Contents
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
- Spirometry – RACGP
- A Stepwise Approach to the Interpretation of Pulmonary Function Tests
- Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
- Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
Excellent and Clear explanation! Thankyou!
very resourceful for my studies in chest medicine.
Isn’t it the FEV1 which is decreased in obstructive disease and not the FVC?
Yes it definitely is! Thanks for spotting this – I have fixed it up.