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.
Lung function tests, also called pulmonary function tests, measure the size of a person's lungs, how much air can be breathed in and out, how fast air can be breathed out, and how well the person's lungs deliver oxygen to the blood.