Stroke: A sudden loss of Brain Functioning
Chapter – 1
1.1 Background of the study
Stroke is a sudden loss of brain function caused by the interruption of blood flow to the brain. Stroke is a leading cause of disability worldwide. Hippocrates first described the sudden paralysis that is often associated with stroke. The word stroke was used as a synonym for apoplectic seizure as early as 1599, and is a fairly literal translation of the Greek term. In 1658, in his Apoplexia, Johann Jacob Wepfer (1620–1695) identified the cause of hemorrhagic stroke when he suggested that people who had died of apoplexy had bleeding in their brains. Wepfer also identified the main arteries supplying the brain, the vertebral and carotid arteries, and identified the cause of ischemic stroke (also known as cerebral infarction) when he suggested that apoplexy might be caused by a blockage to those vessels.
Stroke or cerebrovascular accident (CVA) also called brain attack, is a brain injury caused by a sudden interruption in the blood supply of the brain. It occurs when part of the brain does not receives the needed blood flow for one of two reasons: 1) either the blood supply to part of the brain is suddenly interrupted, or 2) because a blood clot blocks a blood vessel or artery, or when a blood vessel in the brain ruptures and blood invades the surrounding areas. As a result, the affected area of the brain cannot function, which might result in an inability to move one or more limbs on one side of the body, inability to understand or formulate speech, or an inability to see one side of the visual field. A stroke is a medical emergency and can cause permanent neurological damage, complications, and death. The traditional definition of stroke, devised by the World Health Organization in the 1970s, is a “neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours”
1.3 Epidemiology of stroke
Stroke is one of the leading causes of long term disability, and of death, in the developed world. Approximately 700,000 Americans per year experience a stroke. It is the third leading cause of death and the leading cause of long-term adult disability in the United States. According to the World Health Organization (WHO) 15 million people suffer from stroke worldwide each year. On average, a stroke occurs every 45 seconds and someone dies from a stroke every 3 minutes. Asymptomatic infarctions, usually lacunar, are present in 7% of MRI scans; 2% of scans detect incidental intracranial aneurysms. Risk factors for stroke include atherosclerosis, advanced age, hypertension (high blood pressure), diabetes mellitus, high cholesterol, cigarette smoking, atrial fibrillation, migraine headachesethnic identity, and some blood clotting disorders.
1.4 Anatomy of stroke
Figure 1: This is an x-ray image of the head after a radio-opaque dye was injected into the arterial system; the image is called an angiogram.
The brain is made out of nerve cells and supporting cells, it is covered by protective layers and it is moistened by the constant circulation of a pristine fluid called “cerebrospinal fluid” (CSF). Like all parts of the body, the brain has vessels that pump blood to it from the heart called arteries and vessels that collect the blood after circulating through the organ for return to the heart called veins. As in most organs of the body, the arteries to the brain carry blood loaded with oxygen and glucose (blood sugar) and the veins carry away blood that has delivered these vital supplies to the cells of the brain and had their waste products dumped in it.
There are special features of the vasculature to the brain that are protective since brain cells are more vulnerable to loss of oxygen and glucose than are the cells of any other portion of the body. One of these features is the circular design of the blood delivery system to the brain. This circle of arteries that joins blood pumped up from the front of the neck ( the carotid arteries) from blood pumped up from the back (the vertebral arteries). In most healthy young people, this system of blood flow is so good that even if one of the arteries is lost altogether (from an injury, for example), the others can make up for it and keep delivering a properly working circulation of fresh arterial blood, and no impairment to the brain cells occurs.
1.5 Classification of Stroke
There are three types of stroke .Such as
1. Ischemic stroke.
2. Hemorrhagic infarct
3. Transient ischemic attack (TIA).
Ischemic strokes are those that are caused by interruption of the blood supply.Ischemic stroke is the most common type of stroke, and it accounts for 83 percent of all strokes. An ischemic stroke occurs when the blood vessel (usually an artery) supplying blood to a part of the brain is blocked by fatty deposits or a blood clot. In an ischemic stroke, blood supply to part of the brain is decreased, leading to dysfunction of the brain tissue in that area. There are four reasons why this might happen:
Ø Thrombosis (obstruction of a blood vessel by a blood clot forming locally)
Ø A cerebral embolism (embolic stroke) -the blockage is caused by a blood clot, air bubble, or fat globule that forms in a blood vessel somewhere in the body, and it travels through the bloodstream into the brain.
Ø Systemic hypo perfusion (general decrease in blood supply, e.g., in shock)
Ø A blockage occurs in the tiny blood vessels deep within the brain.
Figure 2: A slice of brain from the autopsy of a person who suffered an acute middle cerebral artery (MCA) stroke
There are various classification systems for acute ischemic stroke. The Oxford Community Stroke Project classification (OCSP, also known as the Bamford or Oxford classification) relies primarily on the initial symptoms; based on the extent of the symptoms, the stroke episode is classified as total anterior circulation infarct (TACI), partial anterior circulation infarct (PACI), lacunars infarct (LACI) or posterior circulation infarct (POCI). These four entities predict the extent of the stroke, the area of the brain affected the underlying cause, and the prognosis. The TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification is based on clinical symptoms as well as results of further investigations; on this basis, a stroke is classified as being due to (1) thrombosis or embolism due to atherosclerosis of a large artery, (2) embolism of cardiac origin, (3) occlusion of a small blood vessel, (4) other determined cause, (5) undetermined cause (two possible causes, no cause identified, or incomplete investigation).
