Dictionary:

acapnia

  (ā-kăp'nē-ə)

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A condition marked by an unusually low concentration of carbon dioxide in the blood and tissues.

[New Latin, from Latin acapnos, without smoke (which contains carbon dioxide), from Greek akapnos : a-, not; see a–¹ + kapnos, smoke.]

A condition characterized by diminished carbon dioxide in the blood.

A condition marked by the presence of less than the normal amount of carbon dioxide in the blood and tissues.

Decrease of carbon dioxide in the blood.

The noun has one meaning:

Meaning #1: a state in which the level of carbon dioxide in the blood is lower than normal; can result from deep or rapid breathing
  Synonym: hypocapnia