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A practical implementation of acoustic reflectometry for determining airway areas in routine clinical use is described. Advances over previous systems include portability, free breathing during measurements. no need to equilibrate with helium/6xygen, and real-time display of airway areas. Validation of the reflectometer with an airway model gave accuracies and reproducibilities (coefficient of variation (cv)) in the range 5-10%. With human volunteers, the within-mn cv was typically IO%, and the day-today c v was 20%. The eKect of breathing pattem on airway areas is demonstrated.In ten normal volunteers, acoustic and magnetic resonance imaging (MRI) methods of assessing pharyngeal and glottal areas were compared. The results (meaniSD) for the oropharynx were l.0+0.3cm2 acoustically and 0.9+0.5cm1 by MRI (p=O.77]. The corresponding figures for glottal areas were 1.3*0.3 cm'and 1.1+0.4cm2 (p=O.O9).

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