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The primary function of your lungs is the exchange of gases between the atmosphere and your pulmonary blood circulation. The main gases are Oxygen, which is transferred from the atmosphere via your lungs to your tissues, and Carbon Dioxide, which is a waste product of respiration and is expired via your lungs.
The Gas Transfer test measures how efficient your lungs are at exchanging gases. Certain lung diseases affect gas exchange in your lungs. For example, gas transfer will be reduced in emphysema and pulmonary fibrosis.
During this test you will be seated and your nose will be sealed with a noseclip. Procedure varies between different laboratories, but generally you will be asked to breathe normally into a mouthpiece, followed by a relaxed blow all the way out until you cannot breathe out any more air, and then asked in breathe in as deep and quickly as possible. When your lungs are full, you will be asked to relax and hold your breathe for approximately 9 seconds and then to relax and blow all the way out. Whilst you were breathing in quickly, you were actually inhaling a specialist mixture of gas, This test gas mixture containing carbon monoxide (CO), but please don't be concerned - at this concentration it is not harmful, and even preganant women can inhale it without it causing any harm to the mother or the baby.
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.