Excitatory drive to the respiratory system in REM sleep.

REM sleep is sometimes divided into tonic and phasic stages. Tonic REM sleep processes are both excitatory and inhibitory to the respiratory system. Inhibitory effects arise from the atonic processes of the REM state and include atonia of thoracoabdominal and extrathoracic airway muscles. Excitatory effects include increases in respiratory rate, central respiratory drive and rate of rise of diaphragmatic activity. The combination of these varying antagonistic effects determines the level of ventilation.