Research:
Tongue-jaw linkage in human feeding
<Research Volunteers Needed!>
Principal Investigator: Jeffrey B. Palmer, M.D.
The Process Model of Feeding provides an understanding of the interrelated processes of mastication, oral food transport, and swallowing. Central to this model is the notion that solid foods are processed in the oral cavity but the bolus is formed in the pharynx (pharyngeal aggregation). A critical implication of the model is that food can be in the oropharynx for a period of time before swallow, while the airway is open. This can be a risk for aspiration of triturated food prior to the swallow. It is likely that the airway protective mechanisms are functioning during the period of bolus aggregation in the oropharynx. Recent studies have shown that the pattern of breathing is altered during feeding and includes a period when breathing stops (deglutitive apnea). The period of deglutitive apnea may be longer than the swallow itself to incorporate the pre-swallow period of bolus aggregation.
The Process Model has clinical implications in that it demands a reassessment of the normal relationship between food position and initiation of swallowing. In addition, it provides a framework for analysis of mastication and oral food transport, processes that are often impaired in dysphagic individuals. Movement of food in and through the oral cavity depends primarily on the coordinated movement of the jaw, hyoid and tongue. Although the basic movements have been described, the muscle activity patterns producing these movements have not.
Our main goal is to study the kinesiology of feeding in normal adults. Movement will be recorded with videofluorography and muscle activity with electromyography. Some experiments will also include respiratory measures (thoraco-abdominal expansion and nasal air pressure).
We hypothesize that:
- Cyclical movements of the hyoid bone in the sagittal plane are produced by the interaction of three muscle groups (jaw adductors, suprahyoid muscles and infrahyoid muscles).
- Although cyclical movements of the tongue surface result primarily from activity of its intrinsic muscles, they are also influenced by linkage to the jaw and hyoid bone, as well as extrinsic muscle contraction.
- Mediolateral tongue surface motion is linked to jaw motion during food processing, and is assisted by differential activity of the jaw adductor muscles on each side.
- The soft palate exhibits cyclical movement during eating and swallowing that is temporally linked to jaw motion.
- Motion patterns of the jaw, hyoid and tongue surface and the muscle activity patterns that produce them are cyclical and semi-rhythmic during eating; the sequential pattern of muscle activation is maintained across behaviors, though the duration and amplitude of contraction may vary.
The results of these studies will further delineate the mechanisms of eating and swallowing, enhance our knowledge on the CNS control of mastication and swallowing, and describe the relationship between mastication, swallowing and respiration. This new knowledge will impact the evaluation and treatment of dysphagic individuals particularly of those with respiratory dysfunction.
Click an image link to movie clips
Soft palate motion during eating banana on VFG (videofluorography)
Figure. Temporo-spatial linkages between the soft palate, jaw and hyoid movements during feeding
Traditional three-phase models of swallowing include sequential oral, pharyngeal, and esophageal phases. In these models, food is held in the oral cavity until the onset of swallow. A new paradigm is the Process Model. We have shown that, when healthy normal subject eat solid food, fully reduced food is propelled into the pharynx and accumulates there while mastication continues. The Process Model of Feeding provides a framework for the integration of mastication, oral food transport, and pharyngeal swallowing.
The Process Model includes four phases: Stage I Transport, Processing, Stage II Tranpsort, and Pharyngeal swallow (see movie clips). Food is moved from the anterior oral cavity to the occlusal surfaces of the postcanine teeth during Stage I Transport. During Processing, food particles are reduced in size by action of the tongue, jaws, teeth and hard palate, and lubricated with saliva. Food is maintained on the occlusal surfaces for chewing by action of the cheeks (pushing medially) and the tongue (pushing laterally) during jaw opening. The actions of the tongue and cheeks result in constant repositioning of the food, so the teeth compress the food on a different trajectory in each chewing cycle. When a portion of the food is suitable for swallowing, it is placed on the middle of the tongue surface, and propelled through the fauces (Stage II Transport). In Stage II, the tongue squeezes the triturated food into the oropharynx where it accumulates, forming a bolus, while chewing continues. Multiple stage II transport cycles may occur in succession during bolus aggregation. The duration of bolus aggregation in the oropharynx ranges from a fraction of a second to about ten seconds. During the pharyngeal swallow, food is propelled from the pharynx into the esophagus, passing through the upper esophageal sphincter. Throughout these processes, tongue and jaw motion have characteristic temporo-spatial linkage patterns that are essential to the mechanisms of food transport.
A critical implication of the Process Model is that food can be in the oropharynx for a period of time before swallow, while the airway is open. This can be a risk for aspiration of triturated food prior to the swallow. It is likely that the airway protective mechanisms are functioning during the period of bolus aggregation in the oropharynx. Recent studies have shown that the pattern of breathing is altered during feeding and includes a period when breathing stops (deglutitive apnea). The period of deglutitive apnea may be longer than the swallow itself to incorporate the pre-swallow period of bolus aggregation.
Click images link to movie clips
Liquid swallow in slow motion on VFG
Eating cookie on VFG
Stage I transport in slow motion
Stage II transport in slow motion
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