Figure 3: Hemorrhagic Stroke and Ischemic stroke
Hemorrhagic strokes are the ones which result from rupture of a blood vessel or an abnormal vascular structure.Hemorrhagic stroke is a less common type of stroke, and accounts for 17 percent of all strokes. A hemorrhagic stroke occurs when a blood vessel in the brain ruptures and the blood invades the surrounding areas. This type of stroke can be caused by –
Ø An aneurism (a weakened region of a blood vessels balloons out, and left untreated can burst) or
Ø An arteriovenous malformation (a cluster of abnormally formed blood vessels where one of the vessels bursts).
There are two types of hemorrhagic strokes:
v Intracerebral hemorrhage, the blood vessel ruptures within the brain.
v Subarachnoid hemorrhage, the blood vessel bursts on the surface of the brain, and it bleeds into the area between the brain and the skull.
Figure 4: An intraparenchymal bleed (bottom arrow) with surrounding edema (top arrow)
Intracranial hemorrhage is the accumulation of blood anywhere within the skull vault. A distinction is made between intra-axial hemorrhage (blood inside the brain) and extra-axial hemorrhage (blood inside the skull but outside the brain). Intra-axial hemorrhage is due to intraparenchymal hemorrhage or intraventricular hemorrhage (blood in the ventricular system). The main types of extra-axial hemorrhage are epidural hematoma (bleeding between the Dura mater and the skull), subdural hematoma (in the subdural space) and subarachnoid hemorrhage (between the arachnoids mater and pia mater). Most of the hemorrhagic stroke syndromes have specific symptoms (e.g., headache, previous head injury).
Transient ischemic attack (TIA): Transient ischemic attack (TIA), also called mini-stroke, is a minor or warning stroke. It occurs when the blood supply to the brain is briefly interrupted. This stroke is similar with the ischemic stroke, but its symptoms tend to disappear within the next 24 hours. The obstruction (blood clot), that causes the transient ischemic attack, occurs for a short time and tends to resolve itself in time. A mini-stroke last for a few minutes up to a day and, in some cases, it can be accompanied by typical stroke signs. Even if the symptoms disappear in a short time, a transient ischemic attack is a strong indicator of a possible major ischemic stroke to come.
1.6 Signs and Symptoms of a Stroke
A stroke often appears suddenly, without warning, and its effects on the body are immediate. The common symptoms of a stroke, which appear afterwards, include:
Ø Sudden numbness, weakness, clumsiness, or paralysis on one side of the body. An example of this symptom can be a dropping arm or leg, eyelid, or dribbling mouth. This is one of the most common and recognizable stroke symptoms. This symptom affects only one side of the body and causes difficulties in controlling the arm or leg. In the worst cases, the weakness or paralysis is accompanied by muscle and joint stiffness.
Ø Sudden confusion, slurred speech, trouble speaking, or understanding speech. This is another common symptom in patients that had a stroke. This symptom also includes difficulties reading and writing.
Ø Sudden blurred vision or loss of sight in one or both eyes. The stroke can damage that part of the brain that receives, processes, and interprets the information sent by the eyes to the brain. This can lead to a variety of problems such as double vision, or losing half of the vision field.
Ø Sudden trouble walking, dizziness, loss of balance, or loss of coordination.
Ø Sudden severe headache with no known cause.
Ø Loss of balance or unsteadiness. This can be the result of damage in the part of the brain responsible with the body’s balance, or as a result of paralysis when the muscles become weak.
Ø Dysphasia or difficulties swallowing is another common symptom in patients with stroke. About 50 percent of those that have a stroke have swallowing problems.
Ø Perception and interpretation difficulties. People that suffered a stroke have difficulties recognizing familiar objects or knowing how to use them.
Ø Mental processes impairment. After a stroke, the person can have problems thinking, learning, remembering, concentrating, making decisions, reasoning, and planning.
Ø Incontinence (difficulties controlling the bladder and bowel) can be common right after a stroke, but the problem resolves itself over.
Ø Mood swings. People that suffer a stroke experience emotional ups and downs. They can become depressed, sad, angry, anxious, experience low self-esteem and low confidence.
1.7 Associated symptoms
Ø Headache, and
Ø Vomiting usually occurs more often in hemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing the brain.
Ø If symptoms are maximal at onset, the cause is more likely to be a subarachnoid hemorrhage or an embolic stroke.
1.8 Causes of stroke
There are many different causes of stroke, but whenever a stroke occurs, there has been an interruption of the normal blood supply to brain cells that has gone on long enough to cause death to at least some of them. If the loss is so brief that the brain tissue can quickly recover, and does not die, then a Transient Ischemic Attack (TIA) has occurred, rather than a stroke. The symptoms and signs of a stroke are highly dependent upon the number of cells that are affected, and exactly where these cells are located in the brain. Accordingly, strokes can have many different clinical presentations – ranging from deep coma with the loss of the ability to breathe; to very limited deficits in the ability to move a part of the body, or changes in sensory perception like partial blindness from a restriction in visual field, without any associated problems with movement.
