Microbubble-Induced Acoustic Softening in Human Blood: A Pilot Translational Study Toward Understanding Unexplained Sudden Cardiac Collapse

Background Many cases of sudden cardiac arrest (SCA) occur in individuals with normal coronary arteries and no detectable structural or electrical abnormalities. Mechanistic explanations for such events remain limited. We conducted a pilot translational study to evaluate whether pressure-driven microbubble dynamics can generate physical conditions capable of destabilizing cardiovascular flow. Methods In this pilot, proof-of-concept investigation, venous blood from healthy adult volunteers (n = 10; age 24–32 years) was subjected to controlled static decompression (760→100 mmHg) at physiological temperature (37–40 °C). Microbubble nucleation, growth, coalescence, and rupture were quantified using high-speed imaging. Smooth and rough metallic substrates were used to model vascular and biomaterial interfaces. Acoustic behavior was evaluated using Wood’s equation to estimate sound-speed reduction and identify acoustic-softening thresholds associated with theoretical multiphase flow choking. Effect sizes and confidence intervals were calculated for primary comparisons. Results Microbubble nucleation reproducibly initiated below ~600 mmHg, followed by bubble growth, coalescence, and formation of vapor-lock–like gas cavities. Increasing void fraction produced marked acoustic softening, with modeled effective sound speed decreasing from ~1500 m/s to <100 m/s. Rough surfaces demonstrated significantly higher nucleation density than smooth surfaces (p < 0.05; large effect size). Bubble rupture generated transient shock-like disturbances. Although bulk flow was not imposed, the observed acoustic-softening minimum defines mechanical conditions permissive for multiphase flow choking in dynamic systems. Conclusions This pilot study suggests a possible mechanistic pathway linking decompression-induced microbubble dynamics, acoustic softening, and theoretical flow instability, which requires validation in dynamic experimental and clinical studies. The findings demonstrate the physical feasibility of this cascade under controlled conditions and should be considered hypothesis-generating. They motivate future adequately powered, dynamic, and in-vivo investigations to assess clinical relevance in unexplained sudden cardiac arrest. Significance Statement This pilot translational study identifies a previously unrecognized, physics-based mechanistic framework by which decompression-induced microbubble dynamics may produce acoustic softening and flow instability in blood. By establishing mechanistic feasibility rather than clinical causality, the findings motivate future investigations into monitoring, prevention, and device design strategies for unexplained sudden cardiac collapse.