Asymmetrical oscillation of a bubble confined inside a micro pseudoelastic blood vessel and the corresponding vessel wall stresses

Asymmetrical oscillation of a micro-bubble confined inside a deformable pseudoelastic vessel with comparable initial radius with the bubble is studied in detail. Unlike the symmetric oscillation in an unconstrained environment, the oscillating bubble under the constraint of a pseudoelastic vessel gradually becomes as an ellipsoid from a sphere (this is called asymmetrical effect), and leads to substantially larger stresses within the vessel wall. Influence of inertial effect, circumferential stiffness and pre-existing blood pressure on bubble’s asymmetrical oscillation are taken into account in the paper. Computational results show that a vessel wall with larger circumferential stiffness corresponds to larger stress amplitude with higher frequency within the wall, where the stress amplitude and the pertinent frequency are the two most dominating parameters in determining the failure event under cyclic loading, as well known in the community of materials science. Similar results have been obtained for the case of decreasing in thickness of vessel walls, and for the case of increasing pre-existing pressure in the liquid filling the vessel. These conclusions support the notion that the asymmetric effect is one of the primary mechanisms for the clinical injuries of those with thinner vessel walls, such as capillary and small blood vessels, and for the higher risk of elder and hypertension patients in the shock-wave lithotripsy and other medical procedures involving shock waves, such as ultrasound-assisted encapsulated drug delivery.