Figure 3. Diffusion through a tissue sheet. The amount of gas transferred is directly proportional to the area (A), a diffusion constant (D), and the difference in partial pressures (P1- P2) and is inversely proportional to the thickness (T). The constant is directly proportional to the gas solubility (Sol) but inversely proportional to the square root of its molecular weight (M. W.). (Reproduced with permission from West JB: Best and Taylor's Physiological Basis of Medical Practice. 12th edition. Baltimore, Williams and Wilkins, 1990, Figure 5.37, Section 5, Chapter 37, p. 548.)