Lung function tests

Techniques

    • Lung volumes

      • Spirometry

    • Flow rates

      • Spirometry

      • Peak flow

    • Maximal respiratory pressures

      • Maximal pressure that can be produced by the patient trying to breath through a blocked mouthpiece

      • Useful in following the course of patients with neuromuscular disorders.

    • Diffusing capacity

    • Oxygen desaturation during exercise

      • The six-minute walk test is a good index of physical function and therapeutic response

    • Arterial blood gases

Spirometry

    • Volume-time curve

      • Volume (liters) along the Y-axis and time (seconds) along the X-axis

  • Flow-volume loop

Parameters

Obstructive Disease

    • In obstructive diseases FEV1 is diminished because of increased airway resistance to expiratory flow

    • The FVC may be decreased as well, due to the premature closure of airway in expiration

      • Generally not in the same proportion as FEV1

    • Therefore the FEV1/FVC ratio, also called Tiffeneau index, falls

    • e.g. asthma, COPD, chronic bronchitis, emphysema

    • The diagnosis of COPD is made when:

      • the FEV1/FVC ratio is less than 70% after bronchodilator medication has been given

      • FEV1% is less than 80% of predicted

Restrictive Disease

    • The FEV1 and FVC are both reduced proportionally

    • Thus the FEV1/FVC value may be normal or even increased as a result of decreased lung compliance

    • e.g. pulmonary fibrosis

Pictures