Lieutenant Axel suspected an air embolism, meaning that Savino had taken a breath and held it before they’d pulled him up. As the pressure around him dropped to sea level, the pressure exerted by the air inside his lungs would have mounted until a bubble was expelled into his bloodstream. It would travel through veins and arteries until it lodged in a passage too small to pass through―in Savino’s case, one bringing blood to the brain. Air embolisms were often deadly, but Savino had survived.
Source: wiktionary