Ischemic Strokes

Ischemic strokes, which account for about 80 percent of all strokes, are caused by an obstruction in an artery, generally one of the carotid arteries, the major arteries in the neck that carry oxygen-rich blood from the heart to the brain. The path to an ischemic stroke begins when atherosclerosis, in which fatty deposits build up on the inner wall of an artery, develops in one of the carotid arteries (see Arteriosclerosis). As the fatty deposit grows, it narrows the space through which blood can flow.

Atherosclerosis does not actually cause ischemic strokes, but it sets up the conditions that make them likely to occur. The actual obstruction that cuts off blood flow in an ischemic stroke is a blood clot. Often the obstruction develops by a process known as thrombosis, the formation of a clot inside a blood vessel. A clot is likely to form at the site of an atherosclerotic deposit because the deposit causes blood to flow in a turbulent, disorderly fashion. This turbulence can cause blood to clot just as it does in response to a wound. When the blood clot, or thrombus, develops at the site of an atherosclerotic deposit and cuts off blood flow to part of the brain, a stroke results.

An ischemic stroke can also be caused by a traveling clot, or embolus (see Embolism). In this case, the clot develops at some other location in the circulation, usually in one of the heart’s chambers. The clot then travels through the bloodstream until it encounters a vessel too small to let it pass through—often a vessel narrowed by atherosclerosis.

A transient ischemic attack (TIA) sometimes precedes an ischemic stroke. In a TIA, also known as a ministroke, strokelike symptoms develop but disappear within five minutes to 24 hours. TIAs can occur when a clot develops at the site of an atherosclerotic deposit but dissolves right away, or an embolism lodges in a narrowed vessel but is soon dislodged on its own. A TIA can also be caused by atherosclerosis alone when the narrowing of blood vessels by atherosclerosis restricts blood flow to part of the brain enough to cause strokelike symptoms. Regardless of the cause, the oxygen deprivation is not severe enough to kill brain cells, and the cells are able to bounce back from their injury. About 10 percent of ischemic strokes are preceded by TIAs.

Stroke

Stroke is a brain damage caused by a lack of blood flow to part of the brain. In order to perform its many functions and direct activities throughout the body—from walking to seeing to reasoning—the brain requires a constant supply of energy, provided by the oxygen and nutrients that are delivered by the flowing blood. If blood flow is restricted or cut off at any point between the heart and the brain, portions of the brain relying on blood from the obstructed blood vessel become deprived of oxygen. Brain cells are extremely sensitive to such oxygen deprivation, and if they are deprived of oxygen and nutrients for more than several minutes, they, in effect, starve to death. A stroke results in permanent damage to the brain tissue—and in many cases, permanent disability for the patient. For example, a patient who has had a stroke may develop paralysis on one or both sides of the body; have difficulty with walking, eating, or other daily activities; or lose the ability to speak or understand speech.

TYPES OF STROKE

Think of a blood vessel as a flexible, cylindrical tube, like a straw. The flow of liquid through a straw can be impeded in two different ways: by an obstruction within the straw, or by compression or pinching from outside the straw. The flow of blood through a blood vessel can also be blocked in these two ways. The two main types of stroke, ischemic stroke and hemorrhagic stroke, correspond to these two mechanisms of flow interruption.

SYMPTOM AND DIAGNOSIS

A key feature of stroke symptoms is that they are unexpected and develop suddenly, though they may worsen over the next several hours or days. The symptoms often primarily affect only one side of the body because blood flow is cut off to only part of the brain during a stroke. One of the most common symptoms is a sudden weakness or numbness of one side of the face or of one arm or leg. Some stroke sufferers experience a sudden dimness or loss of vision, particularly in only one eye. They may also suddenly become unable to speak or have trouble understanding speech. Sudden, severe headaches with no known cause and sudden, unexplained dizziness, unsteadiness, or falls, can also be warning signs of a stroke. Anyone who experiences one or more of these symptoms should seek medical attention immediately.

The key imaging technique used in diagnosing strokes is computed tomography (also known as CT or CAT scanning), which employs X rays to obtain images of the internal structures of the body. A CT scan can tell a doctor whether or not a stroke is occurring, whether the stroke is ischemic or hemorrhagic, and in most instances, the extent of brain damage caused by the stroke.

