6.15: Diseases of the Nervous System
- Page ID
- 84022
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Strokes
Strokes are the fourth leading cause of death among people over age 65, accounting for approximately 9 percent of all these deaths. Beginning at a rate of less than 6 percent at age 65, the percentage of deaths from strokes rises steadily as age increases, surpassing 12 percent for those over age 85. (Suggestion 137.02.06)
Heart disease accounts for 4.5 times as many deaths, and cancer, which is the second leading cause of death among the elderly, accounts for more than twice as many deaths among people above age 65. While the death rate from cancer has remained stable for many years, the death rates from strokes and heart disease have declined steadily since about 1960. These declines are probably due in large part to better prevention of atherosclerosis and better diagnosis and treatment of strokes and heart disease. (Suggestions: Chap 06 - 137-2-6)
Many people who have a stroke survive. Therefore, not only the percentage of deaths but also the overall incidence of strokes increases with age, especially after age 65. About 4.5 percent of those between 65 and 75 years of age have a stroke, and the rate among those over age 75 is about 7.3 percent. Strokes occur more frequently in men than in women and much more frequently in Blacks than in Whites. Those who survive are often left with serious lifelong disabilities.
|
Rank |
Cause of death |
Number (thousands) |
Percent of total |
|---|---|---|---|
|
All causes |
2,814 |
100.0 |
|
|
1 |
Diseases of heart |
647 |
23.0 |
|
2 |
Malignant neoplasms |
599 |
21.3 |
|
3 |
Chronic lower respiratory diseases |
170 |
6.0 |
|
4 |
Cerebrovascular diseases |
160 |
5.7 |
|
5 |
Alzheimer disease |
146 |
5.2 |
|
6 |
Diabetes mellitus |
121 |
4.3 |
|
7 |
Accidents (unintentional injuries) |
84 |
3.0 |
|
8 |
Influenza and pneumonia |
56 |
2.0 |
|
9 |
Nephritis, nephrotic syndrome and nephrosis |
51 |
1.8 |
|
10 |
Parkinson disease |
47 |
1.7 |
|
All others (approx.) |
780 |
26.0 |
|
Rank |
Cause of death |
Number (thousands) |
Percent of total |
|---|---|---|---|
|
All causes |
2,067 |
100.0 |
|
|
1 |
Diseases of heart |
519 |
25.1 |
|
2 |
Malignant neoplasms |
427 |
20.7 |
|
3 |
Chronic lower respiratory diseases |
136 |
6.6 |
|
4 |
Cerebrovascular diseases |
125 |
6.1 |
|
5 |
Alzheimer disease |
120 |
5.8 |
|
6 |
Diabetes mellitus |
59 |
2.9 |
|
7 |
Accidents (unintentional injuries) |
55 |
2.7 |
|
8 |
Influenza and pneumonia |
46 |
2.3 |
|
9 |
Nephritis, nephrotic syndrome and nephrosis |
41 |
2.0 |
|
10 |
Parkinson disease |
31 |
1.5 |
|
All other causes |
503 |
24.4 |
Causes and Types
To understand how and why strokes occur, some additional information about the brain must be understood. Most of these facts are also true of the heart.
Brain neurons are always very active and therefore need a constant supply of energy. This energy is obtained by breaking down glucose in processes that consume oxygen and thereby prevent the formation of lactic acid and other harmful waste products. Flowing blood delivers the glucose and oxygen to the brain. If the supply of glucose or oxygen drops, the brain neurons will be injured or killed. A low oxygen supply for a few seconds will cause the neurons to malfunction, and a very low oxygen supply for several minutes can result in neuron death. The brain can adjust the amount of blood flow it receives by signaling the heart to adjust cardiac output, directing blood vessels throughout the body to adjust blood pressure, and constricting or dilating its own blood vessels.
Blood being pumped to the brain by the left ventricle passes first through part of the aorta and then through the arteries (carotid and vertebral arteries) that lead up the neck and into the skull (Figure 6.9). Blood can be felt pulsing through the carotid arteries on either side of the neck. Branches from these ascending arteries carry blood over the brain's surface and deep into the brain.
Strokes occur when blood flow to and through the brain is disrupted. Because of the sudden and devastating effects on the brain, the victim may appear to have been struck with a heavy blow, hence the name "stroke." Since strokes affect the brain and are almost always caused by abnormalities in the blood vessels or heart, they are also called cerebrovascular accidents (CVAs).
The most common circulatory system problem resulting in strokes is atherosclerosis. As in all arteries, atherosclerosis in brain arteries reduces blood flow by causing them to become narrow, rough, and stiff. Recall that roughness leads to thrombus and embolus formation, blocking blood flow, and that stiffness prevents an artery from dilating when necessary (Figure 4.7, Figure 6.10). Blood flow to the brain can also be reduced by emboli formed on a myocardial infarction that causes roughness of the inner lining of the heart. Additional causes of blocked brain arteries include emboli or pieces of plaque that break free from the wall of an artery leading to the brain. Coronary artery disease may decrease blood flow by reducing heart functioning. Since all these strokes prevent adequate blood flow in the brain, they are called ischemic strokes. Ischemia means inadequate blood flow, and about 80 percent of all strokes are ischemic strokes.
