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Lungs to Brain: Don't Panic!

Carbon dioxide may deserve blame for more than just the panic over global warming. New research involving healthy people inhaling the gas indicates that the brain's reaction to carbon dioxide helps explain panic attacks and other anxious feelings, independent of rising world temperatures. This new insight, reported 3 October in PLoS One, could help physicians prevent the development of depression and other anxiety disorders.

It's long been known that anxiety-prone individuals often experience panic attacks when they breathe in carbon dioxide. Psychiatrists have theorized that emotional distress reflects a built-in response to suffocation. The "false suffocation alarm theory" suggests that the brain has a carbon dioxide sensor and that it is oversensitive in some people, mistakenly spurring panic attacks. Such a sensor could have evolved to alert oxygen-breathing organisms of impending death.

Eric Griez, an experimental psychiatrist at the University of Maastricht, the Netherlands, came up with a test for the false-alarm theory. If it is valid, he surmised, healthy individuals should show some sensitivity to carbon dioxide as well. So he and his colleagues recently asked 64 volunteers to inhale two deep breaths of four mixtures of compressed air containing 9%, 17.5%, 35%, or no carbon dioxide. After inhaling each mixture, the volunteers continuously rated their level of fear and discomfort on a scale from 1 to 100 using a touch screen and rated their panic using a questionnaire that listed 13 common symptoms of panic attacks. As the dose of carbon dioxide increased, so did fear and discomfort. "Panic seems to be a very special kind of anxiety which truly can be called a suffocation alarm," says Griez. Volunteers also experienced a loss of touch with reality and a fear of going crazy, describing their experiences as "frightening," "panicky," and "scaring." Griez says the results show just how closely a person's emotions are linked to physical well-being. "Panic, which is the most dramatic form of acute anxiety, is the cry for life," he says.

The results suggest a new way to experimentally induce panic in the laboratory, which may allow easier and faster testing of new antianxiety drugs. However, Laszlo Papp, a psychiatrist at Columbia University, questions whether the reactions described by the healthy people are true panic attacks. He says the study simply shows that increasing the concentration of carbon dioxide inhaled results in more physical discomfort, such as shortness of breath and lightheadedness. Papp says he has conducted studies in which anxiety-prone individuals and healthy controls inhaled carbon dioxide, and only a small proportion of the latter panicked. "The discomfort rarely translated into the panic attack described by panic patients," he says.

Griez, however, believes the new finding will ultimately help physicians better treat patients with emphysema and asthma. When these patients cannot get enough oxygen, carbon dioxide builds up in their bodies, making them feel as though they are suffocating. They also face a higher risk of anxiety than the rest of the population.