Lung Function Testing
Selecting the right test
The breathing tests most often used are:
Spirometry / Flow Volume Loop.
This is a straightforward but reliable and fundamental test in thoracic medicine, providing key information regarding airflow, in particular the FEV1. This test is used to monitor patients with known asthma or COPD. At NBST, reversibility testing is done with 400mcg salbutamol. This component of the test is useful in differentiating asthma from COPD. For patients with asthma the FEV1 usually normalises with salbutamol, while for patients with COPD the FEV1 will at most partially normalise. This is a common area of misunderstanding – it is important to remember that most patients with COPD will have a bronchodilator response (that’s how most of the inhaled therapies now available work) it’s just that it’s not complete.
Diffusing capacity (DLCO).
This is an easy test to perform in conjunction with spirometry, taking only a few extra minutes and involving minimal discomfort for your patient. It is an extremely useful test of the ability of gas to diffuse into the lungs. The DLCO is low in COPD, but normal in asthma. It is also low in interstitial lung disease, anaemia and pulmonary vascular disease.
Comprehensive lung Function with body plethysmography.
This is usually the best test for patients with undifferentiated respiratory symptoms. A body plethysmograph provides the most accurate measure of lung volumes available. Spirometry / Flow Volume Loop and DLCO are also routinely measured as part of comprehensive lung function testing. As it involves sitting in a closed space, plethysmography may be difficult for patients who suffer from claustrophobia or morbid obesity.