Spirometry Interpretation

In this article we offer information about the interpretation of the flow-volume loop. The other spirometry tests are not covered.

The flow-volume loop can have four distinctive shapes that are linked to certain pathologies: obstructive lung disease, restrictive lung disease, mixed lung disease and upper airway obstructions.

Normal Spirometry

normal spirometry
FEV1: normal
FVC: normal
Tiffeneau: normal

Obstructif Lung Disease

spirometry Obstructive Lung Disease
FEV1: normal or ↓
FVC: normal
Tiffeneau: ↓

Restrictive Lung Disease

spirometry Restrictive Lung Disease
FEV1: normal or ↓
FVC: ↓
Tiffeneau: normal or ↑

Mixed Lung Disease

spirometry Mixed Lung Disease
FEV1: ↓
FVC: ↓
Tiffeneau: ↓

Normal Spirometry

A normal expiratory flow-volume loop has a triangular shape with it's top at the left. The inspiratory part of the loop is shaped like a half circle.

The values of the parameters are higher than 80% of the predicted values, while the Tiffeneau index (FEV1/FVC*100) is higher than 70.

Obstructive Lung Disease

Obstructive lung disease is the most common diagnosis of a lung pathology when using a spirometer. The Tiffeneau index is below 70, which results in an indented or concave expiratory part of the flow-volume loop.

When obstructive lung disease is present, often a post-medication test is performed after administration of a bronchodilator like ventolin. In case the obstruction is reversible (FEV1 post-medication significantly higher than FEV1 premedication), the patient is likely to suffer from asthma.

Restrictive Lung Disease

Restrictive lung disease can not be diagnosed with a spirometer because spirometers can not measure residual volume. A spirometry test can however be suggestive for restrictive lung disease when FVC is too low (less than 80% of the predicted value).

Peak Expiratory Flow and FEV1 can be normal in restrictive lung disease, but are often low as well.

Mixed Lung Disease

A spirometry form a patient with mixed lung disease shows both signs of obstructive and restrictive lung disease: both Tiffeneau and FVC are too low.

Upper Airway Obstructions

With these pathologies the flow volume loop is flattened. Three forms are distinguished:

  • Variable extra-thoracic obstruction: flattening of the expiratory part of the flow-volume loop
  • Variable intra-thoracic obstruction: flattening of the inspiratory part of the flow-volume loop
  • Fixed obstruction: flattening of both the expiratory and the inspiratory part of the flow-volume loop

Upper airway obstructions are rare.

Normal Spirometry

normal spirometry
PEF: normal
PIF: normal

Extrathoracic Obstruction

spirometrie Extra-thoracic upper airway obstruction
PEF: normal
PIF: ↓

Intrathoracic Obstruction

spirometrie intra-thoracic upper airway obstruction
PEF: ↓
PIF: normal

Fixed Obstruction

spirometrie Fixed upper airway obstruction
PEF: ↓
PIF: ↓

More information on spirometry.

 

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