American Sleep Apnea Association Wrote:How does apnea cause nocturia? Umlauf explains that during episodes of sleep apnea, the soft structures in the throat relax and close off the airway, setting into motion a chain of physiological events. “Oxygen decreases, carbon dioxide increases, the blood become more acidic, the heart rate drops and blood vessels in the lung constrict,” says Umlauf. “The body is alerted that something is very wrong. The sleeper must wake enough to reopen the airway. By this time, the heart is racing and experiences a false signal of fluid overload. The heart excretes a hormone-like protein that tells the body to get rid of sodium and water, resulting in nocturia.”