Lung disease is the third leading cause of death and impacts more than 24 million people in the United States, yet many people with the disease are unaware they may have it. Chronic Obstructive Pulmonary Disease, or COPD, is a serious lung disease that over time makes it hard to breathe and can cause serious, long-term disability. More than 12 million people are diagnosed with COPD in the United States and experts estimate that just as many are undiagnosed.