Spatial orientation and mechanical properties of the human trachea: a computed tomography study.

BACKGROUND: The literature generally describes the trachea as oriented toward the right and back, but there is very little detailed characterization. Therefore, the aim of this study was to precisely determine the spatial orientation and to better characterize the physical properties of the human trachea. METHODS: We analyzed lung computed tomography scans of 68 intubated and mechanically ventilated subjects suffering from acute lung injury/ARDS at airway pressures (P-aw) of 5, 15, and 45 cm H2O. At each P-aw, the inner edge of the trachea from the subglottal space to the carina was captured. Tracheal length and diameter were measured. Tracheal orientation and compliance were estimated from processing barycenter and surface tracheal sections. RESULTS: Tracheal orientation at a P-aw of 5 cm H2O showed a 4.2 +/- 5.3 degrees angle toward the right and a 20.6 +/- 6.9 degrees angle downward toward the back, which decreased significantly while increasing P-aw (19.4 +/- 6.9 degrees at 15 cm H2O and 17.1 +/- 6.8 degrees at 45 cm H2O, P <.001). Tracheal compliance was 0.0113 +/- 0.0131 mL/cm H2O/cm of trachea length from 5 to 15 cm H2O and 0.004 +/- 0.0041 mL/cm H2O/cm of trachea length from 15 to 45 cm H2O (P < .001). Tracheal diameter was 19.6 +/- 3.4 mm on the medial-lateral axis and 21.0 +/- 4.3 mm on the sternal-vertebral axis. CONCLUSIONS: The trachea is oriented downward toward the back at a 20.6 +/- 6.9 degrees angle and slightly toward the right at a 4.2 +/- 5.3 degrees angle. Understanding tracheal orientation may help in enhancing postural drainage and respiratory physiotherapy, and knowing the physical properties of the trachea may aid in endotracheal tube cuff design.