1238 SKIN METABOLISM AND BLOOD FLOW MEASUREMENT: ROLE IN TCPo2 ANALYSIS

Abstract

The effect of heating by a tc Po2 electrode on skin metabolism and blood flow, and on the relationship of Pao2 to tcPo2 was determined in 3 normal adults. While breathing O2, skin metabolism was measured as O2 solubility × ΔtcPo2/Δt (torr/min), at 37° and 45° after arterial cuff occlusion. Using this, skin blood flow and diffusion gradients for O2 and heat between capillaries and surface were measured by solution of simultaneous equations for tcPo2 vs Pao2 from 6 steady state correlations at 2 temperatures (43°,45°) and 3 Po2s (75,150,600), using the changes of O2 dissociation and solubility thereby induced. Heating efficiency, (Tc-37)/(Te-37) averaged .84 (c=capillary,e=electrode). (c-e)Do2 was 28±3 torr at 44° Te. Skin O2 consumption and blood flow were .0043±.0001 ml O2 and .75±.10ml blood per gm per min. From these parameters, tcPo2 was computed for O<Pao2<700 defining a sigmoid relationship. At Te=44°, tcPo2 nears O at Pao2=20, approximates Pao2 when 60<Pao2<130, and parallels Pao2, (about 50 torr lower) when Po2>300. TcPo2 was most dependent on blood flow at high O2. The data yield algorithms for “correcting” tcPo2 measurements 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 tcPo2 washin 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 O2 solubility. Similar analysis will be done in children.