Compass is still being developed and is effectively in beta. Some content and features may be incomplete, change, or not work as expected.

Content is anchored to trusted sources where available, but Compass has not yet been clinically reviewed. It provides general information rather than medical advice.

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Tests and measurements

FVC

Forced vital capacity

A breathing test measuring how much air you can blow out after taking the deepest breath you can.

What it means

You breathe in fully and then blow out as hard and as long as you can into a tube. The result is often given as a percentage of what would be expected for someone of your age, height and sex. Because it depends on a good seal at the lips, weak facial muscles can lower the reading for reasons other than the lungs.

Why you might hear it

  • It is usually done at every clinic visit and tracked over time.
  • It is often part of the criteria for equipment funding and trial entry.

People who may help

Where Compass goes into this

About this explanation

These are plain explanations of words you may come across, not advice about your own situation. Where a word matters to a decision, the question pages go into it properly, and your own team is the place to take it.