Several other imaging techniques are used along with computed tomography to gather more information about specific types of stroke. Magnetic resonance imaging (MRI) uses a magnetic field to generate images of the human body and produces high-resolution images that are particularly useful in diagnosing brain vessel abnormalities that may be involved in a hemorrhagic stroke. In X-ray angiography, a dye injected into the bloodstream is viewed using X rays to provide detailed images of blood vessels, enabling doctors to identify the source and location of an obstruction or gather anatomical information about aneurysms or AVMs. Two other imaging techniques, single photon emission computed tomography (SPECT) and positron emission tomography (PET), involve injecting a radioactive substance into the bloodstream. As the substance travels through the circulatory system, it constantly emits radiation, which is collected by a radiation detector. The images produced enable doctors to see regions of the brain with abnormally low blood flow, indicating brain tissue that has been injured or damaged by a stroke.

TREATMENT AND RECOVERY

Once doctors have established that a patient is having a stroke, the treatment focuses on removing the obstruction, restoring blood flow to the deprived region of the brain, and preventing the development of complications. In the past, doctors could do little to treat stroke patients until the stroke had run its course. However, a promising advance occurred in June 1996, when the Food and Drug Administration (FDA) approved the drug tissue plasminogen activator (t-PA) for use in treating ischemic strokes. The drug is a thrombolytic agent—or clot buster—that can break up blood clots and thereby restore flow through the obstructed blood vessel when administered within the first three hours of a stroke. This small window of effectiveness makes it more critical than ever for patients to seek immediate medical attention when strokelike symptoms develop.

Hypertension

Hypertension or High Blood Pressure, medical condition in which constricted arterial blood vessels increase the resistance to blood flow, causing an increase in blood pressure against vessel walls. The heart must work harder to pump blood through the narrowed arteries. If the condition persists, damage to the heart and blood vessels is likely, increasing the risk for stroke, heart attack, and kidney or heart failure. Often called the “silent killer,” hypertension usually causes no symptoms until it reaches a life-threatening stage.

Physicians use two measurements to describe blood pressure. Systolic pressure measures blood pressure as the heart contracts to pump out blood. Diastolic pressure measures blood pressure as the heart relaxes to allow blood to flow into the heart. An instrument called a sphygmomanometer measures systolic and diastolic pressure using units of millimeters of mercury (abbreviated mm Hg).

Blood pressure is classified in four categories: normal, prehypertension, stage 1 hypertension, and stage 2 hypertension. Normal blood pressure in an adult is less than 120/80 mm Hg, in which 120 describes systolic pressure and 80 describes diastolic pressure. Prehypertension is defined as a systolic pressure of 120 to 139 mm Hg or a diastolic pressure of 80 to 89 mm Hg. People with prehypertension are likely to develop hypertension at some point during their life. Stage 1 hypertension is defined as a systolic pressure of 140 to 159 mm Hg or a diastolic pressure of 90 to 99 mm Hg. Stage 2 hypertension is defined as 160/100 mm Hg or higher.

HOW HYPERTENSION DEVELOPS

Two factors determine blood pressure: the amount of blood the heart pumps and the diameter of the arteries receiving blood from the heart. When the arteries narrow, they increase the resistance to blood flow. The heart works harder to pump more blood to make sure the same amount of blood circulates to all the body tissues. The more blood the heart pumps and the smaller the arteries, the higher the blood pressure.

The kidneys play a major role in the regulation of blood pressure. Kidneys secrete the hormone renin, which causes arteries to contract, thereby raising blood pressure. The kidneys also control the fluid volume of blood, either by retaining salt or excreting salt into urine. When kidneys retain salt in the bloodstream, the salt attracts water, increasing the fluid volume of blood. As a higher volume of blood passes through arteries, it increases blood pressure.

Blood Pressure

Blood Pressure, pressure of circulating blood against the walls of the arteries (blood vessels that carry blood from the heart to the rest of the body). Blood pressure is an important indicator of the health of the circulatory system. Any condition that dilates or contracts the arteries or affects their elasticity, or any disease of the heart that interferes with its pumping power, affects blood pressure.

In a healthy human being, blood pressure remains within a certain average range. The complex nervous system mechanisms that balance and coordinate the activity of the heart and arterial muscles permit great local variation in the rate of blood flow without disturbing the general blood pressure.

Hemoglobin, the iron-protein compound that gives blood its red color, also plays a role in regulating local variation in blood pressure. Hemoglobin carries nitric oxide, a gas that relaxes the blood vessel walls. Hemoglobin controls the expansion and contraction of blood vessels, and thus blood pressure, by regulating the amount of nitric oxide to which the vessels are exposed.