Thrombus formation, narrowing, and stiffening in brain arteries develop gradually, and there is some time for enzymes in the blood to dissolve some of the thrombus and for blood vessels to compensate for the reduced flow by dilating. Sometimes this restores blood flow sufficiently so that even though neurons are injured, they survive. Additional neuron injury occurs when blood flow is restored because the increase in O2 combined with injured cells causes an increase in free radical production and damage. Injured neurons can repair themselves and regain their normal functions.
Ischemic strokes from emboli tend to produce greater injury and more neuron death because they cause blood flow to be stopped suddenly and completely. Even if the blocked artery dilates, the embolus is likely to slide farther along until it gets stuck at the next narrowing. Furthermore, since a rough spot in the heart or in an artery may continue to produce emboli, many brain regions may be affected and many strokes can occur in succession.
After a stroke, the neurons that were killed are not replaced since neurons cannot reproduce. However, the remaining neurons may form new dendrites and synapses to compensate for the dead neurons. The surviving neurons may be trained to take on some of the jobs previously performed by the killed neurons.
Atherosclerosis of brain arteries also causes strokes in another way. Arteries weakened by atherosclerosis can rupture and bleed, causing hemorrhagic strokes. These constitute the remaining 20 percent of all strokes. Since they are often associated with high blood pressure, hemorrhagic strokes are also referred to as hypertensive hemorrhagic stokes.
When an artery in the brain ruptures, the region it supplies no longer receives adequate blood flow because some of the blood is leaking. Neurons near the site of the rupture are injured as blood sprays on them and pushes them apart and aside. The hemoglobin that leaks out of the red blood cells further injures these neurons. Part of the injury is from free radicals produced in the presence of iron in hemoglobin.
Hemorrhagic strokes cause additional brain damage because as more blood leaks from the artery, it increases the pressure inside the skull. This condition begins to damage neurons in all parts of the brain. The pressure also tends to compress vessels, reducing blood flow to many parts of the brain. If the blood pushes the brain far out of position, more neurons will be torn and crushed and more blood vessels will be squeezed shut. Pressure within the skull increases further when inflammation in the injured areas causes the brain to swell, and all areas of the brain can be injured. If the brain regions controlling the heart, respiration, or blood pressure are affected, the victim's life is severely threatened.
Since hemorrhagic strokes can injure many parts of the brain, they are more serious than ischemic strokes and are much more likely to cause death. About 80 percent of all hemorrhagic strokes in people with high blood pressure are fatal.
Signs and Symptoms
Malfunctioning of the brain starts as soon as a stroke begins. Depending on which regions are injured and the severity of the damage, the malfunctions are apparent as any of a wide variety of signs and symptoms. Some more common ones are tingling, numbness, and muscle weakness or paralysis in one or more parts of the body. These alterations often occur on only one side of the body. Other frequently encountered changes include loss of balance or muscle coordination, altered vision, difficulty speaking, mental confusion, and diminished or lost consciousness.
Sometimes the signs and symptoms disappear in a few seconds or hours. Strokes of this type are called transient ischemic attacks (TIAs) because they result from a brief decline in blood flow and the injured neurons recover quickly. TIAs frequently occur over and over in exactly the same way because a thrombus forms in the same place in a brain artery. Though TIAs may appear to be unimportant, they are often followed by more serious strokes.
The signs and symptoms of other strokes last for days or weeks and subside very gradually, if at all. Strokes of this type are referred to as reversible ischemic neurological deficits (RINDs) because the brain is able to regain some of its functions.
The third type of stroke is called a completed stroke because the signs and symptoms develop quickly and show no improvement.
Treatments
The best way to reduce the effects of strokes is prevention. Since most strokes result from atherosclerosis, this entails reducing the risk factors for atherosclerosis. This process should begin as soon as possible and continue throughout one's life (Chapter 4).
Other ways of reducing the risk of a stroke in individuals of advanced age include reducing high blood pressure, treating blood disorders, and avoiding exhaustion. When a person seems to be having a stroke, medical attention should be obtained immediately to minimize possible complications.
Treatments for strokes involve reducing the risk of having another stroke and may include medications or surgery. During and after medical treatment, steps should be taken to provide psychological and social support for the stroke patient and the members of his or her family. Physical therapy and rehabilitation often help the patient improve or compensate for functions detrimentally affected by the stroke.
Many stroke patients are disabled for the rest of their lives. The disabilities not only adversely affect their ability to care for their physical needs but also may impinge heavily on their self‑image, mental health, interactions with others, and ability to support themselves economically. The cost of treatment and care may add substantially to the economic difficulties.