Ordinarily, at least some brain tissue is injured by a stroke – yet not killed. The injury to these cells is reversible. That’s one reason why the amount of recovery during the initial time period after a stroke is difficult to predict, and also why treatment at that time can influence the course of recovery. If the stroke patient survives the stroke, some brain cells may actually recover in time if the injury was not too great.
Ten causes of stroke identified by researchers. Scientists have found ten key health problems that cause almost all strokes.
Ø High blood pressure,
Ø A fat stomach,
Ø Poor diet,
Ø Lack of physical activity,
Ø High levels of bad cholesterol,
Ø Drinking too much,
Ø Stress and depression and
Ø Heart disorders accounted for 90 per cent of strokes.
The research conducted by a team at McMaster University on Ontario, Canada, is one of the most comprehensive looking into the causes of stroke. The factor with the strongest link was high blood pressure which more than doubled the risk of a stroke, they said. Around 150,000 people in Britain each year suffer a stroke and there are 67,000 deaths. It is a leading cause of disability. The study published in The Lancet and presented at The World Congress of Cardiology in Beijing looked at 3,000 people who had a stroke and 3,000 similar people who had not suffered a stroke.
They were questioned about:
Ø Their lifestyle,
Ø Including how much they drank,
Ø Who much exercise they did and
Ø Their diets given a score according to how healthy they were and tests and measurements were carried out by professionals.
Alcohol intake was categorized as never or former drinker, moderate drinker of between one and 30 drinks a month, more than 30 drinks a month and binge drinker who had more than five drinks in one day in the last month. They were classed as physically active if they were involved in walking, cycling, gardening, jogging, football or vigorous swimming for four hours a week or more. The findings showed that current smokers doubled their risk of stroke, poor diet increased the risk by 35 per cent, 30 or more drinks a month or binge drinking increased the risk by half, stress raised the risk by 30 percent and depression by 35 per cent. Being active reduced the risk by about 30 per cent. Martin O’Donnell, lead author said: “Our findings suggest that ten simple risk factors are associated with 90% of the risk of ischemic and intracerebral hemorrhagic stroke worldwide.”Targeted interventions that reduce blood pressure and smoking, and promote physical activity and a healthy diet, could substantially reduce the global burden of stroke.”Andrea Lane, Spokesperson for The Stroke Association said: “Over the years there have been a number of research studies into the causes of stroke, which have identified a number of major risk factors.”This is an extensive and in-depth study and so it’s great to see that the findings support previous research and reflect the preventative advice provided by The Stroke Association.”
1.9 Effects of Strokes
The most common problems in daily life are likely to be caused by:
Ø Weakness or lack of movement (paralysis) in legs and/or arms
Ø Shoulder pain.
Ø Trouble swallowing
Ø Changes to way things are seen or felt (perceptual problems)
Ø Changes to the way things are felt when touched (sensory problems)
Ø Problems thinking or remembering (cognitive problems)
Ø Trouble speaking, reading or writing,
Ø Feeling depressed,
Ø Problems controlling feelings,
The specific abilities that will be lost or affected by stroke depend on the extent of the brain damage and, most importantly, where, in the brain, the stroke occurred: the right hemisphere (or half), the left hemisphere, the cerebellum or the brain stem. Each stroke is different and each person that experiences a stroke is affected differently. Some stroke survivors experience mild symptoms, while other faces severe and lasting damage. Once the stroke occurs, the brain immediately undergoes changes. Without the blood supply which provides the brain with nutrients and oxygen, the brain cells are damaged and can die. Once dead, the cells cannot return to life, but the surrounding areas can recover and take over or substitute some of the lost functions. Usually, the recovery process happens in the first few months that follows the stoke, but in some cases can continue for several years.
The disability level differs from patient to patient, and depends on the type of stroke suffered, the area affected, the location of the affected area, and the extent of the damage. A stroke can occur in any part of the brain causing damages according to those functions controlled by that area. Each part of the brain is involved in different essential functions for the body. Usually, the stroke symptoms and signs occur on the opposite side of the body to the stroke side of the brain.
The human brain is divided in four main parts: (1) the right hemisphere, (2) the left hemisphere, (3) the cerebellum, and (4) the brain stem. In most people, the right hemisphere is responsible for perceptual and spatial skills, the left hemisphere is responsible for language, the cerebellum controls balance and coordination, while the brain stem controls those body functions that do not require conscious control (such as breathing rate, blood pressure, heart rate, eye movement, hearing, speech, and swallowing).
The effects of a stroke can be divided into two main categories:
(1) Body functions.
(2) Cognitive functions.
