Araos Joaquin, Cruces Pablo, Martin-Flores Manuel, Donati Pablo, Gleed Robin D, Boullhesen-Williams Tomas, Perez Agustin, Staffieri Francesco, Retamal Jaime, Vidal Melo Marcos F, Hurtado Daniel E
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, United States.
Escuela de Medicina Veterinaria, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile.
Front Vet Sci. 2022 Mar 14;9:839406. doi: 10.3389/fvets.2022.839406. eCollection 2022.
The present study describes the magnitude and spatial distribution of lung strain in healthy anesthetized, mechanically ventilated dogs with and without positive end-expiratory pressure (PEEP). Total lung strain (LS) has a dynamic (LS) and a static (LS) component. Due to lung heterogeneity, global lung strain may not accurately represent regional total tissue lung strain (TS), which may also be described by a regional dynamic (TS) and static (TS) component. Six healthy anesthetized beagles (12.4 ± 1.4 kg body weight) were placed in dorsal recumbency and ventilated with a tidal volume of 15 ml/kg, respiratory rate of 15 bpm, and zero end-expiratory pressure (ZEEP). Respiratory system mechanics and full thoracic end-expiratory and end-inspiratory CT scan images were obtained at ZEEP. Thereafter, a PEEP of 5 cmHO was set and respiratory system mechanics measurements and end-expiratory and end-inspiratory images were repeated. Computed lung volumes from CT scans were used to evaluate the global LS, LS, and LS during PEEP. During ZEEP, LS was assumed zero; therefore, LS was the same as LS. Image segmentation was applied to CT images to obtain maps of regional TS, TS, and TS during PEEP, and TS during ZEEP. Compliance increased ( = 0.013) and driving pressure decreased ( = 0.043) during PEEP. PEEP increased the end-expiratory lung volume ( < 0.001) and significantly reduced global LS (33.4 ± 6.4% during ZEEP, 24.0 ± 4.6% during PEEP, = 0.032). LS by PEEP was larger than the reduction in LS; therefore, LS at PEEP was larger than LS at ZEEP ( = 0.005). There was marked topographic heterogeneity of regional strains. PEEP induced a significant reduction in TS in all lung regions ( < 0.05). Similar to global findings, PEEP-induced TS was larger than the reduction in TS; therefore, PEEP-induced TS was larger than TS at ZEEP. In conclusion, PEEP reduced both global and regional estimates of dynamic strain, but induced a large static strain. Given that lung injury has been mostly associated with tidal deformation, limiting dynamic strain may be an important clinical target in healthy and diseased lungs, but this requires further study.
本研究描述了在有和没有呼气末正压（PEEP）的情况下，健康麻醉、机械通气犬肺应变的大小和空间分布。总肺应变（LS）有一个动态（LS）和一个静态（LS）分量。由于肺的异质性，整体肺应变可能无法准确代表区域总组织肺应变（TS），区域总组织肺应变也可以用区域动态（TS）和静态（TS）分量来描述。将6只健康麻醉的比格犬（体重12.4±1.4千克）置于仰卧位，以15毫升/千克的潮气量、15次/分钟的呼吸频率和零呼气末压力（ZEEP）进行通气。在ZEEP时获取呼吸系统力学以及全胸呼气末和吸气末CT扫描图像。此后，设置5厘米水柱的PEEP，并重复进行呼吸系统力学测量以及呼气末和吸气末图像采集。利用CT扫描计算得到的肺容积来评估PEEP期间的整体LS、LS和LS。在ZEEP期间，假设LS为零；因此，LS与LS相同。对CT图像应用图像分割技术，以获取PEEP期间区域TS、TS和TS以及ZEEP期间TS的图谱。在PEEP期间，顺应性增加（=0.013），驱动压力降低（=0.043）。PEEP增加了呼气末肺容积（<0.001），并显著降低了整体LS（ZEEP期间为33.4±6.4%，PEEP期间为24.0±4.6%，=0.032）。PEEP引起的LS大于LS的降低；因此，PEEP时的LS大于ZEEP时的LS（=0.005）。区域应变存在明显的地形异质性。PEEP导致所有肺区域的TS显著降低（<0.05）。与整体结果相似，PEEP引起的TS大于TS的降低；因此，PEEP引起的TS大于ZEEP时的TS。总之，PEEP降低了动态应变的整体和区域估计值，但诱导产生了较大的静态应变。鉴于肺损伤大多与潮气量变形有关，限制动态应变可能是健康和患病肺的一个重要临床目标，但这需要进一步研究。
