Coordination of Mastication, Swallowing and Breathing

Abstract

The pathways for air and food cross in the pharynx. In breathing, air may flow through either the nose or the mouth, it always flows through the pharynx. During swallowing, the pharynx changes from an airway to a food channel. The pharynx is isolated from the nasal cavity and lower airway by velopharyngeal and laryngeal closure during the pharyngeal swallow. During mastication, the food bolus accumulates in the pharynx prior to swallow initiation. The structures in the oral cavity, pharynx and larynx serve multiple functions in breathing, speaking, mastication and swallowing. Thus, the fine temporal coordination of feeding among breathing, mastication and swallowing is essential to provide proper food nutrition and to prevent pulmonary aspiration. This review paper will review the temporo-spatial coordination of the movements of oral, pharyngeal, and laryngeal structures during mastication and swallowing, and temporal coordination between breathing, mastication, and swallowing.

Figures

Fig. 1

Four sequential model and process model are illustrated in diagrams showing progession from left to right, and aligning the common elements of the two models. A) In the conventional sequential model, the four stages have minimum overlap so that oral propulsive stage starts after oral preparatory stage is completed. B) In the Process Model, food processing (in the oral cavity) and bolus aggregation (in the pharynx) can occur at the same time. After food is ingested into the mouth, it is carried to the post-canine teeth for mastication (stage I transport). The food is reduced in size by chewing and mixed with saliva until it is ready to swallow (Food Processing). A portion of the chewed food is propelled into the oropharynx (stage II transport, ST II), where the bolus gradually accumulates while food processing continues in the mouth. Subsequent stage II transport cycles bring additional food to the oropharynx, and the bolus gradually accumulates there. Arrows indicate stage II transport cycles. Pharyngeal and esophageal stages have essentially the same mechanisms in the two models.

Fig. 2

Vertical movement of the jaw, hyoid bone, and soft palate over time while eating a piece of banana. This is an actual recording of a healthy adult volunteer. Motions were measured with videofluorography and an image analysis system. Movement towards the top of the figure is upwards. Rhythmic movements of the soft palate and hyoid bone are temporally associated with cyclic jaw movement. (Source: Matsuo et al. Jpn J Dysphagia Rehabil 2008;12(1):20–30 [34]).

Fig. 3

Food processing and swallowing: drawings based on a videofluorographic recording. The temporal relationships between the soft palate and jaw are strikingly different between the two behaviors. A) Food Processing. The soft palate moves upward as the jaw opens, and moves downward as the jaw closes B) Swallowing. The soft palate elevates after the jaw has closed, and moves downward as the jaw opens. (Source: Matsuo et al., J Dent Res 2005 Jan;84(1):39–42 [30]).

Fig. 4

Stage II transport: Drawings based on a videofluorographic recording. The anterior tongue surface first contacts the hard palate just behind the upper incisors. The area of tongue-palate contact gradually expands backward, squeezing the triturated food to the oropharynx (Squeeze-back mechanism). The food bolus is positioned on the oropharyngeal surface of the tongue where it will accumulate during subsequent stage II transport cycles.

Fig. 5

Example of VFG images showing the oral cavity and pharynx at the moment of swallow initiation with various food consistencies in (A) upright and (B) facedown positions. Images in (B) are rotated counter-clockwise by 90 degrees to simplify comparisons. Arrows point to the leading edge of the barium in each image. (A) In upright position with liquid, the leading edge is normally in the oral cavity at swallow onset without chewing, but moves to the hypopharynx before swallowing when the subject is instructed to chew and then swallow. With a complex two-phase food including both soft solid and liquid phases, the leading edge is in the hypopharynx at swallow onset. (B) With facedown position, for each foods, the leading edge was in the valleculae at swallow onset but did not enter the hypopharynx. This suggests that propulsion to the oropharynx and to the hypopharynx had different mechanisms, the latter dependent on gravity (Source: Saitoh et al., Dysphagia 2007 Apr;22(2):100–7 [3]).

Fig. 6

Average temporal relationships of vocal cord adduction to other critical events during 5-mL barium swallows. Bolus transit through the pharynx and across the upper esophageal sphincter (UES) begins and ends while the vocal cords are fully adducted. TB-O, onset of tongue base movement; SH-O, onset of superior hyoid movement; SM-O, onset of submental myoelectrical activity; UESO, UES opening; OT-O, onset of bolus movement from the mouth; PT-O, arrival of bolus into pharynx. (Source: Shaker et al. Gastroenterology 1990;98(6):1478–84 [37])

Fig. 7

Respiratory cycle total duration (TRC) and duration of inspiratory (TI) and expiratory (TE) phases, by respiratory cycle type, defined as: pre-feeding cycles (Pre-F), feeding cycles with no swallow (F-noSW), swallow cycles (F-SW) and post-feeding cycles (Post-F). The number of cycles in each group is shown in parentheses. Asterisks indicate statistically significant differences (P < 0.001). TE and TRC durations were shortest in feeding cycles with no swallow and longest in swallow cycles. TI duration was longer for pre- and post-feeding cycles than for feeding or swallowing cycles. (Source: Matsuo et al., J Appl Physiol 2008;104(3):674–81 [50]).