The measurement of oxygen in blood by means of a PO2 electrode involves which of the following?

• A. Wheatstone bridge arrangement of resistive elements sensitive to oxygen concentration
• B. Direct relationship between amount of oxygen in the sample and amount of current flowing in the measuring system
• C. Change in current resulting from an increase of free silver ions in solution
• D. Glass electrode sensitive to H+ ions

Answer: (B)

The measurement relies on an amperometric Clark-type PO2 electrode. Oxygen diffuses through a gas-permeable membrane to a platinum cathode where it is reduced, and the resulting current is proportional to the rate of this reaction. Under steady-state conditions, the rate at which O2 is reduced at the electrode—and thus the measured current—tracks the amount (partial pressure) of oxygen in the blood sample. In other words, more oxygen present means more O2 reaching the cathode per second, producing a larger current. This direct relationship is the essence of how the PO2 electrode quantifies oxygen.

The other concepts don’t describe this setup: a Wheatstone bridge would be for resistive sensors rather than electrochemical reduction; changes due to silver ions pertain to reference electrode effects rather than oxygen sensing; and a glass electrode sensitive to H+ ions measures pH, not oxygen.