Timed (T) or Spontaneous Timed (ST) modes provide a customizable backup rate that forces the machine to switch from exhalation to inhalation. In ST Mode, the machine monitors the breathing cycle and switches from EPAP to IPAP once the backup time is met or whenever the break is detected through the sensors; whichever occurs first. The time aspect is only meant to act as a backup respiratory rate to the (S) function (see Spontaneous). This is used for patients with central sleep apnea, or those who need non-invasive mechanical ventilation.