The importance of an elevated skin temperature in transcutaneous oxygen tension measurement.

The oxygen tension as measured by a heated transcutaneous polarographic electrode has been shown by a number of workers to correlate closely with the arterial blood oxygen tension as measured by accepted invasive methods. The present paper presents a study of the dependence of the measured skin oxygen tension values on the temperature of the sensor. A graph is included that emphasizes that the skin sensor temperature should be greater than 43 degrees C if the device is to be operated in the platequ region. The effect of increasing the skin temperature on both the local blood flow and the associated skin permeability changes has been studied. Skin blood flow studies were performed by means of a radioisotope washout technique using krypton-85 and xenon-133 together with a Huch transcutaneous oxygen electrode. The electrode control system incorporates a heating power monitor that Huch and co-workers suggest can indicate the relative blood flow in the tissues beneath the electrode. Two techniques for localized heating of the skin were employed during the washout experiments. First, a copper tube heating ring supplied from a water bath surrounded the area of measurement. Second, a focused source of light applied heat directly to the area of interest, which was 12 mm in diameter. Information obtained in the course of using a quadrupole mass spectrometer with a heated skin probe has given some information about the permeability of the skin and underlying tissues. In these studies three gases were used. Oxygen and argon are transported by the blood, but carbon dioxide tends to be generated within the tissues, and its skin tension is less affected by the blood content. Between 36 degrees C and 45 degrees C it is possible to relate changes in the oxygen and argon skin tensions to changes in capillary blood flow.