Effects of raising carotid sinus pressure on upper airway resistance and EEG frequency in sleeping dogs.

The purpose of this study was to determine whether acutely raising carotid sinus pressure (Pcs) causes changes in upper airway resistance and/or electroencephalographic (EEG) frequency during wakefulness and non-rapid-eye-movement (NREM) sleep. Five dogs were chronically instrumented so that breathing, tracheal pressure, mouth pressure, EEG, and electrooculogram could be measured while pressure in the vascularly isolated carotid sinus was rapidly increased between 40 and 150 mmHg via an extracorporeal perfusion circuit. Dogs were studied during both wakefulness and NREM sleep. Multiple trials of increased Pcs were conducted in each dog. We observed that increasing Pcs 40-150 mmHg caused not only a reflex cardiovascular response but also a 15-40% decrease in minute ventilation. Raising Pcs caused no physiologically significant changes in upper airway resistance over the range of airway pressures and flow rates encountered during inspiration and expiration. Even dogs that demonstrated moderate to substantial sleep-induced increases in airway resistance did not consistently increase resistance during superimposed baroreceptor stimulation. Small increases in airway resistance were sometimes observed during baroreceptor stimulation, but this was not a consistent finding. Acute increases in Pcs did not cause measurable changes in EEG frequency during wakefulness or NREM sleep. We conclude that acute stimulation of the carotid sinus baroreceptors does not cause physiologically meaningful changes in upper airway resistance or EEG activity in awake or sleeping dogs.