The influence of the epidermal membrane on percutaneous pO₂ and metabolic rate

Abstract

It is accepted that cutaneous pO₂ measurements with polarographic oxygen electrodes measure a pO₂ approximately 5 kPa below the theoretical arterial/capillary oxygen tension in patients with a mature skin surface. This difference is somewhat lower in neonates and prematures. The difference is caused by:

the skin oxygen consumption,

the oxygen diffusion resistance of the epidermal membrane, and

the oxygen consumption of the electrode.

When stripping the epidermal membrane on 10 healthy volunteers, the skin pO₂ measured by the E5250 oxygen electrode, increased on an average by 3.60 ± 0.93 kPa. The computed skin oxygen consumption rate was before stripping 0.327 ± 0.065 ml O2 · (100 g · min)^-1 and 0.230 ± 0.088 ml O₂ · (100 g · min)^-1 after stripping. At an estimated capillary temperature of 43 °C mean arterial pO₂ was estimated to be 18.1 kPa, which was reduced by local metabolism to a mean capillary pO₂ of 14.4 kPa before and 15.2 kPa after stripping. Thus, stripping eliminated 82 % of the gradient between the capillaries and the electrode while reducing the computed oxygen consumption by 23–36 %.

In a further series of experiments on 9 healthy volunteers, the skin oxygen consumption was measured on the forearm by cuff occlusion before and after stripping of the stratum corneum. One of the electrodes used was a multicathode electrode with cathodes of diameters 25,50,150 and 250 microns. The oxygen consumption figures decreased with increasing cathode diameter.

Furthermore, it was observed that the oxygen consumption rate in the skin was age dependent, 0.450 at 20 years of age and 0.250 at the age of 50 and that Q₁₀ is approximately 2.3, very similar to other living tissues.

It is concluded: 1) Stratum corneum constitutes a significant diffusion resistance to oxygen diffusion. 2) It is not possible to obtain reliable oxygen consumption figures with a microcathode electrode without taking the diffusion resistance of stratum corneum into consideration. 3) The skin oxygen consumption is age dependent and has a Q₁₀ of 2.3.

Key-words:

• Oxygen consumption
• oxygen diffusion resistance
• skin pO₂
• transcutaneous pO₂