Increased upper airway resistance to breathing during sleep in the cat.

At the onset of sleep, upper airway resistance shifted to higher levels which were maintained throughout sleep. With each inspiration, there was a decrease in upper airway resistance. These respiratory changes in resistance were smaller in wakefulness (on low baseline resistances) than those in nonrapid eye movement sleep (on high baseline resistances). In rapid eye movement sleep, modulations with inspiration were diminished and were intermittently absent, and baseline resistance was high.