In one breath
Abnormal ventilation comes in two patterns. In obstructive disease air cannot get out fast enough: flow rates fall, FEV₁/FVC drops below 0.75, air is trapped so RV and RV/TLC rise, and TLC is normal or large. In restrictive disease the lung cannot be filled: TLC, VC and RV all fall, FVC is reduced — the hallmark — but the flow rates are preserved, so FEV₁/FVC is normal or even higher than normal. FVC falls in both, which is why the ratio, not the FVC, is what tells them apart.
Builds on: Lung volumes, capacities and spirometry · Leads to: Tests of gas exchange and pulmonary circulation · Hypoxia
The two patterns
| Obstructive | Restrictive | |
|---|---|---|
| Hallmark | Fall in expiratory flow rates | Reduction in FVC |
| Which numbers fall first | MMFR, FEV₁/FVC | FVC, TLC |
| The problem | Getting air out | Getting air in |
Features of obstructive disease
- TLC normal or increased.
- RV raised, because air is trapped during expiration.
- RV/TLC ratio increased.
- VC often decreased — and the reason matters: not because the lungs are smaller, but because the raised RV eats into the VC from below.
- FEV₁ under 80% of FVC.
- FEV₁/FVC decreased.
- MMFR decreased.
In early obstructive disease, which begins in the small airways, FEV₁/FVC can still be normal. What betrays it is a fall in MMFR together with an abnormal shape of the terminal part of the forced expiratory flow–volume curve.
"80% of TLC" is a misprint
Your book’s list of obstructive features says FEV₁ is less than 80% “of TLC”. FEV₁ is always expressed as a percentage of FVC — as the same chapter says everywhere else, and as FEV₁/FVC = 0.75–0.80 implies. Quote 80% of FVC in the exam.
Features of restrictive disease
- TLC decreased.
- VC decreased.
- RV decreased.
- Forced expiratory flow rates preserved: FEV₁ as a percentage of FVC is normal or supernormal.
Restrictive disease splits into parenchymal and extraparenchymal types, and the extraparenchymal type splits again into one that affects inspiration alone and one that affects inspiration plus expiration.
Restrictive parenchymal dysfunction
The lung tissue itself is stiff and shrunken: TLC, RV and VC all decreased, with FEV₁/FVC normal or increased.
Restrictive extraparenchymal dysfunction
- Inspiration only. Usually weak inspiratory muscles or a stiff chest wall, so the adequate distending force never reaches an otherwise normal lung. Result: TLC reduced, RV unaffected, flow rates preserved.
- Inspiration plus expiration. Usually weak expiratory muscles, or a deformed chest wall that becomes abnormally rigid at volumes below FRC, so the lung cannot be emptied either. Result: RV often significantly raised, and FEV₁/FVC may or may not be affected, depending on how strong the expiratory muscles are.
The RV trap in restrictive disease
“Restrictive disease lowers RV” is true of the parenchymal type and of the book’s general list. But in extraparenchymal disease RV is either unchanged (inspiratory weakness) or raised (expiratory weakness). So RV is the one number that separates the three kinds of restriction — say which kind you mean before you quote it.
Common diseases in each pattern
- Obstructive: asthma; COPD (chronic bronchitis, emphysema); bronchiectasis; bronchiolitis; cystic fibrosis.
- Restrictive — parenchymal: pulmonary fibrosis; pneumoconiosis; radiation-induced interstitial lung disease.
- Restrictive — extraparenchymal, neuromuscular: myasthenia gravis; paralysis of the diaphragm; muscular dystrophy.
- Restrictive — extraparenchymal, chest wall: kyphoscoliosis; obesity; ankylosing spondylitis.
Side by side
| Parameter | Obstructive | Restrictive |
|---|---|---|
| TLC | Normal or ↑ | ↓ |
| RV | ↑ (air trapping) | ↓ (parenchymal) |
| VC | Often ↓ | ↓ |
| FVC | ↓ | ↓ (hallmark) |
| FEV₁ | ↓ (under 80% of FVC) | ↓ in absolute litres |
| FEV₁/FVC | ↓ | Normal or ↑ |
| MMFR | ↓ | Preserved |
Draw it: FEV₁ curves in obstruction and restriction
One axis frame, three curves. x-axis time, 0 to 5 s; y-axis volume expired, 0 to 5 L. Every curve starts at the origin (the moment of maximal inspiration) and flattens into a plateau at its own FVC. Draw a vertical dotted line at 1 second and drop a horizontal line from where each curve crosses it: that is FEV₁.
- Normal: rises steeply, plateau at an FVC of 4.6 L, with 80–85% of it already out at one second → ratio 0.75–0.80.
- Obstructive: rises slowly and keeps creeping upward, reaching a plateau late and below normal; the one-second mark catches only a small fraction → ratio low.
