Reproducibility of measurements of upper airway area by acoustic reflection

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Abstract
To evaluate the extent and nature of the variability of measurements of upper airway area by acoustic reflection (AAAR), we made repeated measures of pharyngeal AAR in 10 normal adult volunteers. We selected mean pharyngeal area as a better index of upper airway size than peak pharyngeal area or pharyngeal volume. Within-run variability of this measure was 8 .+-. 4% (SD) (coeff of variation). This variability could not be explained by changes in lung volume or differences in phase of respiration. Five subjects had tracheal and pharyngeal area meausred by using both the custom-made wax mouthpiece (W) and a commercial rubber pulmonary function mouthpiece (R). Reproductibility of pharyngeal AAAR was within 10% (coeff of variation) using R, but measurements of pharyngeal AAAR varied with the differrent types of mouthpiece, as W/R ranged from 0.82 to 1.70. In contrast, measurements of midtracheal ara were similar for both mouthpiece types [mean W/R = 0.07 .+-. 14 (SD)]. The acoustic reflection technique yields a reproducible index of pharyngeal size that does not vary with phase of respiration or modest changes in lung volume. Either W or R may be used to make clinical measurements, but the types of mouthpiece should be consistent and specified.

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