Airway area by acoustic reflections measured at the mouth

TLDR

The study tests whether upper airway and tracheal geometry can be inferred from acoustic reflections recorded at the mouth. Six subjects’ airway cross‑sectional area profiles were inferred from mouth‑recorded acoustic reflections and compared to orthogonal radiographic measurements. Acoustic data showed area maxima at the uvula and hypopharynx and minima at the oropharynx and glottis; in air the inferred tracheal areas exceeded radiographic values, whereas in 80 % He–20 % O₂ there was good intra‑subject agreement with a mean coefficient of variation of 0.16, supporting accurate noninvasive determination of airway geometry.

Abstract

We tested the hypothesis that features of upper airway and tracheal geometry can be inferred from acoustic reflection data recorded at the mouth. In six subjects we computed inferences of airway cross-sectional area vs. distance and compared them with measurements obtained from orthogonal radiographic projections of the trachea. The acoustic data show local area maxima at the uvula and hypopharynx and local minima at the oropharynx and the glottis. With subjects breathing air the inferred tracheal areas markedly exceeded the radiographic measurements. With subjects breathing 80% He-20% O2 there was good intrasubject agreement between acoustic and radiographic data in spite of large intersubject variability. The average coefficient of variation of tracheal area determinations for five trials in all subjects was 0.16. These studies suggest that features of airway geometry between the mouth and carina can be determined accurately and noninvasively in individual subjects from high-frequency reflection data measured at the mouth.