The ups and downs of periodic breathing: implications for mortality in heart failure.

Periodic breathing is a regularly recurring waxing and waning of tidal volume due to oscillations in central respiratory drive. It is a sign of respiratory control system instability. Under normal conditions, the respiratory and circulatory systems work in concert to deliver O2 according to metabolic demands, and to excrete CO2 to maintain acid-base homeostasis. As a result, arterial PO2 (PaO2), PCO2 (PaCO2) and pH are held within narrow limits. To accomplish this precise matching of ventilation with metabolic demands, respiration is regulated by a rapidly responsive negative feedback system consisting of a central controller and a peripheral plant. The central controller is comprised of the peripheral and central chemoreceptors,