Regulation of respiration in sleeping dogs

We have examined the respiratory changes that occur during physiological sleep in three dogs with exteriorized cervical vagal loops. Sleep stage was determined by behavioral and EEG criteria. During non-REM (NREM) sleep breathing was slower (mean change, 23%),deeper (mean change, 18%), and less variable (coefficients of variation, 0.05-0.10) than during wakefulness (W); minute volume of ventilation (Ve) decreased (mean change, 14%) and alveolar CO2 pressure (PAco2) increased slightly (mean change, 1.3 mmHg). In addition, the rate of O2 consumption and ventilatory response to hypercapnia were decreased. In contrast, REM sleep was characterized by rapid, shallow, and considerably more irregular (coefficients of variation, 0.18-0.30) breathing; Ve increased markedly and PAco2 decreased (mean change, 5.2 mmHg). Blockade of both cervical vagus nerves produced comparable changes in each stage of sleep (W, NREM, REM): breathing became slower and deeper, but the differences between stages and the marked irregularity in REM sleep persisted. In contrast, the Hering-Breuer inflation reflex (HBIR) was strong in W and NREM sleep, but weak in REM sleep. The results indicate that changes in respiratory control and stability during sleep are not due to fluctuations in vagal influence despite the fact that one vagal reflex (HBIR) was sleep-state dependent.