Depending on what the problem is, you may also need to undergo body plethysmography and/or a gas transfer test. Body plethysmography involves sitting inside a closed glass box, like a telephone box, and measures the total volume of your lungs. The gas transfer test measures the amount of oxygen that transfers from you lungs into your blood. During this test you will be asked to take a deep breath and hold your breath for about 8 seconds and then breathe out. For all tests you be asked to wear a soft nose clip and breathe on a mouthpiece. All tests will be repeated several times.