1 Department of Physics, University of Helsinki, Helsinki, Finland.
2 Medical Imaging Center, Helsinki University Hospital, Helsinki, Finland.
Am J Respir Cell Mol Biol. 2017 Oct;57(4):459-467. doi: 10.1165/rcmb.2017-0007OC.
Despite the importance of dynamic changes in the regional distributions of gas and blood during the breathing cycle for lung function in the mechanically ventilated patient, no quantitative data on such cyclic changes are currently available. We used a novel gated synchrotron computed tomography imaging to quantitatively image regional lung gas volume (Vg), tissue density, and blood volume (Vb) in six anesthetized, paralyzed, and mechanically ventilated rabbits with normal lungs. Images were repeatedly collected during ventilation and steady-state inhalation of 50% xenon, or iodine infusion. Data were acquired in a dependent and nondependent image level, at zero end-expiratory pressure (ZEEP) and 9 cm HO (positive end-expiratory pressure), and a tidal volume (Vt) of 6 ml/kg (Vt1) or 9 ml/kg (Vt2) at an Inspiratory:Expiratory ratio of 0.5 or 1.7 by applying an end-inspiratory pause. A video showing dynamic decreases in Vb during inspiration is presented. Vb decreased with positive end-expiratory pressure (P = 0.006; P = 0.036 versus Vt1-ZEEP and Vt2-ZEEP, respectively), and showed larger oscillations at the dependent image level, whereas a 45% increase in Vt did not have a significant effect. End-inspiratory Vb minima were reduced by an end-inspiratory pause (P = 0.042, P = 0.006 at nondependent and dependent levels, respectively). Normalized regional Vg:Vb ratio increased upon inspiration. Our data demonstrate, for the first time, within-tidal cyclic variations in regional pulmonary Vb. The quantitative matching of regional Vg and Vb improved upon inspiration under ZEEP. Further study is underway to determine whether these phenomena affect intratidal gas exchange.
尽管在机械通气患者中，呼吸周期内气体和血液的区域性分布变化对肺功能非常重要，但目前尚无关于这种周期性变化的定量数据。我们使用一种新型门控同步加速器计算机断层扫描成像技术，对六只麻醉、麻痹且正常肺部的机械通气兔的区域性肺气体容积（Vg）、组织密度和血液容积（Vb）进行定量成像。在通气和稳态吸入 50%氙气或碘灌注期间，反复采集图像。在零呼气末正压（ZEEP）和 9 cmH2O（呼气末正压）、吸气：呼气比为 0.5 或 1.7 时，分别采用吸气末暂停，以 6ml/kg（Vt1）或 9ml/kg（Vt2）潮气量，在依赖和非依赖图像层面采集数据。呈现了一个动态显示吸气过程中 Vb 减少的视频。Vb 随呼气末正压（P=0.006；P=0.036 分别与 Vt1-ZEEP 和 Vt2-ZEEP 相比）而减少，在依赖图像层面上表现出更大的波动，而潮气量增加 45%则没有显著影响。吸气末暂停会降低吸气末 Vb 最小值（非依赖和依赖水平分别为 P=0.042，P=0.006）。正常化区域性 Vg:Vb 比值随吸气而增加。我们的数据首次证明，在呼吸周期内，区域性肺 Vb 存在周期性变化。在 ZEEP 下，吸气时区域性 Vg 和 Vb 的定量匹配得到改善。进一步的研究正在进行中，以确定这些现象是否会影响潮气量内的气体交换。
