By Marshall Brain
McCLATCHY-TRIBUNE
Saturday, May 10, 2008

David Blaine is a magician and performer best known for highly public stunts. For example, he has been frozen in ice. He has lived in a transparent box for 44 days without food. And so on.
But recently Blaine set what might be his most surprising record. He held his breath underwater for more than 17 minutes. And as usual he did it in a very public way -- on "The Oprah Winfrey Show."

If you take a minute right now and try to hold your breath for as long as you can, you will realize how much of an achievement Blaine's 17 minutes are. If you are a typical person, chances are that you can't hold your breath for more than a minute or two.

So how did Blaine do it? What could he possibly do to make it possible to hold his breath for so long? It turns out that he combined a variety of techniques to reach this endurance record.

But first, let's take a look at what is happening when you hold your breath. In your lungs you have trapped about six liters of air (think of two three-liter soda bottles in your chest filled with air). The air is about 80 percent nitrogen and 20 percent oxygen. Your body doesn't do anything with the nitrogen, but your body really needs the oxygen. Cells use oxygen to release energy from sugar molecules. Without oxygen, your cells shut down very quickly from lack of energy. At the same time, your cells are creating carbon dioxide as the waste product of the sugar reaction. So the oxygen in your lungs gets used up and the amount of carbon dioxide in your body is rising.
The reason most people can't hold their breath for more than two minutes is because there are sensors in our lungs that detect the rising carbon-dioxide level. Those sensors send signals to the diaphragm telling it to breathe. Eventually the signals get so loud that they cause pain. You feel like you are about to explode.

To hold your breath for more than two minutes, you must first train your body to get past that pain and suppress the diaphragm's complaints. You can do this with relaxation exercises, and many people can learn to hold their breath for four minutes after an hour or so of instruction.

Blaine clearly has mastered this discipline, and then he kept adding techniques. For example, instead of breathing normal air, he breathed pure oxygen before his attempt. That meant his lungs held five times more oxygen than normal (since normal air is four-fifths nitrogen).

For more than a month Blaine slept in a special tent, called a hypoxic tent, that reduces the amount of oxygen in the air. When inside the tent, he was breathing air that contained is same amount of oxygen that you would find at 15,000 feet -- about 10 percent oxygen. By sleeping in the tent for weeks, his body compensated by increasing the number of red blood cells flowing in his veins. This gave his blood more capacity for carrying oxygen and carbon dioxide.

Right before holding his breath, Blaine also used a technique for gulping extra air into his lungs. In the same way that you can force a whole lot more food than normal into your stomach, you can learn to force an extra liter or air into your lungs, giving you extra capacity.

Blaine also fasted before his attempt. That did two things. First, fasting shrinks the size of the stomach and intestines, giving more room for the lungs to expand. Second, it reduces oxygen demand. The stomach and intestines contain a lot of muscle for grinding and moving the food along. With no food in the system, those muscles can relax.

Finally, with the help of good coaching and supervision, Blaine practiced for many weeks. It helped him get comfortable with the feelings and signals that would be coming from his body, and also allowed him to refine his techniques.

Putting all these things together at one time gave Blaine everything he needed to set a world record. Seventeen minutes is an incredibly long time to go without breathing.

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