Which statement about impedance and dose is true?

• A. Higher impedance reduces current flow at a given voltage and can reduce delivered dose.
• B. Higher impedance increases current flow and dose.
• C. Impedance has no effect on current or dose.
• D. Impedance only affects patient comfort, not dose.

Answer: (A)

The key idea is that impedance directly affects how much current flows when a voltage is applied. With a fixed voltage, current through the tissue is I = V / Z. So when impedance increases, current decreases. Since the delivered dose depends on the amount of charge delivered (roughly current times time, Q = I × t), higher impedance at the same voltage means less current and less dose. Clinically, impedance can vary with skin prep, electrode contact, and electrode size, so improving contact lowers impedance and increases the current toward the intended dose. The other statements misstate the relationship: impedance does affect current and dose, it doesn’t only affect comfort, and higher impedance does not increase current.