Two measurements are used to describe blood pressure. Systolic pressure measures blood pressure when the heart contracts to empty its blood into the circulatory system. Diastolic pressure measures blood pressure when the heart relaxes and fills with blood. Systolic and diastolic pressure are measured in millimeters of mercury (abbreviated mm Hg) using an instrument called a sphygmomanometer. This instrument consists of an inflatable rubber cuff connected to a pressure-detecting device with a dial. The cuff is wrapped around the upper arm and inflated by squeezing a rubber bulb connected to it by a tube. Meanwhile, a health-care professional listens to a stethoscope applied to an artery in the lower arm. As the cuff inflates, it gradually compresses the artery. The point at which the cuff stops the circulation and at which no pulsations can be heard through the stethoscope is read as the systolic pressure. As the cuff is slowly deflated, a spurting sound can be heard when the heart contraction forces blood through the compressed artery. The cuff is then allowed gradually to deflate further until the blood is flowing smoothly again and no further spurting sound is heard. A reading at this point shows the diastolic pressure that occurs during relaxation of the heart. Normal blood pressure in an adult is less than 120/80 mm Hg. The first number describes systolic pressure, while the second number describes diastolic pressure.

Blood pressure is influenced by a wide range of factors and varies between individuals and in the same individual at different times. For instance, blood pressure naturally increases with age because the arteries lose the elasticity that, in younger people, absorbs the force of heart contractions. Other factors, such as emotions, exercise, or stress, may temporarily raise blood pressure.

Abnormally high blood pressure, known as hypertension, that remains untreated can lead to stroke, heart attack, and kidney or heart failure. Hypertension may have no known cause or it may result from heart or blood vessel disorders or from diseases affecting other parts of the body. Abnormally low blood pressure, known as hypotension, may be caused by shock, malnutrition, or some other disease or injury.

First Aid

First Aid, emergency care for a victim of sudden illness or injury until more skillful medical treatment is available. First aid may save a life or improve certain vital signs including pulse, temperature, a patent (unobstructed) airway, and breathing. In minor emergencies, first aid may prevent a victim’s condition from worsening and provide relief from pain. First aid must be administered as quickly as possible. In the case of the critically injured, a few minutes can make the difference between complete recovery and loss of life.

First-aid measures depend upon a victim’s needs and the provider’s level of knowledge and skill. Knowing what not to do in an emergency is as important as knowing what to do. Improperly moving a person with a neck injury, for example, can lead to permanent spinal injury and paralysis.

Despite the variety of injuries possible, several principles of first aid apply to all emergencies. The first step is to call for professional medical help. Determine that the scene of the accident is safe before attempting to provide first aid. The victim, if conscious, should be reassured that medical aid has been requested, and asked for permission to provide any first aid. Next, assess the scene, asking bystanders or the injured person’s family or friends about details of the injury or illness, any care that may have already been given, and preexisting conditions such as diabetes or heart trouble. The victim should be checked for a medical bracelet or card that describes special medical conditions. Unless the accident scene becomes unsafe or the victim may suffer further injury, do not move the victim.

First aid requires rapid assessment of victims to determine whether life-threatening conditions exist. One method for evaluating a victim’s condition is known by the acronym ABCs, which stands for:

A — Airway—is it open and unobstructed?

B — Breathing—is the person breathing? Look, listen, and feel for breathing.

C — Circulation—is there a pulse? Is the person bleeding externally? Check skin color and temperature for additional indications of circulation problems.

Once obvious injuries have been evaluated, the injured person’s head should be kept in a neutral position in line with the body. If no evidence exists to suggest potential skull or spinal injury, place the injured person in a comfortable position. Positioned on one side, a victim can vomit without choking or obstructing the airway.

Before treating specific injuries, protect the victim from shock—a depression of the body’s vital functions that, left untreated, can result in death. Shock occurs when blood pressure (pressure exerted against blood vessel walls) drops and the organs do not receive enough blood, depriving them of oxygen and nutrients. The symptoms of shock are anxiety or restlessness; pale, cool, clammy skin; a weak but rapid pulse; shallow breathing; bluish lips; and nausea. These symptoms may not be apparent immediately, as shock can develop several hours after an accident. To prevent shock, the victim should be covered with blankets or warm clothes to maintain a normal body temperature. The victim’s feet should be elevated. Because of the danger of abdominal injuries, nothing should be administered by mouth.