The Neuroscience on the Web Series:
CMSD 642 Neuropathologies of Swallowing and Speech

CSU, Chico, Patrick McCaffrey, Ph. D

Chapter 5. The Nature of the Swallow

The Nature of Dysphagia (Logemann, 1983, 1989, 1997; Cherney, 1994)

Aspiration occurs whenever food enters the airway below the true vocal folds. Aspiration can occur before, during, or after the swallow.

Aspiration before the swallow

Aspiration occurs before the swallow in the case of a delayed or absent initiation of the swallow. It may also be the result of poor tongue control, which allows food to trickle into the pharynx while the patient is still chewing. Apparently, a "neurological override" exists which prevents the initiation of the swallow while one is still chewing (Logemann, 1983, 1989, 1997). TRY IT!

Aspiration during the swallow

Aspiration occurs during the swallow when the vocal folds fail to adduct or the larynx fails to elevate. (Remember that this type of dysphagia is uncommon. Only 5% of dysphagias involve problems with airway closure).

Aspiration after the swallow

Aspiration can occur after the swallow in several different circumstances:

    The patient may pocket food in the oral cavity. Later, when he or she lies down to sleep, the food will fall down into the airway.

    Food may get stuck in the pharyngeal recesses. This happens to everyone, but someone with a normal system would realize that the food was there and swallow again. A CVA or TBI patient may have a sensory impairment and allow the food to drop into the larynx.

    Due to reduced laryngeal elevation, food may remain on top of the larynx (Logemann, 1989, 1997).

Types of Dysphagia

The most common type of dysphagia is delayed or absent initiation of the pharyngeal stage of the swallow. Eighty percent of CVA patients who have dysphagia have this type of problem (Logemann, 1989, 1997).

It is common for patients with this type of disorder to keep trying to push the bolus into the pharynx with the tongue. Eventually, they will succeed. Where the food goes when this happens depends on three things: the posture of the patient, the consistency of the food and size of the bolus. Smaller amounts of thick substances will generally lodge in the pharyngeal recesses rather than going directly down the airway.

As a patient moves the tongue and tries to push the bolus into the pharynx, the movements of the tongue and the hyoid bone look a lot like a swallow. It will be difficult to tell whether or not the patient is aspirating. A number of patients aspirate without coughing. Also, food may be lodging in the pharyngeal recesses, which will hold several teaspoons of material, before being aspirated.

Disorders of the pharyngeal stage of the swallow are the most prevalent type of dysphagia among the CVA population; over 90% have pharyngeal stage problems. Reduced tongue driving force or poor pharyngeal stripping action is an especially common problem among those who have had CVAs. This causes food residue to accumulate in the valleculae and may lead to aspiration after the swallow. Pharyngeal stripping action is usually the last part of the swallowing process to recover. No specific site of lesion is associated with this problem.

The majority of patients who are NPO have pharyngeal stage problems.

Fifty percent of those who have pharyngeal stage problems also have oral stage problems.

Half of CVA patients with dysphagia have problems that affect the oral stage of the swallow. Fifty percent of those have reduced or abnormal tongue movements that affect the initiation of the swallow. Typically, tongue control problems are not sufficiently severe to cause aspiration. No specific site of lesion is associated with tongue movement problems.

Only 5% of CVA patients have problems with vocal fold adduction. This type of difficulty only occurs with brain stem (cranial nerve x) lesions.

There are generally no problems with airway closure following a cortical stroke, unless there are bi-lateral upper motor neuron lesions (pseudo bulbar palsy).

Only 5% of CVA patients have swallowing problems caused by the failure of the cricopharyngeus muscle (p.e. segment) to relax. If the p.e. segment does fail to relax, food will build up in the pharynx and may be aspirated. In this case food residue will be accumulated in the pyriform sinuses, or in cases of severe problems, throughout the lower portion of the pharynx, and may cause aspiration after the swallow.

