There are many ways in which cancer can cause fatigue. The growth of a tumor, in general, can be taxing for your body. Other symptoms of cancer such as shortness of breath, anemia, pain, or a decreased level of oxygen in your blood (hypoxia) can cause fatigue.
A pulmonary function test may take 30 to 60 minutes to complete. This will vary according to the amount of trials necessary for you to get repeatable test results.
The pulmonary function tests that are customarily used for diagnosis include spirometry, lung volume tests and diffusing capacity tests. In spirometry, a person breathes out into a tube attached to a spirometer, which measures how much air is being exhaled and how quickly.