Effects of Right Hemisphere Strokes
The right hemisphere of the brain controls the movement of the left side of the body so stroke in the right hemisphere often causes paralysis in the left side of the body. This is known as left hemiplegic. Survivors of right-hemisphere strokes may also have problems with their spatial and perceptual abilities. This may cause them to misjudge distances (leading to a fall) or be unable to guide their hands to pick up an object, button a shirt or tie their shoes. They may even be unable to tell right side up from upside-down when trying to read. Along with these physical effects, survivors of right-hemisphere strokes often have judgment difficulties that show up in their behaviour. They often act impulsively, unaware of their impairments and certain of their ability to perform the same tasks as before the stroke. This can be extremely dangerous. It may lead them to try to walk without aid or to try to drive a car. Survivors of right-hemisphere strokes may also experience left-sided neglect. This is a result of visual difficulties that cause them to “forget” or “ignore” objects or people on their left side. Some survivors of right-hemisphere strokes will experience problems with short-term memory. Although they may be able to recall a visit to the seashore that took place 30 years ago, they may be unable to remember what they ate for breakfast that morning.
Effects of Left Hemisphere Strokes
The left hemisphere of the brain controls the movement of the right side of the body. It also controls speech and language abilities for most people. A left-hemisphere stroke often causes paralysis of the right side of the body. This is known as right hemiplegic. Someone who has had a left-hemisphere stroke may also develop aphasia. Aphasia is a catch all term used to describe a wide range of speech and language problems. These problems can be highly specific, affecting only one part of the patient’s ability to communicate, such as the ability to move their speech-related muscles to talk properly. The same patient may be completely unimpaired when it comes to writing, reading or understanding speech. In contrast to survivors of right-hemisphere stroke, patients who have had a left-hemisphere stroke often develop a slow and cautious behaviour. They may need frequent instruction and feedback to finish tasks. Patients with left-hemisphere stroke may develop memory problems similar to those of right-hemisphere stroke survivors. These problems can include shortened retention spans, difficulty in learning new information and problems in conceptualizing and generalizing.
Effects of Brain Stem Strokes
Strokes that occur in the brain stem are especially devastating. The brain stem is the area of the brain that controls all of our involuntary functions, such as breathing rate, blood pressure and heart beat. The brain stem also controls abilities such as eye movements, hearing, speech and swallowing. Since impulses generated in the brain’s hemispheres must travel through the brain stem on their way to the arms and legs, patients with a brain stem stroke may also develop paralysis in one or both sides of the body.
Effects of Cerebellum Strokes
The cerebellum controls many of our reflexes and much of our balance and coordination. A stroke that takes place in the cerebellum can cause abnormal reflexes of the head and torso, coordination and balance problems, dizziness, nausea and vomiting.
Effect of stroke on vision
Visual problems are more common in people who have suffered a stroke affecting the right side of their brain. The damage the stroke does in the brain impacts the visual pathways of the eye which can result in visual field loss, blurry vision, double vision and moving images. When stroke affects the areas of the brain that processes the information we see, it can cause ‘visual neglect’ (lack of awareness to one half of the body or space) as well as difficulties with judging depth and movement. In a few cases, visual problems caused by stroke can improve on their own with time.
Some of the vision problems that occur as a result of a stroke include loss of part of vision or loss of visual field. Visual field is the term used to describe the whole of our vision, from the centre to the periphery. It refers to everything we can see in the periphery (around the edges of our vision) as well as what we are directly looking at (central vision). Strokes can cause whole sections of the visual field to be missing. Other visual problems that may occur as a result of stroke include eye muscle and nerve problems which can result in double vision and moving images as well as other effects such as sensitivity to light.
Other Effects of Stroke
Depression is very common amongst people who have had a stroke. It can be quite severe, affecting both the survivor and his/her family. A depressed person may refuse or neglect to take medications, may not be motivated to take part in physical rehabilitation or may be irritable with others. This in turn makes it difficult for those who wish to help, and tends to deprive the survivor of valuable social contacts that could help dispel the depression. In time the depression may lift gradually, but counseling and appropriate medication may be necessary. In the past, researchers speculated that some of the older anti-depressant drugs might interfere with a person’s mental performance but recent studies suggest that anything that can effectively treat post-stroke depression, whether an old or new treatment, may also improve mental ability and enhance rehabilitation.
Sudden laughing or crying for no apparent reason and difficulty controlling emotional responses also affects many stroke survivors. There may be little happiness or sadness involved, and the excessive emotional display will end as quickly as it started. Apparent changes in personality following a stroke may be very disturbing to the survivor’s family. Stroke affected people may not seem the same person as before. The way in which they think, feel and react may be altered. Problems and activities once tackled easily may be difficult or impossible, while other tasks are unaffected.
The way in which the person affected by stroke reacts to these changes will affect their personality, and may cause changes in control of emotions and behaviour. People affected by stroke may become confused, self-centered, uncooperative and irritable, and may have rapid changes in mood. They may not be able to adjust easily to anything new and may become anxious, annoyed or tearful over seemingly small matters.
