Two faces of one disease
COPD (chronic obstructive pulmonary disease) is an umbrella over two kinds of damage that usually travel together. Emphysema is destruction of the air sacs themselves: their delicate walls dissolve, several sacs merge into floppy bigger ones, and the lung loses elastic recoil — the springiness that normally helps squeeze air out. Chronic bronchitis is the airway side: glands enlarge, mucus pours out, and the person has a productive cough on most days for months. One destroys air sacs; the other clogs and inflames the tubes.
Why it happens, and who is at risk
The overwhelming cause is cigarette smoking. Each lungful of smoke recruits inflammatory cells whose enzymes nibble at the alveolar walls; over decades the lung is slowly outpaced in repairing itself. Risk is dose-related, which is why we quantify exposure in pack-years. Other causes matter too: long-term biomass smoke from indoor cooking fires, occupational dusts, and air pollution.
Pack-years = (cigarettes per day / 20) x years smoked Example: 1 pack (20/day) for 30 years = (20 / 20) x 30 = 30 pack-years Example: 15/day for 40 years = (15 / 20) x 40 = 0.75 x 40 = 30 pack-years A heavy history (~20+ pack-years) makes COPD much more likely in a breathless smoker.
One inherited cause deserves a flag: alpha-1 antitrypsin deficiency. This protein normally shields the lung from its own enzymes; without enough of it, emphysema can appear young, in the lower lungs, even in someone who barely smoked. It is worth testing for when COPD shows up unusually early.
Staging and grading
Once spirometry confirms fixed obstruction, doctors describe its severity with a GOLD stage, based on how far the FEV1 has fallen below predicted. But modern practice never stops at a number: symptoms and exacerbation history matter at least as much as the spirometry grade, because two people with the same FEV1 can live very different lives.
One more test paints emphysema cleanly: the DLCO, or transfer factor, measures how well gas crosses from air sac to blood. In emphysema, with fewer walls left to do the crossing, the DLCO drops — a fingerprint that helps separate emphysema-heavy COPD from pure asthma, where the DLCO is typically normal.