Using Pulmonary Angiogram to Estimate Vascular Remodeling in Mice

Abstract

BackgroundPulmonary vascular remodeling is a major cause for the elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension (PAH) and animals with experimental pulmonary hypertension (PH). Utilizing pulmonary angiography technique, we are able to visualize vascular blockade and structural changes in the lung vasculature of patients with PAH and animals with experimental PH. Given the differences in ventilation (V), perfusion (Q) and V/Q relationship in different regions of the lung, it is important to know whether vascular structure and density are different in various areas of the lung. In this study, we aimed to examine whether pulmonary vascular structure and density are different in the upper (apical), middle and lower (basal) regions of the lung in mice and whether pulmonary hemodynamic measurement via right heart catheterization affects the angiographic measurement.MethodsA polyethylene tube was cannulated into the pulmonary artery (PA) via the right ventricle in anesthetized mice to perfuse microfilm polymer (yellow) into the lung vasculature using an automated pump. The lungs filled with microfil were dehydrated using ethanol and placed in methyl salicylate for overnight to show only the vasculature. Lungs were then photographed with a digital camera. The peripheral lung vascular images from the upper, middle and lower regions were selected and converted to binary images for quantitative analysis.ResultsIn the skeletonized images (showing only the vasculature), the length of branches, the number of branches, and the number of junctions were first measured and compared among the upper, middle and lower regions of normal mouse lungs. The data showed that there was no significant difference among different regions in terms of the length of branches as well as the numbers of branches and junctions. Furthermore, we compared these three parameters in different regions between the lungs isolated from mice in which we measured right ventricular pressure using right heart catheterization and the lungs isolated from control mice. The data indicated that the length of branches (22±3, 20±3 and 21±1 vs. 21±1, 22±1 and 19±2 mm/mm2, respectively), the number of branches (420±70, 364±83 and 411±44 vs. 388±50, 426±26 and 353±27 per mm2, respectively, and the number of junctions (186±34, 186±14 and 212±38 vs. 183±35, 191±13 and 155±18 per mm2, respectively) in the upper, middle and lower regions of the lungs from mice with right heart catheterization were not significantly different from the lungs of control mice.ConclusionPeripheral vascular structure and density in the mouse lung, determined by the length of branches and the numbers of branches and junctions, are not significantly different among the apical, middle and basal regions of the mouse lung. Lung hemodynamic measurement or invasive right heart catheterization has little effect on the peripheral vascular density. These results suggest that lung angiogram on the peripheral vasculature is a reliable experimental tool to evaluate lung vascular structural changes in small animals.Support or Funding InformationNational Natural Science Foundation of China (81800035)