Like silver said, it doesn't only have to be related to smoking, but also environmental and work hazards you may have encountered.

Chronic Obstructive Pulmonary Disease (COPD) usually causes "barrel chest" to develop [eventually] from not being able to release the air already in the lungs. It usual causes wheezing and overinflation of the lungs (the alveoli in the lungs become swollen with air).

The general treatment of this is a bronchodilator (what people with asthma use), as well as other treatments as it can, and most likely, will become worse.

But hey, I'm no doctor.