Montesantos Spyridon, Katz Ira, Venegas Jose, Pichelin Marine, Caillibotte Georges
Medical R&D, Air Liquide Santé International, Paris Saclay, France.
Department of Mechanical Engineering, Lafayette College, Easton, PA, United States of America.
PLoS One. 2017 Jul 31;12(7):e0182052. doi: 10.1371/journal.pone.0182052. eCollection 2017.
Computational models of gas transport and aerosol deposition frequently utilize idealized models of bronchial tree structure, where airways are considered a network of bifurcating cylinders. However, changes in the shape of the lung during respiration affect the geometry of the airways, especially in disease conditions. In this study, the internal airway geometry was examined, concentrating on comparisons between mean lung volume (MLV) and total lung capacity (TLC). A set of High Resolution CT images were acquired during breath hold on a group of moderate persistent asthmatics at MLV and TLC after challenge with a broncho-constrictor (methacholine) and the airway trees were segmented and measured. The airway hydraulic diameter (Dh) was calculated through the use of average lumen area (Ai) and average internal perimeter (Pi) at both lung volumes and was found to be systematically higher at TLC by 13.5±9% on average, with the lower lobes displaying higher percent change in comparison to the lower lobes. The average internal diameter (Din) was evaluated to be 12.4±6.8% (MLV) and 10.8±6.3% (TLC) lower than the Dh, for all the examined bronchi, a result displaying statistical significance. Finally, the airway distensibility per bronchial segment and per generation was calculated to have an average value of 0.45±0.28, exhibiting high variability both between and within lung regions and generations. Mixed constriction/dilation patterns were recorded between the lung volumes, where a number of airways either failed to dilate or even constricted when observed at TLC. We conclude that the Dh is higher than Din, a fact that may have considerable effects on bronchial resistance or airway loss at proximal regions. Differences in caliber changes between lung regions are indicative of asthma-expression variability in the lung. However, airway distensibility at generation 3 seems to predict distensibility more distally.
气体传输和气溶胶沉积的计算模型经常使用理想化的支气管树结构模型，其中气道被视为分支圆柱体网络。然而，呼吸过程中肺部形状的变化会影响气道的几何形状，尤其是在疾病状态下。在本研究中，对气道内部几何形状进行了检查，重点是平均肺容积（MLV）和肺总量（TLC）之间的比较。在一组中度持续性哮喘患者中，在使用支气管收缩剂（乙酰甲胆碱）激发后，于屏气状态下在MLV和TLC时采集了一组高分辨率CT图像，并对气道树进行了分割和测量。通过使用两个肺容积下的平均管腔面积（Ai）和平均内部周长（Pi）计算气道水力直径（Dh），发现TLC时Dh平均系统地高出13.5±9%，下叶与上叶相比显示出更高的百分比变化。对于所有检查的支气管，平均内径（Din）经评估比Dh低12.4±6.8%（MLV）和10.8±6.3%（TLC），该结果具有统计学意义。最后，计算出每个支气管段和每个代的气道扩张性，其平均值为0.45±0.28，在肺区域和代之间以及内部均表现出高度变异性。在肺容积之间记录到混合的收缩/扩张模式，即在TLC时观察到一些气道未能扩张甚至收缩。我们得出结论，Dh高于Din，这一事实可能对近端区域的支气管阻力或气道损失有相当大的影响。肺区域之间管径变化的差异表明肺部哮喘表现的变异性。然而，第3代的气道扩张性似乎更能预测更远端的扩张性。
