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

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.