An abnormally rapid resting respiratory rate (see RESPIRATION). If voluntarily induced, it causes light-headedness and then unconsciousness by lowering the blood partial pressure of carbon dioxide.

Hyperventilation occurs with chest and heart diseases which raise carbon dioxide tension or cause HYPOXIA (e.g. severe CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) or PULMONARY OEDEMA). Mechanically ventilated patients may be hyperventilated to lower carbon dioxide tension in order to reduce INTRACRANIAL PRESSURE. (See also HYPOCAPNIA.)