obstructive pattern
An obstructive pattern is the spirometry signature of airways that resist the outflow of air — like trying to empty a bottle through a narrow straw. The lungs may hold plenty of air, but they cannot let it out quickly, so emptying is slow and often incomplete.
Its hallmark is a low FEV1/FVC ratio: airflow in the first second is disproportionately reduced relative to the total volume. The flow–volume loop shows a scooped-out, concave expiratory limb, and severe cases trap air, leaving an enlarged residual volume and hyperinflated lungs.
Asthma, COPD, bronchiectasis and bronchiolitis all produce this pattern; the bronchodilator response often separates them, with asthma typically showing large reversibility and COPD showing little. Severity is graded by how far the FEV1 falls below predicted, not by the ratio itself.
A long-term smoker's spirometry shows FEV1 45 percent predicted, FVC 80 percent predicted and a ratio of 0.48, with a concave flow–volume loop — a moderately severe obstructive pattern typical of COPD.
A low ratio with a scooped expiratory curve marks obstruction.
An obstructive pattern can coexist with restriction in a mixed defect — confirmed only when lung-volume testing shows both a low ratio and a low total lung capacity.