MCQ – 74596

A spirometry curve of a patient has been provided below. Calculate the FEV₁/FVC ratio from the curve:

A.	60-69%
B.	70-79%
C.	80-89%
D.	90-99%

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Correct Answer » A Explanation

• The graph represents a volume–time spirometry curve.
• After a maximal inspiration, a forced expiration is performed.
• The curve shows a relatively slow and prolonged expiration instead of a steep drop.
• This indicates reduced expiratory flow.

Explanation of the Clinical Question

• FEV1 = volume exhaled in first 1 second of forced expiration
• FVC = total volume exhaled after full forced expiration

Formula
FEV1/FVC ratio = (Volume exhaled in first 1 second / Total forced vital capacity) × 100

Explanation of the Correct Answer

• In the curve, early expiration is not rapid, indicating reduced FEV1.
• Total FVC is relatively preserved compared to FEV1.
• Therefore, the ratio is reduced.
• Estimated value falls below normal (~80%) and lies in the range 60–69%.

Spirometry Definitions

• FEV1: Forced expiratory volume in first second
• FVC: Total forced vital capacity

Normal Values

• Normal FEV1/FVC ≈ 75–80%

Obstructive Lung Disease

• FEV1 markedly decreased
• FVC normal or mildly decreased
• FEV1/FVC decreased (<70%)
• Examples: Asthma, COPD, bronchiectasis

Restrictive Lung Disease

• FEV1 decreased
• FVC decreased proportionately
• FEV1/FVC normal or increased
• Examples: Pulmonary fibrosis, sarcoidosis

Key Exam Points

• FEV1/FVC < 70% indicates obstructive pattern
• Normal or increased ratio with low volumes indicates restrictive pattern
• Volume–time curve: used to calculate FEV1 and FVC
• Flow–volume loop: used to identify pattern visually

Quick Interpretation Rule

• Slow, prolonged expiration → Obstructive → Decreased ratio
• Rapid expiration with low volume → Restrictive → Normal or increased ratio