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Why can low carbon dioxide levels during sleep or anesthesia lead to apnea?

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A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

Breathing is regulated by chemoreceptors that monitor the partial pressure of carbon dioxide and oxygen in the body to maintain stable ventilation levels.1

Under normal conditions, an increase in carbon dioxide stimulates these receptors, which in turn increases the rate and depth of breathing to restore balance. Conversely, excessive ventilation lowers the partial pressure of carbon dioxide, which reduces chemoreceptor activity and subsequently diminishes ventilation.1

During sleep or anesthesia, the respiratory system becomes highly sensitive to these fluctuations. If carbon dioxide levels drop just three to four millimetres of mercury below the levels typically maintained during wakefulness, the resulting reduction in chemoreceptor activity is sufficient to cause a total cessation of breathing, known as apnea.1