- Restrictive: rises as steeply as normal but stops early at a low plateau; FEV₁ and FVC are both small, and they shrink together → ratio normal or higher than normal. Label each plateau “FVC”, label the one-second drops “FEV₁”, and write the ratio beside each curve. The steep-but-short restrictive curve against the slow-and-long obstructive curve is the whole answer.
Alterations in lung volumes and capacities
- Normal volumes vary widely with age, sex and height. Indian values are significantly lower than western ones, and predicted nomograms exist for these factors.
- A deviation of up to 20% from the predicted value is common in normal people.
- But in one individual, a change of even 5% from his own earlier value may be significant. That is why serial measurements matter so much in diagnosis.
Conditions that decrease vital capacity
- Loss of functioning lung tissue: interstitial pulmonary fibrosis; chest deformity; neuromuscular disease; thickened pleura.
- Loss of distensibility of lung tissue or pleura: atelectasis; consolidation; pulmonary edema; pulmonary resection.
Worth knowing, though not in your pages: the two groups in your book are not tidy — chest deformity and neuromuscular disease restrict an otherwise normal lung rather than destroying tissue, and resection removes tissue rather than distensibility. Learn the eight conditions; do not defend the grouping.
Conditions that decrease static lung compliance
Pulmonary edema · chronic pulmonary congestion · kyphoscoliosis · fibrothorax · interstitial fibrosis · atelectasis.
These patients must use more respiratory muscle effort for the same alveolar ventilation, so they are very often dyspneic.
Conditions that increase airway resistance
Bronchial asthma · chronic bronchitis · emphysema · any other disease marked by airway obstruction.
These patients are usually dyspneic too, in proportion to how severe the obstruction is.
Compliance list vs resistance list
Examiners love this pair, because both lists end in dyspnea. Keep them apart by mechanism: stiff, wet or scarred lung lowers compliance (edema, congestion, fibrosis, atelectasis, kyphoscoliosis, fibrothorax); narrowed airways raise resistance (asthma, chronic bronchitis, emphysema).
What each flow index tells you
| Index | What it reflects | When it changes |
|---|---|---|
| FVC | Air trapping | ↓ when obstruction traps air, e.g. asthma |
| FEV₁ | Generalized airway obstruction | ↓ in obstructive disease, e.g. asthma |
| FEV₁/FVC | Airway obstruction, most sensitively | Normally 0.75–0.80; ↓ in obstruction |
| MMFR (FEF25–75%) | Small airway patency | Slowed in small airway obstruction |
| FEF200–1200 | Larger airway patency | Slowed in large airway obstruction |
| PEFR | Flow at the peak of expiration | ↓ in airway obstruction |
| MVV | Overall breathing capacity | ↓ with subjective dyspnea |
- FEV₁ is effort-dependent, so a badly performed blow gives a false result, and it is not specific for small airway obstruction.
- FEV₁/FVC is a more sensitive indicator of obstruction than FVC or FEV₁ on their own.
- PEFR is the weakest of the three: MMFR and FEF200–1200 report obstruction better than it does.
- MVV is 150 L/min in men and 125 L/min in women, but the figure is fallacious if the patient will not cooperate or does not give maximal effort.
Reduced FVC does not mean restriction
Your book gives “reduction in FVC” as the hallmark of restrictive disease and then lists air-trapping obstruction, such as asthma, among the causes of a low FVC. Both are true: FVC falls in both patterns. The decision is made by FEV₁/FVC — low in obstruction, normal or high in restriction — and by TLC, which is small in restriction and normal or large in obstruction.
Applied: reading a report in three steps
- Look at FEV₁/FVC. Below 0.75 → obstructive.
- If the ratio is normal but FVC and TLC are low → restrictive.
- Then place the restriction: RV low → parenchymal; RV normal with low TLC → extraparenchymal inspiratory; RV clearly raised → extraparenchymal inspiratory plus expiratory. A normal ratio with a low MMFR and an odd tail on the flow–volume curve is early small-airway obstruction, not restriction.
Exam-answer skeleton: "Describe the changes in lung function in obstructive and restrictive lung disease" (long essay)
- Name the two patterns and give each one’s hallmark — flow rates fall in obstruction, FVC falls in restriction.
- Features of obstructive disease, item by item, with the reason VC falls (raised RV, not smaller lungs).
- Early obstructive disease: normal ratio, but low MMFR and an abnormal tail on the flow–volume curve.
- Features of restrictive disease; then parenchymal versus extraparenchymal, and the two extraparenchymal subtypes with what happens to RV in each.
- Draw the FEV₁ curves of normal, obstructive and restrictive lungs on one graph, with FEV₁, FVC and the ratio marked.
- Give the side-by-side table of TLC, RV, VC, FVC, FEV₁, FEV₁/FVC and MMFR.
- Name common diseases of each type.
- Close with how you would read a report: the ratio first, then TLC, then RV.
Asked in exams
- Timed vital capacity (FEV₁): Jul 2012, 4 marks · Jan/Feb 2022, MCQ · Jan/Feb 2022, 4 marks
- Lung function in obstructive and restrictive disease: Mar 2024, essay