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Nitsch, narcosis "is just a bitch," making him feel out of control on every dive, as though everything is about to slip from his grasp, a terrible feeling when you're riding nearly 200 pounds of lead to the bottom of the sea.
    Still, the greatest threat to a submerged Nitsch has nothing to do with nitrogen. It has nothing to do with his brain or his heart or his lungs. It has to do with the ears and the reality that we are limited in the depths we can reach by their delicate architecture. What keeps Nitsch from reaching 1,000 feet is a mere fraction of an inch thick: the translucent tympanic membranes in the auditory canals otherwise known as eardrums.
    It doesn't take much pressure to burst an eardrum. If you go swimming and don't equalize your ears by plugging your nose and pushing air into your Eustachian tubes, the weight of the water knocking on your door can snap that thin membrane at a dozen feet, give or take. It has never happened to Nitsch, but he knows it's an extraordinarily painful sensation. In cold water—and deep water is always cold water—it can also be deadly. When cold water rushes in, your ears' mechanics cramp and seize, affecting your sense of spatial awareness, including the sense of up and down. You don't know which way points toward permanent blackness and which way points toward light. Eventually, your body will warm the water trapped inside your head, and your ears will relax, opening up the world to you once more. By then, though, your lungs will have opened up too, and the water in your ears will be low on your list of concerns.
    The only way to counter this danger is to pressurize the inside of your ears. But Nitsch's lungs—your lungs—only hold a finite amount of air. And when that air is compressed the deeper he travels, there is less and less to push into his Eustachian tubes. Eventually, he runs out. He always runs out. And always at the moment his eardrums inform him they're about to break.
    He has searched for every known fix. In addition to conserving air, Nitsch takes in as much as he can. For his final breath, he practices what free-divers call packing: taking a normal breath, then 30 or so small swallows of air to fill every nook and cranny of his respiratory system with oxygen. Once below water, he stops his weighted sled at around the 75-foot mark and expels that stored air, through a tube, into a plastic Coke bottle. (These are the homespun instruments of a pioneering profession.) As he continues to descend, he takes sips from the bottle whenever his ears cry out. At depth, it is easier to sip air from a bottle than to squeeze it from crushed lungs.
    It's also one more mind trick Nitsch is playing, fooling his brain into thinking he's actually breathing, even if the air he's taking in has already been stripped of oxygen. It's the same as a thirsty man spitting back a glass of water without swallowing it; he would feel as if he were drinking, but his body would be drying out all the same. The charade can't go on forever, maybe not even as far as 1,000 feet. The air in the Coke bottle may protect his eardrums, but packing expands the esophagus, restricting blood flow to the brain. To prevent a blackout, Nitsch's body amps up his heart rate, which burns a lot of oxygen. What air gives him, it also takes away.
    Nitsch and other free-divers, then, are trying to determine if it's more effective to dive with nearly empty lungs, to sacrifice oxygen for the body's reaction to the absence of it: the slow, gradual shutting down, the gentle drift to death's door. He has begun to wonder if air is the enemy.
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    Liquid is life—Nitsch finds himself thinking that over and over again. Maybe we drown only because we haven't learned enough about what we're capable of. Maybe we drown only because our brain associates air with breathing and liquid with drowning. Aren't we made mostly of water? Weren't we born in the oceans?
    And so he has experimented with a technique used by a