[Pharyngeal area measured by acoustic reflection technique while breathing room-air]

Although there have been many reports on the airway area measured by breathing 80% He-20% O2 (He-O2) using the acoustic reflection technique (ART), there have been no reports on that by breathing room-air (Air) because of the lack of accuracy in evaluating the trachea. When measuring with He-O2, accidental introduction of Air into the airway makes the measurement inaccurate. Moreover, it is a time-consuming method and is hardly applicable to dyspneic patients. Therefore, we tried to assess whether the airway area, especially the upper airway, can be measured while breathing Air. In order to compare the areas determined by the two methods, area-distance functions from the pharynx to the trachea were arbitrarily divided into 9 divisions at interval of 2.8 cm. Each of these divisions was respectively compared. We took averages of the pharyngeal, tracheal areas in 8 normal subjects. We found no significant difference between the oropharyngeal area measured by breathing Air and that measured by breathing He-O2, and found a significant correlation between them. There was a significant correlation between the hypopharyngeal areas when using the two methods. The average tracheal area by breathing Air is 4.96 +/- 0.50 cm2, which is 40% above that when measured using He-O2 (3.55 +/- 0.32 cm2). In contrast, the average pharyngeal area when breathing Air is 4.13 +/- 0.93 cm2, which overestimates that by breathing He-O2, namely 3.54 %/- 0.84 cm2 by only 17%. In conclusion, it is possible and useful to estimate the pharyngeal area by breathing Air.