Nocturnal swallowing augments arousal intensity and arousal tachycardia

Introduction : Cortical arousals from sleep vary considerably in their
frequency, duration and in their effects on the autonomic nervous
system. Yet mechanisms that modify the arousal intensity and autonomic activity remain enigmatic. We wondered if nocturnal episodic
swallowing – an essential airway defence mechanism regulated by
brainstem Central Pattern Generator (CPG) networks – influenced
sleep arousability and cardiac autonomic activity.
Methods : 24 healthy volunteers participated. One group ( N = 14; 8
female) were examined for supine blood pressure and heart rate responses to swallows during wakefulness with epiglottic manometry.
The second group ( N = 10; 5 female) undertook overnight polysomnography to examine the relationships between EEG arousal, swallows, heart rate and breathing during sleep.
Results : In all subjects we observed swallows trigger robust and patterned tachycardia conserved across wake, sleep and arousal states.
Tachycardia onset was temporally matched to glottic closure – the
first phase of swallow motor program. Multiple swallows increases
the magnitude of tachycardia via temporal summation, and blood
pressure increases as a function of the degree of tachycardia. During
sleep, swallows were overwhelmingly associated with arousal.
Swallows were causally linked to the intense, prolonged cortical
arousals and marked tachycardia. Arousal duration and tachycardia
increased in parallel as a function of swallow incidence.
Conclusions : Our findings identify a fundamental mechanism driving
both autonomic activity and heightened arousal via cortical feedback
from swallow Central Pattern Generator networks of the brainstem.
These findings challenge the widely held view that arousal generates
stereotyped autonomic responses by feedforward inputs from cortical and subcortical systems implicated in the arousal.