* Assistant Professor, Department of Anesthesiology and Critical Care, † Research Specialist, ‡ Project Manager, § Student, ‖ Research Assistant Professor, # Technical Director, ‡‡ Professor, Department of Radiology, †† Professor, Department of Anesthesiology and Critical Care and Stavropoulos Sepsis Research Program, University of Pennsylvania, Philadelphia, Pennsylvania. ** Professor, Departments of Critical Care Medicine and Anesthesia, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
Anesthesiology. 2013 Dec;119(6):1402-9. doi: 10.1097/ALN.0b013e3182a9b0c1.
Although it is recognized that pulmonary hysteresis can influence the effects of positive end-expiratory pressure (PEEP), the extent to which expansion of previously opened (vs. newly opening) peripheral airspaces contribute to increased lung volume is unknown.
Following a recruitment maneuver, rats were ventilated with constant tidal volumes and imaged during ascending and descending ramps of PEEP.
The authors estimated peripheral airspace dimensions by measuring the apparent diffusion coefficient of He in 10 rats. In a separate group (n = 5) undergoing a similar protocol, the authors used computerized tomography to quantify lung volume. Hysteresis was confirmed by larger end-inspiratory lung volume (mean ± SD; all PEEP levels included): 8.4 ± 2.8 versus 6.8 ± 2.0 ml (P < 0.001) and dynamic compliance: 0.52 ± 0.12 versus 0.42 ± 0.09 ml/cm H2O (P < 0.001) during descending versus ascending PEEP ramps. Apparent diffusion coefficient increased with PEEP, but it was smaller during the descending versus ascending ramps for corresponding levels of PEEP: 0.168 ± 0.019 versus 0.183 ± 0.019 cm/s (P < 0.001). Apparent diffusion coefficient was smaller in the posterior versus anterior lung regions, but the effect of PEEP and hysteresis on apparent diffusion coefficient was greater in the posterior regions.
The authors' study results suggest that in healthy lungs, larger lung volumes due to hysteresis are associated with smaller individual airspaces. This may be explained by opening of previously nonaerated peripheral airspaces rather than expansion of those already aerated. Setting PEEP on a descending ramp may minimize distension of individual airspaces.
尽管人们认识到肺滞后会影响呼气末正压（PEEP）的效果，但先前开放（与新开放）的周边气腔扩张对增加肺容积的贡献程度尚不清楚。
在复张手法后，大鼠以恒定潮气量通气，并在 PEEP 的上升和下降斜坡期间进行成像。
作者通过测量 10 只大鼠中 He 的表观扩散系数来估计周边气腔尺寸。在遵循类似方案的另一组（n=5）中，作者使用计算机断层扫描来量化肺容积。滞后通过更大的吸气末肺容积（所有 PEEP 水平均包括）得到证实：8.4±2.8 与 6.8±2.0 ml（均 P<0.001）和动态顺应性：0.52±0.12 与 0.42±0.09 ml/cm H2O（P<0.001）在下降与上升 PEEP 斜坡期间。表观扩散系数随 PEEP 增加，但在对应 PEEP 水平下，下降与上升斜坡期间的表观扩散系数更小：0.168±0.019 与 0.183±0.019 cm/s（P<0.001）。表观扩散系数在肺后区比前区小，但 PEEP 和滞后对表观扩散系数的影响在后区更大。
作者的研究结果表明，在健康肺中，由于滞后导致的更大肺容积与较小的单个气腔有关。这可能是通过先前非充气周边气腔的开放而不是已经充气的气腔的扩张来解释的。在下降斜坡上设置 PEEP 可能会最小化单个气腔的膨胀。
