The estimation of the diffusion constant and solubility of O(2)in 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 (zeta) 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 both D, the diffusion coefficient, and alpha, solubility, directly from the kinetic data. We do this by recording the exponential change in P(O(2))on 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 alpha for distilled water at a number of temperatures, olive oil, and the belly skin of Rana catesbeiana.