What is a lung function test?

A lung function test takes around 45 minutes to complete and it contains three main components; spirometry, diffusion capacity and static lung volumes. These tests help to determine the overall health of your lungs.

Spirometry is a measure of air flow over time. These measures, termed flow volume loops (FVL), are performed before and after administration of a puffer, also known as a bronchodilator, to assess for reversibility. The most important parameters measured during spirometry include forced expiratory flow volume in one second (FEV1) and forced vital capacity (FVL) measured in litres per second.

Spirometry alone may not be sufficient to completely define the extent of lung disease, perioperative risk, response to therapy or level of impairment. Often spirometry is used as a screening procedure.

Diffusion Capacity measures the effectiveness of the gas exchange occurring in the deepest part of your lungs across the alveolar capillary membrane in to the blood stream. Single breath carbon monoxide diffusion capacity (DLCO) or transfer factor (TLCO) is recorded. As DLCO is sensitive to haemoglobin levels, a haemoglobin sample from a finger prick is obtained. Results are reported in both corrected and uncorrected forms.

Static Lung Volumes are measured via body plethysmography. This determines how much air the lungs can hold. The term static lung volumes is used to describe the measurement of various subdivisions of the lungs. This includes inspiratory capacity (IC), vital capacity (VC), functional residual capacity (FRC) and total lung capacity (TLC). Further subdivisions of capacities measured include residual volume (RV), expiratory reserve volume (ERV), inspiratory volume reserve (IRV) and tidal volume (Vt).

Measuring lung volumes can be very useful in distinguishing between restrictive lung disorders such as pulmonary fibrosis and scoliosis where lung volumes tend to be decreased, from obstructive lung disorders, such as COPD or bronchiectasis, where lung volumes tend to be increased, and is a useful adjunct to spirometry.

Please do not hesitate to call the lung function lab on 8250 0311 should you wish to discuss any aspect of lung function testing.

Special thanks to our Senior Respiratory Scientist, Silas John, for putting this article together for Northern Specialist Suites.