Airway stenosis alters the balance between tidal volume, air entrainment, and oxygen-source delivery during normal frequency and superimposed jet ventilation: a bench model study

Background Severe airway stenosis alters gas mixing and volume delivery during open-system jet ventilation. How high-frequency (HF) superimposition and component titration modify these effects remains incompletely characterized. Objective To compare stenosis-induced changes in distal oxygen concentration (FiO 2 ), tidal volume (VT), pressure, flow, and estimated gas composition among pure normal-frequency jet ventilation (NFJV) and superimposed HF jet ventilation (SHFJV) with titration of either the NF (SHFJV-NF) or HF component (SHFJV-HF). Methods An open rigid-bronchoscopy bench model was tested with and without 90% fixed airway stenosis. Pure NFJV and SHFJV-NF shared 56 NF parameter settings; SHFJV-HF included 60 HF settings with a fixed NF component. Linear mixed-effects models evaluated strategy × airway interactions and Holm-adjusted pairwise contrasts. A separate matched model assessed HF addition. Gas-component fractions and volumes were estimated at each setting using a two-source mixing model. Results Strategy × airway interactions were significant for all five measured outcomes (all P < 0.001). Median stenosis-induced changes were +4.7, +29.1, and +24.7 percentage points for FiO 2 and −454, −577, and −232 mL for VT during pure NFJV, SHFJV-NF, and SHFJV-HF, respectively. At identical NF settings, HF addition modified the stenosis response by +24.1 percentage points for FiO 2 , −111.7 mL for VT (95% CI −173.6 to −49.8), +2.02 cmH 2 O for measured positive end-expiratory pressure (PEEP), and −8.11 L·min −1 for expiratory flow magnitude (all P < 0.001). Estimated entrained-air volume decreased in all strategies, whereas oxygen-source volume did not increase uniformly. Conclusion At identical NF settings, HF addition amplified the stenosis-associated FiO 2 rise, VT loss, and PEEP increase. HF-component titration produced a different response across its tested parameter range. Estimated gas-composition changes were consistent with reduced oxygen dilution. Distal FiO 2 did not establish preserved ventilation or arterial oxygenation, and CO 2 elimination was not measured.