Blood flow rate, temperature, oxygen tension and consumption in the skin of adults measured by a heated microcathode oxygen electrode.

Reliable transcutaneous measurements of arterial oxygen tension are based on a maximum skin blood flow rate which is created by heating the skin, typically at an electrode temperature of 44 to 45 degrees C. This increase in skin blood flow rate creates an arterialization of the oxygen tension in the capillaries and the surrounding tissue. The heat conducted to the skin surface is removed by a combination of convection (skin perfusion) and conduction to the deeper layers of the skin. This heat transport to and through the skin surface causes a measurable temperature profile from the electrode surface to the capillary layer. By a blood flow cessation it is possible to change the temperature profile because the convective part of the heat consumption is eliminated and the conductive part can then be measured and subtracted. Using the forearm as measuring area and a heated tc-PO2 electrode several observations were made. The mean temperature gradient over epidermis down to the capillary layer at an electrode temperature of 43, 44, and 45 degrees C was 2.1, 2.4 and 2.7 degrees C, respectively. The change in temperature profile caused by the blood flow cessation enabled primarily an estimation of the skin blood flow rate by temperature measurements, ranging from 0.07 to 0.24 ml.cm-2.min-1. Increasing blood flow rates correlated to increasing tc-PO2 values. By means of a dynamically, thermally shielded tc-PO2 electrode it was possible to determine the skin blood flow rates in the same arbitrary units computed on the basis of the heat dissipation to the skin surface. Furthermore, it was possible to correlate these blood flow estimations to the cutaneous blood flow rates measured by 133Xe washout technique. By increasing the electrode temperature the cutaneous blood flow rates increased from 12 to 50 ml.(100 g)-1.min-1. It was possible to calculate a conversion factor on the basis of the correlation between the heat determinations of the skin blood flow rate and the 133Xe measurements. Using this conversion factor the highest blood flow rate did not exceed 55 ml.(100 g)-1.min-1. The subcutaneous blood flow rate increased accordingly with increasing electrode temperature. It was concluded that the measured heat consumption of the skin is effected by the heat removing capacity of the cutaneous as well as the subcutaneous blood flow. The cutaneous blood flow, however, was considered predominant in the transport of heat from the skin surface. By 50 times of stripping the skin surface, the cornified epidermal membrane was removed. This procedure increased the tc-PO2 values by on an average 3.6 kPa (27.1 mmHg).(ABSTRACT TRUNCATED AT 400 WORDS)