Effect of carotid sinus nerve stimulation pattern on cardiorespiratory responses

The reflex responses to steady and intermittent stimulation of the carotid sinus nerve (CSN) were compared in anesthetized dogs. Intermittent stimulation was less effective than steady stimulation in reducing the arterial blood pressure, and the disparity was exaggerated after acute sinoaortic denervation. With the sinoaortic nerves intact, at low mean stimulation frequencies the heart rate responses were greater during intermittent than during steady CSN stimulation. At higher mean stimulation frequencies, however, steady CSN stimuli were more effective than were the intermittent type. After sinoaortic denervation, steady stimuli evoked greater heart rate responses than did intermittent stimuli over the entire mean frequency range studied. Reflex changes in respiratory depth and frequency were also greater during steady than during intermittent CSN stimulation. The greater efficacy of steady than of intermittent stimulation in evoking.the observed reflex cardiovascular and respiratory changes is probably ascribable to the pronounced frequency limitation at the first synapse of the baroreceptor reflex in the brain.