Introduction

This article gives a brief explanation about volume-time curves which are used to assist the distinction between obstructive and restrictive lung disease.

These are only part of a full panel of respiratory function tests (spirometry), and a full, detailed explanation can be seen in the spirometry article.

Normal Lung function on spirometry

  • Note the shape of the graph:
    • Fast rising in the first 1 second – FEV1>80% FVC
    • Flat plateau
 

Obstructive lung disease

Characteristics

  • ‘Obstructive pattern’ on PFT’s – see below
  • Disease mechanisms affect the bronchi and bronchioles, usually in a diffuse pattern across the whole lung

Obstructive pattern lung disease

  • Reduced FEV1 (<80% of normal)
  • Reduced FEV1:FVC ratio (<70%)
  • Often normal or slightly increased FVC
    • Total lung capacity is increased – but this is mainly due to an increased residual capacity due to hyperexpansion
  • Reduced peak flow
 

Restrictive Lung Disease

Restrictive lung disease is typically caused by disease in the interstitium of the lung – and this is usually an increase in the amount of tissue in the interstitium of the lung.
  • The lung x-ray will show increased density of the lung tissue
  • The lung will be stiff with reduced compliance
  • In obesity – the reduced compliance is largely just due to the extra weight carried not he chest

Restrictive pattern of lung disease

  • Reduced FVC
  • Reduced FEV1
  • Normal FEV1:FVC ratio
  • Normal PEFR

Causes of restrictive lung disease

The underlying mechanism is usually fibrosis of the lung. As the normal lung tissue is destroyed it is replaced by scar tissue, which is interspersed with pockets of air. This often leads the lung to have a honeycomb like appearance on x-ray.
The main symptoms are SOB and cough.
Common causes
  • Asbestosis
  • Radiation fibrosis
  • Drugs – common ones include amiodarone (anti-arrhythmic) and methotrexate (anti-folate and anti-metabolite drug – used in cancer and auto-immune diseases)
  • Rheumatoid arthritis
  • ARDS – acute respiratory distress syndrome
    • this is an acute onset syndrome, which present with shortness of breath, bilateral infiltrates on the CXR and may occur within 48 hours of an acute illness

Mixed Pattern of Disease

Remember also you could see somebody who has both restrictive and obstructive disease – in which case they would have a mixed pattern of disease:

References

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