The Estimation of the Diffusion Constant and Solubility of O2in Tissue Using Kinetics

The diffusion of a gas through a substance in which it is soluble is analogous to the passage of electric current through a circuit with both capacitance and resistance. We model steady-state diffusion employing this analogy, and extend the model to include a description of the kinetics of systems under circumstances of changing partial pressure, applying two physical constants from electrical circuitry to gas diffusion: capacitance (ζ) and resistance (R). We represent the substrate of the diffusion as a capacitor being charged through a resistor after the rapid imposition of a voltage change. Using the insight derived from this model we have devised an experimental system that allows us to approximate bothD , the diffusion coefficient, and α, solubility, directly from the kinetic data. We do this by recording the exponential change in PO2on one side of a sheet of material both with and without the addition of a purely resistive barrier of known resistivity. The method was used to estimate D and α for distilled water at a number of temperatures, olive oil, and the belly skin of Rana catesbeiana.