensures a consistent, safe level of stimulation. With constant current, the device adjusts the voltage as needed to maintain that set current, so if the skin becomes more conductive or later resistance changes, the dose remains the same. This minimizes the risk of unexpectedly high currents that could cause burns or discomfort and ensures the therapy achieves its intended effect.

If you were to rely on constant voltage instead, the current would change as tissue impedance changes (I = V/R). Lower impedance could allow a surge in current, increasing safety risks, while higher impedance could yield insufficient stimulation. Because of these unpredictable changes, constant current is considered safer and is commonly preferred in therapy. The idea that constant mode isn’t used, or that there’s no safety difference between modes, doesn’t hold, since current control directly affects the safety and reliability of the treatment.