AIRWAY AREA BY ACOUSTIC RESPONSE MEASUREMENTS AND COMPUTERIZED-TOMOGRAPHY

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Abstract
In order to determine more precisely the accuracy with which the acoustic retention technique (ART) can infer airway area during the spontaneous breathing, we compared acoustic measurements of airway can with equivalent areas measured from computerized tomographic (CT) scans of the neck and chest in 7 patients (mean age, 54 yr; range, 33 to 69 yr) with a history of upper airway abnormalities. At the time of the study, all patients with clinically stable and had no recurrent nerve palsy. Measurements of airway area by ART and CT were performed in the supine posture while patients breathed quietly at FRC. We found that there was considerable intersubject variability in area-distance functions determined by acoustic reflections. None of the subjects had a flat tracheal plateau. Once the acoustic and CT data were aligned, we compared cross-sectional areas at various distances from the glottis. Comparison points were separated by 1 cm, and as many as 13 different CT sections were used in some subjects. Mean values for all data points (n=83) were 24.5 .+-. SD = 0.69 cm2 and 2.56 .+-. SD = 0.82 cm2 for the acoustic and CT methods, respectively, Z = 0.93; p < 0.05. Linear regression analysis revealed a correlation coefficient (r) of 0.92; p < 0.0001. On the basis of these findings, we conclude that the acoustic reflection technique may be used reliably for clinical and physiologic studies of the upper airways in humans.