Spirometry is a medical test used to assess the functioning of the lungs. This pulmonary function test is performed to measure the volume and flow of air that the patient inhales and exhales over time to diagnose pulmonary diseases such as asthma, pulmonary fibrosis, and cystic fibrosis. When taking a spirometry test, the standard procedure is to sit and breathe using a spirometer apparatus. This medical device records the volume of air you breathe in and out, in mL, over time, in seconds.

For this test, the amount of air the patient inhales and exhales from a sitting position should be the same compared to a standing position as long as the patient sits up straight and with flat feet on the floor.

The spirometer is depicted here. It is a square-shaped apparatus with a screen that shows a graph that measures volume on the y-axis and time on the x-axis. It has a switch to turn the device on and off. There is a tube connected to the apparatus, which has a mouthpiece on the other end to allow air to be blown into.

Figure 1. The spirometer apparatus with a diagram showing the test result on the screen.