It’s a warm spring afternoon. Fourteen year old Michael and his friends hang out at the
Naviglio Grande Canal in Milan, Italian. The five boys dive off a bridge into the murky cool water.
They pop up laughing and splashing each other. But something’s wrong.
Michael’s friends realize that he’s missing--he never returned to the surface.
They quickly dive back down and find Michael. He’s about 6 feet (1.8 meters) under water,
caught in the grip of a strong current. Worse yet, his foot is stuck in a
barricade of wooden poles used to guide boats. Michael’s friends frantically try to free him.
The commotion attracts the attention of a man jogging by. He strips down and dives
in to help. But Michael’s foot won’t come loose. Someone calls the emergency services. Firefighters
quickly arrive and send divers down to free Michael. Finally, about 42 minutes after he
first dived, rescuers return Michael to the surface. He’s limp, cold, and unconscious.
They lay Michael on the bank and check for signs of life. Surprisingly, they detect a faint
heartbeat. The rescuers do chest compressions and attempt to resuscitate him on the spot,
but to no avail. Michael is rushed to a local hospital and hospitalized
in the cardiac surgery intensive care unit. He spends the next month in a coma attached
to machines which breathe on his behalf and keep his heart pumping. When Michael awakes,
he’s alert and able to recognize his parents. He even asks about his favorite soccer team.
Miraculously, he has no brain damage and is able to make a complete recovery.
How did someone survive underwater for nearly an hour without air? Although Michael’s 42
minute ordeal is the longest we were able to find, there have been a few other accounts of
people stuck underwater for 15 or 20 minutes who survived. Many were able to make a full recovery.
Generally, brain damage begins after about 1-2 minutes without oxygen.
At 4-6 minutes the occurring brain damage is severe and likely permanent.
Around 10 minutes without oxygen death occurs. While doctors cannot fully explain Michael’s
miraculous survival, there are two main theories of why he was able to survive.
First, the bradycardic response which is part of the mammalian diving reflex.
This physiological response is the same reflex that babies up to 6 months old have
when their heads are submerged in water. They hold their breath, their hearts slow down and blood is
shifted away from extremities and less essential organs to conserve oxygen for their brains and
hearts. This reflex also protects babies from getting milk in their lungs while nursing.
Around 6 months in age, babies begin to gradually lose the reflex. However adults
often retain vestiges of it. If you dunk your face in cold water, you’ll gasp and hold your breath.
Unfortunately, the bradycardic response is hard to study in humans, especially adults, as it would
involve recreating near-drowning experiences. The second theory as to how Michael could have
survived so long underwater is the selective brain cooling hypothesis. Studies have determined that
the quicker the brain cools, the more likely it is to survive. When immersed in water,
the human body retains carbon dioxide as a result of not breathing, which causes blood
vessels in the brain to dilate to allow increased blood flow so the brain can receive more oxygen.
This function is called hypercapnic vasodilation. When submerged in cool water,
the blood in the extremities begins to cool and as hypercapnic vasodilation happens, the cool blood
flows to the brain. As a result, the brain cools faster. The colder the water, the more quickly
cool blood flows to the brain and the longer the brain may be sustained. The water Michael
dived into was a chilly 59 degrees F (15 C). It’s been noted that most of the survivors of near
drownings with minimal effects tend to be young and the water they’ve been submerged in is cold,
suggesting that both theories play a role with the brain cooling hypothesis being aided
by the bradycardic response. Michael’s near drowning fits this profile. Also essential to
Michael’s survival was the emergency CPR that was administered to him immediately
after he had been pulled from the river. And now that you've reached the end of our video,
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