Bayat Sam, Degrugilliers Loïc, Porra Liisa, Strengell Satu, Petak Ferenc, Habre Walid
Department of Pulmonology & Physiology, Grenoble University Hospital, Grenoble, France.
Univ. Grenoble Alpes, INSERM UA07, STROBE Laboratory, Grenoble, France.
J Appl Physiol (1985). 2023 Apr 1;134(4):995-1003. doi: 10.1152/japplphysiol.00051.2023. Epub 2023 Mar 17.
We analyzed the fractal dimension (Df) of lung gas and blood distribution imaged with synchrotron radiation K-edge subtraction (KES), in six anesthetized adult New Zealand White rabbits. KES imaging was performed in upright position during stable Xe gas (64% in O) inhalation and iodine infusion (Iomeron, 350 mg/mL), respectively, at baseline and after induced bronchoconstriction by aerosolized methacholine (125 mg/mL, 90 s) and bronchodilator (salbutamol, 10 mg/mL, 90 s) inhalation, at two axial image levels. Lung Xe and iodine images were segmented, and maps of regional lung gas and blood fractions were computed. The Df of lung gas (Df) and blood (Df) distribution was computed based on a log-log plot of variation coefficient as a function of region volume. Df decreased significantly during bronchoconstriction ( < 0.0001), and remained low after salbutamol. Df depended on the axial image level ( < 0.0001), but did not change with bronchoconstriction. Df was significantly associated with arterial [Formula: see text] ( = 0.67, = 0.002), and negatively associated with [Formula: see text] ( = -0.62, = 0.006), respiratory resistance ( = -0.58, = 0.011), and elastance ( = -0.55, = 0.023). These data demonstrate the reduced Df of gas distribution during acute bronchoconstriction, and the association of this parameter with physiologically meaningful variables. This finding suggests a decreased complexity and space-filling properties of lung ventilation during bronchoconstriction, and could serve as a functional imaging biomarker in obstructive airway diseases. Here, we used an energy-subtractive imaging technique to assess the fractal dimension (Df) of lung gas and blood distribution and the effect of acute bronchoconstriction. We found that Df of gas significantly decreases in bronchoconstriction. Conversely, Df of blood exhibits gravity-dependent changes only, and is not affected by acute bronchoconstriction. Our data show that the fractal dimension of lung gas detects the emergence of clustered rather than scattered loss of ventilatory units during bronchoconstriction.
我们分析了6只麻醉成年新西兰白兔通过同步辐射K边减法（KES）成像的肺气体和血液分布的分形维数（Df）。在基线时以及雾化吸入乙酰甲胆碱（125 mg/mL，90秒）诱导支气管收缩后和吸入支气管扩张剂（沙丁胺醇，10 mg/mL，90秒）后，分别在两个轴向图像层面，于稳定吸入Xe气（64%于O中）和注入碘（碘海醇，350 mg/mL）期间在直立位进行KES成像。对肺Xe和碘图像进行分割，并计算区域肺气体和血液分数图。基于变异系数随区域体积变化的双对数图计算肺气体（Df）和血液（Df）分布的Df。支气管收缩期间Df显著降低（<0.0001），沙丁胺醇治疗后仍保持较低水平。Df取决于轴向图像层面（<0.0001），但不随支气管收缩而变化。Df与动脉[公式：见正文]显著相关（=0.67，=0.002），与[公式：见正文]呈负相关（=-0.62，=0.006）、与呼吸阻力（=-0.58，=0.011）以及弹性（=-0.55，=0.023）呈负相关。这些数据表明急性支气管收缩期间气体分布的Df降低，且该参数与生理上有意义的变量相关。这一发现提示支气管收缩期间肺通气的复杂性和空间填充特性降低，并且可作为阻塞性气道疾病的功能成像生物标志物。在此，我们使用能量减法成像技术评估肺气体和血液分布的分形维数（Df）以及急性支气管收缩的影响。我们发现支气管收缩时气体的Df显著降低。相反，血液的Df仅表现出与重力相关的变化，且不受急性支气管收缩影响。我们的数据表明，肺气体的分形维数可检测支气管收缩期间通气单位出现的是成簇而非分散的损失。
