Hypoxic arousal in intact and carotid chemodenervated sleeping cats

To determine whether the carotid chemoreceptors or hyperpnea are required for arousal from sleep by hypoxia, 14 sleep-deprived cats were studied during slow-wave (SWS) and rapid-eye-movement (REM) sleep. Rapid hypoxia was produced by inhalation of 5% O₂ in N₂ or 6% CO in 40% O₂ by intact cats and 5% O₂ in N₂ after carotid body denervation. Preliminary studies identified a period of SWS unassociated with spontaneous arousals. In 69 studies during SWS unassociated with spontaneous arousals, arterial O₂ saturation (SaO₂) values at arousal were: 47.1 ± 1.5% (mean ± SE) (5% O₂, intact); 48.9 ± 1.4% (6% CO, intact); and 49.9 ± 2.0% (5% O₂, denervated). During SWS associated with spontaneous arousals, SaO₂, values at arousal were 71.6% ± 1.8% (5% O₂, intact). Arousal from REM occurred at significantly lower values: 31.7 ± 3.9% (6% CO, intact) and 43.5 ± 2.3% (5% O₂, intact). During both SWS and REM, inhalation of 5% O₂ by intact animals caused a substantial increase in ventilation while 6% CO did not. We conclude that more severe hypoxia is required for arousal from SWS when studies are done in a period unassociated with spontaneous arousals than from SWS associated with spontaenous arousals. Hypoxic arousal does not appear to require activation of the carotid bodies or hyperpnea.