Whether transcutaneous oxygen tension (TcPO2) is independent of minor variations in perfusion under the TcPO2 electrode, as is claimed, was studied in 18 feet of 16 young healthy adults. The TcPO2 electrode was mounted on the dorsum of the foot and operated at 43 degrees C, while the blood pressure was changed by elevating and lowering the foot. During elevation the mean arterial blood pressure decreased corresponding to the hydrostatic pressure of the column of blood between the heart and the position of the foot. In every experiment TcPO2 decreased when the foot was elevated at an average rate of 1.2% per millimeter Hg change in mean arterial blood pressure. TcPO2 was negatively correlated to blood flow in normal unheated tissue, but significantly and positively correlated to blood flow in the heated, vasodilated tissue under the TcPO2 electrode. In the heated tissue normal blood flow regulation was abolished, and the perfusion under the electrode was mainly determined by the arterial blood pressure. It is concluded that TcPO2 in adults--and probably also in neonates--is affected by the minor or large variations in the perfusion under the electrode caused by fluctuations in arterial blood pressure.
Adult Blood Gas Analysis