Yawning and airway physiology: a scoping review and novel hypothesis

Abstract

Background and purpose Yawning is a stereotypical complex muscular movement and is commonly executed by most vertebrates. In seconds, the entire airway is fully dilated and surrounding muscles are powerfully stretched, most prominently around the pharynx. To date, yawning has been rarely studied, and as of yet there is no consensus on its main function. Material and methods To investigate a mechanical airway function for yawning, a literature search was conducted to relate the frequency of yawning and obstructive airway conditions. Results The results show that changes in obstructive airway conditions and alteration of the frequency of yawning are temporally related. Interpretation These relationships, however, cannot be interpreted as causal, nor can they be extrapolated to explain the function of yawning. Yet airway management and yawning share many physiological characteristics. We therefore propose a novel hypotheses: yawning plays a significant role in airway physiology by muscle repositioning and widening the airway lumen, thereby securing long-term oxygenation.

Functions of Spontaneous Yawning: A Review

“…The functions of spontaneous are evaluated in the review. As previously shown, the circadian hypothesis demonstrates that yawning is a behavior that reflects the circadian rhythm, the oxygenation theory believes yawning is an anticipant of airway collapse, while the brain cooling hypothesis indicates yawning is contributed to decreasing the temperature of the brain [9]; [11]; [10]. However, they all have flaws and drawbacks.…”

“…Some scientists suggested that yawning is for longterm oxygenation. Specifically, yawning creates an enlarged airway by muscle repositioning in the upper airway to anticipate airway collapse [11].…”

“…In addition, healthy children also yawn more frequently than adults. The scientists proposed it can be explained by their relatively narrow airway, which in turn makes yawning as anticipation of airway collapse, more crucial and more frequent [11].…”

“…This review will examine the current theories of the functions of spontaneous yawning, as well as proposes a novel hypothesis, and offers suggestions for future investigations. Current explorations of spontaneous yawning are generally divided into three main categories: circadian hypothesis [9], brain cooling or thermoregulatory hypothesis [10], and respiration or airway hypothesis [11]. Each hypothesis is supported by numerous empirical evidence, but there still exist heated debates and the exact mechanism of yawning remains inconclusive.…”

“Optoanesthesia”: The Application of Transcranial Photobiomodulation to General Anesthesia

“…Such yawning responses may occur one minute after the injection of thiopental or propofol, with an occurrence rate of approximately 50% [58]. Upper-airway collapse during the induction of anesthesia coincides with increased yawning, while upper-airway muscle dilation and decreased yawning caused either by either teeth clenching or opioids administrations coincides with obstructive sleep apnea-like symptoms [59]. Yawning after tPBM administration mimics the yawning that is elicited by thiopental or propofol administration during induction of general anesthesia.…”