Gas mixing in the human upper airways.

The longitudinal dispersion of gas in the upper airways (oropharynx and larynx) was studied in 5 healthy subjects by measuring the response after injection of a bolus of 133Xe into the inspired airstream. The radioxenon concentration was measured during inspiration and expiration with two counter probes, one in front of the lips and one under the glottis. Assuming that the output tracer concentration follows a Gaussian distribution, the dispersion is expressed by the variance. The dispersion coefficient for the upper airways can then be readily computed with a simple mathematical model. This coefficient is found to be a function of the Peclet number.