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

CSU, Chico, Patrick McCaffrey, Ph.D


Chapter 1. The Role of the Speech-Language Pathologist in Dysphagia / Causes, Prevention, and Incidence

Speech-language pathologists teach patients compensatory techniques for eating and swallowing. They also make recommendations about diets, specifying the consistency of foods that a patient can safely consume. e.g. thick/thin liquids, puree/mechanical soft etc.

Assessment of Swallowing and Remediation Techniques

Speech pathologists assess the swallowing abilities of patients through bed-side evaluations and also through the use of radiographic techniques when necessary.a video fluoroscopic study may be done.

The speech pathologist should be aware that a swallowing patient's neurological status may change due to additional stroke(s). A patient who was previously able to swallow safely may begin to aspirate and require re-evaluation. Silent aspiration, or aspiration of food and liquids without coughing, can occur as a result of neurological damage. (If food or liquid enters the respiratory system of a normal, healthy individual, it induces coughing.) Silent aspiration can cause pneumonia, with a temperature spike being the first indication that food or liquids are entering the lungs

Causes, Prevention, and Incidence of Dysphagia 
(Logemann, 1989,1998; Miller and Groher, 1984, Cherney 1994)

Patients may be treated for dysphagia after suffering a stroke or after traumatic brain injury. Other causes of dysphagia include brain tumor, spinal cord injuries, progressive diseases like Parkinson's Disease and multiple sclerosis and ALS as well as metabolic encephalopathy (liver disease that will cause brain damage).

The exact incidence of dysphagia in the population of adults with neurogenic disorders is unknown. However, when the Rehabilitation Institute of Chicago surveyed their records, they found that about one third of such patients in their facility had some type of dysphagia (Cherney, 1994).

According to Cherney (1994), stroke was the most common cause of dysphagia, accounting for about half of the cases. Bilateral cortical stroke was the type of CVA most likely to cause dysphagia. Unilateral right hemisphere lesions cause more dysphagia than do unilateral left hemisphere lesions. This probably occurs because right hemisphere lesions often cause impulsivity, poor judgment, and reduced ability to follow instructions. Approximately one third of stroke patients have some type of dysphagia.

Traumatic Brain Injury (TBI) was the second most common cause of dysphagia, being the cause of about 20% of swallowing problems seen at that facility. Overall, about 25% of patients suffering from Traumatic Brain Injury have some type of dysphagia. As with CVA it seems reasonable to assume that those with right hemisphere lesions would have more problems.

Stroke tends to cause mild or moderate dysphagia. However I have worked with many CVAs who were quite severe. TBI more often causes severe dysphagia.

Stroke

A stroke or cerebral vascular accident is the temporary or permanent loss of functioning brain tissue due to an interruption in the blood supply. There are two types of stroke; those that result from a full or partial blockage of an artery and those caused by hemorrhages, or ruptures of intracranial blood vessels.

Approximately 300,000 people have strokes in the U.S. each year. The following factors predispose an individual to stroke:

Primary Hypertension greatly increases a person's risk of suffering a CVA. Primary hypertension refers to elevated diastolic or systolic blood pressure. Systolic blood pressure (upper number) is measured when the heart is contracting, while diastolic pressure (lower number) is measured when the heart muscle is between beats. Normal blood pressure is 120/80 (mm. of mercury Hg.), while upper limits of normal are 140/90 (Tabor's Cyclopedic Medical Dictionary). During strenuous exercise, a normal person's blood pressure will go up into the high range temporarily. In cases of primary hypertension, blood pressure remains in the high range regardless of activity level. Untreated hypertension increases the likelihood of stroke by pushing plaque up against arterial walls, causing stenosis which sometimes leads to thrombosis. The cause of primary hypertension is unknown, but is seems to be inherited.

Smoking and obesity further increase the risk of vascular problems in those who have hypertension. Mild hypertension seems to respond to exercise.

High Cholesterol Levels (hypercholesterolemia) also increase the risk of stroke. HDL or High Density Lipoprotein is the "good" cholesterol. LDL or Low Density Lipoprotein is the "bad" cholesterol. It is all right to have elevated levels of HDL, but having a high concentration of LDL in the blood is a health risk. Overall cholesterol levels should be under 200.

Hypercholesterolemia can cause stroke even in very young people

There is research that supports the position that arterial inflammation may be more predective of stroke and heart attack than cholesterol level. A simple blood test that measures C-reactive factor can indicate the amount of inflammation.

Eating Red Meat

A study in the journal Nature Medicine (2013), points out that carnitine is a compound in red meat that is also in some energy drinks. Certain bacteria in the digestive tract convert carnitine into TMAO which promotes atherosclerosis, or a thickening of the artieries. Researchers led by Stanley Hazen, chief of cellular and molecular medicine at the Cleveland Clinic, tested the carnitine and TMAO levels of omnivores, vegans and vegetarians. Robert A. Koeth etal. 2013 examined records of 2,595 patients undergoing cardiac evaluations. Patients with high levels of TMAO, the more carnitine in the blood, were more likely to develop cardiovascular disease, heart attacks, stroke and death. A number of other studies have linked consumption of red and processed meat with cardiovascular disease and some cancers.

