Dynamic measurement of gas composition in the middle ear. I: Technique

The middle ear is a balanced gas pocket which loses and gains gas constantly. This balance depends on the continuous interchange of gases from the atmosphere, through the eustachian tube and the circulating blood by diffusion. The relative contribution of each of these two sources can be determined by measuring the gas composition of the middle ear (ME). Because of the small quantity of gas in the ME, adequate sampling and accurate measurement of its composition are extremely difficult. An on-line system for middle ear gas composition measurements is described. The measuring instrument is mass spectrometer. ME gas samples are withdrawn by diffusion, and therefore are very small. Sampling and measurements are performed in a continuous mode.