Fractal Dimension of Pulmonary Gas and Blood Distribution Assessed by Synchrotron K-Edge Subtraction Imaging: Effect of Bronchoconstriction
Résumé
We analyzed the fractal dimension (Df) of lung gas and blood distribution imaged with synchrotron radiation K-edge Subtraction imaging, in 6 anesthetized adult New Zealand White rabbits. KES imaging was performed during stable Xe gas (64% in O 2 ) inhalation and iodine infusion (Iomeron, 350 mg/ml), respectively, at baseline and after induced bronchoconstriction by aerosolized methacholine (125mg/ml, 90s) and bronchodilator (salbutamol, 10 mg/ml, 90s) inhalation, at 2 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 Xe ) and blood (Df Iodine ) distribution was computed based on a log-log plot of variation coefficient as a function of region volume. Df Xe decreased significantly during bronchoconstriction (p<0.0001), and was not modified by salbutamol. Df Iodine depended on the axial image level (p<0.0001), but did not change with bronchoconstriction. Df Xe was significantly associated with arterial PaO 2 (adjusted R 2 =0.42, p=0.002), and negatively associated with PaCO 2 (R 2 =0.35, p=0.006), respiratory resistance (R 2 =0.3, p=0.011) and elastance (R 2 =0.25, p=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 biomarker of lung functional images in obstructive airway diseases.