Emphysema is a debilitating disease that afflicts more than three million Americans. The disease is caused primarily by smoking and leads to a progressive, irreversible breakdown of lung tissue. This breakdown reduces the amount of lung tissue available for gas exchange and also impairs the lung's ability to inflate and deflate normally. As the disease advances, the most damaged areas of the lung over inflate within the chest cavity, trapping air and preventing the healthier lung areas from functioning normally. Eventually breathing becomes more difficult, leaving patients constantly feeling out-of-breath.