Hyperventilation

Hyperventilation is breathing that increases alveolar ventilation, the amount of fresh air reaching the gas-exchanging regions of the lungs, beyond that required for the body's current rate of carbon dioxide production. As a result, carbon dioxide is expelled faster than it is generated, causing the partial pressure of carbon dioxide in arterial blood (PaCO₂) to fall. This decrease is called hypocapnia .^1,2

Hyperventilation can result from breathing more deeply, more rapidly, or both. It is therefore not defined simply by a high breathing rate. Rapid breathing does not necessarily produce hyperventilation if alveolar ventilation does not increase sufficiently, while deeper breathing can substantially increase alveolar ventilation even without a large increase in breathing frequency .²

Hyperventilation is distinct from hyperpnea. Hyperpnea is an increase in breathing associated with increased metabolic demand, as commonly occurs during exercise. Carbon dioxide production and ventilation can rise together, allowing arterial carbon dioxide to remain relatively stable. In hyperventilation, alveolar ventilation is excessive relative to carbon dioxide production, so PaCO₂ decreases .^1,2

Because carbon dioxide participates in acid-base regulation, a fall in PaCO₂ tends to increase blood pH and can produce respiratory alkalosis. Increased ventilation can occur in response to stimuli including hypoxemia, pain, anxiety, and metabolic acidosis. In metabolic acidosis, the resulting decrease in PaCO₂ can represent an appropriate compensatory respiratory response rather than a primary respiratory alkalosis .¹