Department of Biomedical Engineering, Boston University, Boston, MA 02114, USA.
J Appl Physiol (1985). 2012 Sep;113(6):947-57. doi: 10.1152/japplphysiol.01631.2011. Epub 2012 Jun 7.
Heterogeneous, small-airway diameters and alveolar derecruitment in poorly aerated regions of normal lungs could produce ventilation heterogeneity at those anatomic levels. We modeled the washout kinetics of (13)NN with positron emission tomography to examine how specific ventilation (sV) heterogeneity at different length scales is influenced by lung aeration. Three groups of anesthetized, supine sheep were studied: high tidal volume (Vt; 18.4 ± 4.2 ml/kg) and zero end-expiratory pressure (ZEEP) (n = 6); low Vt (9.2 ± 1.0 ml/kg) and ZEEP (n = 6); and low Vt (8.2 ± 0.2 ml/kg) and positive end-expiratory pressure (PEEP; 19 ± 1 cmH(2)O) (n = 4). We quantified fractional gas content with transmission scans, and sV with emission scans of infused (13)NN-saline. Voxel (13)NN-washout curves were fit with one- or two-compartment models to estimate sV. Total heterogeneity, measured as SD[log(10)(sV)], was divided into length-scale ranges by measuring changes in variance of log(10)(sV), resulting from progressive filtering of sV images. High-Vt ZEEP showed higher sV heterogeneity at <12- (P < 0.01), 12- to 36- (P < 0.01), and 36- to 60-mm (P < 0.05) length scales compared with low-Vt PEEP, with low-Vt ZEEP in between. Increased heterogeneity was associated with the emergence of low sV units in poorly aerated regions, with a high correlation (r = 0.95, P < 0.001) between total heterogeneity and the fraction of lung with slow washout. Regional mean fractional gas content was inversely correlated with regional sV heterogeneity at <12- (r = -0.67), 12- to 36- (r = -0.74), and >36-mm (r = -0.72) length scales (P < 0.001). We conclude that sV heterogeneity at length scales <60 mm increases in poorly aerated regions of mechanically ventilated normal lungs, likely due to heterogeneous small-airway narrowing and alveolar derecruitment. PEEP reduces sV heterogeneity by maintaining lung expansion and airway patency at those small length scales.
正常肺的通气不均区域中小气道直径和肺泡萎陷的异质性可能导致这些解剖水平的通气异质性。我们使用正电子发射断层扫描来模拟 (13)NN 的清除动力学，以研究不同长度尺度的特定通气 (sV) 异质性如何受到肺充气的影响。三组麻醉仰卧绵羊接受研究：大潮气量 (Vt；18.4 ± 4.2 ml/kg) 和零呼气末正压 (ZEEP) (n = 6)；低 Vt (9.2 ± 1.0 ml/kg) 和 ZEEP (n = 6)；以及低 Vt (8.2 ± 0.2 ml/kg) 和呼气末正压 (PEEP；19 ± 1 cmH(2)O) (n = 4)。我们使用透射扫描量化了部分气体含量，并用输注的 (13)NN-生理盐水的发射扫描来量化 sV。用单室或双室模型拟合体素 (13)NN 清除曲线，以估计 sV。总异质性，以 log(10)(sV) 的标准差 (SD) 衡量，通过测量 sV 图像的方差变化来衡量，方差变化是由于 sV 图像的逐步过滤而产生的。与低 Vt PEEP 相比，高 Vt ZEEP 在 <12-(P < 0.01)、12-36-(P < 0.01) 和 36-60-mm(P < 0.05) 长度尺度上具有更高的 sV 异质性，而低 Vt ZEEP 则介于两者之间。异质性增加与通气不良区域中低 sV 单位的出现有关，总异质性与慢速清除的肺部分数之间存在高度相关性 (r = 0.95，P < 0.001)。区域性平均部分气体含量与 <12-(r = -0.67)、12-36-(r = -0.74) 和 >36-mm(r = -0.72) 长度尺度上的区域性 sV 异质性呈负相关 (P < 0.001)。我们得出结论，在机械通气正常肺的通气不良区域中，<60 mm 的 sV 异质性增加，这可能是由于小气道狭窄和肺泡萎陷的异质性所致。PEEP 通过在这些小长度尺度上维持肺膨胀和气道通畅来减少 sV 异质性。
