In vitro evidence of bubble-induced acoustic softening and Sanal flow choking in cardiovascular decompression

When astronauts or divers experience a rapid drop in surrounding pressure, tiny gas bubbles can form in their blood—a condition that can threaten heart and vessel function. In this study, we simulated such decompression using fresh, warmed blood samples (37–40 °C) placed in a vacuum chamber. Bubbles consistently appeared near 600 mmHg. Their formation led to acoustic softening , a sharp drop in the speed of sound through blood. As flow velocity remained unchanged, the rising local Mach number brought the system closer to Sanal flow choking, triggered at a critical pressure ratio. Once choking occurs, it can lead to localized supersonic zones and abrupt pressure jumps. Additionally, bubbles may coalesce and block narrow vessels—a phenomenon akin to vapor lock—further impeding circulation. These findings reveal a novel mechanistic link between microbubble formation, acoustic softening, and flow choking, offering valuable insights for protecting cardiovascular health during spaceflight and rapid decompression events.