1.10 Complications after Stroke
Common complications of a stroke:
- Edema – brain swelling
· Seizu Breathing food into the airway (aspiration)
· Loss of mobility
· Loss of movement or feeling in one or more parts of the body
- Muscle spasticityres – abnormal electrical activity in the brain, which causes convulsions
- Clinical depression – a treatable illness that causes uncontrollable emotional and physical reactions to changes and losses
- Bedsores – ulcers that result from a decreased ability to move
- Limb contractures – shortened muscles in arms or legs that are caused by a reduced range of motion or lack of exercise
- Shoulder pain – a consequence of lack of support or exercise of the arm
- Blood vessel problems – formation of blood clots in the veins
- Urinary tract infection and bladder control – urgency and incontinence
- Pneumonia – results in breathing problems.
· Poor nutrition
· Problems speaking and understanding
· Problems thinking or focusing.
Chapter – 2
Risk factors for stroke
Stroke risk factors are medical conditions or behaviors or traits that make you more likely to develop a stroke. Having one or more risk factors does not mean that you definitely will have a stroke, only that you are more likely to do so. More than 750 thousand people suffer from stroke in the U.S. each year, but up to 50% of strokes could be prevented. In the case of stroke, many of the risk factors can be treated, modified or controlled. However, some risk factors for stroke cannot be changed. Knowing ones risk factors is the first step in preventing stroke. One can change or treat some risk factors, but others can’t. By having regular medical checkups and knowing the risk, one can focus on what can change and lower risk of stroke.
2.1 Risk factors of stroke that can’t control
Ø Age: The risk of stroke increases with advancing age.
Ø Ethnicity: People of First Nations, African, Hispanic, and South Asian descent have greater rates of high blood pressure and diabetes. These conditions increase the risk of stroke.
Ø Family history: The risk of stroke may be higher if a parent or sibling has had a stroke before the age of 65.
Ø Gender: In most age groups, more men than women have stroke, but more women die from stroke. Men have a higher risk of stroke than women who have not reached menopause.
Ø Heredity and race: People whose close blood relations have had a stroke have a higher risk of stroke. African Americans have a higher risk of death and disability from stroke than whites, because they have high blood pressure more often. Hispanic Americans are also at higher risk of stroke.
Ø Prior stroke or transient ischemic attack (TIA): Someone who has had a stroke is at higher risk of having another one. Up to one-third of people who survive a first stroke or TIA will have another stroke within 5 years.
2.2 Risk factors of stroke that can control
Ø Hypertension (High blood pressure).
Ø Atrial fibrillation( an abnormal heart rhythm)
Ø Cigarette smoking.
Ø Excessive alcohol intake
Ø Obesity, unhealthy diet
Ø High cholesterol
Ø Physical inactivity.
Hypertension (High Blood Pressure)
High blood pressure is the most important modifiable risk factor for stroke. The risk of stroke increases 4 to 6 times when the person has high blood pressure. The blood pressure measures the force of blood pushing against the walls of the arteries. When the blood pressure is high, the heart has to pump harder to move the blood through the body, which leads to weak blood vessels and damage to major organs in the body. Normal blood pressure is 120/80 or below, whiles a blood pressure reading of 140/90 and above is considered high blood pressure (or hypertension).
Atrial fibrillation (an abnormal heart rhythm)
Atrial Fibrillation (AF) is a medical condition where the heart beats irregularly because the two upper chambers of the heart beat rapidly and unpredictably. Atrial fibrillation increases the risk of stroke up to 6 times because the heart does not fully pump the blood out, which pools in the heart. When the blood pools in the heart, the risk of blood clots forming is high. Once formed, these blood clots will travel through the bloodstream into the brain obstructing a blood vessel.
Tobacco use damages blood vessels. Don’t smoke and avoid second-hand smoke. This can contribute to atherosclerosis and can also cause the blood vessels to constrict, which leads to restrictions in blood flow. Smoking increases the heart rate and blood pressure. The associated risk increases with the number of cigarettes smoked per day, and passive smoking also increases this risk.
Excessive alcohol intake
It is thought that excessive alcohol intake may also increase the risk of ischemic stroke by bringing about a rise in blood pressure. However, although drinking too much alcohol is known to inflate the risk, people who consume moderate amounts (less than 3 units per day) actually have a lower risk than those who do not drink at all. This may be because moderate alcohol intake can improve blood lipid levels, and so protect against vascular diseases such as stroke.
Obesity, unhealthy diet
Being obese or overweight increases the risk of high blood pressure, high cholesterol, diabetes, heart disease, which all increase the risk for stroke. Unhealthy diet (including a low fruit and vegetable intake and a high salt intake).
Cholesterol is a waxy, fat-like substance produced by the liver and is used in different functions essential for the body. If present in high amounts, cholesterol builds up in the veins and clogs them (a condition called atherosclerosis). The build-up of plaque inside the artery causes the walls to lose their elasticity and become weak and hard.
Figure 5: Image ofHigh Cholesterol
Diabetes is a medical condition where the body either does not produce enough insulin, or the insulin is not properly used. This disease is another major cause of stroke because the body can’t properly process sugar (the basic fuel of the body’s cells) and fats. Diabetes also leads to other medical complications such as high blood pressure, high cholesterol, atherosclerosis, and obesity or excessive weight. Diabetes interferes with the body’s ability to break down blood clots, which leads to an increased risk of ischemic strokes. In general, those that suffer from diabetes have a 2 to 4 times the risk of stroke than the non-diabetic population.
