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Physiology · Respiratory

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

What it is

An obstructive pattern comes from narrowed or collapsing airways: FEV₁ falls more than FVC and the FEV₁/FVC ratio drops. A restrictive pattern comes from a lung or chest wall that cannot expand: both fall in proportion and the ratio is normal or high. Spirometry suggests restriction, but only a low TLC confirms it.

How it works, step by step

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

Lung volumes and capacities

Lung volumes and capacities: Obstructive 01234567Lung volume (L)Time →RV: spirometry cannot measure itRVERVTVIRVICFRCVCTLCIRV2.7 LTV0.5 LERV0.9 LRV*2.6 LIC3.2 LFRC*3.5 LVC4.1 LTLC*6.7 L* not measured by spirometryForced expiration (FEV1/FVC)0123456012345Time (s)Exhaled (L)FEV1 1.7 L · 45 %FVC 3.8 L

TLC 6.7 LVC 4.1 LFRC 3.5 LRV 2.6 LFEV1/FVC 0.45

Obstructive (COPD, asthma): air is trapped: ↑ RV and ↑ FRC, TLC normal or ↑, VC ↓. FEV1 falls more than FVC: FEV1/FVC < 0.70.

Tap a volume, a capacity or FEV1.

  • 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

Lung volumes and capacities: Restrictive 01234567Lung volume (L)Time →RV: spirometry cannot measure itRVERVIRVICFRCVCTLCIRV1.8 LTV0.4 LERV0.6 LRV*0.8 LIC2.2 LFRC*1.4 LVC2.8 LTLC*3.6 L* not measured by spirometryForced expiration (FEV1/FVC)0123456012345Time (s)Exhaled (L)FEV1 2.4 L · 87 %FVC 2.8 L

TLC 3.6 LVC 2.8 LFRC 1.4 LRV 0.8 LFEV1/FVC 0.87

Restrictive (pulmonary fibrosis, chest wall or neuromuscular disease, obesity): all volumes ↓ (TLC < 80% predicted); FEV1 and FVC fall together: FEV1/FVC normal or ↑.

Tap a volume, a capacity or FEV1.

  • 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

MeasureObstructiveRestrictive
FEV₁Very lowLow
FVCNormal or lowLow
FEV₁/FVCLow (< 0.70)Normal or high
TLCNormal or highLow (confirms)
RVHigh (air trapping)Low
ExamplesAsthma, COPD, bronchiectasisInterstitial fibrosis, obesity, kyphoscoliosis, neuromuscular disease

Clinical notes

  • 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.

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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← All of 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 (OpenStax (Rice University), 2022); Chronic Obstructive Pulmonary Disease (COPD) (StatPearls (NCBI Bookshelf), 2024); Interstitial Lung Disease (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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Representative model, for educational purposes only.