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 cmH₂O showed a 4.2_5.3° angle toward the right and a 20.6_6.9° angle downward toward the back, which decreased significantly while increasing P_aw (19.4_6.9° at 15 cm H₂O and 17.1_6.8° 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° angle and slightly toward the right at a 4.2_5.3° 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.