Obstructive vs restrictive lung disease: FEV1/FVC and loops
How the FEV1/FVC ratio, total lung capacity and the shape of the flow-volume loop separate obstructive from restrictive lung disease in a patient who is short of breath.
Distinguish obstructive from restrictive lung disease using FEV1/FVC, total lung capacity (TLC) and the shape of the flow-volume loop.
The short version
- FVC is the total air blown out forcefully after a full breath in; FEV1 is the amount blown out in the first second.
- An FEV1/FVC ratio below 0.70 after a bronchodilator is the exam convention for obstruction; a healthy adult is about 0.8.
- Obstruction: low ratio, normal or high TLC from air trapping, and a scooped (concave) expiratory limb on the flow-volume loop.
- Restriction: normal or high ratio, low TLC (classically below 80% of predicted), and a smaller loop of normal shape.
- Ratio low: think obstruction. Ratio normal with low TLC: think restriction.
Obstructive vs restrictive lung disease: two breathless patients
Two patients are short of breath. One has lungs that are over-full and cannot empty. The other has lungs that cannot fill. The question this lesson answers is how a lung function report tells obstructive vs restrictive lung disease apart.
Three pieces of the report do the work: the FEV1/FVC ratio, total lung capacity and the flow-volume loop. TLC cannot be measured by spirometry; it needs plethysmography or gas dilution.[1][2]
The lesson ends with an original practice question that uses the same three tools.
The forced manoeuvre: FVC and FEV1
Spirometry is built on one forced manoeuvre, and both FVC and FEV1 come from it. The test asks the patient to breathe in fully, then blast the air out as hard and as fast as possible.[1][5]
The FEV1/FVC ratio and its cut-offs
The ratio of the two, FEV1/FVC, is the first number to look at. In a healthy adult it is about 0.8.[5]
Healthy adult about 0.8. Exam convention: below 0.70 after a bronchodilator means obstruction.
- GOLD cut-off (exam convention): a post-bronchodilator ratio below 0.70 means obstruction.[3][4]
- ATS and ERS: prefer the lower limit of normal, the fifth percentile for age, height and sex.[3][4]
The fixed 0.70 cut-off is simple and is the one the exam uses. The lower limit of normal is the fifth percentile for age, height and sex, and is what ATS and ERS prefer.[3][4]
Obstructive lung disease: low ratio, high TLC, scooped loop
Obstruction is a problem of getting air out: the airways are narrowed, or collapse early. FEV1 falls a lot while FVC is normal or falls less, so the ratio falls.[5][1]
The lungs also fill up. Air trapped behind closing airways raises the residual volume, and TLC is normal or high.[5][4]
On the flow-volume loop, flow is on the vertical axis and volume on the horizontal, with expiration drawn above the line.[1] In obstruction, flow is very low for the lung volume, so the expiratory limb sags inward. A scooped, concave expiratory limb means obstruction.[5][1][2]
Restrictive lung disease: normal ratio, low TLC, smaller loop
Restriction is the opposite problem to obstruction: the lungs cannot fill rather than cannot empty. FEV1 and FVC both fall, FVC as much as or more than FEV1, so the ratio is normal or even high.[5][1][2]
TLC is low, and that confirms restriction.[4][2] The classic exam cut-off is below 80% of predicted; current standards use the lower limit of normal instead.[4]
The loop keeps a normal outline, with no scooping, but is smaller and narrower: less volume, with flow normal or even high for the lung volume.[5][1][2]
| Feature | Obstructive | Restrictive |
|---|---|---|
| FEV1/FVC ratio | Low (below 0.70 after a bronchodilator) | Normal or high |
| FEV1 and FVC | FEV1 falls a lot; FVC normal or falls less | Both fall, about in proportion |
| TLC | Normal or high (air trapping, raised residual volume) | Low (classically below 80% of predicted) |
| Flow-volume loop | Scooped, concave expiratory limb | Smaller loop of normal shape, no scooping |
Two worked patients
Apply the rule: ratio low, think obstruction; ratio normal with low TLC, think restriction. Each patient below is read the same way: take the ratio first, then look at TLC.
