This article is from the Asthma FAQ, by Patricia Wrean and Marie Goldenberg email@example.com with numerous contributions by others.
A spirometer is a machine for testing lung function that you
breathe in and out of through a hose attached to a mouthpiece.
You are usually given nose clips so that all the air you breathe
goes through the machine. One I've been tested on had a little
expanding tank surrounded by water into which the air goes, and
I could see the top rising and falling as I breathed out and in.
It can measure a fair number of characteristics of your lungs,
including FVC, FEV1, and PEPR. FVC, or forced vital capacity,
is the amount of air that you can exhale forcefully after taking
a deep breath. FEV1, or forced expiratory volume in one second,
is the amount of air that you can be exhale in one second.
Peak flow, or PEPR, is described in section 1.2.2.
The sophisticated spirometers I've seen have a PC attached, and
have neat little curves generated with each breath, which
apparently have characteristic shapes for different respiratory
There is a slightly less sophisticated machine that I've blown
into, and I'm not sure if this is also classed as a spirometer or
not, but you take a deep breath and blow into it, much like a
peak flow meter, except that it draws a little graph of how much
volume you've blown out, and I'd imagine that you can get the
FVC and FEV1 off this graph.
For more information, I recommend the book by Drs. Haas,
_The Essential Asthma Book_, which goes into more detail about
the various things you can find out from spirometry.