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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
therefore, receive convergent informa­tion from both cortical and peripheral inputs that trigger swallowing. Finally, the two hemicentral pattern generators located in each half of the medulla are tightly synchronized, and it is thought that this connection occurs within the dorsal swallowing group of interneu­rons (Cunningham & Sawchenko, 2000; Jean, 2001; Kessler & Jean, 1985).
The interneurons of the ventral swallowing group are thought to be “switching” neurons that distribute and coordinate the swallowing drive to the various pools of motoneurons involved in swallowing. The firing behavior of these neurons also exhibits a sequen­tial pattern, but with more overlap, longer latency, greater duration vari­ability, and lower frequency than the interneurons of the dorsal swallowing group. This type of firing behavior indi­cates that the connections between the ventral swallowing group interneurons and their afferent fibers are likely to be polysynaptic. The ventral swallowing group interneurons are probably acti­vated by the interneurons of the dor­sal swallowing group. They, in turn, are connected to all the various groups of motoneurons involved in swallow­ing, and within the ventral swallowing group interneurons, each neuron can project to more than one motor nucleus. The trigeminal and hypoglossal motor nuclei are connected only to the ventral swallowing group interneurons and not to the dorsal swallowing group. Swallowing motoneurons only receive input from the ipsilateral efferent fibers of the ventral swallowing interneurons (Amri et al., 1990; Jean, 2001; Kessler & Jean, 1985; Larson et al., 1994).
In addition to the interneurons of the ventral and dorsal swallowing groups,
swallowing interneurons have been identified within the trigeminal and hypoglossal motor nuclei, or in close proximity. They may play the role of premotor neurons or be involved in the organization of the swallowing drive to the various motoneurons involved in swallowing within a single motor nucleus. They might also be involved in the bilateral coordination of the moto­neuron pools (Car & Amri, 1987; Jean, 2001; Kessler & Jean, 1985; Ono et al.,
1998). There is also a population of inter-
neurons, identified more rostrally in the pons, that fire during the oropharyn­geal phase of swallowing. These inter­neurons have been classified as sensory relay neurons and are thought to pro­vide information from the oropharyn­geal receptors to the higher nervous centers and may help coordinate swal­lowing and respiration (Dutschmann & Dick, 2012; Jean et al., 1994).
In conclusion, the dorsal swallow-
ing group interneurons are involved in initiating the swallowing sequence. They stimulate the interneurons of the ventral swallowing group, which then modulate and coordinate the stimu­lation of the various motoneurons involved in the swallowing sequence (Bieger, 2001; Roda et al., 2002).
ESOPHAGEAL PHASE
The bolus is transported down the esophagus into the stomach. The esophageal phase is quite simple and consists of a peristaltic wave of contrac­tion that propagates down the esopha­gus. There is considerable variability in the speed and strength of the esopha­geal contractile wave. Once initiated,
1. ANATOMY AND PHYSIOLOGY OF DEGLUTITION
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it is not an all-or-none phenomenon but may dissipate before reaching the lower esophageal sphincter. Sensory feedback likely plays a role in regu­lating the speed and intensity of the esophageal peristaltic wave, depend­ing on the characteristics of the bolus. The lower esophageal sphincter is a site of high pressure, resulting from tonic contraction of the smooth muscle mak­ing up the sphincter. Increased pressure within the sphincter prevents reflux of stomach contents into the esophagus. During swallowing, the lower esopha­geal sphincter tone is inhibited, relax­ing the sphincter for bolus passage into the stomach (Jean, 2001).
Secondary esophageal peristalsis is defined as peristalsis without a pre­ceding oropharyngeal phase of swal­lowing. Secondary peristalsis occurs in response to stimulation of esopha­geal sensory receptors by distension of the esophageal lumen and is other­wise similar in character, with regard to strength and speed of contraction, to primary esophageal peristalsis. Ter­tiary peristalsis of the esophagus refers to peristalsis of the smooth muscle portion of the esophagus, unrelated to extrinsic innervation (Jean, 2001).
The esophageal phase of swallowing requires both excitatory and inhibitory input to the muscles of the esophagus. At rest, the esophagus is electromyo­graphically silent. All of the esopha­geal motoneurons are strongly inhib­ited during the oropharyngeal phase of swallowing, and the contractile wave of the esophagus during the esophageal phase is preceded by inhibitory input. Once the bolus enters the esophagus, bolus movement involves the coordi­nated contraction of the smooth and striated muscles of the esophagus. Con-
traction of esophageal striated muscle is controlled by the motor nuclei of the brainstem (nucleus ambiguus) while smooth muscle contraction is con­trolled by the autonomic nervous sys­tem. Smooth muscle of the esophagus is innervated by preganglionic fibers originating in the vagal motor nucleus. Similar to the muscles of the orophar­ynx, the muscles of the esophagus are inhibited and stimulated by motoneu­rons under the control of interneurons associated with the swallowing central pattern generator. They regulate the esophagus and coordinate the oropha­ryngeal and esophageal phases of swal­lowing. It is believed that fewer inter­neurons are involved in regulating the esophageal phase of deglutition and that central control may be more depen­dent on afferent input than during oro­pharyngeal swallowing (Jean, 2001).
STUDY QUESTIONS
1. What are the four phases of deglu­tition? Which are under voluntary control, and which are primar­ily involuntary or “reflexive” in nature?
2. What are the three sphincters in the upper aerodigestive tract? Which chambers do they divide? How do they open and close?