- FEV1 2.1 L, FVC 3.5 L, TLC 118% of predicted
- Ratio = 2.1 ÷ 3.5 = 0.6, below 0.70
- TLC is not low (normal or high)
- Low ratio, TLC not low: obstructive
- FEV1 2.2 L, FVC 2.6 L, TLC 64% of predicted
- Ratio = 2.2 ÷ 2.6 ≈ 0.85, not reduced
- TLC is low, below 80% of predicted
- Normal ratio with low TLC: restrictive
Practice question
Original · USMLE styleA 58-year-old woman has had a dry cough and breathlessness on exertion for 8 months. Pulmonary function testing shows an FVC of 2.1 L (55% of predicted), an FEV1 of 1.8 L (60% of predicted) and a total lung capacity of 3.2 L (58% of predicted).
Common questions
How do you tell obstructive from restrictive lung disease on spirometry?
Start with the FEV1/FVC ratio. A low ratio suggests obstruction; a normal or high ratio with a low total lung capacity suggests restriction.
What FEV1/FVC ratio means obstruction?
The exam convention (GOLD) is a post-bronchodilator ratio below 0.70. ATS and ERS prefer the lower limit of normal, the fifth percentile for age, height and sex.
What does a scooped flow-volume loop mean?
A scooped, concave expiratory limb means obstruction: flow is very low for the lung volume, so the limb sags inward.
Why is total lung capacity needed to confirm restriction?
A reduced TLC, classically below 80% of predicted, confirms restriction. Spirometry cannot measure TLC; it needs plethysmography or gas dilution.
What does the flow-volume loop look like in restriction?
It keeps a normal outline with no scooping, but is smaller and narrower: less volume, with flow normal or even high for the lung volume.
Transcript
Read the full narration, by chapter639 words
0:00Two breathless patients: how does the report tell them apart?
Two patients are short of breath. One has lungs that are over-full and cannot empty. The other has lungs that cannot fill. How can a lung function report tell them apart? Today: use FEV one over FVC, total lung capacity and the flow-volume loop.
0:19The forced manoeuvre: FVC and FEV1
From the last lesson: spirometry cannot measure total lung capacity, which needs plethysmography or gas dilution. Today's test asks the patient to breathe in fully, then blast the air out as hard and as fast as possible. The total amount blown out is the forced vital capacity, or FVC. The amount blown out in the first second is the FEV one.
0:44The ratio: FEV1/FVC, the 0.70 exam cut-off and the lower limit of normal
The ratio of the two, FEV one over FVC, is the first number you look at. In a healthy adult it is about 0.8. The exam convention: a ratio below 0.7 means obstruction. That is the GOLD cut-off, used after a bronchodilator. The ATS and ERS prefer the lower limit of normal, the fifth percentile for age, height and sex.
1:12Obstruction: low ratio, air trapping, high TLC
Obstruction is a problem of getting air out: the airways are narrowed, or collapse early. FEV one falls a lot. FVC falls less. So the ratio falls: FEV one drops more than FVC. The lungs also fill up. Air trapped behind closing airways raises the residual volume, and total lung capacity is normal or high.
1:39The flow-volume loop and the scooped expiratory limb
Now the flow-volume loop: flow on the vertical axis, volume on the horizontal, with expiration drawn above the line. In obstruction, flow is very low for the lung volume, so the expiratory limb sags inward. A scooped, concave expiratory limb means obstruction.
1:58Restriction: normal ratio, low TLC, a smaller loop
Restriction is the opposite problem: the lungs cannot fill. FEV one and FVC both fall, about in proportion, so the ratio is normal or even high. Total lung capacity is low, and that confirms restriction, classically below 80% of predicted. The loop keeps a normal outline, with no scooping, but is smaller: less volume and lower flow. Ratio low: think obstruction. Ratio normal with low total lung capacity: think restriction.
