Abstract
Polarographic oxygen electrodes have been used to measure partial pressure of oxygen (pO2) in living tissue. The electrode provides a reliable measure in a specific location based on an electrolysis reaction induced at the electrode tip made by a combination of platinum cathode and silver anode. When a fixed polarization voltage was applied, oxygen is reduced at the cathode surface and a current flows. Because the current is stoichiometrically related to an amount of oxygen reduced, it can be converted to a pO2 based on a calibration curve, determined with standard solutions. The electrode consumes oxygen, which can be minimized by downsizing the electrode tip. The miniaturizing electrode allows for a minimum invasion of tissue measured, and ideally provides a rapid pO2 recording. However, this technique limits to a single point measurement. A phosphorescence quenching method allows for pO2 imaging. According to a Stern-Volmer relationship, the pO2 can be determined by either phosphorescence intensity or lifetime. The lifetime is independent of tissue optical property and concentration of the dissolved phosphor. Thus, the lifetime imaging is preferably used for mapping tissue pO2.
