Extract
110 Minutes
ALL MAMMALS SHARE SOMETHING
called the diving reflex, a primitive defense against drowning that's triggered when the face comes in contact with cold water. It's stronger in aquatic animals than in other creatures, and in humans, stronger in children than adults. Often, the reflex allows someone to survive longer underwater than they could if deprived of oxygen on land.When receptors inside the nose and elsewhere on the face are submerged, the brain sends a signal to the autonomie nervous system, which orders the body to begin conserving oxygen. The heart slows. Capillaries close, restricting blood flow to the extremities in order to preserve oxygen for the heart and brain. Deep dives provoke the most curious response: Fluids travel freely through organs and other tissues, redistributing themselves to equalize and maintain pressure in the thoracic cavity.In people, the diving reflex is most effective when someone is holding their breath. Eventually, though, carbon dioxide builds up in the blood and the body inhales involuntarily. After that, how long the reflex helps stave off death depends on a host of factors. There are stories of resuscitating people after they've been submerged in frigid water for more than an hour, but most people get just a few extra moments.Lindsay Petterson has no idea how long she was underwater after her car sailed off the bridge that carried Interstate 35W over the Mississippi River. She can rerun the collapse in her mind like a movie. She was traveling south toward downtown Minneapolis, nearly halfway across the span, when a chasm opened in the roadway directly in front of her car. For a split second, she wondered whether it was the seam where two slabs of asphalt had been joined together.Petterson, 25, had stayed late at her job in Shoreview, at a group home for teens, for a class on money...See the full content of this document
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