The one ratio that defines obstruction
Spirometry asks you to take the deepest breath you can and then blow out as hard and as long as possible. Two numbers come out. FVC is the total volume you blow — your usable capacity. FEV1 is how much of that you get out in the *first second*. In healthy lungs you empty most of it fast, so FEV1 is a big slice of FVC. When tubes are narrowed, the first second is throttled, so FEV1 shrinks relative to FVC.
Their ratio, the FEV1/FVC ratio, is the linchpin. A low ratio is the signature of an obstructive pattern. Hold this against the restrictive pattern from Guide 1, where both numbers shrink together so the ratio stays normal or even high.
Spirometry report (post-bronchodilator): FEV1 = 1.60 L (52% of predicted) FVC = 3.20 L (84% of predicted) FEV1/FVC = 1.60 / 3.20 = 0.50 (50%) Reading it: - FEV1/FVC = 0.50 -> below ~0.70 -> OBSTRUCTION confirmed - FEV1 52% predicted -> moderate-to-severe in degree - Did not normalise after bronchodilator -> fixed -> COPD picture (In asthma the ratio would often climb back toward normal after the reliever.)
Why the lungs over-inflate
Recall the stacking-up problem. If each breath cannot fully escape before the next one arrives, leftover air accumulates — air trapping. Over time the resting lung volume climbs and the chest becomes permanently over-expanded: hyperinflation. You can measure its footprint as a rising residual volume — the air still stuck in the lungs after the hardest possible exhalation.
Bronchiectasis: airways stretched and scarred
Bronchiectasis is a distinct kind of obstructive trouble: the larger airways become permanently widened and scarred, usually after repeated infection or chronic inflammation. The damaged walls cannot clear themselves, so mucus pools, bacteria settle in, and infection inflames the walls further — a self-feeding cycle. The classic story is a daily cough bringing up large volumes of sputum, with recurrent chest infections.
It often overlaps with COPD and severe asthma, which is why it lives in this track. The practical messages are simple: keep the airways clear with daily physiotherapy and, when sputum turns thick and discoloured, recognise an infection early.