Revisiting high-frequency oscillatory ventilation in vitro and in silico in neonatal conductive airways

Abstract

The linear relation observed suggests that differences in flow characteristics between conventional mechanical ventilation and high frequency oscillatory ventilation conditions do not substantially influence convective mass transport mechanisms. Lower tidal volumes thus cannot be compensated straightforwardly by selecting higher frequencies to maintain similar ventilation efficiencies.

Ventilation-induced jet suggests biotrauma in reconstructed airways of the intubated neonate

“…This airway model (figure 5a) is based on a previously published hybrid geometry [66], following the seminal works of Weibel [67] and Horsfield et al [68]. The computer-aided design (CAD) model was homothetically scaled down to the size of an approximately 2 kg preterm neonate following previously reported methods [35]. The airway tree was limited to five bifurcating airway generations (i.e.…”

“…Ventilatory scenarios spanning HFV (table 1) were reached by altering the frequency and tidal volume of the prescribed oscillatory flow profile. The frequency and tidal volume product f × V T , which is associated with the effectiveness of HFV and CO 2 removal [53], was kept constant [35], thereby imposing a peak Re constant across all cases investigated. The corresponding peak Reynolds number Re 0 = 4V T f/D 0 ν (at peak velocity in the trachea) and Womersley number a ¼ D 0 =2 ffiffiffiffiffiffiffiffiffiffiffiffi ffi 2pf=n p are also reported in table 1.…”

“…The duty cycle, or ratio of inspiratory to expiratory times in a breathing cycle, is approximately 1 : 1 with a peak inspiratory flow rate of 10 ml s −1 . Typical tidal volumes for neonates range between 1 and 3 ml kg −1 body weight, representing approximately 50% or less of the anatomical dead space [35]. Note that, following dynamic similarity, the experimental flow parameters (Re and α) correspond to clinical ventilation settings in air scaled by 0.5 and ffiffi ffi 2 p , respectively.…”

“…Several studies have alluded to the increase in convective-driven recirculation from local secondary flows [30,31] and pendelluft [32][33][34] near reversal times between inhalation and exhalation. However, these phenomena are known to be transient relative to the breathing cycle [35], leaving their overall contribution to HFV-specific gas mixing unknown. Han & Hirahara [36] attributed enhanced mixing to steady streaming measured in a symmetric double bifurcation, while others have reported a minimal [37], if not negative [38], correlation between steady streaming and ventilation frequency.…”

Ventilation-induced epithelial injury drives biological onset of lung traumain vitroand is mitigated with anti-inflammatory therapeutics

“…The model spans the trachea to the first three bronchial generations of the airway tree (Figure 1 b) and adheres 33,34 closely to the idealized planar double-bifurcating Weibel 35 lung model. Following previously reported methods 30,36 we homothetically scaled the model’s geometric dimensions to the anatomical size of a ~2 kg (33 weeks old) preterm infant based on the tracheal diameter. We used additive manufacturing (i.e., 3D printing) to fabricate a cast (Figure 1c) and filled it with liquid polydimethylsiloxane (PDMS).…”