Acoustic Softening in Human Blood Induced by Microbubble Dynamics Under Decompression: Implications for Sudden Cardiac Collapse

Sudden cardiac arrest (SCA) in individuals without structural or electrical abnormalities remains an unresolved clinical problem. Here we report a pilot translational study investigating whether pressure-driven microbubble dynamics in human blood can generate physical conditions capable of destabilizing cardiovascular flow. Venous blood from healthy adult volunteers (n = 10) was subjected to controlled decompression (760→100 mmHg) at physiological temperature (37–40 °C), while high-speed imaging quantified microbubble nucleation, growth, coalescence and rupture. Microbubble formation consistently initiated below ~600 mmHg, followed by coalescence into transient gas cavities resembling vapor-lock structures. Increasing void fraction was associated with pronounced acoustic softening, with modeled effective sound speed decreasing from ~1500 m s⁻¹ to <100 m s⁻¹. Surface roughness significantly increased nucleation density (p < 0.05). Bubble rupture events produced localized transient pressure disturbances. Although bulk flow was not imposed, the observed acoustic-softening regime defines mechanical conditions permissive for multiphase flow choking in dynamic systems. These findings establish mechanistic feasibility for a physics-based cascade linking decompression-induced microbubble dynamics, acoustic softening and potential flow instability, motivating future in vivo and dynamic investigations into unexplained sudden cardiac collapse.