Gas transfer measurement

The main function of the lungs is to exchange gases between the atmosphere and blood as it flows through our lungs. The main gases are:

• Oxygen (often shortened to ‘O2’) which is transferred from the atmosphere through the alveolar-capillary membranes within our lungs and into our blood, which is then transported around the body, and
• Carbon Dioxide (often shortened to ‘CO2’) and it moves in the opposite direction to oxygen in that it is transported to the lungs via blood and then transfers from the blood (through the alveolar-capillary membranes) into the air within our lungs and we then exhale it

The Gas Transfer test measures gas transfer factors which in turn tells us how efficient the lungs are at exchanging gases. Lung diseases often affect gas exchange in the lungs by either increasing or decreasing gas exchange efficiency. For example, gas transfer will be reduced in emphysema and pulmonary fibrosis, whereas asthma may actually increase gas exchange efficiency (but this may have detrimental effects elsewhere).

The actual test procedure may vary between different laboratories, but in general you will be seated and your nose will be sealed with a noseclip. You will then be asked to breathe in and out normally through a mouthpiece, followed by a relaxed blow all the way out until you cannot breathe out any more air. You will then be asked to breathe in as deep and quickly as possible and whilst you are doing this, you will be inhaling a specialist gas mix.

Again the specialist gas mix may differ depending on which equipment the laboratory is using but will likely contain trace concentrations of carbon monoxide (CO), helium (He) and possibly methane (CH4) – but please do not be concerned – the concentration used are very low and is considered safe enough to test pregnant women with without causing any harm to either the mother or the baby. If you do have any concerns, please contact the department to discuss further.

When your lungs are full, you will be asked to relax and hold your breath for approximately 9 seconds and then to relax and blow all the way out. Once complete, you will then be asked to come off of the mouthpiece and to relax and breathe normally. This test will be performed a minimum of two times, up to a maximum of 5 times, and you will be given a minimum of 4 minutes rest between each test.