When was the last time you thought about breathing? Most people usually do not.

When we are healthy, breathing happens naturally and easily. Without much effort on our part, the human respiratory system works hard. Experts say we take about 20,000 breaths every day.

One such expert is James Hoyt, a doctor at the University of Colorado’s Health Pulmonology Clinic, also called UCHealth. Hoyt is a pulmonologist -- a specialist on respiratory disorders.

On the UCHealth website, he notes that our “respiratory muscles are working every minute of the day, every day of our lives.”

A muscle called the diaphragm separates the chest and abdominal cavities. As we breathe in, the diaphragm tightens. The chest cavity opens, and the lungs expand. When we breathe out, the diaphragm relaxes and moves upward, pushing air out.

When you breathe deeply, the air coming in through your nose fully fills your lungs, and the lower belly rises. On its website, Harvard Medical School notes that deep breathing may slow the heartbeat, lower blood pressure and lower stress. Deep breaths help your body fully exchange incoming oxygen with outgoing carbon dioxide.

However, many people do the opposite of deep breathing. They take short breaths and have shallow breathing. Experts call this “chest breathing.”

Shallow breathing limits the expansion of the diaphragm and its movement. The lower part of the lungs does not get a full share of oxygenated air. This can make you feel short of breath and worried, or anxious.

The American Lung Association notes that shallow breathing, over time, leaves old, stale air in the lungs. This leaves less room for the diaphragm to bring in fresh oxygen. And that means lower oxygen levels and less oxygen for exercise and activity.

Several health websites explain an easy deep breathing exercise.

Find a place to sit or lie down. Place one hand just below your ribs. Take a slow, deep breath -- or inhale -- through your nose. Feel your hand go up. Your stomach should rise and expand. Now breathe out slowly through your mouth. Make sure to breathe out -- or exhale -- all the way. Feel your hand and stomach go down.

The American Lung Association website states that if done repeatedly, breathing exercises can help remove stale air from the lungs. This will increase oxygen levels and get the diaphragm to return to its job of helping you breathe.

Pulmonologist James Hoyt adds that “deep breathing is a good way to reduce stress and relax.”

Hoyt tells patients to avoid smoking, to eat a good diet and to get a good night’s rest. He also urges them to seek help for respiratory conditions as soon as they are observed.

Shortness of breath happens when you are worried, frightened, or are in poor physical shape. But it can also be a sign of health problems.