3. What muscles are involved in bolus propulsion through the pharynx?
4. What sensory nerves are important in triggering the pharyngeal phase of swallowing and what areas of the mucosa do they supply?
5. Describe in general terms what is known about the central control of pharyngeal swallowing. What is the central pattern generator?
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DYSPHAGIA ASSESSMENT AND TREATMENT PLANNING: A TEAM APPROACH
What are the inputs to the central pattern generator? How does the central pattern generator control swallowing?
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constrictor
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the salivatory nucleus
2/3 of the tongue and
parasympathetic fibers to
Sensation from the anterior
pharyngeal mucosa
Sensation to posterior
1/3 of the tongue and
phase of swallowing
and stabilization of tongue
base during transition from the
Bolus preparation (mastication)
Temporalis
Lateral Pterygoid
Medial Pterygoid
Muscles of
Divided Cranial Nerve Chart for Chapter 1
Mastication
preparatory phase to the oral
Masseter
Elevation of the hyoid bone
during the pharyngeal phase of
Mylohyoid
pharyngeal chamber
the tongue base, opening the
swallowing. Pull the larynx under
the Digastric
Anterior Belly of
Muscles
Suprahyoid
3
V
Tenses the soft palate during
elevation against the superior
Palatini
Tensor Veli
Palatal Muscle
Orbicularis Oris Anterior oral sphincter
during preparatory phase
Maintain bolus between teeth
Buccinator
Stylopharyngeus Shorten the pharynx
Muscles
Pharyngeal
Plexus
Pharyngeal
Cranial Nerve Branch Muscle Group Muscles Role During Swallowing Other
Nerve
V, Trigeminal
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VII, Facial Nerve Facial Muscles
IX,
Nerve
Glossopharyngeal
continues
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Depresses the palate and elevates the tongue base
during the preparatory phase of swallowing: posterior oral
Palatoglossus
cavity sphincter
Elevates the palate against the nasopharyngeal walls during
Palatal
Muscles
the pharyngeal phase of swallowing: sphincter between
Levator Veli
oropharynx and nasopharynx
Palatini
of swallowing
Shorten the pharynx during the pharyngeal phase
Palatopharyngeus
Muscles
Pharyngeal
the nasopharynx
Contracts against the soft palate to close off
Superior
Constrictor
Pharyngeal
bolus from the pharynx
phase of swallowing and is required for clearance of the
Contracts against the tongue base during the pharyngeal
Middle
Constrictor
Pharyngeal
Muscles
Constrictor
Pharyngeal
Contracts against the tongue base to clear bolus from
the pharynx during the pharyngeal phase of swallowing.
Inferior
Pharyngeal
pharyngo-esophageal sphincter.
Confluent with the cricopharyngeus muscle that forms the
Constrictor/
Cricopharyngeus
Cranial Nerve Branch Muscle Group Muscles Role During Swallowing
Plexus
Pharyngeal
X, Vagus Nerve
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Sensation from
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the larynx above
the vocal folds
Sensation from
the larynx below
the vocal folds
and the trachea
esophagus
Elevate the hyoid bone
continued
Cricothyroid
Nerve
Superior
Laryngeal
Thyroarytenoid
Cricoarytenoid
Recurrent
muscles adduct the vocal folds
The cricoarytenoid and thyroarytenoid
Posterior
Inner Arytenoid
Muscles
Laryngeal
Nerve
Laryngeal
preparatory phase, move the bolus
Move and position the bolus during
Cricoarytenoid
and contract against the pharyngeal
into the pharynx during the oral phase,
constrictors to propel the bolus into the
Hyoglossus
Styloglossus
Genioglossus
Tongue
Muscles
Thyrohyoid
Geniohyoid
Elevator
Muscles
Laryngeal
Chart for Chapter 1
Cranial Nerve Branch Muscle Group Muscles Role During Swallowing Other
Nerve
X, Vagus Nerve
XII, Hypoglossal
C1
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History and Physical
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Examination in Dysphagia
Katherine A. Kendall
Dysphagia is the sensation that solids or liquids are not being swallowed correctly. A comprehensive dysphagia evaluation includes determining not only the cause of dysphagia but also the dysphagia consequences, includ­ing the patient’s nutritional status, food management, oral care, swallowing issues, weight fluctuations, and airway protection.
Possible etiologies of dysphagia in­clude neuromuscular disease involving the oral and pharyngeal musculature normally active during swallowing, altered anatomy (such as occurs after surgical resections), radiation therapy, trauma, cervical osteophytes, pharyn­geal diverticuli, cricopharyngeal spasm, foreign bodies, tumors, and mucosal irritation or injury. Patients at risk for dysphagia may have an underlying medical condition that predisposes them to difficulty swallowing, such as head or chest trauma, neuromuscular
disease, brain tumor, head and neck cancer, or stroke. It is more difficult to identify dysphagic patients with condi­tions that may not clearly signal dys­phagia. Patients with dementia or other mental debilitation, elderly patients, and malnourished or deconditioned patients may fall into this category.
All critically ill patients are at risk for dysphagia due to altered levels of con­sciousness and general deconditioning. Deconditioning leads to weakness of the musculature involved in both bolus propulsion and preparation and airway protection during deglutition. Decon­ditioned patients lack breath support and have a poor cough in response to airway penetration by food or liquid, making them less able to respond effec­tively to even mild aspiration. Evidence of repeated fevers, tachycardia, tach­ypnea, or pneumonia in a patient should stimulate concern these symp­toms could be related to aspiration.
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