Coordination of mastication and swallowing

Abstract

The coordination of mastication, oral transport, and swallowing was examined during intake of solids and liquids in four normal subjects. Videofluorography (VFG) and electromyography (EMG) were recorded simultaneously while subjects consumed barium-impregnated foods. Intramuscular electrodes were inserted in the masseter, suprahyoid, and infrahyoid muscles. Ninety-four swallows were analyzed frame-by-frame for timing of bolus transport, swallowing, and phases of the masticatory gape cycle. Barium entered the pharynx a mean of 1.1 s (range -0.3 to 6.4 s) before swallow onset. This interval varied significantly among foods and was shortest for liquids. A bolus of food reached the valleculae prior to swallow onset in 37% of sequences, but most of the food was in the oral cavity at the onset of swallowing. Nearly all swallows started during the intercuspal (minimum gape) phase of the masticatory cycle. Selected sequences were analyzed further by computer, using an analog-to-digital convertor (for EMG) and frame grabber (for VFG). When subjects chewed solid food, there were loosley linked cycles of jaw and hyoid motion. A preswallow bolus of chewed food was transported from the oral cavity to the oropharynx by protraction (movement forward and upward) of the tongue and hyoid bone. The tongue compressed the food against the palate and squeezed a portion into the pharynx one or more cycles prior to swallowing. This protraction was produced by contraction of the geniohyoid and anterior digastric muscles, and occurred during the intercuspal (minimum gape) and opening phases of the masticatory cycle. The mechanism of preswallow transport was highly similar to the oral phase of swallowing. Alternation of jaw adductor and abductor activity during mastication provided a framework for integration of chewing, transport, and swallowing.

Volitional control of food transport and bolus formation during feeding

“…The videotapes were first analyzed using the slow motion and stop-frame features on the VCR [2,13] and then digitized for further analysis.…”

“…There is, however, no comparable internal pharyngeal reference. The radiographic shadow of the mandible is commonly used as a reference point in studies of human swallowing [1,2,4,5,12,14].…”

“…The Process model paradigm was used to divide each recording into four temporal stages, each beginning immediately upon termination of the last [2]. This model was selected because it was developed specifically to define the events occurring during feeding on sold food, and has been validated in several studies [5,7,14].…”

“…Additional aliquots of prepared food can be transported to the oropharynx, where a bolus gradually accumulates (for up to ten seconds). When bolus aggregation in the oropharynx is completed, a swallow is initiated, and the bolus is transported through the upper esophageal sphincter to the esophagus [2][3][4][5].…”

“…This gradually expands the area of tongue-palate contact from anterior to posterior, gradually squeezing the triturated food into the oropharynx. Food can be transported either to the immediate post-faucial region or to the valleculae [2,5]. This transport is active, and does not depend on gravity [4].…”