Persson Per, Lundin Stefan, Stenqvist Ola
Department of Anesthesiology and Intensive Care, Sahlgrenska University Hospital, Blå Stråket 5, 413 45, Gothenburg, Sweden.
Intensive Care Med Exp. 2016 Dec;4(1):26. doi: 10.1186/s40635-016-0103-4. Epub 2016 Sep 20.
We have shown in acute lung injury patients that lung elastance can be determined by a positive end-expiratory pressure (PEEP) step procedure and proposed that this is explained by the spring-out force of the rib cage off-loading the chest wall from the lung at end-expiration. The aim of this study was to investigate the effect of the expanding chest wall on pleural pressure during PEEP inflation by building a model with an elastic recoiling lung and an expanding chest wall complex.
Test lungs with a compliance of 19, 38, or 57 ml/cmH2O were placed in a box connected to a plastic container, 3/4 filled with water, connected to a water sack of 10 l, representing the abdomen. The space above the water surface and in the lung box constituted the pleural space. The contra-directional forces of the recoiling lung and the expanding chest wall were obtained by evacuating the pleural space to a negative pressure of 5 cmH2O. Chest wall elastance was increased by strapping the plastic container. Pressure was measured in the airway and pleura. Changes in end-expiratory lung volume (ΔEELV), during PEEP steps of 4, 8, and 12 cmH2O, were determined in the isolated lung, where airway equals transpulmonary pressure and in the complete model as the cumulative inspiratory-expiratory tidal volume difference. Transpulmonary pressure was calculated as airway minus pleural pressure.
Lung pressure/volume curves of an isolated lung coincided with lung P/V curves in the complete model irrespective of chest wall stiffness. ΔEELV was equal to the size of the PEEP step divided by lung elastance (EL), ΔEELV = ΔPEEP/EL. The end-expiratory "pleural" pressure did not increase after PEEP inflation, and consequently, transpulmonary pressure increased as much as PEEP was increased.
The rib cage spring-out force causes off-loading of the chest wall from the lung and maintains a negative end-expiratory "pleural" pressure after PEEP inflation. The behavior of the respiratory system model confirms that lung elastance can be determined by a simple PEEP step without using esophageal pressure measurements.
我们在急性肺损伤患者中发现，可通过呼气末正压（PEEP）阶梯法测定肺弹性，并提出这是由于胸廓的弹力在呼气末将胸壁从肺上卸载所致。本研究的目的是通过构建一个具有弹性回缩肺和扩张胸廓复合体的模型，来研究PEEP充气过程中扩张胸廓对胸膜压力的影响。
将顺应性为19、38或57 ml/cmH₂O的测试肺置于一个与塑料容器相连的盒子中，该塑料容器3/4装满水，并与一个10升的水袋相连，代表腹部。水面上方和肺盒内的空间构成胸膜腔。通过将胸膜腔抽至-5 cmH₂O的负压来获得回缩肺和扩张胸廓的反向力。通过捆绑塑料容器来增加胸壁弹性。在气道和胸膜处测量压力。在孤立肺中，气道压力等于跨肺压，在完整模型中，作为累计吸气-呼气潮气量差，测定4、8和12 cmH₂O的PEEP阶梯过程中呼气末肺容积（ΔEELV）的变化。跨肺压通过气道压力减去胸膜压力来计算。
无论胸壁硬度如何，孤立肺的肺压力/容积曲线与完整模型中的肺P/V曲线一致。ΔEELV等于PEEP阶梯的大小除以肺弹性（EL），即ΔEELV = ΔPEEP/EL。PEEP充气后呼气末“胸膜”压力没有增加，因此，跨肺压的增加与PEEP的增加量相同。
胸廓弹力使胸壁从肺上卸载，并在PEEP充气后维持呼气末负的“胸膜”压力。呼吸系统模型的行为证实，无需测量食管压力，通过简单的PEEP阶梯法即可测定肺弹性。
