A comparison of changes in the transcutaneous oxygen tension and capillary blood flow in the skin with increasing compressive weights.

Two measures are being advocated to evaluate physiologic changes associated with compression of skin: transcutaneous oxygen tension (tcO2) and laser-Doppler blood flow. This study asked: 1) What changes occur in tcO2 and laser-Doppler blood flow with increasing compressive weight; and 2) do these measures respond differently to increasing weight? An indenter was used to apply incremental weight to the trochanter of healthy volunteers. During the first session, tcO2 was measured, and laser-Doppler blood flow was measured during the second session. The mean values of tcO2 and laser-Doppler blood flow were analyzed for significant changes over the range of applied weight. If significant change occurred, the polynomial that best described the data was determined. Mean values for tcO2 showed a significant decrease with increasing compressive weight. Its decrease was described by a second degree polynomial (quadratic). The weight that resulted in the tcO2 reaching zero for individual subjects ranged from 400-1000. Mean values for laser-Doppler blood flow showed a significant decrease with increased weight. The decrease was best described by a first degree polynomial (line), which is a different pattern from the tcO2. Laser-Doppler blood flow continued to decline with increasing weight beyond the point where tcO2 reached zero. During low-flow states, tissue oxygen utilization may exceed oxygen delivery and lead to ischemia even though capillary closure has not occurred.