Halsøy Kathrine, Kondratiev Timofey, Tveita Torkjel, Bjertnaes Lars J
Anesthesia and Critical Care Research Group, Faculty of Health Sciences, Department of Clinical Medicine, University of Tromsø, The Arctic University of Norway , Tromsø , Norway.
Front Med (Lausanne). 2016 Dec 23;3:70. doi: 10.3389/fmed.2016.00070. eCollection 2016.
Victims of severe accidental hypothermia are prone to fluid extravasation but rarely develop lung edema. We hypothesize that combined hypothermia-induced increase in pulmonary vascular resistance (PVR) and a concomitant fall in cardiac output protect the lungs against edema development. Our aim was to explore in hypothermic-isolated blood-perfused rat lungs whether perfusion at constant pressure influences fluid filtration differently from perfusion at constant flow.
Isolated blood-perfused rat lungs were hanging freely in a weight transducer for measuring weight changes (ΔW). Fluid filtration coefficient (Kfc), was determined by transiently elevating left atrial pressure (Pla) by 5.8 mmHg two times each during normothermia (37°C) and during hypothermia (15°C). The lung preparations were randomized to two groups. One group was perfused with constant flow (Constant flow group) and the other group with constant pulmonary artery pressure (Constant PPA group). Microvascular pressure (Pmv) was determined before and during elevation of Pla (ΔPmv) by means of the double occlusion technique. Kfc was calculated with the formula Kfc = ΔW/ΔPmv/min. All Kfc values were normalized to predicted lung weight (P), which was based on body weight (BW) according to the formula: P = 0.0053 BW - 0.48 and presented as Kfc in mg/min/mmHg/g. At cessation, bronchoalveolar lavage (BAL) fluid/perfusate protein concentration (B/P) ratio was determined photometrically. Data were analyzed with parametric or non-parametric tests as appropriate. < 0.05 considered as significant.
Perfusate flow remained constant in the Constant flow group, but was more than halved during hypothermia in the Constant PPA group concomitant with a more fold increase in PVR. In the Constant flow group, Kfc and B/P ratio increased significantly by more than 10-fold during hypothermia concerted by visible signs of edema in the trachea. Hemoglobin and hematocrit increased within the Constant flow group and between the groups at cessation of the experiments.
In hypothermic rat lungs perfused at constant flow, fluid filtration coefficient per gram P and B/P ratio increased more than 10-fold concerted by increased hemoconcentration, but the changes were less in hypothermic lungs perfused at constant PPA.
严重意外低温的受害者容易发生液体外渗，但很少发生肺水肿。我们假设低温诱导的肺血管阻力（PVR）增加与心输出量同时下降可保护肺部免受水肿形成。我们的目的是探讨在低温离体血液灌注大鼠肺中，恒压灌注与恒流灌注对液体滤过的影响是否不同。
将离体血液灌注大鼠肺自由悬挂在重量传感器上以测量重量变化（ΔW）。在正常体温（37°C）和低温（15°C）期间，通过两次将左心房压力（Pla）短暂升高5.8 mmHg来测定液体滤过系数（Kfc）。将肺标本随机分为两组。一组采用恒流灌注（恒流组），另一组采用肺动脉压恒定灌注（恒肺动脉压组）。通过双阻断技术在Pla升高之前和期间（ΔPmv）测定微血管压力（Pmv）。Kfc用公式Kfc = ΔW/ΔPmv/min计算。所有Kfc值均根据预测肺重量（P）进行标准化，预测肺重量基于体重（BW），公式为：P = 0.0053 BW - 0.48，并以mg/min/mmHg/g的Kfc表示。实验结束时，通过比色法测定支气管肺泡灌洗（BAL）液/灌注液蛋白浓度（B/P）比值。根据情况使用参数或非参数检验分析数据。P < 0.05认为具有显著性。
恒流组灌注液流量保持恒定，但在恒肺动脉压组中，低温期间灌注液流量减少超过一半，同时PVR增加了更多倍。在恒流组中，低温期间Kfc和B/P比值显著增加超过10倍，同时气管出现明显水肿迹象。实验结束时，恒流组内以及两组之间血红蛋白和血细胞比容增加。
在恒流灌注的低温大鼠肺中，每克预测肺重量的液体滤过系数和B/P比值增加超过10倍，同时伴有血液浓缩增加，但在恒肺动脉压灌注的低温肺中变化较小。
