1238 SKIN METABOLISM AND BLOOD FLOW MEASUREMENT: ROLE IN TCPo2ANALYSIS

The effect of heating by a tc Po2electrode on skin metabolism and blood flow, and on the relationship of Pao2to tcPo2was determined in 3 normal adults. While breathing O2, skin metabolism was measured as O2solubility × ?tcPo2/?t (torr/min), at 37° and 45° after arterial cuff occlusion. Using this, skin blood flow and diffusion gradients for O2and heat between capillaries and surface were measured by solution of simultaneous equations for tcPo2vs Pao2from 6 steady state correlations at 2 temperatures (43°,45°) and 3 Po2s (75,150,600), using the changes of O2dissociation and solubility thereby induced. Heating efficiency, (Tc-37)/(Te-37) averaged .84 (c=capillary,e=electrode). (c-e)Do2was 28±3 torr at 44° Te. Skin O2consumption and blood flow were .0043±.0001 ml O2and .75±.10ml blood per gm per min. From these parameters, tcPo2was computed for O<Pao2<700 defining a sigmoid relationship. At Te=44°, tcPo2nears O at Pao2=20, approximates Pao2when 60<Pao2<130, and parallels Pao2, (about 50 torr lower) when Po2>300. TcPo2was most dependent on blood flow at high O2. The data yield algorithms for “correcting” tcPo2measurements to obtain Pao2. Skin metabolism increases 7%/°C, while blood flow (after 30 min. heating at 45°C) fell only 1.2%/°C with brief reduction of Te to 43°C. Skin blood flow, independently determined from tcPo2washin time constant after release of occlusion while breathing O2, averaged about 33% higher than above, possibly due to post-ischemic hyperemia, and uncertainty regarding skin O2solubility. Similar analysis will be done in children.