Cavitation bubble dynamics following lithotripter-induced shock wave-gas bubble interaction in viscous compressible blood.

The equation of motion for a cavitation bubble following lithotripter-induced shock wave and gas bubble nucleus interaction in a viscous compressible blood is derived using the Keller-Miksis model, together by applying a Casson equation as a constitutive equation for blood flow, and numerical calculations have been performed for the initial bubble radii R0, 1-10 μm. Following the shock wave-gas bubble interaction, a cavitation bubble is formed when the shock wave pressure tail enters the negative pressure region, and it expands to reach the maximum radius Rmax. The Rmax value decreases linearly as R0 decreases for whole blood, plasma, and water. Among the three types of liquids, whole blood tends to exhibit the smallest Rmax value due to the influence of apparent viscosity. During cavitation bubble collapse, a high Reynolds number flow is developed in the whole blood, in which the apparent viscosity approaches Casson viscosity. Eventually, the bubble collapse dominated by inertial effect can produce impulsively high pressures on the order of several hundreds to thousands of gigapascals with the pulse width of 7.5 ps to 0.11 ns (i.e., full width at half maximum). A pair of impulsive collapse pressure pulses, with the collapse pressure ratio of 27-789, occur with the occurrence frequency of approximately 9 kHz for whole blood.