2:33Try two patients
Try two patients. The first: FEV1 2.1 litres, FVC 3.5, total lung capacity 118% of predicted. Ratio 0.6, high capacity: obstructive. The second: FEV1 2.2, FVC 2.6, total lung capacity 64%. Ratio 0.85, low capacity: restrictive.
3:05Practice question
Your turn. A 58-year-old woman has a dry cough and breathlessness on exertion for eight months. Her FVC is 2.1 litres, 55% of predicted. Her FEV one is 1.8 litres, 60% of predicted. Her total lung capacity is 3.2 litres, 58% of predicted. Which pattern best describes her lung function? A, reduced ratio, high total lung capacity, scooped expiratory limb. B, reduced ratio, normal total lung capacity, normal loop shape. C, preserved ratio, reduced total lung capacity, small loop of normal shape. D, preserved ratio, normal total lung capacity, scooped expiratory limb. E, reduced ratio, reduced total lung capacity, scooped expiratory limb.
4:04Wrong options first, then the answer
Pause here and decide. A is out: that is obstruction with hyperinflation, and her total lung capacity is low, not high. B is out: her ratio is 1.8 over 2.1, about 0.86, which is not reduced. D is out: a scooped limb is the signature of obstruction, and hers is not obstructed. E is out: a reduced ratio with a reduced total lung capacity would be a mixed pattern, and her ratio is preserved. So the answer is C. A preserved ratio with a low total lung capacity is restriction, and the loop is a smaller copy of a normal one.
4:47Recap and next lesson
Three things to keep. One: a low ratio with a high total lung capacity is obstruction, with a scooped loop. Two: a normal ratio with a low total lung capacity is restriction, with a small normal-shaped loop. Three: for the exam, the usual cut-offs are a ratio below 0.7, after a bronchodilator, and a total lung capacity below 80% of predicted. Next lesson: compliance, surface tension and surfactant.
Sources
Numbers in the text, e.g. [1], point here- Basic spirometry testing and interpretation for the primary care provider. PMC. pmc.ncbi.nlm.nih.gov/articles/PMC6516140/
- Indian Chest Society-NCCP(I) spirometry guidelines 2019. PMC. pmc.ncbi.nlm.nih.gov/articles/PMC6489506/
- Halpin D, Stanojevic S, et al. GOLD/GLI joint statement on spirometric interpretation. Eur Respir J 2026. pmc.ncbi.nlm.nih.gov/articles/PMC13084305/
- Routine pulmonary function test interpretive strategies (2024). PMC. pmc.ncbi.nlm.nih.gov/articles/PMC11625406/
- LITFL. Spirometry. litfl.com/spirometry/
The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.
Image credits. Illustrations: Servier Medical Art (smart.servier.com), CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/), adapted (recoloured, outlined, resized): lungs, healthy bronchus, inflamed bronchus, emphysema. The spirograms, flow-volume loops, number line, table, charts, cards and all handwriting are drawn in code (original). No AI-generated teaching images.
Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-RESP-002.
For exam study only, not medical advice. Read the medical disclaimer.
In this series
Playlist on YouTube- EP 01Lung volumes and capacities, explained5:26
- EP 02Obstructive vs restrictive lung disease: FEV1/FVC and loops5:23
- EP 03Lung compliance, Laplace and surfactant: why alveoli stay open5:23
- EP 04V/Q mismatch: shunt, dead space and the oxygen test5:18
- EP 05A-a gradient: the alveolar gas equation and the causes of hypoxaemia5:39
- EP 06Oxygen-hemoglobin dissociation curve: P50, shifts and content5:19
- EP 07CO₂ transport: bicarbonate, the chloride shift, Bohr vs Haldane5:29
- EP 08Central vs peripheral chemoreceptors and oxygen-induced hypercapnia5:27
- EP 09Hypoxic pulmonary vasoconstriction and cor pulmonale5:41
- EP 10CO, cyanide and methaemoglobin: why SpO₂ and PaO₂ fool you5:34