Effect of electrode temperature on orthostatic changes in forefoot transcutaneous oxygen tension (tc-PO2)

The influence of increasing the temperature of the transcutaneous oxygen tension (tc-PO2) electrode from 37 to 45 degrees C on the orthostatic changes in tc-PO2 was studied in six normal subjects. The tc-PO2 electrode was mounted on the forefoot. The blood pressure of the forefoot was changed by elevating and lowering the forefoot in relation to heart level. At all electrode temperatures tc-PO2 decreased about 35% when the forefoot was elevated. At electrode temperatures between 41 and 45 degrees C tc-PO2 increased about 20% when the electrode was lowered below heart level. This indicates a passive vascular bed in the heated tissue under the electrode. However, at 37 degrees C tc-PO2 decreased about 40% when the forefoot was lowered. This indicates that the local vasoconstrictor response to increased venous transmural pressure is preserved when the tissue under the electrode is heated to 37 degrees C only. The study suggest that tc-PO2 monitoring at 37 degrees C may be used for continuous, non-invasive monitoring of the local vasoconstrictor response, and thus of arteriolar contractility and intact sympathetic innervation.