There are two principle types of stroke, ischemic and hemorrhagic.

Ischemic strokes

The term "ischemia" refers to a lack of blood-borne oxygen. Ischemic strokes are more common than hemorrhagic strokes and may be caused by stenosis, thrombosis, or thrombo-emboli.

Stenosis is a general term that means "narrowing." In this case, it refers to the narrowing of an artery due to the build-up of plaque. As the artery is not completely blocked, some blood does pass through it. However, if at least 50% of normal blood pressure is not maintained, brain damage will occur.

Thrombosis refers to a complete blockage of an artery due to a build-up of plaque.

Thrombo-emboli are pieces of plaque which break lose from thrombi and travel through the arterial system of the brain until they reach a narrowed area and lodge there, cutting off blood supply to brain tissue beyond that point. This sometimes occurs when a normally sedentary person engages in strenuous activity. A blockage in the middle cerebral artery could result in aphasia.

Two different type of ischemic events are warning signs that a stroke is likely to occur in the near future.

TIA or Transient Ischemic Attack

This is a transient disturbance of the blood supply to a localized part of the brain which produces a temporary focal lesion. Unlike strokes, TIAs resolve in spontaneous and complete recovery within one day. TIAs typically last between two and fifteen minutes, although such an event could conceivably last as long as twenty-four hours. It is also possible to have a series of many brief TIAs during one day. For example, a patient might have 20 transient ischemic attacks within a twenty-four hour period. The communicating arteries in the circle of Willis may prevent an actual stroke by shunting blood around a thrombosis.

Symptoms of TIAs mimic those of stroke. These attacks may cause temporary aphasia, numbness, and impairments of speaking, reading, and writing abilities. Dizziness and visual problems, such as blindness in part of the visual field, also occur. Sometimes TIA's are very mild and involve only numbness in a limb, or loss of sight in one eye. Severe TIAs can not be differentiated from a stroke until recovery occurs. I had one patient whose first TIA occurred while he was eating lunch with his wife. She noticed that he had stopped eating and was just sitting there with food falling out of his mouth. He recovered completely within twelve hours. A change of lifestyle after a TIA may prevent a cerebral vascular accident (CVA). Patients should see their doctors about an appropriate exercise and diet program. The doctor may advise a vegan or vegetarian diet which might help prevent an actual stroke
.

RIND or Reversible Ischemic Neurological Defect

Some professionals feel that the term RIND is no longer applicable. That it is really a stroke. A RIND is a lengthy TIA. The term RIND is usually applied to attacks that continue for more than twelve hours without interruption, although some RINDs endure for several days. As is the case with TIAs, patients make a complete recovery from RINDs. (There is some evidence that RINDs do cause some extremely subtle neurological damage, but these minor changes are nothing like the disabilities seen after an actual stroke.)

Sometimes, events that last for twenty-four hours are called TIAs rather than RINDs, so there is some inconsistency in the application of this terminology.

Strokes, TIAs and RINDs are most likely to occur in the morning, when blood pressure is at its lowest. When a person gets out of bed the change in activity level causes a change in blood pressure.

Hemorrhagic Strokes

Hemorrhagic stroke occurs when a cerebral artery ruptures, causing bleeding within the cranium. Such ruptures may be caused by aneurysms or weak spots on the arterial walls. Aneurysms can balloon rather than bursting. The excess pressure resulting from this swelling can also damage brain tissue. The striata artery, a branch of the middle cerebral is quite thin and in some people can rupture easily. Because it takes blood to the internal capsule and basal ganglia a hemorrhage there can damage the axons of descending upper motor neurons (pyramidal tract) or the basal ganglia (nucleus), resulting in weakness or paralysis.

Bleeding due to stroke or TBI can result in hemotoma or pools of congealed blood in the epidural or subdural spaces. The former is usually arterial while the latter is usually venous. Bleeding can also occur within brain tissue. According to Coch and Metter, 1994, this parenchymal bleeding occurs most frequently in the putamen, thalamus, pons and cerebellum. Before the advent of sophisticated scanning technology that allows identification of the affects of light as well as heavy bleeding it was believed that prognosis following hemorrhage was extremely poor. It is now recognized that patients sometimes make a better recovery after a hemorrhagic stroke than an ischemic one. Bleeding, if it is light may irritate brain tissue rather that damaging it. As the brain absorbs the blood the irritated areas may recover completely and normal function is restored.

Strokes can be divided into the categories of completed or progressive.

Completed strokes are the type most commonly seen. In this case the infarction or death of brain tissue has already occurred.

Progressive strokes are those still evolving; meaning that the patient's condition is continuing to deteriorate. Progressive strokes can last for a week or more. This condition is usually due to a severe hemorrhage.

If called in to evaluate a patient with this diagnosis, the speech/language pathologist should test the patient, but explain in the report that major changes could occur shortly. Particular caution should be used when evaluating the swallowing status of such a patient. He/she may be able to swallow safely initially, but develop dysphagia later as his/her condition worsens. Also, progressive strokes tend to happen to people who have very poor cerebral vascular health and are therefore at risk for having other strokes soon.

 

 


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

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