In epidemiological studies comparing highly active to sedentary individuals, physical activities are observed to reduce the risk of both ischemic and hemorrhagic strokes. The 2008 Physical Activity Guidelines for Americans concur in recommending regular physical activity to reduce adverse health outcomes. In this guideline, most health benefits occur with at least 150 minutes a week of moderate intensity, or 75 minutes a week of vigorous intensity of aerobic physical activity. When adults with disabilities are not able to meet these guidelines, they should engage in regular physical activity according to their abilities, and they should avoid inactivity. Exercise reduces blood pressure, decreases body weight, and improves other risk factors, including metabolic syndrome the role of the health provider is important and the physician’s advice regarding physical activity to patients can significantly modify exercise and diet style, including those with a prior stroke. One recent observation of note is associated with the onset of stroke with physical activity. There might be an increased risk of stroke occurrence within 1 hour of moderate or vigorous physical activity.
Drug abuse (certain kinds)
Intravenous drug abuse carries a high risk of stroke from cerebral embolisms (blood clots). Cocaine use has been closely related to strokes, heart attacks, and a variety of other cardiovascular complications. Some of them, even among first-time cocaine users, have been fatal.
Cardiac structural abnormalities
Damaged heart valves can cause chronic heart damage, which can ultimately increase the risk of developing stroke. This is known as valvular heart disease. New evidence shows that heart structure abnormalities including patent foramen ovale and atrial septal defect may possibly increase risk for embolic stroke.
2.3 Risk factors for Ischemic stroke
In general, the risk factors for having an ischemic stroke – a stroke that is caused by a blockage in an artery supplying the brain – may be divided into those that can be modified (improved upon), and those that cannot, as discussed below.Although some risk factors cannot be changed – for example, a person’s gender or age – it is still important to be aware of them. This is because people who have a number of unmodifiable risk factors may benefit from making a greater effort to improve those risk factors that can be modified.In addition to these risk factors, which are often classed as ‘traditional’, we are also starting to learn about more recently identified risk factors.
Modifiable risk factors for Ischemic stroke
Fortunately, we do have control over many of the risk factors for ischemic strokes. These include the following:
- High blood pressure – the most important modifiable risk factor for stroke
- Smoking – this can contribute to atherosclerosis and can also cause the blood vessels to constrict, which leads to restrictions in blood flow. The associated risk increases with the number of cigarettes smoked per day, and passive smoking also increases this risk
- Excessive alcohol intake
- Obesity, unhealthy diet (including a low fruit and vegetable intake and a high salt intake)
- Physical inactivity
- Abnormal lipid levels (dyslipidaemia)
- Diabetes mellitus (associated with stroke and other forms of vascular disease at a younger than average age) and metabolic syndrome
- Carotid artery disease
- Atrial fibrillation, an abnormal heart rhythm
- Patent foramen oval (otherwise known as a ‘hole in heart’) – present in around 25 per cent of the general population, compared with 40 per cent of people who have had a stroke where no other cause is found
- Heart failure, endocarditis and other forms of heart disease
- Oral contraceptives – thought to increase the likelihood of the blood to clot
- Polycythaemia, a condition in which the red blood cell count is increased
- Sleep apnoea, which causes interruptions in breathing while a person sleeps and appears to be associated with a higher risk of stroke and other cardiovascular diseases
- Sickle cell disease, an inherited condition that results in the formation of abnormal, sickle-shaped red blood cells that can block small blood vessels, increasing the risk of an ischemic stroke. There is insufficient evidence to support the suggestion that sickle cell trait – a milder version of the disease – might also increase the risk.
It is thought that excessive alcohol intake may also increase the risk of ischemic stroke by bringing about a rise in blood pressure. However, although drinking too much alcohol is known to inflate the risk, people who consume moderate amounts (less than 3 units per day) actually have a lower risk than those who do not drink at all. This may be because moderate alcohol intake can improve blood lipid levels, and so protect against vascular diseases such as stroke.
Non-modifiable risk factors for Ischemic stroke
Risk factors for stroke that cannot be modified include the following:
- Male gender
- Older age
- Family history
- Past heart attack or stroke
It has also been suggested that migraine may increase the risk of an ischemic stroke, particularly in women under the age of 35. Migraine with aura (in other words, migraine accompanied by additional symptoms such as visual disturbance and numbness or tingling) is associated with reduced blood flow to the brain and inflammation.
Transient ischemic attack, or TIA, is often referred to as a ‘mini-stroke’. Like a stroke, it is a disturbance in the function of the nervous system that is caused by a problem with the blood supply to the brain. However, unlike stroke, the symptoms of TIA settle down within 24 hours.
People who have had a TIA are known to have a higher risk of a stroke in the future. The chance of someone who’s had a TIA having a stroke within 3 months has been estimated to be between 15 and 20 per cent.
Conditions that increase the likelihood of the blood to clot also increase the risk of stroke; examples include Factor V Leiden mutation and Hughes syndrome (also known as anti phospholipid syndrome), although these risks may be reduced by taking anticoagulant treatment.
