Pillow J J, Neil H, Wilkinson M H, Ramsden C A
Newborn Services, Monash Medical Centre, Clayton, Victoria 3168, Australia.
J Appl Physiol (1985). 1999 Jul;87(1):407-14. doi: 10.1152/jappl.1999.87.1.407.
This study investigated factors contributing to differences between mean alveolar pressure (PA) and mean pressure at the airway opening (Pao) during high-frequency oscillatory ventilation (HFOV). The effect of the inspiratory-to-expiratory time (I/E) ratio and amplitude of oscillation on the magnitude of - Pao (Pdiff) was examined by using the alveolar capsule technique in normal rabbit lungs (n = 4) and an in vitro lung model. The effect of ventilator frequency and endotracheal tube (ETT) diameter on Pdiff was further examined in the in vitro lung model at an I/E ratio of 1:2. In both lung models, fell below Pao during HFOV when inspiratory time was shorter than expiratory time. Under these conditions, differences between inspiratory and expiratory flows, combined with the nonlinear relationship between resistive pressure drop and flow in the ETT, are the principal determinants of Pdiff. In our experiments, the magnitude of Pdiff at each combination of I/E, frequency, lung compliance, and ETT resistance could be predicted from the difference between the mean squared inspiratory and expiratory velocities in the ETT. These observations provide an explanation for the measured differences in mean pressure between the airway opening and the alveoli during HFOV and will assist in the development of optimal strategies for the clinical application of this technique.
本研究调查了高频振荡通气（HFOV）期间平均肺泡压（PA）与气道开口处平均压（Pao）之间差异的影响因素。通过在正常兔肺（n = 4）和体外肺模型中使用肺泡囊技术，研究了吸气与呼气时间（I/E）比值和振荡幅度对 -Pao（Pdiff）大小的影响。在体外肺模型中，以1:2的I/E比值进一步研究了通气频率和气管内导管（ETT）直径对Pdiff的影响。在两个肺模型中，当吸气时间短于呼气时间时，HFOV期间PA低于Pao。在这些条件下，吸气和呼气流量的差异，以及ETT中阻力压降与流量之间的非线性关系，是Pdiff的主要决定因素。在我们的实验中，I/E、频率、肺顺应性和ETT阻力各组合下的Pdiff大小可根据ETT中吸气和呼气平均流速平方的差异来预测。这些观察结果解释了HFOV期间气道开口与肺泡之间平均压的测量差异，并将有助于制定该技术临床应用的最佳策略。
