Human middle ear gas composition studied by mass spectrometry.

The purpose of this study was to develop a procedure for mass spectrometric measurement fitted to analyse the human middle ear gas composition, and to determine the partial pressures of the middle ear gases in adults with healthy ears. To avoid the risks of admixture of the gas sample with atmospheric air we used "on-line" sampling from the middle ear to the analysing equipment, and a new protective technique at the site of puncture. The inlet system was modified to achieve sufficiently low gas consumption. The system had excellent linearity, and model experiments showed that the described procedure gives a very high accuracy. Measurements of the gas composition in the middle ear in 10 adult subjects with healthy ears gave the following values: pO2 = 612.38 +/- 3.97 mmHg, pO2 = 40.85 +/- 3.68 mmHg, pAr = 7.09 +/- 0.08 mmHg and pCO = 52.69 +/- 5.54 mmHg.