The diagnosis of aneurysms is informed by empirically tracking their size and growth rate. Here, by analysing the growth of aortic aneurysms from first principles via linear stability analysis of flow through an elastic blood vessel, we show that abnormal aortic dilatation is associated with a transition from stable flow to unstable aortic fluttering. This transition to instability can be described by the critical threshold for a dimensionless number that depends on blood pressure, the size of the aorta, and the shear stress and stiffness of the aortic wall. By analysing data from four-dimensional flow magnetic resonance imaging for 117 patients who had undergone cardiothoracic imaging and for 100 healthy volunteers, we show that the dimensionless number is a physiomarker for the growth of thoracic ascending aortic aneurysms and that it can be used to accurately discriminate abnormal versus natural growth. Further characterization of the transition to blood–wall fluttering instability may aid the understanding of the mechanisms underlying aneurysm progression in patients.

动脉瘤的诊断是通过凭经验跟踪动脉瘤的大小和生长速度来进行的。在这里，通过对弹性血管血流的线性稳定性分析，从第一原理分析主动脉瘤的生长，我们发现异常的主动脉扩张与从稳定血流到不稳定主动脉扑动的转变有关。这种向不稳定的转变可以通过无量纲数的临界阈值来描述，该阈值取决于血压、主动脉的大小以及主动脉壁的剪切应力和刚度。通过分析 117 名接受过心胸影像的患者和 100 名健康志愿者的四维血流磁共振成像数据，我们表明无量纲数是胸升主动脉瘤生长的生理标志物，可用于准确地评估胸升主动脉瘤的生长情况。区分异常生长和自然生长。进一步表征血壁扑动不稳定性的转变可能有助于理解患者动脉瘤进展的机制。