Tracheal stenosis measured by the acoustic reflection technique.

We examined the usefulness of the acoustic reflection technique for measurement of airway area in 6 patients with tracheal stenosis. In each patient, we obtained airway area by acoustic reflections in the upright position, maximal expiratory and inspiratory flow-volume curve, and radiographs of the trachea. We identified acoustic and radiographic stenotic segments and compared their length, their distances from the glottis, and their cross-sectional areas. We found that (1) in all subjects except one, flow-volume curves did not suggest upper airway obstruction, (2) tracheal stenosis was confirmed by acoustic and radiographic measurements in all subjects, and (3) area of the stenotic segment showed less variation with lung volume than that of the nonstenotic segment. Length of the stenotic segment (mean +/- SE) was found to be 4.9 +/- 0.2 cm (acoustic versus 4.8 +/- 0.3 cm (radiographic); distance between the midglottis and maximal stenosis was 5.7 +/- 0.4 cm (acoustic) and 5.6 +/- 0.6 cm (radiographic); minimal acoustic cross-sectional area was 1.7 +/- 0.1 cm2 versus a radiographic circular cross-sectional area of 1.2 +/- 0.1 cm2. During slow expiration from total lung capacity to residual volume, average cross-sectional area of the stenotic segment decreased by 19.5 +/- 3.0% (mean +/- SE), whereas that of the distal nonstenotic segment decreased by 48.5 +/- 2.2% and that of the proximal nonstenotic segment by 43.6 +/- 5%. We conclude that the acoustic technique, which is rapid and noninvasive, is useful in confirming tracheal stenosis in patients with normal flow-volume curves, and in assessing elastic properties of the trachea.