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# Obstructive and restrictive patterns, and flow–volume loops

- Measurement
- Exam priority: high

In obstruction the air comes out slowly; in restriction the lung is small. The FEV₁/FVC ratio tells them apart.

Updated 2026-11-01

Also called: Spirometry interpretation, Flow–volume loop

## Key points

- Obstructive: FEV₁/FVC
- Obstruction: bronchospasm, mucus or lost elastic tethering narrow the airway.
- During a forced blow, positive pleural pressure squeezes the already narrow airways and flow becomes limited.
- Air leaves slowly, FEV₁ drops sharply and some air stays trapped (high RV).
- Restriction: fibrosis, filled alveoli, a stiff chest wall or weak muscles prevent the lung from filling.
- TLC and FVC fall; radial traction on the airways is preserved or increased, so FEV₁/FVC stays normal or high.

### Lung volumes and capacities

**TLC** 6.7 L **VC** 4.1 L **FRC** 3.5 L **RV** 2.6 L **FEV1/FVC** 0.45

Obstructive (COPD, asthma): air is trapped: ↑ RV and ↑ FRC, TLC normal or ↑, VC ↓. FEV1 falls more than FVC: FEV1/FVC
- IRV · Inspiratory reserve volume
- TV · Tidal volume
- ERV · Expiratory reserve volume
- RV · Residual volume
- Capacity (sum of volumes)
- Current forced expiration
- Normal

Obstructive: compare the forced expiration with normal.

### Lung volumes and capacities

**TLC** 3.6 L **VC** 2.8 L **FRC** 1.4 L **RV** 0.8 L **FEV1/FVC** 0.87

Restrictive (pulmonary fibrosis, chest wall or neuromuscular disease, obesity): all volumes ↓ (TLC
- IRV · Inspiratory reserve volume
- TV · Tidal volume
- ERV · Expiratory reserve volume
- RV · Residual volume
- Capacity (sum of volumes)
- Current forced expiration
- Normal

Restrictive: small volumes, preserved FEV₁/FVC.

## What each pattern looks like

| Measure | Obstructive | Restrictive |
| --- | --- | --- |
| FEV₁ | Very low | Low |
| FVC | Normal or low | Low |
| FEV₁/FVC | Low (
- Asthma: variable, reversible obstruction; spirometry can be normal between attacks.
- COPD: obstruction persists after bronchodilator; in emphysema diffusion (DLCO) also falls.
- Obesity: extrapulmonary restriction with a normal DLCO; FRC and ERV fall first.

## Memory aid

Obstructive: the air is in there but can't get out. Restrictive: it gets out fine, there just isn't much of it.

## Test yourself

Think of the answer, then tap the question to see it.

## FEV₁ 60% predicted, FVC 62%, FEV₁/FVC 0.82. Which pattern does this suggest, and which test confirms it?

Restriction (preserved ratio with a low FVC). It is confirmed by measuring TLC with plethysmography or gas dilution.

## Why can FEV₁/FVC be high in pulmonary fibrosis?

The stiff lung has strong elastic recoil and pulls the airways open, so the little air it holds comes out very fast.

## Why does expiratory flow fall in emphysema even without bronchial inflammation?

Elastic fibres are destroyed: there is less recoil pressure driving air out and less tethering holding small airways open, so they collapse on expiration.

## What shape is the expiratory limb of the flow–volume loop in obstruction?

Concave or scooped: after a lower peak, flow falls off quickly at high volumes because small airways limit flow.

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## Related topics

- [Lung volumes, capacities and spirometry](https://durgical.com/en/physiology/lung-volumes-capacities-and-spirometry/)
- [Airway resistance](https://durgical.com/en/physiology/airway-resistance/)
- [Lung and chest wall compliance](https://durgical.com/en/physiology/lung-and-chest-wall-compliance/)
- [Diffusion across the respiratory membrane and DLCO](https://durgical.com/en/physiology/diffusion-across-the-respiratory-membrane-and-dlco/)
- [The work of breathing](https://durgical.com/en/physiology/the-work-of-breathing/)

## Related conditions

- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Obesity](https://durgical.com/en/conditions/obesity/)
- [Bronchiectasis](https://durgical.com/en/conditions/bronchiectasis/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [22.3 The Process of Breathing](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-3-the-process-of-breathing) (OpenStax (Rice University), 2022); [Chronic Obstructive Pulmonary Disease (COPD)](https://www.ncbi.nlm.nih.gov/books/NBK559281/) (StatPearls (NCBI Bookshelf), 2024); [Interstitial Lung Disease](https://www.ncbi.nlm.nih.gov/books/NBK541084/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 43). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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