Recently identified risk markers
Additional markers (indicators) associated with an increased risk of ischemic stroke include elevated levels in the blood of:
- Homocysteine (a marker that is associated with early-onset atherosclerosis)
- Lipoprotein(a) (a type of lipid in the bloodstream that is similar to LDL-cholesterol)
- High-sensitivity C-reactive protein (CRP; a protein in the blood that suggests inflammation)
- High blood levels of fibrinogen (a protein that helps the blood to clot)
- Apolipoprotein B (APOB; the protein part of low-density lipoprotein (LDL).
2.4 Risk factors for Hemorrhagic stroke
Some of the risk factors for a hemorrhagic stroke – a stroke caused by a bleed – differ from those of an ischemic stroke and so are looked at separately.
Modifiable risk factors for Hemorrhagic stroke
Those risk factors for hemorrhagic stroke that we can improve upon include:
- High blood pressure – one of the most important modifiable risk factors for stroke
- Impaired ability of the blood to clot due to medication (‘anti-clotting’ drugs, anticoagulants; or ‘clot-busting’ drugs, thrombolytic)
- Smoking, excess alcohol intake and substance misuse (for example, amphetamines and cocaine)
- Lipid levels. Unlike ischemic strokes, it seems that reducing cholesterol levels actually increases the risk of hemorrhagic strokes
- Vascular malformations. These may include arteriovenous malformations, cavernous haemangiomas and aneurysms (an aneurysm is an abnormal dilation, or bulge, in the wall of an artery.) Vascular malformations are prone to rupture. Fortunately, they can sometimes be treated with surgery to reduce the risk.
- Conditions that interfere with blood clotting, for example, blood dyscrasia (an abnormality in the balance of the different components of the blood). Treatment may lower the risk.
Non-modifiable risk factors for Hemorrhagic stroke
The risk factors for hemorrhagic stroke that cannot be modified include the following:
- Increasing age. This may be partly because older age is associated with small blood vessel disease, which can increase the risk of blood vessel rupture. Increasing age also increases the likelihood of the condition amyloid angiopathy, which leads to protein build-up in the arteries of the brain, increasing the risk of bleeding.
Symptoms similar to a stroke can also sometimes arise as a result of damage to blood vessels in the brain following a head injury.
2.5 Other risk factors that can lead to a stroke
Ø Other factors such as oral contraceptive use
Ø Hormone replacement therapy or
Ø Pregnancy and childbirth in women with pre-existing medical conditions may increase the risk of stroke in specific cases.
Ø Other medical conditions such as amyloid angiopathy and antiphospholipid antibody syndrome
Ø Use of illicit drugs such as cocaine or LSD.
Ø Some medications, such as tamoxifen, phenylpropanolamine, and thrombolytic.
In general, the risk factors for having an ischaemic stroke – a stroke that is caused by a blockage in an artery supplying the brain – may be divided into those that can be modified (improved upon), and those that cannot, as discussed below. Although some risk factors cannot be changed – for example, a person’s gender or age – it is still important to be aware of them. This is because people who have a number of unmodifiable risk factors may benefit from making a greater effort to improve those risk factors that can be modified.In addition to these risk factors, which are often classed as ‘traditional’, we are also starting to learn about more recently identified risk factors. Some of the risk factors for a hemorrhagic stroke – a stroke caused by a bleed – differ from those of an ischemic stroke and so are looked at separately.
2.6 Self Assessment Chart of Stroke Risk
This is just a guide, but it demonstrates measures that can take to decrease your risk of stroke.
|never smoked||quit after smoking for less than 5 years||current smoker less than 20/day||current smoker more than 20/day|
|1 hour strenuous activity at least 3 times per week||very active once or twice a week||moderately active once or twice a week||very little physical activity|
|none known||n/a||family history||diabetic|
|normal||mild high blood pressure||moderate high blood pressure||severe high blood pressure|
|0 – 44||45 – 64||65 – 74||75 +|
|0-4 standard drinks/week||up to 4 drinks/day||more than 4 drinks a day 2 or more days a week||more than 6 drinks, 4 or more days a week|
|0-2 standard drinks a week||up to 2 drinks a day||more than two drinks a day, 2 or more days a week||more than 4 drinks, 4 or more days a week|
|about average for height||slightly overweight||moderately overweight||obese|
|no strokes known||a relative has had a stroke||a relative has had a stroke while younger than 65||several relatives have suffered from stroke|
|below average||average||moderately raised||severely raised|
Chapter – 3
3.1 Mechanisms of Stroke
3.1.1 Biophysical Mechanisms of Stroke
Although the consequences of both ischemic and hemorrhagic stroke are similar in that a vessel obstruction and the resultant reduced blood flow to the brain may lead to neurological deficits and possibly death, the biophysical and hemodynamic mechanisms behind the obstruction of blood flow are different. Biophysical mechanisms for the development of obstructions that ultimately lead to stroke can arise by six distinct processes: atherosclerosis, embolus, thrombus, reduced systemic pressure, hemorrhage, and vasospasm.
