Gas Diffusion Through the Tympanic Membrane: A model study in the diffusion chamber

Abstract

The diffusion of CO₂ through the tympanic membrane—removed after death—has been studied in a diffusion chamber under laboratory conditions. Thirteen measurements have been made and the mean value of CO₂-diffusion through the membrane per mm² and minute is 6.691 × 10⁻-⁶ ml at atmospheric pressure. This makes 0.482 ml for the whole tympanic membrane (approx. 50 mm²) for 24 hours. When the relation in diffusion capacity between O₂, N₂ and CO₂ is known, the amount of oxygen and nitrogen diffusing at prevailing difference in partial pressure can be calculated to 0.3 and 1.26 microliters respectively. When the 24-hour ventilation through the Eustachian tube is 1–2 ml (Ingelstedt et al.) the values for oxygen and nitrogen are only 0.5–1 0/00 of the tubal amount. The figures calculated in the experiments seem to be higher than those in vivo, where circulation with a metabolic uptake of O₂ and carrying away of N₂ plays an important role. The normal tympanic membrane, therefore, does not seem to be able to contribute to the ventilation of the middle ear and the cellular system.