Heyer L, Louis B, Isabey D, Lofaso F, Brochard L, Fredberg J J, Harf A
Institut National de la Santé et de la Recherche Médicale-Unitaé de Physiologie (INSERM U.296), Hôpital Henri Mondor, Créteil, France.
Anesthesiology. 1996 Dec;85(6):1324-33. doi: 10.1097/00000542-199612000-00013.
Although evidence suggests that secretions lining the inner wall of the endotracheal tube (ETT) often reduce its cross-sectional area, no data are available on the work of breathing as affected by the ETT. A noninvasive method is proposed for estimating the additional work of breathing necessitated by the ETT in patients whose lungs are mechanically ventilated. This method (the acoustic-Blasius method) involves (1) determining the inner geometry of the ETT using the acoustic reflection method and (2) using these geometric data to solve the Blasius equation that characterizes the ETT pressure drop-flow relation.
To evaluate the acoustic-Blasius method in vivo, the authors computed the work of breathing due to the ETT in four healthy persons breathing through an ETT connected to a pressure-support device and in five tracheally intubated patients receiving mechanical assistance in the pressure-support mode. For the tracheally intubated patients, the reference value was the work calculated from the ETT pressure drop measured between the two ends of the ETT using a pressure catheter.
In the healthy participants and the tracheally intubated patients, there was close agreement between inspiratory work per cycle values estimated by directly measuring the ETT pressure drop and calculated using the acoustic-Blasius method: The difference was consistently less than 0.08 joules (< 10% of the reference value).
The data show that the acoustic-Blasius method allows noninvasive quantification of the ETT-related work of breathing in situ.
尽管有证据表明气管内导管（ETT）内壁的分泌物常常会减小其横截面积，但尚无关于ETT对呼吸功影响的数据。本文提出一种非侵入性方法，用于估算机械通气患者因ETT而额外需要的呼吸功。该方法（声学-布拉修斯方法）包括：（1）使用声学反射法确定ETT的内部几何形状；（2）利用这些几何数据求解表征ETT压降-流量关系的布拉修斯方程。
为了在体内评估声学-布拉修斯方法，作者计算了4名通过连接压力支持装置的ETT进行呼吸的健康人和5名接受压力支持模式机械辅助通气的气管插管患者因ETT产生的呼吸功。对于气管插管患者，参考值是使用压力导管测量ETT两端之间的压降计算得出的功。
在健康参与者和气管插管患者中，通过直接测量ETT压降估算的每周期吸气功值与使用声学-布拉修斯方法计算的值之间具有高度一致性：差异始终小于0.08焦耳（<参考值的10%）。
数据表明，声学-布拉修斯方法能够对原位ETT相关的呼吸功进行非侵入性定量分析。
