Zabner J, Angeli L S, Martinez R R, Sánchez de León R
Physiology Department, Medical Faculty Universidad Central de Venezuela, Caracas.
Intensive Care Med. 1990;16(2):89-94.
The influence of positive end expiratory pressure (PEEP) on the fluid filtration rate (FFR) in the pulmonary circulation has been the subject of considerable investigation but data are conflicting. We studied twenty-nine isolated rabbit lung preparations, FFR was sensed by a force transducer. Autologous blood was used to prime the perfusion circuit. Hydrostatic oedema was achieved by increasing the left atrial pressure to 16 mmHg. In order to bring about increased membrane permeability oleic acid was injected through the pulmonary artery. Increasing and decreasing levels of PEEP at 0, 5, 10 and 15 cm H2O were each used for ten minutes in each of three experimental models. The FFR, pH, mean pulmonary arterial pressure (MPAP), mean left atrial pressure (MLAP), PaO2, PaCO2 and oncotic pressure were measured in each experiment. There was a significant correlation between PEEP and FFR (+0.94) in non-oedema lungs. With no PEEP the FFR was 0 g/min and with 15 cm of PEEP it increased to 0.07 g/min, on removing the PEEP the FFR returned to 0 g/min. In the hydrostatic lung oedema model the correlation was also significant but negative (r = -0.94). With no PEEP the FFR was 0.33 g/min, with PEEP of 15 cm H2O it decreased to 0.08 g/min. No correlation between PEEP and FFR was found in the oleic acid preparation. In the normal lung PEEP increases capillary hydrostatic pressure and total lung vascular area and decreases interstitial pressure. It is by these mechanisms that PEEP causes an increase in FFR. In the hydrostatic oedema model PEEP decreases FFR by increasing the interstitial pressure and by decreasing the total lung vascular area. In the oleic acid preparation the coefficient of filtration is so large that small changes in pressure or vascular area do not modify the FFR. We suggest that PEEP may be beneficial by decreasing FFR in hydrostatic lung oedema, but it may increase the FFR in the normal lung, while having no effect in oleic acid lung injury.
呼气末正压（PEEP）对肺循环中液体滤过率（FFR）的影响一直是大量研究的主题，但数据存在矛盾。我们研究了29个离体兔肺标本，FFR由力传感器感知。使用自体血灌注回路。通过将左心房压力升高至16 mmHg实现静水压性肺水肿。为了增加膜通透性，通过肺动脉注射油酸。在三个实验模型中，分别在0、5、10和15 cm H₂O的PEEP升高和降低水平下各使用10分钟。在每个实验中测量FFR、pH、平均肺动脉压（MPAP）、平均左心房压（MLAP）、PaO₂、PaCO₂和胶体渗透压。在非水肿肺中，PEEP与FFR之间存在显著相关性（+0.94）。无PEEP时FFR为0 g/min，PEEP为15 cm时增加至0.07 g/min，去除PEEP后FFR恢复至0 g/min。在静水压性肺水肿模型中，相关性也很显著但为负（r = -0.94）。无PEEP时FFR为0.33 g/min，PEEP为15 cm H₂O时降至0.08 g/min。在油酸制剂中未发现PEEP与FFR之间的相关性。在正常肺中，PEEP增加毛细血管静水压和肺血管总面积，并降低间质压力。正是通过这些机制，PEEP导致FFR增加。在静水压性肺水肿模型中，PEEP通过增加间质压力和减少肺血管总面积来降低FFR。在油酸制剂中，滤过系数非常大，以至于压力或血管面积的微小变化不会改变FFR。我们认为，PEEP可能通过降低静水压性肺水肿中的FFR而有益，但它可能增加正常肺中的FFR，而对油酸所致肺损伤无影响。
