What spirometry actually measures
Spirometry is the workhorse of lung testing. You take the deepest breath you can, seal your lips around a mouthpiece, and blow out as hard and as long as possible. A sensor records how much air comes out and how fast. From that single forced breath out we get two foundational numbers that the rest of this track builds on.
The first is FVC — forced vital capacity — the total volume of air you can blow out from a full breath. The second is FEV1 — the volume you blow out in just the first second. Think of FVC as “how big is the tank” and FEV1 as “how fast can you empty it.” A healthy person empties most of the tank quickly; in many lung diseases either the tank shrinks or the emptying slows.
What a good test takes
Spirometry is effort-dependent, which means a half-hearted blow gives misleadingly low numbers. The technologist coaches loudly on purpose. A valid maneuver has a sharp, explosive start, a steady continuous blow with no coughing or leaks, and a long enough exhalation — usually at least six seconds — so the curve flattens at the end.
- Sit upright, apply a nose clip, and breathe normally through the mouthpiece for a few breaths.
- Take the deepest possible breath in — fill the lungs completely.
- Blast the air out instantly and forcefully, then keep blowing until empty.
- Repeat at least three times; the best efforts should agree closely before the test is accepted.