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.

Feedback helps us identify gaps, errors, usability problems and opportunities to improve Compass over time.

How Compass is developedGive feedback

Tests and measurements

Sleep study

An overnight recording of breathing, oxygen and sleep, done to see what happens when you are not awake to compensate.

What it means

Sensors record breathing, oxygen levels, heart rate and sleep stages through the night, at home or in a unit. Breathing muscles are least supported during sleep, so changes often show there first, and daytime testing on its own may not pick them up.

Why you might hear it

  • It is often arranged after morning headaches or poor sleep are reported.
  • Results frequently decide whether NIV is offered.

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.