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.