Former First Lady Barbara Bush has decided not to seek any more treatment for COPD and congestive heart failure.

Instead, she’s chosen comfort care and is surrounded by family.

Millions of people in the United States have been diagnosed with COPD, an umbrella term that describes progressive lung diseases like emphysema and chronic bronchitis which can make breathing difficult.

The full name is Chronic Obstructive Pulmonary Disease. Here’s what happens:

When you inhale, air goes down the trachea, into large tubes called bronchi, then into smaller ones called bronchioles before finally ending up in alveoli, tiny air sacks that take oxygen in and gets rid of carbon dioxide.

Chronic bronchitis causes inflammation of the airways and a buildup of excess mucus.

Emphysema causes the alveoli to lose elasticity and causes the sacks to breakdown leading to fewer, larger sacks.

COPD affects at least 16 million people in the United States and, according to the American Lung Associate, 90 percent of cases are caused by smoking.

Mrs. Bush smoked for 25 years before quitting in 1968.

There are other causes including environmental factors like chemicals and fumes. Genetics can also play a role.

Symptoms include shortness of breath, coughing, fatigue and tightness in chest.

Although there is no cure, COPD can be managed and there is no limit on how long a person can live with it.