Optimal ventilatory settings during high frequency oscillatory ventilation in the viewpoint of lung protection in a lung injured-rat model

我们为动物研究开发了一种高频振荡器。基本原理是振荡器中的振膜由来回射流产生的压力驱动。我们在正常肺大鼠（n=5）中测试了该振荡器。因此，动物可以在5至40赫兹的频率范围内通风，尽管潮汐量随着频率的增加而减少。该振荡器在15 Hz时产生的气道压力摆动比市售振荡器（Metran hummingv）大50%。然后探讨频率对肺损伤的影响。用38 cm H_2O高气道压通气诱导肺损伤。在吸入氧含量为100%的情况下，将PaO_2降至200 mmHg以下。然后将动物随机分为两组（5 Hz和30 Hz）。两组均在平均气道压力15 cmH_2O下振荡4小时，并滴定气道压力波动以维持正常呼吸功能。4小时平均PaO_2为5hz时410 mmHg， 30hz时200 mmHg。平均潮气量在5 Hz时为0.79 mL，在30 Hz时为0.29 mL。此外，我们还评估了PaCO_2在高频振荡中的作用。盐酸灌胃可致大鼠肺损伤。将随机分配的两组进行比较。一组的目标PaCO_2为40mmhg，另一组为80mmhg。两组间除PaCO_2、肺组织、炎症因子外，血气指标无统计学差异。

We developed a high-frequency oscillator for animal research. Basic mechanism is that a diaphragm in the oscillator is driven by the pressure produced by the to-and-fro jet. We tested this oscillator in the normal lung rats (n=5). As a result the animals could be ventilated with frequencies ranged from 5 to 40 Hz although tidal volume decreased as frequency increased. Airway pressure swing produced by this oscillator was 50% greater than the commercially available oscillator (Metran Humming V) at 15 Hz.Then we investigated the effect of frequency on lung injury. Lung injury was induced by ventilating animals with high airway pressure of 38 cm H_2O. This injurious ventilation was performed until PaO_2 decreased below 200 mmHg at fraction of inspiratory oxygen of 100%. Then animals were randomly divided into two groups (5 Hz and 30 Hz). Both groups were oscillated at mean airway pressure of 15 cmH_2O for 4 hours and airway pressure swings were titrated to maintain normocapnia. Mean PaO_2 at 4 hours were 410 mmHg with 5 Hz and 200 mmHg with 30 Hz. Mean tidal volumes were 0.79 mL with 5 Hz and 0.29 mL with 30 Hz.In addition we evaluated the effect of PaCO_2 during high frequency oscillation. Lung injury was induced by the instillation of hydrochloric acid. Two groups randomly assigned were compared. Target PaCO_2 was 40 mmHg in one group and 80 mmHg in the other. There were no statistical differences in blood gas data except for PaCO_2, lung histology and inflammatory cytokines between groups.