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

Abstract

The influence of increasing the temperature of the transcutaneous oxygen tension (tc-PO₂) electrode from 37 to 45°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°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°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°C only. The study suggest that tc-PO₂ monitoring at 37°C may be used for continuous, non-invasive monitoring of the local vasoconstrictor response, and thus of arteriolar contractility and intact sympathetic innervation.

Key Words:

• arterioles
• blood flow
• blood flow regulation
• cutaneous
• local heating
• skin temperature
• subcutaneous
• sympathetic nervous system
• transcutaneous oxygen tension