One Neglected Yawning Function like Slow Wave Sleep: The Hypothetic Neurovascular Regulation from Mouth to Eye Driven by Expiration

Abstract

In this article, it is considered that the mechanism of yawning function is correlative to sleep. It was revealed from the electrophysiological studies that the slow wave sleep (SWS) was characterized as decrease in excitation from inspiratory motoneurons more than from expiration, manifesting the expiratory activity dominating in SWS. To analogize yawning to SWS, herein it is only considered the expiration during yawning, pressing the sensory posterior palate and maxillary sinuses with air flow, so that yawns similarly regulate the vascular circulations from mouth to eye as SWS, as evidenced by the closure of eyelid in sleep and the association of ophthalmic diseases with obstructive sleep apnea. Besides, it is pointed out that the yawning expiration of high muscular tone elicits the muscular constriction at the back of neck, potentiating the expiratory press in mouth stronger than that of SWS. Accordingly, it is hypothesized that the yawning resembles the SWS to play the neurovascular regulation in head driven by expiration. It is speculated that the initiative mouth opening in yawns may have functions other than that considered here. It is expected that this new and neglected function of yawning with expiratory neurovascular regulation in head may add more to understand the complex functions of yawns.

Classification of three forms of regulations on emotional/autonomic nervous system by slow wave sleep

“…Besides, it has also been demonstrated that the obstructive sleep apnea is mainly related to expiratory breath in assaying (Bikov, Hull & Kunos, 2016;Oliveira, et al, 2011). Both of these electrophysiological and pathological observations demonstrate that the ratio of inspiratory/expiratory activity decreases in SWS (Cai, 2018a).…”

“…Yawning is the correlative behavior of sleep in humans, frequently occurs before and after sleep. Yawning consists of an involuntary sequence of mouth opening, deep inspiration, brief apnea, and slow powerful expiration (Cai, 2018a;Corey, Shoup-Knox, Gordis & Gallup, 2012;Guggisberg, Mathis, Schnider & Hess, 2010), driven by the movements of mouth and respiration. In contrary to the drastic and powerful respiratory movements (Cai, 2018a;Corey, Shoup-Knox, Gordis & Gallup, 2012;Guggisberg, Mathis, Schnider & Hess, 2010), a little increase in heart rate and eye muscle tension has been reported during or immediately following yawning (Corey, Shoup-Knox, Gordis & Gallup, 2012).…”

“…The air flow of inspiration/expiration in SWS can certainly press against the sensory posterior palate and maxillary sinuses, which can in turn signal and elicit neurovascular regulation in head (Cai, 2018a). It has been reported that the palate may cause snoring and obstructive sleep apnea (MacLean, Fitzsimons, Fitzgerald & Mbbs, 2017), while the maxillary expansion can treat the obstructive sleep apnea (Vale et al, 2017), demonstrating the presence of pressure from the inspiratory/expiratory air flow in SWS onto the posterior palate and maxillary sinuses (Cai, 2018a).…”

“…In the induction or initiation of SWS, this decrease in ratio of inspiratory/expiratory pressure of air against the sensory posterior palate and maxillary sinuses can be relayed in head up to the vascular circulation in eye (Cai, 2018a), necessary for eye closure in SWS. For evidence, on the one hand, it has been demonstrated that the closure or tiredness of eyelids manifests the extent of drowsiness and sleepiness (Alvaro, Jackson, Berlowitz, Swann & Howard, 2016;Filtness et al, 2014).…”

“…Obviously, from decrease in ratio of inspiration/ expiration to regulation of vascular circulation in eye (Cai, 2018a;Huon, Liu, Camacho & Guilleminault, 2016;Skorin & Knutson, 2016), it constitutes one form of regulation on the autonomic nervous system by SWS. This form of regulation on the autonomic nervous system does not require the participation of slow wave in the forebrain in SWS.…”