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.