A teenager in Italy recently beat some incredible odds when he survived for 42 minutes underwater, according to news reports.
The 14-year-old boy, identified only as “Michael” by the Italian newspaper Milan Chronicle, reportedly dove off a bridge into a canal with some friends last month and never resurfaced. His foot became caught on something underwater and it took firefighters and other first responders nearly an hour to free him from the depths. Though Michael remained on life support for an entire month, he recently woke up and seems to be doing fine, Time reported.
While Michael’s story is certainly unusual, it’s not unheard of for people to survive prolonged stints underwater, according to Dr. Zianka Fallil, a neurologist at North Shore-LIJ’s Cushing Neuroscience Institute in New York. Fallil, who called the teenager’s recovery “quite remarkable,” told Live Science that there are two physiological processes that may come into play when a person is submerged underwater for an extended period of time with no oxygen.
The first of these processes is known as the “diving reflex,” or bradycardic response, a physiological response that has been observed most strongly in aquatic mammals, but which is also believed to take place in humans. (This is the same reflex that results in newborn babies holding their breath and opening their eyes when submerged in water). When a person’s face is submerged in water, blood vessels constrict and the heart slows down considerably, Fallil explained. Blood is then diverted to parts of the body that need it most.
“The body protects the most efficient organs — the brain, the heart, the kidneys — and pulls the blood away from the extremities and other, not-as-essential, organs,” Fallil said.
The diving reflex is often cited as the thing that saves people from nearly drowning. However, it’s difficult to study this reflex in humans (likely because of the obvious dangers of recreating near-drowning experiences in a lab), said Fallil, who pointed to another, less controversial explanation for how people survive long stretches underwater — the selective brain cooling hypothesis.
“The selective brain cooling hypothesis [states] that, the quicker the brain cools, the more likely it is to survive,” she said.
When you’re immersed in cold water for a prolonged period of time, your body may carry out several processes that allow cooled blood to enter the brain, according to Fallil. One of these processes, hypercapnic vasodilation, occurs when the body retains carbon dioxide as a result of not breathing. This extra carbon dioxide causes blood vessels in your brain to dilate (become wider), which in turn allows more cool blood to enter the brain.
Photo by felizfeliz 
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