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David can remain underwater without drowning as long as blood continues to circulate between his heart and brain...but there are serious risks. If he passes out from lack of oxygen, he may reflexively inhale water, which would fill his lungs with water and cause him to drown. Other critical dangers include having a stroke, suffering brain damage or rupturing a lung. "Could he lose consciousness and not survive it? Yes, that's definitely a possibility," Dr. Potkin says. "He could have a total cardiac arrest and not get resuscitated from that. He could potentially die from that."
In his preshow interview, Oprah asked David why he's doing something so dangerous. Does he have some kind of death wish?
"No, no, no, no, no. The opposite," he says. "There is a lot of risk, but I meet experts in the field, and I learn. I like to find out what we are capable of pushing ourselves to do and then studying it with the people that have done it."