A spirometer is an instrument that doctors use to measure how well a person's lungs
are working. To use one, a person breathes into a mouthpiece. The doctor may ask the
person to breathe normally or to take a deep breath and blow the air out quickly.
A recording device measures the amount of air inhaled or exhaled and how much time
each breath took. These measurements can help the doctor find out if a person has
a lung problem, such as asthma.