Skin surface PO2 measurement and the effect of externally applied pressure.

The effect of externally applied load on the partial pressure of oxygen in tissue, measured at the skin surface (PSO2) was examined by applying a load to a transcutaneous O2 monitor mounted on the skin of healthy subjects. The load was increased every 4 minutes, and the PSO2 was recorded at the end of the 4-minute period. Three sites were investigated: the sacrum, the greater trochanteric area, and the lateral aspect of the thigh. Mean initial values for the 3 sites were found to be 10.1, 11.1, and 10.1 kPa, respectively. On increasing the applied load, values were found to reduce gradually at first and then at an increasing rate to zero at the "cut-off" load. The mean cut-off pressure for the 3 areas was 15.2, 18.8, and 18.1 kPa.