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Breathing and ventilation

Carbon dioxide build-up

Carbon dioxide collecting in the blood because breathing is not clearing it fast enough.

What it means

Carbon dioxide is the waste gas breathing carries away. If breathing is too shallow it gathers rather than leaving, and that can cause headaches on waking, drowsiness and muddled thinking. It is measured rather than guessed at, from blood, from breath, or through a sensor on the skin.

Why you might hear it

  • It explains why morning headaches are asked about so often.
  • Test results may name it as hypercapnia.

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.