Chris Pekios, a respiratory therapist at Genesis Health System, has helped treat patients with chronic obstructive pulmonary disorder, or COPD.

"It's very scary to be breathless," she said, adding that some people with COPD don't realize they have the disorder until it's too late for effective treatment.

Staying physically fit and doing breathing exercises can help, she added. 

COPD surpassed stroke in 2010 to become the third-leading cause of death in the United States, according to the National Institutes of Health, or NIH.

It is a serious lung disease that, over time, makes it harder to breathe. It affects an estimated 24 million Americans, but as many as 12 million of those may be undiagnosed.

That is partly because the symptoms come on slowly and worsen over time. They include: shortness of breath, chronic coughing or wheezing, and production of excess sputum or a feeling of being unable to take a deep breath.

Lack of communication between patients and health care providers is a major barrier to diagnosis of the disease, according to a recent online survey by the National Heart, Lung and Blood Institute, a division of the NIH.

However, more Americans are speaking to their doctors about the symptoms of COPD, which is a sign that awareness efforts are taking hold.

"A good conversation between patients and providers about COPD can make a real difference for disease sufferers," said James Kiley, the director of the NIH. "It's no secret that early diagnosis and treatment can improve daily living for those who have COPD, but you can't get there without an open line of dialogue in the exam room," he added.

Those 40 years and older who have a history of smoking are most likely to be diagnosed with COPD. However, as many as one person in every six with COPD has never smoked. It also may occur in some people with a genetic condition, and it happens to those with long-term exposure to substances that irritate the lungs, such as dust or fumes.

The disease is diagnosed with a simple test called spirometry, a breath measurement that is often done in a doctor's office. That involves breathing out as hard and fast as possible into a tube connected to a machine that measures lung function.

— Deirdre Cox Baker with information from the National Institutes of Health