Discontinuous gas-exchange cycles (DGC), also called discontinuous ventilation or discontinuous ventilatory cycles, follow one of several patterns of arthropod gas exchange that have been documented primarily in insects; they occur when the insect is at rest. During DGC, oxygen (O2) uptake and carbon dioxide (CO2) release from the whole insect follow a cyclical pattern characterized by periods of little to no release of CO2 to the external environment. Discontinuous gas exchange is traditionally defined in three phases, whose names reflect the behaviour of the spiracles: the closed phase, the flutter phase, and the open phase.