Electroencephalographic and respiratory activities during acute intermittent hypoxia in anesthetized rats

Cortical activity and respiratory responses to intermittent hypoxia were studied in anesthetized, paralyzed, vagotomized, and artificially ventilated rats. Respiratory responses to hypoxic exposure consisted of stimulation of phrenic and hypoglossal activity and a subsequent decline of the activity up to apnea. The respiratory response to hypoxia was accompanied by a gradual decrement of the total power of EEG. Relative EEG power increased in the delta frequency range and decreased in the remaining frequency ranges. During hypoxic bradypnea or apnea, the total power of EEG strongly diminished or ceased. Each episode of hypoxia caused similar respiratory and cortical effects. However, in comparison with the baseline level, the total power of EEG decreased gradually while the power of the delta frequency range increased in subsequent hypoxic episodes. EEG activity after the last hypoxic exposure recovered within 40-60 min. We conclude that hypoxia initially induces modest changes in the cortical activity that grow with the severity of hypoxia. The persistence of changes in EEG activity following intermittent hypoxia may contribute to disorders present in the sleep apnea syndrome.