During healthy respirations in NREM sleep, the brain relies on the hypoxic drive to trigger breaths. The hypoxic drive triggers a breath when which blood gas increases sufficiently?

During healthy respirations in NREM sleep, the brain relies on the hypoxic drive to trigger breaths. The hypoxic drive triggers a breath when which blood gas increases sufficiently?

• A. Bicarbonate
• B. Oxygen partial pressure
• C. Carbon dioxide
• D. Oxygen

Answer: (C)

Rising carbon dioxide is the key trigger for breathing. When PaCO2 increases enough, CO2 diffuses into the cerebrospinal fluid and forms carbonic acid, lowering pH. The central chemoreceptors in the medulla detect this change and drive the respiratory center to increase ventilation, producing the next breath. In healthy individuals during NREM sleep, this CO2-driven mechanism is the primary stimulus. Bicarbonate only alters pH more slowly, and oxygen levels don’t acutely trigger breaths when they rise; a drop in O2 can contribute under certain conditions, but the immediate trigger is the CO2 rise.

Rising carbon dioxide is the key trigger for breathing. When PaCO2 increases enough, CO2 diffuses into the cerebrospinal fluid and forms carbonic acid, lowering pH. The central chemoreceptors in the medulla detect this change and drive the respiratory center to increase ventilation, producing the next breath. In healthy individuals during NREM sleep, this CO2-driven mechanism is the primary stimulus. Bicarbonate only alters pH more slowly, and oxygen levels don’t acutely trigger breaths when they rise; a drop in O2 can contribute under certain conditions, but the immediate trigger is the CO2 rise.