Overview of spirometry
Spirometry can be performed and interpreted in the general practice setting; training courses are recommended before conducting spirometry. Testing equipment is relatively inexpensive and portable. Testing may be subsidised through the Medicare Benefits Schedule (MBS)1.
Spirometry measures flow and volume during a forced expiratory manoeuvre, in which the patient first inhales to total lung capacity (TLC) and then exhales with maximum effort to residual volume (RV). Airflow measured at the mouth during this manoeuvre depends on lung elastic recoil, respiratory muscle strength, airway diameter, and patient cooperation when performing the test.
The common parameters measured with spirometry are:
- forced expiratory volume in 1 second (FEV1)—the volume of air exhaled in the first second
- forced vital capacity (FVC)—the total volume of air exhaled
- FEV1/FVC ratio (or forced expiratory ratio [FER])—FEV1 expressed as a percentage or fraction of FVC (eg 70% or 0.7).
Appropriately performed spirometry can identify obstructive and restrictive ventilatory defects; see Classification of ventilatory defects by spirometry for classification of ventilatory defects by spirometry.
Useful spirometry resources include:
- Spirometry Handbook from the National Asthma Council
- Spirometry Users’ and Buyers’ Guide from the National Asthma Council
- Spirometry calculator in the Primary Care Respiratory Toolkit from the Lung Foundation Australia.