Effect of high‐frequency jet ventilation on preterm and rabbit tracheal mechanics

The effect of high‐frequency jet ventilation (HFJV) on both tracheal dimensions and mechanics was evaluated in preterm and term rabbit airways. Seven tracheal segments were studied at 27 days (group I) and 31 days (group II) of gestation, respectively. Tracheal dimensions and segmental pressure‐volume relationships were determined before and after 60 minutes of HFJV (peak pressure 20 cm H₂O; mean airway pressure 6.7 to 6.8 cm H²O at 10 Hz). Both tracheal lengths and diameters increased significantly (p < 0.01) in each group and resulted in increased tracheal volumes: 109% in group I (p< 0.01) and 60% in group II (p < 0.01). The mean specific tracheal compliance decreased in group I, from 0.036 cm H₂O⁻¹ to 0.015 cm H₂O⁻¹ (p < 0.01), and in group II from 0.029 cm H₂O⁻¹ to 0.021 cm H₂O⁻¹ (p < 0.01). Furthermore, the collapsing transmural pressure (the pressure required for total collapse of tracheal segments) decreased significantly (p< 0.01) in both groups. These data demonstrate significant dimensional and mechanical deformation of tracheal segments after HFJV. An increased propensity toward collapsibility is also observed following HFJV. These changes are similar to those with tracheomala‐cia. The influence of such deformation on tracheal gas flow during HFJV needs to be further investigated.