Atherosclerosis, commonly referred to as “hardening of the arteries,” is a pathological process in which calcified lipid or fatty deposits from the flowing blood accumulate circumferentially along the innermost intimal layer of the vessel wall (Fig 1?). Atherosclerotic plaques are found almost exclusively at the outer wall (hip) of one or both daughter vessels at major bifurcations, including the carotid. Atherosclerosis and the development of arterial plaques are the product of a host of independent biochemical processes including the oxidation of low-density lipoproteins, formation of fatty streaks, and the proliferation of smooth muscle cells. As the plaques form, the walls become thick, fibrotic, and calcified, and the lumen narrows, reducing the flow of blood to the tissues the artery supplies.
Figure 6 : Schematic diagram of the distribution of atherosclerotic plaque along the inner wall of the carotid artery bifurcation.
Atherosclerotic deposits promote the development of blood clots or the process of thrombosis due in part to flow obstruction and to high shear stresses exerted on the vessel wall by the blood. High wall shear stress might mechanically damage the inner wall of the artery, initiating a lesion. On the other hand, low wall shear stress might encourage the deposition of particles on the artery wall, promoting the accumulation of plaque. Turbulence has also been implicated in atherosclerotic disease both because it can increase the kinetic energy deposited in the vessel walls and because it can lead to areas of stasis, or stagnant blood flow, that promote clotting. In addition, the presence of atherosclerotic lesions introduces an irregular vessel surface that, as a result of turbulent blood flow, can cause the dislodgment of plaques of varying size into the bloodstream until the plaque lodges into a vessel of smaller size, preventing further passage of blood flow. Atherosclerotic thrombosis accounts for 33% of all stroke cases.
An embolus represents gaseous or particulate (eg, atheromata) matter that acts as traveling “clots.” A common example of emboli is a platelet aggregate dislodged from an atherosclerotic lesion. The dislodged platelet aggregate is transported by the bloodstream through the cerebrovasculature until it reaches vessels too small for further propagation. The clot has nowhere to go and remains there, clogging the vessel and preventing blood flow from entering the distal vasculature. Although our discussion at the present is focused primarily on the carotid arteries and associated cerebrovasculature, emboli can originate from distant sources such as the heart, lungs, and peripheral circulation, which could eventually travel within the cerebral blood vessels, obstructing flow and causing stroke. Other sources of emboli include atrial fibrillation and valvular disease. The severity of stroke depends on the size of the embolus and the location of the obstruction. The bigger the embolus and the larger the vessel obstruction, the larger the territory of brain at risk. Approximately 31% of all stroke cases are attributed to emboli.
Thrombosis is an internal physiological mechanism responsible for the clotting of blood. A thrombus is a blood clot, an aggregation of platelets and fibrin formed in response either to an atherosclerotic lesion or to vessel injury. In response to vessel or tissue injury, the blood coagulation system is activated, which initiates the following cascade of processes transforming prothrombin and resulting in a fibrin clot:
Prothrombin?Thrombin?Fibrinogen? Fibrin?Fibrin Clot
Although a host of mechanisms and causes are responsible for vessel injury, vessel injury can occur as a result of forces (shear stresses)7 coupled with the excess energy created by the turbulent flow8 9 10 exerted against the inner (intimal) lining of the vessel wall, particularly an atherosclerotic vessel wall. Approximately 33% of all stroke cases are attributed to thrombi.
Reduced Systemic Pressure
The previously described mechanisms of blood flow obstruction leading to stroke occur along localized regions of the cerebral arteries. It is assumed in this instance that the heart is functioning normally under proper systemic pressure. Cardiovascular diseases such as atrial fibrillation and myocardial infarction weaken the cardiac wall and introduce abnormalities in the physiological function of the heartbeat, which ultimately result in reduced systemic pressure and conditions of ischemia.
Blood vessels are typically structurally adept to withstand the dynamic quantities required to maintain circulatory function. For reasons that are not entirely understood, the vessel wall can become fatigued and abnormally weak and possibly rupture. With vessel rupture, hemorrhage occurs with blood seeping into the surrounding brain tissue. As the blood accumulates within the brain, the displaced volume causes the blood, now thrombosed, to ultimately compress the surrounding vessels. The compression of vessels translates into a reduced vessel diameter and a corresponding reduction in flow to surrounding tissue, thereby enlarging the insult. Among the vascular lesions that can lead to hemorrhagic strokes are aneurysms and arteriovenous malformations (AVMs).
A brain aneurysm, shown in Fig 2?, is a form of cerebrovascular disease that manifests itself as a pouching or ballooning of the vessel wall. The vascular dilatation develops at a diseased site along the arterial wall into a distended sac of stressed and thinned arterial tissue. The fully developed cerebral aneurysm typically ranges in size from a few millimeters to 15 mm but can attain sizes greater than 2.5 cm. If left untreated; the aneurysm may continue to expand until it ruptures, causing hemorrhage, severe neurological complications and deficits, and possibly death. In the United States, approximately 28 000 aneurysms rupture each year; approximately 50% of these patients die or become permanently disabled as a result of the initial hemorrhage, and another 25% to 35% die of a future hemorrhage.
Blood flow in most aneurysms is regular and predictable primarily according to the geometric relations