What is a simple definition of FEV1?

The Forced Expiratory Volume
of air in breathing is a measurement of air that is forcibly expelled from the lungs in
an exhalation (this is different from a resting exhalation, which uses the natural
relaxation of the lungs and surrounding muscles). FEV1 is the measurement of air
forcibly expelled from the lungs in the first second of an exhalation; this is measured
after a full-volume inhalation, and measures the strength of the lungs both in volume
and in force of exhalation. These tests are commonly performed on patients with
lung-related illnesses or conditions such as asthma, which can impair lung volume and
strength. These measurements are collected into a practice called
Spirometry (a sub-field of Pulmonary Function
Tests), and are vital in the diagnosis and treatment of conditions that
impair lung function.