Estimation of Skin Metabolism and Blood Flow with tcP_o2 and tcP_co2 Electrodes by Cuff Occlusion of the Circulation

In subjects breathing 100% O₂, arterial circulation was occluded proximal to transcutaneous O₂ and CO₂ electrodes. The linear fall of tcP_o2, ΔP_o2, was used to quantitate skin metabolic rate, V_o2. At 45d̀C, mean ΔP_o2 was 16.8 kPa/min (127.2 mmHg/min). Multiplying by solubility, 0.0219 ml ml^-1atm^-1, gives skin V_o2 = 0.00366 ml 0₂ gm^-1min^-1. At 37d̀C (after vasodilation at 45d̀C), V_o2 was 0.00278. Assuming skin RQ, = 0.8, the initial ΔP_co2 was used to estimate skin CO₂ dissociation curve slope to be 1.48 ml gm^-1atm^-1. tcP_co2 rose two to three times more rapidly when skin became hypoxic, suggesting anaerobic titration of skin HCO^-₃. After release of occlusion both electrodes yielded quasi-exponential returns to control from which blood flow was estimated to be 1.2 ml gm^-1min^-1 from O₂ rate, and 0.3 ml gm^-1min^-1 from CO_2. Flow was also computed from the Vo₂ and the (a-v)Po₂> estimated to be twice the arterial to capillary Po₂ difference. Capillary Po₂ (cP_o2) was computed from tcP_o2 by adding 30 mmHg (diffusion gradient at 45d̀C) and correcting cP_o2 to 37d̀C. Flow from this (a-v)0₂ content difference and V_o2 averaged 0.39 ± 0.10 ml gm^-1min^-1 at 45d̀C in 11 runs.

Computer programs have been developed to solve four simultaneous equations after determining tcP_o2 and Pa_o2 at high and low P_o2 at two temperatures. Preliminary data in three adults gave mean blood flow values of 0.45 ml gm^-1min^-1. Equations also determine capillary temperature, Tc, and capillary to surface diffusion gradient, D:Tc = 0.92(Te-37) ± 37, and D = 4 kPa (30 mmHg) at 45d̀C, where Te is electrode temperature.