REGULATION OF AIRWAY SMOOTH-MUSCLE TONE IN SLEEPING DOGS

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Abstract
The influence of sleep state on airway smooth muscle tone in 4 unanesthetized dogs trained to sleep in the laboratory was examined. The dogs were prepared with a permanent sidehole tracheostomy and bilateral cervical vagal loops. The dogs breathed through a cuffed endotracheal tube inserted through the tracheostomy. To monitor changes in tracheal smooth muscle tone, the pressure in the water-filled cuff of the endortracheal tube was measured. The technique was validated by examining changes in cuff pressure after administration to the dogs of a series of chemical agents and physiologic stimuli known to constrict or relax tracheobronchial smooth muscle. Sleep state of the dogs was determined by behavioral, EEG and EMG criteria. During quiet wakefulness, tracheal smooth muscle tone was stable. With the onset and progression of sleep through the nonrapid-eye-movement stages, airway smooth muscle tone relaxed (decrease in cuff pressure of 20-40 cm H2O), reaching a new steady level during slow-wave sleep. During rapid-eye-movement [REM] sleep, tracheal smooth muscle tone fluctuated markedly and erratically, as reflected by changes in cuff pressure as large as 90 cm H2O. Parital blockade of the vagus nerves, by cooling the exteriorized cervical vagal loops, decreased or abolished the fluctuations in tracheal smooth muscle tone during REM sleep at temperatures that did not abolish resting tone, demonstrating that the changes in tone during REM sleep were related to variability in neural control of airway smooth muscle.