Determinants of delivered tidal volume during high-frequency oscillatory ventilation in a pediatric mechanical test lung

Background: Contemporary pediatric high-frequency oscillatory ventilators may differ in how set oscillatory parameters are translated into delivered tidal volume under varying respiratory mechanical loads.We evaluated determinants of delivered tidal volume during high-frequency oscillatory ventilation in a pediatric mechanical test lung using a device-specific full-factorial bench model.Methods: A Fabian high-frequency oscillatory oscillator was connected to an IngMar pediatric mechanical test lung through a standard dry pediatric circuit.Tidal volume was measured with a Florian respiratory monitor placed between the circuit and lung model.We tested 1,512 combinations of frequency, pressure amplitude, mean airway pressure, inspiratory-to-expiratory ratio, compliance, and resistance.Measurements were recorded after at least 2 minutes of steady state at each condition.Analysis of variance and multiple linear regression were used to evaluate associations with delivered tidal volume.Results: Delivered tidal volume was associated with frequency, pressure amplitude, mean airway pressure, inspiratory-to-expiratory ratio, and resistance (all P<0.001), but not compliance across the tested range (P=0.18).Tidal volume increased with higher pressure amplitude and mean airway pressure and decreased with higher frequency and resistance.In the regression model, tidal volume (mL)=25.9-(1.3×frequency)+(0.14×pressureamplitude)+(0.08×meanairway pressure)-(0.18×resistance).The model explained 80.8% of the variance in delivered tidal volume (R 2 =0.808, adjusted R 2 =0.808).Conclusions: In this pediatric mechanical test lung, delivered tidal volume during high-frequency oscillatory ventilation reflected both oscillator settings and respiratory load.Lower frequency and higher pressure amplitude produced the largest delivered volumes, whereas higher resistance reduced volume delivery.These findings are device-specific and should be interpreted as bench physiology rather than evidence of clinical outcome benefit.