*** Typically, each patient will have more than one type of swallowing problem.

Site of lesion

There is currently enough evidence to specify the specific type of swallowing problem associated with particular sites of lesion caused by stroke.

Brain stem stroke typically causes the most severe cases of dysphagia. Damage to the medulla is particularly devastating as is to be expected since the "swallowing center" and the nuclei of most of the cranial nerves involved in swallowing are located there. As the cranial nerves are lower motor neurons, they form the final common pathway for all motor (pyramidal and extrapyramidal tracts) impulses traveling from the brain to the muscles involved in deglutition and speech (Logemann, 1983, 1997, Reed, 2011).

According to Reed, 2011 "Many people with brainstem strokes cannot eat and drink safely due to the risk of aspiration." Patients with unilateral medullary lesions may have functional or even normal oral control. However, they usually have significant problems with the pharyngeal stage of the swallow (the cranial nerves that innervate the pharynx and larynx originate in the medulla). They may have one or more of the following problems: extreme delay in the initiation of the swallow response (10-15 seconds) and reduction in both elevation and anterior movement of the larynx. This in turn may lead to reduced opening of the criopharyngeus muscle. They may also have unilateral pharyngeal weakness and unilateral vocal fold paralysis. In some cases, patients will not recover their swallow for 4 to 6 months or ever.

Subcortical stroke can affect both sensory and motor pathways. It may cause problems in both the oral and pharyngeal stages of the swallow, including:

• Mild delays in oral transit time (3-5 seconds)

• Mild delays in initiation of the pharyngeal swallow ( 2-3 seconds)

• Impairments in the timing of the neuromuscular components of the pharyngeal swallow. (Logemann, 1989)g

Unilateral Left Hemisphere Stroke (Cortical)  
(Cherney, Pannell, and Cantieri, 1994; Logemann, 1983, 1989, 1997)

A lesion in this area may cause apraxia of the swallow. The tongue may not respond to food or may make searching movements prior to transporting the bolus. Patients with this kind of problem may have more success with oral feeding if they are allowed to feed themselves. This makes the swallow more "automatic." Other problems that occur with this type of lesion include:

  • Mild delays in oral transit (3-5 seconds)
  • Mild delays in the initiation of the pharyngeal swallow (2-3 seconds)
  • The pharyngeal stage should be normal once it is initiated since it does not require a lot of cortical input.

Unilateral Right Hemisphere Stroke (Cortical)

The following problems may be experienced:

    Mild oral transit delays (2-3 seconds)

    Slightly longer pharyngeal delays (3-5 seconds)

    Delayed laryngeal elevation

      The dysphagias produced by right hemisphere lesions while anatomically and physiologically no more severe than those resulting from left hemisphere damage have poorer outcomes. Patients with right hemisphere damage tend to have attentional problems and exhibit poor judgment including impulsivity. These characteristics reduce their ability to use compensatory strategies for safe swallowing.

Multiple Strokes often cause significant swallowing problems that affect both the oral and the pharyngeal stages. Also, cognitive ability may be impaired, reducing the patient's ability to use compensatory strategies. According to Logemann (1989), the swallow is never quite the same after a stroke even when a patient is able to return to a regular diet. When a patient has another stroke later, the already compromised mechanism is further damaged.

In recovery of the swallow, tongue movement is generally the first part of the process to improve, followed by the initiation of the swallow. Pharyngeal stripping action is usually the last part of the process to improve in recovery.

Recovery is most rapid in the first 3 or 4 weeks after a stroke. Therefore, an SLP should always re-evaluate an NPO patient about one month after a stroke.

Generally, if the swallow is going to recover it will do so within 6 or 7 weeks after a stroke.


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Other courses in the Neuroscience on the Web series:
CMSD 620 Neuroanatomy | CMSD 636, Neuropathologies of Language and Cognition

Copyright, 1998-2013. Patrick McCaffrey, Ph. D. .