Studies on gas tension in the normal middle ear. Gas chromatographic analysis and a new sampling technique.

In studying mechanisms regulating the middle ear pressure it is essential to know the gas compositions of the middle ear. We have constructed a device which made it possible to sample middle ear gas without creating a negative pressure, thus eliminating the risk of admixture of atmospheric air. The samples were analysed by gas chromatography. In 26 normal subjects we found relatively stable values of carbon dioxide (median 52 mmHg, range 31-69 mmHg) and nitrogen (median 605 mmHg, range 563-627 mmHg). The values of oxygen were more fluctuating (median 54 mmHg, range 23-111 mmHg). In 10 of the subjects, arterial gases were determined simultaneously. No correlation could be shown between middle ear and arterial oxygen and carbon dioxide tensions. This investigation provides evidence contradicting the classical theory of a high negative middle ear pressure in Eustachian tube closure. We found strong indications that the Eustachian tube plays an active role in regulating the pressure in the normal middle ear, but variations in blood flow through the middle ear capillaries may also be an important regulating factor.