Development and validation of a dynamic finite element model of oropharyngeal swallowing.
C.M. Steele, M.R. Popovic, A. Morris
Funder: CIHR

Swallowing is a behaviour that we take for granted, and carry out effortlessly many times per day. It is essential for nourishment and hydration, yet also affords us pleasure and is central to social events in our daily lives. Swallowing impairment (dysphagia) is a prominent component of many diseases.

Dysphagia secondary to stroke affects up to 20,000 new Canadians per year (Heart and Stroke Foundation of Canada). Up to 5,000 Canadians are diagnosed with Parkinson’s disease annually (Canadian Centre for Behavioural Neuroscience, Lethbridge) and approximately 50 per cent of these individuals will develop dysphagia.Visible signs of swallowing difficulty are present in an estimated 165,000 (i.e., 80 per cent) of the institutionalized elderly in Canada. In total, more than 200,000 people suffer from dysphagia in Canada at any given time.

Dysphagia places individuals at risk for negative nutritional and respiratory sequelae (e.g. pneumonia) , with costly economic consequences for the health-care system (the cost of treating pneumonia in Canada has been estimated at $1,000 per day of hospitalization). Dysphagia also has significant quality of life consequences, denying individuals the enjoyment usually associated with eating and drinking. The aging demographics of our population underscore the importance of research that will further our understanding of dysphagia and facilitate the delivery of effective interventions.

The act of swallowing a liquid is analogous to the task of squeezing frosting or toothpaste through a tube. The tube comprises the oropharynx, an L-shaped chamber, bordered in its upper section by the surfaces of the tongue and the hard palate, and in its lower section by the tongue base, larynx and the posterior pharyngeal wal l. Behind these surfaces lie muscles, whose collective contributions shape the oropharyngeal chamber by generating channels, local constrictions and pressure-flow gradients that facilitate bolus transport from the mouth through the pharynx into the esophagus.

Common interventions for dysphagia include modifying food textures (e.g., thickening liquids or pureeing solid foods), positional manoeuvres (e.g., swallowing with the chin tucked, or head rotated maximally to one side), breath-control manoeuvres (e.g., holding breath intentionally and forcefully prior to initiating a swallow) and techniques designed to improve bolus propulsion (e.g., increasing the effort of tongue-to-palate contact during the swallow, or squeezing hard with the throat muscles during swallowing).

Unfortunately, limited empirical evidence exists to support the effectiveness of these strategies. The available literature is principally comprised of radiographic studies in which small numbers of patients with dysphagia have performed selected manoeuvres during a limited number of swallows. Our literature lacks data to explicate the physiological impact of these manoeuvres on the ultimate dependent variable: the configuration and associated pressure dynamics of the oropharynx (both in healthy and disordered systems).

In order for the field of dysphagia intervention to advance, it is essential that the physiological effects of treatment techniques be understood. We must develop methods for understanding why and how specific interventions alter oropharyngeal swallowing physiology and facilitate improved motility. For this, we need a comprehensive model of the oropharynx.

The current proposal seeks to develop and validate two comprehensive, subject-specific finite elements models of the oropharyngeal chamber (one based on a healthy male participant, and the other on a healthy female). The resulting models will take into account the various structural and muscular elements that influence the shape and pressure dynamics of the oropharyngeal chamber. Data for the models will be collected using a variety of methods (magnetic resonance imaging, videofluoroscopy, electromagnetic articulography, electromyography, orolingual manometry and intraluminal pharyngeal manometry).

These elements will then be selectively manipulated, both in isolation and combination, to mimic different physiological manifestations of dysphagia and the influences of four different swallowing intervention techniques: the Chin-tuck swallow, the Effortful swallow, the Mendelsohn Manoeuvre and the Masako manoeuvre. In this manner, the models will enable us to better understand and predict the mechanisms by which swallowing function can be altered.